TGFB1 and glioblastoma: Moreover, studies have shown that GBM cells inhibit the ability of microglia to produce pro-inflammatory cytokines such as TNF, IL-6, and IL1-β and stimulate the secretion of transforming growth factor β (TGF-β) and IL-10, a phenomenon correlated with increased expression of STAT-3 [6,9,10,37,38,39].