CTLA4 and Autoimmunity: Treg cells characterized by the expression of CD4, CD25, and Foxp3 are a subpopulation of CD4+ T cells specialized to modulate the immune system, maintain immune tolerance, and prevent autoimmunity.34, 54, 55 Intrinsic expression of GATA3 controls Treg cell polarization and maintains Treg cell Foxp3 expression during inflammation in mice.56 CTLA‐4 is an inhibitory receptor crucial for the suppressive function of Treg cells in vivo.