Product and process for T lymphocyte immunosuppression

[0002] This application is a divisional of U.S. Pat. application Ser. No. 08/630,172, filed Apr. 10, 1996, now U.S. Pat. No. 6,060,054, issued on May 9, 2000.

[0004] The present invention relates to a product and process for immunosuppression of subjects having undesired immunological reactivities and in subjects in need of cell, tissue or organ transplant survival. More particularly, the present invention relates to a T lymphocyte veto molecule (hereinafter defined) and the use of such a molecule as an immunoregulator to effect therapeutic objectives.

[0005] A wide variety of medical treatments require regulation of the immune response in a patient. Such treatments include, for example, vaccinations, treatments for autoummune diseases, immunodeficiency diseases, immunoproliferative diseases and treatments involving the transplantation of organs and skin. Traditional reagents and methods used to regulate a subject's immune response often results in unwanted side effects. For example, immunosuppressive reagents such as cyclosporin A, azathioprine and prednisone are used to suppress the immune system of a patient with an autoimmune disease or patients receiving transplants. Such reagents, however, suppress a patient's entire immune response, thereby crippling the ability of the patient to mount an immune response against infectious agents not involved in the original disease. Due to such harmful side effects and the medical importance of immune regulation, reagents and methods to regulate specific parts of the immune system have been the subject of study for many years.

[0006] Introduction of an antigen into a host initiates a series of events culminating in an immune response. In addition, self-antigens can result in immunological tolerance or activation of an immune response against self-antigens. A major portion of the immune response is regulated by the interaction of a stimulator cell (defined in detail below) with a responding cell (defined in detail below).

[0007] Particular reagents having immunoregulatory potential of cell to cell interactions have been suggested by various investigators. Tykocinski et al. disclose in U.S. Pat. No. 5,242,687, issued Sep. 7, 1993, a composition comprising a CD8 peptide associated with a secondary ligand, including an Fc domain of immunoglobulin or a major histocompatibility molecule (MHC). Tykocinski et al. do not teach or suggest such a composition involving CD4, CD2, CD28, CTLA4 or fas-ligand proteins which are known to have significantly different functions in various immunity mechanisms.

[0008] In U.S. Pat. No. 5,336,603, issued Aug. 9, 1994, Capon et al. disclose “immunoadhesons” useful for immunomodulatory therapy. Capon et al. disclose adhesons as cell surface polypeptides, examples of which include CD8, CD4 and CD2, that can be combined with an immunologically active non-adheson polypeptide. Capon et al., however, do not teach or suggest a T cell veto molecule useful for immunosuppression and particularly a molecule that prevents the specific activation of responding cells by stimulator cells to suppress an immune response.

[0009] As such, there remains a need for therapeutic reagents and strategies that suppress an immune response in a safe and effective manner.

[0010] The present invention relates to a novel product and process for treatment of subjects in need of the abrogation of immunological reactivities. According to the present invention there are provided soluble or membrane-bound T lymphocyte veto molecules for immunosuppression in vivo or in vitro. The present invention overcomes traditional problems with immunoregulatory reagents by specifically regulating stimulator cell activation of responding cells capable of killing transplanted cells or capable of responding to autoantigens. This act of regulation is referred to herein as T cell veto. A molecule capable of T cell veto is referred to herein as a T cell veto molecule. In addition, the immunoregulatory reagents of the present invention can be administered locally, thereby alleviating problems that arise from extensive immunosuppression in an animal.

[0011] More specifically, one embodiment of the present invention includes a T lymphocyte veto molecule which includes a chimeric molecule having a protein selected from the group consisting of CD4 protein, CD2 protein, CD28 protein, CTLA4 protein, Fas-ligand protein, CD5 protein, CD7 protein, CD9 protein, CD11 protein, CD18 protein, CD27 protein, CD43 protein, CD45 protein, CD48 protein, B7.1 protein and B7.2 protein. The protein is linked to a targeting polypeptide that binds to a molecule that differentiates a host cell from a tissue graft cell. A further embodiment of the present invention is a T lymphocyte veto molecule which includes a chimeric molecule having one of such proteins. In this embodiment, the protein is linked to a targeting polypeptide that binds to a molecule which selectively targets a stimulator cell involved in an autoimmune response. In further aspects of these embodiments, the targeting polypeptide can be an immunoglobulin molecule, a growth factor or a tissue specific antigen. Such T lymphocyte veto molecules can be included in therapeutic compositions which also include pharmaceutically acceptable carriers.

[0012] A further embodiment of the present invention includes a recombinant cell, which has a first recombinant molecule having a nucleic acid molecule operatively linked to an expression vector, wherein the nucleic acid molecule has a sequence which encodes one of the proteins mentioned above. The recombinant cell further includes a second recombinant molecule having a nucleic acid molecule operatively linked to an expression vector wherein the nucleic acid molecule encodes a protein which is a targeting molecule that differentiates between a host cell and a tissue graft cell.

[0013] A further aspect of the present invention includes a method for producing a T lymphocyte veto molecule. This method includes providing a first protein as mentioned above, providing a second protein which is a targeting molecule that differentiates a host cell from a tissue graft cell, and linking the first protein to the second protein to form a chimeric molecule.

[0014] The present invention also includes a method to suppress an immune response which includes exposing chimeric molecules of the present invention to a stimulator cell that can interact specifically with the chimeric molecule under conditions for reduction of an immune response.

[0015] A further aspect of the present invention is a method to alleviate tissue transplant rejection. This method includes administering to an animal an effective amount of a therapeutic composition which includes a T lymphocyte veto molecule of the present invention.

[0016] FIGS. 1A-1D show the results of an experiment in which a T lymphocyte veto molecule is capable of specifically inhibiting the proliferation of CD4+ responder T cells.

[0017] FIG. 2 shows the results of an experiment in which a T lymphocyte veto molecule of the present invention is capable of specifically inhibiting the production of IL-2 and IL-4 by CD4+ responder T cells.

[0018] The present invention relates to a therapeutic reagent and process for treatment of subjects in need of the abrogation of immunological reactivities. The reagents and processes of the present invention are applicable to, but not limited to, the clinical settings of transplantation and autoimmunity, allergic disorders and other immunological disorders. Embodiments of the present invention include a novel T lymphocyte veto (TLV) molecule, also referred to herein as a T cell veto molecule, that regulates the activation of a responding cell by a stimulator cell, thereby suppressing an immune response.

[0019] As used herein, a stimulator cell includes any cell that, under appropriate conditions, binds to a responding cell in such a manner that the responding cell is either activated, anergized or killed. Traditional stimulator cells include “professional” antigen presenting cells (APC; e.g., dendritic cells, macrophages and B cells). According to the present invention, stimulator cells can also include a cell having a T cell veto molecule of the present invention on its surface by, for example, a tissue graft cell-specific antibody. A stimulator cell can also include a tissue graft cell, including allogeneic and xenogeneic tissue graft cells. Such graft cells can include, for example, T lymphocyte (also referred to herein as a T cell).

[0020] A responding cell includes any cell capable of being activated by a stimulator cell. Traditional responding cells include CD4−CD8+ (CD8+), CD4+CD8+, CD4−CD8−, CD4+CD8− (CD4+), αB and γ8 T cells. According to the present invention, responding cells can also include B lymphocytes (also referred to herein as B cells), as well as “naive” or “precursor” T cells. As used herein, a “naive” T cell refers to a T cell that is not activated by a T cell veto molecule of the present invention when tested using a standard effector T cell assay, such as by cytotoxic T cell (CTL) assays, T cell proliferation assays, interleukin secretion assays and assays measuring cell death (e.g., apoptosis assays). Preferably, a responding cell of the present invention includes a T cell, in particular a naive CD4+ or CD8+ T cell.

