Transduction of nondividing cells using pseudotyped defective high-titer HIV type 1 particles

Stable transgene expression in tumors and metastases after transduction with lentiviral vectors based on human immunodeficiency virus type 1

The relatively low efficiency of target cell transduction and variations in the stability of transgene expression by retroviral vectors based on the Moloney murine leukemia virus (MoMLV) are major impediments to the use of such vectors in cancer gene therapy approaches. The present study was designed to investigate the stability and efficiency of transgene expression in human lung and breast cancer cell lines transduced with vectors based on human immunodeficiency virus type 1 (HIV-1) in vitro and in vivo in nude mouse models of metastasis. H460 lung carcinoma cells and MDA-MB-231 breast carcinoma cells were transduced with lentiviral vectors encoding enhanced green fluorescent protein (EGFP) and beta-galactosidase (beta-Gal), respectively. Transduced H460 cells were administered to nude mice by either intravenous or subcutaneous injection and MDA-MB-231 cells were implanted orthotopically into the mammary fat pad of such mice to induce primary tumor and metastatic lung tumor formation. High-level EGFP expression was maintained in transduced H460 cells in metastatic lung nodules for up to 6 weeks and transgene expression in vitro persisted for at least 23 days after retrieval of EGFP-positive H460 cells from the lungs of tumor-bearing mice and subsequent cultivation in vitro. Likewise, beta-Gal expression levels in metastatic MDA-MB-231 cells in lungs remained high for up to 11 weeks. Southern blot analyses carried out with DNA from lung nodules showed that proviral DNAs in H460 cells were maintained stably over many cell generations and during subsequent reimplantation in vivo. However, molecular analyses revealed variations in transgene copy numbers and expression levels among individual lung clones. These results demonstrate the usefulness of HIV-1-based lentiviral vectors for sustained and stable transgene expression in human lung and breast cancer cell lines in vitro and in vivo.

Targeting platelet GPIbalpha transgene expression to human megakaryocytes and forming a complete complex with endogenous GPIbbeta and GPIX

Bernard-Soulier Syndrome (BSS) is a severe congenital platelet disorder that results from a deficiency of the platelet membrane glycoprotein (GP) Ib/IX complex that is composed of four subunits (GPIbalpha, GPIbbeta, GPIX, and GPV). Mutations in either GPIbalpha, GPIbbeta, or GPIX can result in BSS with many of the known mutations occurring in GPIbalpha. In this study, we have developed a gene therapy strategy to express hemagglutinin (HA)-tagged GPIbalpha in megakaryocytes and potentially correct a hereditary deficiency. To direct GPIbalpha expression in megakaryocytic lineage cells, we designed a GPIbalpha cassette where human GPIbalpha cDNA was placed under control of the megakaryocytic/platelet-specific alphaIIb promoter and inserted into a lentiviral vector. Human CD34+ peripheral blood cells (PBC) and Dami cells were transduced with alphaIIb-HA-GPIbalpha-WPT virus. Flow cytometry analysis demonstrated that 50.1% of the megakaryocytes derived from CD34+ stem cells and 97.3% of Dami cells were transduced and expressed transgene GPIbalpha protein. Immunoprecipitation with Western blot analysis demonstrated that transgene protein associated with endogenous GPIbbeta and GPIX proteins. To address further the lineage-specific expression of the alphaIIb-HA-GPIbalpha construct, three cell lines, Dami, AtT-20 and HepG2, were transfected with GPIbalpha expression plasmids and analyzed by confocal microscopy. The results demonstrated that among these three cell lines, the tissue-specific alphaIIb promoter was active only in Dami cells. Thus, GPIbalpha can be efficiently and specifically expressed in the megakaryocytic compartment of hematopoietic cells and the transgene product associates with endogenous GPIbbeta and GPIX forming a complete complex. This strategy could potentially be utilized for gene therapy of BSS.

