CD4 and COVID-19: In keeping with the observation that expanded CD8 T cell clones show increased expression of cytotoxicity markers (Watson et al, 2020), using a composite gene score for cytotoxicity, we found that the number of expanded clones correlated with the average cytotoxicity score across all cells for that individual in both CD4+ T effector (CD4.TEFF/TEFF.prolif) and CD8+ T effector (CD8.TEFF/TEFF.prolif) populations (Figure S7M), and was higher in mild and community COVID-19 cases with reduced cytotoxicity observed in critical and severe disease (Figure 5H).