[0021] Activation of a responding cell refers to induction of signal transduction pathways in the responding cell resulting in production of cellular products (e.g., interleukin-2) by that cell. Anergy refers to the diminished reactivity by a responding cell.

[0022] Embodiments of the present invention include a novel T cell veto molecule having at least two components: (1) a responding cell activating protein (RCA protein; as defined below); and (2) a stimulator cell marker molecule (SCM molecule; as defined below) that differentiates a stimulator cell from a responding cell, in one embodiment, a host cell from a tissue graft cell. As used herein, the term “targeting polypeptide” is synonymous with the term SCM molecule. The two components of a T cell veto molecule of the present invention are associated with each other, such as by being linked by chemical or peptide binds (described in detail below).

[0023] As noted, a T cell veto molecule of the present invention comprises an RCA protein an SCM molecule. It should be noted that reference herein to an RCA protein, an SCM molecule or specific embodiments thereof, such as a CD4 protein in the case of an RCA protein, refers to the full length protein or molecule as well as a portion of a protein or molecule (e.g., non-protein with similar binding characteristics) that is at least sufficient to have the functional aspects of the referenced protein or molecule. Therefore, such a reference can refer to a full-length or partial polypeptide sequence that is capable of performing a desired function. For example, reference to a “CD4 protein” includes any portion of a CD4 molecule that is capable of binding to a CD4 co-receptor under conditions in which a complete CD4 protein binds to a co-receptor, and is capable of being linked to an SCM molecule. Similarly, a “CD2 protein” includes any portion of a CD2 molecule that is capable of binding to a CD2 co-receptor under conditions in which a complete CD2 protein binds to a co-receptor, and is capable of being linked to an SCM molecule. In addition, an SCM molecule includes any portion of a specific SCM molecule that is capable of binding to a molecule on the surface of a cell under conditions in which a complete SCM molecule would bind to a molecule on the surface of a cell, and is capable of being linked to an RCA protein of the present invention.

[0024] An RCA protein and an SCM molecule useful for the present invention is derived from an animal including, but not limited to, a human, a non-human primate, a pig, a mouse, a rat, a hamster, a rabbit, a horse and a goat, and preferably a human, a baboon and a pig.

[0025] A suitable RCA protein of the present invention comprises a protein that is capable of interfacing with a stimulator cell activating a responding cell in such manner that the action of the responding cell is altered. The resulting action of the responding cell can be inability of the responding cell to bind to a stimulator cell, apoptosis or anergy. According to the present invention, an RCA protein is preferably able to regulate the activity of a T lymphocyte, more preferably a cytotoxic and helper T lymphocyte.

[0026] One embodiment of a responding cell activation protein of the present invention comprises a CD4 protein having one variable (V) and one constant (C2) domain. A CD4 protein of the present invention preferably comprises first and second V domains and first and second C2 domains of CD4. A CD4 protein of the present invention more preferably comprises the amino acid sequence extending from about residue 1 to about residue 203 of a processed human CD4, in which the initiating Met is residue 1. For human CD4 coding sequence, see Parnes, 1989, Adv. Immunol.44: 265-311; Genbank M12807; and Swissprot P01730. A CD4 protein of the present invention even more preferably comprises the amino acid sequence disclosed in SEQ ID NO:1 and a leader sequence. A preferred leader sequence to be used with a CD4 protein of the present invention is disclosed in SEQ ID NO:29.

[0027] According to the present invention, a leader sequence is an amino acid sequence that naturally occurs at the amino terminus of a protein and functions to target the protein to a membrane for secretion. A leader sequence of the present invention can also be synthesized or isolated independently of the amino acid sequence with which the leader sequence naturally occurs. It should be noted that leader sequences of the present invention can be used with the protein with which the leader sequence naturally occurs (for example, a CD4 leader sequence with a CD4 protein), or can be interchanged with another leader sequence, including any of the leader sequences presented herein or other known leader sequences as will be known to those skilled in the art. It should also be noted that leader sequences of the present invention can be inserted anywhere into the amino acid sequences of RCA proteins of the present invention, provided that the functions of the leader sequence and the RCA are preserved.

[0028] Another embodiment of a responding cell activation protein of the present invention includes a CD2 protein having one extracellular domain of CD2 protein. A CD2 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 208 of CD2 protein, in which the initiating Met is residue 1. For human CD2 coding sequence, see Moingean et al., 1989, Immunol. Rev.111: 111-144; Genbank M16445; and Swissprot P06729. A CD2 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:2 and a leader sequence. A preferred leader sequence to be used with a CD2 protein of the present invention is disclosed in SEQ ID NO:30.

[0029] Another embodiment of a responding cell activation protein of the present invention includes a CD28 protein having a homodimer of the pseudo-V-region of CD28 protein. A CD28 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 161 of CD28 protein, in which the initiating Met is residue 1. For human CD28 coding sequence, see Aruffo et al., 1987, Proc. Nat. Acad. Sci. USA84: 8573-8577; Genbank J02988; and Swissprot P10747. A CD28 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:3 and a leader sequence. A preferred leader sequence to be used with a CD28 protein of the present invention is disclosed in SEQ ID NO:31.

[0030] Another embodiment of a responding cell activation protein of the present invention includes a cytotoxic T cell antigen 4 (CTLA4) protein having a homodimer of the pseudo V region of CTLA4 protein. A CTLA4 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 161 of CTLA4 protein, in which the initiating Met is residue 1. For human CTLA4 coding sequence, see Danavach et al., 1988, Eur. J. Immunol.18: 1901-1905; Genbank X15070; and Swissprot P16410. A CTLA4 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:4 and a leader sequence. A preferred leader sequence to be used with a CTLA4 protein of the present invention is disclosed in SEQ ID NO:32.

[0031] Another embodiment of a responding cell activation protein of the present invention includes a fas-ligand protein having the extracellular domain of fas-ligand protein. A fas-ligand protein of the present invention preferably comprises the amino acid sequence extending from about residue 137 to about residue 283 of fas-ligand protein, in which the initiating Met is residue 1. For human fas-ligand coding sequence, see Takahashi et al., 1994, Intern. Immunol.6: 1567-1574. A fas-ligand protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:5 and a leader sequence. An acceptable leader sequence to be used with a Fas-ligand protein of the present invention is disclosed, for example, in SEQ ID NO:29.

[0032] Another embodiment of a responding cell activation protein of the present invention includes a CD5 protein having the domains 1 through 3 of CD5 protein. A CD5 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 372 of CD5 protein, in which the initiating Met is residue 1. For human CD5 coding sequence, see Jones et al., 1986, Nature323: 346-349. A CD5 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:6 and a leader sequence. A preferred leader sequence to be used with a CD5 protein of the present invention is disclosed in SEQ ID NO:33.

[0033] Another embodiment of a responding cell activation protein of the present invention includes a CD7 protein having the pseudo V region of CD7 protein. A CD7 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 180 of CD7 protein, in which the initiating Met is residue 1. For human CD7 coding sequence, see Aruffo et al., 1987, EMBO J.6: 3313-3316; Genbank X06180; and Swissprot P09564. A CD7 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:7 and a leader sequence. A preferred leader sequence to be used with a CD7 protein of the present invention is disclosed in SEQ ID NO:34.

[0034] Another embodiment of a responding cell activation protein of the present invention includes a CD9 protein having the extracellular domain of CD9 protein. A CD9 protein of the present invention preferably comprises the amino acid sequence extending from about residue 113 to about residue 192 of CD9 protein, in which the initiating Met is residue 1. For human CD9 coding sequence, see Boucheix et al., 1990, J. Biol. Chem.266: 117-122; Genbank M38690; and Swissprot P21926. A CD9 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:8 and a leader sequence. An acceptable leader sequence to be used with a CD9 protein of the present invention is disclosed, for example, in SEQ ID NO:29.

