IL21 and COVID-19: In the T cell cluster from the primary dataset, the most abundantly expressed transcripts among patients with COVID-19 were those derived from IFNG (ndonors = 20, fcells = 31%), followed by TNF (ndonors = 20, fcells = 16%), FASLG (ndonors = 18, fcells = 13%), CD40LG (ndonors = 12, fcells = 3%), and, less frequently, IL2, IL10, and IL21 (Supplementary Fig. 7).