I-Delta1^ext-myc enhances engraftment of human cells in marrow of NOD/SCID β2m^–/– or NOD/SCID mice. (a and b) We transplanted 4.7 × 10³ fresh CD34⁺CD38^– cells along with 2 × 10⁶ irradiated (15 Gy) CD34^– cord blood cells (day 0), or all the progeny of 4.7 × 10³ CD34⁺CD38^– cells cultured for 16, 23, or 29 days with Delta1^ext-myc (I-Delta) or control medium (Control), into sublethally irradiated NOD/SCID β2^–/– mice (n = 7). At 3 and 6 weeks, marrow was aspirated from both knee joints (a), and at 9 weeks, mice were sacrificed and marrow was harvested from both femurs and both tibiae (b). We assessed human cell engraftment by counting the number of cells, in aspirated marrow, that stained with Peridinin chloropyll protein–conjucated (PerCP-conjugated) anti–human CD45 and PE-conjugated anti–human CD33, CD19, or CD34, excluding cells staining with FITC-conjugated anti–mouse CD45.1 and DAPI-staining dead cells (see Methods). Mean (± SEM) engraftment of human cells in mice in each group is shown. Data are representative of four different experiments. (c) We transplanted 5 × 10³ fresh CD34⁺CD38^– cells along with 2 × 10⁶ irradiated (15 Gy) CD34^– cord blood cells (Noncultured), or all the progeny of 5 × 10³ CD34⁺CD38^– cells cultured for 21 days with I-Delta1^ext-myc (I-Delta) or control medium (Control), into sublethally irradiated NOD/SCID mice (n = 10). At 3 and 6 weeks, marrow was aspirated from both knee joints, and at 12 weeks, mice were sacrificed and marrow was harvested from both femurs and both tibiae. Mean percentage (± SEM) of human cells in marrow is shown.