Retroviral-mediated transfer of the human glucocerebrosidase gene into cultured Gaucher bone marrow.

Gaucher disease, a lysosomal glycolipid storage disorder, results from the genetic deficiency of an acidic glucosidase, glucocerebrosidase (GC). The beneficial effects of allogeneic bone marrow transplantation (BMT) for Gaucher disease suggest that GC gene transduction and the transplantation of autologous hematopoietic stem cells (gene therapy) may similarly alleviate symptoms. We have constructed a retroviral vector, L-GC, produced by a clone of the amphotropic packaging cell line PA317, which transduces the normal human GC cDNA with high efficiency. Whole-marrow mononuclear cells and CD34-enriched cells from a 4-yr-old female with type 3 Gaucher disease were transduced by the L-GC vector and studied in long-term bone marrow culture (LTBMC). Prestimulation of marrow with IL-3 and IL-6, followed by co-cultivation with vector-producing fibroblasts, produced gene transfer into 40-45% of the hematopoietic progenitor cells. The levels of GC expression in progeny cells (primarily mature myelomonocytic) produced by the LTBMC were quantitatively analyzed by Northern blot, Western blot, and glucocerebrosidase enzyme assay. Normal levels of GC RNA, immunoreactive protein, and enzymatic activity were detected throughout the duration of culture. These studies demonstrate that retroviral vectors can efficiently transfer the GC gene into long-lived hematopoietic progenitor cells from the bone marrow of patients with Gaucher disease and express physiologically relevant levels of GC enzyme activity.     

SDF-1alpha/CXCL12 enhances retroviral-mediated gene transfer into immature subsets of human and murine hematopoietic progenitor cells

Genetic modification of hematopoietic stem and progenitor cells has the potential to treat diseases affecting blood cells. Oncoretroviral vectors have been used for gene therapy; however, clinical success has been limited in part by low gene transfer efficiencies. We found that the presence of stromal-derived factor 1 (SDF-1alpha)/CXCL12 during retroviral transduction significantly enhanced, in a dose-dependent fashion, gene transfer into immature subsets of high proliferative human and murine hematopoietic progenitor cells. Murine mononuclear bone marrow cells and purified c-Kit(+)Lin(-) bone marrow cells were prestimulated and transduced with the bicistronic retroviral vector MIEG3 on Retronectin-coated surfaces in the presence and absence of SDF-1. SDF-1 enhanced gene transduction of murine bone marrow and c-Kit(+)Lin(-) cells by 35 and 29%, respectively. Moreover, SDF-1 enhanced transduction of progenitors in these populations by 121 and 107%, respectively. SDF-1 also enhanced transduction of human immature subsets of high proliferative progenitors present in either nonadherent mononuclear or CD34(+) umbilical cord blood cells. Transduction of hematopoietic progenitors was further increased by preloading Retronectin-coated plates with retrovirus using low-speed centrifugation followed by increasing cell-virus interactions through brief centrifugation during the transduction procedure. These results may be of clinical relevance.     

Human cord blood cells as targets for gene transfer: potential use in genetic therapies of severe combined immunodeficiency disease

Human cord blood (CB) contains large numbers of both committed and primitive hematopoietic progenitor cells and has been shown to have the capacity to reconstitute the lympho-hematopoietic system in transplant protocols. To investigate the potential usefulness of CB stem and progenitor cell populations to deliver new genetic material into the blood and immune systems, we have transduced these cells using retroviral technology and compared the efficiency of gene transfer into CB cells with normal adult human bone marrow cells using a variety of infection protocols. Using two retroviral vectors which differ significantly in both recombinant viral titers and vector design, low density CB or adult bone marrow (ABM) cells were infected, and committed progenitor and more primitive hematopoietic cells were analyzed for gene expression by G418 drug resistance (G418r) of neophosphotransferase and protein analysis for murine adenosine deaminase (mADA). Standard methylcellulose progenitor assays were used to quantitate transduction efficiency of committed progenitor cells, and the long term culture-initiating cell (LTC-IC) assay was used to quantitate transduction efficiency of more primitive cells. Our results indicate that CB cells were more efficiently transduced via retroviral- mediated gene transfer as compared with ABM-derived cells. In addition, stable expression of the introduced gene sequences, including the ADA cDNA, was demonstrated in the progeny of infected LTC-ICs after 5 wk in long-term marrow cultures. Expression of the introduced ADA cDNA was higher than the endogenous human ADA gene in the LTC-IC-derived colonies examined. These studies demonstrate that CB progenitor and stem cells can be efficiently infected using retroviral vectors and suggest that CB cells may provide a suitable target population in gene transfer protocols for some genetic diseases.     

