Therefore, we then conducted cell–cell communication analyses which confirmed the presence of interaction between exhausted T cells and macrophages in severe COVID-19 via cytokine–receptor axes (CXCL2-DPP4, CXCL11-DPP4, CCL3L1-DPP4, CCL3L1-CCR1, CCL3-CCR1, CCL2-CCR2, CCL3-CCR5, CCL4-CCR5, and CCL4L2-VSIR). This evidence concerns the gene DPP4 and COVID-19.