Forskolin inhibits basal and IR-induced cell death in cultured BCP-ALL blasts but not in normal BCPs. (A) Freshly isolated BCP-ALL blasts from 11 patients and normal BCPs from 7 healthy donors were cultured in the presence or absence of 60 μM forskolin for 45 min prior to treatment with 2 Gy IR as indicated. After 20 h, cell death was assessed in the CD19⁺ cell fraction by co-staining with FITC-labeled anti-CD19 and PI as described in Materials and Methods (n = 11 [BCP-ALL], n = 7 [normal BCPs], lines indicate median values; *P < .05 by Wilcoxon signed rank test). (B) The relative reduction in cell death by forskolin in nonirradiated and irradiated samples was calculated for each sample in Figure 1A. The resulting values are displayed in a histogram according to the cytogenetic subgroup of BCP-ALL.