CD8A and COVID-19: Other studies have detected and characterized SARS-CoV-2-reactive CD8+ and CD4+ T cells using ex vivo antigen stimulation-based assays, including interferon (IFN)-γ ELISpot assays, intracellular cytokine staining (ICS), and activation-induced marker (AIM) assays.4 Intriguingly, SARS-CoV-2-reactive CD8+ and CD4+ T cells have been detected not only in COVID-19 patients and convalescents, but also unexposed individuals.