Expression of RCSD1-ABL2 and SSBP2-CSF1R in Arf^−/−pre-B cells induces B-ALL in C57Bl/6 mice. (A) Immunoblot of Arf^−/− pre-B cells showing expression of ABL2, CSF1R, IKAROS, and actin. (B) Kaplan-Meier curve of sublethally irradiated C576Bl/6 mice receiving Arf^−/− pre-B cells by tail vein injection (5 × 10⁵ cells/mouse). (C) Spleen weight of C576Bl/6 mice transplanted with Arf^−/− pre-B cells (n = 5). MIG, MSCV-ires-GFP. (D) Bone marrow, spleen, and brain sections from a representative mouse transplanted with Arf^−/− pre-B cells stained with hematoxylin and eosin (H&E) or a B220-specific antibody. (E) Analysis of bone marrow of diseased animals by flow cytometry. Immunophenotype is consistent with arrest at the pre-B stage of development.