TDO2 and neoplasm: IFN-γ induces tumor-repopulating cells (TRCs) to enter dormancy and escape immune surveillance through an IDO/TDO/Kyn-dependent pathway [112] Blocking IDO/AhR abrogates IFN-γ-induced dormancy and decreases tumor growth through inhibition of the STAT3/p53 pathway [113,114].