CD4 and COVID-19: High-dimensional analysis of circulatory immune profiles in mild, moderate and severe COVID-19 patients by mass cytometry revealed that proportions of naïve CD4+ T cells, TGFβ+CD28− naïve CD4+ T cells, DCs, and macrophages are associated with mild cases, whereas a sharp decline in the proportion of CD8+ T cells and NK cells was observed in severe cases (3).