Identification of an immunodominant H‐2D b ‐restricted CTL epitope of human PSA

BACKGROUND Human prostate specific antigen (PSA) is expressed selectively in prostate epithelium and is a potential target for the immunotherapy against prostate cancer. Various PSA‐based vaccines have been reported to induce cytotoxic T lymphocyte (CTL) responses in animal models. Here, we present the identification and validation of an immunodominant CTL epitope of PSA in C57Bl/6 mice (H‐2 b ). METHODS PSA‐specific CTLs were induced by immunization with a plasmid expressing PSA. Epitope specificity of the CTLs was determined by their reactivity against a panel of C‐terminus truncated or mutated PSA proteins and use of bioinformatical prediction with the SYFPEITHI algorithm. RESULTS The majority of PSA‐specific CTLs were directed against a single H‐2D b restricted epitope corresponding to the amino acid residues 65–74 (HCIRNKSVIL) of the protein. The CTLs had similar functional avidity against two putative H‐2D b binding peptides: a 9‐aa‐long psa65‐73 (HCIRNKSVI) and a 10‐aa‐long psa65‐74 (HCIRNKSVIL). CONCLUSIONS We demonstrate that the psa65‐73 peptide can be used for reactivation of PSA‐specific CTLs in vitro and ex vivo, and H‐2D b pentamers assembled with this peptide are an efficient tool for monitoring of PSA‐specific CTL responses after DNA vaccination. © 2005 Wiley‐Liss, Inc.