title: Immunotherapy with bispecific antibodies.
abstract: With rare exceptions, monoclonal antibodies as therapeutic agents for cancer, have had limited anti-tumor effects. Attempts to improve the cytotoxicity of antibodies by using them as guiding agents for immune effector cells, have been developed. Numerous in vitro studies have shown that T lymphocytes can be targeted towards any target cell by using bispecific antibodies with specificity of the CD3/TCR complex and a target cell antigen. This approach works extremely efficiently in vitro and justified the hope that bispecific antibodies might be useful for focusing T cells towards tumor cells in vivo. Therefore we have produced bispecific antibodies directed against the membrane expressed idiotype of the murine B cell lymphomas BCL1 and 38C13, and against the murine CD3 complex present on all T lymphocytes. The dual specificity of the hybrid-hybridoma produced bispecific antibodies could be demonstrated by flow cytometry, the induction of T cell proliferation, the induction of IL-2 secretion by polyclonal T cells, and redirected lysis of the relevant target cells. Immunotherapy of tumor bearing animals demonstrated that bispecific antibodies could efficiently target T cells towards the tumor cells, that tumor cell--T cell bridging is established in vivo, and that both T cell subsets contribute to tumor regression resulting in long-term survival and cure of the lymphomas. To streamline the production of bispecific antibodies we recently engineered recombinant bispecific proteins produced by bacteria. Two scFv fragments, one derived from the anti-tumor antibody and one derived from the anti-mouse CD3 monoclonal antibody were produced in E. Coli. Both antibody fragments could be easily purified by IMAC chromatography. After in vitro refolding of the recombinant proteins the antigen specificity was retained. Both scFv were expressed as one fusion protein by engineering a 15 amino acid linker between the antibody fragments. The purified bispecific fusion protein behaved in vitro tests as active as the hybrid-hybridoma produced bispecific antibody (induction of T cell proliferation and lymphokine secretion, retargeted lysis of tumor cells). Also the fusion protein is able to target T cells towards the tumor cells in vivo, resulting in long term survival of the treated animals. In conclusion, these studies form a sound basis for further investigation of the potential of bispecific antibodies for treatment of patients with cancer.
mesh_terms: D000818:Animals; D018033:Antibodies, Bispecific / Q000096:biosynthesis / Q000627:therapeutic use*; D007130:Immunoglobulin Idiotypes / Q000276:immunology; D016393:Lymphoma, B-Cell / Q000628:therapy*; D051379:Mice; D008815:Mice, Inbred Strains; D009374:Neoplasms, Experimental / Q000628:therapy; D011948:Receptors, Antigen, T-Cell / Q000276:immunology
chemical_list: D018033:Antibodies, Bispecific; D007130:Immunoglobulin Idiotypes; D011948:Receptors, Antigen, T-Cell