Identification of the population of cells accumulating in leukemic bone marrow of MRP8 hPML-RARα mice. (A) Cytospins of single-cell suspensions of total bone marrow from wild-type (top) and leukemic mice (bottom) after ACK treatment stained with Wright-Giemsa (original magnification ×63). The leukemia developed after transplantation with 2.5 × 10⁵ to 5 × 10⁶ cells from total leukemic spleen of a MRP8 hPML-RARα mouse. Mice were killed and analyzed when moribund. (B) Phenotypic analysis of leukemic cells (bottom panel) isolated from bone marrow display an increase of immature cells (CD34⁺/c-kit⁺ fraction) and accumulation of cells in subpopulations 3 and 4 that reflects the block at promyelocytic stage of differentiation (red rectangle) together with a decrease of more mature cells (subpopulations 5-9) compared with wild-type bone marrow (top panel). Negatively selected cells (Bi) from bone marrow were separated into CD34⁺/c-kit⁺ and CD34⁻/c-kit⁻ fractions (Bii). CD34/c-kit double-positive cells were further fractionated into 4 fractions (subpopulations 1-4) according to Gr1 levels (Biii), and CD34/c-kit double-negative cells were further fractionated into 5 fractions according to Gr1 levels (subpopulations 5-9; Biv).