Animal xenograft models for evaluation of gene transfer into human hematopoietic stem cells

Animal xenograft models of gene therapy have become increasingly popular to study the effects of various transduction strategies on human hematopoietic stem cells (HSC). Xenograft models provide an in vivo setting in which to monitor the duration and effects of vector expression in the progeny of the transduced stem and progenitor cells. Also, the ability of HSC to home to the bone marrow and differentiate into multilineage progeny following ex vivo manipulation can only be tested in a transplantation system. The current review will discuss the murine xenograft models that have been used recently to determine optimized methods for gene transfer into normal human hematopoietic stem cells.     

Comparison of the effects of growth factors on retroviral vector-mediated gene transfer and the proliferative status of human hematopoietic progenitor cells

We have examined the ability of the recombinant hematopoietic growth factors (HGF) interleukin-3 (IL-3), IL-6, and granulocyte-macrophage colony-stimulating factor (GM-CSF) to increase retroviral vector-mediated gene transfer into human hematopoietic progenitor cells (HPC). The efficiency of neo gene transfer by the N2 vector into human HPC was enhanced by preculture with either GM-CSF or IL-3 (but not IL-6) and with each combination of the three factors. The combination of IL-3 plus IL-6 consistently produced significantly higher levels of G418-resistant colonies (50-60%) than any of the other combinations of HGF tested. Following preculture with HGF and transduction by N2, marrow was maintained in long-term bone marrow culture (LTBMC) for 2 months. The levels of G418-resistant HPC remained stable, and no apparent depletion of total HPC content resulted from the prior exposure to highly stimulatory doses of factors. The proliferative status of the HPC, following exposure to the HGF, was measured as the percentage of HPC that were inhibited from forming colonies by exposure to the S-phase-specific drug, hydroxyurea. The ability of the different HGF to increase the rate of gene transfer by N2 correlated significantly with the extent to which they stimulated HPC proliferation. These results suggest that the mechanism by which HGF increase rates of gene transfer into HPC is by stimulating cell proliferation. Techniques that produce high rates of gene transfer into long-lived human HPC will facilitate studies to quantitate expression of exogenous genes in hematopoietic cells and may be applicable to clinical gene therapy.     

In vivo gene transfer into adult stem cells in unconditioned mice by in situ delivery of a lentiviral vector.

The potential of in vivo lentivirus-mediated bone marrow stem cell gene transfer by bone cavity injection, which could take full advantage of any source of stem cells present there, has not been previously explored. Such an approach may avoid several difficulties encountered by ex vivo hematopoietic stem cell (HSC) gene transfer. We sought to determine if efficient gene transfer could be achieved in HSC and mesenchymal stem/progenitor cells (MSC) by intrafemoral injection of a lentivirus vector in mice. Four months after injection, up to 12% GFP-expressing cells were observed in myeloid and lymphoid subpopulations. Significant transduction efficiencies were seen in Lin(-)c-kit(+)Sca1(+) HSC/progenitors and CFU with multilineage potential, which were also confirmed by duplex PCR analysis of progenitor-derived colonies. Four months after secondary BMT, we observed 8.1 to 15% vector(+) CFU in all recipients. Integration analysis by LAM-PCR demonstrated that multiple transduced clones contributed to hematopoiesis in these animals. We also showed that GFP-expressing MSC retained multilineage differentiation potential, with 2.9 to 8.8% GFP-containing CFU-fibroblasts detected in both injected and BMT recipients. Our data provide evidence that adult stem cells in bone marrow can be efficiently transduced "in situ" by in vivo vector administration without preconditioning. This approach could lead to a novel application for treatment of human diseases.     

