TGFB1 and glioblastoma: The GBM TME has been shown to be more immunosuppressive compared to other malignancies due to the release of potent immunosuppressive cytokines (e.g., IL-10 and TGF-β) [598]), negative regulators of effector cell functions (e.g., programmed death-ligand 1 and IDO), and oncometabolites (e.g., (R)-2-hydroxyglutarate6 and O6-methylguanine-DNA methyltransferase promoter methylation) [599].