PI3Kδ protein expression in BCR/ABL⁺ leukemia. (A) Immunoblotting for PI3Kδ in cell extracts from 6 patients with BCR/ABL⁺ ALL and 7 patients with CML (right panel, top and bottom). All samples express PI3Kδ. Healthy human bone marrow and naive murine PI3Kδ^+/− and PI3Kδ^−/− bone marrow preparations served as controls. (B) Typical example of FACS-based analysis of CD19 and CD43 surface expression of v-abl—transformed murine PI3Kδ^+/− and PI3Kδ^−/− cell lines (n = 6 for each genotype analyzed). (C) Representative RT-PCR analysis of PI3Kα, β, γ, and δ isoform expression in freshly isolated bone marrow cells and in v-abl–transformed PI3Kδ^+/+, PI3Kδ^+/−, and PI3Kδ^−/− cell lines (left panel). Western blot analysis of PI3Kα, β, δ, and PI3Kγ in stable v-abl–transformed cell lines (right panel). MACS-purified pro-B cells derived from PI3Kδ^+/− and PI3Kδ^−/− bone marrow served as positive and negative controls, respectively. (D) Western blot analysis of phosphorylated Akt in v-abl–transformed PI3Kδ^+/− and PI3Kδ^−/− cell lines. NIH3T3 cells were used as control (ctr). (E) Cell-cycle profiles of v-abl–transformed PI3Kδ^+/− and PI3Kδ^−/− cell lines.