NUCLEIC ACID INFLUENZA VACCINES AND RESPIRATORY VIRUS COMBINATION VACCINES

[0001] This application is a continuation of U.S. application Ser. No. 19/320,264, filed Sep. 5, 2025, which is a continuation of International Patent Application No. PCT/US2024/019210, filed Mar. 8, 2024, which claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 63/489,707, filed Mar. 10, 2023, U.S. Provisional Application No. 63/518,923, filed Aug. 11, 2023, and U.S. Provisional Application No. 63/582,208, filed Sep. 12, 2023, the contents of each of which are incorporated by reference herein in their entirety.

[0002] The contents of the electronic sequence listing (M137870260WO00-SEQ-NTJ.xml; Size: 400,770 bytes; and Date of Creation: Mar. 8, 2024) are incorporated by reference herein in their entirety.

[0003] Respiratory diseases, encompassing a range of conditions affecting the gas exchange organs, pose significant health challenges globally. Among these, seasonal influenza, caused by influenza A and B viruses, is a common affliction with substantial health and economic impacts. The sudden onset of symptoms such as fever, cough, and muscle pain can lead to high levels of absenteeism and productivity losses.

[0004] In addition to influenza, other respiratory viruses, such as human coronaviruses and the human Respiratory Syncytial Virus (hRSV), contribute to the burden of respiratory illnesses. Certain strains of coronaviruses are commonly associated with mild to moderate upper respiratory tract infections. Some strains, such as Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), have led to global health crises, as seen with the COVID-19 pandemic.

[0005] hRSV, a negative-sense, single-stranded RNA virus, presents another significant concern, particularly in children and older adults. In these populations, hRSV infection can progress to more severe conditions like bronchiolitis or pneumonia.

[0006] Provided are compositions and methods for vaccination against seasonal influenza viruses, and optionally other respiratory viruses including hRSV and SARS-CoV-2. The compositions and methods are based, at least in part, on the finding that certain substitutions in influenza B virus (IBV) hemagglutinin (HA) proteins allows for stabilization of the HA proteins, and consequently improved cell surface expression and immunogenicity. Stabilization was also achieved in influenza A virus (IAV) HA proteins. Such influenza virus HA proteins allow for improved influenza vaccines, such as those containing RNAs (e.g., mRNAs) encoding the influenza virus HA proteins, or other compositions for vaccination (e.g., viral vector or protein-based vaccines).

[0007] Accordingly, some aspects relate to an influenza B/Victoria lineage virus hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference influenza B/Victoria lineage virus HA protein amino acid sequence, wherein the influenza B/Victoria lineage virus HA protein comprises one or more of (a)-(s):

• • [0008] (a) a tyrosine at position 381 and a valine at position 288;
  • [0009] (b) a cysteine at position 27 and a cysteine at position 349;
  • [0010] (c) a cysteine at position 295 and a cysteine at position 328;
  • [0011] (d) a cysteine at position 399 and a cysteine at position 473;
  • [0012] (e) a cysteine at position 422 and a cysteine at position 444;
  • [0013] (f) a cysteine at position 118 and a cysteine at position 216;
  • [0014] (g) a cysteine at position 237 and a cysteine at position 261;
  • [0015] (h) a cysteine at position 363 and a cysteine at position 480;
  • [0016] (i) a cysteine at position 364 and a cysteine at position 483;
  • [0017] (j) a cysteine at position 365 and a cysteine at position 476;
  • [0018] (k) a cysteine at position 366 and a cysteine at position 479;
  • [0019] (l) a cysteine at position 367 and a cysteine at position 483;
  • [0020] (m) a cysteine at position 435 and a cysteine at position 428;
  • [0021] (n) a cysteine at position 494 and a cysteine at position 483;
  • [0022] (o) a cysteine at position 494 and a cysteine at position 480;
  • [0023] (p) a proline at position 416, a proline at position 417, a proline at position 434, and a proline at position 433;
  • [0024] (q) a proline at position 434 and a proline at position 433;
  • [0025] ® a proline at position 515, and a proline at position 516;
  • [0026] (s) a phenylalanine at position 473;
  • [0027] wherein the positions of (a)-(s) are numbered by alignment of the reference influenza B/Victoria lineage virus HA protein amino acid sequence to SEQ ID NO: 71.

[0028] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises one or more of (a)-(s):

• • [0029] (a) H381Y and A288V substitutions;
  • [0030] (b) S27C and Y349C substitutions;
  • [0031] (c) I295C and K328C substitutions;
  • [0032] (d) S399C and H473C substitutions;
  • [0033] (e) L422C and D444C substitutions;
  • [0034] (f) K118C and L216C substitutions;
  • [0035] (g) V237C and D261C substitutions;
  • [0036] (h) G363C and K480C substitutions;
  • [0037] (i) A364C and K483C substitutions;
  • [0038] (j) I365C and A476C substitutions;
  • [0039] (k) A366C and R479C substitutions;
  • [0040] (l) G367C and K483C substitutions;
  • [0041] (m) E435C and A428C substitutions;
  • [0042] (n) N494C and K483C substitutions;
  • [0043] (o) N494C and K480C substitutions;
  • [0044] (p) E416P, L417P, N434P, and H433P substitutions;
  • [0045] (q) N434P and H433P substitutions;
  • [0046] (r) T515P and F516P substitutions; and
  • [0047] (s) an H473F substitution.

[0048] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381 and valine at position 288.

[0049] In some embodiments, the influenza B/Victoria lineage HA protein comprises H381Y and A288V substitutions.

[0050] In some embodiments, the influenza B/Victoria lineage HA protein further comprises one or more of (a)-(r):

• • [0051] (a) S27C and Y349C substitutions;
  • [0052] (b) I295C and K328C substitutions;
  • [0053] (c) S399C and H473C substitutions;
  • [0054] (d) L422C and D444C substitutions;
  • [0055] (e) K118C and L216C substitutions;
  • [0056] (f) V237C and D261C substitutions;
  • [0057] (g) G363C and K480C substitutions;
  • [0058] (h) A364C and K483C substitutions;
  • [0059] (i) I365C and A476C substitutions;
  • [0060] (j) A366C and R479C substitutions;
  • [0061] (k) G367C and K483C substitutions;
  • [0062] (l) E435C and A428C substitutions;
  • [0063] (m) N494C and K483C substitutions;
  • [0064] (n) N494C and K480C substitutions;
  • [0065] (o) E416P, L417P, N434P, and H433P substitutions;
  • [0066] (p) N434P and H433P substitutions;
  • [0067] (q) T515P and F516P substitutions;
  • [0068] (r) an H473F substitution.

[0069] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 422, and cysteine at position 444.

[0070] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 364, and cysteine at position 483.

[0071] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 367, and cysteine at position 483.

[0072] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 494, and cysteine at position 483.

[0073] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 71.

[0074] Some aspects relate to influenza B/Yamagata lineage virus hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference influenza B/Yamagata lineage virus HA protein amino acid sequence, wherein the influenza B/Yamagata lineage virus HA protein comprises one or more of (a)-(i):

• • [0075] (a) a cysteine at position 231 and a cysteine at position 273;
  • [0076] (b) a cysteine at position 295 and a cysteine at position 332;
  • [0077] (c) a cysteine at position 396 and a cysteine at position 510;
  • [0078] (d) a cysteine at position 239 and a cysteine at position 276;
  • [0079] (e) a cysteine at position 367 and a cysteine at position 401;
  • [0080] (f) a cysteine at position 363 and a cysteine at position 404;
  • [0081] (g) a cysteine at position 437 and a cysteine at position 429;
  • [0082] (h) a cysteine at position 451 and a cysteine at position 422; and
  • [0083] (i) a tyrosine at position 381 and a valine at position 290;
  • [0084] wherein the positions of (a)-(i) are numbered by alignment of the reference influenza B/Yamagata lineage virus HA protein amino acid sequence to SEQ ID NO: 70.

[0085] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises one or more of (a)-(i):

• • [0086] (a) A231C and G273C substitutions;
  • [0087] (b) K295C and I332C substitutions;
  • [0088] (c) A396C and L510C substitutions;
  • [0089] (d) V239C and V276C substitutions;
  • [0090] (e) I367C and S401C substitutions;
  • [0091] (f) F363C and E404C substitutions;
  • [0092] (g) E437C and G429C substitutions;
  • [0093] (h) D451C and K422C substitutions; and
  • [0094] (i) H381Y and A290V substitutions.

[0095] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises tyrosine at position 381 and valine substitution at position 290.

[0096] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises cysteine at position 239, cysteine at position 276, cysteine at position 451, and cysteine at position 422.

[0097] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises cysteine at position 367, cysteine at position 401, cysteine at position 451, and cysteine at position 422.

[0098] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 70.

[0099] Some aspects relate to an influenza A virus (IAV) H1 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H1 HA protein amino acid sequence, wherein the IAV H1 HA protein comprises one or more of (a)-(o):

• • [0100] (a) a cysteine at position 391 and a cysteine at position 37;
  • [0101] (b) a cysteine at position 395 and a cysteine at position 36;
  • [0102] (c) a cysteine at position 461 and a cysteine at position 348;
  • [0103] (d) a proline at position 404 and a proline at position 416;
  • [0104] (e) an isoleucine at position 395 and an isoleucine at position 447;
  • [0105] (f) a glycine at position 456 and an isoleucine at position 402;
  • [0106] (g) a cysteine at position 391, a cysteine at position 37, a proline at position 404, and a proline at position 416;
  • [0107] (h) a cysteine at position 391, a cysteine at position 37, an isoleucine at position 395, and an isoleucine at position 447;
  • [0108] (i) a cysteine at position 391, a cysteine at position 37, a glycine at position 456, and an isoleucine at position 402;
  • [0109] (j) a cysteine at position 395, a cysteine at position 36, a proline at position 404, and a proline at position 416;
  • [0110] (k) a cysteine at position 395, a cysteine at position 36, a glycine at position 456, and an isoleucine at position 402;
  • [0111] (l) a cysteine at position 461, a cysteine at position 348, a proline at position 404, and a proline at position 416;
  • [0112] (m) a cysteine at position 461, a cysteine at position 348, an isoleucine at position 395, and an isoleucine at position 447;
  • [0113] (n) a cysteine at position 461, a cysteine at position 348, a glycine at position 456, and an isoleucine at position 402; and
  • [0114] (o) a cysteine at position 391, a cysteine at position 37, a proline at position 404, a glycine at position 456, and an isoleucine at position 402;
  • [0115] wherein the positions of (a)-(o) are numbered by alignment of the reference IAV H1 HA protein amino acid sequence to SEQ ID NO: 83.

[0116] In some embodiments, the IAV H1 HA protein comprises one or more of (a)-(o):

• • [0117] (a) K391C and L37C substitutions;
  • [0118] (b) K395C and V36C substitutions;
  • [0119] (c) N461C and G348C substitutions;
  • [0120] (d) N404P and H416P substitutions;
  • [0121] (e) K395I and E447I substitutions;
  • [0122] (f) D456G and K402I substitutions;
  • [0123] (g) K391C, L37C, N404P, H416P substitutions;
  • [0124] (h) K391C, L37C, K395I, E447I substitutions;
  • [0125] (i) K391C, L37C, D456G, K402I substitutions;
  • [0126] (j) K395C, V36C, N404P, H416P substitutions;
  • [0127] (k) K395C, V36C, D456G, K402I substitutions;
  • [0128] (l) N461C, G348C, N404P, H416P substitutions;
  • [0129] (m) N461C, G348C, K395I, E447I substitutions;
  • [0130] (n) N461C, G348C, D456G, K402I substitutions; and
  • [0131] (o) K391C, L37C, N404P, H416P, D456G, K402I substitutions.

[0132] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 395, and cysteine at position 36.

[0133] In some embodiments, the IAV H1 HA protein comprises cysteine at position 456, isoleucine at position 402, cysteine at position 395, and cysteine at position 36.

[0134] In some embodiments, the IAV H1 HA protein comprises glycine at position 456, isoleucine at position 402, cysteine at position 395, and cysteine at position 36.

[0135] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 391, and cysteine at position 36.

[0136] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 391, cysteine at position 37, glycine at position 456, and isoleucine at position 402.

[0137] In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 83.

[0138] Some aspects relate to an influenza A virus (IAV) H1 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H1 HA protein amino acid sequence, wherein the IAV H1 HA protein comprises one or more of (a)-(t):

• • [0139] (a) a cysteine at position 410 and a cysteine at position 462;
  • [0140] (b) a cysteine at position 120 and a cysteine at position 419;
  • [0141] (c) a cysteine at position 391 and a cysteine at position 37;
  • [0142] (d) a cysteine at position 395 and a cysteine at position 36;
  • [0143] (e) a cysteine at position 406 and a cysteine at position 430;
  • [0144] (f) a cysteine at position 457 and a cysteine at position 346;
  • [0145] (g) a cysteine at position 461 and a cysteine at position 348;
  • [0146] (h) a proline at position 404 and a proline at position 419;
  • [0147] (i) a proline at position 404 and a proline at position 416;
  • [0148] (j) a proline at position 405 and a proline at position 406;
  • [0149] (k) a proline at position 415 and a proline at position 416;
  • [0150] (l) a tyrosine at position 25 and a glutamate at position 45;
  • [0151] (m) a tyrosine at position 370 and a tryptophan at position 497;
  • [0152] (n) a glycine at position 402, a glycine at position 405, and a glycine at position 407;
  • [0153] (o) an isoleucine at position 395 and an isoleucine at position 447;
  • [0154] (p) a glycine at position 456 and a glycine at position 402;
  • [0155] (q) a cysteine at position 442 and a cysteine at position 423;
  • [0156] (r) a glycine at position 391;
  • [0157] (s) a cysteine at position 410, a cysteine at position 462, a cysteine at position 457, and a cysteine at position 346; and
  • [0158] (t) a cysteine at position 391, a cysteine at position 37, a phenylalanine at position 370, and a phenylalanine at position 455;
  • [0159] wherein the positions of (a)-(t) are numbered by alignment of the reference IAV H1 HA protein amino acid sequence to SEQ ID NO: 95.

[0160] In some embodiments, the IAV H1 HA protein comprises one or more of (a)-(t):

• • [0161] (a) V410C and L462C substitutions;
  • [0162] (b) E120C and K419C substitutions;
  • [0163] (c) K391C and L37C substitutions;
  • [0164] (d) K395C and V36C substitutions;
  • [0165] (e) Q406C and D430C substitutions;
  • [0166] (f) S457C and L346C substitutions;
  • [0167] (g) N461C and G348C substitutions;
  • [0168] (h) N404P and K419P substitutions;
  • [0169] (i) N404P and H416P substitutions;
  • [0170] (j) T405P and Q406P substitutions;
  • [0171] (k) N415P and H416P substitutions;
  • [0172] (l) H25Y and H45E substitutions;
  • [0173] (m) H370Y and K497W substitutions;
  • [0174] (n) K402G, T405G, and F407G substitutions;
  • [0175] (o) K395I and E447I substitutions;
  • [0176] (p) D456G and K402I substitutions;
  • [0177] (q) L442C and N423C substitutions;
  • [0178] (r) a K391G substitution;
  • [0179] (s) V410C, L462C, S457C, L346C substitutions; and
  • [0180] (t) K391C, L37C, H370F, H455F substitutions.

[0181] In some embodiments, the IAV H1 HA protein comprises cysteine at position 391 and cysteine at position 37.

[0182] In some embodiments, the IAV H1 HA protein comprises cysteine at position 395 and cysteine at position 36.

[0183] In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 95.

[0184] Some aspects relate to an influenza A virus (IAV) H3 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H3 HA protein amino acid sequence, wherein the IAV H3 HA protein comprises one or more of (a) (j):

[0185] (a) a cysteine at position 40 and a cysteine at position 55;

• • [0186] (b) a cysteine at position 123 and a cysteine at position 421;
  • [0187] (c) a cysteine at position 260 and a cysteine at position 237;
  • [0188] (d) a cysteine at position 392 and a cysteine at position 46;
  • [0189] (e) a cysteine at position 411 and a cysteine at position 428;
  • [0190] (f) a proline at position 402, a proline at position 421, and a proline at position 414;
  • [0191] (g) a glycine at position 403;
  • [0192] (h) a glycine at position 408 and a glycine at position 409;
  • [0193] (i) an isoleucine at position 396; and
  • [0194] (j) an isoleucine at position 219 and a proline at position 504;
  • [0195] wherein the positions of (a)-(j) are numbered by alignment of the reference IAV H3 HA protein amino acid sequence to SEQ ID NO: 82.

[0196] In some embodiments, the IAV H3 HA protein comprises one or more of (a)-(j):

• • [0197] (a) T40C and A55C substitutions;
  • [0198] (b) S123C and R421C substitutions;
  • [0199] (c) L260C and P237C substitutions;
  • [0200] (d) Q392C and T46C substitutions;
  • [0201] (e) I411C and Y428C substitutions;
  • [0202] (f) G402P, R421P, and E414P substitutions;
  • [0203] (g) a K403G substitution;
  • [0204] (h) F408G and H409G substitutions;
  • [0205] (i) a K396I substitution; and
  • [0206] (j) T219I and H504P substitutions.

[0207] In some embodiments, the IAV H3 HA protein comprises proline at position 402, proline at position 421, and proline at position 414.

[0208] In some embodiments, wherein the IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82.

[0209] In some embodiments, the HA protein is a recombinant protein.

[0210] Some aspects relate to a nucleic acid encoding:

• • [0211] (a) the influenza B/Victoria lineage virus HA protein;
  • [0212] (b) the influenza B/Yamagata lineage virus HA protein;
  • [0213] (c) the IAV H1 HA protein; or
  • [0214] (d) the IAV H3 HA protein.

[0215] In some embodiments, the nucleic acid is a DNA, a messenger ribonucleic acid (mRNA), a circular ribonucleic acid (RNA), or a self-amplifying ribonucleic acid (saRNA).

[0216] Some aspects relate to a viral vector comprising:

• • [0217] (a) the influenza B/Victoria lineage virus HA protein, and/or a nucleic acid encoding the influenza B/Victoria lineage virus HA protein;
  • [0218] (b) the influenza B/Yamagata lineage virus HA protein, and/or a nucleic acid encoding the influenza B/Yamagata lineage virus HA protein;
  • [0219] (c) the IAV H1 HA protein, and/or a nucleic acid encoding the IAV H1 HA protein; and/or
  • [0220] (d) the IAV H3 HA protein, and/or a nucleic acid encoding the IAV H3 HA protein.

[0221] Some aspects relate to a vaccine comprising:

• • [0222] (a) the HA protein;
  • [0223] (b) the nucleic acid; or
  • [0224] (c) the viral vector.

[0225] In some embodiments, the nucleic acid is mRNA.

[0226] Some aspects relate to a messenger ribonucleic acid (mRNA) comprising an open reading frame (ORF) encoding an influenza B/Victoria lineage virus hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference influenza B/Victoria lineage virus HA protein amino acid sequence, wherein the influenza B/Victoria lineage virus HA protein comprises one or more of (a)-(s):

• • [0227] (a) a tyrosine at position 381 and a valine at position 288;
  • [0228] (b) a cysteine at position 27 and a cysteine at position 349;
  • [0229] (c) a cysteine at position 295 and a cysteine at position 328;
  • [0230] (d) a cysteine at position 399 and a cysteine at position 473;
  • [0231] (e) a cysteine at position 422 and a cysteine at position 444;
  • [0232] (f) a cysteine at position 118 and a cysteine at position 216;
  • [0233] (g) a cysteine at position 237 and a cysteine at position 261;
  • [0234] (h) a cysteine at position 363 and a cysteine at position 480;
  • [0235] (i) a cysteine at position 364 and a cysteine at position 483;
  • [0236] (j) a cysteine at position 365 and a cysteine at position 476;
  • [0237] (k) a cysteine at position 366 and a cysteine at position 479;
  • [0238] (l) a cysteine at position 367 and a cysteine at position 483;
  • [0239] (m) a cysteine at position 435 and a cysteine at position 428;
  • [0240] (n) a cysteine at position 494 and a cysteine at position 483;
  • [0241] (o) a cysteine substitution at position 494 and a cysteine at position 480;
  • [0242] (p) a proline at position 416, a proline at position 417, a proline at position 434, and a proline at position 433;
  • [0243] (q) a proline at position 434 and a proline at position 433;
  • [0244] (r) a proline at position 515, and a proline at position 516; and
  • [0245] (s) a phenylalanine at position 473;
  • [0246] wherein the positions of (a)-(s) are numbered by alignment of the reference influenza B/Victoria lineage virus HA protein amino acid sequence to SEQ ID NO: 71.

[0247] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381 and valine at position 288.

[0248] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 422, and cysteine at position 444.

[0249] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 364, and cysteine at position 483.

[0250] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 367, and cysteine at position 483.

[0251] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381, valine at position 288, cysteine at position 494, and cysteine at position 483.

[0252] Some aspects relate to a messenger ribonucleic acid (mRNA) comprising an open reading frame (ORF) encoding an influenza B/Yamagata lineage virus hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference influenza B/Yamagata lineage virus HA protein amino acid sequence, wherein the influenza B/Yamagata lineage virus HA protein comprises one or more of (a)-(i):

• • [0253] (a) a cysteine at position 231 and a cysteine at position 273;
  • [0254] (b) a cysteine at position 295 and a cysteine at position 332;
  • [0255] (c) a cysteine at position 396 and a cysteine at position 510;
  • [0256] (d) a cysteine at position 239 and a cysteine at position 276;
  • [0257] (e) a cysteine at position 367 and a cysteine at position 401;
  • [0258] (f) a cysteine at position 363 and a cysteine at position 404;
  • [0259] (g) a cysteine at position 437 and a cysteine at position 429;
  • [0260] (h) a cysteine at position 451 and a cysteine at position 422; and
  • [0261] (i) a tyrosine at position 381 and a valine at position 290;
  • [0262] wherein the positions of (a)-(i) are numbered by alignment of the reference influenza B/Yamagata lineage virus HA protein amino acid sequence to SEQ ID NO: 70.

[0263] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises tyrosine at position 381 and valine at position 290.

[0264] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises cysteine at position 239, cysteine at position 276, cysteine at position 451, and cysteine at position 422.

[0265] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises cysteine at position 367, cysteine at position 401, cysteine at position 451, and cysteine at position 422.

[0266] Some aspects relate to a messenger ribonucleic acid (mRNA) comprising an open reading frame (ORF) encoding an influenza A virus (IAV) H1 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H1 HA protein amino acid sequence, wherein the IAV H1 HA protein comprises one or more of (a)-(o):

• • [0267] (a) a cysteine at position 391 and a cysteine at position 37;
  • [0268] (b) a cysteine at position 395 and a cysteine at position 36;
  • [0269] (c) a cysteine at position 461 and a cysteine at position 348;
  • [0270] (d) a proline at position 404 and a proline at position 416;
  • [0271] (e) an isoleucine at position 395 and an isoleucine at position 447;
  • [0272] (f) a glycine at position 456 and an isoleucine at position 402;
  • [0273] (g) a cysteine at position 391, a cysteine at position 37, a proline at position 404, and a proline at position 416;
  • [0274] (h) a cysteine at position 391, a cysteine at position 37, an isoleucine at position 395, and an isoleucine at position 447;
  • [0275] (i) a cysteine at position 391, a cysteine at position 37, a glycine at position 456, and an isoleucine at position 402;
  • [0276] (j) a cysteine at position 395, a cysteine at position 36, a proline at position 404, and a proline at position 416;
  • [0277] (k) a cysteine at position 395, a cysteine at position 36, a glycine at position 456, and an isoleucine at position 402;
  • [0278] (l) a cysteine at position 461, a cysteine at position 348, a proline at position 404, and a proline at position 416;
  • [0279] (m) a cysteine at position 461, a cysteine at position 348, an isoleucine at position 395, and an isoleucine at position 447;
  • [0280] (n) a cysteine at position 461, a cysteine at position 348, a glycine at position 456, and an isoleucine at position 402; and
  • [0281] (o) a cysteine at position 391, a cysteine at position 37, a proline at position 404, a glycine at position 456, and an isoleucine at position 402;
  • [0282] wherein the positions of (a)-(o) are numbered by alignment of the reference IAV H1 HA protein amino acid sequence to SEQ ID NO: 83.

[0283] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 395, and cysteine at position 36.

[0284] In some embodiments, the IAV H1 HA protein comprises cysteine at position 456, isoleucine at position 402, cysteine at position 395, and cysteine at position 36.

[0285] In some embodiments, the IAV H1 HA protein comprises glycine at position 456, isoleucine at position 402, cysteine at position 395, and cysteine at position 36.

[0286] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 391, and cysteine at position 36.

[0287] In some embodiments, the IAV H1 HA protein comprises proline at position 404, proline at position 416, cysteine at position 391, cysteine at position 37, glycine at position 456, and isoleucine at position 402.

[0288] Some aspects relate to a messenger ribonucleic acid (mRNA) comprising an open reading frame (ORF) encoding an influenza A virus (IAV) H1 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H1 HA protein amino acid sequence, wherein the IAV H1 HA protein comprises one or more of (a)-(t):

• • [0289] (a) a cysteine at position 410 and a cysteine at position 462;
  • [0290] (b) a cysteine at position 120 and a cysteine at position 419;
  • [0291] (c) a cysteine at position 391 and a cysteine at position 37;
  • [0292] (d) a cysteine at position 395 and a cysteine at position 36;
  • [0293] (e) a cysteine at position 406 and a cysteine at position 430;
  • [0294] (f) a cysteine at position 457 and a cysteine at position 346;
  • [0295] (g) a cysteine at position 461 and a cysteine at position 348;
  • [0296] (h) a proline at position 404 and a proline at position 419;
  • [0297] (i) a proline at position 404 and a proline at position 416;
  • [0298] (j) a proline at position 405 and a proline at position 406;
  • [0299] (k) a proline at position 415 and a proline at position 416;
  • [0300] (l) a tyrosine at position 25 and a glutamate at position 45;
  • [0301] (m) a tyrosine at position 370 and a tryptophan at position 497;
  • [0302] (n) a glycine at position 402, a glycine a position 405, and a glycine at position 407;
  • [0303] (o) an isoleucine at position 395 and an isoleucine at position 447;
  • [0304] (p) a glycine at position 456 and a glycine at position 402;
  • [0305] (q) a cysteine at position 442 and a cysteine at position 423;
  • [0306] (r) a glycine at position 391;
  • [0307] (s) a cysteine at position 410, a cysteine at position 462, a cysteine at position 457, and a cysteine at position 346; and
  • [0308] (t) a cysteine at position 391, a cysteine at position 37, a phenylalanine at position 370, and a phenylalanine at position 455;
  • [0309] wherein the positions of (a)-(t) are numbered by alignment of the reference IAV H1 HA protein amino acid sequence to SEQ ID NO: 95.

[0310] In some embodiments, the IAV H1 HA protein comprises cysteine at position 391 and cysteine at position 37.

[0311] In some embodiments, the IAV H1 HA protein comprises cysteine at position 395 and cysteine at position 36.

[0312] Some aspects relate to a messenger ribonucleic acid (mRNA) comprising an open reading frame (ORF) encoding an influenza A virus (IAV) H3 hemagglutinin (HA) protein having an amino acid sequence comprising an amino acid substitution relative to a reference IAV H3 HA protein amino acid sequence, wherein the IAV H3 HA protein comprises one or more of (a)-(j):

• • [0313] (a) a cysteine at position 40 and a cysteine at position 55;
  • [0314] (b) a cysteine at position 123 and a cysteine at position 421;
  • [0315] (c) a cysteine at position 260 and a cysteine at position 237;
  • [0316] (d) a cysteine at position 392 and a cysteine at position 46;
  • [0317] (e) a cysteine at position 411 and a cysteine at position 428;
  • [0318] (f) a proline at position 402, a proline at position 421, and a proline at position 414;
  • [0319] (g) a glycine at position 403;
  • [0320] (h) a glycine at position 408 and a glycine at position 409;
  • [0321] (i) an isoleucine at position 396; and
  • [0322] (j) an isoleucine at position 219 and a proline at position 504;
  • [0323] wherein the positions of (a)-(j) are numbered by alignment of the reference IAV H3 HA protein amino acid sequence to SEQ ID NO: 82.

[0324] In some embodiments, the IAV H3 HA protein comprises proline at position 402, proline at position 421, and proline at position 414.

[0325] Some aspects relate to an mRNA vaccine comprising:

• • [0326] (a) the mRNA encoding the IAV H1 HA protein;
  • [0327] (b) the mRNA encoding the IAV H3 HA protein; and
  • [0328] (c) the mRNA encoding the influenza B/Victoria lineage virus HA protein.

[0329] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises tyrosine at position 381 and valine at position 288.

[0330] In some embodiments, the mRNA vaccine further comprises an additional mRNA encoding an additional IAV H3 HA protein.

[0331] In some embodiments, the mRNA vaccine further comprises two or more additional mRNAs, each independently encoding an additional IAV H3 HA protein.

[0332] In some embodiments, the mRNA vaccine further comprises the mRNA encoding influenza B/Yamagata lineage virus HA protein of any one of claims 45-48.

[0333] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises tyrosine at position 381 and valine at position 290.

[0334] In some embodiments, the mRNA vaccine does not comprise an mRNA encoding an influenza B/Yamagata lineage virus HA protein.

[0335] In some embodiments, substantially equal masses of different mRNAs encoding different influenza virus HA proteins are present in the mRNA vaccine.

[0336] In some embodiments, the mRNA vaccine further comprises:

• • [0337] (i) a first additional mRNA encoding a first IAV neuraminidase (NA) protein of a first IAV NA subtype;
  • [0338] (ii) a second additional mRNA encoding a second IAV NA protein of a different IAV NA subtype than the first IAV NA subtype; and
  • [0339] (iii) a third additional mRNA encoding an influenza B/Victoria lineage virus NA protein.

[0340] In some embodiments, the second IAV NA subtype is N2, wherein the mRNA vaccine further comprises an additional mRNA encoding an additional IAV N2 NA protein.

[0341] In some embodiments, the second IAV NA subtype is N2, wherein the mRNA vaccine further comprises two or more additional mRNAs each encoding an additional IAV N2 NA protein.

[0342] In some embodiments, the mRNA vaccine further comprises an additional mRNA encoding an influenza B/Yamagata lineage virus NA protein.

[0343] In some embodiments, the mRNA vaccine does not comprise an mRNA encoding an influenza B/Yamagata lineage virus NA protein.

[0344] In some embodiments, substantially equal masses of different mRNAs encoding different influenza virus NA proteins are present in the mRNA vaccine.

[0345] In some embodiments, substantially equal masses of (a) mRNAs encoding influenza virus HA proteins, and (b) mRNAs encoding influenza virus NA proteins are present in the mRNA vaccine.

[0346] In some embodiments, the mRNA vaccine comprises a 3:1 mass ratio of (a) mRNAs encoding influenza virus HA proteins, to (b) mRNAs encoding influenza virus NA proteins.

[0347] In some embodiments, the mRNA vaccine further comprises an mRNA encoding a full-length SARS-CoV-2 Spike (S) glycoprotein comprising one or more proline substitutions relative to SEQ ID NO: 78.

[0348] In some embodiments, further comprises an mRNA encoding a protein comprising one or more fragments of a SARS-CoV-2 Spike (S) glycoprotein.

[0349] In some embodiments, the one or more fragments comprises a fusion protein comprising (i) an N-terminal domain (NTD) of the SARS-CoV-2 S glycoprotein, (ii) a receptor-binding domain (RBD) of the SARS-CoV-2 S glycoprotein, and (iii) a transmembrane domain.

[0350] In some embodiments, the mRNA vaccine further comprises an mRNA encoding a fusion (F) glycoprotein of a human respiratory syncytial virus (hRSV), or a fragment of the hRSV F glycoprotein.

[0351] In some embodiments, the mRNA vaccine further comprises a lipid delivery vehicle in contact with the mRNA.

[0352] In some embodiments, the lipid delivery vehicle is a lipid nanoparticle comprising 20-60 mol % ionizable lipid, 5-25 mol % non-cationic lipid, 2-4 mol % PEG-modified lipid, and 25-55 mol % sterol.

[0353] In some embodiments, the ionizable lipid is a compound of Formula (IL*):

• • [0354] or a salt thereof, wherein:
  • [0355] R¹ is —OH, —NR^N—C_4-10 cycloalkenyl optionally substituted with one or more oxo or —N(R^N′R^N″);
  • [0356] R^N is H or C_1-6 alkyl;
  • [0357] R^N′ is H or C_1-6 alkyl;
  • [0358] R^N″ is H or C_1-6 alkyl;
  • [0359] is 1, 2, 3, or 4;
  • [0360] n is 4, 5, 6, 7, or 8;
  • [0361] m is 4, 5, 6, 7, or 8;
  • [0362] M is —C(═O)—O—* or —O—C(═O)—*, wherein * indicates attachment to R²;
  • [0363] M′ is —C(═O)—O—* or —O—C(═O)—*, wherein * indicates attachment to R³;
  • [0364] R² is

• •  or —(C_1-6 alkylene)-(C_3-8 cycloalkyl)-C_1-6 alkyl;
  • [0365] R^2a is —H or C_1-10 alkyl;
  • [0366] R^2b is —H or C_1-10 alkyl;
  • [0367] R^2c is C_1-8 alkyl or C_2-8 alkenyl;
  • [0368] R³ is

• • [0369] R^3a is H or C_1-10 alkyl;
  • [0370] R^3b is H or C_1-8 alkyl; and
  • [0371] R^3c is C_1-10 alkyl or C_2-8 alkenyl.

[0372] In some embodiments, the ionizable lipid is

[0373] In some embodiments, the ionizable lipid is

[0374] In some embodiments, 0.25 mol % to 1.0 mol % of the PEG-modified lipid is present in a core of the lipid nanoparticle.

[0375] In some embodiments, 2.0 mol % to 2.75 mol % of the PEG-modified lipid is not in the core of the lipid nanoparticle.

[0376] In some embodiments, the PEG-modified lipid is PEG-DMG or 134-hydroxy-3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57,60,63,66,69,72,75,78,81,84,87,90,93,96,99,102,105,108,111,114,117,120,123,126,129,132-tetratetracontaoxatetratriacontahectyl stearate.

[0377] In some embodiments, each mRNA comprises one or more chemically modified nucleotides.

[0378] In some embodiments, each mRNA comprises N1-methylpseudouridine.

[0379] In some embodiments, substantially all uracil nucleotides of each mRNA are modified to comprise N1-methylpseudouridine.

[0380] In some embodiments, each mRNA comprises 5-methylcytidine and 5-methyluridine.

[0381] In some embodiments, substantially all cytosine nucleotides of each mRNA are modified to comprise 5-methylcytidine, and substantially all uracil nucleotides of each mRNA are modified to comprise 5-methyluridine.

