Immunization with a HSP65-HER2 fusion peptide selectively eliminates HER2+ B16 melanoma cells in a xenograft tumor mouse model

HER2/neu peptide-based vaccines can eliminate human tumors overexpressing the human epidermal growth factor receptor 2 (HER2/neu), but the efficacy of this therapeutic strategy is suboptimal. Heat shock proteins (HSPs) are capable of eliciting efficient cytotoxic T lymphocyte (CTL) responses by cross-presentation. To evaluate whether immunization with a HSP65-HER2 fusion peptide could selectively eliminate HER2(+) B16 melanoma cells in a xenograft tumor mouse model, a HSP65-HER2 fusion peptide was incubated with immature dendritic cells (iDCs) in vitro to determine whether loading of iDCs with HSP65-HER2 could induce the expression of the immunomodulatory cell surface molecule, CD86. In vivo mouse immunizations with HSP65-HER2 or PBS (control) were performed to determine the antitumor effects by longitudinally monitoring changes in tumor volume, weight, and incidence. The effects on percentages of HER2(+) B16 cells in tumors were assessed by confocal microscopy and flow cytometry. The results indicated that loading of iDCs with HSP65-HER2 induced the expression of CD86 in vitro, suggesting that the hybrid antigen was able to stimulate an immune response. Immunization with HSP65-HER2 had no significant influence on tumor weight or volume but significantly reduced tumor incidence (62.5 % in mice injected with 25 mu g of HSP65-HER2 vs. 100 % in PBS-injected controls; P < 0.05). Confocal microscopy and flow cytometry analyses revealed that HSP65-HER2 immunization significantly reduced the percentages of HER2(+) B16 cells in xenografted tumors (1.86 % vs. 30.56 % in PBS-injected controls; P = 0.01). Our findings suggest that immunization with the HSP65-HER2 fusion peptide selectively eliminates HER2(+) B16 melanoma cells in a xenograft tumor mouse model and may represent a novel and efficacious targeted therapy of HER2/neu(+) tumors.