NOS2 and graft versus host disease: A metabolite of Trp, kynurenine-pretreated MSCs together with IFN-γ and TGF-β upregulate immunomodulatory genes in MSCs, such as Nos2, Ido, Ptgs2, Hmox1, Pge2, Lif, and CD274. The administration of those cytokine-pretreated MSCs decreased GVHD scores and improved mouse survival compared with untreated MSCs [20].