T cell surveillance of oncogene-induced prostate cancer is impeded by T cell-derived TGF-β1 cytokine.

Tolerance induction in T cells takes place in most tumors and is thought to account for tumor evasion from immune eradication. Production of the cytokine TGF-β is implicated in immunosuppression, but the cellular mechanism by which TGF-β induces T cell dysfunction remains unclear. With a transgenic model of prostate cancer, we showed that tumor development was not suppressed by the adaptive immune system, which was associated with heightened TGF-β signaling in T cells from the tumor-draining lymph nodes. Blockade of TGF-β signaling in T cells enhanced tumor antigen-specific T cell responses and inhibited tumor development. Surprisingly, T cell- but not Treg cell-specific ablation of TGF-β1 was sufficient to augment T cell cytotoxic activity and blocked tumor growth and metastases. These findings reveal that T cell production of TGF-β1 is an essential requirement for tumors to evade immunosurveillance independent of TGF-β produced by tumors.