Design of artificial myocardial microtissues

Cultivation technologies promoting organization of mammalian cells in three dimensions are essential for gene-function analyses as well as drug testing and represent the first step toward the design of tissue replacements and bioartificial organs. Embedded in a three-dimensional environment, cells are expected to develop tissue-like higher order intercellular structures (cell-cell contacts, extracellular matrix) that orchestrate cellular functions including proliferation, differentiation, apoptosis, and angiogenesis with unmatched quality. We have refined the hanging drop cultivation technology to pioneer beating heart microtissues derived from pure primary rat and mouse cardiomyocyte cultures as well as mixed populations reflecting the cell type composition of rodent hearts. Phenotypic characterization combined with detailed analysis of muscle-specific cell traits, extracellular matrix components, as well as endogenous vascular endothelial growth factor (VEGF) expression profiles of heart microtissues revealed (1). a linear cell number-microtissue size correlation, (2). intermicrotissue superstructures, (3). retention of key cardiomyocyte-specific cell qualities, (4). a sophisticated extracellular matrix, and (5). a high degree of self-organization exemplified by the tendency of muscle structures to assemble at the periphery of these myocardial spheroids. Furthermore (6). myocardial spheroids support endogenous VEGF expression in a size-dependent manner that will likely promote vascularization of heart microtissues produced from defined cell mixtures as well as support connection to the host vascular system after implantation. As cardiomyocytes are known to be refractory to current transfection technologies we have designed lentivirus-based transduction strategies to lead the way for genetic engineering of myocardial microtissues in a clinical setting.

Toward construction of a self-sustained clock-like expression system based on the mammalian circadian clock

Despite recent advances in circadian biology, detailed understanding of how a biological pacemaker system is assembled, maintained, and regulated continues to be a significant challenge. We have assembled and characterized a first-generation, regulatable, self-sustained clock-like expression system based on key components of the mammalian circadian clock. The molecular setup of the clock-like oscillator was reduced to the core set of positive and negative elements common to all known circadian pacemakers. Sophisticated tetracycline-responsive multi-cistronic expression integrated with forefront lentiviral transduction tools enabled autoregulated reporter transgene expression in a human cell line. We characterized transgene expression kinetics of an artificial oscillator and showed that its expression profiles could be modulated by a serum shock and administration of regulating tetracycline antibiotics. Design of a generic mammalian clock-like expression system will offer novel opportunities to study circadian biology and may provide a unique tool for rhythmic expression of desired transgenes fostering advances in biopharmaceutical manufacturing, gene therapy, and tissue engineering.

Design and in vivo characterization of self-inactivating human and non-human lentiviral expression vectors engineered for streptogramin-adjustable transgene expression

Adjustable transgene expression is considered key for next-generation molecular interventions in gene therapy scenarios, therapeutic reprogramming of clinical cell phenotypes for tissue engineering and sophisticated gene-function analyses in the post-genomic era. We have designed a portfolio of latest generation self-inactivating human (HIV-derived) and non-human (EIAV-based) lentiviral expression vectors engineered for streptogramin-adjustable expression of reporter (AmyS(DeltaS), EYFP, SAMY, SEAP), differentiation-modulating (human C/EBP-alpha) and therapeutic (human VEGF) transgenes in a variety of rodent (CHO-K1, C2C12) and human cell lines (HT-1080, K-562), human and mouse primary cells (NHDF, PBMC, CD4+) as well as chicken embryos. Lentiviral design concepts include (i) binary systems harboring constitutive streptogramin-dependent transactivator (PIT) and PIT-responsive transgene expression units on separate lentivectors; (ii) streptogramin-responsive promoters (P(PIR8)) placed 5' of desired transgenes; (iii) within modified enhancer-free 3'-long terminal repeats; and (iv) bidirectional autoregulated configurations providing streptogramin-responsive transgene expression in a lentiviral one-vector format. Rigorous quantitative analysis revealed HIV-based direct P(PIR)-transgene configurations to provide optimal regulation performance for (i) adjustable expression of intracellular and secreted product proteins, (ii) regulated differential differentiation of muscle precursor cell lines into adipocytes or osteoblasts and (iii) conditional vascularization fine-tuning in chicken embryos. Similar performance could be achieved by engineering streptogramin-responsive transgene expression into an autoregulated one-vector format. Powerful transduction systems equipped with adjustable transcription modulation options are expected to greatly advance sophisticated molecular interventions in clinically and/or biotechnologically relevant primary cells and cell lines.

Efficient Marking of Murine Long-Term Repopulating Stem Cells Targeting Unseparated Marrow Cells at Low Lentiviral Vector Particle Concentration

HIV-1-derived lentivirus vectors offer unique biological properties for gene delivery to hematopoietic stem cells and, when used at high multiplicities of infection (m.o.i.), permit efficient gene transfer after minimal target cell stimulation. However, such a strategy has been shown to promote multicopy proviral integration, potentially increasing the risk of insertional mutagenesis. To minimize cell manipulation, we targeted unseparated marrow and demonstrated that transduction at an m.o.i. of 1 resulted in up to 12% vector-modified peripheral blood leukocytes and successful repopulation of secondary recipients with vector-marked cells. Real-time PCR showed on average 1.8 proviral integrants per GFP-marked cell. By comparison, a cohort of animals transplanted with cells transduced at m.o.i. of 10 under otherwise unchanged conditions showed up to 45% marking with an average of 7 copies per GFP-expressing cell. Both m.o.i. groups demonstrated sustained proviral expression with stable GFP fluorescence intensity. In summary, we have identified conditions for lentiviral gene transfer involving minimal ex vivo target cell manipulation and have shown that the m.o.i. is a critical determinant of proviral copy number in lentivirus-transduced murine long-term repopulating cells. Thus, gene transfer efficiencies may be limited when single-copy integration is desired and additional strategies such as in vivo selection may be required to improve the frequency of gene-modified cells.

