Id3 inhibits B-cell development at an early stage of development. The inhibition by Id3 is much stronger than by a mutant of Id3 that is unable to dimerize with bHLH factors. CD34⁺CD38⁻CD10⁻ FL cells were sorted, transduced either with Id3-IRES-GFP or with Did3-IRES-GFP, and subsequently cocultured with S17 stroma. After 14 days, the cultures were analyzed with the indicated antibodies. This experiment is representative of 3 similar experiments.