Tamoxifen treatment restores B cell development from E2AER/ER pre-proB cells. Sorted E2AER/+ and E2AER/ER pre-proB cells were plated in hormone-free media on S17 stromal cells on Day 0 in the presence of IL-7 with tamoxifen or DMSO (untreated control). (A) Cells are pre-gated on 7AAD-B220+ lymphocytes. Percents of CD19+ cells on Day 1, 3, and 5 are displayed. Data are representative of 4 independent experiments. (B) Expression of Pax5 was analyzed by quantitative RT-PCR from RNA collected from Day 1, 3, and 5 cultures shown in (A). Samples were normalized to the expression of GAPDH. Graphed results are means from triplicate runs (n = 3) with error bars representing standard error of the mean (SEM).