HAVCR2 and COVID-19: For example, increases in the expression of inhibitory receptors such as programmed cell death protein 1 (PD-1), T cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), lymphocyte activation gene 3 (LAG-3), and cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) have been observed in highly activated or possibly exhausted T cells in severe acute COVID-19 cases (8–12).