IDO1 and central nervous system cancer: Zhang et al. observed that IDO1, PD-L1 (CD274), PD-L2 (PDCD1LG2), TIM-3 (HAVCR2), PD-1 (PDCD1), LAG3, ICOS, and CD27 were highly expressed in the high-risk compared to the low-risk gliomas, which suggests that high risk glioma groups can be more sensitive to immunotherapy [53].