TDO2 and neoplasm: Additionally, 2‐HG can increase the activity of macrophage tryptophan 2,3‐dioxygenase (TDO) in the tumor microenvironment, allowing l‐tryptophan to be metabolized to the AhR ligand kynurenine (Kyn), activating the AhR signaling pathway, inducing AhR translocation to the nucleus [19], increasing IL‐10 production, leading to decreased macrophage antigen presentation and increased T cell inhibition, and forming an immunosuppressive tumor microenvironment [19].