CR4 inhibits Ph^- ALL and AML cell growth. (A) Ph^- ALL cells, (B) AML cells, and (C) primary AML patient cells were cultured in colony-forming assays in the presence of increasing concentrations of CR4, as indicated. Colony numbers were assessed after 9 to 14 days. The average of 2 independent experiments is shown in each case. Primary AML cells were prepared by Percoll gradient centrifugation of patient samples. Each condition was assayed in duplicate, and one representative experiment of 3 is shown with standard deviations. The solvent for CR4 (DMSO/Iscove) alone did not affect cell growth (not shown). (D) Median inhibitory concentrations (IC50s) (± standard error) for primary ALL (n = 5) and AML (n = 6) and normal bone marrow (n = 5) were obtained by culturing each sample in the presence of varying concentrations of CR4 (0-20 μM).