Anti-tumor immunity elicited by cross-linking vaccine heat shock protein 72 and alpha-fetoprotein epitope peptide

Abstract

Hepatocellular carcinoma (HCC) is one of the most common malignancies over the world. Alpha-fetoprotein (AFP) is an oncofetal protein during HCC development, which could generate weaker and less reproducible antitumor protection, and may serve as a target for immunotherapy. Therefore, it is imperative to enhance its immunogenicity and develop therapeutic vaccines to eliminate AFP-expressing tumors. In this study, by using glutaraldehyde cross-linking, we constructed a potential therapeutic peptide vaccine, heat shock protein 72 (HSP72) and AFP epitope peptide (HSP72/AFP-P). ELISPOT was applied to evaluate the quantity of AFP-specific CD8+ T cell that secreted IFN-γ in immunized BALB/C mice. Granzyme B released from natural killer cells and AFP-specific antibody responses in immunized mice were detected by ELISA. The anti-tumor effects were investigated by in vitro cytotoxic T-lymphocyte assays and in vivo tumor therapeutic experiments. The results showed that reconstructed HSP72 and AFP epitope peptide vaccine synergistically exhibited significant increases in AFP-specific CD8+ T cells, natural killer cells responses and impressive antitumor effects against AFP-expressing tumors. Immunization of BALB/C mice with HSP72/AFP-P vaccine elicited stronger T-cells responses. The numbers of IFN-γ-producing CD8+ T cells from mice immunized with HSP72/AFP-P were 30 times more than those from mice immunized with AFP-P, HSP72 or PBS (P < 0.01). The concentration of granzyme B in natural killer cells from mice immunized with HSP72/AFP-P were 15 times higher than that from other groups (P < 0.01). In vitro effector cells from mice immunized with HSP72/AFP-P showed much stronger cytolytic effect on H22 target cells than those from mice vaccinated with AFP-P, HSP72 or PBS (P < 0.01). Priming mice with the reconstructed vaccine exhibited robust strong protective immunity. Mice immunized with HSP72 or AFP-P alone demonstrated higher average tumor volumes than mice immunized with HSP72/AFP-P (P < 0.05). Our study suggests that constructing a tumor vaccine by cross-linking AFP antigen epitope peptide and HSP72 is a promising approach for cancer therapy.