CD4 and COVID-19: Although many studies have found that TIGIT is up-regulated in patients with acute COVID-19, ICU patients, and the deceased, the Treg, CD4+ TM cell, and CD8+ T cell subgroups are up-regulated and recovered in the rehabilitation cohort.40 Reports also have shown a decrease in TIGIT in NK cells2 and normal TIGIT expression on CTLs from COVID-19 patients regardless of the need for hospitalization.22,25