Expression of AML1-ETO, MPO, and clonality in leukemic cells. (A) Western blot analysis of 2 independent mice spleen cell samples and one bone marrow cell sample showing the expression of AML1-ETO. Kasumi cells serve as a positive control. (B) Bone marrow and spleen cells from recipient mice of p21^Waf1-deficient cells expressing AML1-ETO and a control mouse were cytospun and stained for MPO and counterstained with Wright-Giemsa for the analysis of immature blasts. The arrows indicate MPO⁺ immature blasts in the leukemic mice and in the control sample MPO⁺ neutrophils in the bone marrow. Image acquisition was performed as described for Figure 2, using a 100×/1.30 oil-immersion objective lens. (C) gDNA was isolated from 3 leukemic p21^Waf1−/− mice expressing AML1-ETO. The DNA was digested with BamHI and a Southern blot prepared. The blot was hybridized with the ETO probe 5′ of the BamHI site in ETO, washed, and exposed to film. The black dots indicate the integration signals.