Role of P- and E-selectins in the homing of human CD34⁺ cells to the BM of NOD/SCID mice. Sublethally irradiated NOD/SCID or P/E^–/– NOD/SCID mice were injected intravenously with 2 × 10⁷ human MNCs from mPB samples. Cells were allowed to home for 2 hours, and the femoral BM was harvested. (a) Double staining of the transplanted human MNCs for human CD34 and CD45. (b) BM cells recovered from an uninjected control mouse stained for human CD34 and CD45. (c) Wild-type NOD/SCID mouse transplanted with human MNCs. (d) P/E^–/– NOD/SCID mouse transplanted with human MNCs. (e) Number of human CD34⁺ cells homed per femur in transplanted wild-type NOD/SCID and P/E^–/– NOD/SCID mice. The percentage of gated CD34⁺/CD45⁺ human cells (upper region in the scattergrams in c–d) in the recipient BM was determined by FACS analysis, and the number of homed cells per femur was calculated based on the femoral cellularity. The number of homed human CD34⁺ cells is drastically reduced in P/E^–/– NOD/SCID mice. n = 6 mice injected with MNCs from two different human donors. *P = 0.0008.