Abnormally accelerated apoptosis of Eμ-myc/bcl-2^−/− B cells in culture. Survival assays were performed on purified populations of preneoplastic bone marrow–derived pro-B (Ly5.2⁺ B220⁺ sIg⁻ c-Kit⁺) or pre-B cells (Ly5.2⁺ B220⁺ sIg⁻ c-Kit⁻) and splenic immature (Ly5.2⁺ B220⁺ sIgM^hi sIgD^lo) or mature B lymphocytes (Ly5.2⁺ B220⁺ sIgM^lo sIgD^hi) from mice 8 to 12 weeks following reconstitution with fetal liver cells from wt (▴), bcl-2^−/− (▵), Eμ-myc (■), and Eμ-myc/bcl-2^−/− (□) E14.5 embryos. The purified donor-derived B-cell populations were cultured in the absence of cytokines for the indicated time periods, and cell viability was measured by staining with PI plus annexin V and FACS analysis. Data represent means ± SEM from 4 to 8 independent experiments for each cell subset and genotype.