Cell cycle requirements for transduction by foamy virus vectors compared to those of oncovirus and lentivirus vectors

Retroviral vectors based on foamy viruses (FV) are efficient gene delivery vehicles for therapeutic and research applications. While previous studies have shown that FV vectors transduce quiescent cell cultures more efficiently than oncoviral vectors, their specific cell cycle requirements have not been determined. Here we compare the transduction frequencies of FV vectors with those of onco- and lentiviral vectors in nondividing and dividing normal human fibroblasts by several methods. FV vectors transduced serum-deprived fibroblast cultures more efficiently than oncoretroviral vectors and at rates comparable to those of lentiviral vectors. However, in these cultures FV vectors only transduced a subpopulation of proliferating cells, as determined by bromodeoxyuridine staining for DNA synthesis. In contrast to lentiviral vectors, FV vectors were unable to transduce human fibroblasts arrested by aphidicolin (G(1)/S phase) or gamma-irradiation (G(2) phase), and a partial cell cycle that included mitosis but not DNA synthesis was required. We could not determine if mitosis facilitated nuclear entry of FV vectors, since cell-free vector preparations contained long terminal repeat circles, precluding their use as nuclear markers. In contrast to oncoviral vectors, both FV and lentiviral vectors efficiently transduced G(0) fibroblasts that were later stimulated to divide. In the case of FV vectors, this was due to the persistence of a stable transduction intermediate in quiescent cells. Our findings support the use of FV vectors as a safe and effective alternative to lentiviral vectors for ex vivo transduction of stem cells that are quiescent during culture but divide following transplantation.

Transduction of bone-marrow-derived mesenchymal stem cells by using lentivirus vectors pseudotyped with modified RD114 envelope glycoproteins

Bone-marrow-derived mesenchymal stem cells (MSCs) have attracted considerable attention as tools for the systemic delivery of therapeutic proteins in vivo, and the ability to efficiently transfer genes of interest into such cells would create a number of therapeutic opportunities. We have designed and tested a series of human immunodeficiency virus type 1 (HIV-1)-based vectors and vectors based on the oncogenic murine stem cell virus to deliver and express transgenes in human MSCs. These vectors were pseudotyped with either the vesicular stomatitis virus G (VSV-G) glycoprotein (GP) or the feline endogenous virus RD114 envelope GP. Transduction efficiencies and transgene expression levels in MSCs were analyzed by quantitative flow cytometry and quantitative real-time PCR. While transduction efficiencies with virus particles pseudotyped with the VSV-G GP were found to be high, RD114 pseudotypes revealed transduction efficiencies that were 1 to 2 orders of magnitude below those observed with VSV-G pseudotypes. However, chimeric RD114 GPs, with the transmembrane and extracellular domains fused to the cytoplasmic domain derived from the amphotropic Moloney murine leukemia virus 4070A GP, revealed about 15-fold higher titers relative to the unmodified RD114 GP. The transduction efficiencies in human MSCs of HIV-1-based vectors pseudotyped with the chimeric RD114 GP were similar to those obtained with HIV-1 vectors pseudotyped with the VSV-G GP. Our results also indicate that RD114 pseudotypes were less toxic than VSV-G pseudotypes in human MSC progenitor assays. Taken together, these results suggest that lentivirus pseudotypes bearing alternative Env GPs provide efficient tools for ex vivo modification of human MSCs.

