PDCD1 and neoplasm: From these results, high expression levels of NK cell-activating receptors, activated T cell markers (PD-1, CXCR3, and especially IFNγ), and tumor's T cell recruitment-associated markers (IFNγ receptor, PD-L1, and CXCL9) were necessary for successful T cell infiltration and tumor killing (Higgs et al., 2018).