CCR7 and COVID-19: In particular, severe COVID-19 patients linked to pulmonary failure and requiring mechanical ventilation were evidenced to have upregulated cytotoxic T cell CCR4 and CCR5 levels, responsible for migration to lung tissue and promoting recruitment to the site of inflammation, respectively, whereas the percentage of CCR7+ cells was decreased compared not only to control subjects but also patients with mild COVID-19 [52].