Flow cytometric analysis of AML1-ETO–expressing p21^WAF1-deficient cells. Bone marrow and spleen cells were collected from leukemic mice transplanted with p21^Waf1−/−-expressing AML1-ETO cells and analyzed for the expression of CD3/B220, Gr-1/CD11b, and c-kit/Sca-1. Depicted are the EGFP⁺ and EGFP⁻ cells within a particular mouse.