CYTOTOXIC T-CELL RECOGNITION OF A HUMAN-MELANOMA DERIVED PEPTIDE WITHA CARBOXYL-TERMINAL ALANINE-PROLINE SEQUENCE

Recently, we defined the antigenic epitope recognized by the human mon oclonal antibody L94 to be a protein with a C-terminal sequence of ala nine-proline (AP). An antigenic peptide no. 707 (RVAALARDAP), which wa s identified by the use of cDNA libraries of an antigen positive melan oma cell line M14, was evaluated for cellular immune responses in mela noma patients. PBMC from 16 of 19 melanoma patients were shown to lyse autologous B lymphoblastoid cell lines (BCL) pulsed with synthetic pe ptide no. 707 (hereafter no. 707). This specific cytotoxicity to the p eptide significantly increased in 84% of melanoma patients after in vi vo immunization with a melanoma cell vaccine (MCV). In contrast, pepti de specific cytotoxicity was observed in only one of 19 normal volunte er donors. In vitro restimulation of MCV treated patients' PBMC with n o. 707 augmented cytotoxicity against autologous no. 707-pulsed BCL. T his cytotoxicity was specific to the C-terminal sequence AP, since the removal of C-terminal AP completely abolished the specific lysis. no. 707 restimulation of PBMC enhanced cytotoxicity against autologous me lanomas. Autologous melanoma and peptide-pulsed BCL targets were lysed by CDs + CTL in a HLA class I-restricted manner. The strong cytotoxic ity was obtained from patients of HLA A24. CTL lysis of autologous no. 707-pulsed BCL was partially blocked by unlabeled autologous melanoma s in a cold target inhibition test. This suggested that the epitope id entical or cross-reactive to no. 707 may be presented on the melanoma cell surface by HLA class I antigens. Our findings suggest that peptid e no. 707 presented on human melanoma cells is recognized by CTL and t hat C-terminal AP plays a critical role in both antibody and T cell re cognition.