PDCD1 and neoplasm: To look more broadly at coinhibitory receptor (CTLA-4, TIM-3, LAG-3, TIGIT, and KLRG1) and costimulatory receptor (GITR, OX40, and 4-1BB) CD8 tumor expression correlation with PD-1, public domain single cell RNAseq gene expression datasets with available processed gene counts were obtained, and CD8 T cell data analyzed.