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PD-1 expression on NK cells can be related to cytokine stimulation and tissue residency

Although PD-1 was shown to be a hallmark of T cells exhaustion, controversial studies have been reported on the role of PD-1 on NK cells. Here, we found by flow cytometry and single cell RNA sequencing analysis that PD-1 can be expressed on MHC class I-deficient tumor-infiltrating NK cells in vivo. We also demonstrate distinct alterations in the phenotype of PD-1-deficient NK cells which in part could be attributed to a decrease in tumor-infiltrating NK cells in PD-1-deficient mice. NK cells from PD-1-deficient mice exhibited a more mature phenotype which might reduce their capacity to migrate and kill in vivo. Finally, our results demonstrate that PD-L1 molecules in membranes of PD-1-deficient NK cells migrate faster than in NK cells from wildtype mice, suggesting that PD-1 and PD-L1 form cis interactions with each other on NK cells.