E2F1 knockdown induces a block in proliferation and increased cell death in CML SPCs. mRNA levels of (A) E2F1 and (B) p21 by Q-PCR in E2F1 knockdown GFP⁺ healthy and CML SPCs. Transfection with scrambled vector was used as negative control. (C) CFC analysis to measure colony-forming ability following E2F1 knockdown in (i) CML and (ii) healthy SPCs. (iii) Representative images for CFC from healthy and CML SPCs upon E2F1 knockdown (phase-contrast images, ×10 magnification). (D) Representative histogram of cell divisions by CellTrace Violet staining in E2F1 knockdown healthy and CML SPCs. Colcemid treatment was used to visualize undivided cells. (E) Percentage of early apoptosis indicated by Annexin V⁺/7-AAD⁻ cells. Each experiment had N = 3 biological replicates. *P < .05; **P < .01.