ABT-263 and ABT-737 induce platelet apoptosis. (A-B) Washed human platelets were incubated in HBS with different concentrations of ABT-737 (open boxes) or ABT-263 (filled boxes) for 1 hour (A) or 2 hours (B). Apoptosis was assessed by PS externalization and staining with annexin V/FITC before analysis by flow cytometry. *P < .05. **P < .01. (C-D) Washed platelets were incubated in HBS with (♦,♢) or without (■,□) 3% human serum albumin and different concentrations of ABT-737 (C, open symbols) or ABT-263 (D, filled symbols) for 4 hours. Alternatively, whole blood (▴,▵) was incubated with different concentrations of ABT-737 (C) or ABT-263 (D) for 4 hours before analysis of platelet apoptosis by PS externalization and staining with annexin V/FITC. Data are mean ± SD (n = 6). (E-F) Citrated blood of patients with CLL was incubated with different concentrations of ABT-737 (E) or ABT-263 (F) for 4 hours. Apoptosis of CLL cells (♦) was investigated in whole blood by staining with CD5/CD19 antibodies and annexin V/allophycocyanin. Apoptosis of platelets (□) was investigated in plasma by staining with CD41 antibodies and annexin V/FITC. Data are mean ± SD (n = 4). *P < .05. **P < .01.