Methylation-specific quantitative PCR (qPCR) results demonstrated an altered degree of PD1 promoter methylation in CD8+ T cells — but not in CD4+ T cells — of subjects who recovered from COVID-19 as compared with healthy controls, confirming dysregulation of the PD-1/PD-L1 axis in patients who recovered from COVID-19 (Figure 3L). This evidence concerns the gene CD4 and COVID-19.