CD28 and COVID-19: In contrast, relative numbers of CD3+CD4+CD45RA+Foxp3+CD25+CD127‐ T regulatory cells (P = .047) and of antigen‐experienced(AE)3 cytotoxic CD3+CD8+CD27+CD28‐CD45RA+/‐ T cells (P = .012) were significantly lower in COVID‐19 convalescent patients when compared to HC subjects.