Wilms' tumor gene WT1 is highly expressed in
leukemia and in various types of solid
tumors and exerts an oncogenic function. Thus,
WT1 protein is a most promising
tumor-associated
antigen. We have been successfully performing WT1 vaccination with a 9-mer modified WT1(235)
peptide, which has one amino acid substitution (M→Y) at position 2 of 9-mer natural WT1(235)
peptide (235-243 a.a.), for close to 700
HLA-A*24:02-positive patients with
leukemia or solid
tumors. Although vaccination of modified WT1(235)
peptide induced natural WT1(235)
peptide-recognizing cytotoxic T-lymphocytes (CTLs) and exerted cytotoxic activity towards
leukemia and solid
tumor cells that expressed the natural WT1(235)
peptide (
epitope) but not the vaccinated modified WT1(235)
peptide (
epitope), the molecular basis has remained unclear. In this study, we established a modified WT1(235)
peptide-specific CTL clone, we isolated
T-cell receptor (TCR) genes from it and transduced the TCR genes into CD8(+) T-cells. The TCR-transduced CD8(+) T-cells produced
interferon-γ (IFNγ) and
tumor necrosis factor-α (TNFα) in response to stimulation not only with the modified WT1(235)
peptide but also with the natural WT1(235)
peptide and lysed modified or natural WT1(235)
peptide-pulsed target cells and endogenously WT1-expressing
leukemia cells in a
HLA-A*24:02-restriction manner. These results provided us, for the first time at molecular basis, with a proof-of-concept of modified WT1(235)
peptide-based
immunotherapy for natural WT1(235)
peptide-expressing
malignancies.