Flow cytometric analysis of unstimulated whole-blood samples revealed a significant increase in the percentage of IFN-γ+CD8+ T cells in COVID-19 patients relative to HVs, while IFN-γ production was comparable in CD4+ T cells, NK cells, and NKT cells between COVID-19 patients and HVs (Supplemental Figure 11A). Here, CD8A is linked to COVID-19.