CD4 and COVID-19: Lymphopenia is one of the immunological responses characteristic of severe cases of COVID-19 accompanied by a marked decrease in the absolute number of circulating CD4+ cells, CD8+ cells, B cells, and natural killer cells (NK) (Zhou et al., 2010; Tan et al., 2020a), as well as a decrease in other cell types and increased levels of pro-inflammatory cytokines (Moore and June, 2020; Verdecchia et al., 2020).