Absence of CR4 resistance in AML self-renewal assay. AML cells were cultured in the presence of varying concentrations of CR4 for 7 days. Cells surviving culture with 160 nM CR4 were rescued and replated in fresh medium containing CR4 as indicated. Cells from several of the original cultures were pooled for the second phase. After a further 7 days of incubation, colony numbers were assessed. Normal cell growth is unaffected at these concentrations of CR4. Shown is one representative experiment of 2 with standard deviations.