PDCD1 and Immunodeficiency: KEGG pathway enrichment results showed that CD8+T hub genes were mainly enriched in primary immune deficiency, T cell receptor signaling pathway, cytokine-cytokine receptor interaction, NK cell-mediated cytotoxicity, Th1 and Th2 cell differentiation, Th17 cell differentiation, and tumor PD-L1 and PD-1 pathways (Figure 2D).