Flt3⁺CD150^– preGMs are susceptible to ICN1-medated T-ALL. Flt3⁺CD150^–, Flt3^–CD150^– preGMs, and MPPs were sorted from WT B6 BM (CD45^B6) and transduced with either control-MIGR or ICN1-MIGR retrovirus for 2 days. Live transduced GFP⁺ cells (5000) from each group of cells were intravenously transferred into sublethally irradiated recipients (CD45^SJL). Recipient mice were assessed regularly for signs of cachexia. (A) Cachectic mice with peripheral WBC count > 5 × 10⁶/mL were promptly killed and various organs were harvested and prepared for histology study. Shown are representative H&E staining of spleen, liver, lung, and BM from mice that received empty MIGR-transduced MPPs and Flt3⁺CD150⁻ and ICN1-transduced MPPs, Flt3⁺CD150⁻, and Flt3⁻CD150⁻. Magnification is as indicated. (B) BM cells (5 × 10⁵) from mice that received ICN1-transduced progenitors in panel A were intravenously transferred to sublethally irradiated secondary recipients (CD45^SJL). Shown are representative flow cytometry analysis of primary BM cells used in transfer. (C) The secondary recipient mice were monitored for signs of cachexia. Cachectic mice were killed. Shown are representative H&E staining of spleen, liver, lung, and BM from secondary mice that received BM cells from panel B. Magnification is as indicated. (D) Flow cytometric analysis of BM cells from secondarily transplanted mice that received BM from panel B. Results shown are from 2 independent experiments. n = 4-5.