Anti human ovarian cancer-anti CD3 bispecific antibody

[0001] 1. Field of the Invention

[0002] The present invention relates to an anti-cancer bispecific antibody constructed by gene engineering, nucleotide sequences encoding the said bispecific antibody, the expression vectors containing the said nucleotide sequences and host cells containing the vectors.

[0003] 2. Description of the Related Art

[0004] Different from natural antibodies, two antigen-binding sites of bispecific antibody (BsAb) bear different specificities, therefore, it is bivalent in chemical structure but monovalent in binding function. BsAb directed to both tumor-associated antigens and trigger molecules on effector cells can recruit the immunological effector cells to tumor sites efficiently and activate them to kill tumor cells specifically. BsAbs are hybrid proteins that can be generated by chemical cross-link, hybridoma technology or genetic methods. In the chemical cross-link method, two kinds of monoclonal antibodies and fragments thereof were dissociated by reductants to generate monovalent antibodies and fragments thereof. The resulting BsAb is constructed via chemical cross-linking of two monovalent antibodies and fragments thereof from different parental antibodies. This strategy can be used for rapid production of BsAb in large scale but BsAb can be inactivated sometimes during cross-link and it is difficult to guarantee the homogeneity of products. Another strategy for production of BsAb is hybridoma technology by which an established hybridoma cell line secreting one monoclonal antibody was fused to spleen cells immunized with the other antigen or two established hybridoma cell lines secreting two different monoclonal antibodies were fused each other to create hybrid hybridomas. The former resulting hybridoma is called dimeric hybridoma and tetrameric hybridoma. Generally, BsAb produced by hybridoma technology keeps high bioactivities. However, the procedures are tedious and time-consuming and it is not easy to isolate BsAb from other non-active and unwanted antibodies generated simultaneously. These BsAb formats encountered another predictable problems: too large size and murine components contained in BsAb are immunogenic in patients and will induce the production of human anti-mouse antibodies (HAMA), which may prevent reuse of these BsAbs in clinic. Furthermore, production and purification of these formats of BsAb are expensive, which limits the application of BsAbs in clinic. Replacement of these traditional methods with gene recombination approaches has accelerated progress in this area. Based on the technology of small molecular antibodies, production of BsAb by gene engineering has advantages over those described above, such as the stability of process, large scale production, low cost and easy-to-use. Gene engineering has led to the development of various small molecular BsAb formats by connecting two different kinds of scFvs. There are three kinds of BsAb formats classified by different links. (1) mini-antibodies are heterodimers assembled by connecting two scFv fragments together with an oligomerized domain (e.g. leucine zipper motifs derived from Fos or Jun transcription factors). (2) Diabodies are non-covalently associated dimmers which are assembled by two single chains VH1-VL2 and VH2-VL1, both connected by a short linker that is too short to allow pairing between V-domains from the same chain. Thus, each chain alone is not capable of binding antigen, but co-expression of two chains (VH₁-VL₂ and VH₂-VL₁) leads to assembly of heterodimeric diabodies which can bind to two kinds of antigens. (3) ScBsAb: a interlinker was used for connecting two different scFvs with different specificities and ScBsAb was expressed in the host cells as a single polypeptide. The intralinker between two domains within scFv is often (Gly₄Ser)₃. As for the interlinker between two scFvs, there are two strategies for designing it. For the purpose of avoiding false paring between heterogenous variable regions, the interlinker is often a short peptide linker less than ten amino acid residues such as Gly₄Ser. Another strategy is to select a longer linker for the interlinker. In our lab, an interlinker with 25 amino acids named 205c′, devised by Gruber in construction anti-TCR×anti-fluorescent scBsAb, was cited for one of three interlinkers. Another two interlinkers named Fc (26 residues) and HSA were devised, which both result in the proper folding of two scFvs and the formation of BsAb with two antigen-binding sites with high activities. In a word, the most important for designing interlinkers is to ensure the proper pairing between variable domains and folding of proteins, resulting in the formation of BsAb which maintains biological activities and stability. Some novel properties for facilitating purification and extending the plasma half-life time should be introduced.

[0005] BsAb-mediated immunotherapy plays a promising role in the clinical biotherapy for tumors. The following is two characteristics of BsAb. First, tumor-killing effects mediated by BsAb are based on stimulating the immune system, highly specific with tumors and free of MHC restriction. Second, due to lacking Fc domain, BsAb is harmless to normal tissues. Therefore, BsAb-mediated therapy is the complementarity of traditional methods such as surgery, radiotherapy and chemotherapy. The major effect of this approach is based on clearing up sub-clinical residuals and preventing or eliminating the tumor from recurrence and metastasis. BsAb can not only cure tumors but also stimulate the immune system to provide and keep the immune protection for a long time. Based on results of experiments in mouse and clinic, BsAb prepared for trial use should have at least five characteristics as follows: {circle around (1)} It targets to the relevant tumor antigens with high specificity and affinity; {circle around (2)} It can bind monovalently to trigger factors on effector cells-cytotoxic cells and result in cross link only when BsAb binds to tumor antigens due to lack of Fc domain; {circle around (3)} BsAb is able to promote the effective cytotoxicity and inflammation selectively produced by the corresponding group of leukocytes at tumor sites; {circle around (4)} BsAb must be humanized to minimize induction of human anti-mouse response following repeated uses; Finally, {circle around (5)} BsAb should be not only small enough to penetrate into tumors but also large enough to keep in the circulation for a sufficient time.

