For example, Gzma, Gzmk, and Ccl5 were significantly more expressed in CD8_EM cells from most cancer types, both murine and human; Pdcd1, Havcr2, and Prf1, among other genes, identified CD8+ exhausted cells; Xcl1, Tnfsf4, and Tox, among others, marked precursor exhausted CD8+ T cells; Sell, Tcf7, Il7r, and Ccr7 were enriched in both CD4+ and CD8+ naive-like cells; Foxp3, Il2ra, Ctla4 and several other genes identified Tregs; Tox2 and Tbc1d4 were differentially expressed in Tfh; and Cd40lg, Anxa1 and Rora were enriched in T helper cells. Here, PDCD1 is linked to cancer.