BrdU incorporation by thymocytes in the Tg(Lck-Cre)/Cbfb^+/56M mice. (A) Percentages of BrdU⁺ cells among total thymocytes, DP cells, and DN cells in the littermate control (□, n = 3) and the Tg(Lck-Cre)/Cbfb^+/56M mice (▪, n = 6). *Only the difference in DP BrdU⁺ cells between the littermate control and the Tg(Lck-Cre)/Cbfb^+/56M mice reached statistical significance (P = .05). (B) Distribution of BrdU⁺ cells relative to CD4 and CD8 expression.