Ebf1 and Pax5 heterozygosity cooperates with STAT5 activation to initiate highly penetrant ALL. (A) Kaplan-Meier survival analysis of mice of the indicated genotype. (B) Pictures of spleens and lymph nodes from leukemic Stat5b-CA x Ebf1^+/− and Stat5b-CA x Pax5^+/− tumor mice compared with a wild-type C57BL/6 control littermate (LMC) mouse. Tick marks represent millimeter measurement. (C) Flow cytometric analysis of lymph node cells from Stat5b-CA x Ebf1^+/− and Stat5b-CA x Pax5^+/− tumor mice. Representative flow cytometric analysis of B220, AA4.1, IL-7R, pre–BCR, CD19, IgM, and IgD expression on lymph node cells is shown. Doublets were gated out and a lymphocyte gate was set based on side and forward scatter properties. All gates shown are based on bone marrow isolated from LMC. In histogram plots, LMC is represented as shaded plot with line and the black line referred to as tumor represents cells isolated from the lymph nodes of indicated leukemic mouse. Each mouse designated in A was analyzed. (D) Flow cytometric analysis of Stat5b-CA x Pax5^+/− leukemia cells before and after transfer (2–3 wk) into wild-type C57BL/6 recipients. At least three independent experiments were completed with at least one mouse per group per experiment.