Kinetic analysis of HaMDR1 transduced stem cell expansion. BM cells were transduced with the HaMDR1 retrovirus and expanded for the indicated time periods. HaMDR1 cells (0.02 hind limb volumes/HW80 background) were combined with fresh competed marrow (0.25 hind limb volumes/C57 background) and injected into lethally irradiated mice. Unexpanded MDR1 BM (day 0) did not result in reconstitution with MDR1-transduced cells. However, expansion for 3 to 12 days resulted in a progressive increase in the percentage of engraftment of MDR1 (HW80) marrow. The data shown are for mice analyzed 9 months after transplant. Identification numbers for mice engrafted with expanded BM are indicated below each lane. Due to the large number of cells on day 12, mice were injected with 0.01 hind limb volumes of HaMDR1 cells versus 0.125 hind limb volumes of fresh C57 cells.