B-cell differentiation of Id3-transduced FL progenitors is strongly blocked but not completely inhibited in a reaggregation culture with human stromal cells. CD34⁺CD38⁻CD10⁻ FL cells were sorted, transduced with the IRES-GFP or Id3-IRES-GFP vectors, and reaggregated with the SV19 human stromal cell line for 2 to 3 weeks. After the culture period, cells were harvested, stained with the indicated antibodies, and analyzed by flow cytometry. Quadrant limits defining positive and negative cells were set up using cells stained with isotype-matched control antibodies. Thirty percent and 28% of the cells were GFP⁺ 2 days after transduction in control- and Id3-transduced samples, respectively. The results shown are representative of 2 similar experiments.