IDO1 and glioma: Previous studies have shown that the therapeutic inhibition of indoleamine 2,3‐dioxygenase 1, cytotoxic T lymphocyte antigen 4, and PD ligand 1 in glioma models significantly reduced the tumor‐infiltrating Treg cells and improved long‐term survival, indicating immune checkpoint blockade appears to be a promising strategy for glioma immunotherapy.3, 8