Cluster 1 contained all the 107 HSC/MPPs from the HC but only two HSC/MPPs from mild cases and four HSC/MPPs from severe COVID-19 cases, and the other 31 cells in mild cases and 40 cells in severe cases were clustered into cluster 2 unsupervisedly, indicating marked difference between regulatory TF landscapes of the HSC/MPPs from COVID-19 patients and those from HC (Fig. 4e and Supplementary Fig. S4a). Here, TF is linked to COVID-19.