Assessments of clonal and growth potential of B-ALL arising from p19^ARF-null HSC versus pro-B cells. Primary recipients injected with p210BCR/ABL-expressing p19^ARF-null HSC or pro-B cells were killed approximately 2 to 3 weeks after transplantation. EGFP⁺ B-ALL (B220⁺, CD19⁺, IgM⁻) cells from bone marrow were isolated by FACS for analyses. (A) B-ALL cells were directly sorted into semi-solid methycellulose medium (with murine SCF, IL-3, IL-6, Flt3 ligand, and IL-7), 500 cells per well, and colonies were scored 2 weeks later. Significance was determined with Student paired, one-tailed t test (****P < .001). (B) Photographs of colonies (100× magnified) grown from cultures in panel A. (C) B-ALL cells were directly sorted into U-bottom 96-well culture plate, 1 cell per well, 5 plates per group, with 100 μL culture medium (IMDM + 10% FBS + 55 μM 2-ME). Cell clones that arose from each well were scored 2 weeks later. Significance was determined with Student paired, one-tailed t test (*P < .05). (D) Fresh isolated B-ALL cells from both groups were transplanted into sublethally irradiated wild-type secondary recipients (6 per group) at a dose of 5000 cells per mouse. Results are presented as Kaplan-Meier analysis to compare the survival of recipients that engrafted with B-ALL arising from p19^ARF-null HSC and pro-B cells. Significance was determined with survival analysis method of Prism software (*P < .05).