[0035] Another embodiment of a responding cell activation protein of the present invention includes a CD11 protein having the CD11 alpha extracellular domain complexed with the CD18 extracellular domain of the CD11 protein. A CD11 alpha protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 1089 of CD11 alpha protein, in which the initiating Met is residue 1. For human CD11 alpha coding sequence, see Larson et al., 1990, Immunol. Rev.114: 181-217; Genbank Y00796; and Swissprot P20701. A CD11 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:9 and a leader sequence. A preferred leader sequence to be used with a CD11 protein of the present invention is disclosed in SEQ ID NO:35.

[0036] Another embodiment of a responding cell activation protein of the present invention includes a CD18 protein having the extracellular domain of CD18 protein. A CD18 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 750 of CD18 protein, in which the initiating Met is residue 1. For human CD18 coding sequence, see Larson et al., 1990, Immunol. Rev.114: 181-217; Genbank Y00057; and Swissprot P05107. A CD18 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:10 and a leader sequence. A preferred leader sequence to be used with a CD18 protein of the present invention is disclosed in SEQ ID NO:36.

[0037] Another embodiment of a responding cell activation protein of the present invention includes a CD27 protein having the extracellular domain of CD27 protein. A CD27 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 191 of CD27 protein, in which the initiating Met is residue 1. For human CD27 coding sequence, see Camerinin et al., 1991, J. Imnmunol.147: 3165-3169; Genbank M62928. A CD27 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:11 and a leader sequence. A preferred leader sequence to be used with a CD27 protein of the present invention is disclosed in SEQ ID NO:37.

[0038] Another embodiment of a responding cell activation protein of the present invention includes a CD43 protein having the extracellular domain of CD43 protein. A CD43 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 384 of CD43 protein, in which the initiating Met is residue 1. For human CD43 coding sequence, see Pallant et al., 1989, Proc. Nat. Acad. Sci. USA86: 1328-1332; Genbank J04168; and Swissprot 16150. A CD43 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:12 and a leader sequence. A preferred leader sequence to be used with a CD43 protein of the present invention is disclosed in SEQ ID NO:38.

[0039] Another embodiment of a responding cell activation protein of the present invention includes a CD45 protein comprising an extracellular domain of an isoform of a CD45 protein. A CD45 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 556 of CD45 protein, in which the initiating Met is residue 1. For human CD45 coding sequence, see Streuli et al., 1987, J.Exp. Med.166: 1548-1566; Genbank Y00638; and Swissprot P08575. According to the present invention, an isoform of a CD45 protein is any CD45 protein that is formed by the alternative splicing of exons A, B, and C of CD45; such isoforms are well known to those skilled in the art. CD45 isoforms of the present invention include an isoform in which none of the exons are spliced out, an isoform in which all of the exons are spliced out, an isoform in which any one of exons A, B, or C is spliced out, and an isoform in which any combination of exons A, B, and C are spliced out. A CD45 protein of the present invention more preferably comprises any isoform of the amino acid sequence disclosed in SEQ ID NO:13 and a leader sequence. A preferred leader sequence to be used with a CD45 protein of the present invention is disclosed in SEQ ID NO:39.

[0040] Another embodiment of a responding cell activation protein of the present invention includes a CD48 protein having a pseudovariable and a pseudoconstant extraellular domains of CD48 protein. A CD48 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 220 of CD48 protein, in which the initiating Met is residue 1. For human CD48 coding sequence, see Killeen et al., 1988, EMBO J.7: 3087-3091; Genbank X06341, M37766, M59904; and Swissprot P09326. A CD48 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:14 and a leader sequence. A preferred leader sequence to be used with a CD48 protein of the present invention is disclosed in SEQ ID NO:40.

[0041] Another embodiment of a responding cell activation protein of the present invention includes a B7.1 protein having a pseudovariable and a pseudoconstant extracellular domain of B7.1 protein. A B7.1 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 242 of B7.1 protein, in which the initiating Met is residue 1. For human B7.1 coding sequence, see Freeman et al., 1989, J. Immunol.143: 2714-2722; Genbank M27533. A B7.1 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:15 and a leader sequence. A preferred leader sequence to be used with a B7.1 protein of the present invention is disclosed in SEQ ID NO:41.

[0042] Another embodiment of a responding cell activation protein of the present invention includes a B7.2 protein having an extracellular domain of B7.2 protein. A B7.2 protein of the present invention preferably comprises the amino acid sequence extending from about residue 1 to about residue 74 of B7.2 protein, in which the initiating Met is residue 1. For human B7.2 coding sequence, see Kubota et al., 1990, J. Immunol.145, 3924-3931; Genbank M55561. A B7.2 protein of the present invention more preferably comprises the amino acid sequence disclosed in SEQ ID NO:16 and a leader sequence. An acceptable leader sequence to be used with a B7.2 protein of the present invention is disclosed, for example, in SEQ ID NO:29.

[0043] It is within the scope of the present invention that an RCA protein can be a portion of CD8 comprising a peptide that is capable of binding to a MHC Class I molecule in such a manner that cytotoxic T cell activity is regulated.

[0044] According to the present invention, at least a portion of an RCA protein of the present invention can be linked to at least a portion of an immunoglobulin (Ig) molecule to form an RCA:Ig chimeric molecule. An RCA protein is preferably linked to an Ig molecule by a peptide bond, which refers to the covalent chemical interaction between two amino acids. A preferred portion of an Ig molecule to link to an RCA protein includes the constant region of an immunoglobulin molecule. Suitable C_Land C_Hregions for use with an RCA:Ig chimeric molecule of the present invention include κ, λ, μ, γ1, γ2, γ2a, γ2b, γ3, γ4, α, α1, α2, σ and ε constant regions, with human κ, λ, μ, γ1, γ2, γ3, γ4, α1, α2, σ and ε constant regions being more preferred and human IgG2a being even more preferred. Any constant region of any antibody is suitable for use with the present invention. A preferred portion of a constant region to use includes at least one amino acid that enables an RCA:Ig molecule to be di-sulfide bonded to an SCM molecule of the present invention.

[0045] In a preferred embodiment, an RCA:Ig chimeric molecule of the present invention comprises a CD4:Ig chimeric molecule having the amino acid sequence disclosed in SEQ ID NO:17 and a leader sequence. A preferred leader sequence to be used with a CD4:Ig protein of the present invention is disclosed in SEQ ID NO:29.

[0046] In another preferred embodiment, an RCA:Ig chimeric molecule of the present invention comprises a CD2:Ig chimeric molecule having the amino acid sequence disclosed in SEQ ID NO:18 and a leader sequence. A preferred leader sequence to be used with a CD2:Ig protein of the present invention is disclosed in SEQ ID NO:30.

[0047] In another preferred embodiment, an RCA:Ig molecule of the present invention comprises a CD28:Ig chimeric molecule having the amino acid sequence disclosed in SEQ ID NO:19 and a leader sequence. A preferred leader sequence to be used with a CD28:Ig protein of the present invention is disclosed in SEQ ID NO:31.

[0048] In another preferred embodiment, an RCA:Ig chimeric molecule of the present invention comprises a CTLA4:Ig molecule having the amino acid sequence disclosed in SEQ ID NO:20 and a leader sequence. A preferred leader sequence to be used with a CTLA4:Ig protein of the present invention is disclosed in SEQ ID NO:32.

