Melanoma-reactive human cytotoxic T lymphocytes (CTLs) mediate
tumor regression in vivo through specific recognition of MHC-associated
peptide epitopes, many of which are encoded by the melanocytic tissue differentiation
proteins gp100/Pme117 and MART-1/
Melan-A.
Vaccines using these
peptides may induce protective or therapeutic immunity against
melanoma. Rational design of such approaches is aided by a clear understanding of the identity of these antigenic
peptides; however, most CTL
epitopes described to date were identified indirectly. Especially where these
peptides may be used in human clinical trials for the treatment or prevention of
cancer, there is substantial need for direct evaluation of
HLA-A*0201-associated
peptides from MART-1 and gp100 that are naturally processed and presented. To that end, we have isolated
peptides directly from
HLA-A*0201 molecules of human
melanoma cells and have determined that naturally processed
epitopes for
HLA-A*0201-restricted,
melanoma-reactive CTLs include the nonamers MART-1(27-35) (AAGIGILTV), gp100(154-162) (KTWGQYWQV), gp100(209-217) (ITDQVPFSV) and gp100(280-288) (
YLEPGPVTA) and the decamer gp100(476-485) (VLYRYGSFSV). Among these, the one that appears to be most abundant at the cell surface is gp100(154-162) (KTWGQYWQV). The others are among the less abundant
peptides.
HLA-A*0201-restricted CTLs from one
melanoma patient who has survived metastatic disease recognized MART-1(27-35) (AAGIGILTV), gp100(280-288) (
YLEPGPVTA) and gp100(154-162) (KTWGQYWQV) and were cross-reactive on longer
peptides that contained these nonamer sequences. These
peptides, identified by both an indirect genetic approach and by a direct
peptide approach, can be used for
tumor vaccine strategies with confidence that they are identical to the naturally processed
peptide epitopes presented at the surface of
melanoma cells in association with
HLA-A*0201 molecules.