CD4 and COVID-19: Recent studies of identification and characterization of SARS-CoV-2-specific T cell epitopes covered the most prevalent human leukocyte antigen (HLA) allelic variants worldwide (14–38), reporting that CD4+ and CD8+ T cell responses in each individual recognize at least 30 to 40 SARS-CoV-2 antigen epitopes (13), and different epitopes-specific T cell responses associate with COVID-19 disease severity and clinical outcome (23).