Effects of Fas blocking by MoAb ZB4 on Fas-mediated regulation of p210 and apoptosis of total and CD34⁺ BM cells from a CML patient in chronic phase who had optimal response to IFN-α. Total BM and CD34⁺ cells were cultured for 48 hours in the absence or presence of Fas triggering (by MoAb CH11) and/or Fas blocking (by MoAb ZB4), without or with IFN-α (1,000 U/mL). For (A), (B), and (C), see legend to Fig 1. (D), (E), and (F) show apoptotic CD34⁺ CML cells stained positively with peroxidase (black cells) after the indicated treatment. In (C), bars represent the mean number of apoptotic cells determined in triplicate experiments ± SEM. Statistical analysis (pairedt-test) showed P < .05 for untreated cells versus Fas triggering + IFN-α and for Fas blocking versus Fas blocking + IFN-α + Fas triggering, while there was no statistical difference between untreated and Fas blocking.