[0382] Some aspects relate to a method comprising administering the vaccine to a subject.

[0383] In some embodiments, the subject has not been vaccinated against an influenza virus for at least 6 months prior to administration of the vaccine.

[0412] Respiratory viruses are common agents of disease, having a significant impact on morbidity and mortality worldwide. Vaccines to respiratory viruses are designed to stimulate an immune response protective against the viruses. Various types of vaccines exist, including nucleic acid vaccines (e.g., DNA, and RNA such self-amplifying RNA or mRNA vaccines) that use the genetic instructions for antigenic polypeptide production to stimulate the immune response. Protein-based vaccines use an antigenic polypeptide or fragment thereof, either from inactivated viruses or purified subunits. Live attenuated vaccines use weakened live viruses comprising or encoding the antigenic polypeptide(s), while viral vector vaccines employ a virus to deliver the antigenic polypeptide(s) and/or nucleic acid(s) encoding the antigenic polypeptide(s) to cells. Mutations to stabilize the antigenic polypeptide(s) can enhance the effectiveness of these diverse types of vaccines, leading to improved immune responses and protection against the viruses. Some aspects relate to compositions and methods with improved vaccine efficacy, e.g., due to increased stability of the viral antigens. Preferred compositions comprise mRNA vaccines.

[0413] Seasonal influenza is a contagious respiratory illness caused by influenza viruses, which can lead to annual epidemics with symptoms ranging from mild to severe, and potentially causing complications, particularly in high-risk groups. Without being bound by theory, influenza viruses are believed to spread through respiratory droplets and aerosols, but can also spread through contact with surfaces (fomites). Upon entering the respiratory tract, virions attach to cells via hemagglutinin (HA) proteins, which bind to sialic acid receptors on the cell surface. Virions then enter the cell, where they replicate and produce new virions that bud from the cell membrane. NA proteins on the virion surface cleave sialic acid from the cell surface, leading to release of free virions that may then infect other cells. This process continues until the immune system can clear the infection.

[0414] Influenza viruses belong to the Orthomyxoviridae family and are categorized into types A, B, C, and D. Among these, influenza A and B viruses are of significant concern for human health.

[0415] Influenza A viruses (IAVs) can be further classified based on two surface proteins, hemagglutinin (sometimes referred to as H or HA) and neuraminidase (sometimes referred to as N or NA). There are 18 known HA subtypes and 11 known N subtypes. However, only H1, H2, and H3, and N1 and N2 subtypes (e.g., A/(H1N1); A(H1N2); A(H2N2); and A(H3N2)) have caused widespread human disease. The genetic diversity of influenza A viruses, due to frequent mutation and reassortment, can result in novel strains with pandemic potential.

[0416] Influenza B viruses (IBVs) are not divided into subtypes, but can be broken down into lineages and strains within those lineages. Currently, two lineages circulate in humans: B/Yamagata (e.g., B/Yamagata/16/1988-like) and B/Victoria (e.g., B/Victoria/2/1987-like).

[0417] Non-exhaustive lists of A/(H1N1) subtype, A/(H3N2) subtype, B/Victoria lineage, and B/Yamagata lineage isolates are provided in Table IV-1.

[0418] A key challenge in influenza control through vaccination is rapid evolution of the viruses, which can alter their antigenic properties and result in evasion of pre-existing immunity (e.g., through infection with, or vaccination with, previously circulating strains). This necessitates regular updates to influenza vaccines to match currently circulating strains. Yet, stability deficiencies associated with vaccine antigens can limit the efficacy of such strain-matched vaccines. Thus, some aspects relate to compositions and methods that improve the stability of influenza virus antigenic polypeptides.

[0419] An influenza virus HA protein may comprise one or more mutations relative to a reference influenza virus HA protein. In the context of proteins having one or more mutations (e.g., substitutions), a “reference protein” (e.g., reference HA protein) refers to a protein into which a mutation is introduced to yield a protein having the mutation.

[0420] A reference HA protein may be an HA protein of an influenza virus isolate. An “influenza virus isolate” or “isolate of an influenza virus” refers to an influenza virus that has been obtained from an infected host and grown in cell culture. Amino acid sequences of proteins of a virus isolate (e.g., HA) may be determined by sequencing the isolate's genome segments (e.g., segment 4) and/or viral RNA from cells infected with the isolate. As used herein, a reference HA protein amino acid sequence of an influenza virus isolate is the HA protein amino acid sequence encoded by a consensus nucleotide sequence of segment 4 of the isolate. The skilled artisan will appreciate that a replicating virus (e.g., in cell culture) forms a population of virions, that each virion contains a genome that may have one or more mutations relative to a consensus nucleotide sequence (or set of consensus nucleotide sequences, for viruses with segmented genomes like influenza viruses), and that viral genomes may be defined in terms of that consensus nucleotide sequence (or set of consensus nucleotide sequences of genome segments, for segmented viral genomes). See, e.g., Domingo et al., Gene. 1985. 40(1):1-8; and Kuroda et al., PLoS ONE. 2010. 5(4):e10256. A reference HA protein amino acid sequence of an isolate will be understood not to encompass HA protein amino sequences that are not encoded by the consensus nucleotide sequence of genome segment 4 of the isolate, even if such other HA protein amino acid sequences may be encoded by a minority of genomes in a virion population of the isolate. A reference HA protein may be an engineered HA protein that is not encoded by a consensus nucleotide sequence of genome segment 4 of a naturally occurring influenza virus isolate.

[0421] The skilled artisan will appreciate that mutations may be applied to any B/Victoria lineage HA protein, B/Yamagata lineage HA protein, H1 HA protein, or H3 HA protein amino acid sequence that is extant at the time this specification is filed. The skilled artisan will also appreciate that the mutations may be applied to B/Victoria lineage HA protein, B/Yamagata lineage HA protein, H1 HA protein, or H3 HA protein amino acid sequences that do not yet exist at the time of filing this specification. Indeed, it is the continued evolution of influenza viruses that leads public health authorities to update the influenza virus isolates recommended for inclusion in seasonal vaccines each year. Thus, when a given influenza virus isolate is recommended for inclusion in a seasonal influenza vaccine, for instance, the skilled artisan could apply a mutation described below to the HA protein of that influenza virus isolate, to produce a mutated form of that recommended isolate's HA protein.

[0422] Recommendations for candidate vaccine viruses are typically made annually by the World Health Organization (WHO), following review of surveillance data and discussion of candidate vaccine viruses, which typically occurs early in the calendar year (e.g., February). World Health Organization. (2023 Feb. 24). Recommended composition of influenza virus vaccines for use in the 2023-2024 northern hemisphere influenza season: Questions and answers.

[0423] For example, the WHO recommended the following viruses for inclusion in vaccines to be used in the 2023-2024 northern hemisphere influenza season:

• • [0424] an A/Victoria/4897/2022(H1N1)pdm09-like virus;
  • [0425] an A/Darwin/9/2021(H3N2)-like virus; and
  • [0426] a B/Austria/1359417/2021 (B/Victoria lineage)-like virus.

• • [0427] an A/Wisconsin/67/2022(H1N1)pdm09-like virus;
  • [0428] an A/Darwin/6/2021(H3N2)-like virus; and
  • [0429] a B/Austria/1359417/2021 (B/Victoria lineage)-like virus. Id.

[0430] For quadrivalent vaccines of any (egg, cell culture-, or recombinant-based) type, the WHO recommended inclusion of a B/Phuket/3073/2013 (B/Yamagata lineage)-like virus as the B/Yamagata lineage component. Id. Regarding the term “-like virus”, recommended vaccine viruses are representative of the antigenic group of viruses anticipated to circulate widely in the forthcoming influenza season, and that multiple candidate vaccine viruses may be available that possess HA proteins that are antigenically similar to the recommended vaccine viruses. Id. The term “-like virus” is included in recommendations to allow for use of other candidate vaccine viruses in manufacturing. Id.

[0431] Sequence information for influenza viruses recommended for inclusion in seasonal influenza vaccines (e.g., HA and NA protein amino acid sequences and corresponding genome segment nucleotide sequences) is typically available in publicly available databases, such as GenBank and GISAID.

[0432] The skilled artisan will appreciate that mutations described in the context of H1 HA proteins may be applied to extant or later-arising H1 HA proteins, mutations described in the context of H3 HA proteins may be applied to extant or later-arising H3 HA proteins, mutations described in the context of B/Victoria lineage HA proteins may be applied to extant or later-arising B/Victoria lineage HA proteins, and mutations described in the context of B/Yamagata lineage HA proteins may be applied to extant or later-arising B/Yamagata lineage HA proteins, as HA proteins within a given subtype or lineage are more similar to each other than to HA proteins of other subtypes or lineages.

[0433] At the time of filing of the instant specification, seasonal influenza vaccines are quadrivalent and intended to elicit immunity to an influenza A/(H1N1)pdm09 virus, an influenza A/(H3N2) virus, an influenza B/Victoria lineage virus, and an influenza B/Yamagata lineage virus. However, reassortment between influenza A viruses may result in the formation of novel IAVs that go on to predominate in the population, replacing the predominantly circulating influenza A/(H1N1)pdm09 and A/(H3N2) subtypes. The skilled artisan will appreciate that where mutations are disclosed in the context of H1 HAs of influenza A/(H1N1)pdm09 viruses (e.g., influenza A/Wisconsin/67/2022(H1N1)pdm09 and A/Sydney/5/2021(H1N1)pdm09 viruses), such mutations may also be applied to H1 HA proteins of other IAV subtypes containing H1 HAs (e.g., A/(H1N2). Mutations disclosed in the context of H3 HAs of influenza A/(H3N2) viruses (e.g., influenza A/Darwin/6/2021(H3N2) virus) may similarly be applied to H3 HA proteins of other IAV subtypes containing H3 HAs (e.g., A/(H3N8)).

[0434] Influenza virus HA proteins are discussed below in the section entitled “Influenza Virus HA Proteins”. Those skilled in the art will appreciate that influenza virus proteins discussed therein are useful in multiple types of vaccine compositions. In some embodiments, the composition comprises one or more influenza virus proteins. In some embodiments, the composition comprises one or more nucleic acids (e.g., mRNAs) encoding one or more influenza virus proteins. These and other vaccine compositions are discussed below in the section entitled “Vaccine Compositions.”

[0435] Thus, discussion of influenza virus proteins can also be applied to nucleic acids encoding said influenza virus proteins and vice versa unless otherwise clear from context. Thus, disclosure related to particular polypeptide mutations is also relevant to nucleic acids encoding those polypeptides with those mutations, unless otherwise clear from context. Likewise, disclosure related to mRNA encoding mutated influenza virus proteins may also be relevant to the mutated influenza virus proteins. Thus, when a composition comprising an mRNA encoding an influenza virus protein having a particular mutation is disclosed, the skilled artisan can infer that the influenza virus protein per se, and compositions comprising the influenza virus protein, are also disclosed. In some embodiments, an influenza virus protein is a recombinant protein. A “recombinant protein” refers to a protein that is produced in a heterologous organism that does not naturally produce the protein or a variant thereof. Non-limiting examples of organisms in which recombinant proteins may be produced include bacteria (e.g., Escherichia coli), yeast (e.g., Saccharomyces cerevisiae), and mammalian cells.

TABLE IV-1
Exemplary IAV and IBV isolates
		SEQ ID	SEQ ID
		NO.	NO.
		of HA	of NA
Subtype		protein	protein
(IAV) or		amino	amino
lineage		acid	acid
(IBV)	Isolate	sequence	sequence
A/(H1N1)	A/Beijing/262/1995 (H1N1)	122	180
subtype	A/New Caledonia/20/1999 (H1N1)	123	181
	A/Solomon Islands/3/2006 (H1N1)	124	182
	A/Brisbane/59/2007 (H1N1)	125	183
	A/California/7/2009 (H1N1)pdm09	127	185
	A/Michigan/45/2015	128	186
	(H1N1)pdm09
	A/Brisbane/02/2018 (H1N1)pdm09	129	187
	A/Guangdong-	130	188
	Maonan/SWL1536/2019
	(H1N1)pdm09
	A/Hawaii/70/2019 (H1N1)pdm09	131	189
	A/Victoria/2570/2019	132	190
	(H1N1)pdm09
	A/Wisconsin/588/2019	133	191
	(H1N1)pdm09
	A/Victoria/4897/2022	134	192
	(H1N1)pdm09
	A/Wisconsin/67/2022	135	193
	(H1N1)pdm09
A/(H3N2)	A/Sydney/5/97 (H3N2)	136	194
subtype	A/Moscow/10/1999 (H3N2)	137	195
	A/Fujian/411/2002 (H3N2)	138	196
	A/California/7/2004 (H3N2)	139	197
	A/Wisconsin/67/2005 (H3N2)	140	198
	A/Brisbane/10/2007 (H3N2)	141	199
	A/Perth/16/2009 (H3N2)	142	200
	A/Victoria/361/2011 (H3N2)	143	201
	A/Texas/50/2012 (H3N2)	144	202
	A/Switzerland/9715293/2013	145	203
	(H3N2)
	A/Hong Kong/4801/2014 (H3N2)	146	204
	A/Singapore/INFIMH-16-	147	205
	0019/2016 (H3N2)
	A/Kansas/14/2017 (H3N2)	148	206
	A/Hong Kong/2671/2019 (H3N2)	149	207
	A/Hong Kong/45/2019 (H3N2)	150	208
	A/Cambodia/e0826360/2020	151	209
	(H3N2)
	A/Darwin/9/2021 (H3N2)	152	210
	A/Darwin/6/2021 (H3N2)	153	211
B/Victoria	B/Shangdong/7/1997	154	212
lineage	B/Hong Kong/330/2001	155	213
	B/Malaysia/2506/2004	156	214
	B/Brisbane/60/2008	157	215
	B/Colorado/06/2017	158	216
	B/Washington/02/2019	159	217
	B/Austria/1359417/2021	160	218
B/Yamagata	B/Beijing/184/1993		219
lineage	B/Sichuan/379/1999		220
	B/Shanghai/361/2002		221
	B/Florida/4/2006	164	222
	B/Wisconsin/1/2010	165	223
	B/Massachusetts/2/2012	166	224
	B/Phuket/3073/2013	167	225

[0436] It was surprisingly discovered that influenza virus HA proteins having one or more mutations (such as a substitution) relative to a wild-type HA protein sequence exhibit increased stability, surface expression, and/or immunogenicity as compared to the wild-type influenza virus HA protein. Without being bound by theory, it is believed that such mutations in influenza virus HA proteins can stabilize the conformation of the HA proteins.

[0437] Mutations that may be applied to influenza virus HA proteins are described in Tables HA-1 to HA-5 below. For clarity, mutations are described using amino acid numbering corresponding to specific listed HA amino acid sequences (e.g., of recent vaccine strains A/Wisconsin/67/2022 (H1N1)pdm09 (SEQ ID NO: 83), A/Darwin/6/2021(H3N2) (SEQ ID NO: 82), B/Austria/1359417/2021 (B/Victoria lineage) (SEQ ID NO: 71), and B/Phuket/3073/2013 (B/Yamagata lineage) (SEQ ID NO: 70), and additional strain A/Sydney/5/2021(H1N1)pdm09 (SEQ ID NO: 95)). The person of ordinary skill in the art will appreciate that mutations disclosed in relation to a listed HA amino acid sequence may be applied to other HA amino acid sequences of that IAV HA subtype (e.g., H1, H3), or other HA amino acid sequences of that IBV lineage (i.e., B/Victoria or B/Yamagata lineage). To apply a mutation disclosed with numbering corresponding to a listed amino acid sequence (e.g., SEQ ID NO: 71) to a different reference HA protein, the skilled artisan may align that different reference HA protein's amino acid sequence to the listed amino acid sequence with which the mutation is numbered. For example, to apply an H381Y substitution numbered according to SEQ ID NO: 71 (the listed amino acid sequence), to a reference HA protein, the skilled artisan would align the reference HA protein amino acid sequence to SEQ ID NO: 71, and introduce a tyrosine (Y) at the residue of the reference HA protein that corresponds to H381 of SEQ ID NO: 71. An example of such an alignment is presented in FIG. 19E, the influenza B/Brisbane/60/2008 virus HA protein amino acid sequence of SEQ ID NO: 157, showing that residue H384 of SEQ ID NO: 157 aligns to residue H381 of SEQ ID NO: 71. Accordingly, to apply an H381Y substitution (or tyrosine substitution at position 381 generally) to SEQ ID NO: 157, the skilled artisan would replace residue 384 of SEQ ID NO: 157 with a tyrosine, because residue 384 of SEQ ID NO: 157 aligns to H381 of SEQ ID NO: 71. Another example is presented in FIG. 19F, showing alignment of the influenza A/Beijing/262/1995(H1N1) virus HA protein amino acid sequence of SEQ ID NO: 123 to the influenza A/Wisconsin/62/2022(H1N1)pdm09 virus HA protein amino acid sequence. While both SEQ ID NOs: 123 and 83 contain an L37 residue, residue G390 of SEQ ID NO: 123 aligns to K391 of SEQ ID NO: 83. Thus, to apply a K391C substitution (numbered according to SEQ ID NO: 83) to the amino acid sequence of SEQ ID NO: 123, the skilled artisan would replace G390 of SEQ ID NO: 123 with a cysteine (C), because G390 aligns to K391 of SEQ ID NO: 83.

[0438] An Influenza virus HA protein may comprise one or more substitutions relative to a reference HA protein. For example, an influenza B/Victoria lineage virus HA protein having the amino acid sequence of SEQ ID NO: 77 comprises a tyrosine substitution and a valine substitution relative to the reference influenza B/Victoria lineage virus HA protein sequence of SEQ ID NO: 71. The skilled artisan will appreciate the substitutions disclosed in relation to a listed amino acid sequence (e.g., SEQ ID NO: 71) may be referred to in the form X₁[#]X₂, where X₁ is the amino acid at position [#] in a listed amino acid sequence, and X₂ is the amino acid introduced by replacement of the X₁ at position [#]. For example, a tyrosine substitution at position 381 may also be referred to as an H381Y substitution, when using SEQ ID NO: 71 as a listed amino acid sequence, because the histidine (H) at position 381 of SEQ ID NO: 71 is replaced with a tyrosine (Y). Such a substitution may also be referred to as an “X₂ substitution at position [#]”, meaning that a protein comprises an X₂ residue at position [#] (numbered by alignment to a listed sequence), regardless of whether the residue that was present at position [#] in the reference amino acid sequence was X₁, or a different residue other than X₂. The skilled artisan will understand that substitutions disclosed in the form X₁[#]X₂ may also be applied to a reference amino acid sequence in the form of “X₂ substitution at position [#]” that is agnostic to the residue present in the reference amino acid sequence (numbered by alignment to a listed sequence). While the preceding paragraph uses SEQ ID NO: 71 (HA protein of influenza B/Austria/1359417/2021 (B/Victoria lineage) virus) as a reference HA protein amino acid sequence, a reference HA protein may be an HA protein of another influenza virus isolate, or an engineered HA protein that is not encoded by a genome of an isolate.

[0439] An influenza virus HA protein may comprise a specified residue at a specified position, with positions being numbered according to a listed amino acid sequence (e.g., SEQ ID NO: 71). As with determining the positions of substitutions numbered according to a listed amino acid sequence, the skilled artisan may align the HA protein sequence to the listed amino acid sequence, to determine whether the HA protein contains the specified residue at that position corresponding to the specified position of the listed amino acid sequence. For example, to determine whether an HA protein contains a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment to SEQ ID NO: 71, the skilled artisan would align the amino acid sequence of the HA protein to SEQ ID NO: 71, determine whether the amino acid of the HA protein that aligns to residue 381 of SEQ ID NO: 71 is a tyrosine, and determine whether the amino acid of the HA protein that aligns to residue 288 of SEQ ID NO: 71 is a valine.

[0440] Unless otherwise clear from context, mutations in the instant specification are numbered according to full-length amino acid sequences of influenza virus HA proteins (e.g., SEQ ID NOs: 70, 71, 82, 83, and 95), each of which includes the signal peptide of the HA protein (i.e., residue 1 of each sequence is the methionine encoded by the start codon of an ORF encoding the HA protein). The person of ordinary skill will understand that other numbering schemes exist for reference to other forms or subunits of an HA protein, such as a post-signal peptide cleavage form (where residue 1 is the N-terminal amino acid after signal peptide cleavage). For instance, the skilled artisan will understand that reference to A270V+H363Y substitutions in influenza B/Austria/1359417/2021 virus HA protein would correspond to A288V+H381Y of SEQ ID NO: 71, because SEQ ID NO: 71 includes the signal peptide protein at its N-terminus, and after including that signal peptide, the A and H residues separated by 93 amino acids are found at positions 288 and 381 of SEQ ID NO: 71, respectively.

[0441] Some embodiments relate to HA proteins comprising one or more mutations selected from: (i) one or more introduced cysteines, where a disulfide bond is formed by at least one of the introduced cysteines; (ii) one or more proline or glycine substitutions in a B loop of the HA protein; (iii) one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue; (iv) one or more substitutions of a pH-sensitive histidine in the HA protein; and/or (v) a mutation in, or removal of, a polybasic cleavage site of the HA protein.

[0442] In some embodiments, an HA protein comprises one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0443] In some embodiments, an HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more proline substitutions in the B loop.

[0444] In some embodiments, an HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0445] In some embodiments, an HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue, and one or more proline substitutions in the B loop.

[0446] In some embodiments, an HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and an intraprotomer disulfide bond formed by at least one introduced cysteine, where the introduced cysteine(s) of the interpromoter disulfide bond are at different positions than the introduced cysteine(s) of the intraprotomer disulfide bond.

[0447] In some embodiments, an HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0448] In some embodiments, an HA protein comprises one or more cysteine substitutions, such that a disulfide bond is formed between the introduced cysteines. In some embodiments, the disulfide bond is an interprotomer disulfide bond, which covalently links two protomers of an HA protein containing multiple protomers (e.g., three protomers). In some embodiments, the disulfide bond is an intraprotomer disulfide bond, which covalently links two residues of a single protomer of the HA protein. In some embodiments, the disulfide bond is in the head region (also referred to as the “globular head”, “head”, or HA1 subunit) of the HA protein. In some embodiments, the disulfide bond is in the stalk region (also referred to as the “stem”, “stalk”, or HA2 subunit) of the HA protein. Translation of an open reading frame encoding a full-length HA protein sequence produces a precursor HA0 polypeptide, which is then cleaved (e.g., by a serine protease) to produce an HA1 subunit (N-terminal to the cleavage site) and HA2 subunit (C-terminal to the cleavage site), which are connected by a disulfide bond. See, e.g., Wang et al., J Virol. 89(20):10602-10611. The positions of cleavage sites in IAV H1 HA, IAV H3 HA, influenza B/Victoria lineage virus HA, and influenza B/Yamagata lineage HA proteins are known in the art, allowing the skilled artisan to identify the residues of a given reference full-length HA protein sequence that correspond to HA1 and HA2 subunits of that reference HA protein.

[0449] In some embodiments, an HA protein comprises one or more proline substitutions in the B loop of the HA protein. In some embodiments, an HA protein comprises one or more glycine substitutions in the B loop of the HA protein. HA proteins comprise multiple subdomains, including a B loop, which enables the fusion of the viral envelope and endosomal membrane. Proline and glycine are among residues considered helix breakers, such that the introduction of proline or glycine residues can stabilize or destabilize proteins by altering their conformation (Lyu et al. 1990. Science. 250(4981), 669-673). In some embodiments, an HA protein comprises 2, 3, or 4 proline substitutions in the B loop. The location of the B loop in IAV H1 HA, IAV H3 HA, influenza B/Victoria lineage virus HA, and influenza B/Yamagata lineage HA proteins are known in the art, allowing the skilled artisan to identify the residues of a given reference full-length HA protein sequence that correspond to the B loop of that reference HA protein. See, e.g., Mair et al., Biochim Biophys Acta. 2014. 1838(4):1153-1168.

[0450] In some embodiments, an HA protein comprises one or more substitutions of a pH-sensitive histidine residue. The protonation state and charge of certain histidine residues of influenza virus HA proteins are sensitive to pH, such that histidine residues that are unprotonated at neutral pH may become protonated, and thus positively charged, as the pH of an endosome drops. Such protonation may result in a conformational change that allows the viral envelope to fuse with the endosomal membrane. For example, H5 HA1 residue His184 is located near positively charged residues in prefusion HA protein structures, and its protonation state acts as molecular switch triggering a conformational change in HA. See, e.g., Kampmann et al., Structure. 2006. 14(10):1481-1487; Mair et al., J Virol. 2014. 88(22):13189-13200. Accordingly, replacement of one or more pH-sensitive histidines can inhibit or prevent a conformational change that occurs at low pH (e.g., transition to postfusion conformation), thereby stabilizing the HA protein.

[0451] In some embodiments, an HA protein comprises a substitution in, or removal of, a polybasic cleavage site. Cellular infection by influenza viruses involves cleavage of immature HA monomers at a cleavage site; differences in cleavage motifs of influenza viruses confer distinct tissue- and cell-specificity in which the viruses can replicate, resulting in different pathogenicity (Klenk et al. 1975. Virology. 68:426-439). Highly pathogenic avian influenza (HPAI) viruses typically possess polybasic HA cleavage sites (e.g., RKTR (SEQ ID NO: 120) or RKKR (SEQ ID NO: 121)), a feature which low pathogenic avian influenza (LPAI) viruses lack. In some embodiments, the mutation is a replacement of a polybasic cleavage site of an HPAI virus by a protease cleavage site of a LPAI virus. In some embodiments, the mutation is deletion of a polybasic cleavage site. In some embodiments, the mutation is deletion of an HPAI polybasic cleavage site. In some embodiments, the mutation is substitution of a polybasic cleavage site with an amino acid sequence that does not comprise a polybasic cleavage site. In some embodiments, the mutation is substitution of one or more arginine residues of an HPAI polybasic cleavage site with one or more non-basic residues (e.g. glycine and/or serine).

[0452] In some embodiments, an HA protein comprises one or more substitutions of a polar or charged cavity-lining residue with a hydrophobic residue. In some embodiments, a HA protein comprises one or more substitutions of a polar or charged cavity-lining residue with a glycine. Protein interiors may comprise tightly packed side chains which influence the stability of the protein, wherein larger cavities are less stable than narrow cavities (Bueno et al. J Mol Bio. 2006. 358(3):701-712). By replacing small cavity-lining residues with larger, hydrophobic residues, the stability of proteins can be increased by such cavity-filling mutations. Any suitable hydrophobic residue may be used in such a substitution, such as serine, alanine, valine, phenylalanine, histidine, leucine, methionine, valine, or tryptophan.

[0453] Some embodiments relate to influenza B virus HA proteins. Influenza B virus HA proteins may comprise one or more mutations (e.g., substitutions) relative to an amino acid sequence of a reference influenza B virus HA protein. The reference IBV HA protein may be an HA protein of an IBV isolate. The reference IBV HA protein may be an engineered IBV HA protein. Non-limiting examples of mutations include (i) one or more introduced cysteines, where a disulfide bond is formed by at least one of the introduced cysteines; (ii) one or more proline or glycine substitutions in a B loop of the HA protein; (iii) one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue; (iv) one or more substitutions of a pH-sensitive histidine in the HA protein; and/or (v) a mutation in, or removal of, a polybasic cleavage site of the HA protein.

[0454] Some embodiments relate to influenza B/Victoria lineage virus HA proteins comprising an amino acid substitution relative to a reference influenza B/Victoria lineage virus HA protein. The reference influenza B/Victoria lineage virus HA protein may be an HA protein of an influenza B/Victoria lineage virus isolate. The reference influenza B/Victoria lineage virus HA protein may be an engineered influenza B/Victoria lineage virus HA protein. Non-limiting examples of influenza B/Victoria lineage virus isolates include B/Shangdong/7/1997, B/Hong Kong/330/2001, B/Malaysia/2506/2004, B/Brisbane/60/2008, B/Colorado/06/2017, B/Washington/02/2019, and B/Austria/1359417/2021. Representative amino acid sequences of influenza B/Victoria lineage virus HA proteins of previous seasonal influenza vaccines are provided as SEQ ID NOs: 154-160.

[0455] Those of ordinary skill in the art will appreciate that mutations disclosed in relation to a listed sequence, e.g., of influenza B/Austria/1359417/2021 virus HA, may be applied to HA proteins of other influenza B/Victoria lineage viruses or other reference influenza B/Victoria lineage virus HA proteins. For example, in applying an H381Y substitution to an influenza B/Victoria lineage virus HA protein, the skilled artisan would align the amino acid sequence of that reference HA protein to the B/Austria/1359417/2021 virus HA protein sequence of SEQ ID NO: 71, and introduce a Y (tyrosine) at the residue of the reference HA protein amino acid sequence that aligns to H381 (the histidine at position 381) of SEQ ID NO: 71.

[0456] Exemplary substitutions that may be present in influenza B/Victoria lineage HA proteins are provided below in Table HA-1. In the event a reference HA protein sequence (e.g. of an isolate) already includes a substitution mentioned in the table, then it will be appreciated that some embodiments will include the residues set forth at positions below without a substitution being made at that particular position. For example, if an isolate already contains a tyrosine at position 381, then embodiments comprising 381Y and 288V can be obtained with only a 288V substitution.

TABLE HA-1
B/Victoria lineage HA substitutions
(B/Austria/1359417/2021 (SEQ ID NO: 71) numbering)
	Substitution(s)	Mutation class
	H381Y A288V	pH Switch / cavity filling
	S27C Y349C	Intra-protomer DS (Head)
	I295C K328C	Intra-protomer DS (Head)
	S399C H473C	Intra-protomer DS (Stalk)
	L422C D444C	Intra-protomer DS (Stalk)
	K118C L216C	Inter-protomer DS (Head)
	V237C D261C	Inter-protomer DS (Head)
	G363C K480C	Inter-protomer DS (Stalk)
	A364C K483C	Inter-protomer DS (Stalk)
	I365C A476C	Inter-protomer DS (Stalk)
	A366C R479C	Inter-protomer DS (Stalk)
	G367C K483C	Inter-protomer DS (Stalk)
	E435C A428C	Inter-protomer DS (Stalk)
	N494C K483C	Inter-protomer DS (Stalk)
	N494C K480C	Inter-protomer DS (Stalk)
	E416P L417P N434P H433P	Prolines
	N434P H433P	Prolines
	T515P F516P	Prolines
	H473F	pH Switch

[0457] In preferred embodiments, the influenza B/Victoria lineage HA protein comprises a tyrosine substitution at position 381 and a valine substitution at position 288 (e.g., H381Y, A288V). These preferred substitutions can be combined with one or more additional substitutions set forth in the above table.

[0458] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises H381Y and A288V substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. An H381Y substitution is a replacement of a pH-sensitive histidine residue, and A290V is a cavity-filling substitution.

[0459] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 27 and a cysteine at position 349, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 27 and a cysteine substitution at position 349 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises S27C and Y349C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. S27C and Y349C substitutions result in the formation of an intraprotomer disulfide bond in the head region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0460] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 295 and a cysteine at position 328, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 295 and a cysteine substitution at position 328 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises I295C and K328C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. I295C and K328C substitutions result in the formation of an intraprotomer disulfide bond in the head region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0461] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 399 and a cysteine at position 473, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 399 and a cysteine substitution at position 473 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises S399C and H473C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. S399C and H473C substitutions result in the formation of an intraprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0462] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 422 and a cysteine at position 444, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 422 and a cysteine substitution at position 444 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises L422C and D444C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. L422C and D444C substitutions result in the formation of an intraprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine at position 381, a valine at position 288, a cysteine at position 422, and a cysteine at position 444, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71

[0463] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 118 and a cysteine at position 216, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 118 and a cysteine substitution at position 216 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises K118C and L216C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. K118C and L216C substitutions result in the formation of an interprotomer disulfide bond in the head region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0464] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 237 and a cysteine at position 261, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 237 and a cysteine substitution at position 261 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises V237C and D261C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. V237C and D261C substitutions result in the formation of an interprotomer disulfide bond in the head region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0465] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 363 and a cysteine at position 480, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 363 and a cysteine substitution at position 480 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises G363C and K480C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. G363C and K480C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0466] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 364 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 364 and a cysteine substitution at position 483 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises A364C and K483C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. A364C and K483C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine at position 381, a valine at position 288, a cysteine at position 364 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71.

[0467] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 365 and a cysteine at position 476, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 365 and a cysteine substitution at position 476 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises 1365C and A476C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. 1365C and A476C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0468] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 366 and a cysteine at position 479, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 366 and a cysteine substitution at position 479 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises A366C and R479C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. A366C and R479C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0469] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 367 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 367 and a cysteine substitution at position 483 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises G367C and K483C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. G367C and K483C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine at position 381, a valine at position 288, a cysteine at position 367 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71.

[0470] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 435 and a cysteine at position 428, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 435 and a cysteine substitution at position 428 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises E435C and A428C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. E435C and A428C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0471] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 494 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 494 and a cysteine substitution at position 483 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises N494C and K483C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. N494C and K483C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a tyrosine at position 381, a valine at position 288, a cysteine at position 494 and a cysteine at position 483, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71.

[0472] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine at position 494 and a cysteine at position 480, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a cysteine substitution at position 494 and a cysteine substitution at position 480 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises N494C and K480C substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. N494C and K480C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0473] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline at position 416, a proline at position 417, a proline at position 434, and a at position 433, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline substitution at position 416, a proline substitution at position 417, a proline substitution at position 434, and a substitution at position 433 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises E416P, L417P, N434P, and H433P substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. Proline is a residue considered a helix breaker, and substitution of a residue in the B loop of an HA protein with proline (e.g., E416P, L417P, N434P, and H433P) can the protein by altering its conformation. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0474] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline at position 434 and a proline at position 433, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline substitution at position 434 and a proline substitution at position 433 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises N434P and H433P substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0475] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline at position 515 and a proline at position 516, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a proline substitution at position 515 and a proline substitution at position 516 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises T515P and F516P substitutions relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. Proline is a residue considered a helix breaker, and substitution of one or more residues in the B loop of an HA protein with proline (e.g., T515P and F516P) can the protein by altering its conformation. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0476] In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a phenylalanine at position 473, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises a phenylalanine substitution at position 473 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein comprises an H473F substitution relative to a reference influenza B/Victoria lineage virus HA protein, where the numbering of the amino acid replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71. Substitution of a pH-sensitive histidine (e.g., H473) can inhibit or prevent the conformational change that occurs at low pH (e.g., during viral fusion), thereby stabilizing the HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein also comprises a tyrosine at position 381 and a valine at position 288, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises a tyrosine substitution at position 381 and a valine substitution at position 288 relative to a reference influenza B/Victoria lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Victoria lineage virus HA protein to SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage virus HA protein further comprises H381Y and A288V substitutions relative to the reference HA protein, where the numbering of the amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 71.

