IDO1 and cancer: IDO- and PGE2-mediated reduction in NK receptors level leading to the impairment of NK cell-mediated cytolytic activity against cancer cells [70]Induction of phenotype switching of melanoma cells toward an undifferentiated and more invasive variant (characterized by downregulation of MITF and elevated expression of stemness markers) driven by cytokines released by the NK cells (e.g., IFN-γ and TNF-α) [131]