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.