CD4 and Autoimmunity: In early studies examining the functional specialization of Treg cell developmental subsets by adoptive transfer immunotherapy of newborn scurfy mice (20), total Foxp3+ Treg cells prevented disease lethality, but did not suppress chronic inflammation and autoimmunity, which required the provision of Foxp3-sufficient CD4+ T cells to facilitate the extrathymic conversion of initially Foxp3– T cells into functional Foxp3+ Treg cells (20).