Colorectal cancer cells suppress CD4+ T cells immunity through canonical Wnt signaling

Understanding how colorectal cancer escapes from immunosurveillance and immune attack is important for developing novel immunotherapies for colorectal cancer. In this study we evaluated the role of canonical Wnt signaling in the regulation of T cell function in a mouse colorectal cancer model. We found that colorectal cancer cells expressed abundant Wnt ligands, and intratumoral T cells expressed various Frizzled proteins. Meanwhile, both active beta-catenin and total beta-catenin were elevated in intratumoral T cells. In vitro study indicated that colorectal cancer cells suppressed IFN-gamma expression and increased IL-17a expression in activated CD4(+) T cells. However, the cytotoxic activity of CD8(+) T cells was not altered by colorectal cancer cells. To further evaluate the importance of Wnt signaling for CD4+ T cell-mediated cancer immunity, beta-catenin expression was enforced in CD4(+) T cells using lentiviral transduction. In an adoptive transfer model, enforced expression of beta-catenin in intratumoral CD4(+) T cells increased IL-17a expression, enhanced proliferation and inhibited apoptosis of colorectal cancer cells. Taken together, our study disclosed a new mechanism by which colorectal cancer impairs T cell immunity.