IDO1 and glioblastoma: The Gene Expression Profiling Interactive Analysis database (GEPIA2, http://gepia2.cancer-pku.cn) revealed a significantly higher expression of PD-L1 and IDO1 transcripts in GBM patient samples compared to normal tissue, and in both cases the difference in expression was marked when compared to low grade glioma (LGG) (Fig. 5A).