TGFB1 and glioblastoma: The GBM TME is also characterized by immunosuppressive cytokines including IL-1, TGF-β, and IL-10, as well as factors (CSF-1 and Arginase I) that impair effector T cell function and maintain tumorigenic cellular populations (Tregs, immunosuppressive TAMs, and MDSCs) that ultimately contribute to immune escape (17).