[0049] In another preferred embodiment, an RCA:Ig chimeric molecule of the present invention comprises a fas-ligand:Ig chimeric molecule having the amino aid sequence disclosed in SEQ ID NO:21 and a leader sequence. An acceptable leader sequence to be used with a Fas-ligand:Ig protein of the present invention is disclosed, for example, in SEQ ID NO:29.

[0050] One embodiment of a stimulator cell marker (SCM) molecule of the present invention includes a molecule capable of targeting an RCA protein of the present invention to a desired cell. In particular, an SCM molecule of the present invention includes, but is not limited to an immunoglobulin molecule (an antibody), a growth factor or a tissue-specific antigen. A suitable antibody for use as an SCM molecule of the present invention binds to a protein on the surface of a stimulator cell of the present invention. A preferred antibody of the present invention binds to a protein on the surface of a tissue graft cell or a cell involved in an autoimmune response. A more preferred antibody of the present invention binds to a major histocompatibility molecule (MHC), including Class I and Class II, or an organ-specific molecule, such as molecules expressed on the surface of kidney cells (e.g., sodium-potassium-chloride cotransporters; see Herbert et al., 1994, Clin. Invest.72: 692-694), liver cells (e.g., asialoglycoprotein receptor; see Merwin et al., 1994, Bioconjugate Chem.5: 612-620; bile acid receptors; see Krmaer et al., 1992; J. Bio. Chem.267: 18598-18604; LMA surface target molecules; see Stemerowicz et al., 1990, J.Clin. Lab. Immunol.32: 13-19); heart cells (e.g., heart specific auto-antibodies; see Neumann, et al., 1992, J. Immunol.148: 3806-3813; Traystman et al., 1991, Clin. Exp. Immunol.86: 291-298); pancreas cells or bone marrow cells (e.g., c-kit receptor; see Okayama et al., 1994, J. Immunol. Meth.169: 153-161; Bridell et al., 1992, Blood79: 3159-3167.

[0051] In a preferred embodiment, an antibody useful as an SCM molecule of the present invention includes the immunoglobulin molecules WFL4F12.3, WFL3C6.1, BB7.2, PA2.1, 2.28M1, MA2.1, GAP A3, A11.1M, 4D12, BB7.1, B27M1, ME1, BB7.6, MB40.2, MB40.2, B27M2, SFR8-B6, Genox 3.53, G2a.5 and SFR3-DR5 (each described in ATCC Catalogue of Cell Lines and Hybridomas, 7th Edition, 1992 American Type Culture Collection).

[0052] It is within the scope of the present invention that an antibody can include a full-length antibody, an Fab fragment, an F(ab′)₂fragment or an F_Vfragment of an antibody. An Fab fragment comprises one arm of an immunoglobulin molecule containing a light chain (VL region+C_Lregion) paired with the heavy chain variable region (V_Hregion) and a portion of a heavy chain constant region (C_Hregion) CH1 domain. An F(ab′)₂fragment corresponds to two di-sulfide bonded arms of an immunoglobulin molecule, each arm containing a L chain (V_Lregion+C_Lregion) paired with a V_Hregion and a CH1 domain. An F_Vfragment refers to a portion of an immunoglobulin molecule V_Lregion paired with a V_Hregion. Thus, an antibody of the present invention can include the variable (V), diversity (D) and junction (J) regions, the V,D, J and CH1 regions or the full-length protein of any preferred antibody described herein.

[0053] A suitable growth factor for use as an SCM molecule of the present invention binds to a receptor on the surface of a stimulator cell of the present invention. A preferred growth factor of the present invention binds to a receptor on the surface of a tissue graft cell or a cell involved in an autoimmune response. A more preferred growth factor of the present invention includes, but is not limited to thyroid stimulating hormone (TSH), vasopressin or corticotropin.

[0054] A suitable growth factor for use as an SCM molecule of the present invention binds to a tissue-specific marker on the surface of a stimulator cell of the present invention. A preferred SCM molecule of the present invention binds to a tissue specific marker on the surface of a tissue graft cell or a cell involved in an autoimmune response. A more preferred SCM molecule of the present invention includes, but is not limited to asialoglycoprotein receptor, (TSH) receptor, vasopressin receptor or corticotropin receptor.

[0055] According to the present invention, an RCA protein or an SCM molecule can comprise a derivative of an RCA protein or an SCM molecule. In accordance with the present invention, a “derivative” refers to any compound that is able to mimic the ability of a component of an RCA protein or an SCM molecule of the present invention. A derivative of an RCA protein or an SCM molecule can be an amino acid sequence that has been modified to decrease its susceptibility to degradation but that still retains binding activity. Other examples of derivatives include, but are not limited to, protein-based compounds, carbohydrate-based compounds, lipid-based compounds, nucleic acid-based compounds, natural organic compounds, synthetically derived organic compounds, anti-idiotypic antibodies and/or catalytic antibodies, or fragments thereof having desired T cell regulatory activity. A derivative can be obtained by, for example, screening libraries of natural and synthetic compounds for compounds capable of binding to a CD4 or CD2 co-receptor or an MHC antigen, as disclosed herein. A derivative of a CD4, CD2 or immunoglobulin molecule can also be obtained by, for example, rational drug design. In a rational drug design procedure, the three-dimensional structure of a compound of the present invention can be analyzed by, for example, nuclear magnetic resonance (NMR) or x-ray crystallography. The three-dimensional structure can then be used to predict structures of potential derivatives by, for example, computer modelling. The predicted derivative structures can then be produced by, for example, chemical synthesis, recombinant DNA technology, or by isolating a mimetope from a natural source (e.g., plants, animals, bacteria and fungi).

[0056] In particular, a derivative of an RCA protein or an SCM molecule can include amino acid substitution or insertion mutants into which an amino acid has been substituted or inserted, the amino acid being capable of forming a di-sulfide bond with another amino acid (e.g., a cysteine or a proline).

[0057] An RCA protein or an SCM molecule of the present invention can be soluble or membrane-bound. Amino acid sequences can be genetically engineered to create soluble forms by introducing a translational stop codon into the coding sequences of an RCA protein or an SCM molecule, upstream of the cytoplasmic domains and/or the hydrophobic transmembrane domains, using technologies known to those of skill in the art (e.g., site-directed mutagenesis or PCR modification). An example of a soluble CD4 molecule includes SEQ ID NO:17. An example of a soluble CD2 molecule includes SEQ ID NO:18. The resulting truncated CD4- or CD2-encoding nucleic acid molecules can be operatively linked to an expression vector containing one or more transcription or translation control regions to form a recombinant molecule, and the recombinant molecules can be expressed in a host cell.

[0058] Amino acid sequences can be genetically engineered to create membrane-bound forms by linking, or retaining the linkage of, the amino acid sequences of an RCA protein or an SCM molecule to amino acid sequences for transmembrane domains and/or amino acid sequences for cytoplasmic domains. Preferably, a membrane-form of an RCA protein or an SCM molecule of the present invention is designed such that the molecule can be inserted into the plasma membrane of a cell and remain associated with the membrane over time. An embodiment of a plasma membrane-bound form of an RCA protein or an SCM molecule preferably comprises a full-length transmembrane domain and cytoplasmic domain of an RCA protein or an SCM molecule. Such membrane-bound forms can be produced by operatively linking nucleic acid molecules encoding full-length RCA protein or SCM molecule to an expression vector containing one or more transcription or translation control regions to form a recombinant molecule, and expressing the recombinant molecules in a host cell. Alternatively, an RCA protein or an SCM molecule can be designed such that the molecule can be anchored in a lipid bilayer when incorporated into lipid-containing substrates by being added exogenously. As used herein, the term “anchoring” refers to the insertion of a molecule in a lipid-containing substrate such that any extracellular domains are on the outside of the substrate.

