In summary, several studies regarding T cell differentiation in T1D clearly demonstrated not only the role of Th1 cells but also the possible involvement of other kind of T-effector cells co-expressing IFN-γ and IL-17, IL-21 producing T cells such as Tfh cells as well as circulating and pancreatic-resident Tregs. The gene discussed is IFNG; the disease is type 1 diabetes mellitus.