IDO1 and glioblastoma: High intratumoral expression of immunosuppressive mediators including programmed cell death protein-1 (PD-1) and indoleamine 2,3 dioxygenase 1 (IDO), is prognostic for decreased GBM patient survival (Wainwright et al., 2012; Nduom et al., 2016; Zhai et al., 2017).