Figure 1.

Leukemogenesis in adults and neonates. (A) Representative morphology of leukemic BM of mice engrafted with MLL-AF9–transformed 127-LSKs transplanted at P0 (N) or 8 wk of age (scale bar, 20 µm; arrowheads indicate cells with lymphoid morphology). (B) B220⁺ cells were quantified by flow cytometry in BM from mice engrafted at the indicated ages (n = 5 neonatal and 4 congenic adults; by Student’s t test; results are mean ± SEM compiled from two independent transplantation experiments; *, P = 0.04). (C) Flow cytometry analysis of leukemias arising from the indicated recipients. Representative morphology of sorted B220⁺ (top) and B220⁻ (bottom) neonatal leukemia cells is shown (scale bar, 10 µm; samples from animals analyzed in B; numbers on plots indicate percentage of cells in each gate). (D) Representative photomicrographs of tissue stained with H&E or for myeloperoxidase (MPO), CD11b, or B220 (with inset showing B220⁺ focus; arrows indicate foci of B220 staining; scale bars, 100 µm [10 µm in the inset]; samples from animals analyzed in B).