CD28 and COVID-19: In particular, CD3+ CD4+ helper T (Th) cells and CD3+ CD8+ suppressor T cells were detected below normal levels in patients with COVID-19, and CD3+ CD4+ CD45RO+ memory Th cells and CD3+ CD8+ CD28+ cytotoxic suppressor T cells were found to be decreased in severe COVID-19 patients as compared to non-severe patients in Wuhan, China [36].