[0059] In one embodiment, an RCA protein or an SCM molecule of the present invention is produced by culturing a cell transformed with a recombinant molecule comprising a nucleic acid molecule operatively linked to an expression vector, in which the nucleic acid molecule comprises a nucleic acid sequence encoding an RCA protein or an SCM molecule.

[0060] A recombinant molecule of the present invention comprises a nucleic acid molecule, encoding an RCA protein or an SCM molecule of the present invention, operatively linked to a vector capable of being expressed in a host cell. As used herein, “operatively linked” refers to insertion of a nucleic acid sequence into an expression vector in such a manner that the sequence is capable of being expressed when transformed into a host cell. As used herein, an “expression vector” is an RNA or DNA vector capable of transforming a host cell and effecting expression of an appropriate nucleic acid sequence, preferably replicating within the host cell. An expression vector can be either prokaryotic or eukaryotic, and typically is a virus or a plasmid.

[0061] Construction of desired expression vectors can be performed by methods known to those skilled in the art and expression can be in eukaryotic or prokaryotic systems. Procaryotic systems typically used are bacterial strains including, but not limited to various strains of E. coli, various strains of bacillior various species of Pseudomonas. In prokaryotic systems, plasmids are used that contain replication sites and control sequences derived from a species suitable for use with a host cell. Control sequences can include, but are not limited to promoters, operators, enhancers, ribosome binding sites, and Shine-Dalgarno sequences. Expression systems useful in eukaryotic host cells comprise promoters derived from appropriate eukaryotic genes. Useful mammalian promoters include early and late promoters from SV40 or other viral promoters such as those derived from baculovirus, polyoma virus, adenovirus, bovine papilloma virus or avian sarcoma virus. Expression vectors of the present invention include any vectors that function (i.e., direct gene expression) in recombinant cells of the present invention including bacterial, yeast, other fungal, insect and mammalian cells. Preferred expression vectors of the present invention include vectors containing immunoglobulin H chain promoters and/or L chain promoters. In particular, an expression vector of the present invention includes a polyhedrin promotor for CD4 or CD2 for use in a baculovirus expression system or a CMV immediate early promotor or a RSV-LTR promotor for use in a eukaryotic cell system. Useful mammalian enhancers include immunoglobulin H chain enhancers and/or L chain enhancers. Particularly preferred expression vectors for use with the present invention include baculovirus transfer vectors pVL1393, pAcUw51 or pAcAB3. In a preferred embodiment, an expression vector of the present invention comprises pVLCD2-IgG2a or pVLCD4-IgG2a.

[0062] An expression system can be constructed from any of the foregoing control elements operatively linked to the nucleic acid sequences of the present invention using methods known to those of skill in the art (see, for example, Sambrook et al., ibid.).

[0063] Host cells of the present invention can be cells naturally capable of producing an RCA protein or an SCM molecule, or cells that are capable of producing an RCA protein or an SCM molecule when transfected with a nucleic acid molecule encoding such molecules. Host cells of the present invention include, but are not limited to bacterial, fungal, insect and mammalian cells. Suitable host cells include mammalian cell, preferably a fibroblast, a pluripotent progenitor cell, an epithelial cell, a neural cell, a T cell line and a B cell line.

[0064] In one embodiment, a host cell is transformed with: (1) a first recombinant molecule comprising a nucleic acid molecule operatively linked to an expression vector, the nucleic acid molecule having a sequence encoding a first protein including an RCA protein, particularly CD4, CD2, CD28, CTL4A, fas-ligand, CD5, CD7, CD9, CD11, CD18, CD27 CD43, CD45, CD48, B7.1 and B7.2, and even more particularly CD4, CD2, CD28, CTL4A, fas-ligand; and (2) a second recombinant molecule comprising a nucleic acid molecule operatively linked to an expression vector, the nucleic acid molecule having a sequence encoding a second protein comprising a stimulatory cell marker molecule that differentiates a host cell from a tissue graft cell to form a recombinant cell.

[0065] Transformed recombinant cells of the present invention are cultured under conditions effective to produce such an RCA protein and SCM molecule. The protein and molecule can then be recovered from the culture medium and/or the cells. Effective conditions to produce an RCA or SCM molecule include, but are not limited to appropriate culture media, cell density, temperature, pH and oxygen conditions. One of skill in the art can choose appropriate culture conditions based on the type of cell being cultured and the amount of protein one desires to produce.

[0066] Depending on the expression vector used for production, resultant molecules can either remain within the recombinant cell, be retained on the outer surface of the recombinant cell, or be secreted into the culture medium. As used herein, the term “recovering” refers to collecting the culture medium containing the molecule and/or recombinant cells. Recovery need not imply additional steps of separation or purification.

[0067] After recovery, an RCA protein or SCM molecule can be purified using a variety of standard protein purification techniques such as, but not limited to, size separation chromatography, reverse phase chromatography, chromatofocussing, hydroxyapatite adsorption and electrophoresis systems, affinity chromatography, ion exchange chromatography, ammonium sulfate precipitation, filtration, centrifugation, hydrophobic interaction chromatography, gel filtration chromatography, high pressure liquid chromatography and differential solubilization. Isolated proteins are preferably retrieved in substantially pure form. As used herein, “substantially pure” refers to a purity that allows for the effective use of the molecule as a heretofore described T cell veto molecule.

[0068] Soluble RCA proteins or SCM molecules of the present invention can be purified using, for example, immunoaffinity chromatography using an antibody capable of binding to CD4, CD2, CD28, CTL4A, fas-ligand or the C region of an immunoglobulin molecule or an antigen capable of binding to the V region of immunoglobulin molecule. RCA proteins or SCM molecules anchored in a lipid-containing substrate can be recovered by, for example, density gradient centrifugation techniques.

[0069] One aspect of the present invention is a method for producing a T cell veto molecule, comprising: (a) providing a first protein comprising an RCA protein, in particular CD4, CD2, CD28, CTL4A, fas-ligand protein, CD5 protein, CD7 protein, CD9 protein, CD11 protein, CD18 protein, CD27 protein, CD43 protein, CD45 protein, CD48 protein, B7.1 protein and B7.2 protein; (b) providing a second protein comprising an SCM molecule; and (c) linking the first protein to the second protein to form a chimeric molecule. As used herein, the term “linked” can refer to covalently attaching an RCA protein to an SCM molecule. A suitable reagent for the linking step includes any reagent capable of creating di-sulfide bonds between an RCA protein and an SCM molecule. Preferably, an RCA protein can be covalently associated to an SCM molecule by several methods including, for example, treatment with chemicals capable of linking di-sulfide bonds, glutaraldehyde linkage, photoaffinity labelling, treatment with carbodiimides and treatment with other cross-linking chemicals standard in the art. Preferably, an RCA protein can be covalently associated to an SCM molecule by treatment with chemicals capable of linking di-sulfide bonds, in particular using N-succinimidyl-3-1-(1-pyridyldthio)-propionate.

[0070] Following chemical cross-linking of an RCA protein to an SCM molecule, the resulting chimeric T cell veto molecules are recovered from those proteins that have not been linked using methods standard in the art. Preferably, T cell veto molecules are recovered by size separation chromatography.

[0071] A T cell veto molecule of the present invention preferably comprises a CD4:Ig protein having the amino acid sequence represented by SEQ ID NO:17, di-sulfide bonded to an antibody that binds specifically to an MHC molecule, in particular 14-4-4 to form the CD4:14 T cell veto molecule (see Examples section). A T cell veto molecule of the present invention also preferably comprises a CD2:Ig having the amino acid sequence represented by SEQ ID NO:18, di-sulfide bonded to an antibody that binds specifically to an MHC molecule, in particular 14-4-4 to form the CD2:14 T cell veto molecule.

