PDCD1 and neoplasm: Although it has been suggested that NK cells may express PD-1 through trogocytosis and because we observed differences in the phenotype of NK cells from WT and PD-1−/− mice, we performed single cell RNA-sequencing (scRNA-SEQ) using the SMART-SEQ2 platform (Picelli et al., 2013) on tumor-infiltrating NK cells from mice inoculated with the MTAP1A tumor.