CD4 and COVID-19: Accordingly, we and others have described that immune cells from patients with COVID-19 show significantly higher levels of exhaustion markers such as PD-1 and Tim-3 (7, 43, 58), increased regulatory T cell (Treg) counts, CD4 lymphopenia, and impaired direct cytotoxicity (DCC) (7, 59, 60), which may consequently influence on the reactivation of CMV and EBV proviruses.