Elevated Mcl-1 protects thymocytes and pre-B cells against apoptosis in vitro. (A) Thymocytes from Mcl-1 transgenic mice are resistant to cytokine deprivation. Thymocytes from WT, VavP-BCL-2 (69), and 4 independent strains of VavP-Mcl-1 mice (n = 2 for each) were cultured in vitro for 6 days without cytokines and viability assayed by flow cytometry at the indicated intervals. Data are mean ± SD. (B) Immature CD4⁺CD8⁺ thymocytes from Mcl-1(33) transgenic mice have increased resistance to apoptosis induced by γ-irradiation (5 Gy). (C-F) Pre-B cells from Mcl-1(33) transgenic mice have increased resistance to apoptosis. Pre-B cells (B220⁺ IgM⁻) sorted from BM of individual mice were cultured in medium alone (C) or in medium after being subjected to γ-irradiation (5 Gy) (D) or in medium containing etoposide (1 μg/mL) (E) or dexamethasone (10⁻⁶) (F). Viability (proportion of cells negative for propidium iodide uptake and annexin V surface staining) was determined by flow cytometry. Values have been normalized to viability in control (untreated) cultures to show stimuli-specific apoptosis. WT (black, n = 5-9 mice); Mcl-1(33) transgenic (red, n = 5-9), BCL-2(69) transgenic (blue, n = 2-5). (B-F) Values are mean ± SEM.