IL2RA and COVID-19: By contrast, in severe COVID-19 patients, the immune responses are marked by exhausted T cells displaying high levels of terminal differentiation/senescence markers (immune checkpoints like Programmed Death-1 (PD-1), T cell immunoglobulin and mucin domain-containing protein 3 [TIM-3), T cell immunoreceptor with Ig and ITIM domains (TIGIT)], with proinflammatory CD25+ CD8+ T cells of reduced cytotoxic potential dominating the T cell profile (9, 10).