Forced expression of wild-type IKAROS (IK1) in CP-CML cells inhibits total cell outputs and progenitor expansion and compromises the effects of IK6, which include promoting the growth of CP-CML cells in vivo. (A) Cumulative cell outputs in serial primary and secondary cultures (6 weeks + 6 weeks) initiated with cells from CP-CML patient #1 transduced with IK6, IK1, or a control vector. Values shown are the mean ± SEM of results from 3 replicate cultures. P values: IK1 or IK6 vs control. (B) Numbers of CD34⁺ cells and CFCs (as enumerated in a 14-day methylcellulose assay) present after 6 weeks in the individual cultures shown in panel A. Values shown are the mean ± SEM of results from 3 replicate cultures, expressed as CD34⁺ cells or CFCs per 10⁴ starting cells. P values: IK1 or IK6 vs control. (C) Representative flow cytometric profiles of cell-surface expression of CD14 (monocyte) and CD15 (neutrophil) on nonadherent cells in 2- to 3-week cultures initiated with CD34⁺ CP-CML cells transduced with IK1, IK6, or a combination of IK1 and IK6 (total of 4 CP-CML samples tested showing similar results). (D) Experimental design used to assess the effects of IK6 on the growth of CD34⁺ CP-CML cells in immunodeficient mice cotransplanted with equal numbers of IK6 (GFP⁺)- and control (YFP⁺)-transduced CD34⁺CD38⁻ cells from CP-CML #1 (10⁵ cells of each per mouse). (E) Levels of BM chimerism (total human and subsets thereof) obtained 5 weeks posttransplant. Values shown are the mean ± SEM of results from 5 individually assessed mice. P values: IK6 vs control. *P < .05; **P < .01; ***P < .001. BMA, bone marrow aspirate; IK1, wild-type (full-length) IKAROS.