IL-2Rβ cytoplasmic domain delivers lineage conversion signal in CLPs. (A) Schematic representation of receptors and their domains. Shown are WT IL-2Rβ (closed), WT IL-7Rα (open), and 7α/2β/2β. The chimeric receptor 7α/2β/2β is composed of the extracellular domain of IL-7Rα and the transmembrane and cytoplasmic domains of IL-2Rβ. The cytoplasmic tail of IL-2Rβ can be divided into 3 subdomains, S, A, and H regions. (B) Flow chart of experimental system. (C) Introduction of 7α/2β/2β chimera can initiate lineage conversion in CLPs in response to IL-7. CLPs were retrovirally transduced with empty vector, IL-7Rα, IL-2Rβ, and 7α/2β/2β. GFP⁺ cells were sorted and cultured on OP9 stromal cell layers in the presence of IL-3 and GM-CSF for 5 days. B220⁺ B-cell and Mac-1⁺ myeloid-cell readout was analyzed by FACS. Numbers shown are the percentage of total cells in the gates. B220⁺ cells from IL-2Rβ⁺ CLPs proliferated more than B220⁺ cells from 7α/2β/2β⁺ CLPs in this culture condition. (D) Myeloid differentiation potential of chimeric receptor-expressing CLPs was assessed in methylcellulose medium supplemented with IL-3 and GM-CSF. The plating efficiency was determined by enumerating the number of GM colonies formed after 5 to 7 days in the culture. Error bars represent standard deviation from the triplicate samples.