Analysis of cell surface antigens expressed on a human lung carcinoma by monoclonal antibodies

Monoclonal antibodies were produced by immunizing BALB/c mice with a human lung squamous carcinoma line (UCLA-SO-P3) or with freshly obtained lung carcinoma cells and by fusing the immunized splenocytes to mouse myeloma S194. Six monoclonal antibodies were selected after testing the reactivity to a panel of human tumors and non-tumors by an indirect 125I-protein A binding assay, a complement dependent microcytotoxicity assay or an immunofluorescence assay. As a result, four types of antigens were identified. MoAb 169D4 is of IgM class and reacted only to P3 lung carcinoma and to one of the colon carcinomas. This antibody actually possessed the A1 Lewis d specificity. MoAb 172D5 reacted to 8 out of 11 carcinomas but did not react to other types of tumor or lymphoid cells while detecting a carcinoma-associated antigen. MoAb 170C5, 754A3 and 806B4 reacted to carcinomas and embryonic cells, but detected antigenic determinants other than the carcinoembryonic antigen. By means of a protein antigen analysis using immunoprecipitation and SDS-polyacrylamide gel electrophoresis, MoAb 170C5, 754A3 and 806B4 detected molecular weights of 130,000, 55,000, and 135,000, respectively. MoAb 169F3 reacted to all the tested carcinomas, sarcomas, and melanomas, and some of the leukemias. This antibody also reacted to human peripheral monocytes and platelets and was shown to detect an antigen widely distributed among tumors and parts of normal cells.