The mice lacking IL-21 or mice with specific deletion of STAT3 in T cells fed with HFD showed an increase of VAT Treg cells and an improvement of adipose inflammation and insulin sensitivity, suggesting an important role for IL-21 and STAT3 signaling in regulating VAT Treg cells in obesity (63, 66). The gene discussed is STAT3; the disease is obesity due to melanocortin 4 receptor deficiency.