Evaluating strategies to enhance the anti-tumor immune response to a carbohydrate mimetic peptide vaccine.

Carbohydrate mimetic peptides of tumor associated carbohydrate antigens (TACA) are T-cell-dependent antigens and, therefore, immunization with these surrogates is predicted to overcome the low immunogenicity of carbohydrate antigens. Consistent with this hypothesis, we show that among the potential immune cells involved, peptide immunization led to an increase in T-cell populations. While peptide mimetics may also function as TLR binding ligands, we did not observe evidence of involvement of NK cells. Examining tumor challenged animals, we observed that peptide immunization and not tumor cells rendered IL-12 responsiveness to T-cells, as T-cells from peptide-immunized mice produced IFN-gamma upon stimulation with IL-12. Cyclophosphamide administration enhanced the anti-tumor efficacy of the vaccine, which was achieved by enhancing T-cell responses with no effect on NK cell population. Prophylactic immunization of mice with a DNA construct encoding carbohydrate mimetic peptides indicated a specific role for the mimotope vaccine in anti-tumor immune responses. These data suggest a role for both CD4(+) and CD8(+) T-cells induced by mimotopes of TACA in protective immunity against tumor cells.