TGFB1 and glioblastoma: Myeloid cells and Tregs inhibit cytotoxic T cells by multiple mechanisms, including the secretion of immunosuppressive cytokines such as IL10 and TGFβ; these have multiple inhibitory effects on cytotoxic T cells including promotion of their exhaustion [80], a common state for cytotoxic T cells in the glioblastoma tumor microenvironment [81].