Differential effects of ectopic Gfi1b expression in primary T-lymphocyte progenitors cultured in vitro. (A) Fetal liver-derived HSCs (Lin⁻CD27⁺CD117⁺) were cultured on OP9-DL1 for 6 days prior to infection with MigR1 (◊) or MigR1-Gfi1b (▪). The percent of cells expressing GFP 1, 3, 5, 7, and 9 days after infection was determined by flow cytometry. One of 2 independent experiments is shown. (B) Expression of CD44 and CD25 on GFP⁺Lin⁻ cells 5 days after infection with MigR1 or MigR1-Gfi1b retrovirus. The percent of cells in each quadrant is indicated. Results are representative of 4 experiments. (C) Total number of DN3 cells (Lin⁻CD44⁻CD25⁺) in cultures of wild-type HSCs infected with MigR1 (⊡) or MigR1-Gfi1b (▪) virus on day 6 of culture and examined at the indicated time after infection. The initial infection efficiency was similar for both retroviruses.