[0477] Substitutions described in this subsection relating to B/Victoria lineage HA proteins may be combined. For example, any of the pairs of cysteine substitutions may be combined with one or more proline substitutions in the B loop and/or substitutions of pH-sensitive histidines. Pairs of cysteine substitutions that form different disulfide bonds (e.g., interprotomer versus intraprotomer bonds, head versus stalk region bonds) may also be combined. In some embodiments, the influenza B/Victoria lineage HA protein comprises one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0478] In some embodiments, the influenza B/Victoria lineage HA protein comprises an amino acid sequence with at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of SEQ ID NO: 71. In some embodiments, the influenza B/Victoria lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 71.

[0479] Some embodiments relate to influenza B/Yamagata lineage virus HA proteins comprising an amino acid substitution relative to a reference influenza B/Yamagata lineage virus HA protein. The reference influenza B/Yamagata lineage virus HA protein may be an HA protein of an influenza B/Yamagata lineage virus isolate. The reference influenza B/Yamagata lineage virus HA protein may be an engineered influenza B/Yamagata lineage virus HA protein. Non-limiting examples of influenza B/Yamagata lineage virus isolates include B/Beijing/184/1993, B/Sichuan/379/1999, B/Shanghai/361/2002, B/Florida/4/2006, B/Wisconsin/1/2010, B/Massachusetts/2/2012, and B/Phuket/3073/2013. Representative amino acid sequences of influenza B/Yamagata lineage virus HA proteins of previous seasonal influenza vaccines are provided as SEQ ID NOs: 164-167.

[0480] Those of ordinary skill in the art will appreciate that mutations disclosed in relation to a listed sequence, e.g., of influenza B/Phuket/3073/2013 virus HA, may be applied to HA proteins of other influenza B/Yamagata lineage viruses or other reference influenza B/Victoria lineage virus HA proteins. For example, in applying an A231C substitution to another influenza B/Yamagata lineage virus HA protein, the skilled artisan would align the amino acid sequence of that reference HA protein to the influenza B/Phuket/3073/2013 virus HA protein sequence of SEQ ID NO: 70, and introduce a C at the residue of the reference HA protein amino acid sequence that aligns to A231 of SEQ ID NO: 70.

[0481] Exemplary substitutions that may be present in influenza B/Yamgata lineage HA proteins are provided below in Table HA-2. In the event a reference HA protein sequence (e.g. of an isolate) already includes a substitution mentioned in the table, then it will be appreciated that some embodiments will include the residues set forth at positions below without a substitution being made at that particular position. For example, if an isolate already contains a tyrosine at position 381, then embodiments comprising 381Y and 290V can be obtained with only a 290V substitution.

TABLE 2
B/Yamagata lineage HA substitutions
(B/Phuket/3073/2013 (SEQ ID NO: 70) numbering)
	Substitution(s)	Mutation class
	A231C G273C	Intra-protomer DS (Head)
	K295C I332C	Intra-protomer DS (Head)
	A396C L510C	Intra-protomer DS (Stalk)
	V239C V276C	Inter-protomer DS (Head)
	I367C S401C	Inter-protomer DS (Stalk)
	F363C E404C	Inter-protomer DS (Stalk)
	E437C G429C	Inter-protomer DS (Stalk)
	D451C K422C	Inter-protomer DS (Stalk)
	H381Y A290V	pH Switch (H381Y) / Cavity Filling (A290V)

[0482] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 231 and a cysteine at position 273, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 231 and a cysteine substitution at position 273 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises A231C and G273C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. A231C and G273C substitutions result in the formation of an intraprotomer disulfide bond in the head region of the HA protein.

[0483] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 295 and a cysteine at position 332, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 295 and a cysteine substitution at position 332 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises K295C and I332C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. K295C and I332C substitutions result in the formation of an intraprotomer disulfide bond in the head region of the HA protein.

[0484] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 396 and a cysteine at position 510, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 396 and a cysteine substitution at position 510 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises A396C and L510C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. A396C and L510C substitutions result in the formation of an intraprotomer disulfide bond in the stalk region of the HA protein.

[0485] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 239 and a cysteine at position 276, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 239 and a cysteine substitution at position 276 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises V239C and V276C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. V239C and V276C substitutions result in the formation of an interprotomer disulfide bond in the head region of the HA protein. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 239, a cysteine at position 276, a cysteine at position 451, and a cysteine at position 422, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70.

[0486] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 367 and a cysteine at position 401, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 367 and a cysteine substitution at position 401 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises I367C and S401C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. I367C and S401C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 367, a cysteine at position 401, a cysteine at position 451, and a cysteine at position 422, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70.

[0487] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 363 and a cysteine at position 404, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 363 and a cysteine substitution at position 404 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises F363C and E404C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. F363C and E404C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0488] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 437 and a cysteine at position 429, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 437 and a cysteine substitution at position 429 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises E437C and G429C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. E437C and G429C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0489] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine at position 451 and a cysteine at position 422, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a cysteine substitution at position 451 and a cysteine substitution at position 422 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises D451C and K422C substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. D451C and K422C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0490] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a tyrosine at position 381 and a valine at position 290, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises a tyrosine substitution at position 381 and a valine substitution at position 290 relative to a reference influenza B/Yamagata lineage virus HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference influenza B/Yamagata lineage virus HA protein to SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises H381Y and A290V substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70. H381Y is a pH-sensitive histidine residue replacement substitution, and A290V is a cavity-filling substitution.

[0491] Substitutions described in this subsection relating to B/Yamagata lineage HA proteins may be combined. For example, any of the pairs of cysteine substitutions may be combined with one or more substitutions of pH-sensitive histidines and/or cavity-filling substitutions. Pairs of cysteine substitutions that form different disulfide bonds (e.g., interprotomer v. intraprotomer bonds, head v. stalk region bonds) may also be combined. In some embodiments, the influenza B/Yamagata lineage HA protein comprises one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0492] In some embodiments, the influenza B/Yamagata lineage virus HA protein comprises H381Y and A290V substitutions relative to a reference influenza B/Yamagata lineage virus HA protein, where the numbering of amino acids replaced in the reference HA protein corresponds to the numbering of SEQ ID NO: 70 in addition to one or more other substitutions described in this section.

[0493] In some embodiments, the influenza B/Yamagata lineage HA protein comprises an amino acid sequence with at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of SEQ ID NO: 70. In some embodiments, the influenza B/Yamagata lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 70.

[0494] Some embodiments relate to influenza A virus HA proteins. Influenza A virus HA proteins may comprise one or more mutations (e.g., substitutions) relative to an amino acid sequence of an HA protein of an influenza A virus isolate.

[0495] Some embodiments relate to IAV H1 HA proteins comprising an amino acid substitution relative to a reference IAV H1 HA protein. The reference IAV H1 HA protein may be an HA protein of an isolate of an influenza A virus of an IAV subtype containing an H1 HA protein, such as an influenza A/(H1N1)pdm09 virus. H1 HA proteins are present, e.g., on influenza A viruses of the A/(H1N1)pdm09 subtype, but other IAV subtypes expressing H1 HA proteins have been identified (such as the H1N2 subtype endemic in pigs and occasionally observed in humans). Non-limiting examples of influenza A/(H1N1)pdm09 virus isolates (and related influenza A/(H1N1) virus isolates preceding the 2009 influenza A/(H1N1) virus pandemic) include A/Beijing/262/1995 (H1N1), A/New Caledonia/20/1999(H1N1), A/Solomon Islands/3/2006(H1N1), A/Brisbane/59/2007(H1N1), A/California/7/2009(H1N1)pdm09, A/Michigan/45/2015 (H1N1)pdm09, A/Brisbane/02/2018(H1N1)pdm09, A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09, A/Hawaii/70/2019(H1N1)pdm09, (A/Victoria/2570/2019(H1N1)pdm09, A/Wisconsin/588/2019(H1N1)pdm09, A/Victoria/4897/2022(H1N1)pdm09, and A/Wisconsin/67/2022(H1N1)pdm09. Representative amino acid sequences of influenza A/(H1N1)pdm09 virus HA proteins of previous seasonal influenza vaccines are provided as SEQ ID NOs: 122-135.

[0496] Those of ordinary skill in the art will appreciate that mutations disclosed in relation to a listed sequence, e.g., of influenza A/Wisconsin/67/2022(H1N1)pdm09 virus HA, may be applied to other IAV H1 HA proteins. For example, in applying a K391C substitution to another IAV H1 HA protein, the skilled artisan would align the amino acid sequence of that reference HA protein to the influenza A/Wisconsin/67/2022(H1N1)pdm09 virus HA protein sequence of SEQ ID NO: 83, and introduce a C at the residue of the reference HA protein amino acid sequence that aligns to K391 of SEQ ID NO: 83. Similarly, mutations disclosed in relation to a reference sequence of influenza A/Sydney/5/2021(H1N1)pdm09 virus HA may be applied to a different reference HA protein by alignment of the reference HA protein amino acid sequence to the amino acid sequence of SEQ ID NO: 95. Such alignment allows the skilled artisan to identify the residue in the reference HA protein amino acid sequence that corresponds to the mutated residue of the influenza A/Sydney/5/2021(H1N1)pdm09 virus HA protein (e.g., to identify the residue of the reference HA protein amino acid sequence that corresponds to V410 of the A/Sydney/5/2021(H1N1)pdm09 virus HA protein amino acid sequence, to determine where to introduce a C, in applying a V410C substitution).

[0497] Exemplary substitutions that may be present in IAV H1 HA proteins are provided below in Tables HA-3 and HA-4. In the event a reference HA protein sequence (e.g. of an isolate) already includes a substitution mentioned in the table, then it will be appreciated that some embodiments will include the residues set forth at positions below without a substitution being made at that particular position. For example, if an isolate already contains an isoleucine at position 395, then embodiments comprising 395I and 447I can be obtained with only a 447I substitution.

TABLE HA-3
A/(H1N1) subtype HA substitutions
(A/Wisconsin/67/2022 (H1N1)pdm09 (SEQ ID NO: 83) numbering)
	Substitution(s)	Mutation class
	K391C L37C	Inter-protomer DS (Stalk)
	K395C V36C	Inter-protomer DS (Stalk)
	N461C G348C	Inter-protomer DS (Stalk)
	N404P H416P	Proline (Pro)
	K395I E447I	Hydrophobic Interaction (Hyd)
	D456G K402I	Hydrophobic Interaction (Hyd)
	K391C L37C N404P H416P	InterDS + Pro
	K391C L37C K395I E447I	InterDS + Hyd
	K391C L37C D456G K402I	InterDS + Hyd
	K395C V36C N404P H416P	InterDS + Pro
	K395C V36C D456G K402I	InterDS + Hyd
	N461C G348C N404P H416P	InterDS + Pro
	N461C G348C K395I E447I	InterDS + Hyd
	N461C G348C D456G K402I	InterDS + Hyd
	K391C L37C N404P H416P	InterDS + Pro + Hyd
	D456G K402I

TABLE HA-4
A/(H1N1) subtype HA substitutions
(A/Sydney/5/2021(H1N1)pdm09 (SEQ ID NO: 95) numbering)
	Substitution(s)	Mutation class
	V410C L462C	Intra-protomer DS
	E120C K419C	Inter-protomer DS
	K391C L37C	Inter-protomer DS
	K395C V36C	Inter-protomer DS
	Q406C D430C	Inter-protomer DS
	S457C L346C	Inter-protomer DS
	N461C G348C	Inter-protomer DS
	N404P K419P	Proline
	N404P H416P	Proline
	T405P Q406P	Proline
	N415P H416P	Proline
	H25Y H45E	pH Switch
	H370Y K497W	pH Switch
	K402G T405G F407G	Glycine
	K395I E447I	Cavity Filling
	D456G K402I	Glycine(s) (D456G) / Cavity
		Filling (K402I)
	L442C N423C	Inter-protomer DS
	K391G	Glycine(s)
	V410C L462C S457C L346C	Intra- and Inter-protomer DS
	K391C L37C H370F H455F	Inter-protomer DS + pH Switch

[0498] Some embodiments relate to IAV H1 HA proteins having one or more substitutions relative to a reference H1 HA protein, wherein the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83, which represents the HA protein of the influenza A/Wisconsin/67/2022(H1N1)pdm09 virus isolate.

[0499] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391 and a cysteine at position 37, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391 and a cysteine substitution at position 37 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K391C and L37C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. K391C and L37C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0500] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 395 and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 395 and a cysteine substitution at position 36 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K395C and V36C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. K395C and V36C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0501] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 461 and a cysteine at position 348, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 461 and a cysteine substitution at position 348 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises N461C and G348C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. N461C and G348C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0502] In some embodiments, the IAV H1 HA protein comprises a proline at position 404 and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a proline substitution at position 404 and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises N404P and H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. N404P and H416P are proline substitutions in the B loop of the HA protein, stabilizing the HA protein by changing its conformation. In some embodiments, the IAV H1 HA protein comprises a proline at position 404, a proline at position 416, a cysteine at position 395, and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a proline at position 404, a proline at position 416, a cysteine at position 391, and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a proline at position 404, a proline at position 416, a cysteine at position 391, a cysteine at position 37, a glycine at position 456, and an isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83.

[0503] In some embodiments, the IAV H1 HA protein comprises a isoleucine at position 395 and a isoleucine at position 447, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a isoleucine substitution at position 395 and a isoleucine substitution at position 447 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K395I and E447I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. K395I and E447I substitutions are replacements of charged lysine and glutamate residues with hydrophobic isoleucine residues.

[0504] In some embodiments, the IAV H1 HA protein comprises a glycine at position 456 and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a glycine substitution at position 456 and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises D456G and K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. D456G and K402I substitutions are replacements of charged aspartate and lysine residues with uncharged glycine and uncharged, hydrophobic isoleucine residues. In some embodiments, the IAV H1 HA protein comprises a glycine at position 456, an isoleucine at position 402, a cysteine at position 395, and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83.

[0505] In some embodiments, the amino acid substitution comprises a cysteine substitution at position 456 and a isoleucine substitution at position 402, where the positions are numbered by alignment of the amino acid sequence of the influenza B/Victoria lineage virus HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 456 and a isoleucine substitution at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises D456C and K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine at position 456, an isoleucine at position 402, a cysteine at position 395, and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83.

[0506] In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 83.

[0507] Some embodiments relate to IAV H1 HA proteins having one or more substitutions relative to a reference H1 HA protein, wherein the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95, which represents the HA protein of the influenza A/Sydney/5/2021(H1N1)pdm09 virus isolate.

[0508] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 410 and a cysteine at position 462, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 410 and a cysteine substitution at position 462 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises V410C and L462C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. V410C and L462C substitutions result in the formation of an intraprotomer disulfide bond in the HA protein.

[0509] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 120 and a cysteine at position 419, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 120 and a cysteine substitution at position 419 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises E120C and K419C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. E120C and K419C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0510] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391 and a cysteine at position 37, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391 and a cysteine substitution at position 37 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises K391C and L37C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. K391C and L37C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0511] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 395 and a cysteine at position 36, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 395 and a cysteine substitution at position 36 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises K395C and V36C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. K395C and V36C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0512] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 406 and a cysteine at position 430, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 406 and a cysteine substitution at position 430 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises Q406C and D430C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. Q406C and D430C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0513] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 457 and a cysteine at position 346, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 457 and a cysteine substitution at position 346 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises S457C and L346C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. S457C and L346C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0514] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 461 and a cysteine at position 348, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 461 and a cysteine substitution at position 348 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises N461C and G348C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. N461C and G348C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0515] In some embodiments, the IAV H1 HA protein comprises a proline at position 404 and a proline at position 419, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a proline substitution at position 404 and a proline substitution at position 419 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises N404P and K419P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. N404P and K419P substitutions are proline substitutions in the B loop of the HA protein.

[0516] In some embodiments, the IAV H1 HA protein comprises a proline at position 404 and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a proline substitution at position 404 and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises N404P and H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. N404P and H416P substitutions are proline substitutions in the B loop of the HA protein.

[0517] In some embodiments, the IAV H1 HA protein comprises a proline at position 405 and a proline at position 406, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a proline substitution at position 405 and a proline substitution at position 406 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises T405P and Q406P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. T405P and Q406P substitutions are proline substitutions in the B loop of the HA protein.

[0518] In some embodiments, the IAV H1 HA protein comprises a proline at position 415 and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a proline substitution at position 415 and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises N415P and H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. N415P and H416P substitutions are proline substitutions in the B loop of the HA protein.

[0519] In some embodiments, the IAV H1 HA protein comprises a tyrosine at position 25 and a glutamic acid at position 45, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a tyrosine substitution at position 25 and a glutamic acid substitution at position 45 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises H25Y and H45E substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. H25Y and H45E substitutions are replacements of pH-sensitive histidines.

[0520] In some embodiments, the IAV H1 HA protein comprises a tyrosine at position 370 and a tryptophan at position 497, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a tyrosine substitution at position 370 and a tryptophan substitution at position 497 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises H370Y and K497W substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. An H370Y substitution is a replacement of a pH-sensitive histidine, and a K497W substitution is a cavity-filling substitution.

[0521] In some embodiments, the IAV H1 HA protein comprises a glycine at position 402, a glycine at position 405, and a glycine at position 407, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a glycine substitution at position 402, a glycine substitution at position 405, and a glycine substitution at position 407 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises K402G, T405G, and F407G substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. K402G, T405G, and F407G substitutions are glycine substitutions in the B loop of the HA protein.

[0522] In some embodiments, the IAV H1 HA protein comprises a isoleucine at position 395 and a isoleucine at position 447, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a isoleucine substitution at position 395 and a isoleucine substitution at position 447 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises K395I and E447I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. K395I and E447I substitutions are cavity-filling substitutions

[0523] In some embodiments, the IAV H1 HA protein comprises a glycine at position 456 and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a glycine substitution at position 456 and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises D456G and K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. AD456G substitution is a glycine substitution in the B loop, and a K402I substitution is a cavity-filling substitution.

[0524] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 442 and a cysteine at position 423, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 442 and a cysteine substitution at position 423 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises L442C and N423C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. L442C and N423C substitutions result in the formation of an interprotomer disulfide bond in the HA protein.

[0525] In some embodiments, the IAV H1 HA protein comprises a glycine at position 391, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a glycine substitution at position 391 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a K391G substitution relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95. A K391G substitution is a glycine substitution in the B loop of the HA protein.

[0526] In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 95.

[0527] Substitutions described in this subsection relating to IAV H1 HA proteins may be combined. For example, any of the pairs of cysteine substitutions may be combined with one or more proline substitutions in the B loop, glycine substitutions in the B loop, substitutions of pH-sensitive histidines, and/or cavity-filling substitutions. Pairs of cysteine substitutions that form different disulfide bonds (e.g., interprotomer versus intraprotomer bonds, head versus stalk region bonds) may also be combined. Preferred combinations of substitutions are discussed below.

[0528] In some embodiments, the IAV H1 HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more proline substitutions in the B loop. In some embodiments, the IAV H1 HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue. In some embodiments, the IAV H1 HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue, and one or more proline substitutions in the B loop.

[0529] In some embodiments, the IAV H1 HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and an intraprotomer disulfide bond formed by at least one introduced cysteine, where the introduced cysteine(s) of the interpromoter disulfide bond are at different positions than the introduced cysteine(s) of the intraprotomer disulfide bond.

[0530] In some embodiments, the IAV H1 HA protein comprises an interprotomer disulfide bond formed by at least one introduced cysteine, and one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0531] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391, a cysteine at position 37, a proline at position 404, and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391, a cysteine substitution at position 37, a proline substitution at position 404, and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K391C, L37C, N404P, H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0532] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391, a cysteine at position 37, a isoleucine at position 395, and a isoleucine at position 447, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391, a cysteine substitution at position 37, a isoleucine substitution at position 395, and a isoleucine substitution at position 447 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K391C, L37C, K395I, E447I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0533] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391, a cysteine at position 37, a glycine at position 456, and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391, a cysteine substitution at position 37, a glycine substitution at position 456, and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K391C, L37C, D456G, K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0534] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 395, a cysteine at position 36, a proline at position 404, and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 395, a cysteine substitution at position 36, a proline substitution at position 404, and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K395C, V36C, N404P, H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0535] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 395, a cysteine at position 36, a glycine at position 456, and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 395, a cysteine substitution at position 36, a glycine substitution at position 456, and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K395C, V36C, D456G, K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0536] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 461, a cysteine at position 348, a proline at position 404, and a proline at position 416, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 461, a cysteine substitution at position 348, a proline substitution at position 404, and a proline substitution at position 416 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises N461C, G348C, N404P, H416P substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0537] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 461, a cysteine at position 348, a isoleucine at position 395, and a isoleucine at position 447, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 461, a cysteine substitution at position 348, a isoleucine substitution at position 395, and a isoleucine substitution at position 447 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises N461C, G348C, K395I, E447I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0538] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 461, a cysteine at position 348, a glycine at position 456, and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 461, a cysteine substitution at position 348, a glycine substitution at position 456, and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises N461C, G348C, D456G, K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0539] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391, a cysteine at position 37, a proline at position 404, a proline at position 416, a glycine at position 456, and a isoleucine at position 402, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391, a cysteine substitution at position 37, a proline substitution at position 404, a proline substitution at position 416, a glycine substitution at position 456, and a isoleucine substitution at position 402 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises K391C, L37C, N404P, H416P, D456G, K402I substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 83.

[0540] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 410, a cysteine at position 462, a cysteine at position 457, and a cysteine at position 346, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 410, a cysteine substitution at position 462, a cysteine substitution at position 457, and a cysteine substitution at position 346 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises V410C, L462C, S457C, L346C substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95.

[0541] In some embodiments, the IAV H1 HA protein comprises a cysteine at position 391, a cysteine at position 37, a phenylalanine at position 370, and a phenylalanine at position 455, where the positions are numbered by alignment of the amino acid sequence of the IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises a cysteine substitution at position 391, a cysteine substitution at position 37, a phenylalanine substitution at position 370, and a phenylalanine substitution at position 455 relative to a reference IAV H1 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H1 HA protein to SEQ ID NO: 95. In some embodiments, the IAV H1 HA protein comprises K391C, L37C, H370F, H455F substitutions relative to a reference IAV H1 HA protein, where the numbering of amino acids replaced in the reference IAV H1 HA protein corresponds to the numbering of SEQ ID NO: 95.

[0542] Some embodiments relate to IAV H3 HA proteins comprising an amino acid substitution relative to a reference IAV H3 HA protein. The reference IAV H3 HA protein may be an HA protein of an influenza A virus of an IAV subtype containing an H3 HA protein, such as an influenza A/(H3N2) virus. H3 HA proteins are present, e.g., on influenza A viruses of the H3N2 subtype, but other IAV subtypes expressing H3 HA proteins have been identified (such as the H3N8 subtype endemic in birds, horses, and dogs). Non-limiting examples of influenza A/(H3N2) virus isolates include A/Sydney/5/97(H3N2), A/Moscow/10/1999(H3N2), A/Fujian/411/2002(H3N2), A/California/7/2004(H3N2), A/Wisconsin/67/2005(H3N2), A/Brisbane/10/2007(H3N2), A/Perth/16/2009(H3N2), A/Victoria/361/2011(H3N2), A/Texas/50/2012(H3N2), A/Switzerland/9715293/2013(H3N2), A/Hong Kong/4801/2014(H3N2), A/Singapore/INFIMH-16-0019/2016(H3N2), A/Kansas/14/2017(H3N2), A/Hong Kong/2671/2019(H3N2), A/Hong Kong/45/2019(H3N2), A/Cambodia/e0826360/2020(H3N2), A/Darwin/9/2021(H3N2), and A/Darwin/6/2021(H3N2). Representative amino acid sequences of influenza A/(H3N2) virus HA proteins of previous seasonal influenza vaccines are provided as SEQ ID NOs: 136-153.

[0543] Those of ordinary skill in the art will appreciate that mutations disclosed in relation to a listed sequence, e.g., of influenza A/Darwin/6/2021(H3N2) virus HA, may be applied to HA proteins of other influenza A/(H3N2) viruses or other reference IAV H3 HA proteins. For example, in applying a T40C substitution to another IAV H3 HA protein, the skilled artisan would align the amino acid sequence of that reference HA protein to the influenza A/Darwin/6/2021(H3N2) virus HA protein sequence of SEQ ID NO: 82 and introduce a C at the residue of the reference HA protein amino acid sequence that aligns to T40 of SEQ ID NO: 82.

[0544] Exemplary substitutions that may be present in IAV H1 HA proteins are provided below in Table HA-5. In the event a reference HA protein sequence (e.g. of an isolate) already includes a substitution mentioned in the table, then it will be appreciated that some embodiments will include the residues set forth at positions below without a substitution being made at that particular position. For example, if an isolate already contains an isoleucine at position 219, then embodiments comprising 219I and H504P can be obtained with only a 504P substitution.

TABLE HA-5
A/(H3N2) subtype HA substitutions
(A/Darwin/6/2021(H3N2) (SEQ ID NO: 82) numbering)
Substitution(s)	Mutation class
T40C A55C	Intra-protomer DS (Head)
S123C R421C	Inter-protomer DS (Head)
L260C P237C	Inter-protomer DS (Head)
Q392C T46C	Inter-protomer DS (Stalk)
I411C Y428C	Inter-protomer DS (Stalk)
G402P R421P E414P	Proline(s)
K403G	Glycine(s)
F408G H409G	Glycine(s)
K396I	Cavity Filling
T219I H504P	Cavity Filling (T219I) / Proline (H504P)

[0545] In some embodiments, the IAV H3 HA protein comprises a cysteine at position 40 and a cysteine at position 55, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a cysteine substitution at position 40 and a cysteine substitution at position 55 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises T40C and A55C substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. T40C and A55C substitutions result in the formation of an intraprotomer disulfide bond in the head region of the HA protein.

[0546] In some embodiments, the IAV H3 HA protein comprises a cysteine at position 123 and a cysteine at position 421, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a cysteine substitution at position 123 and a cysteine substitution at position 421 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises S123C and R421C substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. S123C and R421C substitutions result in the formation of an interprotomer disulfide bond in the head region of the HA protein.

[0547] In some embodiments, the IAV H3 HA protein comprises a cysteine at position 260 and a cysteine at position 237, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a cysteine substitution at position 260 and a cysteine substitution at position 237 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises L260C and P237C substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. L260C and P237C substitutions result in the formation of an interprotomer disulfide bond in the head region of the HA protein.

[0548] In some embodiments, the IAV H3 HA protein comprises a cysteine at position 392 and a cysteine at position 46, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a cysteine substitution at position 392 and a cysteine substitution at position 46 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises Q392C and T46C substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. Q392C and T46C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0549] In some embodiments, the IAV H3 HA protein comprises a cysteine at position 411 and a cysteine at position 428, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a cysteine substitution at position 411 and a cysteine substitution at position 428 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises I411C and Y428C substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. I411C and Y428C substitutions result in the formation of an interprotomer disulfide bond in the stalk region of the HA protein.

[0550] In some embodiments, the IAV H3 HA protein comprises a proline at position 402, a proline at position 421, and a proline at position 414, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a proline substitution at position 402, a proline substitution at position 421, and a proline substitution at position 414 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises G402P, R421P, and E414P substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. G402P, R421P, and E414P substitutions are proline substitutions in the B loop of the HA protein.

[0551] In some embodiments, the IAV H3 HA protein comprises a glycine at position 403, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a glycine substitution at position 403 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a K403G substitution relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. A K403G substitution is a glycine substitution in the B loop of the HA protein.

[0552] In some embodiments, the IAV H3 HA protein comprises a glycine at position 408 and a glycine at position 409, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a glycine substitution at position 408 and a glycine substitution at position 409 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises F408G and H409G substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. F408G and H409G substitutions are glycine substitutions in the B loop of the HA protein.

[0553] In some embodiments, the IAV H3 HA protein comprises a isoleucine at position 396, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a isoleucine substitution at position 396 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a K396I substitution relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. A K396I substitution is a cavity-filling substitution.

[0554] In some embodiments, the IAV H3 HA protein comprises a isoleucine at position 219 and a proline at position 504, where the positions are numbered by alignment of the amino acid sequence of the IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises a isoleucine substitution at position 219 and a proline substitution at position 504 relative to a reference IAV H3 HA protein, where the positions are numbered by alignment of the amino acid sequence of the reference IAV H3 HA protein to SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises T219I and H504P substitutions relative to a reference IAV H3 HA protein, where the numbering of amino acids replaced in the reference IAV H3 HA protein corresponds to the numbering of SEQ ID NO: 82. A T219I substitution is a cavity-filling substitution, and an H504P substitution is a proline substitution in the B loop of the HA protein.

[0555] Substitutions described in this subsection relating to IAV H3 HA proteins may be combined. For example, any of the pairs of cysteine substitutions may be combined with one or more proline substitutions in the B loop, glycine substitutions in the B loop, substitutions of pH-sensitive histidines, and/or cavity-filling substitutions. Pairs of cysteine substitutions that form different disulfide bonds (e.g., interprotomer v. intraprotomer bonds, head v. stalk region bonds) may also be combined. In some embodiments, the IAV H3 HA protein comprises one or more substitutions of a pH-sensitive histidine in the HA protein and one or more substitutions of a charged or polar cavity-lining residue with a hydrophobic residue.

[0556] In some embodiments, the IAV H3 HA protein comprises an amino acid sequence with at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% sequence identity to the amino acid sequence of SEQ ID NO: 82. In some embodiments, the IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82.

[0557] Influenza viruses and protein sequences thereof may be classified as belonging to a given IAV subtype or IBV lineage using any suitable classification method. Non-limiting examples of classification methods include sequence-based analyses (e.g., sequence comparison and phylogenetic tree building) and antigenic characterization (e.g., HAI assays, microneutralization assays, and immunofluorescence).

[0558] Amino acid sequences of influenza virus antigens may be analyzed to classify them as belonging to a given IAV subtype or IBV lineage. For example, an HA amino acid sequence is classified into the H1 subtype, H3 subtype, B/Victoria lineage, B/Yamagata lineage on the basis of similarity to extant H1 HA, H3 HA, B/Victoria lineage HA, or B/Yamagata lineage HA amino sequences. As another example, an HA amino acid sequence may be fit into a phylogenetic tree of extant HA amino acid sequences, and classified as belonging to a given IAV subtype or IBV lineage according to its most likely place in the phylogenetic tree.

[0559] Nucleotide sequences of influenza virus genome segments may similarly be compared to extant genome segments to classify the influenza virus as belonging to a given IAV subtype or IBV lineage, on the basis of percentage identity to extant sequences of a given subtype or lineage. As another example, an influenza virus genome segment nucleotide sequence may be fit into a phylogenetic tree of extant genome segment nucleotide sequences, and classified as belonging to a given IAV subtype or IBV lineage according to its most likely place in the phylogenetic tree.

[0560] Serological methods such as the HAI test are useful for many epidemiological and immunological studies and for evaluation of the antibody response following vaccination. Serological methods are also useful in situations where identification of the virus is not feasible (e.g. after viral shedding has stopped). The HAI test is used to identify circulating influenza viruses that are antigenically similar to influenza viruses from previous seasons.

[0561] The hemagglutination inhibition (HAI) test is a classical laboratory procedure for the classification or subtyping of hemagglutinating viruses and further determining the antigenic characteristics of influenza viral isolates provided that the reference antisera used contain antibodies to currently circulating viruses (see, e.g., Pedersen J C Methods Mol Biol. 2014; 1161:11-25). The antisera used are based on antigen preparations derived from either the wild-type strain or a high-growth reassortant made using the wild-type strain or an antigenically equivalent strain. Effective hemagglutinin inhibition by sera or antibodies specific to H1 HA but not sera or antibodies specific to H3 HA, for example, indicates that an influenza virus expresses an HA belonging to the H1 subtype.

[0562] The microneutralization assay is a highly sensitive and specific assay for detecting virus-specific neutralizing antibodies to influenza viruses in human and animal sera, and in some embodiments, includes the detection of human antibodies to avian subtypes. Testing can be carried out quickly once a novel virus is identified and often before purified viral proteins become available for use in other assays. Neutralization of an influenza virus cells by sera or antibodies specific to H1 HA but not sera or antibodies specific to H3 HA, for example, indicates that an influenza virus expresses an HA belonging to the H1 subtype.

[0563] Immunofluorescence antibody (IFA) staining of virus-infected cells in original clinical specimens and field isolates is a rapid and sensitive method for diagnosing respiratory and other viral infections. In some embodiments, IFA staining is performed on isolates rather than original clinical specimens, as this allows any virus that is present to first be amplified, and if required used in other studies. Staining of influenza virus-infected cells by antibodies specific to H1 HA but not antibodies specific to H3 HA, for example, indicates that an influenza virus expresses an HA belonging to the H1 subtype.

[0564] Some aspects relate to compositions for use as vaccines against seasonal influenza viruses, and optionally other respiratory viruses (e.g., coronaviruses and/or respiratory syncytial viruses).

[0565] Some embodiments relate to compositions comprising nucleic acids (e.g., RNAs, (e.g., mRNAs)) encoding respiratory virus (e.g., influenza virus, RSV, SARS-CoV-2) antigens, where the nucleic acids encoding different antigens are present at certain ratios. A “ratio” of two nucleic acids (e.g., encoding proteins A and B) may refer to a molar ratio (the number of nucleic acid molecules encoding protein A, relative to the number of nucleic acid molecules encoding protein B), or a mass ratio (the mass of nucleic acids encoding protein A, relative to the mass of nucleic acids encoding protein B). Unless indicated otherwise or otherwise clear from context, reference to nucleic acids (e.g., RNAs (e.g., mRNAs)) being present at a “ratio” refers to a mass ratio of the nucleic acids.

[0566] Some aspects relate to multivalent vaccines that comprise components to protect a subject against more than one influenza virus. Multivalent influenza vaccines can include three (trivalent), four (quadrivalent), five (pentavalent), or more (such as octavalent) components that each independently are designed to protect against one of a variety of influenza virus strains. For instance, a trivalent vaccine can include RNA(s) encoding an influenza A/(H1N1) virus protein, an influenza A/(H3N2) virus protein, and an influenza B/Victoria lineage virus protein. Some trivalent compositions comprise RNA(s) encoding two influenza A virus HA proteins and one influenza B virus HA proteins. Quadrivalent vaccines can include RNA(s) encoding three influenza A virus proteins (e.g., HA proteins) and one influenza B virus protein (e.g., HA protein). Some quadrivalent vaccines include mRNA encoding two influenza A virus proteins (e.g., HA proteins) and two influenza B virus proteins (e.g., HA proteins).

[0567] In some aspects, a multivalent vaccine comprises three mRNAs, a first encoding an influenza A/(H1N1) virus HA protein, a second encoding an influenza A/(H3N2) virus HA protein, and a third encoding an influenza B/Victoria lineage virus HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1 mass ratio.

