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Major histocompatibility complex (MHC) class I antigens (Ag), particularly human lymphocyte antigen (HLA)-A2, have been shown to function as restriction elements in human cytotoxic T lymphocyte recognition of tumor. This study was undertaken to determine the function of non-A2 MHC class I Ag in tumor recognition by tumor-infiltrating lymphocytes (TILs) cultured from six melanomas, and to find evidence for shared or unique tumorassociated Ag. Four predominantly CD8+ and two mixed CD4+, CD8+ population TIL cultures were tested for lysis in short-term 51Cr-release assays against a panel of targets including 29 fresh melanomas, 2 fresh sarcomas, 11 cultured melanoma lines, and 14 nonmelanoma cell lines derived from HLA-typed patients. All six melanoma TILs lysed the autologous melanoma. Two of three TILs from HLA-A2+ patients lysed allogeneic melanomas matched for HLA-A2, giving evidence for shared tumor Ag; one of these TILs also used HLA-B44 as a restriction element. The third HLA-A2+ TIL lysed autologous melanoma but not autologous Epstein-Barr virus-transformed B cells nor 14 HLA-A2 matched allogeneic melanomas, suggesting the possibility of a unique tumor Ag in this system. The three HLA-A2- TILs each lysed multiple HLA-matched melanomas, using HLA-A24, HLA-A31, and HLA-Cw7 as restriction elements. Blocking of autologous and allogeneic melanoma lysis by TILs with mAb w6/32 (anti-MHC class I) and anti-CD3, as well as cold target inhibition assays, confirmed that specific interaction of the T-cell receptor with MHC class I Ag and the relevant tumor Ag on the target cell surface is required for tumor lysis. These data provide evidence for specific recognition of shared melanoma Ag by human TILs.