[0072] According to the present invention, different embodiments of a T cell veto molecule of the present invention can be combined to form a composition of the present invention. A preferred composition comprises a CD4 protein linked to a target molecule that differentiates a host cell from a tissue graft cell, a chimeric molecule having a CD2 protein linked to target molecule that differentiates a host cell from a tissue graft cell, a chimeric molecule having a CD28 protein linked to target molecule that differentiates a host cell from a tissue graft cell, a chimeric molecule having a CTL4A protein linked to target molecule that differentiates a host cell from a tissue graft cell, a chimeric molecule having a fas-ligand protein linked to target molecule that differentiates a host cell from a tissue graft cell and mixtures thereof. A more preferred composition comprises CD4:14 T cell veto molecule, CD2:14 T cell veto molecule and mixtures thereof.

[0073] Another aspect of the present invention comprises formulating a T cell veto molecule of the present invention with a pharmacologically acceptable carrier to form a therapeutic composition of the present invention. As used herein, a “carrier” refers to any substance suitable as a vehicle for delivering a T cell veto molecule to a suitable in vitro or in vivo site of action. As such, carriers can act as an excipient for formulation of a therapeutic or experimental reagent containing a T cell veto molecule. Preferred carriers are capable of maintaining a T cell veto molecule in a form that is capable of binding to a stimulating cell and regulating the activity of a responding cell. Examples of such carriers include, but are not limited to water, phosphate buffered saline, saline, Ringer's solution, dextrose solution, serum-containing solutions, Hank's solution and other aqueous physiologically balanced solutions. Aqueous carriers can also contain suitable auxiliary substances required to approximate the physiological conditions of the recipient, for example, enhancement of chemical stability and isotonicity. Suitable auxiliary substances include, for example, sodium acetate, sodium chloride, sodium lactate, potassium chloride, calcium chloride, sorbitan monolaurate, triethanolamine oleate, and other substances used to produce phosphate buffer, Tris buffer and bicarbonate buffer. Auxiliary substances can also include preservatives, such as thimerosal, m or o-cresol, formalin and benzyl alcohol. Preferred auxiliary substances for aerosol delivery include surfactant substances nontoxic to a recipient, for example, esters or partial esters of fatty acids containing from about 6 to about 22 carbon atoms. Examples of esters include, caproic, octanoic, lauric, palmitic, stearic, linoleic, linolenic, olesteric and oleic acids. Therapeutic compositions of the present invention can be sterilized by conventional methods and/or lyophilized. Standard formulations can either be liquid injectables or solids which can be taken up in a suitable liquid as a suspension or solution for injection. Thus, in a non-liquid formulation, the excipient can comprise dextrose, human serum albumin, preservatives, etc., to which sterile water or saline can be added prior to administration.

[0074] A therapeutic composition can further comprise a T cell veto molecule combined with a compound capable of suppressing an immune response. Such regulatory compounds include, but are not limited to, immunosuppressive drugs or antibodies that specifically bind to interleukins.

[0075] Useful carriers for membrane-bound T cell veto molecules include any artificial or natural lipid-containing substrate, preferably cells, cellular membranes, liposomes and micelles. Cellular carriers of the present invention include cells capable of producing a T cell veto molecule. Preferred cells are disclosed in detail herein.

[0076] Embodiments of the present invention comprise the use of a T cell veto molecule, as disclosed in the present invention, to suppress the activity of immune cells in vivo or in vitro. In particular, a T cell veto molecule of the present invention is useful for administration to subjects to immunosuppress subjects against, for example, autoantigens, allergens, engraftments and agents perfused into subjects (i.e., blood factors and platelets). This process is particularly applicable for purposes of specific immunosuppression, and derives from the novel structure of a T cell veto molecule of the present invention. Immune cells refers to cells typically involved in an immune response (e.g., T cells, APCs etc.). Immunosuppression refers to inhibiting an immune response by, for example, killing or anergizing (i.e., diminishing reactivity by a T cell to an antigenic peptide) particular cells involved in the immune response.

[0077] One aspect of the present invention is a method to suppress an immune response comprising: (a) providing a chimeric molecule having a protein, selected from the group consisting of CD4, CD2, CD28, CTL4A, fas-ligand, CD5 protein, CD7 protein, CD9 protein, CD11 protein, CD18 protein, CD27 protein, CD43 protein, CD45 protein, CD48 protein, B7.1 protein and B7.2 protein linked to a responding cell marker molecule; and (b) exposing the chimeric molecule to an antigen presenting cell that can respond to the chimeric molecule, for a time and under conditions sufficient to reduce a cellular immune response of a T lymphocyte to an antigen. The present method is particularly useful for reducing the response of a T cell to an antigen comprising an alloantigen or a processed antigen.

[0078] Preferably, the chimeric molecule is contacted with the antigen presenting cell in vivo. Acceptable protocols to administer therapeutic compositions in vivo in an effective manner include individual dose size, number of doses, frequency of dose administration and mode of administration. Determination of such protocols can be accomplished by those skilled in the art depending upon a variety of variables, including the animal to be treated, the type of treatment being administered (e.g., graft rejection prevention or treatment of an autoimmune disease) and the stage of disease.

[0079] Effective doses to immunosuppress an animal include doses administered over time that are capable of alleviating an immune response by the animal. For example, a single suppressing dose can comprise an amount of a therapeutic composition of the present invention that sufficiently ablates an immune response against an alloantigen, compared with an immune response in the absence of the therapeutic composition. Alternatively, a single suppressing dose can comprise an amount of a therapeutic composition of the present invention that partially reduces an immune response against an alloantigen, compared with an immune response in the absence of the therapeutic composition. In this case, repeated administrations of the single dose could be given to an animal until the immune response is sufficiently ablated. A suitable single dose of a therapeutic composition of the present invention is a dose that is capable of substantially inhibiting a T cell response to an antigen when administered one or more times over a suitable time period. A single dose of a therapeutic composition preferably ranges from about 1 micrograms (μg) to about 100 milligrams (mg), more preferably ranges from about 10 μg to about 10 mg and even more preferably ranges being from about 100 μg to about 1 mg of a therapeutic composition per subject, of a toleragenic therapeutic reagent per subject. Effective doses to suppress an animal include doses administered over time that are capable of decreasing T cell activation to an antigen by an animal. For example, a first suppressing dose can comprise an amount of a therapeutic composition of the present invention that prevents an immune response when administered to an animal. A second suppressing dose can comprise a lesser amount of the same therapeutic composition than the first dose to continue prevention of an immune response. For example, if a first dose can comprise about 10⁶arbitrary units of a TLV molecule, then a second dose can comprise about 10³arbitrary units of a TLV molecule. Effective suppressing doses can comprise decreasing concentrations of a therapeutic composition of the present invention necessary to maintain an animal in a suppressed state, such that the animal does not have an immune response to subsequent exposure to an antigen.

[0080] The manner of administration of a therapeutic composition of the present invention can depend upon the particular purpose for the delivery (e.g., treatment of disease or prevention of graft rejection), the overall health and condition of the recipient and the judgement of the physician or technician administering the therapeutic composition. A therapeutic composition of the present invention can be administered to an animal using a variety of methods. Such delivery methods can include parenteral, topical, oral or local administration, such as intradermally or by aerosol. A therapeutic composition can be administered in a variety of unit dosage forms depending upon the method of administration. For example, unit dosage forms suitable for oral administration to the intestinal region of an animal include powder, tablets, pills and capsules. Preferred delivery methods for a therapeutic composition of the present invention include intravenous administration and local administration by, for example, injection or topical administration. For particular modes of delivery, a therapeutic composition of the present invention can be formulated in an excipient of the present invention. A therapeutic reagent of the present invention can be administered to any animal, preferably to mammals, and more preferably to humans.

