Modification of the HER2/NEU‐derived tumor antigen GP2 improves induction of GP2‐reactive cytotoxic T lymphocytes

GP2 (IISAVVGIL), the p654–662 HER2/neu‐derived tumor antigen, induces HLA‐A2‐restricted cytotoxic T lymphocytes (CTL) reactive to various epithelial cancers. The binding affinity of GP2 for HLA‐A2, however, is very low. To improve the immunogenicity of GP2, we tested 10 different amino acid substitutions into GP2 at the C‐ and N‐ terminus. Five out of 10 modified peptides, especially those containing phenylalanine at position 1 (1F), showed a significantly improved binding affinity to HLA‐A2. 1F‐based modified peptides were well recognized by GP2‐specific CTL. These peptides were used to stimulate peripheral blood lymphocytes from HLA‐A2 healthy donors using peptide‐pulsed autologous dendritic cells (DC). After 3 or more weekly stimulations, CTL activity against GP2 pulsed T2 (T2‐GP2) and HER2/neu‐overexpressing tumor cells was measured in 51Cr release and IFN‐γ secretion assays. The modified peptides significantly enhanced GP2‐specific CTL activity in some donors. In particular, the peptide with phenylalanine at position 1, leucine at position 2 and valine at position 10 (1F2L10V) maximized the CTL activity against both T2‐GP2 and HER2/neu‐positive tumor cells. Peptide 1F2L10V increased not only the binding affinity to HLA‐A2 but also improved recognition of GP2. These data suggest that DC + modified GP2 may improve immune therapies for the treatment of HER2/neu overexpressing tumors. © 2001 Wiley‐Liss, Inc.