[0006] Based on these points described above, numerous BsAbs triggering many kinds of immune effector cells and targeting different tumor cells have been developed in the past few years, wherein the effector cells include T lymphocytes, NK cells, monocytes, macropghages, neutrophils, LAK cells (lymphokine-activated cytotoxic cells) and TIL cells (tumor infiltrating lymphocytes) etc. T cells are commonly recognized as the major specific cells for immune responses. CD3 expressed on the surface of all mature T cells is the common surface marker for T cells. CD3 binds to TCR non-covalently, forming the whole TCR-CD3 complex, and involves in immune responses against antigen stimulus. Now CD3 is surface trigger molecule on immune effector cells used most widely and successfully. Following anti-CD3 antibody within BsAb binds to CD3 molecule on the surface of T cells, numerous effects as follows will be produced to kill tumor cells. These effects include: (1) proliferation and differentiation of T cells. Firstly, BsAb can activate the rest T cells, resulting in Th cell and Tc cell derived from the premature effector T cells with CD4⁺ or CD8⁺. Secondly, BsAb can activate numerous memory cells to proliferate and differentiate into effector T cells which will attack and kill tumor cells. The number of effector cells is directly related to the rate of tumor elimination. (2) release of cytokines: CD4⁺ Th cells activated by BsAb can secrete a great deal of IL-2. IL-2 not only stimulates the proliferation of Th cells in autocrine, but also activates naive CD8⁺ T cells in paracrine to become Tc cells, resulting in enlargement of cytotoxicity of Tc cells. In addition, IL-2 is a costimulating signal for activating T cells. Therefore, IL-2 plays a vital role in BsAb-mediated immune effects. Some other cytokines, such as TNF-α and IFN—Y are produced in the process of T-cell activation and can produce ‘stander-by’ effect by inhibiting the growth of ‘stander-by’ tumor cells through the medium among cells. (3) cytotoxicity: In vitro experiments indicate that mediated by BsAb, CD8⁺ Tc interacts with tumor cells directly, releases cytotoxic materials through granule exocytosis and lyses target cells, which takes place rapidly usually within 4-6 hours following targeting tumor cells. The major components in the cytotoxic materials are perforin and serine easterases or granzymes. Perforins can attack the plasma membrane and form ion channels, thus causing entry of plenty of ions and water, resulting in the lysis and necrosis of cells while granzymes are similar to lymphotoxin, capable of activating DNases in the cell, thus causing lysis of nucleic DNA, resulting in the apoptosis of target cells.

[0007] Currently, Fv fragment is widely used for construction of BsAb, since it is the minimal unit with the complete antigen-binding site, small (about ⅙ of the whole antibody), absence of Fc domain, lower immunogenicity, easily penetration into the wall of blood vessels and solid tumors, easily expressed in E. coli and lower production cost. However, Fv is unstable and easy to dissociate in vivo because the covalent bond between VH and VL domains is unable to generate. In order to improve the stability of Fv fragment, a polypeptide intralinker between VH and VL domains is used to form so called ScFv. The intralinker is commonly a short flexible peptide with 15 amino acid residues in length such as (Gly₄Ser)₃. In the present invention, the said intralinker was used in both ScFvs. As mentioned above, there are several methods to construct BsAb. In the present invention, we constructed the single-chain bispecific antibody (ScBsAb) connected by an interlinker. The general principle for designing interlinkers is to ensure the proper pairing and folding of variable domains from two antibodies, furthermore keep the biological activities and stability of the said antibody. In addition, the said interlinker should endow BsAb some novel properties, such as easy purification and prolonged half-life time in the plasma etc. Two kinds of interlinkers, Fc and HSA originally designed in the present invention as a useful provide a novel idea for designing interlinkers. 205c′ interlinker cited from literature was used to compare and verify the efficacy of interlinkers designed in the present invention and the value of the said design in construction of anti-ovarian BsAb. (1) Design of Fc interlinker: in order to minimize the immunogenicity and molecule size, small molecular antibodies are absent of Fv domains resulting in lack of several biological function, such as ADCC, CDC and the classic complement activating pathway. To resolve this problem, we devised the interlinkers to make up the said shortcoming of genetically engineered antibodies. IgG1 is the most potent molecule in inducing ADCC and CDC among four subtypes of IgGs. It can induce the classic complement activating pathway by combining to C1q with its C-terminal sequence of CH₂, wherein Gly318, Lys320 and Lys322 sites locate in the surface of Fc molecule to form a cluster in conformation and combine to C1q directly. In addition, Asn297 of CH₂ contains a glycosylation site which is vital to the effect of ADCC and CDC induced by Fc. Thus, a fragment from 297 to 322 of CH₂ in human IgG was selected to construct the interlinker of ScBsAb. It has 26 residues in length and contains the glycosylation site Asn297, the C1q-binding site Glu318, Lys320 and Lys322 etc as well as an EcoRI site at the 5′ end and a SacI site at the 3′ end for the purpose of gene clone. ScBsAb constructed by this strategy is expected to have the prolonged half life time in vivo and the effect for inducing CDC similar to Fc. (2) HSA interlinker: Because of the smaller size, small molecular antibodies have fast renal clearance, which results in a short retention time in immunotherapy thus causing curative effects unperfect although the shorter half life time is benefit for immunoimaging diagnosis of tumors. Therefore, we devised HSA interlinker which is expected to prolong the half life time of ScBsAb in vivo, improve the stability and solubility of ScBsAb. HSA (human serum album) is an important component of human serum. It is widely used as a stable natural vector because of its stability, several week half-life time, lack of specific enzymatic and immunological activities and slow clearance in liver. It was showed in research that the stability of proteins fused with HSA increased 20 to 40 times in animals. HSA molecule with 585 amino acids in length is composed of three domains, wherein the third domain DIII alone possesses the vector function of the whole molecule. Herein, a fragment with 25 residues from 403 to 427 of DIII domain, which is lack of Cys but rich in polar amino acids in HSA was used as another interlinker in construction of BsAb to improve the stability and prolong the half-life time in vivo. (3) 205c′ interlinker: This interlinker is 25 amino acids in length devised by Gruber in construction of anti-TCRxanti-fluorescence scBsAb. The purpose of utilizing 205c′ interlinker was to compare and verify the efficacy of interlinkers designed in the present invention and the value of the said design in construction of anti-ovarian BsAb.

