WT1 is a tumor‐associated antigen in colon cancer that can be recognized by in vitro stimulated cytotoxic T cells

Abstract

The Wilms' tumor suppressor gene (WT1) has been shown to be overexpressed in acute and chronic leukemias and in a variety of solid human malignancies, including cancers of the breast and lung. In our present study, we investigated the potential role of WT1 gene in human colon cancer. WT1 mRNA and protein expression was analyzed in a panel of human colon cancer cell lines and primary colon carcinomas by RT-PCR and Western blot analysis, respectively. A mutational screen of WT1′ zinc-finger region was carried out by sequence analysis. Finally, using peptide-stimulated cytotoxic T cells it was investigated whether WT1-expressing colon tumor cells are a potential target for antigen-specific immunotherapy. Medium to high abundant levels of WT1 mRNA were detected by RT-PCR in 10 of 12 (83%) colon cell lines and by quantitative, real-time RT-PCR in 13 of 15 (87%) primary tumors, whereas only very low levels of expression were found in 2 primary tumors. Interestingly, however, low levels of WT1 mRNA were also detected in all samples derived from normal colon mucosa. When RT-PCR products were examined by sequence analysis, both +KTS and −KTS splice isoforms but no zinc-finger mutations were found, suggesting that the wild-type form of the WT1 gene is expressed. To determine whether the WT1 protein can serve as a target antigen for immunotherapy, 2 HLA-A2.1-restricted WT1 peptides (Db126 and WH187) were used for the in vitro induction of WT1-specific cytotoxic T lymphocytes (CTLs). The WH187-specific CTLs not only lysed target cells pulsed exogenously with cognate peptide but also WT1-expressing colon tumor cells in a HLA-restricted manner. These findings identify the WT1 protein as an attractive target for the development of antigen-specific immunotherapy in human colon cancer.