Transforming growth factor-beta (TGF-β) is deeply involved in colorectal cancer development and the disruption of the TGF-β signaling in dysplastic cells is required for tumor to grow. Nevertheless, tumor cells express TGF-β to escape the immune surveillance mediated by T cells. T-cell expression of Smad7, an intracellular inhibitor of the TGF-β signaling, protects against colitis-associated colorectal cancer. However, whether Smad7 in T cells might influence colorectal cancer growth independently of chronic inflammation and which T-cell subset is involved in this process is unknown. To address this issue, T-cell-specific Smad7 transgenic mice and wild-type (WT) littermates were subcutaneously transplanted with syngenic MC38 colon carcinoma cells. Smad7Tg mice were resistant to tumor development compared with WT mice and protection was dependent on CD4(+) T cells. Smad7 expression in T cells increased the number of tumor-infiltrating Tbet/ROR-γ-t double-positive CD4 T cells characterized by the expression of tumor necrosis factor-alpha (TNF-α) and interferon-gamma but lower IL17A. The low expression of IL17A caused by the Smad7 expression in tumor-infiltrating CD4(+) T cells enabled the TNF-α-mediated killing of cancer cells both in vitro and in vivo, thus indicating that the Smad7-mediated plastic effect on T-cell phenotype induces protection against colorectal cancer.
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