Delta1^ext-IgG affects the number and apoptosis of CD34⁺ precursors and the number of myeloid and lymphoid precursors in a dose-dependent manner. CD34⁺CD38^– cord blood precursors were incubated with increasing Delta1^ext-IgG densities or human control IgG (designated in the figures as Delta1^ext-IgG at 0 μg/mL). (A) Total number of cells (▪), and number of CD34⁺ cells (▴) generated following 21 days of culture. Results are the mean of 7 independent experiments ± SEM (R² = 0.97; P = .002 for total cells and .001 for CD34). (B) Maximum percentage of CD34⁺ cells that are annexin V positive and propidium iodide negative] following 3 to 6 days in culture. Percent apoptosis was measured on days 3, 6, 10, and 14 in 3 independent experiments and maximum apoptosis of the CD34⁺ cells was seen at 3 and 6 days. Results are the mean of 3 independent experiments ± SEM. (C-D) Total number of CD14⁺ (R² = 0.95; P = .004) and CD7⁺ cells, respectively, generated following 21 days of culture. Results are the mean of 7 independent experiments ± SEM.