Requirement of MHC class I antigen expression on human tumors for in vitro recognition by autologous blood lymphocytes.

: Expression of class I antigens on ex-vivo tumor cells was found to be required for their recognition by autologous blood lymphocytes in vitro. Lymphocyte stimulation (auto-tumor stimulation ATS) in mixed lymphocyte tumor cell cultures (MLTC) and cytolysis in short term assays (autologous lymphocyte-mediated cytotoxicity ALC) were positive with cells of a proportion of sarcoma and carcinoma patients. In addition to the class I antigens, these tumors also carried the adhesion molecule ICAM-1. Monoclonal antibodies (MAb) to the MHC class I, but not to class II antigens inhibited lymphocyte proliferation in the MLTC and lysis of tumor cells in the ALC tests. In a proportion of originally negative or low expressor tumors, in vitro treatment with Interferon gamma and tumor necrosis factor alpha induced the expression of class I antigens and/or ICAM-1. In the MLTC the cytokine treated tumor cells stimulated the blood lymphocytes and generated cytotoxic effectors which reacted also with the untreated tumor cells.