Wilms' tumor gene (WT1) possesses oncogenic functions and is expressed in various kinds of
malignancies, which suggests that the gene's product, the
WT1 protein, should be one of the most promising
cancer antigens. In fact, the
WT1 protein was shown to be highly immunogenic in
cancer patients. WT1
peptides that could induce WT1-specific CTLs (WT1 CTL
peptides) were identified, and vaccination of
cancer patients with these WT1 CTL
peptides induced immunological responses, which were assessed by ex vivo immuno-monitoring, such as the tetramer assay, and in vivo immuno-monitoring, such as the
peptide-specific delayed type
hypersensitivity reaction. The induced immunological responses then led to clinical responses such as solid
tumor shrinkage, a decrease in
leukemia cells, and reduction of
M-protein (multiple myeloma). Long-term stabilization of disease with good quality of life, which might be characteristic of
cancer vaccine therapy, was also reported. It is noteworthy that injection with a "single" kind of WT1
peptide elicited an immunological response strong enough to induce a clinical response, indicating that the WT1
peptide vaccine has therapeutic potential. The number of reports of the successful treatment of
cancer patients (not only adult but also childhood
malignancies) with WT1 vaccination is increasing. Strategies for further improvement in the efficacy of
therapy, including combined use of
chemotherapy drugs, molecular-target-based drugs, or WT1 helper
peptides, are being proposed. WT1
peptide vaccination in an "adjuvant setting" should be considered a promising treatment to protect against progression or relapse of
malignancies in cases with
minimal residual disease.