CbfbF/F CD4-cre mouse cells and iT reg cells generated from human naive CD4+ T cells undergoing siRNA-mediated RUNX1 and RUNX3 knock down show a diminished suppressive activity. Experimental setup (A) and results of the mouse suppression assay (B), FACS-purified naive CD4+8- T cells from CbfbF/F CD4-cre (left) and control CbfbF/+ CD4-cre mice (Cd45.2; right) were activated in vitro with anti-CD3/28 mAb, 50 U/ml IL-2, and 2.5 ng/ml TGF-beta. After 3 d, Foxp3-GFP+ cells were FACS-sorted and mixed with CFSE-loaded naive CD45.1+ CD4+ cells at the indicated ratios. These were then incubated with inactivated splenocytes and anti-CD3 mAb. After a further 4 d, CD45.1+ cells were analyzed for CFSE dilution. (C) As a control, CbfbF/+ CD4-cre CD4+ T cells activated in absence of TGF-beta were mixed with CFSE-loaded naive CD45.1+ CD4+ cells at the indicated ratios. Four days later CD45.1+ cells were analyzed for CFSE dilution. The median division number (of the naive CD45.1+ CD4+ cells in the cultures containing Foxp3-GFP+ cells) is indicated in each of the histograms. One of three experiments is shown. (D) Human naive CD4+ T cells, transfected with RUNX1 and RUNX3 siRNA and cultured under iT reg differentiating conditions were used in an in vitro suppression assay, cultured together with autologous CFSE-labeled CD4+ T cells, and stimulated with anti-CD3 mAb. The CFSE dilution of the CD4+ T cell responder cells was analyzed after 5 d by flow cytometry. The T reg/responder CD4+ T cell ratios used were 1:20, 1:10, and 1:5. One of two experiments is shown. 
