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Effects of Retroviral-Mediated MDR1 Expression on Hematopoietic Stem Cell Self-Renewal and Differentiation in Culture


  • aSupported in part by National Heart, Lung, and Blood Institute Program Project Grant No. P01 HL 53749, The James S. McDonnell Foundation Grant No. 94-50, US Public Health Service Grant No. P01 CA 31922, Cancer Center Support Grant No. P30 CA 21765, and the American Lebanese Syrian Associated Charities (ALSAC).

Address correspondence to: Brian P. Sorrentino, M.D., Dept. of Biochemistry and Hematology/Oncology, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, TN 38105. Phone, 901/495-2727; fax, 901/495-2176; e-mail:


Abstract: Ex vivo expansion of hematopoietic stem cells would be useful for bone marrow transplantation and gene therapy applications. Toward this goal, we have investigated whether retrovirally-transduced murine stem cells could be expanded in culture with hematopoietic cytokines. Bone marrow cells were transduced with retroviral vectors expressing either the human multidrug resistance 1 gene (HaMDR1), a variant of human dihydrofolate reductase (HaDHFR), or both MDR1 and DHFR in an internal ribosomal entry site (IRES)-containing bicistronic vector (HaMID). Cells were then expanded for 15 days in cultures stimulated with interleukin (IL)-3, IL-6, and stem cell factor. When very low marrow volumes were injected into lethally irradiated recipient mice, long-term reconstitution with 100% donor cells was seen in all mice injected with HaMDR1- or HaMID-transduced cells. By contrast, engraftment with HaDHFR- or mock-transduced cells ranged from partial to undetectable despite injection of significantly larger marrow volumes. In addition, mice transplanted with expanded HaMDR1- or HaMID-transduced stem cells developed a myeloproliferative disorder that was characterized by an increase in abnormal peripheral blood leukocytes. These results show that MDR1-transduced stem cells can be expanded in vitro with hematopoietic cytokines, but indicate that an increased stem cell division frequency can lead to stem cell damage.