Mining the melanosome for tumor vaccine targets: P. polypeptide is a novel tumor-associated antigen

To identify novel, tumor-specific target antigens for vaccine development, we studied immune responses to P. polypeptide, an M_r 110,000 integral melanosomal membrane protein associated with the Prader-Willi syndrome. Together with expressed sequence tag (EST) and serial analyses of gene expression (SAGE) library analyses, reverse transcription-PCR and Northern blotting verified that P. polypeptide expression was limited to melanoma and melanocytes. A single dominant epitope corresponding to positions 427-435 (IMLCLIAAV) was identified using allele-specific epitope forecasting combined with work in HLA-A*0201/K^b transgenic mice. This epitope was then used to generate de novo human P. polypeptide-specific CD8⁺ T cells capable of recognizing P. polypeptide expressing human tumor cell lines in an HLA-A*0201-restricted fashion. Thus, P. polypeptide may be valuable in the creation of novel therapeutic anticancer vaccines.