Compared to non-GBM controls, GBM and other gliomas can isolate peripheral circulating T cells in the bone marrow, leading to relative lymphopenia.201 In addition, GBM can evoke the invading CD4+ and CD8+ T cell apoptosis via the Fas/FasL signaling.202–204 Tregs, by producing TGF-β and IL10, affect tumor immune escape, thereby reducing the capability of CD8+ T cells to respond to their cancer cells.205 GBM cells express chemokine (C–C motif) ligand 2 (CCL2), leukocyte-specific protein-1 (LSP-1), STAT3, HIF-1α, and IDO to enhance the activity and survival of Tregs within the TME.206–211. Here, IDO1 is linked to glioma.