T-cell differentiation is blocked in a CBFβ dosage-dependent manner. (A) Proliferation of Lin− (Ter119, CD19, Gr-1, F4/80) 17.5 dpc FL cells cocultured on OP9-DL1 in the presence of Flt3L and IL-7, counted at weekly intervals. Each data point is averaged from at least 9 fetal livers. Error bars in all panels represent SEM. (B) Bar graph depicting the fold expansion of Lin− FL cells from an allelic Cbfb dosage reduction series, after 14 days of OP9-DL1 coculture. The percentage of CBFβ protein relative to wild-type levels is indicated below the bars.13 The number of independent animals analyzed was: Cbfb+/+ = 13; Cbfb+/− = 7; Cbfbrss/rss = 5; Cbfbrss/− = 10. *indicates significant (P < .05) difference relative to Cbfb+/+ animals (unpaired, 2-tailed Student t test). (C) CD4 and CD8 expression after 14 days of coculture on OP9-DL1. (D) Mean (± SEM) percentages of CD4+CD8+ (DP) cells. Cbfb+/+ = 17; Cbfb+/− = 7; Cbfbrss/rss = 5; Cbfbrss/− = 16. *Significant (P < .05) difference relative to Cbfb+/+ animals. **indicates significant (P < .05) difference relative to Cbfbrss/rss animals. (E) Cell surface TCRγ expression in the bulk cocultured cells. (F) Mean (± SEM) percentages of TCRγ+ cells after 14 days of culture. Cbfb+/+ = 17; Cbfb+/− = 7; Cbfbrss/rss = 5; Cbfbrss/− = 16. (G) Intracellular TCRβ staining in DN cells (DN = CD8−Gr-1− because CD4 expression is inappropriately unregulated in Cbfbrss/− DN cells13,72 ) after 6 and 9 days of OP9-DL1 culture. Cbfb+/+ = 4; Cbfbrss/− = 3.
