While peripheral regulatory T cell (pTreg) and T helper type 17 (Th17) cell share a common precursor cell (the naïve CD4 T cell) and require a common signal for initial differentiation (tumor growth factor- (TGF-) β), they turn to elicit opposite functions via terminal differentiation: Treg is anti-inflammatory, inhibits autoimmunity, and maintains immune homeostasis, whereas Th17 cell causes autoimmunity and inflammation [12]. The gene discussed is CD4; the disease is Autoimmunity.