Transduction Patterns of Pseudotyped Lentiviral Vectors in the Nervous System

We have developed a non-primate-based lentiviral vector based on the equine infectious anemia virus (EIAV) for efficient gene transfer to the central and peripheral nervous systems. Previously we have demonstrated that pseudotyping lentiviral vectors with the rabies virus glycoprotein confers retrograde axonal transport to these vectors. In the present study we have successfully produced high-titer EIAV vectors pseudotyped with envelope glycoproteins from Rhabdovirus vesicular stomatitis virus (VSV) serotypes (Indiana and Chandipura strains); rabies virus [various Evelyn-Rokitnicki-Abelseth ERA strains and challenge virus standard (CVS)]; Lyssavirus Mokola virus, a rabies-related virus; and Arenavirus lymphocytic choriomeningitis virus (LCMV). These vectors were delivered to the striatum or spinal cord of adult rats or muscle of neonatal mice by direct injection. We report that the lentiviral vectors pseudotyped with envelopes from the VSV Indiana strain, wild-type ERA, and CVS strains resulted in strong transduction in the striatum, while Mokola- and LCMV-pseudotyped vectors exhibited moderate and weak transduction, respectively. Furthermore ERA- and CVS-pseudotyped lentiviral vectors demonstrated retrograde transport and expression in distal neurons after injection in brain, spinal cord, and muscle. The differences in transduction efficiencies and retrograde transport conferred by these envelope glycoproteins present novel opportunities in designing therapeutic strategies for different neurological diseases.

Ligand-Modified Vesicular Stomatitis Virus Glycoprotein Displays a Temperature-Sensitive Intracellular Trafficking and Virus Assembly Phenotype

The production of potentially targetable VSV-G-pseudotyped retrovirus vectors has been hampered by inadequate understanding of the structure-function relationships of the VSV-G protein. In these studies we demonstrate assembly and production of MLV-based and HIV-1-based vector particles using VSV-G proteins modified by the insertion of a peptide ligand into a site corresponding to amino acid position 24 of the native VSV-G molecule. The inserted ligand represents the decapeptide encoding the collagen-binding domain of von Willebrand factor. We have used deconvolution microscopy to demonstrate that the modified VSV-G molecules sequester in perinuclear structures and are unavailable for assembly of infectious virus particles at the cell surface under standard tissue culture conditions at 37 degrees C. In contrast, at a lower permissive temperature of 30 degrees C, the modified VSV-G protein traffics appropriately to the cell surface and participates in useful titers. Furthermore, VSV-G-pseudotyped MLV-based and HIV-1-based vectors displaying the collagen-binding domain demonstrate a statistically significant increased attachment to a collagen matrix as indicated by an ELISA-like cell binding assay and by a focus transduction assay.

New-generation multicistronic expression platform: pTRIDENT vectors containing size-optimized IRES elements enable homing endonuclease-based cistron swapping into lentiviral expression vectors

Capitalizing on a proven multicistronic expression vector platform we have designed novel pTRIDENT vectors which (1). enable coordinated expression of three desired transgenes, (2). are size-optimized, (3). take advantage of small highly efficient internal ribosome entry sites of the GTX or Rbm3 type, (4). harbor various sites specific for homing endonucleases facilitating promoter/multicistronic expression unit/polyadenylation site swapping as well as (5). straightforward integration into human HIV-l-based lentiviral expression vectors tailored to contain compatible homing endonucleases. Multicistronic expression profiles of novel pTRIDENT vectors engineered for different tricistronic expression configurations encoding human low-molecular-weight urokinase-type plasminogen activator (u-PA(LMW)) or Bacillus stearothermophilus-derived alpha-amylase (SAMY), human vascular endothelial growth factor (hVEGF), and human placental secreted alkaline phosphatase (SEAP) have been quantified in Chinese hamster ovary cells (CHO-K1), mouse fibroblasts (NIH/3T3), and/or human fibrosarcoma (HT-1080) cells. In addition, a pTRIDENT-derived SAMY-VEGF-SEAP expression cassette transferred into a compatible lentiviral expression vector enabled simultaneous high-level transgene expression following transduction of transgenic lentiviral particles into primary human chondrocytes.

Gaucher and Fabry diseases: from understanding pathophysiology to rational therapies

Over the past 40 years there has been remarkable development in our understanding of the pathophysiology of lysosomal storage disorders. This review describes the research carried out on the sphingolipid storage disorders from the first demonstration of the underlying metabolic abnormality in Gaucher disease to the development of enzyme replacement therapy for Gaucher and Fabry diseases. Initial developments in gene therapy are also described.

CONCLUSION

The introduction of enzyme replacement therapy has provided a lifeline for patients with Gaucher or Fabry disease. It is anticipated that future developments, including gene therapy, will provide additional therapeutic options.