[0568] In some aspects, a multivalent vaccine comprises four mRNAs, a first encoding an influenza A/(H1N1) virus HA protein, a second encoding an influenza A/(H3N2) virus HA protein, a third encoding an influenza B/Victoria lineage virus HA protein, and a fourth encoding influenza B/Yamagata lineage virus HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1 mass ratio.

[0569] In some aspects, a multivalent vaccine comprises eight mRNAs, a first encoding an IAV H1 HA protein, a second encoding an IAV H3 HA protein, a third encoding an influenza B/Victoria lineage virus HA protein, an influenza B/Yamagata lineage virus HA protein, a fifth encoding an IAV N1 NA protein, a sixth encoding an IAV N2 NA protein, a seventh encoding an influenza B/Victoria lineage virus NA protein, and an eighth encoding an influenza B/Yamagata lineage virus NA protein. In some embodiments, the mRNAs are present at a 1:1:1:1:1:1:1:1 mass ratio. In some embodiments, the mRNAs are present at a 3:3:3:3:1:1:1:1 mass ratio (i.e., the mRNAs encoding the HA proteins are present at 3 times the amount (by mass) of mRNAs encoding the NA proteins).

[0570] In some aspects, a multivalent vaccine comprises five mRNAs, a first encoding an IAV H1 HA protein, a second encoding a first IAV H3 HA protein, a third encoding a second IAV H3 HA protein, a fourth encoding an influenza B/Victoria lineage virus HA protein, and a fifth encoding an influenza B/Yamagata lineage HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1:1 mass ratio.

[0571] In some aspects, a multivalent vaccine comprises four mRNAs, a first encoding an IAV H1 HA protein, a second encoding a first IAV H3 HA protein, a third encoding a second IAV H3 HA protein, and a fourth encoding an influenza B/Victoria lineage virus HA protein, where the vaccine does not comprise an mRNA encoding an influenza B/Yamagata lineage virus HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1 mass ratio.

[0572] In some aspects, a multivalent vaccine comprises six mRNAs, a first encoding an IAV H1 HA protein, a second encoding a first IAV H3 HA protein, a third encoding a second IAV H3 HA protein, a fourth encoding a third IAV H3 HA protein, a fifth encoding an influenza B/Victoria lineage virus HA protein, and a sixth encoding an influenza B/Yamagata lineage HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1:1:1 mass ratio.

[0573] In some aspects, a multivalent vaccine comprises five mRNAs, a first encoding an IAV H1 HA protein, a second encoding a first IAV H3 HA protein, a third encoding a second IAV H3 HA protein, a fourth encoding a third IAV H3 HA protein, and a fifth encoding an influenza B/Victoria lineage virus HA protein, where the vaccine does not comprise an mRNA encoding an influenza B/Yamagata lineage HA protein. In some embodiments, the mRNAs are present at a 1:1:1:1:1 mass ratio.

[0574] Some embodiments relate to multivalent vaccines comprising mRNAs encoding multiple H3 HA proteins derived from distinct influenza A/(H3N2) viruses. Separate H3 HA proteins may belong to different clades of the A/(H3N2) subtype. In some embodiments, each H3 HA protein encoded by an mRNA of a vaccine is derived from an influenza virus of a distinct clade within the A/(H3N2) subtype. In some embodiments, each H3 HA protein encoded by an mRNA of a vaccine differs from each other H3 HA protein encoded by other mRNAs of the vaccine by at least 1, at least 2, at least 3, at least 4, at least 5, at least 6, at least 7, at least 8, at least 9, at least 10, at least 11, at least 12, at least 13, at least 14, at least 15, at least 16, at least 17, at least 18, at least 19, at least 20 substitutions. Where two H3 HA proteins vary in length, the number of substitutions present between their amino acid sequences is calculated after aligning the amino acid sequences as discussed in the section entitled “Protein variants and alignment.”

[0575] In some embodiments of multivalent vaccines, the influenza B/Victoria lineage virus HA protein is an influenza B/Victoria lineage virus HA protein described in the section entitled “B/Victoria lineage HA proteins.” In some embodiments, the influenza B/Victoria lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 71.

[0576] In some embodiments of multivalent vaccines, the influenza B/Yamagata lineage virus HA protein is an influenza B/Yamagata lineage virus HA protein described in the section entitled “B/Yamagata lineage HA proteins.” In some embodiments, the influenza B/Yamagata lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 70.

[0577] In some embodiments of multivalent vaccines, the IAV H1 HA protein is an IAV H1 HA protein described in the section entitled “H1 HA proteins.” In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 95.

[0578] In some embodiments of multivalent vaccines, the IAV H3 HA protein is an IAV H3 HA protein described in the section entitled “H3 HA proteins.” Where a multivalent vaccine includes multiple H3 HA proteins (e.g., comprises multiple mRNAs encoding different H3 HA proteins), the different H3 HA proteins may each comprise the same substitutions, or different substitutions described in the section entitled “H3 HA proteins.” In some embodiments, one or more H3 HA proteins does not comprise a substitution described in the section entitled “H3 HA proteins.” In some embodiments, the IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82. In some embodiments, each IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82.

[0579] Some embodiments of vaccines include combination vaccines. A “combination vaccine”, as used herein, refers to a vaccine comprising one or more components for eliciting an immune response (i) to one or more influenza viruses, and (ii) to one or more viruses other than an influenza virus. As noted previously, discussion of combination vaccines comprising one or more RNAs (e.g., mRNAs) encoding proteins of different viruses may also be applied, inter alia, to combination vaccines comprising the same proteins (e.g., as isolated proteins or proteins present in viral vectors). The skilled artisan will appreciate that for combination vaccines comprising one or more RNAs (e.g., mRNAs) encoding two or more proteins, the two or more proteins may be encoded a single RNA, or different RNAs of the combination vaccine.

[0580] For example, a combination vaccine may include one or more RNAs, each encoding an antigen of a virus of a different family (e.g., a first antigen of an influenza virus (Orthomyxoviridae), and a second antigen of a coronavirus (Coronaviriade) or respiratory syncytial virus (Pneumoviridae)). In some embodiments, a composition includes one or more RNAs (e.g., mRNAs) encoding at least one influenza virus antigen, and at least one antigen of a different virus (e.g., a coronavirus or a virus from the Pneumoviridae family (e.g., respiratory syncytial virus (RSV)). In some embodiments, the different virus is SARS-CoV-2; that is, in some embodiments, a composition comprises one or more RNAs collectively encoding at least one influenza virus antigen, and at least one SARS-CoV-2 antigen. In some embodiments the different virus is human respiratory syncytial virus (hRSV); that is, in some embodiments, a composition comprises one or more RNAs collectively encoding at least one influenza virus antigen and at least one hRSV antigen. In some embodiments, a composition includes one or more RNAs collectively encoding at least one influenza virus antigen and at least one antigen of each of two different viruses (e.g. a coronavirus and an hRSV). In some embodiments, the different viruses are SARS-CoV-2 and hRSV; that is, in some embodiments, a composition comprises one or more RNAs collectively encoding at least one influenza virus antigen, at least one SARS-CoV-2 antigen, and at least one hRSV antigen.

[0581] With respect to the SARS-CoV-2 antigens of the combination vaccines, in some embodiments, the combination vaccine comprises 1, 2, 3, 4, 5, or 6 RNAs (e.g., mRNAs) encoding different coronavirus antigens, wherein each antigen comprises at least one mutation and/or at least one deletion relative to the amino acid sequence of SEQ ID NO: 78. In some embodiments, the combination vaccine comprises an RNA encoding a wild-type SARS-CoV-2 S protein antigen or the antigenic fragment thereof. In some embodiments, a combination vaccine includes an RNA encoding a fusion protein comprising at least two domains of a SARS-CoV-2 Spike (S) protein, and less than the full-length spike protein. In some embodiments, a combination vaccine comprises a first RNA encoding a first fusion protein comprising at least two domains of a SARS-CoV-2 Spike (S) protein and less than the full-length S protein, and a second RNA encoding a second fusion protein comprising at least two domains of a SARS-CoV-2 Spike (S) protein and less than the full-length S protein. In some embodiments, the two RNAs are present in the combination vaccine in a 1:1 ratio. In some embodiments, the two RNAs are present in the combination vaccine in a 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10 ratio.

[0582] With respect to the antigens of viruses from the Pneumoviridae family, in some embodiments, the combination vaccine comprises 1, 2, 3, 4, 5, or 6 RNAs (e.g., mRNAs) encoding different antigens of viruses from the Pneumoviridae family (e.g., RSV) wherein each antigen comprises at least one mutation and/or at least one deletion relative to a reference Pneumoviridae family virus antigen. In some embodiments, the combination vaccine comprises an RNA encoding a wild-type hRSV F glycoprotein antigen or antigenic fragment thereof. In some embodiments, a combination vaccine includes an RNA encoding a hRSV F glycoprotein variant lacking a cytoplasmic tail. In some embodiments, a combination vaccine includes an RNA encoding a hRSV F glycoprotein variant lacking a cytoplasmic tail and further comprising one or more modifications relative to a wild-type hRSV F glycoprotein. In some embodiments, a combination vaccine comprises a first RNA encoding a first hRSV F glycoprotein variant lacking a cytoplasmic tail, and a second RNA encoding a second hRSV F glycoprotein variant lacking a cytoplasmic tail and further comprising one or more modifications relative to the wild-type hRSV F glycoprotein. In some embodiments, the two RNAs are present in the combination vaccine in a 1:1 ratio. In some embodiments, the two RNAs are present in the combination vaccine in a 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10 ratio.

[0583] In some embodiments, the combination vaccine comprises one or more RNAs (e.g., mRNAs) encoding influenza virus antigens (e.g., mRNA encoding HA antigens) and one or more RNAs (e.g., mRNAs) encoding antigens of at least one different respiratory virus (e.g., mRNA encoding a SARS-CoV-2 fusion protein or an hRSV F glycoprotein). In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 5:1, 4:1, 3:1, 2:1, or 1:1. In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 10:1. In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 15:1. In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 20:1. In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 25:1. In some embodiments, the ratio of RNAs encoding influenza virus antigens to RNAs encoding the at least one different respiratory virus antigen in the combination vaccine is 30:1.

[0584] In some embodiments, the combination vaccine comprises (i) one or more RNAs (e.g., mRNAs) encoding one or more influenza virus proteins, (ii) one or more RNAs (e.g., mRNAs) encoding one or more SARS-CoV-2 proteins, and (ii) one or more RNAs (e.g., mRNAs) encoding one or more hRSV proteins. In some embodiments, each of (i) RNA(s) encoding influenza virus protein(s), (ii) RNA(s) encoding SARS-CoV-2 protein(s), and (iii) RNA(s) encoding hRSV protein(s) are present in the combination vaccine in substantially equal masses. In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 3 times the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 3 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 4 times the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 4 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 5 times the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 5 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 2 times the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 4 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 4 times the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 2 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the RNA(s) encoding influenza virus protein(s) are present in the combination vaccine at 0.5 the mass of RNA(s) encoding SARS-CoV-2 protein(s), and 0.5 times the mass of RNA(s) encoding hRSV protein(s). In some embodiments, the mass ratio of (i) RNA(s) encoding influenza virus protein(s), to (ii) RNA(s) encoding SARS-CoV-2 protein(s), to (iii) RNA(s) encoding hRSV protein(s) in the combination vaccine is 4:1:1, 4:2:1, 4:3:2, 4:3:3, or 2:1:1.

[0585] In some embodiments, the combination vaccine comprises mRNA polynucleotide wherein each polynucleotide encodes a different respiratory virus antigenic polypeptide. In some embodiments, the first, second and third mRNA polynucleotides are present in the combination vaccine in a ratio of 1:1:1. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 4:1:1 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 3:1:1 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 5:1:1 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 4:2:1 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 1:2:1 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 1:2:2 from the first virus (e.g., influenza virus) to the second virus to the third virus. In some embodiments, the combination vaccine comprises a ratio of mRNA polynucleotides encoding respiratory virus antigenic polypeptides of 8:2:2, 4:1:1, 4:2:2, 4:2:1, 4:3:2, 4:3:3, 4:3:2, or 4:2:2 from the first virus to the second virus to the third virus.

[0586] In some embodiments, each of the mRNA polynucleotides in the combination vaccine is complementary with and does not interfere with each other mRNA polynucleotide in the combination vaccine. That is, an antigen produced from administration of the combination vaccine do not significantly interfere with the immune response to any other of the antigens produced in response to the vaccine in such a way that would diminish the ability of the antigens to provoke a protective immune response in a subject. In some embodiments, the combination vaccine is additive with respect to neutralizing antibodies relative to each individual antigen in a vaccine.

[0587] Thus, compositions (e.g., RNA vaccines (e.g., mRNA vaccines)) may target one or more antigen(s) of the same strain/species, or one or more antigen(s) of different strains/species, e.g., antigens which induce immunity to organisms which are found in the same geographic areas where the risk of respiratory virus (e.g. influenza virus and/or coronavirus and/or respiratory syncytial virus) infection is high.

[0588] Combination vaccines comprising RNA (e.g., mRNA) polynucleotides encoding at least two respiratory virus antigenic polypeptides from at least two different respiratory virus families (e.g., influenza viruses of Orthomyxoviridae, respiratory syncytial virus of Pneumoviridae, and coronavirus of Coronaviridae) may be used for treating and/or preventing respiratory virus infections. In some embodiments, a combination vaccine comprises mRNA polynucleotides encoding antigens from the Orthomyxoviridae family (e.g., influenza virus antigens) and the Coronaviridae family (e.g., SARS-CoV-2). In some embodiments, a combination vaccine comprises mRNA polynucleotides encoding antigens from the Orthomyxoviridae family (e.g., influenza virus) and the Pneumoviridae family (e.g., human respiratory syncytial virus). In some embodiments, a composition comprises RNA (e.g., mRNA) polynucleotides encoding at least three respiratory antigenic polypeptides from at least three different respiratory viruses. In some embodiments, the three different viruses are from the Orthomyxoviridae (e.g., influenza virus), Coronaviridae (e.g., SARS-CoV-2) and Pneumoviridae families (e.g., human respiratory syncytial virus).

[0589] In some embodiments, one or more RNAs (e.g., mRNAs) encoding polypeptides from at least two different respiratory virus families are encapsulated in a single lipid nanoparticle. Some embodiments comprise one or more RNAs (e.g., mRNAs) encoding polypeptides from at least two different respiratory virus families, wherein the composition comprises lipid nanoparticles encapsulating one or more RNAs (e.g., mRNAs) encoding polypeptides from a single respiratory virus family.

[0590] In some embodiments, a combination vaccine comprises a combination of proteins or nucleic acids (e.g., RNAs (e.g., mRNAs)) collectively encoding the combination, the combination comprising: (i) an IAV H1 HA protein, (ii) an IAV H3 HA protein, (iii) an influenza B/Victoria lineage virus HA protein, and (iv) a SARS-CoV-2 S protein or fragment thereof.

[0591] In some embodiments, a combination vaccine comprises a combination of proteins or nucleic acids (e.g., RNAs (e.g., mRNAs) collectively encoding the combination, the combination comprising: (i) an IAV H1 HA protein, (ii) an IAV H3 HA protein, (iii) an influenza B/Victoria lineage virus HA protein, and (iv) an hRSV F protein or fragment thereof.

[0592] In some embodiments, a combination vaccine comprises a combination of proteins or nucleic acids (e.g., RNAs (e.g., mRNAs) collectively encoding the combination, the combination comprising: (i) an IAV H1 HA protein, (ii) an IAV H3 HA protein, (iii) an influenza B/Victoria lineage virus HA protein, (iv) a SARS-CoV-2 S protein or fragment thereof, and (v) an hRSV protein or fragment thereof.

[0593] In some embodiments, the combination comprises 2 IAV H3 HAs. In some embodiments, the combination comprises 3 IAV H3 HAs. In some embodiments, the combination comprises 4, 5, 6, 7, 8, 9, or 10 IAV H3 HAs.

[0594] In some embodiments, the combination further comprises an influenza B/Yamagata lineage HA protein. In some embodiments, the combination does not comprise an influenza B/Yamagata lineage HA protein.

[0595] In some embodiments, the combination further comprises: (i) an IAV N1 NA protein, (ii) an IAV N2 NA protein, and (iii) an influenza B/Victoria lineage NA protein. In some embodiments, the combination further comprises an influenza B/Yamagata lineage NA protein. In some embodiments, the combination does not comprise an influenza B/Yamagata lineage NA protein.

[0596] In some embodiments of combination vaccines, the influenza B/Victoria lineage virus HA protein is an influenza B/Victoria lineage virus HA protein described in the section entitled “B/Victoria lineage HA proteins.” In some embodiments, the influenza B/Victoria lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 71.

[0597] In some embodiments of combination vaccines, the influenza B/Yamagata lineage virus HA protein is an influenza B/Yamagata lineage virus HA protein described in the section entitled “B/Yamagata lineage HA proteins.” In some embodiments, the influenza B/Yamagata lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 70.

[0598] In some embodiments of combination vaccines, the IAV H1 HA protein is an IAV H1 HA protein described in the section entitled “H1 HA proteins.” In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 95.

[0599] In some embodiments of combination vaccines, the IAV H3 HA protein is an IAV H3 HA protein described in the section entitled “H3 HA proteins.” Where a combination vaccine includes multiple H3 HA proteins (e.g., comprises multiple mRNAs encoding different H3 HA proteins), the different H3 HA proteins may each comprise the same substitutions, or different substitutions described in the section entitled “H3 HA proteins.” In some embodiments, one or more H3 HA proteins does not comprise a substitution described in the section entitled “H3 HA proteins.” In some embodiments, the IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82. In some embodiments, each IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82.

[0600] In some embodiments, the SARS-CoV-2 S protein or fragment thereof is a full-length S glycoprotein described in the “Coronaviruses” section below. In some embodiments, the SARS-CoV-2 S protein or fragment thereof is a protein comprising one or more fragments of the SARS-CoV-2 S glycoprotein, described in the “Coronaviruses” section below.

[0601] In some embodiments, the hRSV F protein or fragment thereof is an hRSV protein or fragment thereof described in the “Respiratory Syncytial Virus (hRSV)” section below.

[0602] Some embodiments of combination vaccines include coronavirus antigens or nucleic acids encoding coronavirus antigens. Coronaviruses are a family of enveloped, positive-sense, single-stranded RNA viruses that infect mammals and birds. Notable human coronaviruses that cause respiratory illnesses include 229E, NL63, OC43, HKU1, Middle East Respiratory Syndrome Coronavirus (MERS-CoV), and Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV). Coronaviruses derive their name from the crown-like spikes on their surface, which are formed by the viral spike glycoprotein (S protein). The S protein binds to host receptors and mediates viral entry into cells. Other viral structural proteins include the envelope (E), membrane (M), and nucleocapsid (N) proteins. SARS-CoV-2 belongs to the betacoronavirus genus and is the causative agent of COVID-19. It has a size of 29.8-30 kb (see, e.g., Chan et al. 2000, supra; Kim et al. 2020 Cell, May 14; 181(4):914-921.e10.). The SARS-CoV-2 genome and is organized into specific genes encoding structural proteins and nonstructural proteins (Nsps). The order of the structural proteins in the genome is 5′-replicase (open reading frame (ORF)1/ab)-structural proteins [Spike (S)-Envelope I-Membrane (M)-Nucleocapsid (N)]-3′. The genome of coronaviruses includes a variable number of open reading frames that encode accessory proteins, nonstructural proteins, and structural proteins (Song et al. 2019 Viruses; 11(1): p. 59). Most of the antigenic epitopes are located in the structural proteins (Cui et al. 2019 Nat. Rev. Microbiol.; 17(3):181-192). Spike surface glycoprotein(S), a small envelope protein (E), matrix protein (M), and nucleocapsid protein (N) are four main structural proteins. Since S-protein contributes to cell tropism and virus entry and also it is capable to induce neutralizing antibodies (NAb) and protective immunity, it can be considered one of the most important targets in coronavirus vaccine development among all other structural proteins.

[0603] Variant viral strains of SARS-CoV-2 may emerge at times. These strains may emerge, for instance, seasonally. Thus, in exemplary aspects, the vaccines may be designed to combat seasonal coronavirus strains, and as such are vaccines for use in an upcoming or forthcoming Northern hemisphere season or Southern hemisphere season. Based on an understanding of circulating coronaviruses at a given point in time, the vaccines can be designed to combat such viruses as they are predicted to be those that will be circulating or prevalent in the upcoming or forthcoming virus season.

[0604] A preferred protein is the Spike (S) protein, which is on the surface of coronaviruses, including SARS-CoV-2. An example of a wild-type SARS-CoV-2 Spike protein is provided by the amino acid sequence of SEQ ID NO: 78. In some embodiments, the SARS-CoV-2 antigen is a full-length S protein. In some embodiments, the SARS-CoV-2 antigen comprises a full-length S protein with two or more proline substitutions. In some embodiments, the S protein comprises two proline substitutions at residues corresponding to K986V and V987P of SEQ ID NO: 78. In some embodiments, the S protein does not comprise a proline substitution.

[0605] In some embodiments, the SARS-CoV-2 antigen does not comprise a full-length S protein. For example, in some embodiments, the SARS-CoV-2 antigen comprises a receptor binding domain (RBD) of the S protein. In some embodiments, the SARS-CoV-2 antigen comprises a fusion protein comprising an RBD and an N-terminal domain (NTD) of the S protein. In some embodiments, the fusion protein comprises an RBD and an NTD of the S protein, and a transmembrane domain (TD). In some embodiments, the fusion protein comprises, in N-to-C-terminal order, the NTD-RBD-TD. In some embodiments, the RBD and NTD are linked through a linker. In some embodiments, the linker is a cleavable linker. In some embodiments, the linker is a non-cleavable linker. In some embodiments, the linker is a glycine-serine (GS) linker.

[0606] In some embodiments, the TD is a betacoronavirus TD. In some embodiments, the TD is a heterologous TD. In some embodiments the TD is a non-betacoronavirus TD. In some embodiments, the TD is an influenza virus hemagglutinin (HA) TD. In some embodiments, the TD is an influenza A virus H1 HA TD.

[0607] In some embodiments, the SARS-CoV-2 antigen comprises at least one mutation present in an S protein of a circulating SARS-CoV-2 isolate, as compared to the S protein amino acid sequence of SEQ ID NO: 78. In some embodiments, the SARS-CoV-2 antigen comprises at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 mutations present in a circulating SARS-CoV-2 S protein, as compared to SEQ ID NO: 78. In some embodiments, the SARS-CoV-2 antigen comprises an amino acid sequence with at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to SEQ ID NO: 78.

[0608] In some embodiments, the SARS-CoV-2 antigen comprises at least one mutation present in an RBD of an S protein of a circulating SARS-CoV-2 isolate, as compared to the S protein of SEQ ID NO: 78. In some embodiments, the SARS-CoV-2 Spike protein antigen comprises at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 RBD mutation(s) compared to SEQ ID NO: 78. In SEQ ID NO: 78, the RBD corresponds to amino acids 330-528, and so the skilled artisan will appreciate that “a mutation present in an RBD of an S protein” as compared to the S protein of SEQ ID NO: 78 refers to (i) a substitution at a position corresponding to any one of amino acids 330-528 of SEQ ID NO: 78, (ii) a deletion of any one or more of amino acids 330-528 of SEQ ID NO: 78, and/or (iii) an insertion of one or more amino acids at a position from amino acids 330-528 of SEQ ID NO: 78. In some embodiments, the SARS-CoV-2 antigen comprises an amino acid sequence with at least 80%, at least 81%, at least 82%, at least 83%, at least 84%, at least 85%, at least 86%, at least 87%, at least 88%, at least 89%, 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to SEQ ID NO: 60.

[0609] Mutations present in a SARS-CoV-2 antigen of a combination vaccine may be present on any circulating SARS-CoV-2 isolate. For example, at the time of filing the instant specification, isolates of the JN.1 variant are circulating. The SARS-CoV-2 sub-variant JN.1 (also known as BA.2.86.1.1), is a subvariant (sublineage) of the SARS-CoV-2 “Omicron” variant, and was first observed in August 2023; this variant is closely related to BA.2.86. The mutations observed in this variant are believed to provide high potential for immune evasion, particularly the L455F “FLip” mutation—a mutation also observed in XBB lineage variants (e.g., HK.3 and EG.5.1). Mutations observed in JN.1 include A31D, V238L, K1155R, N1708S, A1892T, V24F, R252K, T35I, ins16MPLF, R21T, S50L, Δ69-70, V127F, F157S, R158G, N211del, L212I, V213G, L216F, H245N, A264D, I332V, K356T, R403K, V445H, N450D, L452W, L455S, N481K, V483del, E484K, E554K, A570V, P621S, P681H, S939F, and P1143L.

[0610] Several sub-variants of the XBB variant have also been identified recently: HV.1, JD.1.1, HK.3, and EG.5. These sub-variants share several mutations, including T19I, L24S, del25/27, V83A, G142D, del144/144, H146Q, Q183E, V213E, G252V, G339H, R346T, L368I, S371F, S373P, S375F, T376A, D405N, R408S, K417N, N440K, V445P, G446S, F456L, N460K, S477N, T478K, E484A, F486P, F490S, Q498R, N501Y, Y505H, D614G, H655Y, N679K, P681H, N764K, D796Y, Q954H, and N969K; some variants include additional mutations, such as: Q52H, F157L, L452R, L455F, and A475V.

[0611] The skilled artisan will appreciate that SARS-CoV-2 antigens of combination vaccines may include mutations present in any SARS-CoV-2 S protein that is extant at the time the instant specification. The skilled artisan will also appreciate that SARS-CoV-2 S protein amino acid sequences that do not exist at the time of filing the instant specification may be analyzed for mutations relative to SEQ ID NO: 78, and those mutations may be applied to SARS-CoV-2 antigens of the combination vaccines.

[0612] In some embodiments, a combination vaccine comprises two or more coronavirus antigens or nucleic acids encoding two or more coronavirus antigens, such as SARS-CoV-2 antigens from different SARS-CoV-2 variant strains. In some embodiments, the composition comprises one or more RNAs collectively encoding two or more SARS-CoV-2 variant antigens.

[0613] Some embodiments of combination vaccines include human respiratory syncytial virus antigens or nucleic acids encoding human respiratory syncytial virus antigens. Human respiratory syncytial virus (hRSV; also known as human orthopneumovirus) is a negative-sense, single-stranded ribonucleic acid (RNA) virus of the Pneumoviridae family. The virus is present in at least two antigenic subgroups, known as Group A and Group B.

[0614] The envelope of hRSV contains three surface glycoproteins: F, G, and SH. The G and F proteins are protective antigens and targets of neutralizing antibodies. The F protein, however, is more conserved across hRSV strains and types (A and B). hRSV F protein is a type I fusion glycoprotein that is well conserved between clinical isolates, including between the hRSV-A and hRSV-B antigenic subgroups. The F protein transitions between prefusion and more stable postfusion states, thereby facilitating entry into target cells. hRSV F glycoprotein is initially synthesized as an F0 precursor protein. hRSV F0 folds into a trimer, which is activated by furin cleavage into the mature prefusion protein comprising F1 and F2 subunits (Bolt, et al., Virus Res., 68:25, 2000). Although targets for neutralizing monoclonal antibodies exist on the postfusion conformation of F protein, the neutralizing Ab response primarily targets the F protein prefusion conformation in people naturally infected with hRSV (Magro M et al., Proc Natl Acad Sci USA 2012; 109(8):3089-94; Ngwuta J O et al., Sci Transl Med 2015; 7(309):309ra162). Consistent with this, hRSV F protein stabilized in the prefusion conformation produces a greater neutralizing immune response in animal models than that observed with hRSV F protein stabilized in the post fusion conformation (McLellan et al., Science, 342:592-598, 2013). Thus, stabilized prefusion hRSV F proteins are good candidates for inclusion in an hRSV vaccine. Other RSV proteins include the small hydrophobic (SH), matrix (M), nucleocapsid (N), phosphoprotein (P), polymerase (L) and nonstructural NS1/NS2 proteins. A preferred protein is the F glycoprotein, which present on the surface of hRSV, including wild-type hRSV and mutant strains, such as the hRSV F protein having an amino acid sequence of SEQ ID NO: 98.

[0615] hRSV commonly causes bronchiolitis. Most infected adults develop mild cold-like symptoms such as congestion, low-grade fever, and wheezing. Infants and small children may suffer more severe symptoms such as bronchiolitis and pneumonia. The disease may be transmitted among humans via contact with respiratory secretions.

[0616] Some embodiments relate to stabilized prefusion RSV F proteins that comprise mutations to prevent the transition of the protein into its post-fusion conformation. For example, in some embodiments, the stabilized prefusion RSV F protein comprises proline residue (e.g., an S215P substitution) and/or isoleucine (e.g., N67I substitution) substitutions. As an example, the DS-Cav1 variant, a stabilized prefusion RSV F protein, contains an additional disulfide bond (S155C/S290C) as well as two cavity-filling mutations (S190F/V207L). Another stabilized prefusion RSV F protein is PR-DM, which comprises one proline substitution (S215P) and one mutation in the F2 subunit (N67I).

[0617] In some embodiments, a stabilized prefusion hRSV F glycoprotein variant lacks a cytoplasmic tail. In some embodiments, the cytoplasmic tail comprises the C-terminal 20-30, 20-25, 15-30, 15-25, 15-20, 10-30, 10-25, 10-20, 10-15, 5-30, 5-25, 5-20, or 5-15 amino acids of the of the hRSV F glycoprotein variant. In some embodiments, the cytoplasmic tail comprises the C-terminal 25 amino acids (e.g., CKARSTPVTLSKDQLSGINNIAFSN(SEQ ID NO: 101)) of the hRSV F glycoprotein. In some embodiments, the cytoplasmic tail comprises the C-terminal 20 amino acids (e.g., TPVTLSKDQLSGINNIAFSN(SEQ ID NO: 102)) of the hRSV F glycoprotein. In some embodiments, the cytoplasmic tail comprises the C-terminal 15 amino acids (e.g., SKDQLSGINNIAFSN(SEQ ID NO: 103)) of the hRSV F glycoprotein. In some embodiments, the cytoplasmic tail comprises the C-terminal 10 amino acids (e.g., SGINNIAFSN(SEQ ID NO: 104)) of the hRSV F glycoprotein.

[0618] In some embodiments, a stabilized prefusion hRSV F glycoprotein variant lacks a cytoplasmic tail, wherein the RSV F glycoprotein variant has at least 80%, at least 85%, at least 90%, at least 95% identity to a wild-type hRSV F glycoprotein (e.g., a wild-type hRSV F glycoprotein comprising the sequence of SEQ ID NO: 98), and lacks a cytoplasmic tail. In some embodiments, stabilized prefusion hRSV F glycoprotein variant lacks a cytoplasmic tail, wherein the RSV F glycoprotein variant has at least 80%, at least 85%, at least 90%, at least 95% identity to the sequence of SEQ ID NO: 99. In some embodiments, stabilized prefusion hRSV F glycoprotein variant comprises the sequence of SEQ ID NO: 99.

[0619] In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a modification, relative to the wild-type hRSV F glycoprotein (e.g., SEQ ID NO: 98), selected from the group consisting of: a P102X substitution, a substitution of amino acids 104-144 with a linker molecule, an A149X substitution, an S155X substitution, an S190X substitution, a V207X substitution, an S290X substitution, a L373X substitution, an I379X substitution, an M447X substitution, and a Y458X substitution, wherein X is any amino acid (e.g., A, R, N, D, C, E, Q, G, H, I, L, K, M, F, P, S, T, W, Y, or V) other than the amino acid replaced in the wild-the hRSV F glycoprotein amino acid sequence. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a modification, relative to the wild-type hRSV F glycoprotein, (SEQ ID NO: 98), selected from the group consisting of: a P102A substitution, a substitution of amino acids 104-144 with a linker molecule, an A149C substitution, an S155C substitution, an S190F substitution, a V207L substitution, an S290C substitution, a L373R substitution, an I379V substitution, an M447V substitution, and a Y458C substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a P102A substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a substitution of amino acids 104-144 with a linker molecule. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an A149C substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an S155C substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an S190F substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a V207L substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an S290C substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an L373R substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an I379V substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises an M447V substitution. In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises a Y458C substitution.

[0620] In some embodiments, an hRSV F glycoprotein variant that lacks a cytoplasmic tail further comprises the following modifications, relative to the wild-type hRSV F glycoprotein: a P102A substitution, a substitution of amino acids 104-144 with a linker molecule, an A149C substitution, an S155C substitution, an S190F substitution, a V207L substitution, an S290C substitution, a L373R substitution, an I379V substitution, an M447V substitution, and a Y458C substitution.

[0621] In some embodiments, an hRSV F glycoprotein comprises an amino acid sequence with at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 99. In some embodiments, the hRSV F glycoprotein comprises the amino acid sequence of SEQ ID NO: 99. In some embodiments, the hRSV F glycoprotein consists of the amino acid sequence of SEQ ID NO: 99.

[0622] In some embodiments, the composition comprises an RNA having an ORF encoding an hRSV F glycoprotein, where the ORF comprises a nucleotide sequence with at least 70%, at least 75%, least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the nucleotide sequence of SEQ ID NO: 113. In some embodiments, the ORF comprises the nucleotide sequence of SEQ ID NO: 113.

[0623] In some embodiments, an hRSV F glycoprotein comprises an F1 subunit and an F2 subunit, the F1 subunit comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 106, and the F2 subunit comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 107. In some embodiments, the F1 subunit comprises the amino acid sequence of SEQ ID NO: 106, and the F2 subunit comprises the amino acid sequence of SEQ ID NO: 107. In some embodiments, the F1 subunit consists of the amino acid sequence of SEQ ID NO: 106, and the F2 subunit consists of the amino acid sequence of SEQ ID NO: 107. In some embodiments, the hRSV F glycoprotein comprises an amino acid sequence with at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 108. In some embodiments, the hRSV F glycoprotein comprises the amino acid sequence of SEQ ID NO: 108. In some embodiments, the hRSV F glycoprotein consists of the amino acid sequence of SEQ ID NO: 108.

[0624] In some embodiments, an hRSV F glycoprotein comprises an F1 subunit and an F2 subunit, the F1 subunit comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 109, and the F2 subunit comprising at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 110. In some embodiments, the F1 subunit comprises the amino acid sequence of SEQ ID NO: 109, and the F2 subunit comprises the amino acid sequence of SEQ ID NO: 110. In some embodiments, the F1 subunit comprises the amino acid sequence of SEQ ID NO: 109, and the F2 subunit comprises the amino acid sequence of SEQ ID NO: 110. In some embodiments, the F1 subunit consists of the amino acid sequence of SEQ ID NO: 109, and the F2 subunit consists of the amino acid sequence of SEQ ID NO: 110. In some embodiments, the hRSV F glycoprotein comprises an amino acid sequence with at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 111. In some embodiments, the hRSV F glycoprotein comprises the amino acid sequence of SEQ ID NO: 111. In some embodiments, the hRSV F glycoprotein consists of the amino acid sequence of SEQ ID NO: 111.

