PDCD1 and neoplasm: Although the frequency of PD-1-expressing tumor infiltrating CD62L+CXCR6- NK cells was low (Figures 4C, 4E, and S7, 1.5%±0.7 n = 9), PD-1 expression was associated with the CD62L−CXCR6+ NK cells, with approximately 25% of tumor infiltrating CXCR6+ NK cells expressing PD-1 (Figures 4D and 4E, 29% ± 11 n = 9).