CD4 and COVID-19: Furthermore, it was also confirmed that the ratio of naïve CD4+ T cells to CD8+ T cells decreased in early recovery-stage (ERS) COVID-19 patients, while the central memory CD4+ T cells were significantly higher than in HCs by scRNA-seq analysis of peripheral blood mononuclear cells during the recovery stage of COVID-19 (Wen et al., 2020a).