[0625] In some embodiments, an hRSV F glycoprotein comprises an amino acid sequence with at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% identity to the amino acid sequence of SEQ ID NO: 112.

[0626] Some embodiments relate to proteins having one or more mutations (e.g., substitutions) relative to a reference amino acid sequence and/or numbered according to a listed amino acid sequence.

[0627] Some embodiments relate to amino acid or nucleotide sequences having a specified percentage sequence identity to a comparator amino acid or nucleotide sequence, respectively. The term “identity” refers to a relationship between the sequences of two or more polypeptides (e.g. antigens) or polynucleotides (nucleic acids), as determined by comparing the sequences. Identity also refers to the degree of sequence relatedness between or among sequences as determined by the number of matches between strings of two or more amino acid residues or nucleic acid residues. “Percent (%) identity” or “percent (%) sequence identity” as it applies to polypeptide or polynucleotide sequences is defined as the percentage of residues (amino acid residues or nucleic acid residues) in the candidate amino acid or nucleic acid sequence that are identical with the residues in the amino acid sequence or nucleic acid sequence of a second sequence after aligning the sequences and introducing gaps, if necessary, to achieve the maximum percent identity.

[0628] The percent sequence identity that a candidate sequence (e.g., as present in a claimed protein or nucleic acid) has to a comparator sequence (e.g., having a SEQ ID NO: specified herein) is calculated by (i) aligning the candidate sequence to the comparator sequence, (ii) determining the number of matching residues (amino acids or nucleotides) between the aligned candidate and comparator sequences, and (iii) dividing the number of matching residues by the length of the comparator sequence, including any gaps introduced into the comparator sequence when the two sequences are aligned.

[0629] For example, alignment of a candidate amino acid sequence of the influenza B/Brisbane/60/2008 virus HA protein amino acid sequence of SEQ ID NO: 157 to a comparator amino acid sequence of the influenza B/Austria/1359417/2021 virus HA protein amino acid sequence of SEQ ID NO: 71 reveals 572 matching residues (FIG. 19E). While SEQ ID NO: 71 is only 582 amino acids long, an internal gap three amino acids in length is introduced into SEQ ID NO: 71 in the alignment (FIG. 19E), making the denominator 585. Thus, candidate sequence SEQ ID NO: 157 has 572/585=97.8% sequence identity to comparator sequence SEQ ID NO: 71.

[0630] The skilled artisan will appreciate that to determine whether a candidate protein or nucleic acid comprises an amino acid sequence or nucleotide sequence with a given percentage sequence identity to a comparator sequence, the denominator (length of comparator sequence plus internal gaps) in calculating sequence identity need not include gaps shown at the ends of the comparator sequence in an alignment, as such gaps are added where a candidate sequence contains additional amino acids or nucleotides that extend beyond the portions that align to the N-terminal end and/or C-terminal end (amino acid sequences), or 5′ end or 3′ end (nucleotide sequences) of the comparator sequence. For example, alignment of the influenza B/Austria/1359417/2021 virus HA protein amino acid sequence of SEQ ID NO: 71, including the signal peptide, to its post-signal peptide cleavage form of SEQ ID NO: 174, results in a gap at the N-terminus of the comparator sequence, where the signal peptide is not present (FIG. 19F). A protein having the full-length amino acid sequence of SEQ ID NO: 71 would still comprise an amino acid sequence with 100% identity to SEQ ID NO: 174, because candidate sequence SEQ ID NO: 71 as aligned to comparator sequence SEQ ID NO: 174 contains 567 matches, and the number of amino acids in the comparator sequence of SEQ ID NO: 174 is 567 (567/567=100%).

[0631] Where an alignment between two sequences is contemplated, the first sequence (e.g., candidate sequence) is aligned to the second sequence (e.g., comparator sequence) using the Needleman-Wunsch algorithm for global alignment of the two sequences. Needleman & Wunsch, J Mol Biol. 1970. 48:443-453. Where two protein sequences are aligned, the Needleman-Wunsch algorithm uses a BLOSUM62 substitution scoring matrix, a Gap Open penalty of 10, a Gap Extend penalty of 0.5, and no End Gap penalties. Where two nucleotide sequences are aligned, the alignment uses an DNAFULL substitution scoring matrix, a Gap Open penalty of 10, a Gap Extend penalty of 0.5, and no End Gap penalties. The skilled artisan will appreciate that at the time of filing the instant specification, these parameters are the default parameters of the EMBOSS Needle pairwise comparison tool provided by European Bioinformatics Institute (see ebi.ac.uk). Other suitable alignment programs may be used to obtain a global alignment using these parameters, such as BLAST, or the Needleman-Wunsch algorithm may be implemented in a scripting language (e.g., Python).

[0632] Some embodiments of proteins include a linker between at least one pair of portions of the protein. The linker may be, for example, a cleavable linker or protease-sensitive linker. In some embodiments, the linker is selected from the group consisting of F2A linker, P2A linker, T2A linker, E2A linker, and combinations thereof (see, e.g., WO 2017/127750). This family of self-cleaving peptide linkers, referred to as 2A peptides, has been described in the art (see, e.g., Kim, J. H. et al., PLoS ONE 2011; 6: e18556).

[0633] In some embodiments, the linker is an F2A linker. In some embodiments, the linker is a GS linker. GS linkers are polypeptide linkers that include glycine and serine amino acids repeats. They comprise flexible and hydrophilic residues and can be used to perform fusion of protein subunits without interfering in the folding and function of the protein domains, and without formation of secondary structures. In some embodiments, a protein comprises a GS linker that is 3 to 20 amino acids long. For example, the GS linker may have a length of (or have a length of at least) 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 amino acids. In some embodiments, a GS linker is (or is at least) 15 amino acids long (e.g., GGSGGSGGSGGSGGG (SEQ ID NO: 114)). In some embodiments, a GS linker is (or is at least) 8 amino acids long (e.g., GGGSGGGS (SEQ ID NO: 115)). In some embodiments, a GS linker is (or is at least) 7 amino acids long (e.g., GGGSGGG (SEQ ID NO: 116)). In some embodiments, a GS linker comprises the amino acid sequence GGGSGG (SEQ ID NO: 117). In some embodiments, a GS linker is (or is at least) 4 amino acid long (e.g., GGGS (SEQ ID NO: 118)). In some embodiments, the GS linker comprises (GGGS)n (SEQ ID NO: 118), where n is any integer from 1-5. In some embodiments, a GS linker is (or is at least) 4 amino acid long (e.g., GSGG (SEQ ID NO: 119)). In some embodiments, the GS linker comprises (GSGG)n (SEQ ID NO: 119), where n is any integer from 1-5. In some embodiments, a linker is a glycine linker, for example having a length of (or a length of at least) 3 amino acids (e.g., GGG). In some embodiments, a protein encoded by an RNA (e.g., mRNA) includes two or more linkers, which may be the same or different from each other. The skilled artisan will appreciate that other linkers may be suitable for use in proteins.

[0634] In some embodiments, a protein comprises a signal peptide. Signal peptides comprise the N-terminal 15-60 amino acids of proteins. In eukaryotes, the signal peptide of a nascent precursor protein (pre-protein) directs the ribosome to the rough endoplasmic reticulum (ER) membrane and initiates the transport of the growing peptide chain across it for processing. ER processing produces mature proteins, wherein the signal peptide is cleaved from precursor proteins, typically by an ER-resident signal peptidase of the host cell, or they remain uncleaved and function as a membrane anchor. A signal peptide may also facilitate the targeting of the protein to the cell membrane.

[0635] A signal peptide may have a length of 15-60 amino acids. For example, a signal peptide may have a length of 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, or 60 amino acids. In some embodiments, a signal peptide has a length of 20-60, 25-60, 30-60, 35-60, 40-60, 45-60, 50-60, 55-60, 15-55, 20-55, 25-55, 30-55, 35-55, 40-55, 45-55, 50-55, 15-50, 20-50, 25-50, 30-50, 35-50, 40-50, 45-50, 15-45, 20-45, 25-45, 30-45, 35-45, 40-45, 15-40, 20-40, 25-40, 30-40, 35-40, 15-35, 20-35, 25-35, 30-35, 15-30, 20-30, 25-30, 15-25, 20-25, or 15-20 amino acids.

[0636] Signal peptides from heterologous genes (e.g., other than influenza virus HA, influenza virus NA, hRSV F, and SARS-CoV-2 S glycoproteins) may also be used in a protein.

[0637] The native signal peptide of a protein may be determined using any suitable method, such as a signal peptide prediction tool. Signal peptide prediction tools use bioinformatic algorithms, such as neural network, machine learning, and/or language model-based approaches, in combination with annotated protein databases (e.g., UniProt) to predict the signal peptide sequence within a given amino acid sequence. See, e.g., Teufel et al., Nat Biotechnol. 2022. 40(7):1023-1025 (SignalP 6.0)

[0638] Non-exhaustive examples of signal peptides of HA and NA proteins of influenza A/(H1N1) subtype, A/(H3N2) subtype, B/Victoria lineage, and B/Yamagata lineage isolates are provided in Table SP-1.

TABLE SP-1
Exemplary IAV and IBV HA and NA protein signal peptides
Subtype		HA protein
(IAV) or		signal	NA protein signal
lineage (IBV)	Isolate	peptide	peptide
A/(H1N1)	A/Wisconsin/	MKAILVVMLYTFTTA	MNPNQKIITIGSVCMTI
subtype	67/2022	NA (SEQ ID NO: 168)	GTANLILQIGNI
	(H1N1)pdm09		(SEQ ID NO: 226)
A/(H3N2)	A/Darwin/6/2021	MKTIIALSNILCLVFA	MNPNQKIITIGSVSLTIS
subtype	(H3N2)	(SEQ ID NO: 169)	TICFFMQIAIL
			(SEQ ID NO: 227)
B/Victoria	B/Austria/	MKAIIVLLMVVTSNA	MLPSTIQTLTLFLTSGG
lineage	1359417/2021	(SEQ ID NO: 170)	VLLSLYVSASLSYL
			(SEQ ID NO: 228)
B/Yamagata	B/Phuket/	MKAIIVLLMVVTSNA	MLPSTIQTLTLFLTSGG
lineage	3073/2013	(SEQ ID NO: 171)	VLLSLYVSASLSYL
			(SEQ ID NO: 229)

[0639] Provided are compositions comprising nucleic acids. In some embodiments, the nucleic acids comprise DNA. In some embodiments, the nucleic acids comprise RNA, such as self-amplifying RNA, circular RNA, or mRNA. Preferably, the nucleic acid comprises mRNA.

[0640] Except where otherwise noted, nucleic acid sequences set forth in the instant application may recite “T”s in a representative DNA sequence but where the sequence represents RNA, the “T”'s would be substituted for “U”s. Thus, any of the DNAs disclosed and identified by a particular sequence herein also discloses the corresponding RNA sequence where each “T” of the DNA sequence is substituted with “U.”.

Messenger RNA (mRNA)

[0641] Messenger RNA (mRNA) is RNA that encodes a (at least one) protein or a fragment thereof and can be translated to produce the encoded protein or fragment in vitro, in vivo, in situ, or ex vivo. mRNA comprises an open reading frame (ORF) encoding the protein or fragment thereof. In some embodiments, the mRNA further comprises a 5′ untranslated region (UTR), 3′ UTR, a polyA tail, and/or a 5′ cap analog.

[0642] The disclosed mRNA may encode a single protein or fragment or they may be polycistronic constructs, which encode more than one protein or fragment separately within the same mRNA molecule. Additionally or alternatively, the disclosed mRNA may encode a fusion protein or fragment thereof.

i. Open Reading Frame (ORF)

[0643] An open reading frame (ORF) is a continuous stretch of DNA or RNA beginning with a start codon (e.g., methionine (ATG or AUG)) and ending with a stop codon or codons (e.g., TAA, TAG, TGA, UAA, UAG, UGA, UGAUGA or UGAUAAUAG). For clarity: the stop codon itself is not considered a part of the ORF. An ORF typically encodes a protein or fragment thereof.

ii. Untranslated Regions (UTRs)

[0644] In some embodiments, mRNA comprises one or more regions or parts which act or function as an untranslated region. A 5′ untranslated region” (5′ UTR) is a region of an mRNA that is upstream (i.e., 5′) from the start codon and does not encode a polypeptide. A 3′ untranslated region” (3′UTR) is a region of an mRNA that is downstream (i.e., 3′) from the stop codon and also does not encode a polypeptide

[0645] The 5′ UTR may start at the transcription start site and continues to the start codon but does not include the start codon. The 3′ UTR may start immediately following the stop codon and continue until a transcriptional termination signal. A variety of 5′ UTR and 3′ UTR sequences are known. Exemplary UTR sequences include SEQ ID NOs: 1-35 (5′ UTRs) and 36-44 (3′ UTRs), which are shown in Tables S-1 (5′ UTRs) and S-2 (3′ UTRs) of the section “Exemplary Sequences”. In some embodiments, the 5′ UTR comprises a sequence provided in Table S-1 or a sequence with at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or 100% identity to a 5′ UTR sequence provided in Table S-1, or a variant or a fragment thereof. In some embodiments, the 3′ UTR comprises a sequence provided in Table S-2 or a sequence with at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99% or 100% identity to a 3′ UTR sequence provided in Table S-2, or a variant or a fragment thereof.

[0646] Each RNA species in a multivalent RNA composition may comprise an IDR sequence that is not a sequence isomer of an IDR sequence of another RNA species in a multivalent RNA composition (e.g., the IDR sequence does not have the same number of adenosine nucleotides, the same number of cytosine nucleotides, the same number of guanine nucleotides, and the same number of uracil nucleotides (and consequently the same mass) as another IDR sequence in the composition, even if those sequences have different sequences).

[0647] Each RNA species in a multivalent RNA composition may comprise an IDR sequence having a mass that differs from the mass of IDR sequences of each other RNA species in a multivalent RNA composition. For example, the mass of each IDR sequence may differ from the mass of other IDR sequences by at least 9 Da, at least 25 Da, at least 25 Da, or at least 50 Da. Use of IDR sequences with distinct masses allows RNA fragments comprising different IDR sequences to be distinguished using mass-based analysis methods (e.g., mass spectrometry), which do not require reverse transcription, amplification, or sequencing of RNAs.

[0648] Each RNA species in an RNA composition may comprises an IDR sequence with a different length. For example, each IDR sequence may have a length independently selected from 0 to 25 nucleotides. The length of a nucleic acid influences the rate at which the nucleic acid traverses a chromatography column, and so the use of IDR sequences of different lengths on different RNA species allows RNA fragments having different IDR sequences to be distinguished using chromatography-based methods (e.g., LC-UV).

[0649] Combinations of features may be included in flanking regions and may be contained within other features. For example, the ORF may be flanked by a 5′ UTR which may contain a strong Kozak translational initiation signal and/or a 3′ UTR which may include an oligo (dT) sequence for templated addition of a poly-A tail. 5′ UTR may comprise a first polynucleotide fragment and a second polynucleotide fragment from the same and/or different genes such as the 5′ UTRs described in US 2010/0293625 and WO 2015/085318.

[0650] In some embodiments, a double, triple or quadruple UTR such as a 5′ UTR or 3′ UTR may be used. As used herein, a “double” UTR is one in which two copies of the same UTR are encoded either in series or substantially in series. For example, a double beta-globin 3′ UTR may be used as described in US 2010/0129877.

[0651] For the purposes of the present disclosure, a UTR may also include one or more translation enhancer elements (TEE). As a non-limiting example, the TEE may include those described in US 2009/0226470, herein incorporated by reference, and those known in the art.

iii. PolyA Tail

[0652] In some embodiments, the mRNA contains a 3′-polyA tail. A polyA tail may contain 10 to 300 adenosine monophosphates. It can, in some instances, comprise up to about 400 adenine nucleotides. For example, a polyA tail may contain 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290 or 300 adenosine nucleotides. In some embodiments, a polyA tail contains 50 to 250 adenosine nucleotides. In some embodiments, a polyA tail has a length of about 50, about 100, about 150, about 200, about 250, about 300, about 350, or about 400 nucleotides. In some embodiments, a polyA tail has a length of 100 nucleotides.

[0653] In some embodiments, an mRNA may comprise two polyA sequences separated by an intervening nucleotide sequence. In some embodiments, the intervening nucleotide sequence comprises no more than 3, no more than two, no more than 1, or no adenosine nucleotides. In some embodiments, the intervening sequence comprises 3 adenosine nucleotides. In some embodiments, the intervening sequence is no more than 30, no more than 25, no more than 20, no more than 15, or no more than 10 nucleotides long. In some embodiments, the intervening sequence consists of 10 nucleotides. In some embodiments, the intervening sequence comprises the sequence of GCAUAUGACU. In some embodiments, the intervening sequence does not begin with an adenosine nucleotide, and does not end with an adenosine nucleotide. In some embodiments, the first polyA sequences comprises at least 15, at least 20, at least 25, or at least 30 consecutive adenosine nucleotides. In some embodiments, the second polyA sequences comprises at least 55, at least 60, at least 65, or at least 70 consecutive adenosine nucleotides. In some embodiments, the first polyA sequence comprises 30 consecutive adenosine nucleotides. In some embodiments, the second polyA sequence comprises 70 adenosine nucleotides.

[0654] In some embodiments, mRNA comprises a 5′ end cap or a “5′ terminal cap.” A cap analog may be, for example, a dinucleotide cap, a trinucleotide cap, or a tetranucleotide cap. In some embodiments, a cap analog is a dinucleotide cap. In some embodiments, a cap analog is a trinucleotide cap. In some embodiments, a cap analog is a tetranucleotide cap.

[0655] 5′-capping of polynucleotides may be completed concomitantly during an in vitro transcription reaction using, for example, the following chemical RNA cap analogs to generate the 5′-guanosine cap structure according to manufacturer protocols: 3′-O-Me-m7G(5′)ppp(5′) G [the ARCA cap]; G(5′)ppp(5′)A; G(5′)ppp(5′)G; m7G(5′)ppp(5′)A; m7G(5′)ppp(5′)G (New England BioLabs, Ipswich, MA). 5′-capping of modified mRNA may be completed post-transcriptionally using, for example, a Vaccinia Virus Capping Enzyme to generate the “Cap 0” structure: m7G(5′)ppp(5′)G (New England BioLabs, Ipswich, MA). A Cap 1 structure may be generated using both Vaccinia Virus Capping Enzyme and a 2′-O methyl-transferase to generate: m7G(5′)ppp(5′)G-2′-O-methyl. A Cap 2 structure may be generated from the Cap 1 structure followed by the 2′-O-methylation of the 5′-antepenultimate nucleotide using a 2′-0 methyl-transferase. A Cap 3 structure may be generated from the Cap 2 structure followed by the 2′-O-methylation of the 5′-preantepenultimate nucleotide using a 2′-O methyl-transferase. Enzymes may be derived from a recombinant source. Other cap analogs, such as a 7 mG(5′)ppp(5′)NlmpNp cap, may be used.

[0656] An mRNA may include nucleotides that are not chemically modified (i.e., unmodified nucleotides), nucleotides that are chemically modified, or both. Nucleotides that are not chemically modified are the standard ribonucleotides consisting of adenosine, guanosine, cytidine, and uridine.

[0657] Some embodiments of mRNAs comprise modified nucleosides and/or nucleotides. A “nucleoside” refers to a compound containing a sugar molecule (e.g., a pentose or ribose) or a derivative thereof in combination with an organic base (e.g., a purine or pyrimidine) or a derivative thereof (also referred to herein as “nucleobase”). A “nucleotide” refers to a nucleoside in combination with a phosphate group. Modifications to nucleotides or nucleosides can be at the sugar or nucleobase. Modified nucleotides may by synthesized by any useful method, such as, for example, chemically, enzymatically, or recombinantly.

[0658] In some embodiments, modified nucleobases in mRNA comprise N1-methyl-pseudouridine (m1ψ), N1-ethyl-pseudouridine (e1ψ), 5-methoxy-uridine (mo5U), 5-methyl-uridine (m5U), 5-methyl-cytidine (m5C), and/or pseudouridine (ψ). In some embodiments, modified nucleobases in mRNAs comprise 5-methoxymethyl uridine, 5-methylthio uridine, 1-methoxymethyl pseudouridine, 5-methyl cytidine, and/or 5-methoxy cytidine. In some embodiments, the mRNA includes a combination of at least two (e.g., 2, 3, 4 or more) of any of the aforementioned modified nucleobases, including but not limited to chemical modifications.

[0659] In some embodiments, a mRNA comprises 1-methyl-pseudouridine (mlv) substitutions at one or more or all uridine positions of the mRNA.

[0660] In some embodiments, a mRNA comprises 1-methyl-pseudouridine (m1ψ) substitutions at one or more or all uridine positions of the mRNA and 5-methyl cytidine substitutions at one or more or all cytidine positions of the mRNA.

[0661] In some embodiments, a mRNA comprises pseudouridine (ψ) substitutions at one or more or all uridine positions of the mRNA.

[0662] In some embodiments, a mRNA comprises pseudouridine (ψ) substitutions at one or more or all uridine positions of the mRNA and 5-methylcytidine substitutions at one or more or all cytidine positions of the mRNA.

[0663] In some embodiments, a mRNA comprises uridine at one or more or all uridine positions of the mRNA.

[0664] In some embodiments, a mRNA comprises 5-methyl-uridine and 5-methyl cytidine at one or more or all uridine and cytidine positions, respectively, of the mRNA.

[0665] In some embodiments, mRNAs are uniformly modified (e.g., fully modified, modified throughout the entire sequence) for a particular modification. For example, a mRNA can be uniformly modified with 1-methyl-pseudouridine, meaning that all uridine residues in the mRNA sequence are replaced with 1-methyl-pseudouridine. Similarly, a nucleic acid can be uniformly modified for any type of nucleoside residue present in the sequence by replacement with a modified residue such as those set forth above. In some embodiments, the ORF is uniformly modified for a particular modification, such as 1-methyl-pseudouridine. In some embodiments, the uniform modification does not include the mRNA cap. For instance, a cap with different modifications from the remainder of the mRNA can be added co-transcriptionally or post-transcriptionally to the mRNA.

[0666] In some embodiments, an ORF encoding a protein or fragment thereof is codon optimized. Codon optimization methods are known in the art. For example, an ORF of any one or more of the sequences listed below may be codon optimized. Codon optimization, in some embodiments, may be used to match codon frequencies in target and host organisms to ensure proper folding; bias GC content to increase RNA stability or reduce secondary structures; minimize tandem repeat codons or base runs that may impair gene construction or expression; customize transcriptional and translational control regions; insert or remove protein trafficking sequences; remove/add post translation modification sites in encoded protein (e.g., glycosylation sites); add, remove or shuffle protein domains; insert or delete restriction sites; modify ribosome binding sites and RNA degradation sites; adjust translational rates to allow the various domains of the protein to fold properly; or reduce or eliminate problem secondary structures within the polynucleotide. Codon optimization tools, algorithms and services are known in the art—non-limiting examples include services from GeneArt (Life Technologies), DNA2.0 (Menlo Park CA) and/or proprietary methods. In some embodiments, the open reading frame (ORF) sequence is optimized using optimization algorithms.

[0667] In some embodiments, a codon optimized sequence shares less than 95%, less than 90%, less than 85%, less than 80%, or less than 75% sequence identity to a naturally-occurring or wild-type sequence open reading frame (e.g., a naturally-occurring or wild-type mRNA sequence encoding a protein or fragment thereof). In some embodiments, a codon optimized sequence shares between 65% and 85% sequence identity to a naturally-occurring or wild-type sequence (e.g., a naturally-occurring or wild-type RNA or DNA sequence encoding a protein or fragment thereof).

[0668] In some embodiments, a codon-optimized sequence encodes an antigen that is as immunogenic as, or more immunogenic than (e.g., at least 10%, at least 20%, at least 30%, at least 40%, at least 50%, at least 100%, or at least 200% more), than a protein or fragment thereof encoded by a non-codon-optimized sequence.

[0669] In some embodiments, an RNA is a self-amplifying RNA. A self-amplifying RNA is an RNA encoding one or more proteins that, individually or in conjunction, are capable of replicating the self-amplifying RNA. In some embodiments, the proteins encoded by the self-amplifying RNA are non-structural proteins nsP1, nsP2, nsP3, and nsP4, which form an RNA-dependent RNA polymerase (RdRp), or replicase, that is capable of replicating the self-amplifying RNA. By encoding proteins that are capable of replicating the RNA, a self-amplifying RNA is capable of self-amplification in a cell, provided that the cell can translate the RNA and produce the encoded protein(s). A self-amplifying RNA may be referred to as an RNA replicon.

[0670] When a self-amplifying RNA is translated, the one or more encoded viral non-structural proteins are translated. A “viral non-structural protein” is a protein encoded by a virus but that is not part of the virus particle. The viral non-structural proteins, in the context of self-amplifying RNA, replicate the nucleotide sequences encoding the desired protein from the self-amplifying RNA via the sub-genomic viral promoters. Such replication driven by the viral sub-genomic promoter using the viral non-structural proteins enhances the expression level of the encoded protein. In some embodiments, the viral non-structural proteins are from a single-strand positive-sense RNA viruses. In some embodiments, the viral non-structural proteins are from an Alphavirus, belonging to the Togaviridae family. In some embodiments, the alphavirus is Sindbis or Venezuelan equine encephalitis virus. In some embodiments, the viral non-structural protein is an RNA-dependent RNA polymerase (RdRp) polyprotein P1234 (also termed NSP1-4).

[0671] Upon translation, P1234 is rapidly cleaved into P123 and nsP4 by autoproteolytic activity originating from the nsP2 (proteinase) portion of the polyprotein. Alphaviral RNA synthesis occurs at the plasma membrane of a cell, where the nsPs, together with alphaviral RNA, form membrane invaginations (or “spherules”). These spherules contain dsRNA created by replication of “+” strand viral genomic RNA into “−” strand anti-genomic RNA. The “−” strand serves as a template from which additional “+” strand genomic RNA (synthesized from the 5′ UTR) or a shorter subsequence of the genomic RNA (termed subgenomic RNA) is synthesized from the subgenomic viral promoter region located near the end of the nonstructural protein ORF. The “+” strand genomic RNA and the subgenomic RNA are exported out of the spherules into the cytoplasm where they are translated by endogenous ribosomes. The exported “+” strand genomic RNA can associate with nsPs and form additional spherules, thus resulting in exponential increase of replicon RNA.

[0672] The viral non-structural proteins facilitate the replication of the nucleotide sequences encoding the desired protein via the subgenomic viral promoters (also referred to as “subgenomic promoters” herein). A “subgenomic viral promoter” refers to a promoter the drives the transcription of subgenomic mRNAs. Typically, an mRNA is transcribed from genomic DNAs and episomal DNAs (e.g., plasmids). Some viruses may transcribe subgenomic mRNAs from a RNA replicon that is produced from its genomic RNA. Many positive-sense RNA viruses produce subgenomic mRNAs as one of the common infection techniques used by these viruses and generally transcribe late viral genes. Subgenomic viral promoters range from 20 nucleotide (Sindbis virus) to over 100 nucleotides (Beet necrotic yellow vein virus) and are usually found upstream of the transcription start. In some embodiments, the subgenomic viral promoter is 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100 nucleotides long, or longer. Subgenomic viral promoters have been described in the art, e.g., in PCT Publication No. WO 2016/040359, and Wagner et al., Nature Chemical Biology, DOI: 10.1038/s41589-018-0146-9 (2018).

[0673] In some embodiments, an RNA is a circular RNA. A circular RNA is an RNA with no 5′ terminal nucleotide or 3′ terminal nucleotide. Every nucleotide in a circular RNA is covalently bonded to both (1) a 5′ adjacent nucleotide; and (2) a 3′ adjacent nucleotide. In a circular RNA with a nucleotide sequence comprising every nucleotide of the circular RNA in 5′-to-3′ order, the last nucleotide of the nucleotide sequence is covalently bonded to the first nucleotide of the nucleotide sequence.

[0674] A circular RNA may be a circular mRNA, comprising one or more 5′ UTRs, an open reading frame, and one or more 3′ UTRs. A circular RNA may comprise a polyA region, as described in the section entitled “PolyA Tails”. The skilled artisan will appreciate that a polyA tail, when incorporated in a circular RNA, is referred to as a polyA region because a circular RNA does not have an end as a linear mRNA does.

[0675] A circular RNA may comprise an internal ribosome entry site (IRES). Inclusion of an IRES permits the translation of one or more open reading frames from a circular RNA, as circular RNAs do not comprise a 5′ from which a ribosome may initiate translation as with capped linear mRNAs. The IRES element attracts a eukaryotic ribosomal translation initiation complex and promotes translation initiation. See, e.g., Kaufman et al., Nucleic Acid Res. 1991 19:4485-4490; Gurtu et al., Biochem Biophys Res Commun. 1996. 229:295-298; Rees et al., BioTechniques. 1996. 20:102-110; Kobayashi et al., BioTechniques. 1996. 21:399-402; and Mosser et al., BioTechniques. 1997. 22:150-161. A multitude of IRES sequences are available and include sequences derived from a wide variety of viruses, such as from leader sequences of picornaviruses such as the encephalomyocarditis virus (EMCV) UTR (Jang et al., J Virol. 1989. 63:1651-1660), the polio leader sequence, the hepatitis A virus leader, the hepatitis C virus IRES, human rhinovirus type 2 IRES (Dobrikova et al., Proc Natl Acad Sci USA. 2003. 100(25):15125-15130), an IRES element from the foot and mouth disease virus (Ramesh et al., Nucleic Acid Res. 1996. 24:2697-2700), a giardiavirus IRES (Garlapati et al., J Biol Chem. 2004. 279(5):3389-3397). Additionally or alternatively, a circular RNA may comprise any of a variety of nonviral IRES sequences, such as IRES sequences from yeast, as well as the human angiotensin II type 1 receptor IRES (Martin et al., Mol Cell Endocrinol. (2003) 212:51-61), fibroblast growth factor IRESs (FGF-1 IRES and FGF-2 IRES, Martineau et al., Mol Cell Biol. 2004. 24(17):7622-7635), vascular endothelial growth factor (VEGF) IRES (Baranick et al., Proc Natl Acad Sci USA. 2008. 105(12):4733-4738, Stein et al., Mol Cell Biol. 1998. 18(6):3112-3119, Bert et al., RNA. 2006. 12(6):1074-1083), and insulin-like growth factor II (IGF-II) IRES (Pedersen et al., Biochem J. 2002. 363 (Pt 1):37-44). These elements are commercially available in plasmids sold, e.g., by Clontech (Mountain View, CA), Invivogen (San Diego, CA), Addgene (Cambridge, MA) and GeneCopoeia (Rockville, MD). See also IRESite: The database of experimentally verified IRES structures. In some embodiments, a circular RNA comprises a coxsackievirus B3 (CVB3) IRES. See Gharbi et al., PLoS One. 2022. 17(10):e0274162. In some embodiments, a circular RNA comprises an EMCV IRES. In some embodiments, a circular RNA comprises a salivirus IRES. See Sweeney et al., J Virol. 2012. 86(3):1468-1486. In some embodiments, the salivirus IRES is present in or derived from Salivirus FHB (SaliFHB). See GenBank Accession No. KM023140.1.

[0676] Some aspects relate to viral vectors comprising or encoding influenza virus proteins. In some embodiments, the protein is comprised in a viral vector. In some embodiments, a viral vector comprises a nucleic acid encoding the protein.

[0677] Any suitable virus may be used as a viral vector. Non-limiting examples of viruses that may be used as viral vectors include retrovirus (e.g., lentivirus), adenovirus, adeno-associated virus (AAV), vesicular stomatitis virus (VSV), herpesvirus, Rous sarcoma virus, measles virus, poxvirus, gammavirus, alphavirus, murine stem cell virus, Moloney murine leukemia virus, and bovine leukemia virus. In some embodiments, the viral vector is a VSV vector. In some embodiments, the viral vector is a measles virus vector. In some embodiments, the viral vector is an adenovirus vector. These and other viral vectors suitable for expression of heterologous proteins (i.e., proteins not naturally expressed by a virus from which the viral vector is derived) are known in the art.

[0678] In some embodiments, a viral vector comprises an influenza B/Victoria lineage HA protein, or a nucleic acid encoding the influenza B/Victoria lineage HA protein. In some embodiments, the influenza B/Victoria lineage virus HA protein is an influenza B/Victoria lineage virus HA protein described in the section entitled “B/Victoria lineage HA proteins.” In some embodiments, the influenza B/Victoria lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 71.

[0679] In some embodiments, a viral vector comprises an influenza B/Yamagata lineage HA protein, or a nucleic acid encoding the influenza B/Yamagata lineage HA protein. In some embodiments, the influenza B/Yamagata lineage virus HA protein is an influenza B/Yamagata lineage virus HA protein described in the section entitled “B/Yamagata lineage HA proteins.” In some embodiments, the influenza B/Yamagata lineage HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 70.

[0680] In some embodiments of viral vectors, a viral vector comprises an IAV H1 HA protein, or a nucleic acid encoding the IAV H1 HA protein. In some embodiments, the IAV H1 HA protein is an IAV H1 HA protein described in the section entitled “H1 HA proteins.” In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 83. In some embodiments, the IAV H1 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 95.

[0681] In some embodiments, a viral vector comprises an IAV H3 HA protein, or a nucleic acid encoding the IAV H3 HA protein. In some embodiments, IAV H3 HA protein is an IAV H3 HA protein described in the section entitled “H3 HA proteins.” Where a combination or multivalent vaccine includes multiple H3 HA proteins (e.g., comprises multiple viral vectors comprising or encoding different H3 HA proteins), the different H3 HA proteins may each comprise the same substitutions, or different substitutions described in the section entitled “H3 HA proteins.” In some embodiments, one or more H3 HA proteins does not comprise a substitution described in the section entitled “H3 HA proteins.” In some embodiments, the IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82. In some embodiments, each IAV H3 HA protein comprises an amino acid sequence with at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 82.

[0682] cDNA encoding RNA polynucleotides may be transcribed using an in vitro transcription (IVT) system. In vitro transcription of RNA is known in the art and is described in International Publication WO 2014/152027, which is incorporated by reference herein to the extent it discloses IVT methods. In some embodiments, the RNA is prepared in accordance with any one or more of the methods described in WO 2018/053209 and WO 2019/036682, each of which is incorporated by reference herein to the extent it discloses RNA production methods.

