CD38 and COVID-19: The proportion of apoptotic Annexin V+ HSCs in total Lin– D34+CD38– D45RA–CD90+CD49f+ HSCs from COVID-19 patients was higher than in HC, but lower than in samples collected from patients diagnosed with avascular necrosis of the femoral head and co-infected with human immunodeficiency virus or hepatitis virus, which worked as positive control (Fig. 3e and Supplementary Fig. S2g–k).