TGFB1 and glioma: The TGFB pathway has also been shown to contribute to a “cold” TME in high-grade gliomas via its immunosuppressive effects characterized by inhibition of CD8-antigen-positive cytotoxic T cells, natural killer (NK) cells, and activation of regulatory T cells (Tregs) as well as myeloid derived suppressor cells (MDSCs) [30,31,32,33,34,35,36].