Long-term tracking of murine hematopoietic cells transduced with a bicistronic retrovirus containing CD24 and EGFP genes

Hematopoietic stem cells (HSCs) are attractive targets for gene therapy, but current gene transfer methodologies are inadequate for efficient HSC transduction and perpetual transgene expression. To improve gene transfer vectors and transduction protocols, it is vital to establish a system to evaluate transgene expression and the long-term behavior of transduced cells in vivo. For this purpose, we constructed a bicistronic retrovirus encoding the human CD24 (as the first cistron) and the enhanced green fluorescent protein (EGFP; as the second cistron). Murine bone marrow cells were transduced with this vector and the transgene expression was monitored along with hematopoietic reconstitution. Stable expression of CD24 and EGFP was demonstrated in the long-term repopulating cells for at least 6 months, and multi-parameter flow cytometry illustrated expression of both markers in all the lymphohematopoietic lineages examined (B and T lymphoid, erythroid and myeloid). Sustained expression was also shown in the secondary transplants for 6 months, suggesting that self-renewing HSCs were transduced by this vector. Overall, EGFP-tagged bicistronic retroviruses would provide powerful tools for detailed in vivo analysis of transduced hematopoietic cells, such as transgene expression in conjunction with lineage differentiation. Gene Therapy (2000) 7, 1193-1199.     

Transduction of long-term-engrafting human hematopoietic stem cells by retroviral vectors

Gene therapy using retroviral vectors to transfer functional exogenous genes into hematopoietic stem cells (HSCs) promises to provide a permanent cure for a wide array of both hematopoietic and nonhematopoietic disorders by virtue of the fact that retroviral vectors permanently integrate into the host cell genome and HSCs are able to self-renew and give rise to differentiated progeny throughout the life span of the patient. However, for transduction and genomic integration to occur, the target cells must undergo cell division and express the appropriate retroviral receptor, requirements that have thus far hindered attempts at inserting exogenous genes into human HSCs in vitro. In the present studies, we used the fetal sheep xenograft model of human hematopoiesis to evaluate whether human long-term engrafting HSCs could be transduced in vivo, within a fetal microenvironment. We transplanted adult human bone marrow-derived CD34(+)Lin(-) cells into preimmune fetal sheep recipients and subsequently (19 days later) administered clinical-grade murine retroviral vector supernatants to these fetal hematopoietic chimeras. Our results demonstrate that this approach successfully transduced adult human HSCs within all seven sheep that survived the procedure, and that these transduced HSCs had the ability to serially engraft primary, secondary, and tertiary fetal sheep recipients. Transgene expression persisted throughout the serial transplantation. The successful in vivo transduction of long-term engrafting human HSCs with the existing generation of murine retroviral vectors has significant implications for developing new approaches to pre- and postnatal gene therapy.     

Simplified retroviral vector gcsap with murine stem cell virus long terminal repeat allows high and continued expression of enhanced green fluorescent protein by human hematopoietic progenitors engrafted in nonobese diabetic/severe combined immunodeficient mice

Despite efforts toward improvements in retrovirus-mediated gene transfer, stable high-level expression of a therapeutic gene in human hematopoietic stem cells remains a great challenge. We have evaluated the efficiency of different viral long terminal repeats (LTRs) in long-term expression of a transgene in vivo, using severe combined immunodeficiency (SCID)-repopulating cell assays. Vectors used were variants of the simplified retroviral vector GCsap with the different LTRs of Moloney murine leukemia virus (MLV), myeloproliferative sarcoma virus (MPSV), and murine stem cell virus (MSCV). The enhanced green fluorescent protein (EGFP) gene was used as a marker to assess levels of transduction efficiency. CD34+ cells isolated from human cord blood were transduced by exposure to virus-containing supernatants on fibronectin fragments and in the presence of stem cell factor, interleukin 6, Flt-3 ligand, and thrombopoietin, and then transplanted into nonobese diabetic/SCID mice. Engraftment of human cells highly expressing EGFP, with differentiation along multiple cell lineages, was demonstrated for up to 18 weeks posttransplant, although the three different vectors showed different transduction frequencies (MLV, <0.1-33.2%; MPSV, <0.1-22.8%; MSCV, 0.3-51.7%). Of importance is that high-level transduction frequencies in human progenitor cells were also confirmed by colony-forming cell assays using bone marrow from transplanted mice, in which EGFP-expressing, highly proliferative potential colonies were observed by fluorescence microscopy. In these mice the vector carrying the MSCV LTR generated more EGFP-expressing human cells than did either of the other two constructs, indicating that GCsap carrying the MSCV LTR may be an efficient tool for stem cell gene therapy.     