[0683] In some embodiments, the RNA transcript is generated using a non-amplified, linearized DNA template in an in vitro transcription reaction to generate the RNA transcript. In some embodiments, the template DNA is isolated DNA. In some embodiments, the template DNA is cDNA. In some embodiments, the cDNA is formed by reverse transcription of an RNA polynucleotide, for example, but not limited to influenza virus mRNA. In some embodiments, cells, e.g., bacterial cells, e.g., E. coli, e.g., DH-1 cells are transfected with the plasmid DNA template. In some embodiments, the transfected cells are cultured to replicate the plasmid DNA which is then isolated and purified. In some embodiments, the DNA template includes a RNA polymerase promoter, e.g., a T7 promoter located 5′ to and operably linked to the gene of interest.

[0684] In some embodiments, an in vitro transcription template encodes a 5′ untranslated (UTR) region, contains an open reading frame, and encodes a 3′ UTR and a poly(A) tail. The particular nucleic acid sequence composition and length of an in vitro transcription template will depend on the mRNA encoded by the template.

[0685] An in vitro transcription system typically comprises a transcription buffer, nucleotide triphosphates (NTPs), an RNase inhibitor, and a polymerase.

[0686] The NTPs may be manufactured in house, may be selected from a supplier, or may be synthesized. The NTPs may be selected from natural and unnatural NTPs, and may be selected from unmodified (e.g., ATP, GTP, UTP, CTP) or modified NTPs.

[0687] Any number of RNA polymerases or variants may be used to transcribe RNA. The polymerase may be selected from, but is not limited to, a phage RNA polymerase, e.g., a T7 RNA polymerase, a T3 RNA polymerase, a SP6 RNA polymerase, and/or mutant polymerases such as, but not limited to, polymerases able to incorporate modified nucleic acids and/or modified nucleotides, including chemically modified nucleic acids and/or nucleotides. Some embodiments exclude the use of DNase.

[0688] In some embodiments, the RNA transcript is capped via enzymatic capping. In some embodiments, the RNA comprises 5′ terminal cap, for example, 7 mG(5′)ppp(5′)NlmpNp.

[0689] In some embodiments the RNA polymerase is a wild-type RNA polymerase. In some embodiments, the RNA polymerase is an RNA polymerase variant, such as those described in WO 2020/172239, incorporated herein by reference to the extent it describes RNA polymerase variants. RNA polymerase variants may include at least one amino acid substitution, relative to the wild-type (WT) RNA polymerase. A WT T7 RNA polymerase is represented by SEQ ID NO: 81. In some embodiments, the RNA polymerase is a variant RNA polymerase comprising the amino acid sequence of any one of SEQ ID NOs: 176-179.

[0690] Purification of the nucleic acids may include, but is not limited to, nucleic acid clean-up, quality assurance and quality control. Clean-up may be performed by methods known in the arts such as, but not limited to, AGENCOURT® beads (Beckman Coulter Genomics, Danvers, MA), poly-T beads, LNATM oligo-T capture probes (EXIQON® Inc, Vedbaek, Denmark); HPLC based purification methods such as, but not limited to, strong anion exchange HPLC, weak anion exchange HPLC, reverse phase HPLC (RP-HPLC), and hydrophobic interaction HPLC (HIC-HPLC); and/or tangential flow filtration. The term “purified” when used in relation to a nucleic acid such as a “purified nucleic acid” refers to one that is separated from at least one contaminant. A “contaminant” is any substance that makes another unfit, impure or inferior. Thus, a purified nucleic acid (e.g., DNA and RNA) is present in a form or setting different from that in which it is found in nature, or a form or setting different from that which existed prior to subjecting it to a treatment or purification method.

[0691] In some embodiments, the nucleic acids are formulated as a lipid composition, such as a composition comprising a lipid nanoparticle, a liposome, and/or a lipoplex. In some embodiments, the lipid composition (e.g., lipid nanoparticle, liposome, and/or lipoplex) does not comprise protamine. In some embodiments, the lipid composition does comprise protamine. In some embodiments, nucleic acids are formulated as lipid nanoparticle (LNP) compositions. Lipid nanoparticles typically comprise ionizable lipid (e.g., ionizable amino lipid), non-cationic lipid (e.g., phospholipid), structural lipid (e.g., sterol), and PEG-modified lipid components along with the nucleic acid cargo of interest. The lipid nanoparticles can be generated using components, compositions, and methods as are generally known in the art, see for example PCT/US2016/052352; PCT/US2016/068300; PCT/US2017/037551; PCT/US2015/027400; PCT/US2016/047406; PCT/US2016000129; PCT/US2016/014280; PCT/US2017/038426; PCT/US2014/027077; PCT/US2014/055394; PCT/US2016/52117; PCT/US2012/069610; PCT/US2017/027492; PCT/US2016/059575; PCT/US2016/069491; PCT/US2016/069493; and PCT/US2014/66242, all of which are incorporated by reference herein in their entirety.

[0692] In some embodiments, the lipid nanoparticle comprises a molar ratio of 20-60% ionizable lipid, 5-25% non-cationic lipid, 25-55% structural lipid, and 0.5-15% PEG-modified lipid.

[0693] In some embodiments, the lipid nanoparticle comprises a molar ratio of 20-60% ionizable lipid, 5-30% non-cationic lipid, 10-55% structural lipid, and 0.5-15% PEG-modified lipid.

[0694] In some embodiments, the lipid nanoparticle comprises 40-50 mol % ionizable lipid, optionally 45-50 mol %, for example, 45-46 mol %, 46-47 mol %, 47-48 mol %, 48-49 mol %, or 49-50 mol % for example about 45 mol %, 45.5 mol %, 46 mol %, 46.5 mol %, 47 mol %, 47.5 mol %, 48 mol %, 48.5 mol %, 49 mol %, or 49.5 mol %.

[0695] In some embodiments, the lipid nanoparticle comprises 20-60 mol % ionizable lipid. For example, the lipid nanoparticle may comprise 20-50 mol %, 20-40 mol %, 20-30 mol %, 30-60 mol %, 30-50 mol %, 30-40 mol %, 40-60 mol %, 40-50 mol %, or 50-60 mol % ionizable lipid. In some embodiments, the lipid nanoparticle comprises 20 mol %, 30 mol %, 40 mol %, 50 mol %, or 60 mol % ionizable lipid. In some embodiments, the lipid nanoparticle comprises 35 mol %, 36 mol %, 37 mol %, 38 mol %, 39 mol %, 40 mol %, 41 mol %, 42 mol %, 43 mol %, 44 mol %, 45 mol %, 46 mol %, 47 mol %, 48 mol %, 49 mol %, 50 mol %, 51 mol %, 52 mol %, 53 mol %, 54 mol %, or 55 mol % ionizable lipid.

[0696] In some embodiments, the lipid nanoparticle comprises 45-55 mole percent (mol %) ionizable lipid. For example, lipid nanoparticle may comprise 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, or 55 mol % ionizable lipid.

[0697] In some embodiments, the ionizable lipid is a compound of Formula (IL*)

• • [0698] or a salt thereof, wherein:
  • [0699] R¹ is —OH, —NR^N—C_4-10 cycloalkenyl optionally substituted with one or more oxo or —N(R^N′R^N″);
  • [0700] R^N is H or C_1-6 alkyl;
  • [0701] R^N′ is H or C_1-6 alkyl;
  • [0702] R^N″ is H or C_1-6 alkyl;
  • [0703] is 1, 2, 3, or 4;
  • [0704] n is 4, 5, 6, 7, or 8;
  • [0705] m is 4, 5, 6, 7, or 8;
  • [0706] M is-C(═O)—O—* or —O—C(═O)—*, wherein * indicates attachment to R²;
  • [0707] M′ is —C(═O)—O—* or —O—C(═O)—*, wherein * indicates attachment to R³;
  • [0708] R² is

• •  or —(C_1-6 alkylene)-(C_3-8 cycloalkyl)-C_1-6 alkyl;
  • [0709] R^2a is —H or C_1-10 alkyl;
  • [0710] R^2b is —H or C_1-10 alkyl;
  • [0711] R^2c is C_1-8 alkyl or C_2-8 alkenyl;
  • [0712] R³ is

• • [0713] R^3a is H or C_1-10 alkyl;
  • [0714] R^3b is H or C_1-8 alkyl; and
  • [0715] R^3c is C_1-10 alkyl or C_2-8 alkenyl.

[0716] In some embodiments, the ionizable lipid is of Formula (IL**—I):

• • [0717] or a salt thereof, wherein:
  • [0718] R¹ is —OH;
  • [0719] is 2, 3, or 4;
  • [0720] n is 4, 5, 6, 7, or 8;
  • [0721] M is —C(═O)—O—*, wherein * indicates attachment to R²;
  • [0722] m is 6, 7, or 8;
  • [0723] M′ is —C(═O)—O—*, wherein * indicates attachment to R³;
  • [0724] R^2c is C_4-8 alkyl;
  • [0725] R^3a is C_7-10 alkyl; and
  • [0726] R^3c is C_3-5 alkyl.

[0727] In some embodiments, the ionizable lipid is of Formula (IL**—III):

• • [0728] or a salt thereof, wherein:
  • [0729] R¹ is NR^N—C_4-10 cycloalkenyl optionally substituted with one or more oxo or —N(R^N′R^N″);
    • [0730] R^N is H;
    • [0731] R^N′ is C_1-2 alkyl;
    • [0732] R^N″ is H;
  • [0733] is 2, 3, or 4;
  • [0734] n is 6, 7, or 8;
  • [0735] M is —C(═O)—O—*, wherein * indicates attachment to R²;
  • [0736] m is 6, 7, or 8;
  • [0737] M′ is —C(═O)—O—*, wherein * indicates attachment to R³;
  • [0738] R^2a is C_7-10 alkyl;
  • [0739] R^2c is C_4-6 alkyl;
  • [0740] R^3a is C_1-3 alkyl; and
  • [0741] R^3c is C_4-6 alkyl.

[0742] In some embodiments, the ionizable lipid is of Formula (IL**—IV):

• • [0743] or a salt thereof, wherein:
  • [0744] R¹ is OH;
  • [0745] is 2, 3, or 4;
  • [0746] n is 6, 7, or 8;
  • [0747] M is —C(—O)—O—*, wherein * indicates attachment to R²;
  • [0748] m is 6, 7, or 8;
  • [0749] M′ is —C(═O)—O—*, wherein * indicates attachment to R³;
  • [0750] R^2b is C_3-5 alkyl;
  • [0751] R^2c is C_2-4 alkyl;
  • [0752] R^3a is C_7-10 alkyl; and
  • [0753] R^3c is C_4-6 alkyl.

[0754] In some embodiments, the ionizable lipid is of Formula (IL*—I):

• • [0755] or a salt thereof, wherein:
  • [0756] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for variable IL*; and
  • [0757] R^3a is C_1-8 alkyl.

[0758] In some embodiments, ionizable lipid is of Formula (IL*-Ia):

• • [0759] or a salt thereof, wherein:
  • [0760] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for Formula IL*; and
  • [0761] R^3a is C_1-8 alkyl.

[0762] In some embodiments, the ionizable lipid is of Formula (IL*-Ia′):

• • [0763] or a salt thereof, wherein:
  • [0764] o, M, M′, R^2c and R^3c are as defined for variable IL*; and
  • [0765] R^3a is C_1-8 alkyl.

[0766] In some embodiments, the ionizable lipid is of Formula (IL*-Iia):

• • [0767] or a salt thereof, wherein:
  • [0768] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for Formula IL*; and
  • [0769] R^3a is C_1-8 alkyl.

[0770] In some embodiments, the ionizable lipid is of Formula (IL*-II′):

• • [0771] or a salt thereof, wherein:
  • [0772] o, M, M′, R^2c and R^3c are as defined for variable IL*; and
  • [0773] R^3a is C_1-8 alkyl.

[0774] In some embodiments, the ionizable lipid is of Formula (IL*—III):

• • [0775] or a salt thereof, wherein:
  • [0776] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0777] R^2a is a C_1-8 alkyl; and
  • [0778] R^3a is C_1-8 alkyl.

[0779] In some embodiments, the ionizable lipid is of Formula (IL*-IIIa):

• • [0780] or a salt thereof, wherein:
  • [0781] R¹, o, m, n, M, M′, R^2c, and R^3e are as defined for variable IL*;
  • [0782] R^2b is a C_1-8 alkyl; and
  • [0783] R^3a is C_1-8 alkyl.

[0784] In some embodiments, the ionizable lipid is of Formula (IL*-IIIa):

• • [0785] or a salt thereof, wherein:
  • [0786] R¹, o, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0787] R^2a is a C_1-8 alkyl; and
  • [0788] R^3a is C_1-8 alkyl.

[0789] In some embodiments, the ionizable lipid is of Formula (IL*-IIIa′):

• • [0790] or a salt thereof, wherein:
  • [0791] R¹, o, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0792] R^2a is a C_1-8 alkyl; and
  • [0793] R^3a is C_1-8 alkyl.

[0794] In some embodiments, the ionizable lipid is of Formula (IL*-IIIb):

• • [0795] or a salt thereof, wherein:
  • [0796] R¹, o, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0797] R^2a is a C_1-8 alkyl; and
  • [0798] R^3a is C_1-8 alkyl.

[0799] In some embodiments, the ionizable lipid is of Formula (IL*-IIIb′):

• • [0800] or a salt thereof, wherein:
  • [0801] R¹, o, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0802] R^2a is a C_1-8 alkyl; and
  • [0803] R^3a is C_1-8 alkyl.

[0804] In some embodiments, the ionizable lipid is of Formula (IL*—IV):

• • [0805] or a salt thereof, wherein:
  • [0806] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0807] R^2b is a C_1-8 alkyl; and
  • [0808] R^3a is C_1-8 alkyl.

[0809] In some embodiments, the ionizable lipid is of Formula (IL*-Iva):

• • [0810] or a salt thereof, wherein:
  • [0811] R¹, o, m, n, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0812] R^2b is a C_1-8 alkyl; and
  • [0813] R^3a is C_1-8 alkyl.

[0814] In some embodiments, the ionizable lipid is of Formula (IL*-Iva′):

• • [0815] or a salt thereof, wherein:
  • [0816] o, M, M′, R^2c, and R^3c are as defined for variable IL*;
  • [0817] R^2a is a C_1-8 alkyl; and
  • [0818] R^3a is C_1-8 alkyl.
    Variables o, R¹, R^N, R^N′, R^N″ of Ionizable Lipid

[0819] In some embodiments of the ionizable lipid, o is 1.

[0820] In some embodiments of the ionizable lipid, o is 2.

[0821] In some embodiments of the ionizable lipid, o is 3.

[0822] In some embodiments of the ionizable lipid, o is 4.

[0823] In some embodiments of the ionizable lipid, R¹ is —OH.

[0824] In some embodiments of the ionizable lipid, R^N is H.

[0825] In some embodiments of the ionizable lipid, R^N is methyl.

[0826] In some embodiments of the ionizable lipid, R^N is ethyl.

[0827] In some embodiments of the ionizable lipid, R¹ is —NR^N-cyclobutenyl, wherein the cyclobutenyl is optionally substituted with one or more oxo or —N(R^N′R^N″).

[0828] In some embodiments of the ionizable lipid, R^N′ is H.

[0829] In some embodiments of the ionizable lipid, R^N′ is methyl.

[0830] In some embodiments of the ionizable lipid, R^N′ is ethyl.

[0831] In some embodiments of the ionizable lipid, R^N″ is H.

[0832] In some embodiments of the ionizable lipid, R^N″ is methyl.

[0833] In some embodiments of the ionizable lipid, R^N″ is ethyl.

[0834] In some embodiments of the ionizable lipid, R^N′ is H and R^N″ is methyl.

[0835] In some embodiments of the ionizable lipid, R¹ is

[0836] In some embodiments of the ionizable lipid, R¹ is

[0837] In some embodiments of the ionizable lipid, m is 4.

[0838] In some embodiments of the ionizable lipid, m is 5.

[0839] In some embodiments of the ionizable lipid, m is 6.

[0840] In some embodiments of the ionizable lipid, m is 7.

[0841] In some embodiments of the ionizable lipid, m is 8.

[0842] In some embodiments of the ionizable lipid, m is 4.

[0843] In some embodiments of the ionizable lipid, n is 5.

[0844] In some embodiments of the ionizable lipid, n is 6.

[0845] In some embodiments of the ionizable lipid, n is 7.

[0846] In some embodiments of the ionizable lipid, n is 8.

[0847] In some embodiments of the ionizable lipid, n is 5 and m is 7.

[0848] In some embodiments of the ionizable lipid, n is 7 and m is 7.

[0849] In some embodiments of the ionizable lipid, m is 6 and n is 6.

[0850] In some embodiments of the ionizable lipid, M is —O—C(═O)—*, wherein * indicates attachment to R².

[0851] In some embodiments of the ionizable lipid, M is —C(—O)—O—* wherein * indicates attachment to R².

[0852] In some embodiments of the ionizable lipid, M′ is —O—C(═O)—*, wherein * indicates attachment to R³.

[0853] In some embodiments of the ionizable lipid, M′ is —C(═O)—O—* wherein * indicates attachment to R³.

[0854] In some embodiments of the ionizable lipid, M is —O—C(═O)—*, wherein * indicates attachment to R², and M′ is —C(—O)—O—* wherein * indicates attachment to R³

Variables R², R^2a, R^2b, R^2c of Ionizable Lipid

[0855] In some embodiments of the ionizable lipid, R² is

[0856] In some embodiments of the ionizable lipid, R^2a is hydrogen.

[0857] In some embodiments of the ionizable lipid, R^2a is methyl.

[0858] In some embodiments of the ionizable lipid, R^2a is ethyl.

[0859] In some embodiments of the ionizable lipid, R^2a is propyl.

[0860] In some embodiments of the ionizable lipid, R^2a is butyl.

[0861] In some embodiments of the ionizable lipid, R^2a is pentyl.

[0862] In some embodiments of the ionizable lipid, R^2a is hexyl.

[0863] In some embodiments of the ionizable lipid, R^2a is heptyl.

[0864] In some embodiments of the ionizable lipid, R^2a is octyl.

[0865] In some embodiments of the ionizable lipid, R^2b is hydrogen.

[0866] In some embodiments of the ionizable lipid, R^2b is methyl.

[0867] In some embodiments of the ionizable lipid, R^2b is ethyl.

[0868] In some embodiments of the ionizable lipid, R^2b is propyl.

[0869] In some embodiments of the ionizable lipid, R^2b is butyl.

[0870] In some embodiments of the ionizable lipid, R^2b is pentyl.

[0871] In some embodiments of the ionizable lipid, R^2b is hexyl.

[0872] In some embodiments of the ionizable lipid, R^2b is heptyl.

[0873] In some embodiments of the ionizable lipid, R^2b is octyl.

[0874] In some embodiments of the ionizable lipid, R^2a is hydrogen and R^2b is hydrogen.

[0875] In some embodiments of the ionizable lipid, R^2a is hexyl and R^2b is hydrogen.

[0876] In some embodiments of the ionizable lipid, R^2a is octyl and R^2b is hydrogen.

[0877] In some embodiments of the ionizable lipid, R^2a is hydrogen and R^2b is butyl.

[0878] In some embodiments of the ionizable lipid, R^2c is methyl.

[0879] In some embodiments of the ionizable lipid, R^2c is ethyl.

[0880] In some embodiments of the ionizable lipid, R^2c is propyl.

[0881] In some embodiments of the ionizable lipid, R^2c is butyl.

[0882] In some embodiments of the ionizable lipid, R^2c is pentyl.

[0883] In some embodiments of the ionizable lipid, R^2c is hexyl.

[0884] In some embodiments of the ionizable lipid, R^2c is heptyl.

[0885] In some embodiments of the ionizable lipid, R^2c is octyl.

[0886] In some embodiments of the ionizable lipid, R² is —(C_1-6 alkylene)-(C_3-8 cycloalkyl)-C_1-6 alkyl.

[0887] In some embodiments of the ionizable lipid, R² is —(C_1-6 alkylene)-(cyclohexyl)-C_1-6 alkyl.

[0888] In some embodiments of the ionizable lipid, R² is —(C_1-6 alkylene)-(cyclopentyl)-C_1-6 alkyl.

Variables R³, R^3a, R^3b, and R^3c of Ionizable Lipid

[0889] In some embodiments of the ionizable lipid, R³ is

[0890] In some embodiments of the ionizable lipid, R^3a is hydrogen.

[0891] In some embodiments of the ionizable lipid, R^3a is methyl.

[0892] In some embodiments of the ionizable lipid, R^3a is ethyl.

[0893] In some embodiments of the ionizable lipid, R^3a is propyl.

[0894] In some embodiments of the ionizable lipid, R^3a is butyl.

[0895] In some embodiments of the ionizable lipid, R^3a is pentyl.

[0896] In some embodiments of the ionizable lipid, R^3a is hexyl.

[0897] In some embodiments of the ionizable lipid, R^3a is heptyl.

[0898] In some embodiments of the ionizable lipid, R^3a is octyl.

[0899] In some embodiments of the ionizable lipid, R^3b is hydrogen.

[0900] In some embodiments of the ionizable lipid, R^3b is methyl.

[0901] In some embodiments of the ionizable lipid, R^3b is ethyl.

[0902] In some embodiments of the ionizable lipid, R^3b is propyl.

[0903] In some embodiments of the ionizable lipid, R^3b is butyl.

[0904] In some embodiments of the ionizable lipid, R^3b is pentyl.

[0905] In some embodiments of the ionizable lipid, R^3b is hexyl.

[0906] In some embodiments of the ionizable lipid, R^3b is heptyl.

[0907] In some embodiments of the ionizable lipid, R^3b is octyl.

[0908] In some embodiments of the ionizable lipid, R^3a is octyl and R^3b is hydrogen.

[0909] In some embodiments of the ionizable lipid, R^3a is ethyl and R^3b is hydrogen.

[0910] In some embodiments of the ionizable lipid, R^3a is hexyl and R^3b is hydrogen.

[0911] In some embodiments of the ionizable lipid, R^3c is methyl.

[0912] In some embodiments of the ionizable lipid, R^3c is ethyl.

[0913] In some embodiments of the ionizable lipid, R^3c is propyl.

[0914] In some embodiments of the ionizable lipid, R^3c is butyl.

[0915] In some embodiments of the ionizable lipid, R^3c is pentyl.

[0916] In some embodiments of the ionizable lipid, R^3c is hexyl.

[0917] In some embodiments of the ionizable lipid, R^3c is heptyl.

[0918] In some embodiments of the ionizable lipid, R^3c is octyl.

[0919] It is understood that, for an ionizable lipid, variables o, R¹, R^N, R^N′, R^N′, m, n, M, M′, R², R^2a, R^2b, R^2c, R³, R^3a, R^3b, and R^3c can each be, where applicable, selected from the groups described herein, and any group described herein for any of variables o, R¹, R^N, R^N′, R^N′, m, n, M, M′, R², R^2a, R^2b, R^2c, R³, R^3a, R^3b, and R^3c can be combined, where applicable, with any group described herein for one or more of the remainder of variables o, R¹, R^N, R^N′, R^N′, m, n, M, M′, R², R^2a, R^2b, R^2c, R³, R^3a, R^3b, and R^3c.

[0920] In some embodiments, the ionizable lipid is a compound selected from:

[0921] In some embodiments, the ionizable lipid is

[0922] In some embodiments, the ionizable lipid is

[0923] In some embodiments, the ionizable lipid is

[0924] In some embodiments, the ionizable lipid is

[0925] Without wishing to be bound by theory, it is understood that an ionizable lipid may have a positive or partial positive charge at physiological pH. Such lipids may be referred to as cationic or ionizable (amino) lipids. Lipids may also be zwitterionic, i.e., neutral molecules having both a positive and a negative charge.

[0926] In some embodiments, the ionizable amino lipid of a lipid nanoparticle is a compound of Formula (AI):

or its N-oxide, or a salt or isomer thereof,

• • [0927] wherein R′^a is R′^branched; wherein
  • [0928] R′^branched is:

wherein

denotes a point of attachment;

• • [0929] wherein R^aα, R^aβ, R^aγ, and R^aδ are each independently selected from the group consisting of H, C_2-12 alkyl, and C_2-12 alkenyl;
  • [0930] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [0931] R⁴ is selected from the group consisting of —(CH₂)_nOH, wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [0932] wherein

denotes a point of attachment; wherein

• • [0933] R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;
  • [0934] each R⁵ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0935] each R⁶ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0936] M and M′ are each independently selected from the group consisting of —C(O)O— and —OC(O)—;
  • [0937] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [0938] l is selected from the group consisting of 1, 2, 3, 4, and 5; and
  • [0939] m is selected from the group consisting of 5, 6, 7, 8, 9, 10, 11, 12, and 13.

[0940] In some embodiments of the compounds of Formula (AI), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aα, R^aβ, R^aγ, and R^aδ are each H; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0941] In some embodiments of the compounds of Formula (AI), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aα, R^aβ, R^aγ, and R^aδ are each H; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 3; and m is 7.

[0942] In some embodiments of the compounds of Formula (AI), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aα is C_2-12 alkyl; R^aβ, R^aγ, and R^aδ are each H; R² and R³ are each C_1-14 alkyl; R⁴ is

R¹⁰NH(C_1-6 alkyl); n2 is 2; R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0943] In some embodiments of the compounds of Formula (AI), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aα, R^aβ, and R^aδ are each H; R^aγ is C_2-12 alkyl; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0944] In some embodiments, the compound of Formula (AI) is selected from:

[0945] In some embodiments, the ionizable amino lipid of Formula (AI) is a compound of Formula (AIa):

or its N-oxide, or a salt or isomer thereof,

• • [0946] wherein R′^a is R′^branched, wherein
  • [0947] R′^branched is:

wherein

denotes a point of attachment;

• • [0948] wherein R^aβ, R^aγ, and R^aδ are each independently selected from the group consisting of H, C_2-12 alkyl, and C_2-12 alkenyl;
  • [0949] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [0950] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [0951] wherein

denotes a point of attachment; wherein

• • [0952] R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;
  • [0953] each R⁵ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0954] each R⁶ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0955] M and M′ are each independently selected from the group consisting of —C(O)O— and —OC(O)—;
  • [0956] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [0957] l is selected from the group consisting of 1, 2, 3, 4, and 5; and
  • [0958] m is selected from the group consisting of 5, 6, 7, 8, 9, 10, 11, 12, and 13.

[0959] In some embodiments, the ionizable amino lipid of Formula (AI) is a compound of Formula (AIb):

or its N-oxide, or a salt or isomer thereof,

• • [0960] wherein R′^a is R′^branched, wherein
  • [0961] R′^branched is:

wherein

denotes a point of attachment;

• • [0962] wherein R^aα, R^aβ, R^aγ, and R^aδ are each independently selected from the group consisting of H, C_2-12 alkyl, and C_2-12 alkenyl;
  • [0963] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [0964] R⁴ is —(CH₂)_nOH, wherein n is selected from the group consisting of 1, 2, 3, 4, and 5;
  • [0965] each R⁵ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0966] each R⁶ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0967] M and M′ are each independently selected from the group consisting of —C(O)O— and —OC(O)—;
  • [0968] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [0969] l is selected from the group consisting of 1, 2, 3, 4, and 5; and
  • [0970] m is selected from the group consisting of 5, 6, 7, 8, 9, 10, 11, 12, and 13.

[0971] In some embodiments of Formula (AI) or (AIb), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aβ, R^aγ, and R^aδ are each H; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0972] In some embodiments of Formula (AI) or (AIb), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aβ, R^aγ, and R^aδ are each H; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 3; and m is 7.

[0973] In some embodiments of Formula (AI) or (AIb), R′^a is R′^branched; R′^branched is

denotes a point of attachment; R^aβ and R^aδ are each H; R^aγ is C_2-12 alkyl; R² and R³ are each C_1-14 alkyl; R⁴ is —(CH₂)_nOH; n is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0974] In some embodiments, the ionizable amino lipid of Formula (AI) is a compound of Formula (AIc):

or its N-oxide, or a salt or isomer thereof,

• • [0975] wherein R′^a is R′^branched, wherein
  • [0976] R′^branched is:

wherein

denotes a point of attachment;

• • [0977] wherein R^aα, R^aβ, R^aγ, and R^aδ are each independently selected from the group consisting of H, C_2-12 alkyl, and C_2-12 alkenyl;
  • [0978] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [0979] R⁴ is

• • [0980] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [0981] each R⁵ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0982] each R⁶ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [0983] M and M′ are each independently selected from the group consisting of —C(O)O— and —OC(O)—;
  • [0984] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [0985] l is selected from the group consisting of 1, 2, 3, 4, and 5; and
  • [0986] m is selected from the group consisting of 5, 6, 7, 8, 9, 10, 11, 12, and 13.

[0987] In some embodiments, R′^a is R′^branched, R′^branched is

denotes a point of attachment; R^aβ, R^aγ, and R^aδ are each H; R^aδ is C_2-12 alkyl; R² and R³ are each C_1-14 alkyl; R⁴ is

denotes a point of attachment; R¹⁰ is NH(C_1-6 alkyl); n2 is 2; each R⁵ is H; each R⁶ is H; M and M′ are each —C(O)O—; R′ is a C_1-12 alkyl; l is 5; and m is 7.

[0988] In some embodiments, the compound of Formula (AIc) is:

[0989] In some embodiments, the ionizable amino lipid is a compound of Formula (AII):

or its N-oxide, or a salt or isomer thereof,

• • [0990] wherein R′^a is R′^branched or R′ cyclic, wherein
  • [0991] R′^branched is:

and R′ cyclic is:

and

• • [0992] ′^b is:

• • [0993] wherein

denotes a point of attachment;

• • [0994] R^aγ and R^aδ are each independently selected from the group consisting of H, C_1-12 alkyl, and C_2-12 alkenyl, wherein at least one of R^aγ and R^aδ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [0995] R^bγ and R^bδ are each independently selected from the group consisting of H, C_1-12 alkyl, and C_2-12 alkenyl, wherein at least one of R^bγ and R^bδ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [0996] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [0997] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [0998] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [0999] each R′ independently is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1000] Y^a is a C_3-6 carbocycle;
  • [1001] R*″^a is selected from the group consisting of C_1-15 alkyl and C_2-15 alkenyl; and
  • [1002] s is 2 or 3;
  • [1003] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1004] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1005] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-a):

or its N-oxide, or a salt or isomer thereof,

• • [1006] wherein R′^a is R′^branched or R′ cyclic, wherein
  • [1007] R′^branched is:

• • [1008] wherein

denotes a point of attachment;

• • [1009] R^aγ and R^aδ are each independently selected from the group consisting of H, C_1-12 alkyl, and C_2-12 alkenyl, wherein at least one of R^aγ and R^aδ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1010] R^bγ and R^bδ are each independently selected from the group consisting of H, C_1-12 alkyl, and C_2-12 alkenyl, wherein at least one of R^bγ and R^bδ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1011] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [1012] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [1013] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [1014] each R′ independently is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1015] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1016] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1017] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-b):

or its N-oxide, or a salt or isomer thereof,

• • [1018] wherein R′^a is R′^branched or R′^cyclic; wherein
  • [1019] R′^branched is:

• • [1020] wherein

denotes a point of attachment;

• • [1021] R^aγ and R^bγ are each independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1022] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [1023] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [1024] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [1025] each R′ independently is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1026] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1027] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1028] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-c):

or its N-oxide, or a salt or isomer thereof,

• • [1029] wherein R′^a is R′^branched or R′^cyclic; wherein
  • [1030] R′^branched is:

• • [1031] wherein

• • [1032] denotes a point of attachment;
  • [1033] wherein R^aγ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1034] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [1035] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [1036] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [1037] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1038] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1039] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1040] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-d):

or its N-oxide, or a salt or isomer thereof, wherein R′^a is R′^branched or R′^cyclic; wherein

• • [1041] R′^branched is:

• • [1042] wherein

denotes a point of attachment;

• • [1043] wherein R^aγ and R^bγ are each independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1044] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5, and

• • [1045] wherein

denotes a point of attachment; wherein R¹⁰ is N(R)₂; each R is independently selected from the group consisting of C_1-6 alkyl, C_2-3 alkenyl, and H; and n2 is selected from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10;

• • [1046] each R′ independently is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1047] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1048] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1049] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-e):

or its N-oxide, or a salt or isomer thereof,

• • [1050] wherein R′^a is R′^branched or R′^cyclic; wherein
  • [1051] R′^branched is:

• • [1052] wherein

denotes a point of attachment;

• • [1053] wherein R^aγ is selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1054] R² and R³ are each independently selected from the group consisting of C_1-14 alkyl and C_2-14 alkenyl;
  • [1055] R⁴ is —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5;
  • [1056] R′ is a C_1-12 alkyl or C_2-12 alkenyl;
  • [1057] m is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9;
  • [1058] l is selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9.

[1059] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), m and l are each independently selected from 4, 5, and 6. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), m and l are each 5.

[1060] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), each R′ independently is a C_1-12 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), each R′ independently is a C_2-5 alkyl.

[1061] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′b is:

and R² and R³ are each independently a C_1-14 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^b is:

and R² and R³ are each independently a C_6-10 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^b is:

and R² and R³ are each a C₈ alkyl.

[1062] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

R^aγ is a C_1-12 alkyl and R² and R³ are each independently a C_6-10 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

R^aγ is a C_2-6 alkyl and R² and R³ are each independently a C_6-10 alkyl.

[1063] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

R^aγ is a C_2-6 alkyl, and R² and R³ are each a C₈ alkyl.

[1064] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

and R^aγ and R^bγ are each a C_1-12 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

and R^aγ and R^bγ are each a C_2-6 alkyl.

[1065] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), m and l are each independently selected from 4, 5, and 6 and each R′ independently is a C_1-12 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), m and l are each 5 and each R′ independently is a C_2-5 alkyl.

[1066] In some embodiments of the compound of (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each independently selected from 4, 5, and 6, each R′ independently is a C_1-12 alkyl, and R^aγ and R^bγ are each a C_1-12 alkyl. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each 5, each R′ independently is a C_2-5 alkyl, and R^aγ and R^bγ are each a C_2-6 alkyl.

[1067] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each independently selected from 4, 5, and 6, R′ is a C_1-12 alkyl, R^aγ is a C_1-12 alkyl and R² and R³ are each independently a C_6-10 alkyl.

[1068] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each 5, R′ is a C_2-5 alkyl, R^aγ is a C_2-6 alkyl, and R² and R³ are each a C₈ alkyl.

[1069] In some embodiments of the compound of (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R⁴ is

wherein R¹⁰ is NH(C_1-6 alkyl) and n2 is 2. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R⁴ is

wherein R¹⁰ is NH(CH₃) and n2 is 2.

[1070] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each independently selected from 4, 5, and 6, each R′ independently is a C_1-12 alkyl, R^aγ and R^bγ are each a C_1-12 alkyl, and R⁴ is

wherein R¹⁰ is NH(C_1-6 alkyl), and n2 is 2. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each 5, each R′ independently is a C_2-5 alkyl, R^aγ and R^bγ are each a C_2-6 alkyl, and R⁴ is

wherein R¹⁰ is NH(CH₃) and n2 is 2.