[0008] Facing HAMA problem induced by murine antibodies in clinic that strongly limits repeated use and dose, further causing the poor curative efficacy, murine antibodies must be humanized to minimize their heterology, which is the urgent affairs for preparation of antibodies used in clinic. The scFv against CD3 molecule in ScBsAb used in the present invention is a reshaped antibody through humanization. The reshaped antibody, so-called CDR-grafted antibody or humanized antibody, is constructed by grafting complementarity-determing regions (CDRs) from the variable domains of rodent antibodies into the framemork regions of human variable domains. The space structure of antigen-binding sites of antibodies is mainly determined by six CDRs of variable domains. The said CDRs form three loops, which have decisive effects in antigen-antibody recognition, in the upper site of variable domains supported by four β-sheet domains. The said reshaped antibody remains the antigen-binding ability as well as the most characteristics of human antibody, therefore minimizing HAMA response effectively.

[0009] Ovarian cancer remains the leading cause of death from gynecologic malignancies. The five-year survival rate maintains only 30%. Because of lack of the effective diagnostic methods for ovarian cancer located deep into pelvic cavity and the vague symptoms associated in the earlier stage, most patients with ovarian cancer present with an advanced stage of cancer. Although methods of surgical operation advance, drugs of chemotherapy renew and treatments of radiotherapy improve stepwise, the prognosis of ovarian cancer didn't improve at all. The easy recurrence after surgical operation and the side effects and drug tolerance after repeated use of chemotherapy strongly influence the effects of treatments. Therefore, specific diagnostic methods for earlier stage of cancer and the timely clearance of residual focuses are the key step for improving prognosis. BsAb against the related antigens of ovarian cells is regarded as powerful tools in clinic.

[0010] The object of the present invention is to provide a biological preparation with low toxicity, high efficiency and cost-effectiveness against ovarian cancers-anti-human ovarian cancer×anti-human CD3 bispecific antibody developed by gene engineering technology.

[0011] Another object of the present invention is to provide a nucleotide sequence encoding the said BsAb.

[0012] Another object of the present invention is to provide a vector for the said nucleotide sequence.

[0013] Further object of the present invention is to provide a host cell transformed by the expression vector used in the invention.

[0014] In addition, based on the context of the disclosure, another aspects of the present invention will be apparent to those with skill in the art.

[0028] One antibody molecule consists of two identical heavy chains and light chains, each of which is composed of one variable region and one or more constant region. The variable region is responsible for binding with antigens and the constant region is mainly responsible for binding with effect molecules. There are three flexible loops with high variability in each variable region, termed complementarity-determining regions (CDRs), which are mainly responsible for recognizing antigens. The other parts of variable regions, are composed of the rigid β-sheets and support the so-called framework regions (FRs). CDRs and FRs arrange alternatively forming the “Sandwich” structure. In the present invention, the used terms have meanings as follows:

[0029] “Fab antibody” refers to a heterodimer formed by Fd fragment (consisting of heavy chain V_H and CH1) and the whole light chain which is connected to the former by a interchain disulfide. The size of “Fab antibody” is ⅓ of the whole antibody and it contains only one antigen binding site.

[0030] “Single chain antibody (scFv)” refers to an antibody fragment constructed by gene engineering and a recombinant protein consisting of heavy chain variable region (V_H) and light chain variable region (V_L) which is joined to the former by a linker. The size of scFv is about ⅙ of the whole antibody.

