Abstract： Transforming growth factor-β (TGF-β)is a pleiotropic factor.It regulates many aspects of T-cell biology including thymocyte development, T cell differentiation and effector T cell function.1 Previous work has shown that the loss of TGF-β signaling in the T-cell lineage leads to severe lymphoproliferative autoimmunity.2,3 Until now,it has been unclear to what extent the autoimmunity observed in those mice is driven by TGF-unresponsive conventional T cells,as TGF- is also crucial for the maintenance and function of regulatory T cells (Treg).A recent study published in Nature Immunology revealed a novel role of TGF-β signaling in non-regulatory naive T cells.It was found that TGF-β controls lymphopenia-driven T-cell proliferation in neonatal mice,thereby preventing the development of autoimmunity.4