Identification of NY-ESO-1 peptide analogues capable of improved stimulation of tumor-reactive CTL

Expression of NY-ESO-1 in a high proportion of different human tumors makes this protein a very attractive vaccine target. NY-ESO-1 peptides, recognized by HLA-AZ-restricted CTL, have recently been described. However, it remains unclear how efficiently tumors generate these epitopes, and whether peptide analogues can be used for optimal expansion and activation of NY-ESO-l-specific HLA-AZ-restricted CTL, By generating unique CTL clones, we demonstrate that NY-ESO-l-positive tumor cells are efficiently killed by HLA-AZ-restricted CTL specific for the peptide epitope NY-ESO-1 157-165, Presentation of this epitope is not affected by the presence or absence of the proteasome subunits low molecular proteins 2 and 7 and Is not blocked by proteasome inhibitors, while it is impaired in the TAP-deficient cell line LBL 721.174, NY-ESO-1 157-165 peptide analogues were compared for their antigenicity and immunogenicity using PBL from melanoma patients. Three peptides, containing the carboxyl-terminal cysteine substituted for either valine, isoleucine, or leucine, were recognized at least 100 times more efficiently than the wild-type peptide by specific CTL, Peptide analogues were capable of stimulating the expansion of NY-ESO-l-specific CTL from PBL of melanoma patients much more efficiently than wild-type peptide. These findings define the processing requirements for the generation of the NY-ESO-1 157-165 epitope, Identification of highly antigenic NY-ESO-1 peptide analogues may be important for the development of vaccines capable of expanding NY-ESO-l-specific CTL in cancer patients.