CD274 and neoplasm: The G-CSF/STAT3 pathway and IL-18 are responsible for upregulating PD-L1 expression on TANs and NK cells, respectively; transforming growth factor-β (TGF-β) and interferon-γ (IFN-γ) impair NK cell cytotoxicity by upregulating the expressions of PD-L1 and PD-1 on tumor cells and NK cells, respectively (37).