IDO1 and neoplasm: Additionally, high-grade flow cytometric analysis showed that functional Treg cells can boost the polarization of M2-like TAMs.83 M2-like TAMs have a close association with tumor cells that overexpress indoleamine 2,3-dioxygenase (IDO).76 The secretion of Kynurenine (Kyn) from IDO or tryptophan 2,3-dioxygenase (TDO) is a core molecular mechanism that regulates the Treg-macrophage suppressor axis and promotes tumor progression through the Kyn-AHR signaling pathway, which involves AHR formation.