Phenotype of Lin28b-transduced BM and Let-7–transduced FL generates B cells in recipient spleen that resemble B1 and FO/B2. CD19⁺GFP⁺ mature (CD93⁻) B cells in spleen were generated from transfer of the indicated pro-B–transduced cells, 3 wk after transfer in SCID mice, and analyzed by flow cytometry using the indicated markers. The red boxes indicate an adult-type and the green boxes indicate a fetal-type phenotype. The blue gates represent IgM^hiCD21^hi cells, a marginal zone B cell type. Data are representative of five independent transfer experiments with two mice per group.