In KEGG enrichment analysis, we found that antigen processing and presentation, Natural killer (NK) cell-mediated cytotoxicity, Graft-versus-host disease, PD-L1 expression and PD-1 checkpoint pathway in cancer, and Th1 and Th2 cell differentiation were the most over-represented pathways (Figure 4D). The gene discussed is PDCD1; the disease is cancer.