KYN is a natural endogenous ligand of the human aryl hydrocarbon receptor (AHR) which activates the KYN-AhR-AQP4 signaling pathway supporting tumor growth and glioma cell motility [46], as well as the agonistic activity in the AHR leading to the differentiation onaïveaive to Treg lymphocytes [56]. The gene discussed is AQP4; the disease is glioma.