title: Myeloablation is not required to select and maintain expression of the drug-resistance gene, mutant MGMT, in primary and secondary recipients.
abstract: Gene transduction of hematopoietic progenitors capable of reconstituting both primary and secondary recipients is an important milestone in preclinical development of gene therapy. Myeloablation conditioning prior to infusion of transduced stem cells causes significant host morbidity. In contrast, drug-resistance gene transfer utilizes judicious in vivo selection of transduced stem cells over time, reaching only the level of transduction and expression required. The O(6)-benzylguanine (BG)-resistant mutant O(6)-methylguanine-DNA methyltransferase (MGMT) gene is a potent selection gene for transduced cells. Using two different mutant MGMTs, G156A and P140K, that vary in BG resistance by a factor of 1:20, we asked whether long-term repopulating and secondary mouse-repopulating cells could be transduced, transplanted, and selected for in the nonmyeloablated recipient and whether the mutant MGMT would continue to be expressed in secondary recipient repopulating cells. We found that under stringent drug-selection competition, cells expressing the more BG-resistant variant, P140K-MGMT, were enriched over G156A-MGMT-expressing progenitors. In addition, the MFG retroviral vector transmitted the mutant MGMT gene to long-term repopulating cells that, after selective enrichment in the nonmyeloablated primary recipient, repopulated secondary mice and continued to express the transgene. Thus, MFG mutant MGMT vectors transduce repopulating hematopoietic stem cells that may be used both for chemotherapeutic drug resistance and to enrich for second therapeutic genes.
authors.affiliation: Division of Hematology-Oncology and the Comprehensive Cancer Center, University Hospitals of Cleveland and Case Western Reserve University School of Medicine, 10900 Euclid Avenue, BRB 3-West, Cleveland, Ohio 44106-4937, USA.
authors.forename: Janice E
authors.initials: JE
authors.lastname: Bowman
authors.forename: Jane S
authors.initials: JS
authors.lastname: Reese
authors.forename: Karen T
authors.initials: KT
authors.lastname: Lingas
authors.forename: Stanton L
authors.initials: SL
authors.lastname: Gerson
mesh_terms: D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology; D015139:Blotting, Southern; D001854:Bone Marrow Cells / Q000378:metabolism; D016026:Bone Marrow Transplantation; D002330:Carmustine / Q000494:pharmacology; D002469:Cell Separation; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D018014:Gene Transfer Techniques; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors; D006147:Guanine / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008809:Mice, Inbred C3H; D008957:Models, Genetic; D009154:Mutation; D009368:Neoplasm Transplantation; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000096:biosynthesis / Q000235:genetics*; D016133:Polymerase Chain Reaction; D013234:Stem Cells / Q000378:metabolism; D013997:Time Factors
chemical_list: D018906:Antineoplastic Agents, Alkylating; D004791:Enzyme Inhibitors; C064976:O(6)-benzylguanine; D006147:Guanine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine