Biological behavior of human breast carcinoma-associated antigens expressed during cellular proliferation

The cell surface-binding properties of two murine monoclonal antibodies reactive with human mammary tumor cells are described. Fluorescence-activated cell sorter analyses demonstrate that both monoclonal antibodies, B6.2 and B38.1, are reactive with the surface of the majority of human breast tumor cell lines tested but are unreactive with a variety of normal human cell lines, melanomas, sarcomas, and lymphoid tumors. Antibody B6.2 was also reactive with selective carcinomas, while antibody B38.1 showed even broader reactivity. The two monoclonal antibodies were unreactive with the surface of a variety of normal human tissues obtained at biopsy, including lymph nodes, bone marrow, and spleen, but were reactive with mammary tumor cells obtained from four of six pleural effusions. Surface binding to mammary tumor cells by both monoclonal antibodies was shown to decrease during density-dependent arrest; further cell cycle analysis demonstrated differential antibody surface binding during S phase. Prolonged exposure of mammary tumor cells to antibody showed no evidence of antigen capping or internalization. Both monoclonal antibodies were shown to lyse mammary tumor cells in antibody-dependent cell-mediated cytotoxicity.