[0031] “Single domain antibody” consists of the heavy chain variable region (V_H) or the light chain variable region (V_L). Since this antibody fragment consists of only one domain, it is called single domain antibody. The size of this fragment is 1/12 of the whole antibody.

[0032] “Minimal recognizing unit (MRU)” consists of single CDR and its size is about 1/70 or 1/80 of the whole antibody.

[0033] “Reshaping antibody” is also called “CDR-grafted antibody”. Using gene synthesis or site-directed mutation, CDRs in human antibody are replaced by those from murine antibody, therefore the antigen-binding specificity of murine antibody was kept. However, it should be considered that some amino acid residues in human FRs are capable of interfering the conformation of antigen-binding site formed by murine CDRs. Therefore, individual amino acid residues in FRs need be mutated to obtain antibodies humanized to the most extent and with high affinity.

[0034] The present invention provides a genetically engineered bispecific antibody against ovarian cancers, wherein the antibody is the whole antibody molecule, Fab, single domain antibody or single-chain Fv (ScFv).

[0035] Preferably, the genetically engineered bispecific antibody against ovarian cancer consists of two different single-chain antibodies.

[0036] In the present invention, the genetically engineered bispecific antibody against ovarian cancers is preferably a hybrid protein consisting of the single-chain Fv against ovarian cancer and the reshaped single-chain Fv against human CD3. The said proteins is the expressed products, which are capable of activating T lymphocytes to kill ovarian cancer cells specifically, of anti-ovarian scFv and anti-CD3 reshaped scFv connected by three interlinkers.

[0037] In bispecific antibodies of the present invention, the said anti-ovarian scFv can contain the amino acid sequence of heavy chain variable domain as follows:

[0038]

1	Glu Val Gln Leu Gln Glu Ser Gly Pro Glu
11	Val Lys Lys Pro Gly Glu Thr Val Arg Ile
21	Ser Cys Lys Ala Ser Gly Tyr Thr Phe Thr
31	Thr Ala Gly Met Gln Trp Val Gln Lys Met
41	Pro Gly Lys Gly Leu Lys Trp Leu Gly Trp
51	Ile Asn Thr Asn Ser Glu Val Pro Lys Tyr
61	Ala Glu Asp Phe Arg Gly Arg Phe Ala Phe
71	Ser Leu Glu Thr Ser Ala Ser Thr Ala Tyr
81	Leu Gln Ile Ser Asn Leu Lys Asn Glu Asp
91	Thr Ala Thr Phe Phe Cys Ala Arg Ser Phe
101	Thr Trp Gly Thr Met Asp Tyr Trp Gly Gln
111	Gly Thr Thr Val Thr Val Ser Ser

[0039] In bispecific antibodies of the present invention, the said anti-ovarian scFv can contain the amino acid sequence of light chain variable domain as follows:

[0040]

1	Asp Val Val Met Thr Gln Thr Pro Leu Ser
11	Leu Pro Val Ser Leu Gly Asp Gln Ala Ser
21	Ile Ser Cys Arg Ser Ser Gln Thr Leu Val
31	His Ser Ile Gly Asn Thr Tyr Leu His Trp
41	Tyr Leu Gln Lys Pro Gly Gln Ser Pro Lys
51	Leu Leu Ile Tyr Lys Val Ser Asn Arg Phe
61	Ser Gly Val Pro Asp Arg Phe Ser Gly Ser
71	Gly Ser Gly Thr Asp Phe Thr Leu Lys Ile
81	Ser Arg Val Glu Ala Glu Asp Leu Gly Val
91	Tyr Phe Cys Ser Gln Ser Thr His Val Pro
101	Tyr Thr Phe Gly Gly Gly Thr Lys Leu Glu
111	Leu Lys

[0041] In bispecific antibodies of the present invention, the said anti-human CD3 reshaped scFv can contain the amino acid sequence of heavy chain variable domain as follows:

[0042]

1	Gln Val Gln Leu Val Gln Ser Gly Ala Glu
11	Val Arg Lys Pro Gly Ala Ser Val Arg Val
21	Ser Cys Lys Ala Ser Gly Tyr Thr Phe Thr
31	Arg Tyr Thr Met His Trp Val Arg Gln Ala
41	Pro Gly His Gly Leu Glu Trp Ile Gly Tyr
51	Ile Asn Pro Ser Arg Gly Tyr Thr Asn Tyr
61	Asn Gln Lys Phe Lys Asp Arg Val Thr Met
71	Thr Thr Asp Lys Ser Phe Ser Thr Ala Ile
81	Met Asp Leu Arg Ser Leu Arg Ser Asp Asp
91	Ser Ala Val Tyr Tyr Cys Ala Arg Tyr Tyr
101	Asp Asp His Tyr Cys Leu Asp Tyr Trp Gly
111	Gln Gly Thr Thr Val Thr Val Ser Ser

[0043] In bispecific antibodies of the present invention, the said anti-human CD3 reshaped scFv can contain the amino acid sequence of light chain variable domain as follows:

[0044]

