IDO1 and cancer: IDO1 is expressed in these two cancer types and an explanation of this deleterious effect of dexamethasone has been advanced in relation to interferon actions in COVID-19 infection [110], based on the ability of this steroid to potentiate the IFN-γ induction of IDO1 by prostaglandin PGE2, but to inhibit the corresponding IDO1 induction by IFN-α.