Serum IL-6 is considered a biologically relevant biomarker associated with disease progression in COVID-19, and IL-6 receptor blocking therapy using tocilizumab might help clinical improvement in patients with severe and critical COVID-19.24,25 Although there was no comparative analysis between the two groups because of the small number of patients, the patients in the UC-MSCs-treatment group showed a decrease of serum IL-6. This evidence concerns the gene IL6 and COVID-19.