MPDs derived from old BM^BCR-ABL are characterized by a reduced tumor burden. The frequency of total leukemic GFP⁺ (BCR-ABL⁺) cells and leukemic myeloid GFP⁺Gr-1⁺CD11b⁺ cells in the BM (A) and spleen (B) of recipients of young BM^BCR-ABL cells was increased compared with recipients of old BM^BCR-ABL cells. (C) Decreased frequency of B-lineage cells in the spleen of young BM^BCR-ABL recipients compared with old BM^BCR-ABL recipients. Cell frequency shown in panels A through C is presented as the mean frequency of cells plus or minus SEM from 17 recipients of young and 23 recipients of old BM^BCR-ABL that developed MPDs analyzed in 5 independent experiments. (D) Immunostaining used to define populations enriched for leukemic HSCs (top; GFP⁺Lin⁻Sca-1^HiCD117^Hi), CMPs (middle; GFP⁺Lin⁻Sca-1⁻CD127⁻CD16/32^+/LoCD117^Hi), and GMPs (bottom; GFP⁺Lin⁻ Sca-1⁻CD127⁻CD16/32^+/LoCD117^Hi) in the BM and spleen of BM^BCR-ABL recipients. (E) Recipients of young BM^BCR-ABL cells have more leukemic GFP⁺ HSCs, CMPs, and GMPs in their BM (top panel) and spleen (bottom panel) compared with those that received a transplant with old BM^BCR-ABL cells. The frequency of GFP⁺ HSCs, CMPs, and GMPs is presented as the mean plus or minus SEM of 12 recipients of young and 13 recipients of old BM^BCR-ABL that developed MPDs with no B-lineage involvement.