REJECTION OF A NONIMMUNOGENIC MELANOMA BY VACCINATION WITH NATURAL MELANOMA PEPTIDES ON ENGINEERED ANTIGEN-PRESENTING CELLS

Naturally processed peptides, obtained by acid extraction of tumor cel ls, contain Ags able to activate specific CTL in vitro. We recently re ported that the nonprofessional APC, RMA-S, expressing the B7.1 molecu le (RMA-S/B7), pulsed with naturally processed peptides from the nonim munogenic B16F1 melanoma (B16F1a.e.) primed syngenic CD8(+) T cells ag ainst the tumor in vitro. Here, we show the rejection of B16F1 melanom a by C57BL/6 mice after immunization with RMA-S/B7 cells pulsed with B 16F1a.e, This response is critically dependent on both CD4(+) and CD8( +) cells, but not on NK cells. However, only CD8(+) T cells exert anti -B16F1 cytolitic activity in vitro. Moreover, RMA-S/B7 cells pulsed wi th B16F1a.e. can be used to prevent the growth of 24-h preestablished melanomas. These results may have important implications for the clini cal use of natural peptide fractions of tumor cells as therapeutic can cer vaccines.