FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome: The discovery of genetic Foxp3 gene mutations as the culprit of the fatal autoimmune syndrome in the spontaneous scurfy mouse mutant (1, 2) and human IPEX patients (3, 4) provided the basis for unraveling the key role of Foxp3+ regulatory T (Treg) cells in dominant immunological tolerance.