Last, we analyzed mRNA levels of additional immunoregulatory mechanisms of brain cancers.19–24 Regarding the kynurenine pathway, the expression of the gene encoding for the enzyme tryptophan-2,3-dioxygenase 1 (TDO) was similar in control and tumor samples, while we did not detect indoleamine 2,3-dioxygenase 1 (IDO1) or indoleamine 2,3-dioxygenase 2 (IDO2) genes (Figure S2A). Here, IDO2 is linked to neoplasm.