p53 status is the primary determinant of MDM2 cell kill in CLL (composites). CLL samples (n=106) were enriched for CD19⁺ cells through negative selection and incubated for 36 hours with various concentrations of either MI-63 or Nutlin3. Samples were prepared for annexin-V and PI staining and analyzed by flow cytometry, and the residual live and nonapoptotic cell fraction was calculated for each concentration through comparison with the untreated control incubation. (A) MI-63 assay result composites. Dashed line indicates p53 sequence mutants and cases with absent p53 expression; solid line, wild-type p53 status. (B) Nutlin3 assay results. Dashed line indicates p53 sequence mutants and cases with absent p53 expression; solid line, wild-type p53 status. Standard deviations are indicated by vertical black bars. Statistically different data points (mean) are marked with asterisks. Results are displayed as the mean plus or minus one standard deviation, with an asterisk to denote the comparisons that were significant at the P ≤ .001 level.