GBM-derived tenascin-C (TNC)-mediated inhibition of T cell proliferation and activation Increased T cell expression of PD-1, TIM-3, CTLA-4 and IDO-1 Imbalance of TH1/TH2 resulting in pro-tumor TH2 bias IDO-mediated induction of regulatory T cells HIF-1a, ICOSLG, and IL2-mediated proliferation of regulatory T cells. Here, ICOSLG is linked to glioblastoma.