1	Glu Ile Val Leu Thr Gln Ser Pro Ala Thr
11	Leu Ser Leu Ser Pro Gly Glu Arg Ala Thr
21	Leu Ser Cys Ser Ala Ser Ser Ser Val Ser
31	Tyr Met Asn Trp Tyr Gln Gln Lys Pro Gly
41	Gln Ala Pro Arg Arg Trp Ile Tyr Asp Thr
51	Ser Lys Leu Ala Ser Gly Ile Pro Ala Arg
61	Phe Ser Gly Ser Gly Ser Gly Thr Asp Phe
71	Thr Leu Thr Ile Ser Ser Leu Glu Pro Glu
81	Asp Phe Ala Thr Tyr Tyr Cys Gln Gln Trp
91	Ser Ser Asn Pro Phe Thr Phe Gly Gly Gly
101	Thr Lys Val Glu Ile Lys Arg

[0045] In bispecific antibodies of the present invention, the interlinker connecting two single-chain Fv antibodies can contain the amino acid sequence as follows:

[0046]

1	Asn Ser Thr Tyr Arg Val Val Ser Val Leu
11	Thr Val Leu His Gln Asp Trp Leu Asn Gly
21	Lys Glu Tyr Lys Cys Lys

[0047] In bispecific antibodies of the present invention, the interlinker connecting two single-chain Fv antibodies can contain the amino acid sequence as follows:

[0048]

1	Phe Gln Asn Ala Leu Leu Val Arg Tyr Thr
11	Lys Lys Val Pro Gln Val Ser Thr Pro Thr
21	Leu Val Glu Val Ser

[0049] In bispecific antibodies of the present invention, the interlinker connecting two single-chain Fv antibodies can contain the amino acid sequence as follows:

[0050]

1	Ala Ser Ala Asp Asp Ala Lys Lys Asp Ala
11	Ala Lys Lys Asp Asp Ala Lys Lys Asp Asp
21	Ala Lys Lys Asp Leu

[0051] The present invention still provides a nucleotide sequence encoding the said BsAb, herein containing the nucleotide sequences of two scFvs and the interlinkers between two scFvs. The said interlinker may be any kind of which are capable of ensuring the proper folding of each of two antibodies, furthermore keeping the biological activities of the said antibodies. In addition, the said interlinker should endow BsAb some novel properties to the products. Fc interlinker and HSA interlinker designed and constructed in the present invention and 205c′ interlinker cited in the present invention are preferred.

[0052] The present invention provides the universal E. coli plasmids for construction and expression of BsAb and the expression plasmids containing the nucleotide sequences encoding BsAb of the present invention. In the preferred embodiment of the present invention, one plasmid is pALM derived from plasmid pAL781, which is a universal plasmid for expression of BsAb. The said plasmid has characteristics as follows: Based on the constructed BsAb, different types of BsAbs can be generated by replacing anyone kind of scFv genes. The plasmid from pALM containing the nucleotide sequences encoding BsAb of the present invention was named pALMB. Another plasmid is pETAE, a derivative of pET16 by inactivating EcoRI site, contains lac operator and T7 promoter, which makes pETAE an vector for expression of target proteins with efficiency. The plasmid from pETAE containing the nucleotide sequences encoding BsAb of the present invention was named pEMAB. Another plasmid is pTMF, which was constructed from pET28a according to the restriction endonuclease sites of BsAb and for the sake of the need of further research and is a plasmid for expression of proteins not limited to BsAb with high efficiency. Besides the high efficiency of expression, the plasmid has the characteristics as follows: it has several rare restriction endonuclease sites to facilitate insertion of various foreign genes in the manner of co- or fusion expression; there is a thrombin site between two groups of restriction endonuclease sites, which facilitates the isolation of the desired protein from the fusion protein; there is six codons encoding six His residue at 3′ end of the multiclonig site, which facilitates the purification of expressed products with metal chelating chromatography. The plasmid from pTMF containing the nucleotide sequences encoding BsAb of the present invention was named pTMAB.

[0053] The present invention still provides the host cells containing the above described expression vectors. The said host cells are preferably E. coli.

[0054] The steps for production of genetically engineered BsAbs of the present invention are described as follows:

[0055] 1. VH and VL genes of the monoclonal antibody were amplified from the hybridoma cell line secreting monoclonal antibody against tumor, respectively, by PCR technology using the designed primers.

[0056] 2. The obtained VH and VL genes against tumors were inserted into the universal scFv expression plasmid, which was transformed into E. coli, induced, expressed and characterized.

[0057] 3. The amino acid sequences of reshaped VH and VL were designed, respectively, according to the antigen binding sites of mouse anti-human CD3 monoclonal antibody OKT3 by using molecular modeling. The nucleotide acid sequences were deduced with E. coli bias codons. The whole genes of VH and VL were obtained by splicing the synthetic oligonucleotide fragments using PCR.

[0058] 4. The resulting VH and VL genes of reshaped anti-human CD3 antibody were inserted into the universal single-chain antibody expression vector, which was transformed into E. coli, expressed under induction and characterized.

