IDO1 and cancer: The murine Ido1 promoter is not well characterized but the human Ido1 promoter contains multiple ISRE and GAS sites that respond to ISGF3 (Stat1-Stat2-IRF9) complexes and Stat1 homodimers, respectively.68 An increased amount of such complexes in Tyk2-deficient Paneth-like cancer cells would enhance Ido1 expression.