IDO1 and neoplasm: However, Liu and colleagues showed that IFNγ signaling resulted in IDO1/AhR‐dependent p27 induction when IDO1 and AhR were highly expressed in tumor‐repopulating cells (TRCs).48 The p27 in turn bound to cytosolic pSTAT1, which prevented STAT1‐mediated tumor cell apoptosis.