[0059] 5. The plasmid with a strong promoter was selected as the starting plasmid. A DNA fragment containing the restriction endonuclease sites which are not present in the starting plasmid, two scFvs and three interlinkers was designed, synthesized and used to replace the multicloning site of the starting plasmid. The synthesized oligonucleotide sequences of interlinkers are inserted into the corresponding sites in the new multicloning site, respectively. Therefore, the universal intermediate vectors containing the interlinkers for BsAbs were constructed.

[0060] 6. A pair of primers was designed and scFv gene with flanking suitable digestion sites was amplified by PCR from the plasmid containing anti-CD3 reshaped scFv. The gene fragment was inserted into the intermediate vectors for bispecific antibody to yield anti-human CD3-based universal expression vectors for ScBsAb. The vectors were transformed into E. coli, expressed under induction and the effects of different interlinkers on the expression of scFvs were characterized.

[0061] 7. The gene fragment of anti-human ovarian carcinoma scFv was obtained by digesting the expression vector containing the gene of anti-human ovarian carcinoma scFv with double restriction endonucleases. The expression vector for bispecific antibody was constructed by inserting the said gene fragment into the corresponding restriction sites of anti-human CD3-based universal expression vector for ScBsAb.

[0062] 8. The said expression vector from 7 was transformed into E. coli. BsAb was expressed under induction. The molecular mass, expression amount and expression form were analyzed by SDS-PAGE. The anti-tumor activity of the expressed products was tested by ELISA. The anti-human CD3 activity of the expressed products was tested by FACS. The expressed products mediated anti-tumor capability and specificity was assayed using Jurkat cells or human peripheral blood lymphocytes.

[0063] 9. The expression vector with high efficiency was constructed and the gene of BsAb was inserted into the said vector, resulting in the expression vector with high efficiency for BsAb.

[0064] 10. The constructed vector with high efficiency was transformed into the host cells.

[0065] 11. The transformed host cells were cultured and induced for the expression of the said BsAb.

[0066] 12. The expressed BsAb was isolated.

[0067] In additon, the present invention still relates to the drug compositions for the treatments or prevention of tumors containing anti-human ovarian cancer×anti-human CD3 bispecific antibody and the pharmaceutical vectors of the present invention and uses of anti-human ovarian cancer×anti-human CD3 bispecific antibody in preparation of drugs for the treatments or prevention of tumors and in the treatments or prevention of tumors thereof.

[0068] The present invention will now be described further by way of the following examples which are intended to be illustrative only and not limited to the scope of the present invention.

[0069] An embodiment is disclosed in following paragraphs.

[0070] 1. Construction of Anti-Ovarian Carcinoma scFv and Anti-Human CD3 scFv

[0071] (1) Construction of Anti-Ovarian Carcinoma scFv Antibody

[0072] VH and VL genes of monoclonal antibody COC183B2 against human ovarian carcinoma were cloned, respectively, by RT-PCR and PCR technology with primers hybridizing to FR1 and FR4 sequences of VH or VL region of mouse immunoglobulin (shown in FIG. 2). VH and VL fragments were cloned to plasmid pUC19 and verified by DNA sequencing. Plasmid pFVB2 was created by inserting VH and VL genes to plasmid pFUW80 (shown in FIG. 1) constructed by our lab with the order of VH and VL from 5′ to 3′ end and there is a (Gly₄Ser)₃ linker (SEQ ID NO: 15) between VH and VL. E. coli strain Top10 was used for the propagation of plasmid and the positive plasmid was verified by digestion with proper restriction endonucleases. E. coli strain XL1-Blue was transformed with pFVB2 and infected by helper phage M13KO7. The phage particles were rescued and the binding activity of the phage antibody was assayed by indirect ELISA. The results indicate that the binding activity of the antibody is 2.5 times higher than that of the negative control, which demonstrates that anti-ovarian carcinoma scFv antibody was constructed successfully.

[0073] (2) Construction of Anti-Human CD3 Reshaped scFv Antibody

[0074] The amino acid sequences of reshaped VH and VL were designed, respectively, according to the antigen binding sites of mouse anti-human CD3 monoclonal antibody OKT3 by using molecular modeling. The nucleotide acid sequences were deduced with E. coli bias codons. The genes of VH and VL (shown in FIG. 5) were obtained by splicing the synthetic oligonucleotide fragments using PCR. The VH and VL genes of reshaped anti-human CD3 antibody were inserted into the universal single-chain antibody expression vector pROH80 (shown in FIG. 4) in the orientation of VL-(Gly4Ser)3-VH from 5′ to 3′ end. E. coli strain Top10 was used for propagation of the yielding plasmid pROCD3 and the positive plasmids were verified by digestion with proper restriction endonucleases. Single colony was picked up from the transformed Top10 plate and incubated in LB medium with corresponding antibiotics at 37° C. overnight. An aliquot of the culture was transferred to the fresh medium with the proportion of 1-5% and shaking at 37° C. until an OD600 of 0.5-1.0 was reached. IPTG was added to the final concentration of 0.4 mM to induce expression of target proteins. The antigen-binding activity of reshaped anti-CD3 scFv was assayed by FACS. The results demonstrates that the competitive inhibition rate of anti-CD3 reshaped scFv to anti-CD3 monoclonal antibody was 18% (shown in FIG. 6), which implies anti-human CD3 reshaped scFv was constructed and expressed successfully.

