In addition, we studied the relationship between the expression of KCC2 (SLC12A5) and NKCC1 (SLC12A2) in pan-cancer and immune checkpoint genes, including SIGLEC15, IDO1, CD274, HAVCR2, PDCD1, CTLA4, LAG3, and PDCD1LG2. This evidence concerns the gene IDO1 and cancer.