title: Transduction of murine bone marrow cells with an MDR1 vector enables ex vivo stem cell expansion, but these expanded grafts cause a myeloproliferative syndrome in transplanted mice.
abstract: Attempts to expand repopulating hematopoietic cells ex vivo have yielded only modest amplification in stem cell numbers. We now report that expression of an exogenous human multi-drug resistance 1 (MDR1) gene enables dramatic ex vivo stem cell expansion in the presence of early acting hematopoietic cytokines. Bone marrow cells were transduced with retroviral vectors expressing either the MDR1 gene or a variant of human dihydrofolate reductase (DHFR), and then expanded for 12 days in the presence of interleukin-3 (IL-3), IL-6, and stem cell factor. When these cells were injected into nonirradiated mice, high levels of long-term engraftment were only seen with MDR1-transduced grafts. To verify that expansion of MDR1-transduced repopulating cells had occurred, competitive repopulation assays were performed using MDR1 expanded grafts. These experiments showed progressive expansion of MDR1-transduced repopulating cells over the expansion period, with a 13-fold overall increase in stem cells after 12 days. In all of the experiments, mice transplanted with expanded MDR1-transduced stem cells developed a myeloproliferative disorder characterized by high peripheral white blood cell counts and splenomegaly. These results show that MDR1-transduced stem cells can be expanded in vitro using hematopoietic cytokines without any drug selection, but enforced stem cell self-renewal divisions can have adverse consequences.
authors.affiliation: Division of Experimental Hematology, the Department of Immunology, and the Department of Biochemistry, St Jude Children's Research Hospital, Memphis, TN, USA.
authors.forename: K D
authors.initials: KD
authors.lastname: Bunting
authors.forename: J
authors.initials: J
authors.lastname: Galipeau
authors.forename: D
authors.initials: D
authors.lastname: Topham
authors.forename: E
authors.initials: E
authors.lastname: Benaim
authors.forename: B P
authors.initials: BP
authors.lastname: Sorrentino
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000502:physiology*; D000818:Animals; D002455:Cell Division; D002478:Cells, Cultured / Q000187:drug effects / Q000637:transplantation; D019450:Genes, MDR; D005822:Genetic Vectors; D006085:Graft Survival; D006251:Harvey murine sarcoma virus / Q000235:genetics; D006410:Hematopoiesis / Q000187:drug effects; D018380:Hematopoietic Stem Cell Transplantation / Q000009:adverse effects*; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D015850:Interleukin-6 / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009196:Myeloproliferative Disorders / Q000209:etiology* / Q000235:genetics / Q000473:pathology; D019089:Stem Cell Factor / Q000494:pharmacology; D014162:Transfection
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D007377:Interleukin-3; D015850:Interleukin-6; D019089:Stem Cell Factor