Chimeric mouse-human anti-carcinoma antibodies that mediate different anti-tumor cell biological activities

Two chimeric mouse-human antibodies, ING-1 (IgG1,κ) and ING-2 (IgG1,λ), have been constructed starting from anticarcinoma mouse hybridomas. These antibodies bind to different tumor-associated antigens which are present on human breast carcinoma cell lines at 10⁵–10⁶ antigens/cell; ING-1 binds to a 40-kD membrane glycoprotein, while ING-2 binds to a glycoprotein of >300 kD. In competitive binding experiments, both chimeric antibodies have identical binding activity to the parental mouse antibodies. The antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytolysis (CDC) activities of these antibodies were studied on carcinoma target cell lines. ING-1 mediates potent ADCC, but ING-2 had undetectable or very weak ADCC activity. ING-2 ADCC activity was significantly reduced by the addition of human serum, but ING-1 ADCC was unaffected. Neither ING-1 nor ING-2 mediated CDC of breast carcinoma cell lines, but ING-1 mediated CDC of a colon carcinoma cell line. ING-1 antibody-antigen complexes are stable on the target cell surface for at least 2 hours, while much of bound ING-2 is lost from the surface of cells due to internalization or shedding. The activities of these antibodies confirm that the target antigen plays an important role in the biological effector functions triggered by cell-surface-bound antibodies. Both of these chimeric antibodies are candidates for further study as immunoconjugates for cancer diagnosis or therapy, and the unconjugated ING-1 antibody has promise for cancer therapy due to its potent activation of ADCC.