IDO1 and central nervous system cancer: Notably, global transcriptomic analysis of INCR1 knockdown and PD-L1 knockdown GBM cells revealed that silencing INCR1 reduced the expression of a significantly larger number of immunosuppressive molecules compared to PD-L1 silencing, which showed a reduction of only itself and the immunosuppressive enzyme IDO1. More than 90% of GBM expresses IDO1 [43], and its expression was associated with poor prognosis in patients with glioma [44].