The importance of Treg cells has been demonstrated in murine models—depletion of Foxp3+CD4+ Treg cells resulted in severe autoimmunity, allergy, and immunopathology (e.g., IPEX) in otherwise normal animals and those same diseases can be prevented by reconstituting Treg cells [167,168,169]. The gene discussed is FOXP3; the disease is Autoimmunity.