We found a strong positive correlation between the Treg signature (FOXP3) and T cell exhaustion signatures (TOX, HAVCR2, PDCD1, TIGIT, LAG3, CTLA4, and CXCL13) in various treatment-naive human cancers (Supplemental Figure 13), indicating that elevated Treg numbers in the TME, probably promote CD8+ T cell exhaustion in human cancers. This evidence concerns the gene PDCD1 and cancer.