[1071] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each independently selected from 4, 5, and 6, R′ is a C_1-12 alkyl, R² and R³ are each independently a C_6-10 alkyl, R^aγ is a C_1-12 alkyl, and R⁴ is

wherein R¹⁰ is NH(C_1-6 alkyl) and n2 is 2. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each 5, R′ is a C_2-5 alkyl, R^aγ is a C_2-6 alkyl, R² and R³ are each a C₈ alkyl, and R⁴ is

wherein R¹⁰ is NH(CH₃) and n2 is 2.

[1072] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R⁴ is —(CH₂)_nOH and n is 2, 3, or 4. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R⁴ is —(CH₂)_nOH and n is 2.

[1073] In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each independently selected from 4, 5, and 6, each R′ independently is a C_1-12 alkyl, R^aγ and R^bγ are each a C_1-12 alkyl, R⁴ is —(CH₂)_nOH, and n is 2, 3, or 4. In some embodiments of the compound of Formula (AII), (AII-a), (AII-b), (AII-c), (AII-d), or (AII-e), R′^branched is:

m and l are each 5, each R′ independently is a C_2-5 alkyl, R^aγ and R^bγ are each a C_2-6 alkyl, R⁴ is —(CH₂)_nOH, and n is 2.

[1074] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-f):

or its N-oxide, or a salt or isomer thereof,

• • [1075] wherein R′^a is R′^branched or R′^cyclic; wherein
  • [1076] R′^branched is:

• • [1077] wherein

denotes a point of attachment;

• • [1078] R^aγ is a C_1-12 alkyl;
  • [1079] R² and R³ are each independently a C_1-14 alkyl;
  • [1080] R⁴ is —(CH₂)_nOH wherein n is selected from the group consisting of 1, 2, 3, 4, and 5;
  • [1081] R′ is a C_1-12 alkyl;
  • [1082] m is selected from 4, 5, and 6; and
  • [1083] l is selected from 4, 5, and 6.
  • [1084] In some embodiments of the compound of Formula (AII-f), m and l are each 5, and n is 2, 3, or 4.

[1085] In some embodiments of the compound of Formula (AII-f) R′ is a C_2-5 alkyl, R^aγ is a C_2-6 alkyl, and R² and R³ are each a C_6-10 alkyl.

[1086] In some embodiments of the compound of Formula (AII-f), m and l are each 5, n is 2, 3, or 4, R′ is a C_2-5 alkyl, R^aγ is a C_2-6 alkyl, and R² and R³ are each a C_6-10 alkyl.

[1087] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-g):

or its N-oxide, or a salt or isomer thereof; wherein

• • [1088] R^aγ is a C_2-6 alkyl;
  • [1089] R′ is a C_2-5 alkyl; and
  • [1090] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 3, 4, and 5, and

• • [1091] wherein

denotes a point of attachment, R¹⁰ is NH(C_1-6 alkyl), and n2 is selected from the group consisting of 1, 2, and 3.

[1092] In some embodiments, the ionizable amino lipid of Formula (AII) is a compound of Formula (AII-h):

or its N-oxide, or a salt or isomer thereof; wherein

• • [1093] R^aγ and R^bγ are each independently a C_2-6 alkyl;
  • [1094] each R′ independently is a C_2-5 alkyl; and
  • [1095] R⁴ is selected from the group consisting of —(CH₂)_nOH wherein n is selected from the group consisting of 3, 4, and 5, and

• • [1096] wherein

denotes a point of attachment, R¹⁰ is NH(C_1-6 alkyl), and n2 is selected from the group consisting of 1, 2, and 3.

[1097] In some embodiments of the compound of Formula (AII-g) or (AII-h), R⁴ is

wherein

• • [1098] R¹⁰ is NH(CH₃) and n2 is 2.

[1099] In some embodiments of the compound of Formula (AII-g) or (AII-h), R⁴ is —(CH₂)₂OH.

[1100] In some embodiments, the ionizable amino lipids of a lipid nanoparticle may be one or more of compounds of Formula (AIII):

• • [1101] or their N-oxides, or salts or isomers thereof, wherein:
  • [1102] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;
  • [1103] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1104] R₄ is selected from the group consisting of hydrogen, a C_3-6 carbocycle, —(CH₂)_nQ, —(CH₂)_nCHQR, —CHQR, —CQ(R)₂, and unsubstituted C_1-6 alkyl, where Q is selected from a carbocycle, heterocycle, —OR, —O(CH₂)_nN(R)₂, —C(O)OR, —OC(O)R, —CX₃, —CX₂H, —CXH₂, —CN, —N(R)₂, —C(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)C(O)N(R)₂, —N(R)C(S)N(R)₂, —N(R)R₈, —N(R)S(O)₂R₈, —O(CH₂)_nOR, —N(R)C(═NR₉)N(R)₂, —N(R)C(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, —N(OR)C(O)R, —N(OR)S(O)₂R, —N(OR)C(O)OR, —N(OR)C(O)N(R)₂, —N(OR)C(S)N(R)₂, —N(OR)C(═NR₉)N(R)₂, —N(OR)C(═CHR₉)N(R)₂, —C(═NR₉)N(R)₂, —C(═NR₉)R, —C(O)N(R)OR, and —C(R)N(R)₂C(O)OR, and each n is independently selected from 1, 2, 3, 4, and 5;
  • [1105] each R₅ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1106] each R₆ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1107] M and M′ are independently selected
  • [1108] from —C(O)O—, —OC(O)—, —OC(O)-M″-C(O)O—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group, in which M″ is a bond, C_1-13 alkyl or C_2-13 alkenyl;
  • [1109] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1110] R₈ is selected from the group consisting of C_3-6 carbocycle and heterocycle;
  • [1111] R₉ is selected from the group consisting of H, CN, NO₂, C_1-6 alkyl, —OR, —S(O)₂R, —S(O)₂N(R)₂, C_2-6 alkenyl, C_3-6 carbocycle and heterocycle;
  • [1112] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1113] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1114] each R″ is independently selected from the group consisting of C_3-15 alkyl and C_3-15 alkenyl;
  • [1115] each R* is independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1116] each Y is independently a C_3-6 carbocycle;
  • [1117] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1118] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13; and wherein when R₄ is —(CH₂)_nQ, —(CH₂)_nCHQR, —CHQR, or —CQ(R)₂, then (i) Q is not —N(R)₂ when n is 1, 2, 3, 4 or 5, or (ii) Q is not 5, 6, or 7-membered heterocycloalkyl when n is 1 or 2.

[1119] In some embodiments, another subset of compounds of Formula (AIII) includes those in which:

• • [1120] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;
  • [1121] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1122] R₄ is selected from the group consisting of a C_3-6 carbocycle, —(CH₂)_nQ, —(CH₂)_nCHQR, —CHQR, —CQ(R)₂, and unsubstituted C_1-6 alkyl, where Q is selected from a C_3-6 carbocycle, a 5- to 14-membered heteroaryl having one or more heteroatoms selected from N, O, and S, —OR, —O(CH₂)_nN(R)₂, —C(O)OR, —OC(O)R, —CX₃, —CX₂H, —CXH₂, —CN, —C(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)C(O)N(R)₂, —N(R)C(S)N(R)₂, —CRN(R)₂C(O)OR, —N(R)R₈, —O(CH₂)_nOR, —N(R)C(═NR₉)N(R)₂, —N(R)C(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, —N(OR)C(O)R, —N(OR)S(O)₂R, —N(OR)C(O)OR, —N(OR)C(O)N(R)₂, —N(OR)C(S)N(R)₂, —N(OR)C(═NR₉)N(R)₂, —N(OR)C(═CHR₉)N(R)₂, —C(═NR₉)N(R)₂, —C(═NR₉)R, —C(O)N(R)OR, and a 5- to 14-membered heterocycloalkyl having one or more heteroatoms selected from N, O, and S which is substituted with one or more substituents selected from oxo (═O), OH, amino, mono- or di-alkylamino, and C_1-3 alkyl, and each n is independently selected from 1, 2, 3, 4, and 5;
  • [1123] each R⁵ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1124] each R⁶ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1125] M and M′ are independently selected from —C(O)O—, —OC(O)—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group;
  • [1126] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1127] R₈ is selected from the group consisting of C_3-6 carbocycle and heterocycle;
  • [1128] R₉ is selected from the group consisting of H, CN, NO₂, C_1-6 alkyl, —OR, —S(O)₂R, —S(O)₂N(R)₂, C_2-6 alkenyl, C_3-6 carbocycle and heterocycle;
  • [1129] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1130] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1131] each R″ is independently selected from the group consisting of C_3-14 alkyl and C_3-14 alkenyl;
  • [1132] each R* is independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1133] each Y is independently a C_3-6 carbocycle;
  • [1134] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1135] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13,
  • [1136] or salts or isomers thereof.

[1137] In some embodiments, another subset of compounds of Formula (AIII) includes those in which:

[1138] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;

• • [1139] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1140] R₄ is selected from the group consisting of a C_3-6 carbocycle, —(CH₂)_nQ, —(CH₂)_nCHQR, —CHQR, —CQ(R)₂, and unsubstituted C_1-6 alkyl, where Q is selected from a C_3-6 carbocycle, a 5- to 14-membered heterocycle having one or more heteroatoms selected from N, O, and S, —OR, —O(CH₂)_nN(R)₂, —C(O)OR, —OC(O)R, —CX₃, —CX₂H, —CXH₂, —CN, —C(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)C(O)N(R)₂, —N(R)C(S)N(R)₂, —CRN(R)₂C(O)OR, —N(R)R₈, —O(CH₂)_nOR, —N(R)C(═NR₉)N (R)₂, —N(R)C(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, —N(OR)C(O)R, —N(OR)S(O)₂R, —N(OR)C(O)OR, —N(OR)C(O)N(R)₂, —N(OR)C(S)N(R)₂, —N(OR)C(═NR₉)N(R)₂, —N(OR)C(—CHR₉)N(R)₂, —C(═NR₉)R, —C(O)N(R)OR, and —C(═NR₉)N(R)₂, and each n is independently selected from 1, 2, 3, 4, and 5; and when Q is a 5- to 14-membered heterocycle and (i) R₄ is —(CH₂)_nQ in which n is 1 or 2, or (ii) R₄ is —(CH₂)_nCHQR in which n is 1, or (iii) R₄ is —CHQR, and —CQ(R)₂, then Q is either a 5- to 14-membered heteroaryl or 8- to 14-membered heterocycloalkyl;
  • [1141] each R₅ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1142] each R₆ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1143] M and M′ are independently selected from —C(O)O—, —OC(O)—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group;
  • [1144] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1145] R₈ is selected from the group consisting of C_3-6 carbocycle and heterocycle;
  • [1146] R₉ is selected from the group consisting of H, CN, NO₂, C_1-6 alkyl, —OR, —S(O)₂R, —S(O)₂N(R)₂, C_2-6 alkenyl, C_3-6 carbocycle and heterocycle;
  • [1147] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1148] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1149] each R″ is independently selected from the group consisting of C_3-14 alkyl and C_3-14 alkenyl;
  • [1150] each R* is independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1151] each Y is independently a C_3-6 carbocycle;
  • [1152] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1153] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13,
  • [1154] or salts or isomers thereof.

[1155] In some embodiments, another subset of compounds of Formula (AIII) includes those in which:

• • [1156] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;
  • [1157] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1158] R₄ is selected from the group consisting of a C_3-6 carbocycle, —(CH₂)_nQ, —(CH₂)_nCHQR,
  • [1159] —CHQR, —CQ(R)₂, and unsubstituted C_1-6 alkyl, where Q is selected from a C_3-6 carbocycle, a 5- to 14-membered heteroaryl having one or more heteroatoms selected from N, O, and S, —OR, —O(CH₂)_nN(R)₂, —C(O)OR, —OC(O)R, —CX₃, —CX₂H, —CXH₂, —CN, —C(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)C(O)N(R)₂, —N(R)C(S)N(R)₂, —CRN(R)₂C(O)OR, —N(R)R₈, —O(CH₂)_nOR, —N(R)C(═NR₉)N(R)₂, —N(R)C(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, —N(OR)C(O)R, —N(OR)S(O)₂R, —N(OR)C(O)OR, —N(OR)C(O)N(R)₂, —N(OR)C(S)N(R)₂, —N(OR)C(═NR₉)N(R)₂, —N(OR)C(═CHR₉)N(R)₂, —C(═NR₉)R, —C(O)N(R)OR, and —C(═NR₉)N(R)₂, and each n is independently selected from 1, 2, 3, 4, and 5;
  • [1160] each R₅ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1161] each R₆ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1162] M and M′ are independently selected from —C(O)O—, —OC(O)—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group;
  • [1163] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1164] R₈ is selected from the group consisting of C_3-6 carbocycle and heterocycle;
  • [1165] R₉ is selected from the group consisting of H, CN, NO₂, C_1-6 alkyl, —OR, —S(O)₂R, —S(O)₂N(R)₂, C_2-6 alkenyl, C_3-6 carbocycle and heterocycle;
  • [1166] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1167] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1168] each R″ is independently selected from the group consisting of C_3-14 alkyl and C_3-14 alkenyl;
  • [1169] each R* is independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1170] each Y is independently a C_3-6 carbocycle;
  • [1171] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1172] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13,
  • [1173] or salts or isomers thereof.

[1174] In some embodiments, another subset of compounds of Formula (AIII) includes those in which

• • [1175] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;
  • [1176] R₂ and R₃ are independently selected from the group consisting of H, C_2-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1177] R₄ is —(CH₂)_nQ or —(CH₂)_nCHQR, where Q is —N(R)₂, and n is selected from 3, 4, and 5;
  • [1178] each R₅ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1179] each R₆ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1180] M and M′ are independently selected from —C(O)O—, —OC(O)—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group;
  • [1181] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1182] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1183] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1184] each R″ is independently selected from the group consisting of C_3-14 alkyl and C_3-14 alkenyl;
  • [1185] each R* is independently selected from the group consisting of C_1-12 alkyl and C_1-12 alkenyl;
  • [1186] each Y is independently a C_3-6 carbocycle;
  • [1187] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1188] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13,
  • [1189] or salts or isomers thereof.

[1190] In some embodiments, another subset of compounds of Formula (AIII) includes those in which

• • [1191] R₁ is selected from the group consisting of C_5-30 alkyl, C_5-20 alkenyl, —R*YR″, —YR″, and —R″M′R′;
  • [1192] R₂ and R₃ are independently selected from the group consisting of C_1-14 alkyl, C_2-14 alkenyl, —R*YR″, —YR″, and —R*OR″, or R₂ and R₃, together with the atom to which they are attached, form a heterocycle or carbocycle;
  • [1193] R₄ is selected from the group consisting of —(CH₂)_nQ, —(CH₂)_nCHQR, —CHQR, and —CQ(R)₂, where Q is —N(R)₂, and n is selected from 1, 2, 3, 4, and 5;
  • [1194] each R₅ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1195] each R₆ is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1196] M and M′ are independently selected from —C(O)O—, —OC(O)—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —S—S—, an aryl group, and a heteroaryl group;
  • [1197] R₇ is selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1198] each R is independently selected from the group consisting of C_1-3 alkyl, C_2-3 alkenyl, and H;
  • [1199] each R′ is independently selected from the group consisting of C_1-18 alkyl, C_2-18 alkenyl, —R*YR″, —YR″, and H;
  • [1200] each R″ is independently selected from the group consisting of C_3-14 alkyl and C_3-14 alkenyl;
  • [1201] each R* is independently selected from the group consisting of C_1-12 alkyl and C_1-12 alkenyl;
  • [1202] each Y is independently a C_3-6 carbocycle;
  • [1203] each X is independently selected from the group consisting of F, Cl, Br, and I; and
  • [1204] m is selected from 5, 6, 7, 8, 9, 10, 11, 12, and 13,
  • [1205] or salts or isomers thereof.

[1206] In certain embodiments, a subset of compounds of Formula (AIII) includes those of Formula (AIII-A):

• • [1207] or its N-oxide, or a salt or isomer thereof, wherein l is selected from 1, 2, 3, 4, and 5; m is selected from 5, 6, 7, 8, and 9; M₁ is a bond or M′; R₄ is hydrogen, unsubstituted C_1-3 alkyl, or —(CH₂)_nQ, in which Q is
  • [1208] —OH, —NHC(S)N(R)₂, —NHC(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)R₈, —NHC(═NR₉)N(R)₂, —NHC(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, heteroaryl or heterocycloalkyl;
  • [1209] M and M′ are independently selected
  • [1210] from —C(O)O—, —OC(O)—, —OC(O)-M″-C(O)O—, —C(O)N(R′)—, —P(O)(OR′)O—, —S—S—, an aryl group, and a heteroaryl group; and
  • [1211] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, and C_2-14 alkenyl.

[1212] For example, m is 5, 7, or 9. For example, Q is OH, —NHC(S)N(R)₂, or —NHC(O)N(R)₂. For example, Q is —N(R)C(O)R, or —N(R)S(O)₂R.

[1213] In certain embodiments, a subset of compounds of Formula (AIII) includes those of Formula (AIII-B):

• • [1214] or its N-oxide, or a salt or isomer thereof in which all variables are as defined herein. For example, m is selected from 5, 6, 7, 8, and 9; R⁴ is hydrogen, unsubstituted C_1-3 alkyl, or —(CH₂)_nQ, in which Q is
  • [1215] H, —NHC(S)N(R)₂, —NHC(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)R₈, —NHC(═NR₉)N(R)₂, —NHC(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, heteroaryl or heterocycloalkyl;
  • [1216] M and M′ are independently selected
  • [1217] from —C(O)O—, —OC(O)—, —OC(O)-M″-C(O)O—, —C(O)N(R′)—, —P(O)(OR′)O—, —S—S—, an aryl group, and a heteroaryl group; and
  • [1218] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, and C_2-14 alkenyl.

[1219] For example, m is 5, 7, or 9. For example, Q is OH, —NHC(S)N(R)₂, or —NHC(O)N(R)₂. For example, Q is —N(R)C(O)R, or —N(R)S(O)₂R.

[1220] In certain embodiments, a subset of compounds of Formula (AIII) includes those of Formula (AIII-C):

• • [1221] or its N-oxide, or a salt or isomer thereof, wherein l is selected from 1, 2, 3, 4, and 5; M₁ is a bond or M′; R₄ is hydrogen, unsubstituted C_1-3 alkyl, or —(CH₂)_nQ, in which n is 2, 3, or 4, and Q is OH, —NHC(S)N(R)₂, —NHC(O)N(R)₂, —N(R)C(O)R, —N(R)S(O)₂R, —N(R)R₈, —NHC(═NR₉)N(R)₂, —NHC(═CHR₉)N(R)₂, —OC(O)N(R)₂, —N(R)C(O)OR, heteroaryl or heterocycloalkyl;
  • [1222] M and M′ are independently selected
  • [1223] from —C(O)O—, —OC(O)—, —OC(O)-M″-C(O)O—, —C(O)N(R′)—, —P(O)(OR′)O—, —S—S—, an aryl group, and a heteroaryl group; and
  • [1224] R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, and
  • [1225] C_2-14 alkenyl.

[1226] In some embodiments, the compounds of Formula (AIII) are of Formula (AIII-D),

• • [1227] or their N-oxides, or salts or isomers thereof, wherein R₄ is as described in this Lipid Compositions section.

[1228] In another embodiment, the compounds of Formula (AIII) are of Formula (AIII-E),

• • [1229] or their N-oxides, or salts or isomers thereof, wherein R₄ is as described in this in this Lipid Compositions section.

[1230] In another embodiment, the compounds of Formula (AIII) are of Formula (AIII-F) or (AIII-G):

• • [1231] or their N-oxides, or salts or isomers thereof, wherein R₄ is as described in this in this Lipid Compositions section.

[1232] In another embodiment, the compounds of Formula (AIII) are of Formula (AIII-H):

or their N-oxides, or salts or isomers thereof,

• • [1233] wherein M is —C(O)O— or —OC(O)—, M″ is C_1-6 alkyl or C_2-6 alkenyl, R² and R³ are independently selected from the group consisting of C_5-14 alkyl and C_5-14 alkenyl, and n is selected from 2, 3, and 4.

[1234] In a further embodiment, the compounds of Formula (AIII) are of Formula (AIII-I):

• • [1235] or their N-oxides, or salts or isomers thereof, wherein n is 2, 3, or 4; and m, R′, R″, and R₂ through R₆ are as described in this in this Lipid Compositions section. For example, each of R₂ and R₃ may be independently selected from the group consisting of C_5-14 alkyl and C_5-14 alkenyl.

[1236] In some embodiments, an ionizable amino lipid of comprises a compound having structure:

[1237] In some embodiments, an ionizable amino lipid comprises a compound having structure:

[1238] In a further embodiment, the compounds of Formula (AIII) are of Formula (AIII-J),

or their N-oxides, or salts or isomers thereof,

• • [1239] wherein l is selected from 1, 2, 3, 4, and 5; m is selected from 5, 6, 7, 8, and 9; M₁ is a bond or M′; M and M′ are independently selected
  • [1240] from —C(O)O—, —OC(O)—, —OC(O)-M″-C(O)O—, —C(O)N(R′)—, —P(O)(OR′)O—, —S—S—, an aryl group, and a heteroaryl group; and R₂ and R₃ are independently selected from the group consisting of H, C_1-14 alkyl, and C_2-14 alkenyl. For example, M″ is C_1-6 alkyl (e.g., C_1-4 alkyl) or C_2-6 alkenyl (e.g. C_2-4 alkenyl). For example, R₂ and R₃ are independently selected from the group consisting of C_5-14 alkyl and C_5-14 alkenyl.

[1241] In some embodiments, the ionizable amino lipids are one or more of the compounds described in U.S. Application Nos. 62/220,091, 62/252,316, 62/253,433, 62/266,460, 62/333,557, 62/382,740, 62/393,940, 62/471,937, 62/471,949, 62/475,140, and 62/475,166, and PCT Application No. PCT/US2016/052352.

[1242] The central amine moiety of a lipid according to Formula (AIII), (AIII-A), (AIII-B), (AIII-C), (AIII-D), (AIII-E), (AIII-F), (AIII-G), (AIII-H), (AIII-I), or (AIII-J) may be protonated at a physiological pH. Thus, a lipid may have a positive or partial positive charge at physiological pH. Such amino lipids may be referred to as cationic lipids, ionizable lipids, cationic amino lipids, or ionizable amino lipids. Amino lipids may also be zwitterionic, i.e., neutral molecules having both a positive and a negative charge.

[1243] In some embodiments, the ionizable amino lipids of a lipid nanoparticle may be one or more of compounds of formula (AIV),

• • [1244] or salts or isomers thereof, wherein
  • [1245] W is

• • [1246] ring A is

• • [1247] t is 1 or 2;
  • [1248] A₁ and A₂ are each independently selected from CH or N;
  • [1249] Z is CH₂ or absent wherein when Z is CH₂, the dashed lines (1) and (2) each represent a single bond; and when Z is absent, the dashed lines (1) and (2) are both absent;
  • [1250] R₁, R₂, R₃, R₄, and R₅ are independently selected from the group consisting of C_5-20 alkyl, C_5-20 alkenyl, —R″MR′, —R*YR″, —YR″, and —R*OR″;
  • [1251] R_X1 and R_X2 are each independently H or C_1-3 alkyl;
  • [1252] each M is independently selected from the group consisting of —C(O)O—, —OC(O)—, —OC(O)O—, —C(O)N(R′)—, —N(R′)C(O)—, —C(O)—, —C(S)—, —C(S)S—, —SC(S)—, —CH(OH)—, —P(O)(OR′)O—, —S(O)₂—, —C(O)S—, —SC(O)—, an aryl group, and a heteroaryl group;
  • [1253] M* is C₁-C₆ alkyl,
  • [1254] W¹ and W² are each independently selected from the group consisting of —O— and —N(R₆)—;
  • [1255] each R₆ is independently selected from the group consisting of H and C_1-5 alkyl;
  • [1256] X¹, X², and X³ are independently selected from the group consisting of a bond, —CH₂—, —(CH₂)₂—, —CHR—, —CHY—, —C(O)—, —C(O)O—, —OC(O)—, —(CH₂)_n—C(O)—, —C(O)—(CH₂)_n—, —(CH₂)_n—C(O)O—, —OC(O)—(CH₂)_n—, —(CH₂)_n—OC(O)—, —C(O)O—(CH₂)_n—, —CH(OH)—, —C(S)—, and —CH(SH)—;
  • [1257] each Y is independently a C_3-6 carbocycle;
  • [1258] each R* is independently selected from the group consisting of C_1-12 alkyl and C_2-12 alkenyl;
  • [1259] each R is independently selected from the group consisting of C_1-3 alkyl and a C_3-6 carbocycle;
  • [1260] each R′ is independently selected from the group consisting of C_1-12 alkyl, C_2-12 alkenyl, and H;
  • [1261] each R″ is independently selected from the group consisting of C_3-12 alkyl, C_3-12 alkenyl and —R*MR′; and
  • [1262] n is an integer from 1-6;
  • [1263] wherein when ring A is

then

• • [1264] i) at least one of X¹, X², and X³ is not —CH₂—; and/or
  • [1265] ii) at least one of R₁, R₂, R₃, R₄, and R₅ is —R″MR′.

[1266] In some embodiments, the compound is of any of formulae (AIVa)-(AIVh):

[1267] In some embodiments, the ionizable amino lipid is

or a salt thereof.

[1268] The central amine moiety of a lipid according to Formula (AIV), (AIVa), (AIVb), (AIVc), (AIVd), (AIVe), (AIVf), (AIVg), or (AIVh) may be protonated at a physiological pH. Thus, a lipid may have a positive or partial positive charge at physiological pH.

[1269] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1270] or a pharmaceutically acceptable salt, tautomer, or stereoisomer thereof, wherein:
  • [1271] R¹ is optionally substituted C₁-C₂₄ alkyl or optionally substituted C₂-C₂₄ alkenyl;
  • [1272] R² and R³ are each independently optionally substituted C₁-C₃₆ alkyl;
  • [1273] R⁴ and R⁵ are each independently optionally substituted C₁-C₆ alkyl, or R⁴ and R⁵ join, along with the N to which they are attached, to form a heterocyclyl or heteroaryl;
  • [1274] L¹, L², and L³ are each independently optionally substituted C₁-C₁₈ alkylene;
  • [1275] G¹ is a direct bond, —(CH₂)_nO(C═O)—, —(CH₂)_n (C═O)O—, or —(C═O)—;
  • [1276] G² and G³ are each independently —(C═O)O— or -0(C═O)—; and n is an integer greater than 0.

[1277] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1278] or a pharmaceutically acceptable salt, tautomer, or stereoisomer thereof, wherein:
  • [1279] G¹ is —N(R³)R⁴ or —OR⁵;
  • [1280] R¹ is optionally substituted branched, saturated or unsaturated C₁₂-C₃₆ alkyl;
  • [1281] R² is optionally substituted branched or unbranched, saturated or unsaturated C₁₂-C₃₆ alkyl when L is —C(═O)—; or R² is optionally substituted branched or unbranched, saturated or unsaturated C₄-C₃₆ alkyl when L is C₆-C₁₂ alkylene, C₆-C₁₂ alkenylene, or C₂-C₆ alkynylene;
  • [1282] R³ and R⁴ are each independently H, optionally substituted branched or unbranched, saturated or unsaturated C₁-C₆ alkyl; or R³ and R⁴ are each independently optionally substituted branched or unbranched, saturated or unsaturated C₁-C₆ alkyl when Lis C₆-C₁₂ alkylene, C₆-C₁₂ alkenylene, or C₂-C₆ alkynylene; or R³ and R⁴, together with the nitrogen to which they are attached, join to form a heterocyclyl;
  • [1283] R⁵ is H or optionally substituted C₁-C₆ alkyl;
  • [1284] L is —C(═O)—, C₆-C₁₂ alkylene, C₆-C₁₂ alkenylene, or C₂-C₆ alkynylene; and
  • [1285] n is an integer from 1 to 12.

[1286] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1287] or a pharmaceutically acceptable salt thereof, wherein:
  • [1288] each R^1a is independently hydrogen, R^1c, or R^1d,
  • [1289] each R^1b is independently R^1c or R^1d,
  • [1290] each R^1c is independently —[CH₂]₂C(O)X¹R³,
  • [1291] each R^1d Is independently —C(O)R⁴;
  • [1292] each R² is independently —[C(R^2a)₂]_cR^2b,
  • [1293] each R^2a is independently hydrogen or C₁-C₆ alkyl;
  • [1294] R^2b is —N(L₁-B)₂; —(OCH₂CH₂)₆OH; or —(OCH₂CH₂)_bOCH₃;
  • [1295] each R³ and R⁴ is independently C₆-C₃₀ aliphatic;
  • [1296] each I.₃ is independently C₁-C₁₀ alkylene;
  • [1297] each B is independently hydrogen or an ionizable nitrogen-containing group;
  • [1298] each X¹ is independently a covalent bond or O;
  • [1299] each a is independently an integer of 1-10;
  • [1300] each b is independently an integer of 1-10; and
  • [1301] each c is independently an integer of 1-10.

[1302] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1303] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1304] X is N, and Y is absent; or X is CR, and Y is NR;
  • [1305] L¹ is —O(C═O)R¹, —(C═O)OR¹, —C(═O)R¹, —OR¹, —S(O)_xR¹, —S—SR¹, —C(═O)SR¹, —SC(═O)R¹, —NR^aC(═O)R¹, —C(═O)NR^bR^c, —NR^aC(═O)NR^bR^c, —OC(═O)NR^bR^c, or —NR^aC(═O)OR¹;
  • [1306] L² is —O(C═O)R², —(C═O)OR², —C(═O)R², —OR², —S(O)_xR², —S—SR², —C(═O)SR², —SC(═O)R², —NR^dC(═O)R², —C(═O)NR^eR^f, —NR^dC(═O)NR^eR^f, —OC(═O)NR^eR^f; —NR^dC(═O)OR² or a direct bond to R²;
  • [1307] L³ is —O(C═O)R³ or —(C═O)OR³;
  • [1308] G¹ and G² are each independently C₂-C₁₂ alkylene or C₂-C₁₂ alkenylene;
  • [1309] G³ is C₁-C₂₄ alkylene, C₂-C₂₄ alkenylene, C₁-C₂₄ heteroalkylene or C₂-C₂₄ heteroalkenylene when X is CR, and Y is NR; and G³ is C₁-C₂₄ heteroalkylene or C₂-C₂₄ heteroalkenylene when X is N, and Y is absent;
  • [1310] R^a, R^b, R^d and R^e are each independently H or C₁-C₁₂ alkyl or C₁-C₁₂ alkenyl;
  • [1311] R^c and R^f are each independently C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1312] each R is independently H or C₁-C₁₂ alkyl;

[1313] R¹, R² and R³ are each independently C₁-C₂₄ alkyl or C₂-C₂₄ alkenyl; and x is 0, 1 or 2, and

• • [1314] wherein each alkyl, alkenyl, alkylene, alkenylene, heteroalkylene and heteroalkenylene is independently substituted or unsubstituted unless otherwise specified.

[1315] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1316] or a pharmaceutically acceptable salt, tautomer, prodrug or stereoisomer thereof, wherein:
  • [1317] L¹ and L² are each independently -0(C=0)0-, —(C=0)0-, —C(=0)-, -0-, —S(0)x-_s-S—S—, —C(=0)S—, —SC(=0)-, —NR^aC(=0)-, —C(=0)NR^a—, —NR^aC(=0)NR^a—, —OC(=0)NR^a—, —NR^aC(=0)0- or a direct bond;
  • [1318] G¹ is C, —C₂ alkylene, —(C=0)-, -0(C=0)-, —SC(=0)-, —NR^aC(=0)- or a direct bond;
  • [1319] G² is —C(0)-, —(CO)O—, —C(=0)S—, —C(=0)NR^a— or a direct bond;
  • [1320] G³ is C₁-C₆ alkylene;
  • [1321] R^a is H or C₁-C₁₂ alkyl;
  • [1322] R^1a and R^1b are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^1a is H or C₁-C₁₂ alkyl, and R^Ib together with the carbon atom to which it is bound is taken together with an adjacent R^1b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1323] R^2a and R^2b are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^2a is H or C₁-C₁₂ alkyl, and R^2b together with the carbon atom to which it is bound is taken together with an adjacent R^2b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1324] R^3a and R^3b are, at each occurrence, independently either (a): H or C₁-C₁₂ alkyl; or (b) R^3a is H or C₁-C₁₂ alkyl, and R^3b together with the carbon atom to which it is bound is taken together with an adjacent R and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1325] R^4A and R^4B are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^4A is H or C₁-C₁₂ alkyl, and R^4B together with the carbon atom to which it is bound is taken together with an adjacent R^4B and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1326] R⁵ and R⁶ are each independently H or methyl;
  • [1327] R⁷ is H or C, —C₂₀ alkyl;
  • [1328] R⁸ is OH, —N(R⁹)(C=0)R¹⁰, —(C=0)NR⁹R¹⁰, —NR⁹R¹⁰, —(C=0)OR″¹ or -0(C=0)R″, provided that G³ is C₄-C₆ alkylene when R⁸ is —NR⁹R¹⁰,
  • [1329] R⁹ and R¹⁰ are each independently H or C₁-C₁₂ alkyl;
  • [1330] R″ is aralkyl;
  • [1331] a, b, c and d are each independently an integer from 1 to 24; and x is 0, 1 or 2,
  • [1332] wherein each alkyl, alkylene and aralkyl is optionally substituted.

[1333] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1334] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1335] X and X′ are each independently N or CR;
  • [1336] Y and Y′ are each independently absent, —O(C═O)—, —(C═O)O— or NR, provided that:
  • [1337] a) Y is absent when X is N;
  • [1338] b) Y′ is absent when X′ is N;
  • [1339] c) Y is —O(C═O)—, —(C═O)O— or NR when X is CR; and
  • [1340] d) Y′ is —O(C═O)—, —(C═O)O— or NR when X′ is CR,
  • [1341] L¹ and L^1′ are each independently —O(C═O)R′, —(C═O)OR′, —C(═O)R′, —OR¹, —S(O)_zR′, —S—SR¹, —C(═O)SR′, —SC(═O)R′, —NR^aC(═O)R′, —C(═O)NR^bR^c, —NR^aC(═O)NR^bR^c, —OC(═O)NR^bR^c or —NR^aC(═O)OR′;
  • [1342] L² and L^2′ are each independently —O(C═O)R², —(C═O)OR², —C(═O)R², —OR², —S(O)_zR², —S—SR², —C(═O)SR², —SC(═O)R², —NR^dC(═O)R², —C(═O)NR^eR^f, —NR^dC(═O)NR^eR^f, —OC(═O)NR^eR^f; —NR^dC(═O)OR² or a direct bond to R²;
  • [1343] G¹. G^1′, G² and G^2′ are each independently C₂-C₁₂ alkylene or C₂-C₁₂ alkenylene;
  • [1344] G is C₂-C₂₄ heteroalkylene or C₂-C₂₄ heteroalkenylene;
  • [1345] R^a, R^b, R^d and R^e are, at each occurrence, independently H, C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1346] R^c and R^f are, at each occurrence, independently C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1347] R is, at each occurrence, independently H or C₁-C₁₂ alkyl;
  • [1348] R¹ and R² are, at each occurrence, independently branched C₆-C₂₄ alkyl or branched C₆-C₂₄ alkenyl;
  • [1349] z is 0, 1 or 2, and wherein each alkyl, alkenyl, alkylene, alkenylene, heteroalkylene and heteroalkenylene is independently substituted or unsubstituted unless otherwise specified.

