IDO1 and glioma: Additionally, changes in AhR and AhR target gene levels have been linked to increased IDO1 and TDO2 levels in glioblastoma cells pointing to the fact that increased IDO-activity might promote AhR-mediated changes in glioma cells that enable immune escape and malignant potential (Opitz et al., 2011; Sadik et al., 2020).