Antigenic heterogeneity of a human melanoma tumor detected by autologous CTL clones

Peripheral blood lymphocytes from a melanoma patient were stimulated with autologous melanoma cells in mixed lymphocyte tumor cultures (MLTC). After three restimulations, the lytic activity of the responder cells directed against the autologous melanoma cells was higher than that against K-562 and autologous Epstein-Barr virus-transformed B cell line (EBV-B) cells. From these MLTC-responder cells, we derived specific cytolytic T cell (CTL) clones that lysed the autologous melanoma cells and did not lyse K-562 or autologous EBV-B cells. Autologous melanoma clones were found that were resistant to some or all of these CTL clones. The autologous CTL clones recognized at least two different antigens (A, B) on the melanoma cells and three types of melanoma clones could be distinguished (A+B+, A+B-, A-B-). This antigenic heterogeneity of melanoma clones was confirmed by testing the CTL clones in cold target competition and also in antigen-dependent CTL proliferation assays performed with very small numbers of stimulator cells. The data further indicated an instability of the expression of a melanoma-associated antigen in the course of a long culture period. Among the melanoma clones that expressed antigen A, one was found to stimulate the proliferation of anti-A CTL clones much more effectively than the others. This represents a new type of heterogeneity among tumor cells which may be of significance for the elicitation of an autologous anti-tumoral immune response.