Monoclonal antibodies derived from immunosuppressed mice grafted with human melanoma

Hybridoma cells producing monoclonal antibodies against tumor-shed antigens were generated by fusing mouse myeloma cells with spleen cells from immunosuppressed mice bearing human melanoma xenografts. Thirty-eight fusion experiments were performed at different stages of tumor growth. Hybridomas producing anti-melanoma antibodies were obtained from 12 spleens in mice bearing 1-4-week-old tumors but at later stages of tumor growth, no hybridomas whatsoever could be obtained. However, the sera of all mice tested showed anti-melanoma antibody binding reactivity at the time of fusion. Using radioimmunoassay (RIA) to select specific antibody secreting hybridoma cultures, the majority of cultures were found to produce antibodies which bound to both 3 M KCl melanoma extracts and melanoma culture supernatants. No stable cultures secreting membrane-reactive (live tumor cell targets) antibodies could be obtained. All of the monoclonal antibodies bound not only to melanoma target cell preparations, but also to preparations from tumors of other origins and only 3 did not bind to normal human fibroblasts. The crossreactivity pattern of binding was confirmed in immunoperoxidase (IP) assays by binding to human tissue sections. The immunosuppressed mouse bearing human tumor xenografts has proven a useful system for production of monoclonal antibodies against antigens shed by tumor cells.