CD4 and severe acute respiratory syndrome: Unlike SARS-CoV infection, where memory CD8+ T cell response was found to be higher as compared with the memory CD4+ T cell response which persists for more than 6 years (63, 64), SARS-CoV-2-infected recovered patients showed memory CD4+ T cells in all patients where memory CD8+ T cells are present in 70% individuals, suggesting that memory response in severe cases is predominated by CD4+ Tm cells (45).