CCR7 and COVID-19: After subdividing Tregs into four subclusters (CCR7+ Tregs, CD69+ Tregs, CTLA4+ Tregs, and HLA_DR+ Tregs), the percentage of CCR7+ Tregs in the eight COVID-19 patient groups was lower compared to the healthy controls, while the proportion of HLA_DR+ Tregs in the eight COVID-19 patient groups was higher.