Genetically modified hematopoietic stem cells expressing o6methylguanine dna methyltransferase via a retrovirus vector protect the lymphoid and stem cell compartments in long-term engrafted animals treated with nitrosourea

R. Maze, R. Kapur, D. A. Williams

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Bone marrow {BM) toxicity is a dose-limiting side effect of chloroethylnitrosoureas (CNU). A major determinant of CNU cytotoxidty is the methylation of O6-guanine and the formation of interstrand DNA crosslinks. Methylguanine DNA methyltransferase (MGMT) removes alkyl groups from the Opposition and has been shown to repair CNU-induced DNA damage. BM cells express a low level of MGMT. We have previously demonstrated that reconstitution of marine BM with genetically modified MGMT-expressing hematopoietic stem cells (MGMT-HSCs) significantly reduces CNU-related pancytopenia (Maze et al., PNAS, in press). In the present study, we examined the long-term effect of l,3-bis(2chloroctbylH-nitrosourea (BCNU) treatment and vector-derived expression of MGMT in hematopoietic stem cells (HSCs) on the lymphoid and HSC compartments following bone marrow transplantation (BMT). Mice were transplanted with MGMT or mock-infected (control) BM and treated for 5 weeks with BCNU (40 rag/kg). Five months post-BMT, bom the total thymic cellularity and the percentage of immature CD4+CD8+ double positive cells were significantly reduced in surviving BCNU-treated control mice vs. mice transplanted with MGMT-HSCs (7.3 ±3.6xl06 and 1.68% vs. 28.0i3.6×106 and 57.8%, respectively). Mice transplanted with MGMT-HSCs also had a normal frequency of mature B cells in the spleen (30.3%), based on B220 and IgD cell surface markers, whereas spleen cells from BCNU-treated control mice were depleted of mature B cells (1.63%). BCNU-treated mice transplanted with MGMT-HSCs demonstrated: a greater frequency of stem cells, based on serial transplants; BCNU resistance in vitro; and a higher level of DNA repair activity compared to BCNU-treated control mice. These studies demonstrate that MGMT-HSCs protect both the (ymphoid and HSC compartments from CNU-induced damage. Together with our previous data on myeloid protection, these data suggest an opportunity for CNU dose-intensification following autologous BMT in the treatment of CNU-sensitive tumors using gene therapy.

Original languageEnglish (US)
Pages (from-to)318a
JournalJournal of Investigative Medicine
Issue number3
StatePublished - Jan 1 1996

ASJC Scopus subject areas

  • Biochemistry, Genetics and Molecular Biology(all)

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