I-Delta1^ext-myc induced a multiple-log expansion of hematopoietic precursors with SCF, FL, TPO, IL-6, and IL-3. Culture plates were precoated with anti-myc 9E10 antibody F(ab′)₂ and CH-296. (a) CD34⁺CD38^–cells (600 per well) were cultured with SCF, FL, TPO, IL-6, and IL-3 (5GF), CH-296, and either I-Delta1^ext-myc (I-Delta) or control medium (Control) for up to 5 weeks. Mean numbers (± SEM) of total cells (left panel), CD34⁺ cells (middle panel), and CFU (right panel) in six wells are shown. Data are representative of five independent experiments. (b and c) CD34⁺CD38^– cells (1,000 per well) were cultured for 2 weeks with I-Delta1^ext-myc, CH-296, and 4GF (SCF, FL, TPO, and IL-6), with or without IL-3 (10 ng/ml), GM-CSF (10 ng/ml), or G-CSF (10 ng/ml). Mean numbers (± SEM) of CD34⁺ cells in six wells (b) and expression of myeloid antigens CD15 and CD14 in cultured cells (c) are shown. Data are representative of four independent experiments. Numbers in corners in c are the percentage of gated events within that quadrant.