Identification of a shared epitope recognized by melanoma-specific, HLA-A3-restricted cytotoxic T lymphocytes

We previously established a melanoma-reactive cytotoxic T lymphocyte (CTL) line that recognizes multiple epitopes in the context of HLA-A3. To increase the number of peptides available for use in a vaccine for the treatment of melanoma, we identified one of these epitopes, SQNFPGSQK, through a combination of epitope reconstitution experiments and mass spectrometry. The SQNFPGSQK peptide was also found to be associated with HLA-A3 on an additional melanoma tumor line, thus indicating that the peptide is not unique to the melanoma tumor line from which it was isolated and thus, unlikely to arise through a mutational event. Although the protein origin of SQNFPGSQK has yet to be established, the shared nature of this epitope and the fact that it elicits a natural immune response indicates that it warrants further study to determine its usefulness as a vaccine component for the treatment of melanoma. The peptide may also be useful as a research tool for evaluating spontaneous anti-tumor immune responses in patients with melanoma.