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). This evidence concerns the gene IDO1 and low grade glioma.