High Frequencies of Phenotypically and Functionally Senescent and Exhausted CD56 + CD57 + PD-1 + Natural Killer Cells, SARS-CoV-2-Specific Memory CD4 + and CD8 + T cells Associated with Severe Disease in Unvaccinated COVID-19 Patients.

Significant exhaustion and senescence in both NK and T cells were detected in unvaccinated symptomatic COVID-19 patients, suggesting a weakness in both innate and adaptive immune systems leads to severe disease in critically ill COVID-19 patients.