PDCD1 and COVID-19: Patients with overtly symptomatic COVID-19 showed increased programmed cell death protein-1 (PD-1) and T-cell immunoglobulin domain and mucin domain-3 (TIM-3) expressions on CD8+T cells.97 These results indicate that functional impairment or exhaustion of T cells is correlated with disease severity and prognosis of patients with COVID-19.