KLRF1 and COVID-19: Besides this first CD16+ CD8+ TEMRA population, four strongly clonally expanded subsets (CD16+ CD8+ TEMRA-2 to -5), characterized by high expression of FCGR3A, KLRF1 and surface expression of CD161 were observed in all conditions, whereas a highly activated and less expanded subset (CD16+ CD8+ TEMRA-6) was enriched in severe cases of COVID-19.