This conclusion arose from the overwhelming evidence that systemic autoimmunity ensued in the absence of Tregs, as in day 3 thymectomy mouse models (5), Foxp3 mutation in mice (scurfy) (6) and humans (IPEX syndrome) (7), or even in Foxp3 conditional KO mouse models (8, 9). This evidence concerns the gene FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.