Ectopic RXRα impairs cell proliferation in granulocyte-specific cultures. (A) Human CD34⁺ progenitor cells that were expanded for 72 hours were cultured for 10 days in the presence of M-CSF, IL-6, FL, and SCF (Mo cultures), or G-CSF plus SCF (G cultures). NR ligands were added at initiation (day 0) of Mo and G cultures. Fold expansion represents the ratio of total cell numbers at day 10 over total cell number at day 0. Values represent the mean and SD of 6 (Mo) or 4 (G) independent experiments. (B) CD34⁺ cells were transduced with RXRαΔ or empty control vector shown in Figure 2A. After gene transduction cells were subcultured (48 hours) in Mo- or G-specific serum-free cultures in the presence of the RXR-selective agonist LG100268 (100 nM), VD3 (60 nM), 9cRA (100 nm), ATRA (100 nm), or vehicle (veh). The percentage of GFP⁺ cells was determined by FACS. Index indicates the ratio of the percentage of GFP⁺ cells in the presence of NR ligands over the percentage of GFP⁺ cells in the absence of ligand. Bar diagrams represent the mean and SD calculated from 6 independent experiments (A-B) *Significant differences at P < .05 according to a general linear statistical model; ns indicates not significant. (C) CD34⁺ cells were transduced as in panel B. After gene transduction (48 hours), cells were harvested and labeled with PKH26. Cells were then cultured in G-specific cultures in the presence or absence of the RXRα-selective agonist LG100268 (100 nM). PKH26 fluorescence was analyzed by FACS at days 0, 4, or 8. Histograms represent gated GFP⁺ cells analyzed for PKH26 fluorescence intensity.