Apart from up-regulating the above determinants related to Trp metabolism, various mechanisms of tumoral immune escape have been proposed, including (1) metabolic stress [116], (2) hypoxia-induced NAD+ intervention [111], (3) M2 macrophage-derived exosomal microRNA-155-5p down-regulating ZC3H12B [117], (4) various mechanisms operating during the cancer immune cycle [118], (5) a role for cancer stem cells [119] (6) NAD+ metabolism to maintain inducible PD-L1 expression [120] and (7) non-coding RNAs [121,122]. This evidence concerns the gene CD274 and cancer.