Foxp3 overexpression in CD4+ T cells repressed cytokine gene expression, including IL‐2, IFN‐g, IL‐4, and IL‐17.29 Non‐functional fusion protein of Foxp3 in mice with a Foxp3 allele made CD4+ T cells lack suppressor function, suggesting that the expression of functional Foxp3 protein are required for inhibitory function of Tregs.30 Mice lacking Foxp3 expression have deficits in Tregs and develop autoimmune disease similar to IL‐2R‐/‐ mice. Here, IL4 is linked to autoimmune disease.