Representative examples of chemoresistant and chemosensitive B-CLL specimens. TUNEL data, expressed as a percentage of cells with intact DNA (ie, TUNEL negative), shown for two B-CLL specimens, which are representative of the chemoresistant (▪) and chemosensitive (○) phenotypes. B-CLLs were cultured with the indicated concentrations of fludarabine or 2-CdA for 3 days before TUNEL/flow cytometric analysis was performed. Note that the rates of spontaneous apoptosis for these 2 B-CLL specimens were about 20%.