Background and update to a phase I trial of stem cell gene marking in multiple myeloma

Attractive target cells in gene transfer approaches to cancer treatment are pluripotent hematopoietic stem cells (HSCs) because of their high proliferative potential, self renewal and the wide systemic distribution of their progeny. A retroviral-mediated approach to gene transfer into HSCs is currently favored because the transduced gene is permanently integrated into the genome of the target cell resulting in the long-term stable expression of the gene product. Unfortunately, this approach requires that the target cell be in cycle and thus retroviral transduction of normally quiescent HSCs generally occurs at low efficiency. In previous work we have demonstrated that reinfused genetically marked long term bone marrow culture cells contribute significantly to long term hematopoiesis in a canine model. If also true in humans, such experiments suggest that bone marrow cells could be removed, transduced with a retroviral vector carrying a gene of known therapeutic effect and reinfused into the autologous recipient with minimal toxicity. The demonstration of successful long term gene transfer in humans would be an important prelude to therapeutic trials using genetically modified cells. To proceed in this new direction, important biological questions about the safety and feasibility of treatment with gene marked cells must first be addressed. We have therefore obtained local institutional review board and Canadian Health Protection Branch approval for a phase I clinical trial which it is hoped will extend our understanding of the behavior of gene marked hematopoietic progenitor cells in vivo. In this trial gene marked autologous marrow cells will be reinfused into volunteer patients undergoing myeloablative treatment for multiple myeloma. In this paper we describe the background to our ongoing trial and provide a trial outline.     

携带人Ⅸ因子基因逆转录病毒载体的构建及其在小鼠骨髓细胞中的表达

构建携带人Ⅸ因子。cDNA的逆转录病毒载体MFGⅨ,并观察其在造血细胞中的表达。应用DNA重组技术将人Ⅸ因子cDNA构建入MFG载体,转导入包装细胞系PA317细胞,应用病毒上清转染造血细胞,并用PCR,ELISA及免疫组化方法检测其表达。研究结果表明,酶切鉴定成功构建MFGⅣ逆转录病毒载体,转入HT1080细胞系及小鼠骨髓细胞后,用PCR,ELISA及免疫荧光染色和免疫细胞化学染色证实Ⅸ因子的表达,且ELISA结果显示应用MFGⅨ转染Ⅸ因子蛋白及活性均高于LNCⅨ。结论提示MFGⅨ载体能较好转染造血细胞。     

mdr—1和DHFR双基因共转染入CD^＋34细胞拓宽造血细胞耐药谱的体外研究

目的：探讨将多药耐药基因（mdr-1)和二氢叶酸还原酶基因（DHFR)同时导入人CD^ 34细胞,以拓宽造血细胞耐药谱,改善骨髓耐受联合化疗的可行性,方法：将以造血细胞中高表达的逆转录病毒载体FMCF为基本结构骨架,通过引入IRES序列构建获得含mdr-1和DHFR（L22Y）双耐药基因的塑转录病毒载体pSF－DIM,通过脂质体介导包装,单嗜性和双 包装细胞上清交叉感染提高病毒滴度,低温离心病毒上清转染人脐血CD^ 34细胞,用流式细胞仪检测P－gp的表达,基因组PCR检测外源性耐药基因的整合,CFU－GM培养药性变化,结果：逆转录病毒载体pSF-DIM转人脐血CD^ 34细胞后,P-gp的表达较未转基因组增加了10．98％,基因组PCR同时检测到两种外源性药基因的整合,与未转基因组比较,在48nmol/L甲氢蝶呤和10ng/ml及12ng/ml紫杉醇（商品名Taxol）浓度水平,CFU－GM集落形成显著培养（P＜0．05）。结论：重组双耐药基因逆转录病毒载体pSF-DIM可度水平,CFU－GM集落形成显著增加（P＜0．05）,结论：重组双耐药基因逆转录病毒载体pSF-DIM可以有效介导mdr-1和DHFR双耐药基因进入人脐血CD34^ 细胞并获得共表达,拓宽了造血细胞药谱。     

