[Show abstract][Hide abstract] ABSTRACT: Foamy virus (FV) vectors are promising tools for gene therapy, but low titer is a major challenge for large-scale clinical trials. Here, we increased FV vector titer 50-fold by constructing novel vector plasmids and using polyethylenimine-mediated transfection. FV and lentiviral (LV) vectors were used separately to transduce human CD34+ cells at multiplicities of infection of 25, and those cells were transplanted into immunodeficient mice. FV vector transduction frequencies of repopulating human cells were 37.1±1.9% in unstimulated cells and 36.9±2.2% in pre-stimulated cells, and engraftment frequencies were 40.9±4.9% in unstimulated cells and 47.1±3.3% in pre-stimulated cells. Engraftment frequencies of FV vector-transduced cells were significantly higher than those of LV vector-transduced cells. Linear amplification-mediated PCR with Illumina paired-end runs showed that all human chromosomes contained FV provirus. FV had integration preference near transcriptional start sites and CpG islands of RefSeq genes but not within genes. Repopulating lymphoid and myeloid cells contained common integration sites, suggesting that FV vector could transduce multi-lineage hematopoietic stem/progenitor populations. Our new FV vector backbone may be a suitable candidate for developing therapeutic FV vectors for use in clinical trials.
[Show abstract][Hide abstract] ABSTRACT: Foamy viruses (FVs) (spumaretroviruses) are good alternative to retroviruses as gene therapy vector. Despite four decades since the discovery of FV, its receptor molecule is still unknown. FV vector transduction of human CD34(+) cells was inhibited by culture with fibronectin. Because fibronectin contains heparin-binding domain, the interactions of fibronectin with heparan sulfate (HS) on cells might be inhibitory to FV transduction. These observations led us to investigate whether HS is a receptor for FV. Two mutant CHO cell lines (but not parental wild type) lacking cell surface HS but not chondroitin sulfate (CS) were largely resistant to FV attachment and transduction. Inhibition of HS expression using enzymes or chemicals greatly reduced FV transduction in human, monkey, and rodent cells. Raji cells, which lack HS and were largely resistant to FV, were rendered more permissive through ectopic expression of syndecan-1, which contains HS. In contrast, mutant syndecan-1-expressing cells were largely resistant to FV. Our findings indicate that cellular HS is a receptor for FV. Identifying FV receptor will enable better understanding of its entry process and optimal use as gene therapy vector to treat inherited and pathogenic diseases.
[Show abstract][Hide abstract] ABSTRACT: Excess free alpha-globin is cytotoxic and contributes to the pathophysiology of b-thalassemia. Alpha hemoglobin stabilizing protein (AHSP) is a molecular chaperone that binds free alpha-globin to promote its folding and inhibit its ability to produce damaging reactive oxygen species. Reduced AHSP levels correlate with increased severity of b-thalassemia in some human cohorts, but causal mechanistic relationships are not established for these associations. We used transgenic and lentiviral gene transfer methods to investigate whether supraphysiologic AHSP levels could mitigate the severity of b-thalassemia intermedia by providing an increased sink for the excess pool of alpha-globin chains. We tested wild-type AHSP and two mutant versions with amino acid substitutions that confer 3- or 13-fold higher affinity for alpha-globin. Erythroid overexpression of these AHSP proteins up to 11-fold beyond endogenous levels had no major effects on hematologic parameters in b-thalassemic animals. Our results demonstrate that endogenous AHSP is not limiting for a-globin detoxification in a murine model of b-thalassemia.
American Journal of Hematology 10/2010; 85(10):820-2. · 3.48 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Correction of murine models of beta-thalassemia has been achieved through high-level globin lentiviral vector gene transfer into mouse hematopoietic stem cells (HSCs). However, transduction of human HSCs is less robust and may be inadequate to achieve therapeutic levels of genetically modified erythroid cells. We therefore developed a double gene lentiviral vector encoding both human gamma-globin under the transcriptional control of erythroid regulatory elements and methylguanine methyltransferase (MGMT), driven by a constitutive cellular promoter. MGMT expression provides cellular resistance to alkylator drugs, which can be administered to kill residual untransduced, diseased HSCs, whereas transduced cells are protected. Mice transplanted with beta-thalassemic HSCs transduced with a gamma-globin/MGMT vector initially had subtherapeutic levels of red cells expressing gamma-globin. To enrich gamma-globin-expressing cells, transplanted mice were treated with the alkylator agent 1,3-bis-chloroethyl-1-nitrosourea. This resulted in significant increases in the number of gamma-globin-expressing red cells and the amount of fetal hemoglobin, leading to resolution of anemia. Selection of transduced HSCs was also obtained when cells were drug-treated before transplantation. Mice that received these cells demonstrated reconstitution with therapeutic levels of gamma-globin-expressing cells. These data suggest that MGMT-based drug selection holds promise as a modality to improve gene therapy for beta-thalassemia.