[0081] As an example of a T cell veto molecule-mediated immunosuppressive therapeutic process, the sequence of steps that can be executed for inducing suppression in a prospective transplant recipient for the allogeneic MHC molecule of the transplant donor, in order to prevent immunological rejection of the graft following transplantation, are as follows:

[0082] (a) gene constructs are assembled for producing human CD4, human CD2 and specific antibodies that bind to MHC Class II molecules. In each case, the coding sequence for the extracellular domain of CD4 or CD2 is subcloned into pVL1393 vector.

[0083] (b) The subcloned coding sequences are transfected into insect cells in order to produce recombinant CD4, CD2 and immunoglobulin protein. The transfected cells are maintained in serum-free, protein-free medium.

[0084] (c) Dimers of soluble human CD4 or human CD2 are harvested from the cell cultures by the following method. Tissue culture supernatant, adjusted to pH 8.5, is filtered through a Mono-Q-Sepharose column (Pharmacia, Uppsala, Sweden). The flow-though is loaded onto a Wheatgerm-Lectin-Sepharose column (Pharmacia), and CD4 or CD2 are eluted with 5% N-acetyl-glucosamine. The eluate is dialyzed against 20 mM NaC₂H₃O₂(pH 5.4, Sigma), concentrated and loaded onto Mono-S-Sepharose (Pharmacia) pre-equilibrated with 20 mM HEPES (pH 8.0, Sigma). Soluble CD4 or CD2 is eluted as the first peak of a NaCl-gradient (20 mM to 500 mM, Sigma) in 20 mM HEPES (pH 8.0) and dialyzed against PBS. The purity of the CD4 or CD2 dimers is analyzed by resolution using SDS-PAGE gel electrophoresis. Immunoglobulin molecules are purified from tissue-culture supernatant on a Protein A-Sepharose column (Pharmacia) using a standard protocol.

[0085] (d) Soluble CD4 or CD2, and immunoglobulin are cross-linked using the heterobifunctional cross-linker, N-succinimidyl-3-(1-pyridyldithio)-propionate (SPDP, Pharmacia) according to standard methods, at pH 7.4. Cross-linked proteins are purified from unreacted proteins and SPDP by passage of the preparation over on a Sephadex G25 column (Pharmacia).

[0086] (e) A subject who is to undergo a transplant is assessed for alloreactivity to donor allo-MHC by isolating peripheral blood mononuclear cells (PBMC) from the prospective transplant recipient's blood, and setting up a mixed lymphocyte reaction (MLR) with the recipient's PBMC as responders and irradiated (1500 rads) donor PBMC as stimulators. If a significant proliferative response is noted, a therapeutic composition comprising a TLV molecule or composition thereof, corresponding to the donor allo-MHC, are infused intravenously into the graft recipient about 4 to about 1 weeks prior to the planned transplantation procedure.

[0087] (f) At about 2 to about 1 weeks prior to the transplantation date, the MLR is repeated, and if a residual proliferative response between recipient responders and donor stimulators persists, the therapeutic composition is reinfused into the graft recipient.

[0088] (g) The MIR is repeated post-transplantation to assess the need for booster doses to the graft recipient of a therapeutic composition which can be administered systemically or topically, as required.

[0089] Another example of a TLV molecule-mediated immunosuppressive therapeutic process, the sequence of steps (a) through (d) from the foregoing example are repeated and the cells of a graft are coated with a therapeutic composition of the present invention, and then the graft is transplanted into a recipient. The process is applicable to a variety of graft types, including vascularized solid tissue (e.g., kidney, heart, liver, lung and skin) and dispersed cellular populations (e.g., bone marrow cells). Treatment of a solid graft can comprise the steps of: (1) perfusing the donor organ at the time of surgery and prior to its resection, with about 100 μg/ml of a therapeutic composition comprising TLV molecules contained in normal saline via a bolus injection into a vessel entering the organ; and (2) catherizing the vessel, resecting the organ and storing the organ in a solution supplemented with a therapeutic composition of the present invention until transplantation. Treatment of a dispersed cell population can comprise the steps of: (1) aspirating a cell population from a donor and separating the cells from undesired blood elements using methods standard in the art; and (2) resuspending the isolated donor cells in about 10 μg/ml of a therapeutic composition comprising TLV molecules contained in normal saline for about 2 hours at 5° C. until transplantation.

[0090] It is within the scope of the invention that the pre-treatment of a recipient and the treatment of a graft tissue can be performed separately or in combination, depending on the parameters of the transplantation (e.g., donor-recipient allotype match, type of tissue etc.). It is also within the scope of the present invention that modifications can be made to the therapeutic processes disclosed herein. For example, subjects afflicted with autoimmune disease can treated by systemically administering a therapeutic composition of the present invention using similar steps as those outlined for the pre-treatment of graft recipients. Alternatively, a therapeutic composition can be administered to subjects afflicted with localized autoimmune diseases, such as rheumatoid arthritis, by directly injecting the composition into a diseased area such as a joint. Other examples of autoimmune diseases that can be treated using a therapeutic composition of the present invention include systemic lupus erythematosus, myasthenia gravis, rheumatoid arthritis, insulin-dependent diabetes mellitus, multiple sclerosis, celiac disease, autoimmune thyroiditis, Addison's disease, Graves' disease and rheumatic carditis.

[0091] One embodiment of a therapeutic method of the present invention includes administering a high dose of corticosteroids, for example dexamethason in two injections (about 1 mg per day for two days, followed by the step of administering a T cell veto molecule of the present invention for the next four weeks, at a concentration of about 1 mg per injection (intravenous) twice a week.

[0092] The following experimental results are provided for purposes of illustration and are not intended to limit the scope of the invention.

[0093] This example describes the production of chimeric cDNA clones encoding CD2:Ig or CD4:Ig molecules.

[0094] A. Production of Human Blood or 15.5.5. cDNA

[0095] Two separate samples of cDNA were prepared using mRNA isolated from human blood or 15.5.5 cells (described in Ozato et al., 1980, J. Immunol.124: 533) by the following method. About 2 mL Trizol (Gibco-BRL, Gaithersburg, Md.) was added to the cells. The cells were then extracted 1 time with 100% chloroform. The RNA in the aqueous phase was treated with 100% isopropyl alcohol and the resulting precipitate was pelleted at 12,000×rpm for 10 minutes. The resulting pellet containing RNA was resuspended in water containing 0.1% diethylpyrocarbonate (DEPC).

[0096] The RNA was then reverse transcribed into cDNA according to methods standard in the art using reverse transcriptase, oligo dT as a primer and a mixture of nucleotides.

[0097] B. Production of CD2, CD4 and Immunoglobulin cDNA

[0098] cDNA encoding the extracellular domains of CD2 was produced by polymerase chain reaction (PCR) amplification using the following method. Human cDNA described in Section A was combined with CD2 sense primer (5′ CGC TCT AGA ATG AGC TTT CCA TGT AAA TTT GTA 3′; SEQ ID NO:22) and CD2 anti-sense primer (5′ TGT GGG CCC TCT GGG CTC GTC CAG ACC TTT CTC TGG 3′; SEQ ID NO:23). The mixture was amplified for 3 cycles at 94° C. (60 sec.), 50° C. (30 sec.), 72° C. (60 sec.) followed by 27 cycles at 94° C. (60 sec.), 55° C. (30 sec.), and 72° C. (60 sec.). A 10 minute 72° C. final elongation was then performed to produce amplified CD2 cDNA.

