Murine APL model. (A) Immunophenotype of APL cells. Peripheral blood, splenocytes, and bone marrow cells from a healthy wild-type B6129F1 mouse and a leukemic murine cathepsin G-PML-RARα knock-in (mCG^PR/+) B6129F1 mouse with APL were stained for the myeloid surface antigen Gr-1 and the early hematopoietic progenitor marker CD34. The level of CXCR4 expression on Gr-1⁺/CD34⁺ in mCG^PR/+ APL cells is shown in the histogram along with the isotype control (black line). The indicated gates were used to determine the percentage of cells positive for Gr-1 and CD34. (B) Generation of luciferase-labeled acute myeloid leukemia (APL^luc) cells. APL cells obtained from the spleen of a mCG^PR/+ knock-in mouse were transduced with a bicistronic retroviral vector containing firefly luciferase upstream of EGFP (Fluc-IRES-egfp). Following transduction, EGFP⁺ APL cells were purified by fluorescence-activated cell sorting (FACS) and passaged in genetically compatible B6129FI recipients. These secondary recipients developed a rapidly fatal acute leukemia characterized by pronounced leukocytosis, anemia, thrombocytopenia, and massive hepatosplenomegaly with leukemic cell infiltration. APL^luc cells obtained from the spleens of secondary recipients were frozen and banked 28 days after injection. (C) Kinetics of APL^luc engraftment and expansion. Genetically compatible B6129F1 recipients were injected with 10⁶ APL^luc cells. Tumor trafficking and growth were assessed at various time intervals by bioluminescence imaging. Images of a representative mouse are shown. Photon flux is indicated in the color scale bar. WBC counts were determined by automated counting and the percentage of leukemic blasts in the blood, spleen, and bone marrow by flow cytometry.