[0075] 2. Construction and Expression of Anti-Human Ovarian Carcinoma×Anti-Human CD3 Bispecific Antibody

[0076] (1) Construction of Intermediate Vector for Bispecific Antibody

[0077] An expression vector with suitable restriction endonuclease sites was constructed for the insertion of two above described scFvs and interlinker. Plasmid pAL-781 (shown in FIG. 7) was chosen as the starting vector to construct the vector for bispecific antibodies. In the present invention, an oligonucleotide fragment with 55 bps was designed and synthesized to replace the multiple clone sites (MCS) in pAL-781. This intermediate vector was named pALM. The new MCS contains the start codon ATG integrated in restriction endonucleases site NdeI. The gene fragment of anti-ovarian carcinoma scFv was inserted between XhoI and EcoRI, interlinker was inserted between EcoRI and SacI and the gene fragment of anti-CD3 reshaped scFv was inserted between SacI and BamHI. And the following was DNA fragment (CATCAC)₃ (SEQ ID NO: 16) encoding 6 His and the stop codon TAA. Anyone of the components mentioned above could be substituted for another by digestion and insertion. 3 kinds of the synthetic interlinkers fragments (shown in FIG. 8) were inserted into the proper restriction sites on pALM. Three intermediate vectors for ScBsAb: pALM-Fc; pALM-HSA and pALM-205c′ (shown in FIG. 9) were constructed successfully and verified by digestion and DNA sequencing.

[0078] (2) Construction of CD3-based Universal Expression Vector for ScBsAb

[0079] A pair of primers were designed for amplification of CD3 scFv gene with flanking digestion sites SacI at 5′ end and BamHI at 3′ end from the plasmid containing anti-CD3 reshaped scFv by PCR. The gene fragment was inserted into the intermediate vector for bispecific antibody to yield anti-human CD3-based universal expression vector for ScBsAb. The resulting vector was transformed to E. coli strain GI724 and the protein was expressed. The results indicate that all of three kinds of interlinkers had no negative effects on the expression of scFv.

[0080] (3) Construction of Bispecific Antibody

[0081] The gene fragment of anti-human ovarian carcinoma scFv was obtained by digesting the expression vector containing the gene of anti-human ovarian carcinoma scFv with restriction endonucleases XhoI and EcoRI. The expression vector for bispecific antibody was constructed by inserting the said gene fragment into anti-human CD3-based universal expression vector for ScBsAb. The resulting plasmids were propagated in E. coli strain GI724, verified by digestion with proper restriction endonucleases and named pAMAB.

[0082] (4) Expression of Bispecific Antibody in E. coli

[0083] Single colony of E. coli strain GI724 harboring pAMAB was picked up and incubated in RM medium overnight at 30° C. An aliquot of culture was transferred to fresh medium with the proportion of 20%. When an OD550 of the culture was reached 0.5-1.0, tryptophan was added to the final concentration of 100 ug/ml to induce expression of the target protein. After 3 hours of induction, culture was precipitated by centrifugation at 3,000 rpm for 10 min at 4° C. The cell pellet was resuspended in ½ culture-volume of PBS and broken by ultrasonic in ice bath for 20 s for 6-8 times with 1-min interval followed by centrifugation at 4° C. at 12,000 rpm for 20 min. The precipitate was resuspended in PBS with the same volume to the supernatant. The sonicate, supernatant and precipitate of sonication were analyzed by 12% SDS-PAGE with the empty vector pALM as negative control. Protein with molecular weight of 52 kDa was found in both supernatant and precipitate. The result indicated the target protein was expressed partly in soluble form. The soluble protein could be used directly to identify the biological activity of bispecific antibody.

[0084] 3. Biological Activity Assay of Anti-Human Ovarian Carcinoma×Anti-Human CD3 Bispecific Antibody

[0085] (1) Antigen-Binding Activity of Anti-Human Ovarian Carcinoma scFv

[0086] The antigen-binding activity of anti-ovarian carcinoma scFv in bispecific antibody was assayed by direct ELISA. ELISA plate was coated with bispecific antibody at 4° C. overnight. Wells coated with anti-ovarian monoclonal antibody were set as positive control. Plate was washed 3 times with PBST (PBS-0.05% Tween 20) for 5 min. HRP-OC183B2 diluted in 3% goat serum was added and incubate at 37° C. for 1 h. After washing plate 3 times with PBST, the substrate of HRP was added and incubated for 20 min at room temperature in the dark. 2M H2SO4 was added to stop the reaction. The plates were read at 492 nm (data shown in FIG. 12). All the values of OD492 of bispecific antibody were 2.5 times higher than those of negative control and changed with gradient among the different dilution of bispecific antibody. The data indicates that anti-ovarian scFv in bispecific antibody has the binding activity to antigens associated with ovarian carcinoma.

