A novel α-fetoprotein-derived helper T-lymphocyte epitope with strong immunogenicity in patients with hepatocellular carcinoma

α-Fetoprotein (AFP) is considered a good target for immunotherapy strategies against hepatocellular carcinoma (HCC); however, no immunodominant AFP-derived MHC class II-restricted helper T-lymphocyte (HTL) epitope has been reported. Therefore, we identified novel AFP-derived HTL epitopes possessing high immunogenicity. HTL epitopes were predicted using the online service, and peptides were subsequently synthesized. Four newly synthesized peptides showed positive reactivity in >20% patients on ELISPOT using peripheral blood mononuclear cells (PBMCs). Among these, the highest rate was shown by AFP(1) (MKWVESIFLIFLLNFTESRT), which also showed the highest positive rate in cell proliferation assays. Binding assays demonstrated that AFP(1) had strong binding properties toward MHC molecules. Further, blocking assays performed using an anti-HLA-DR antibody showed that immune response decreased, confirming the binding of AFP(1) to HLA-DR molecules. Furthermore, the survival rates of patients with stages II–IV HCC indicated that T cell response against AFP(1) led to significantly greater survival that of patients without T cell response. When evaluating immune response against AFP(1) before and after HCC treatment, an increase in the frequency of peptide-specific T cells was observed after treatment in patients with HLA-DRB1*1502, *0405, and *0901 alleles. In conclusion, the identified epitopes may be useful for immunotherapy strategies against HCC.