CTLA4 and COVID-19: This revealed that the LAG3+IFNγ+CD8+ T cells (10.12% CD8+ T cells in mildly symptomatic COVID-19 patients and 25.83% CD8+ T cells in severely symptomatic COVID-19 patients) and CTLA4+IL10RA+CD8+ T cells (4.42% CD8+ T in mildly symptomatic COVID-19 patients and 13.88% CD8+ T in severely symptomatic COVID-19 patients) might contribute to the T cell exhaustion associated with the severe phenotype of COVID-19 in patients (Figures 5G–J).