In this study, we determined the mRNA expression of three key genes of T-helper subpopulations, i.e., FOXP3 (Treg), RORγt (Th17), and T-bet (Th1), in patients with COVID-19 and T2D who did or did not take metformin (Figure 2). The gene discussed is FOXP3; the disease is type 2 diabetes mellitus.