Diminished capacity of Cbfb-deficient CD4-cre mice T cells in the generation of Foxp3+ CD4+ T cells. (A) FACS-purified naive CD4+ CD8− T cells from CbfbF/F CD4-cre and control CbfbF/+ CD4-cre mice were activated in vitro with anti-CD3/28 mAb, 50 U/ml IL-2, ± 10 nM retinoic acid (RA), and increasing concentrations of TGF-β.