In summation, in all cases, Treg subgroups were central parts of the top 5 most severity-associated (Ki67+CD38+: critical COVID-19, naïve Tregs and CM-like Treg: moderate COVID-19) or sex-associated (cTfr: female patients, Ki67+CD38+: male patients) cellular populations in COVID-19. Here, MKI67 is linked to COVID-19.