Representative Hb electrophoresis gels from nonirradiated mice engrafted with expanded BM. C57 BM was used as the donor marrow for transduction and expansion. Recipient mice were HW80. The differing Hb patterns for donor and recipient are indicated (upper left). Primary recipients shown are MDR 7, 11, 18 (7 months post BMT), MDR 20 (5 months post-BMT) from experiment 1 and MDR 15 (3 months post-BMT) from experiment 2. Secondary irradiated recipients (HW80) were transplanted with marrow cells from MDR 20 (below) demonstrating persistence of donor engraftment 8 weeks after secondary transplant.