Multiple antigenic peptides of human heparanase elicit a much more potent immune response against tumors

Peptide vaccination for cancer immunotherapy requires an ideal immune response induced by epitope peptides derived from tumor-associated antigens (TAA). Heparanase is broadly expressed in various advanced tumors. Accumulating evidence suggests that heparanase can serve as a universal TAA for tumor immunotherapy. However, due to the low immunogenicity of peptide vaccines, an ideal immune response against tumors usually cannot be elicited in patients. To increase the immunogenicity of peptide vaccines, we designed three 4-branched multiple antigenic peptides (MAP) on the basis of the human leukocyte antigen (HLA)-A2-restricted cytotoxic T lymphocyte (CTL) epitopes of human heparanase that we identified previously as antigen carriers. Our results show that MAP vaccines based on the HLA-A2-restricted CLT epitopes of human heparanase were capable of inducing HLA-A2-restricted and heparanase-specific CTL in vitro and in mice. Moreover, compared with their corresponding linear peptides, heparanase MAP vaccines elicited much stronger lysis of tumor cells by activating CD8(+) T lymphocytes and increasing the releasing of IFN-γ. However, these heparanase-specific CTLs did not lyse heparanase-expressing autologous lymphocytes and dendritic cells, which confirm the safety of these MAP vaccines. Therefore, our findings indicate that MAP vaccines based on CTL epitopes of human heparanase can be used as potent immunogens for tumor immunotherapy because of advantages such as broad spectrum, high effectiveness, high specificity, and safety.