TGFB1 and glioma: The powerful immunosuppressive effect in the TME of gliomas is caused by several mechanisms, including the abnormal function of cells such as the existence of immunosuppressive cells (M2 GAMs, Tregs, and MDSCs) and immunosuppressive cytokines (TGF-β, IL-10), low number of TILs, and the high expression of inhibitory immune checkpoint molecules such as PD-1, TIM-3, and LAG-3 (38, 109–112).