PTL induces apoptosis in CD34⁺CD38^- AML cells but not in normal cells in a dose-dependent manner. In vitro cultures were maintained for 18 hours followed by analysis of viability using annexin-V labeling. Each plot shows the average percent cell viability for CD34⁺CD38^- AML (A,C) and normal (N) cells (B,D) treated with increasing concentrations of PTL (A-B) or Ara-C (C-D). Each error bar represents the SD. All assays were performed in triplicate.