Rapid 1-hour transduction of whole bone marrow leads to long-term repopulation of murine recipients with lentivirus-modified hematopoietic stem cells

Efficient gene transfer to hematopoietic stem cells by Moloney murine leukemia virus-derived retroviral vectors benefits from ex vivo culture and cytokine support. Both also increase the risks of apoptosis and differentiation among cells targeted for transduction. In an effort to maximize the retention of stem cell properties in target cells, we developed a transduction protocol with a focus on minimizing graft manipulation, cytokine stimulation, and ex vivo exposure duration. Based on their wide host range and ability to transduce quiescent cells, human immunodeficiency virus (HIV)-derived lentivirus vectors are ideally suited for this purpose. Our present studies in a murine model show that whole bone marrow cells are readily transduced after a 1-hour vector exposure in the presence of stem cell factor and CH296 fibronectin fragment. Using this rapid transduction protocol, we achieved long-term, multilineage reconstitution of murine recipients with up to 25% GFP-expressing cells in primary and secondary recipients. Our results demonstrate the unique ability of HIV-derived vectors to transduce hematopoietic stem cells in the absence of enrichment, under minimal cytokine stimulation, and following brief exposures.     

Bone marrow stromal cells as a vehicle for gene transfer.

Adoptive transfer of genetically modified somatic cells is playing an increasingly important role in the management of a wide spectrum of human diseases. Hematopoietic stem cells and lymphocytes have been used to transfer a variety of genes, however, they have limitations. In this study, the feasibility of retroviral gene transduction of bone marrow stromal cells, and the engraftment characteristics of these cells following infusion, was investigated in a murine transplantation model. Stromal cells derived from Balb/c mouse bone marrow were transduced with a replication-defective retrovirus containing the LacZ gene. Following three rounds of transduction, between 5 and 40% of the cells were positive for the LacZ gene. A total of 2 x 106 cells were infused into the same mouse strain. After the infusion, the LacZ gene was detected by PCR in the bone marrow, spleen, liver, kidney and lung; however, only the spleen and bone marrow samples were strongly positive. Quantitative PCR demonstrated that between 3 and 5% of spleen and bone marrow cells, and 1% of liver cells contained the LacZ gene at 3 weeks after infusion; <0.2% transduced cells were found in other organs. No difference was noted in engraftment between mice with or without irradiation before transplantation, suggesting that engraftment occurred without myeloablation. The infused transduced cells persisted for up to 24 weeks. Self-renewal of transplanted stromal cells was demonstrated in secondary transplant studies. Ease of culture and gene transduction and tissue specificity to hematopoietic organs (bone marrow, spleen, liver) is demonstrated, indicating that stromal cells may be an ideal vehicle for gene transfer.     

造血干细胞的基因转移及其表达的实验研究

为探索一种安全、有效、简易的非病毒基因转移策略用于介导造血干细胞基因转移的可行性,本研究利用商品化的脂质体将两个标志基因(Neo R和Lac Z)共转导造血细胞。通过G418筛选、富集转导阳性细胞,观察了外源基因在小鼠原代骨髓细胞的基因转移率及其表达的稳定性。结果显示:通过脂质体介导,外源基因在小鼠骨髓细胞可获得有效的瞬时和稳定的表达。同时,经G418筛选,转导阳性细胞可得到明显的富集。提示利用脂质体这一非病毒载体个导造血干细胞基因转移的可行性。     

Gene transfer of adenosine deaminase into primitive human hematopoietic progenitor cells.

