Vaccination with Her2/neu peptides elicits an endogenous anti-Her2/neu antibody response in mice

The Her2 protein, a member of the epidermal growth factor receptor family, is overexpressed on 25-30% of invasive breast cancers. In this study, Her2 peptides of various lengths were tested to determine their potential to induce endogenous anti-Her2 antibodies with a long term goal of abrogating the need for breast cancer patients to receive repeated therapeutic infusions of trastuzumab (Herceptin, Genentech), an anti-Her2 monoclonal antibody. Autoantigens in various autoimmune diseases have undergone isoaspartyl modification. An additional hypothesis of the study is that isoaspartyl modification of these Her2 peptides would increase their immunogenicity, in essence using protein modifications featured in autoimmune reactions to enhance the anti-breast tumor immune response. Balb/c and Her2 transgenic FVB/N mice were immunized with a specific Her2 peptide with Complete Freunds Adjuvant (CFA). Sera were collected from the Balb/c mice via retro-orbital bleed. ELISA, Western Blot, and FACS analysis using 2 human breast cancer cell lines, BT474 and SKBR3, were used to study the antibody response to immunization. Her2 Transgenic FVB/N mice were examined for the development of palpable mammary tumors. Results showed that immunization with the Her2 peptide 21mer sequences P601-621 and P601-621Iso resulted in the formation of anti-Her2 antibodies that bound the full length Her2 protein in Western blotting and also bound Her2 on the surface of both breast cancer cell lines. Sera from these mice also inhibited BT474 cell proliferation in vitro, and immunization with these peptides delayed the development of palpable mammary tumors in Her2 transgenic FVB/N mice. Modified and unmodified peptides of 9 and 10 amino acids (P602-610 and P602-611) were also tested as vaccine candidates, but antibodies raised to these peptides bound Her2 on the cell surface with less affinity and were of lower number than antibodies from mice immunized with either 21mer peptide. In conclusion, the 21mer peptides are strong potential vaccine candidates for breast cancers overexpressing Her2. The unmodified 21mer, P601-621, is a slightly better candidate than P601-621Iso based on antibody binding to the cell surface as noted on FACS. Therefore, it seems that the immunogenicity of the 21mer peptides is due to the exposure of a peptide sequence that is normally hidden from the immune system rather than isoaspartyl modification