CD4 and COVID-19: In contrast, a recent study found that the decrease in CD4+ T cells in COVID-19 patients was accompanied by up-regulation of Tim-3 in TH1, Treg, Tfh cells, and they may reduce the functions described above.32,33,35 In addition, Herrmann et al2 found the expression of LAG-3 and TIM-3 in all subsets of CD8+ and CD4+ T cells (including naive, CM, TM, EM, EMRA, and SARS-CoV-2–specific T cells) of critical COVID-19 patients increased significantly.