To identify highly cytotoxic CD8+ T cell clusters among the ones found (Fig. 2B), we created a cytotoxic scoring using proinflammatory genes that are expressed by cytotoxic T lymphocyte (CTL) in critical patients with COVID-19 as described by Chua et al. (13) and applied this dataset to the CD8+ clusters that we identified in our analysis. The gene discussed is CD8A; the disease is COVID-19.