The inherited deficiency in adenosine deaminase (ADA), which results in severe combined immunodeficiency, is generally regarded as an optimal model for the development of human somatic gene therapy. The ideal target for the correction of ADA deficiency and other lympho-hematopoietic disorders would be the hematopoietic stem cell. We have used a combination of recombinant human interleukins-3 and -6 to stimulate the proliferation of primitive human hematopoietic progenitor cells during a period of co-cultivation with irradiated cells producing high titers of an ADA-transducing retroviral vector packaged in amphotropic particles. In a series of nine experiments, an average of 83% of the clonogenic progenitors (CFU-E and CFU-GM) were found to have acquired the transferred sequence as determined by polymerase chain reaction analysis. In addition, in two experiments, 24-44% of the clonogenic progenitors derived from long-term myeloid cultures 9 weeks post-transduction were found to contain vector sequence. The latter cells are derived from so-called "long-term culture-initiating cells" (LTC-IC), which are primitive cells probably related to hematopoietic stem cells. Moreover, the transduced ADA enzyme was found to be expressed in both normal and ADA-deficient erythroid colonies, and in the nonadherent cells of long-term bone marrow culture for at least 2 weeks at levels that approximate the endogenous ADA levels of normal erythroid cells. These results indicate that the ADA coding sequence can efficiently be introduced by retroviral gene transfer into both committed and primitive human hematopoietic progenitor cells, and that this will result in adequate expression of the transduced enzyme in the progeny of committed hematopoietic progenitors.     

Expression of human glucocerebrosidase in long-term reconstituted mice following retroviral-mediated gene transfer into hematopoietic stem cells

A retroviral vector (GTN) in which the glucocerebrosidase (GCase) cDNA is driven by the Moloney murine leukemia virus (Mo-MuLV) long terminal repeat (LTR) was tested for transfer efficiency and expression of the GCase gene in long-term reconstituted mice. Eleven W/Wv mice were transplanted with unselected GTN-infected bone marrow cells and 10 of these mice were analyzed 3 months later. Seven of these 10 mice (70%) contained the intact proviral genome in bone marrow, spleen, and thymus. Of these 7,3 mice contained a high-copy number of the provirus in all the hematopoietic tissues tested. The mice contained anywhere from one to four proviral integration sites that were the same in all three tissues, indicating that these mice have been repopulated by one or more transduced multipotential hematopoietic stem cells. Five months after transplantation, bone marrow from the eleventh mouse was transplanted into secondary recipient animals. The secondary recipients contained the intact proviral genome in the bone marrow, spleen, thymus, and macrophages 4 months after the secondary transplantation. This further supports the conclusion that hematopoietic stem cells have indeed been targeted. Human GCase RNA was detected in all 7 mice containing the proviral DNA. These results demonstrate expression of the human GCase gene in the progeny of repopulating hematopoietic stem cells of mice following gene transfer.     

Drug selection of MDR1-transduced hematopoietic cells ex vivo increases transgene expression and chemoresistance in reconstituted bone marrow in mice

The MDR1 (multidrug resistance) gene, transferred to hematopoietic cells, is expected to protect them from anticancer chemotherapy and may serve as a selectable marker, restoring gene expression in vivo. Appropriate selection strategies, however, need to be established. To investigate whether preselection ex vivo affects chemoresistance, murine bone marrow cells were retrovirally transduced with high-titer or, as a model for suboptimal gene expression, low-titer retroviruses and exposed to daunomycin or colchicine for 48-96 h. Selection significantly increased chemoresistance of clonogenic progenitor cells. In tissue culture, the entire target population was rendered highly drug resistant after MDR1 transfer with high-titer viruses. If transduction was performed under suboptimal conditions, drug selection increased the frequency of chemoresistant colonies up to 40% over the number of unselected cells. Colchicine and daunomycin were equally efficient in increasing drug resistance ex vivo, but colchicine-preselected cells rescued lethally irradiated mice under conditions where daunomycin-selected bone marrow cells failed to do so. Hence, while hematopoietic cells can be protected by MDR1, the selection strategy is critical for repopulation of bone marrow with transduced cells. Preselection in culture before transplantation significantly increased P-gp expression and chemoresistance in vivo in mice reconstituted with transduced bone marrow cells. This study may help to facilitate the use of MDR1 as a selectable marker in gene therapy of the hematopoietic system. Gene Therapy (2000) 7, 348-358.