TEL-AML1 enhances development of B-cell precursors in vitro. HPCs transduced with MSCV-T/A or MSCV-EGFP were grown in conditions promoting the development of B-cell progenitors in colony-forming serial replating assays. The number of colonies (A) and the total number of cells (B) produced by MSCV-T/A (▪) and MSCV-EGFP (○) transduced HPCs in each round of plating is shown. Plots show means and SDs of duplicate cultures. The data are representative of 3 independent experiments. (C) Number of B220⁺ cells harvested from MSCV-T/A (▪) and MSCV-EGFP (□) B-cell methylcellulose cultures from each round of plating. Plots show means and SDs of duplicate cultures. (D) INT-stained methylcellulose MSCV-T/A and MSCV-EGFP cultures from the first and second rounds of plating. (E) Typical pre–B-cell morphology of colonies generated by MSCV-T/A– and MSCV-EGFP–infected cells in the secondary round of plating. Original magnification, × 40. (F) Flow cytometric analysis of EGFP and of lineage-specific marker expression of cells harvested from the secondary round of methylcellulose plating. Gray lines represent the isotype control (or uninfected cells for analysis of EGFP expression), and black lines indicate staining with antibodies specific to the indicated marker, or EGFP expression.