Effect of TAL1 and ΔbTAL1 enforced expression on the generation of GPA⁺ cells during erythroid culture. CD34⁺ cells transduced with TRIP-EGFP, TAL1, and ΔbTAL1 vectors were cultured for 6 days in serum-free medium with SCF, IL-3, and IL-6. Epo was added at day 6 for 5 additional days. (A) Percent of GPA⁺ cells generated from EGFP- (⋄), TAL1- (▴), and ΔbTAL1-transduced (▪) CD34⁺ cells (n ≥ 2). (B) Quantification of βglobin (n = 2) and erythroid PBGD (n = 2) mRNA expressions in CD34^-CD36⁺ cells sorted 3 days after the end of the transduction using quantitative PCR analysis. Results obtained in the cells transduced with TRIP-TAL1 and TRIP-ΔbTAL1 are expressed as percent of gene expression compared with cells transduced with TRIP-EGFP. (C) Absolute number of GPA⁺ cells generated from transduced cells after 7 days of culture (n = 6). Results are expressed as a proportion of the control EGFP⁺ cells. (D) Flow cytometry analysis of CD34⁺ and GPA⁺ cells after 7 days of culture. Quadrants were set as in Figure 2. Shown are percent of CD34⁺ cells (upper left) and GPA⁺ (lower right) cells. (E) Growth curves of transduced cells in response to 2 concentrations of Epo (50 IU/L and 2 × 10³ IU/L). Shown are cumulative cell numbers and percent of GPA⁺ cells measured by flow cytometry after 10 days of culture. Error bars (A-C) represent standard deviation.