[0099] cDNA encoding the two amino terminal domains of CD4 was produced by PCR amplification using the following method. Human cDNA described in Section A was combined with CD4 sense primer (5′ CGC TCT AGA ATG AAC CGG GGA GTC CCT 3′; SEQ ID NO:24) and CD4 anti-sense primer (5′ GGG CCC TCT GGG CTC AGC TAG CAC CAC GAT GTC T 3′; SEQ ID NO:25). The mixture was then amplified as described above to produce amplified CD4 cDNA.

[0100] cDNA encoding the Fc domain of the 15.5.5 anti-class I (IgG2a isotype) monoclonal antibody was produced as follows. The cDNA produced from the 15.5.5 cell cDNA described in Section A was mixed with either a first IgG2a sense primer(CD2 sense primer: 5′ CCA GAG AAA GGT CTG GAC GAG CCC AGA GGG CCC AC 3′; SEQ ID NO:26) or a second IgG2a sense primer (CD4 sense primer: 5′ AGA CAT CGT GGT GCT AGC TGA GCC CAG AGG GCC C 3′; SEQ ID NO:27), and IgG2a anti-sense primer (5′ GGC GAA TTC TTT ACC CGG AGT CCG GGA GAA GCT 3′; SEQ ID NO:28). The cDNAs were amplified using the conditions described in above to produce a first and a second IgG2a Fc domain cDNA.

[0101] C. Production of Chimeric Molecules

[0102] PCR amplification was then used to link cDNA encoding the extracellular domains of CD2 or CD4 to cDNA encoding the Fc domain of the 15.5.5 anti-class I monoclonal antibody (I.e., CD2-IgG2a fusion cDNA and CD4-IgG2a fusion cDNA).

[0103] CD2-IgG2a fusion cDNA was produced by combining cDNA encoding the extracellular domains of CD2 with cDNA encoding the Fc domain of 15.5.5 antibody produced using the CD2 sense primer. CD4-IgG2a fusion cDNA was produced by combining cDNA encoding the amino terminal domains of CD4 with cDNA encoding the Fc domain of 15.5.5 antibody produced using the CD4 sense primer. Both of the foregoing mixtures were amplified using the amplification conditions described in section B.

[0104] This example describes the production of expression vectors encoding chimeric CD2:IgG2a or CD4:IgG2a fusion molecules.

[0105] Each of the CD2:IgG2a or CD4:IgG2a fusion cDNA described in Example 1 were purified on a 1.0% agarose gel and recovered by Geneclean Kit (BIO 101 Inc., LaJolla, Calif.). The gel purified CD2:IgG2a fragment was direcly ligated into PCRII vector (Invitrogen, San Diego, Calif.). The CD4:IgG2a fragment was also directly ligated into the PCRII vector. The PCRII vector is a linear vector with poly T overhangs for direct ligation.

[0106] InvaF′ E. Coli(obtained from Invitrogen) were then transformed with either pCD2:IgG2a or pCD4:IgG2a and the colonies were grown on LB plates containing about 100 mg/mL ampicillin. Resulting colonies were screened by PCR amplification using appropriate primers.

[0107] pCD2:IgG2a or pCD4:IgG2a plasmid was then isolated from bacterial colonies by propagating in liquid culture comprising LB broth and 50 mg/mL ampicillin and purifying the plasmid using methods standard in the art (see Sambrook et al., ibid.). Purified plasmid DNA was then digested with XbaI and EcoRI to yield a fragment of cDNA encoding a CD2-IgG2a fusion molecule or cDNA encoding a CD4-IgG2a fusion molecule. These fragments were then gel-purified as described above and separately ligated into the baculovirus transfer vector PVL 1393 (obtained from Pharmingen, San Diego, Calif.) which had previously been digested with XbaI and EcoRI, to form the expression vectors pVLCD2:IgG2a or pVLCD4:IgG2a. The expression vectors were then transformed into InvaF′ E. Coli, selected as described above and frozen at −70° C. for later use.

[0108] This Example shows that a CD4:anti-H-2^d, T lymphocyte veto molecule of the present invention, which is targeted to the class II MHC of allogeneic stimulator cells in a T cell proliferation assay, demonstrates significant and specific inhibition of CD4+T-cell responses.

[0109] A transfectant secreting a soluble form of CD4 was obtained from K. Karjalainen (Basel Institute for Immunology). This material was purified by affinity chromatography and chemically (SPDP) cross-linked to the monoclonal antibody 14-4-4 which binds to certain class II MHC molecules (anti-H-2^d, but not anti-H-2^b) to form a hybrid antibody T lymphocyte veto molecule of the present invention.

[0110] Lymph node cells (50 or 200×10⁵per culture), which were enriched for CD4+ T-cells by two-step panning (purity >90% CD4+ T-cells), were challenged with irradiated stimulator cells (200×10⁵) in triplicate cultures (FIG. 1). These mixed lymphocyte cultures (MLCs) were set up in two combinations, C57BL/6 anti-BALB/c, where C57BL/6 cells are responders and BALB/c cells are stimulators (FIGS. 1A and 1B); and BALB/c anti-C57BL/6, where BALB/c cells are responders and C57BL/6 cells are stimulators (FIGS. 1C and 1D). Whereas in the first set of MLCs the hybrid antibody can bind to the stimulator cells (BALB/c H-2^d), in the second set it will not bind to the stimulator cells (C57BL/6 H-2^b), but will bind instead to the responder cells (BALB/c). Either the hybrid antibody, its non-linked components or medium only (nothing) was added to the MLCs. After 3 days, the cultures were pulsed with [³H]-thymidine for 18 hours and then harvested.

[0111] Inhibition of proliferation was only observed when the hybrid antibody bound to the stimulators (FIGS. 1A and 1B), but not when the antibody bound to the responders (FIGS. 1C and 1D). In addition, supplementing cultures with non-linked components of the hybrid antibody, soluble CD4 and 14-4-4, did not result in any reduction of the response. Therefore, in order to inhibit proliferation of allo-reactive CD4+T-cells, the CD4 molecule has to be linked to 14-4-4 in a hybrid antibody and the hybrid antibody has to bind to the stimulator cells. Thus, hybrid antibody-mdeiated ‘veto’ is effective and specific.

[0112] To determine whether other T-cell functions besides proliferation were affected,. MLCs (C57BL/6 anti-BALB/c) were set up with CD4+ T-cells. C57BL/6 CD4+ T-cell responders (200×10⁵per culture) were challenged with irradiated BALB/c stimulator cells (200×10⁵per culture). Either the hybrid antibody (shown in FIG. 2 as ●) or its non-linked components (shown in FIG. 2 as ◯) were added. After 3 days supernatants were harvested and tested for the presence of IL-2 and IL-4 by adding the supernatants to HT-2 cells in different dilutions [neat (1), 30% (0.3), 10% (0.1) and 3% (0.3)]. After 18 hours HT-2 cells were pulsed with [3H]-thymidine. As shown in a representative experiment (FIG. 2), only the hybrid antibody was able to cause inhibition of IL-2/IL-4 production; its non-linked components failed to do so.

[0113] The foregoing experiment establishes the feasibility of this hybrid antibody inhibition by showing that ‘veto’ can be adapted for the inhibition of class II-reactive T-cells.

[0114] While various embodiments of the present invention have been described in detail, it is apparent that modifications and adaptations of those embodiments will occur to those skilled in the art. It is to be expressly understood, however, that such modifications and adaptations are within the scope of the present invention, as set forth in the following claims: