The important role of Foxp3+ Treg cells in protection from autoimmune diabetes is highlighted by the notion that T1D represents a major component of the IPEX (immune dysfunction, polyendocrinopathy, enteropathy, X-linked) syndrome [46–48] that affects humans with abrogated Treg cell function due to mutations in the FOXP3 gene [49–51]. The gene discussed is FOXP3; the disease is polyendocrinopathy.