Early works using day-3 thymectomy or anti-CD25 antibody treatment have implicated Treg presence [6,7], but the most convincing and definitive evidence for Treg came from the genetic studies of Scurfy (Sf) mice and IPEX patients, both display fatal multi-organ inflammation caused by mutations in the transcription factor Foxp3 [8,9]. This evidence concerns the gene FOXP3 and immune dysregulation-polyendocrinopathy-enteropathy-X-linked syndrome.