IDO1 and neoplasm: Takenaka and colleagues reported that increased IDO-mediated release of Kyn by glioblastoma cells promotes AhR activation in tumor-associated macrophages (TAMs); activation of AhR signaling in TAMs increased expression of the ectonucleotidase CD39 and accumulation of adenosine in the tumor microenvironment (TME) leading to suppression of CD8+ T cell function (39).