Characterization of APL cells. (A) Morphology by May-Grünwald-Giemsa staining and flow cytometric analysis for Gr-1 and CD34 is shown for 2 independent splenic tumors arising in hCG–-PML-RARα animals and in 2 mCGPR/PR animals. Numbers represent the percentage of cells in each quadrant. Original magnification, ×400. (B) Peripheral white blood cell (WBC; □) counts and absolute neutrophil counts (ANCs; ▦) determined by automated counting are shown for wild-type littermates, nonleukemic mCG+/PR, and leukemic mCG+/PR and mCGPR/PR animals. For panels B and C, wild type = 7 mice; nonleukemic mCG+/PR = 9 mice; leukemic mCG+/PR = 9 mice; leukemic mCGPR/PR = 10 mice. (C) The fraction of Gr-1+, CD34+, and Gr-1+/CD34+ cells in the spleens of wild-type, nonleukemic, and leukemia cells from mCG+/PR (+/–) and mCGPR/PR (+/+) knock-in animals are shown. Error bars indicate ± SEM. (D) The relative increase in abundance of MMP9 mRNA in individual APL samples after 3 days of treatment with 1 μM ATRA relative to diluent alone is shown. Left panel: 5 independent hCG–PML-RARα tumors; right panel: 6 independent mCGPR/PR tumors. MMP9 is normally expressed at its highest levels in terminally differentiated myeloid cells. Expression levels from each sample were normalized by measuring the abundance of GAPDH mRNA, which is expressed at all stages of myeloid development. Pairwise comparisons that yielded statistical significance of P < .01 are indicated by asterisks (**).
