Ex vivo expansion of HSCs by AML1a expression. (A) Schedule of retrovirus infection and CRU and LTC-IC assays. Cells were sorted for GFP+ on day 2. (B) Result of the CRU assay using fetal liver cells conducted on days 2 (○), 6 (●), and 9 (▴) of TetOFF-GFP-tetO-AML1a virus-infected cells. Cell numbers are presented as day 2 equivalents. (C) Results of LTC-IC assays conducted on days 2 (○), 6 (●), and 9 (▴) of vector-control (left) and TetOFF-GFP-tetO-AML1a (right) virus-infected cells. Cell numbers are presented as day 2 equivalents. Three experiments for each group yielded a similar result. (D) Summary of CRU assays conducted on days 2 and 6 of vector-control (□) and TetOFF-GFP-tetO-AML1a (■) virus-infected cells. Results are presented as the fold-increase of CRUs on day 6 relative to day 2. Fetal liver (*) and adult mouse BM (#) cells were used as cell sources. Bars represent 95% CIs. Results of 3 independent experiments each for the control and AML1a are presented.