[0087] (2) Antigen-Binding Activity of Anti-Human CD3 scFv

[0088] The antigen-binding activity of anti-CD3 reshaped scFv in bispecific antibody was assayed by FACS according to the principle of competitive inhibition. 1×106 fresh Jurkat cells in an FACS tube were washed 3 times with PBS containing 2% fetal bovine serum and 0.1% NaN3. Bispecific antibody was added before the cells were incubated at 4° C. for 45 min. Cells incubated with PBS were set as positive control. After washed 3 times with PBS containing 2% fetal bovine serum and 0.1% NaN3, the cells were incubated with diluted murine anti-CD3 monoclonal antibody for 30 min at 4° C. After washed 3 times with PBS containing 2% fetal bovine serum and 0.1% NaN3, the cells were incubated with goat anti-mouse IgG-FITC (with the dilution of 1:50) for 45 min at 4° C. After washed 2 times with PBS containing 2% fetal bovine serum and 0.1% NaN3, the cells were resuspended in 500 ul PBS and assayed on FACSort. The data indicate bispecific antibody can greatly inhibit the antigen-binding activity of anti-CD3 mouse monoclonal antibody. The inhibition rate is 18%, which demonstrates anti-CD3 reshaped scFv in bispecific antibody has binding activity to CD3. The results indicate two scFvs within bispecific antibody both keep their antigen-binding activities.

[0089] (3) Cytotoxicity of Anti-Ovarian Bispecific Antibody Against Ovarian Carcinoma Cells

[0090] Human ovarian cell line SKOV3 cells (target cells) were seeded in 96-well plate with approximate 1×104/well. Bispecific antibody renatured from inclusion bodies were added at three different volumes of 5 ul, 10 ul and 20 ul. Plates were incubated in the incubator with CO2 overnight. Jurkat cells (effector cells) were added at different effector cells: target cells ratios. Plates were incubated in the incubator with CO2 at 37° C. for 48 h. 25 ul MTT was added to each well. After incubation at 37° C. for 4 h, the plates were emptied and 100 ul acidic SDS (0.1N HCl, 1% SDS) was added to each well. After incubation at 37C overnight, plates were read at 570 nm. The rate of cytotoxicity was calculated according to the formula below.

[0091] $\mathrm{Cytotoxicity}\%=\frac{{\mathrm{OD}}_{E+T}-{\mathrm{OD}}_E}{1-{\mathrm{OD}}_T}\times 100\%$

[0092] As shown in Table 1, the cytotoxicity rate of effector cells against target cells increased in the case of addition of bispecific antibody (shown in FIG. 13). The rate cytotoxicity increases with the increase of the concentration of bispecific antibody, which indicates bispecific antibody triggers the direct killing effect of effector cells against target cells.

[0093]

	TABLE 1
	BsAb 140 μg/ml
	0 μl	5 μl	10 μl	20 μl
E/T	cytotoxicity %
12.5:1	97.39	100.00	110.76	144.64
6.2:1	69.56	55.09	113.27	104.29
3.1:1	33.48	46.30	52.02	64.38

[0094] 4. Construction of High Performance Expression Vector

[0095] For production purpose, high performance expression vector was constructed for overexpression of bispecific antibody. pETΔE (shown in FIG. 10) derived from pET16 by inactivated EcoRI site is a T7 promoter-based high performance expression vector. The bispecific antibody gene fragment digested from pAMAB with XhoI and BamHI was inserted into the same sites of pETAE digested with the same restriction endonucleases, yielding pEMAB. Proteins were expressed after pEMAB was transformed to E. coli strain BL21(DE3). However, expressed from pETAE, the target protein was fused to (His)10 tag which could not be purified by IMAC as effectively as proteins fused to (His)6. Therefore, plasmid pTMF (shown in FIG. 11) derived from pET28a was constructed. pTMF contains T7 promoter for overexpression of target proteins and several unusual restriction sites which were used for facilitating the insertion of foreign genes followed by fusion or co-expression of target proteins. A thrombin site was designed between two groups of restriction sites. Following purification, the target proteins could be separate from the fusion proteins by proteolysis on thrombin site. Flanking 3′ end of MCS is the sequence coding for His6 tag which could be used in IMAC.

[0096] The gene fragment of bispecific antibody digested from pAMAB with XhoI and BamHI was inserted into pTMF to generate plasmid pTMAB. E. coli strains BL21(DE3) was transformed with pTMAB, single colony was picked and grown until an the value of OD550 reached 0.5. Protein expression was induced by adding IPTG to a final concentration of 0.4 mM. After 3 hours of induction, the culture was precipitated by centrifugation, cell pellets were broken by ultrasonic and the sonicate was analyzed by SDS-PAGE (shown in FIG. 13). In the total whole-cell proteins, 27% is bispecific antibody 16% of which is soluble. The expression level is eligible in production area.

[0097] 5. Conclusion

[0098] Anti-human ovarian carcinoma×anti-human CD3 bispecific antibody can simultaneously bind to both T cells and ovarian carcinoma cells and then activate T cells to kill the ovarian carcinoma cells. This model of bispecific antibody can be used as biological drugs for the treatment of ovarian carcinoma.