EphA2-derived peptide vaccine with amphiphilic poly(gamma-glutamic acid) nanoparticles elicits an anti-tumor effect against mouse liver tumor.

The prognosis of liver cancer remains poor, but recent advances in nanotechnology offer promising possibilities for cancer treatment. Novel adjuvant, amphiphilic nanoparticles (NPs) composed of L: -phenylalanine (Phe)-conjugated poly(gamma-glutamic acid) (gamma-PGA-Phe NPs) having excellent capacity for carrying peptides, were found to have the potential for use as a peptide vaccine against tumor models overexpressing artificial antigens, such as ovalbumin (OVA). However, the anti-tumor potential of gamma-PGA-Phe NPs vaccines using much less immunogenic tumor-associated antigen (TAA)-derived peptide needs to be clarified. In this study, we evaluated the effectiveness of immunization with EphA2, recently identified TAA, derived peptide-immobilized gamma-PGA-Phe NPs (Eph-NPs) against mouse liver tumor of MC38 cells (EphA2-positive colon cancer cells). Immunization of normal mice with Eph-NPs resulted in generation of EphA2-specific type-1 CD8+ T cells. Immunization with Eph-NPs tended to provide a degree of anti-MC38 liver tumor protection more than that observed for immunization with the mixture of EphA2-derived peptide and complete Freund's adjuvant (Eph + CFA). Neither Eph-NPs nor Eph + CFA vaccines inhibited tumor growth of BL6, EphA2-negative melanoma cells. Splenocytes isolated from MC38-bearing mice treated with Eph-NPs showed strong and specific cytotoxic activity against MC38 cells. Immunization with Eph + CFA induced liver damage as evidenced by elevation of serum alanine aminotransferase, while Eph-NPs vaccination did not exhibit any toxic damage to the liver. These results demonstrated that immunization with Eph-NPs displayed anti-tumor effects against liver tumor by generating acquired immunity equivalent to the toxic adjuvant CFA, suggesting that safe gamma-PGA-Phe NPs could be applied clinically for the vaccine treatment of liver cancer.