Proliferation of Aml1-excised immortalized BM cells is enhanced in vitro. (A) MLL-ENL was retrovirally transduced into Aml1 intact (Aml1^f/f) and excised (Aml1^Δ/Δ) BM cells, and replating assay was performed using these cells. (B) Genotyping of Aml1 floxed and Δ alleles by PCR from Aml1^f/f and Aml1^Δ/Δ immortalized cells. Each lane indicates the PCR products of an independent case. (C) mRNA levels of Aml1 in Aml1^f/f and Aml1^Δ/Δ immortalized cells were measured. *P < .05. (D) Growth of Aml1^f/f (n = 5; ♦) or Aml1^Δ/Δ (n = 5; □) immortalized cells in liquid medium. Data are on a semilogarithmic plot of cell counts versus time. (E) Growth of the immortalized cells as in Figure 1D after day 9. Cell counts at day 14 relative to those at day 9 are shown as mean ± SD on a linear plot (n = 5 from each group). Day 14 proliferation was significantly different between groups (t test, P < .001). (F) Flow cytometric analyses of the colony-forming cells after 3 rounds of replating. (Top) Representative fluorescence-activated cell sorter plots. (Bottom) Percentages of cells expressing indicated surface markers in each group (mean ± SD).