TGFB1 and cancer: CTL, which are activated by Th1-derived cytokines, show cytotoxic activity and induce apoptosis in cancer cells, but T cell activation is reduced in cancer patients, and one possible mechanism by which this occurs is through transforming growth factor-β (TGF-β), which is released by tumor cells and suppresses the activation of Th1 cells and CTL [19, 20].