IDO1 and hepatocellular carcinoma: Cheng et al reported that CAFs that were derived from hepatocellular carcinoma promoted the production of regulatory DCs, which was associated with low co‐stimulatory molecule expression, high suppressive cytokines production and the enhancement of regulation of the immune response, including the proliferation of Treg cells through the upregulation of indoleamine‐2,3‐dioxygenase (IDO).70 This research also showed that IL‐6 that was derived from CAFs was necessary for the generation of IDO.