We previously evaluated Wilms’ tumor gene 1 (WT1) peptide vaccination in a large number of patients with leukemia or solid tumors and have reported that HLA-A*24:02 restricted, 9-mer WT1-235 peptide (CYTWNQMNL) vaccine induces cellular immune responses and elicits WT1-235-specific cytotoxic T lymphocytes (CTLs). However, whether this vaccine induces humoral immune responses to produce WT1 antibody remains unknown. Thus, we measured IgG antibody levels against the WT1-235 peptide (WT1-235 IgG antibody) in patients with glioblastoma multiforme (GBM) receiving the WT1 peptide vaccine. The WT1-235 IgG antibody, which was undetectable before vaccination, became detectable in 30 (50.8%) of a total of 59 patients during 3 months of WT1 peptide vaccination. The dominant WT1-235 IgG antibody subclass was Th1-type, IgG1 and IgG3. WT1-235 IgG antibody production was significantly and positively correlated with both progression-free survival (PFS) and overall survival (OS). Importantly, the combination of WT1-235 IgG antibody production and positive delayed type-hypersensitivity (DTH) to the WT1-235 peptide was a better prognostic marker for long-term OS than either parameter alone. These results suggested that WT1-235 peptide vaccination induces not only WT1-235-specific CTLs as previously described but also WT1-235-specific humoral immune responses associated with antitumor cellular immune response. Our results indicate that the WT1 IgG antibody against the WT1 peptide may be a useful predictive marker, with better predictive performance in combination with DTH to WT1 peptide, and provide a new insight into the antitumor immune response induction in WT1 peptide vaccine-treated patients.
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