[1350] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1351] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1352] L¹ is —O(C═O)R¹, —(C═O)OR¹, —C(═O)R¹, —OR¹, —S(O)_xR¹, —S—SR¹, —C(═O)SR¹, —SC(═O)R¹, —NR^aC(═O)R¹, —C(═O)NR^bR^c, —NR^aC(═O)NR^bR^c, —OC(═O)NR^bR^c or —NR^aC(═O)OR¹;
  • [1353] L² is —O(C═O)R², —(C═O)OR², —C(═O)R², —OR², —S(O)_xR², —S—SR², —C(═O)SR², —SC(═O)R², —NR^dC(═O)R², —C(═O)NR^eR^f, —NR^dC(═O)NR^eR^f, —OC(═O)NR^eR^f; —NR^dC(═O)OR² or a direct bond to R²;
  • [1354] G¹ and G² are each independently C₂-C₁₂ alkylene or C₂-C₁₂ alkenylene;
  • [1355] G³ is C₁-C₂₄ alkylene, C₂-C₂₄ alkenylene, C₃-C₈ cycloalkylene or C₃-C₈ cycloalkenylene;
  • [1356] R^a, R^b, R^d and R^e are each independently H or C₁-C₁₂ alkyl or C₁-C₁₂ alkenyl;
  • [1357] R^c and R^f are each independently C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1358] R¹ and R² are each independently branched C₆-C₂₄ alkyl or branched C₆-C₂₄ alkenyl;
  • [1359] R³ is —N(R⁴)R⁵;
  • [1360] R⁴ is C₁-C₁₂ alkyl;
  • [1361] R⁵ is substituted C₁-C₁₂ alkyl; and
  • [1362] x is 0, 1 or 2, and
  • [1363] wherein each alkyl, alkenyl, alkylene, alkenylene, cycloalkylene, cycloalkenylene, aryl and aralkyl is independently substituted or unsubstituted unless otherwise specified.

[1364] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1365] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1366] L¹ is —O(C═O)R¹, —(C═O)OR¹, —C(═O)R¹, —OR¹, —S(O)_xR¹, —S—SR¹, —C(═O)SR¹, —SC(═O)R¹, —NR^aC(═O)R¹, —C(═O)NR^bR^c, —NR^aC(═O)NR^bR^c, —OC(═O)NR^bR^c or —NR^aC(═O)OR¹;
  • [1367] L² is —O(C═O)R², —(C═O)OR², —C(═O)R², —OR², —S(O)_xR², —S—SR², —C(═O)SR², —SC(═O)R², —NR^dC(═O)R², —C(═O)NR^eR^f, —NR^dC(═O)NR^eR^f,
  • [1368] —OC(═O)NR^eR^f; —NR^dC(═O)OR² or a direct bond to R²;
  • [1369] G^1a and G^2b are each independently C₂-C₁₂ alkylene or C₂-C₁₂ alkenylene;
  • [1370] G^1b and G^2b are each independently C₁-C₁₂ alkylene or C₂-C₁₂ alkenylene;
  • [1371] G³ is C₁-C₂₄ alkylene, C₂-C₂₄ alkenylene, C₃-C₈ cycloalkylene or C₃-C₈ cycloalkenylene;
  • [1372] R^a, R^b, R^d and R^e are each independently H or C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1373] R^c and R^f are each independently C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1374] R¹ and R² are each independently branched C₆-C₂₄ alkyl or branched C₆-C₂₄ alkenyl;
  • [1375] R^3a is —C(═O)N(R^4a)R^5a or —C(═O)OR⁶;
  • [1376] R^3b is —NR^4bC(=O)R^5b;
  • [1377] R^4a is C₁-C₁₂ alkyl;
  • [1378] R^4b is H, C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1379] R^5a is H, C₁-C₈ alkyl or C₂-C₈ alkenyl;
  • [1380] R^5b is C₂-C₁₂ alkyl or C₂-C₁₂ alkenyl when R^4b is H; or R^5b is C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl when R^4b is C₁-C₁₂ alkyl or C₂-C₁₂ alkenyl;
  • [1381] R⁶ is H, aryl or aralkyl; and
  • [1382] x is 0, 1 or 2, and
  • [1383] wherein each alkyl, alkenyl, alkylene, alkenylene, cycloalkylene, cycloalkenylene, aryl and aralkyl is independently substituted or unsubstituted.

[1384] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1385] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1386] G¹ is —OH, —R³R⁴, —(C=0)R⁵ or —R³(C=0)R⁵;
  • [1387] G² is —CH₂— or —(C=0)-;
  • [1388] R is, at each occurrence, independently H or OH;
  • [1389] R¹ and R² are each independently optionally substituted branched, saturated or unsaturated C₁₂-C₃₆ alkyl;
  • [1390] R³ and R⁴ are each independently H or optionally substituted straight or branched, saturated or unsaturated Ci-C₆ alkyl;
  • [1391] R⁵ is optionally substituted straight or branched, saturated or unsaturated Ci-C₆ alkyl; and
  • [1392] n is an integer from 2 to 6.

[1393] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1394] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1395] one of G¹ or G² is, at each occurrence, —O(C═O)—, —(C═O)O—, —C(═O)—, —O—, —S(O), —S—S—, —C(═O)S—, SC(═O)—, —N(R^a)C(═O)—, —C(═O)N(R^a)—, —N(R^a)C(═O)N(R^a)—, —OC(═O)N(R^a)— or —N(R^a)C(═O)O—, and the other of G¹ or G² is, at each occurrence, —O(C═O)—, —(C═O)O—, —C(═O)—, —O—, —S(O), —S—S—, —C(═O)S—, —SC(═O)—, —N(R^a)C(═O)—, —C(═O)N(R^a)—, —N(R^a)C(═O)N(R^a)—, —OC(═O)N(R^a)— or —N(R^a)C(═O)O— or a direct bond;
  • [1396] L is, at each occurrence, ˜O(C═O)—, wherein ˜ represents a covalent bond to X;
  • [1397] X is CR^a;
  • [1398] Z is alkyl, cycloalkyl or a monovalent moiety comprising at least one polar functional group when n is 1; or Z is alkylene, cycloalkylene or a polyvalent moiety comprising at least one polar functional group when n is greater than 1;
  • [1399] R^a is, at each occurrence, independently H, C₁-C₁₂ alkyl, C₁-C₁₂ hydroxylalkyl, C₁-C₁₂ aminoalkyl, C₁-C₁₂ alkylaminylalkyl, C₁-C₁₂ alkoxyalkyl, C₁-C₁₂ alkoxycarbonyl, C₁-C₁₂ alkylcarbonyloxy, C₁-C₁₂ alkylcarbonyloxyalkyl or C₁-C₁₂ alkylcarbonyl;
  • [1400] R is, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R together with the carbon atom to which it is bound is taken together with an adjacent R and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1401] R¹ and R² have, at each occurrence, the following structure, respectively:

• • [1402] a¹ and a² are, at each occurrence, independently an integer from 3 to 12; b¹ and b² are, at each occurrence, independently 0 or 1;
  • [1403] c¹ and c² are, at each occurrence, independently an integer from 5 to 10; d¹ and d² are, at each occurrence, independently an integer from 5 to 10; y is, at each occurrence, independently an integer from 0 to 2; and n is an integer from 1 to 6,
  • [1404] wherein each alkyl, alkylene, hydroxylalkyl, aminoalkyl, alkylaminylalkyl, alkoxyalkyl, alkoxycarbonyl, alkylcarbonyloxy, alkylcarbonyloxyalkyl and alkylcarbonyl is optionally substituted with one or more substituent.

[1405] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1406] or a pharmaceutically acceptable salt, prodrug or stereoisomer thereof, wherein:
  • [1407] one of L¹ or L² is —O(C═O)—, —(C═O)O—, —C(═O)—, —O—, —S(O)_x—, —S—S—, —C(═O)S—, —SC(═O)—, —R^aC(═O)—, —C(═O)R^a—, R^aC(═O)R^a—, —OC(═O)R^a— or —R^aC(═O)O—, and the other of L¹ or L² is —O(C═O)—, —(C═O)O—, —C(═O)—, —O—, —S(O)_x—, —S—S—, —C(═O)S—, SC(═O)—, —R^aC(═O)—, —C(═O)R^a—, R^aC(═O)R^a—, —OC(═O)R^a— or —NR^aC(═O)O— or a direct bond;
  • [1408] G¹ and G² are each independently unsubstituted C₁-C₁₂ alkylene or C₁-C₁₂ alkenylene;
  • [1409] G³ is C₁-C₂₄ alkylene, C₁-C₂₄ alkenylene, C₃-C₈ cycloalkylene, C₃-C₈ cycloalkenylene;
  • [1410] R^a is H or C₁-C₁₂ alkyl;
  • [1411] R¹ and R² are each independently C₆-C₂₄ alkyl or C₆-C₂₄ alkenyl;
  • [1412] R³ is H, OR⁵, CN, —C(═O)OR⁴, —OC(═O)R⁴ or —R⁵C(═O)R⁴;
  • [1413] R⁴ is C₁-C₁₂ alkyl;
  • [1414] R⁵ is H or C₁-C₆ alkyl; and
  • [1415] x is 0, 1 or 2.

[1416] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1417] or a pharmaceutically acceptable salt, tautomer, prodrug or stereoisomer thereof, wherein:
  • [1418] L¹ and L² are each independently -0(C=0)-, —(C=0)0-, —C(=0)-, -0-, —S(0)_x—, —S—S—, —C(=0)S—, —SC(=0)-, —R^aC(=0)-, —C(=0)R^a—, —R^aC(=0)R^a—, —OC(=0)R^a—, —R^aC(=0)0- or a direct bond;
  • [1419] G¹ is C₁-C₂ alkylene, —(C=0)-, -0(C=0)-, —SC(=0)-, —R^aC(=0)- or a direct bond:
  • [1420] G² is —C(=0)-, —(C=0)0-, —C(=0)S—, —C(=0)NR^a— or a direct bond;
  • [1421] G³ is C₁-C₆ alkylene;
  • [1422] R^a is H or C₁-C₁₂ alkyl;
  • [1423] R^1a and R^1b are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^1a is H or C₁-C₁₂ alkyl, and R^1b together with the carbon atom to which it is bound is taken together with an adjacent R^1b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1424] R^2a and R^2b are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^2a is H or C₁-C₁₂ alkyl, and R^2b together with the carbon atom to which it is bound is taken together with an adjacent R^2b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1425] R^3a and R^3b are, at each occurrence, independently either (a): H or C₁-C₁₂ alkyl; or (b) R^3a is H or C₁-C₁₂ alkyl, and R^3b together with the carbon atom to which it is bound is taken together with an adjacent R and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1426] R^4a and R^4b are, at each occurrence, independently either: (a) H or C₁-C₁₂ alkyl; or (b) R^4a is H or C₁-C₁₂ alkyl, and R^4b together with the carbon atom to which it is bound is taken together with an adjacent R^4b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1427] R⁵ and R⁶ are each independently H or methyl;
  • [1428] R⁷ is C₄-C₂₀ alkyl;
  • [1429] R⁸ and R⁹ are each independently C₁-C₁₂ alkyl; or R⁸ and R⁹, together with the nitrogen atom to which they are attached, form a 5, 6 or 7-membered heterocyclic ring;
  • [1430] a, b, c and d are each independently an integer from 1 to 24; and x is 0, 1 or 2.

[1431] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1432] or a pharmaceutically acceptable salt, tautomer, prodrug or stereoisomer thereof, wherein:
  • [1433] L¹ and L² are each independently -0(C=0)-, —(C=0)0- or a carbon-carbon double bond;
  • [1434] R^1a and R^1b are, at each occurrence, independently either (a) H or C₁-C₁₂ alkyl, or (b) R^1a is H or C₁-C₁₂ alkyl, and R^Ib together with the carbon atom to which it is bound is taken together with an adjacent R^1b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1435] R^2a and R^2b are, at each occurrence, independently either (a) H or C₁-C₁₂ alkyl, or (b) R^2a is H or C₁-C₁₂ alkyl, and R^2b together with the carbon atom to which it is bound is taken together with an adjacent R^2b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1436] R^3a and R^3b are, at each occurrence, independently either (a) H or C₁-C₁₂ alkyl, or (b) R^3a is H or C₁-C₁₂ alkyl, and R^3b together with the carbon atom to which it is bound is taken together with an adjacent R^3b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1437] R^4a and R^4b are, at each occurrence, independently either (a) H or C₁-C₁₂ alkyl, or (b) R^4a is H or C₁-C₁₂ alkyl, and R^4b together with the carbon atom to which it is bound is taken together with an adjacent R^4b and the carbon atom to which it is bound to form a carbon-carbon double bond;
  • [1438] R⁵ and R⁶ are each independently methyl or cycloalkyl;
  • [1439] R⁷ is, at each occurrence, independently H or C₁-C₁₂ alkyl; R⁸ and R⁹ are each independently unsubstituted C₁-C₁₂ alkyl; or R⁸ and R⁹, together with the nitrogen atom to which they are attached, form a 5, 6 or 7-membered heterocyclic ring comprising one nitrogen atom;
  • [1440] a and d are each independently an integer from 0 to 24; b and c are each independently an integer from 1 to 24; and e is 1 or 2,
  • [1441] provided that:
  • [1442] at least one of R^1a, R^2a, R^3a or R^4a is C₁-C₁₂ alkyl, or at least one of L¹ or L² is -0(C=0)- or —(C=0)0-; and
  • [1443] R^1a and R^1b are not isopropyl when a is 6 or n-butyl when a is 8.

[1444] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1445] or a pharmaceutically acceptable salt thereof, wherein
  • [1446] R₁ and R₂ are the same or different, each a linear or branched alkyl with 1-9 carbons, or as alkenyl or alkynyl with 2 to 11 carbon atoms,
  • [1447] L₁ and L₂ are the same or different, each a linear alkyl having 5 to 18 carbon atoms, or form a heterocycle with N,
  • [1448] X₁ is a bond, or is —CG-G-whereby L2-CO—O—R₂ is formed,
  • [1449] X₂ is S or O,
  • [1450] L₃ is a bond or a lower alkyl, or form a heterocycle with N,
  • [1451] R₃ is a lower alkyl, and
  • [1452] R₄ and R₅ are the same or different, each a lower alkyl.
    Compounds (A₁)-(A₁₁)

[1453] In some embodiments, the lipid nanoparticle comprises an ionizable lipid having the structure:

• • [1454] or a pharmaceutically acceptable salt thereof.

[1455] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1456] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1457] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

• • [1458] or a pharmaceutically acceptable salt thereof.

[1459] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1460] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1461] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1462] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1463] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1464] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1465] In some embodiments, the lipid nanoparticle comprises a lipid having the structure:

or a pharmaceutically acceptable salt thereof.

[1466] In certain embodiments, lipid nanoparticles comprise one or more non-cationic lipids. Non-cationic lipids may be phospholipids.

[1467] In some embodiments, the lipid nanoparticle comprises 5-25 mol % non-cationic lipid. For example, the lipid nanoparticle may comprise 5-20 mol %, 5-15 mol %, 5-10 mol %, 10-25 mol %, 10-20 mol %, 10-25 mol %, 15-25 mol %, 15-20 mol %, or 20-25 mol % non-cationic lipid. In some embodiments, the lipid nanoparticle comprises 5 mol %, 10 mol %, 15 mol %, 20 mol %, or 25 mol % non-cationic lipid.

[1468] In some embodiments, a non-cationic lipid comprises 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLPc), 1,2-dimyristoyl-sn-gly cero-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-diundecanoyl-sn-glycero-phosphocholine (DUPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine (18:0 Diether PC), 1-oleoyl-2 cholesterylhemisuccinoyl-sn-glycero-3-phosphocholine (OChemsPC), 1-hexadecyl-sn-glycero-3-phosphocholine (C16 Lyso PC), 1,2-dilinolenoyl-sn-glycero-3-phosphocholine, 1,2-diarachidonoyl-sn-glycero-3-phosphocholine, 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine, 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine (ME 16.0 PE), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilinoleoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilinolenoyl-sn-glycero-3-phosphoethanolamine, 1,2-diarachidonoyl-sn-glycero-3-phosphoethanolamine, 1,2-didocosahexaenoyl-sn-glycero-3-phosphoethanolamine, 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG), sphingomyelin, or mixtures thereof.

[1469] In some embodiments, the lipid nanoparticle comprises 5-15 mol %, 5-10 mol %, or 10-15 mol % DSPC. For example, the lipid nanoparticle may comprise 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 mol % DSPC.

[1470] In certain embodiments, the lipid composition of the lipid nanoparticle compositions can comprise one or more phospholipids, for example, one or more saturated or (poly) unsaturated phospholipids or a combination thereof. In general, phospholipids comprise a phospholipid moiety and one or more fatty acid moieties.

[1471] A phospholipid moiety can be selected, for example, from the non-limiting group consisting of phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, phosphatidyl serine, phosphatidic acid, 2-lysophosphatidyl choline, and a sphingomyelin.

[1472] A fatty acid moiety can be selected, for example, from the non-limiting group consisting of lauric acid, myristic acid, myristoleic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, alpha-linolenic acid, erucic acid, phytanoic acid, arachidic acid, arachidonic acid, eicosapentaenoic acid, behenic acid, docosapentaenoic acid, and docosahexaenoic acid.

[1473] Particular phospholipids can facilitate fusion to a membrane. For example, a cationic phospholipid can interact with one or more negatively charged phospholipids of a membrane (e.g., a cellular or intracellular membrane). Fusion of a phospholipid to a membrane can allow one or more elements (e.g., a therapeutic agent) of a lipid-containing composition (e.g., LNPs) to pass through the membrane permitting, e.g., delivery of the one or more elements to a target tissue.

[1474] Non-natural phospholipid species including natural species with modifications and substitutions including branching, oxidation, cyclization, and alkynes are also contemplated. For example, a phospholipid can be functionalized with or cross-linked to one or more alkynes (e.g., an alkenyl group in which one or more double bonds is replaced with a triple bond). Under appropriate reaction conditions, an alkyne group can undergo a copper-catalyzed cycloaddition upon exposure to an azide. Such reactions can be useful in functionalizing a lipid bilayer of a nanoparticle composition to facilitate membrane permeation or cellular recognition or in conjugating a nanoparticle composition to a useful component such as a targeting or imaging moiety (e.g., a dye).

[1475] Phospholipids include, but are not limited to, glycerophospholipids such as phosphatidylcholines, phosphatidylethanolamines, phosphatidylserines, phosphatidylinositols, phosphatidy glycerols, and phosphatidic acids. Phospholipids also include phosphosphingolipid, such as sphingomyelin.

[1476] In some embodiments, a phospholipid comprises 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC), 1,2-Distearoyl-sn-glycero-3-phosphoethanolamine (DSPE), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine 1,2-dilinoleoyl-sn-glycero-3-(DOPE), phosphocholine (DLPc), 1,2-dimyristoyl-sn-gly cero-phosphocholine (DMPC), 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-diundecanoyl-sn-glycero-phosphocholine (DUPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), 1,2-di-O-octadecenyl-sn-glycero-3-phosphocholine (18:0 Diether PC), 1-oleoyl-2 cholesterylhemisuccinoyl-sn-glycero-3-phosphocholine (OChemsPC), 1-hexadecyl-sn-glycero-3-phosphocholine (C16 Lyso PC), 1,2-dilinolenoyl-sn-glycero-3-phosphocholine, 1,2-diarachidonoyl-sn-glycero-3-phosphocholine, 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine, 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine (ME 16.0 PE), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilinoleoyl-sn-glycero-3-phosphoethanolamine, 1,2-dilinolenoyl-sn-glycero-3-phosphoethanolamine, 1,2-diarachidonoyl-sn-glycero-3-phosphoethanolamine, 1,2-didocosahexaenoyl-sn-glycero-3-phosphoethanolamine, 1,2-dioleoyl-sn-glycero-3-phospho-rac-(1-glycerol) sodium salt (DOPG), sphingomyelin, or mixtures thereof.

[1477] In certain embodiments, a phospholipid is an analog or variant of DSPC. In certain embodiments, a phospholipid is a compound of Formula (HI):

• • [1478] or a salt thereof, wherein:
  • [1479] each R1 is independently optionally substituted alkyl; or optionally two R1 are joined together with the intervening atoms to form optionally substituted monocyclic carbocyclyl or optionally substituted monocyclic heterocyclyl; or optionally three R1 are joined together with the intervening atoms to form optionally substituted bicyclic carbocyclyl or optionally substitute bicyclic heterocyclyl;
  • [1480] n is 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
  • [1481] m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
  • [1482] A is of the formula:

• • [1483] each instance of L2 is independently a bond or optionally substituted C1-6 alkylene, wherein one methylene unit of the optionally substituted C1-6 alkylene is optionally replaced with O, N(RN), S, C(O), C(O)N(RN), NRNC(O), C(O)O, OC(O), OC(O)O, OC(O)N(RN), —NRNC(O)O, or NRNC(O)N(RN);
  • [1484] each instance of R2 is independently optionally substituted C1-30 alkyl, optionally substituted C1-30 alkenyl, or optionally substituted C1-30 alkynyl; optionally wherein one or more methylene units of R² are independently replaced with optionally substituted carbocyclylene, optionally substituted heterocyclylene, optionally substituted arylene, optionally substituted heteroarylene, N(RN), O, S, C(O), C(O)N(RN), NRNC(O), NRNC(O)N(RN), C(O)O, OC(O), OC(O)O, OC(O)N(RN), NRNC(O)O, C(O)S, SC(O), C(═NRN), C(═NRN)N(RN), NRNC(═NRN), NRNC(═NRN)N(RN), C(S), C(S)N(RN), NRNC(S), NRNC(S)N(RN), S(O), OS(O), S(O)O, OS(O)O, OS(O)2, S(O)2O, OS(O)2O, N(RN)S(O), S(O)N(RN), N(RN)S(O)N(RN), OS(O)N(RN), N(RN)S(O)O, S(O)2, N(RN)S(O)2, S(O)2N(RN), N(RN)S(O)2N(RN), OS(O)2N(RN), or N(RN)S(O)2O;
  • [1485] each instance of RN is independently hydrogen, optionally substituted alkyl, or a nitrogen protecting group;
  • [1486] Ring B is optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl; and
  • [1487] p is 1 or 2.

[1488] In certain embodiments, the compound is not of the formula:

• • [1489] wherein each instance of R2 is independently unsubstituted alkyl, unsubstituted alkenyl, or unsubstituted alkynyl.

[1490] In some embodiments, the phospholipids may be one or more of the phospholipids described in PCT Application No. PCT/US2018/037922.

[1491] In some embodiments, the lipid nanoparticle comprises a molar ratio of 5-25% non-cationic lipid relative to the other lipid components. For example, the lipid nanoparticle may comprise a molar ratio of 5-30%, 5-15%, 5-10%, 10-25%, 10-20%, 10-25%, 15-25%, 15-20%, 20-25%, or 25-30% non-cationic lipid. In some embodiments, the lipid nanoparticle comprises a molar ratio of 5%, 10%, 15%, 20%, 25%, or 30% non-cationic lipid.

[1492] In some embodiments, the lipid nanoparticle comprises a molar ratio of 5-25% phospholipid relative to the other lipid components. For example, the lipid nanoparticle may comprise a molar ratio of 5-30%, 5-15%, 5-10%, 10-25%, 10-20%, 10-25%, 15-25%, 15-20%, 20-25%, or 25-30% phospholipid. In some embodiments, the lipid nanoparticle comprises a molar ratio of 5%, 10%, 15%, 20%, 25%, or 30% phospholipid lipid.

[1493] The lipid composition of a pharmaceutical composition can comprise one or more structural lipids. As used herein, the term “structural lipid” includes sterols and also to lipids containing sterol moieties.

[1494] Incorporation of structural lipids in the lipid nanoparticle may help mitigate aggregation of other lipids in the particle. Structural lipids can be selected from the group including but not limited to, cholesterol, fecosterol, sitosterol, ergosterol, campesterol, stigmasterol, brassicasterol, tomatidine, tomatine, ursolic acid, alpha-tocopherol, hopanoids, phytosterols, steroids, and mixtures thereof. In some embodiments, the structural lipid is a sterol. As defined herein, “sterols” are a subgroup of steroids consisting of steroid alcohols. In certain embodiments, the structural lipid is a steroid. In certain embodiments, the structural lipid is cholesterol. In certain embodiments, the structural lipid is an analog of cholesterol. In certain embodiments, the structural lipid is alpha-tocopherol.

[1495] In some embodiments, the structural lipids may be one or more of the structural lipids described in U.S. application Ser. No. 16/493,814.

[1496] In some embodiments, the lipid nanoparticle comprises a molar ratio of 25-55% structural lipid relative to the other lipid components. For example, the lipid nanoparticle may comprise a molar ratio of 10-55%, 25-50%, 25-45%, 25-40%, 25-35%, 25-30%, 30-55%, 30-50%, 30-45%, 30-40%, 30-35%, 35-55%, 35-50%, 35-45%, 35-40%, 40-55%, 40-50%, 40-45%, 45-55%, 45-50%, or 50-55% structural lipid. In some embodiments, the lipid nanoparticle comprises a molar ratio of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or 55% structural lipid.

[1497] In some embodiments, the lipid nanoparticle comprises 30-45 mol % sterol, optionally 35-40 mol %, for example, 30-31 mol %, 31-32 mol %, 32-33 mol %, 33-34 mol %, 35-35 mol %, 35-36 mol %, 36-37 mol %, 38-38 mol %, 38-39 mol %, or 39-40 mol %. In some embodiments, the lipid nanoparticle comprises 25-55 mol % sterol. For example, the lipid nanoparticle may comprise 25-50 mol %, 25-45 mol %, 25-40 mol %, 25-35 mol %, 25-30 mol %, 30-55 mol %, 30-50 mol %, 30-45 mol %, 30-40 mol %, 30-35 mol %, 35-55 mol %, 35-50 mol %, 35-45 mol %, 35-40 mol %, 40-55 mol %, 40-50 mol %, 40-45 mol %, 45-55 mol %, 45-50 mol %, or 50-55 mol % sterol. In some embodiments, the lipid nanoparticle comprises 25 mol %, 30 mol %, 35 mol %, 40 mol %, 45 mol %, 50 mol %, or 55 mol % sterol.

[1498] In some embodiments, the lipid nanoparticle comprises 35-40 mol % cholesterol. For example, the lipid nanoparticle may comprise 35, 35.5, 36, 36.5, 37, 37.5, 38, 38.5, 39, 39.5, or 40 mol % cholesterol.

[1499] The lipid composition of a pharmaceutical composition can comprise one or more polyethylene glycol (PEG)-modified lipids.

[1500] As used herein, the term “PEG-lipid” or “PEG-modified lipid” refers to polyethylene glycol (PEG)-modified lipids. Non-limiting examples of PEG-modified lipids include PEG-modified phosphatidylethanolamine and phosphatidic acid, PEG-ceramide conjugates (e.g., PEG-CerC14 or PEG-CerC20), PEG-modified dialkylamines, and PEG-modified 1,2-diacyloxypropan-3-amines. Such lipids are also referred to as PEGylated lipids. For example, a PEG-modified lipid can be PEG-c-DOMG, PEG-DMG, PEG-DLPE, PEG-DMPE, PEG-DPPC, or a PEG-DSPE lipid.

[1501] In some embodiments, the PEG-modified lipid includes, but not limited to 1,2-dimyristoyl-sn-glycerol methoxypolyethylene glycol (PEG-DMG), 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[amino (polyethylene glycol)] (PEG-DSPE), PEG-disteryl glycerol (PEG-DSG), PEG-dipalmetoleyl, PEG-dioleyl, PEG-distearyl, PEG-diacylglycamide (PEG-DAG), PEG-dipalmitoyl phosphatidylethanolamine (PEG-DPPE), or PEG-1,2-dimyristyloxlpropyl-3-amine (PEG-c-DMA).

[1502] In some embodiments, the PEG-modified lipid is selected from the group consisting of a PEG-modified phosphatidylethanolamine, a PEG-modified phosphatidic acid, a PEG-modified ceramide, a PEG-modified dialkylamine, a PEG-modified diacylglycerol, a PEG-modified dialkylglycerol, and mixtures thereof. In some embodiments, the PEG-modified lipid is PEG-DMG, PEG-c-DOMG (also referred to as PEG-DOMG), PEG-DSG, and/or PEG-DPG.

[1503] In some embodiments, the lipid moiety of the PEG-modified lipids includes those having lengths of from about C₁₄ to about C₂₂, preferably from about C₁₄ to about C₁₆. In some embodiments, a PEG moiety, for example an mPEG-NH₂, has a size of about 1000, 2000, 5000, 10,000, 15,000 or 20,000 daltons. In some embodiments, the PEG-modified lipid is PEG_2k-DMG.

[1504] In some embodiments, lipid nanoparticles can comprise a PEG-modified lipid which is a non-diffusible PEG. Non-limiting examples of non-diffusible PEGs include PEG-DSG and PEG-DSPE.

[1505] PEG-modified lipids are known in the art, such as those described in U.S. Pat. No. 8,158,601 and International Publ. No. WO 2015/130584 A2, which are incorporated herein by reference to the extent they describe PEG-modified lipids.

[1506] In general, some of the other lipid components (e.g., PEG-modified lipids) of various formulae may be synthesized as described International Patent Application No. PCT/US2016/000129, filed Dec. 10, 2016, entitled “Compositions and Methods for Delivery of Therapeutic Agents,” which is incorporated by reference to the extent they disclose lipid components and production.

[1507] The lipid component of a lipid nanoparticle composition may include one or more molecules comprising polyethylene glycol, such as PEG or PEG-modified lipids. Such species may be alternately referred to as PEGylated lipids. A PEG-modified lipid is a lipid modified with polyethylene glycol. A PEG-modified lipid may be selected from the non-limiting group including PEG-modified phosphatidylethanolamines, PEG-modified phosphatidic acids, PEG-modified ceramides, PEG-modified dialkylamines, PEG-modified diacylglycerols, PEG-modified dialkylglycerols, and mixtures thereof. For example, a PEG-modified lipid may be PEG-c-DOMG, PEG-DMG, PEG-DLPE, PEG-DMPE, PEG-DPPC, or a PEG-DSPE lipid.

[1508] In some embodiments the PEG-modified lipids are a modified form of PEG DMG. PEG-DMG has the following structure:

[1509] In some embodiments, PEG-modified lipids can be PEGylated lipids described in International Publication No. WO 2012/099755, which is herein incorporated by reference to the extent it discloses PEG-modified lipids. Any of these exemplary PEG-modified lipids may be modified to comprise a hydroxyl group on the PEG chain. In certain embodiments, the PEG-modified lipid is a PEG-OH lipid. As generally defined herein, a “PEG-OH lipid” (also referred to herein as “hydroxy-PEGylated lipid”) is a PEGylated lipid having one or more hydroxyl (—OH) groups on the lipid. In certain embodiments, the PEG-OH lipid includes one or more hydroxyl groups on the PEG chain. In certain embodiments, a PEG-OH or hydroxy-PEGylated lipid comprises an —OH group at the terminus of the PEG chain. Each possibility represents a separate embodiment.

[1510] In certain embodiments, a PEG-modified lipid is a compound of Formula (PI):

• • [1511] or salts thereof, wherein:
  • [1512] R³ is —OR^O;
  • [1513] R^O is hydrogen, optionally substituted alkyl, or an oxygen protecting group;
  • [1514] r is an integer between 1 and 100, inclusive;
  • [1515] L¹ is optionally substituted C_1-10 alkylene, wherein at least one methylene of the optionally substituted C_1-10 alkylene is independently replaced with optionally substituted carbocyclylene, optionally substituted heterocyclylene, optionally substituted arylene, optionally substituted heteroarylene, O, N(R^N), S, C(O), C(O)N(R^N), NR^NC(O), C(O)O, OC(O), OC(O)O, OC(O)N(R^N), NR^NC(O)O, or NR^NC(O)N(R^N);
  • [1516] D is a moiety obtained by click chemistry or a moiety cleavable under physiological conditions;
  • [1517] m is 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
  • [1518] A is of the formula:

• • [1519] each instance of L² is independently a bond or optionally substituted C_1-6 alkylene, wherein one methylene unit of the optionally substituted C_1-6 alkylene is optionally replaced with O, N(R^N), S, C(O), C(O)N(R^N), NR^NC(O), C(O)O, OC(O), OC(O)O, OC(O)N(R^N), NR^NC(O)O, or NR^NC(O)N(R^N);
  • [1520] each instance of R² is independently optionally substituted C_1-30 alkyl, optionally substituted C_1-30 alkenyl, or optionally substituted C_1-30 alkynyl; optionally wherein one or more methylene units of R² are independently replaced with optionally substituted carbocyclylene, optionally substituted heterocyclylene, optionally substituted arylene, optionally substituted heteroarylene, N(R^N), O, S, C(O), C(O)N(R^N), NR^NC(O), NR^NC(O)N(R^N), C(O)O, OC(O), OC(O)O, OC(O)N(R^N), NR^NC(O)O, C(O)S, SC(O), C(═NR^N), C(═NR^N)N(R^N), NR^NC(═NR^N), NR^NC(═NR^N)N(R^N), C(S), C(S)N(R^N), NR^NC(S), NR^NC(S)N(R^N), S(O), OS(O), S(O)O, OS(O)O, OS(O)₂, S(O)₂O, OS(O)₂O, N(R^N)S(O), S(O)N(R^N), N(R^N)S(O)N(R^N), OS(O)N(R^N), N(R^N)S(O)O, S(O)₂, N(R^N)S(O)₂, S(O)₂N(R^N), N(R^N)S(O)₂N(R^N), OS(O)₂N(R^N), or N(R^N)S(O)₂O;
  • [1521] each instance of R^N is independently hydrogen, optionally substituted alkyl, or a nitrogen protecting group;
  • [1522] Ring B is optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, or optionally substituted heteroaryl; and
  • [1523] p is 1 or 2.