Effects of Cbfb-MYH11 on CD4 expression in vivo and in vitro. (A) CD4 and CD8 distribution of TCRβ^hiHSA^lo thymocytes from Tg(Lck-Cre) and Tg(Lck-Cre)/Cbfb^+/56M mice. (B) CD4 expression in immature thymocytes. The left panel shows the histogram overlay of CD4 expression in TCRβ^loFSC^hiCD8^−/lo thymocytes from Tg(Lck-Cre) (n = 10, gray line) and Tg(Lck-Cre)/Cbfb^+/56M mice (n = 5, black line). The right panel shows the mean fluorescence intensity (MFI) of CD4 expression in TCRβ^loFSC^hiCD8^−/lo cells. (C) CD4 silencer reporter assay. The indicated cDNA constructs were transfected into a CD4⁻ Jurkat cell clone (D1.1) and CAT assays were performed. The CAT expression from the construct with no CD4 silencer was set at 100% and used to normalize the other results. No CD4 silencer: a construct with the CAT gene driven by CD4 enhancer/promoter. CD4 silencer p131-265: the above construct with 3 copies of the CD4 silencer core sequence. Runx1: Runx1 full-length cDNA. Cbfb: Cbfb full-length cDNA. Inv(16): CBFB-MYH11 cDNA.