Evaluation of the HER2/neu-derived peptide GP2 for use in a peptide-based breast cancer vaccine trial

BACKGROUND. E75 and GP2 are human leukocyte antigen (HLA)-A2-restricted immunogenic peptides derived from the HER2/neu protein. In a E75 peptide-based vaccine trial, preexisting immunity and epitope spreading to GP2 was detected. The purpose of this study was to further investigate GP2 for potential use in vaccination strategies. Importantly, a naturally occurring polymorphism (I → V at position 2, 2VGP2) associated with increased breast cancer risk was addressed. METHODS. Prevaccination peripheral blood samples (PBMC) from HLA-A2 breast cancer patients and CD8⁺ T cells from HLA-A2 healthy donors were stimulated with autologous dendritic cells (DC) pulsed with GP2 and tested in standard cytotoxicity assays with HER2/neu⁺ tumor cells or GP2- or 2VGP2-loaded T2 targets. Additional cytotoxicity experiments used effectors stimulated with DC pulsed with E75, GP2, or the combination of E75 + GP2. RESULTS. GP2-stimulated prevaccination PBMC from 28 patients demonstrated killing of MCF-7, SKOV3-A2, and the HLA-A2^- control target SKOV3 of 28.8 ± 3.7% (P<.01), 29.5 ± 4.0% (P<.01), and 16.9 ± 2.7%, respectively. When compared with E75, GP2-stimulated CD8⁺ T cells lysed HER2/neu⁺ targets at 43.8 ± 5.2% versus 44.2 ± 5.7% for E75 (P = .87). When combined, an additive effect was noted with 58.6 ± 5.4% lysis (P = .05). GP2-stimulated CD8⁺ T cells specifically recognized both GP2-loaded (19.6 ± 5.7%) and 2VGP2-loaded T2 targets (17.7 ± 5.2%). CONCLUSIONS. GP2 is a clinically relevant HER2/neu-derived peptide with immunogenicity comparable to that of E75. Importantly, GP2-specific effectors recognize 2VGP2-expressing targets; therefore, a GP2 vaccine should be effective in patients carrying this polymorphism. GP2 may be most beneficial used in a multiepitope vaccine.