Lentiviral vectors pseudotyped with minimal filovirus envelopes increased gene transfer in murine lung

A human immunodeficiency virus (HIV)-based vector pseudotyped with the Ebola Zaire (EboZ) viral envelope glycoprotein (GP) was recently shown to transduce murine airway epithelia cells in vivo. In this study, the vector was further redesigned to improve gene transfer and also to increase safety. We used mutant EboZ envelopes for pseudotyping, which resulted in higher titers and increased transduction of airway cells in vivo compared to vectors pseudotyped with wild-type EboZ GP. As these envelopes lack regions associated with toxicity of the wild-type EboZ GP, they should also be safer to use for pseudotyping of lentiviral vectors. In addition, lentiviral vectors were created based on feline immunodeficiency virus and shown to have similar efficiency of transduction compared to HIV-based vectors. The creation of lentiviral vectors with highly engineered EboZ envelopes improved the performance of the system and should also increase its safety since only minimal regions of the EboZ envelope, which lack the toxic domain, are used.

Treatment of canine cyclic neutropenia by lentivirus-mediated G-CSF delivery

Cyclic neutropenia is a rare disease that occurs both in humans and gray collie dogs and is characterized by recurrent severe neutropenia leading to bacterial infections and shortened life expectancy. Daily injections of recombinant granulocyte colony-stimulating factor (rG-CSF) are effective in shortening the period of severe neutropenia and reducing infections. After demonstrating that rG-CSF induced elevated neutrophil production in an affected dog, cytokine administration was stopped and 109 infectious units (IUs) of a lentivirus pseudotyped with vesicular stomatitis virus G protein (VSV-G) encoding canine G-CSF cDNA was administered intramuscularly. Serial blood cell counts showed elevated neutrophil production for longer than 17 months. Although neutrophil counts continued to cycle, the range at nadirs was from 3710 to 5300 cells/microL, well above the nadirs before lentivirus administration. After the injection of lentivirus, mean neutrophil counts +/- SD were 12 460 +/- 4240 cells/microL, significantly increased over both pretreatment values of 3040 +/- 2540 cells/microL(P <.0001) and neutrophil counts during G-CSF administration of 10 290 +/- 4860 cells/microL(P <.007). The changes in blood counts from lentivirus injection were associated with absence of clinical signs of infection and fever. The gray collie continued to gain weight and was no longer housed in a pathogen-free environment. Genomic DNA from muscle at injection sites was positive for provirus, whereas gonad, lung, spleen, heart, liver, kidney, leukocytes, and noninjected muscle samples were all negative for provirus. Thus, intramuscular administration of lentivirus encoding G-CSF provided sustained therapeutic levels of neutrophils, suggesting this approach may be applied for long-term treatment of patients with cyclic and other neutropenias.

Identification of a novel proliferation-inducing determinant using lentiviral expression cloning

One of the major challenges in the post-genome era is the correlation between genes and function or phenotype. We have pioneered a strategy for screening of cDNA libraries, which is based on sequential combination of lentiviral and oncoretroviral expression systems and can be used to identify proliferation-modulating genes. Screening of a lentiviral expression library derived from adult human brain cDNA resulted in cloning of the potent proliferation-inducing determinant termed pi1 (proliferation inducer 1). Transduction experiments using GFP-expressing oncoretroviruses to target proliferation-competent cells suggested that overexpression of pi1 initiates proliferation of human umbilical vein endothelial cells (HUVECs). Growth induction of HUVECs as well as Swiss3T3 fibroblasts was confirmed by Brd-uridine incorporation assays, which correlated increased DNA synthesis with expression of pi1. The identified pi1 cDNA is 297 bp long and encodes a 10 kDa polypeptide. Since deregulation of proliferation control accounts for a number of today's untreatable human diseases such as neurodegenerative disorders and cancer, discovery of novel proliferation-modulating genes is essential for developing new strategies for gene therapy and tissue engineering.

Lentivirus-mediated gene transfer and expression in established human tumor antigen-specific cytotoxic T cells and primary unstimulated T cells

In this report, we evaluated the efficiency of stable gene transfer into established CD8(+) human tumor antigen-specific cytotoxic T cell (CTL) lines and peripheral blood lymphocytes (PBL) by oncoretroviral and lentiviral vectors. In the oncoretroviral vector, the green fluorescent protein (GFP) reporter gene was regulated by the murine stem cell virus (MSCV) promoter. In three human immunodeficiency virus type 1 (HIV-1)-based lentiviral vectors, the GFP transgene was regulated by either a chimeric MSCV/HIV-1 promoter, or cellular promoters from human housekeeping genes PGK and EF1 alpha. We found that several lines of proliferating tumor-specific CTL were poorly (=2%) transduced by the oncoretroviral vector that transduced Jurkat T cell line efficiently (=80%). In contrast, three lentiviral vectors transduced 38-63% of these proliferating CTL. More interestingly, all lentiviral vectors packaged without the HIV-1 accessory proteins transduced human bulk PBL and purified CD4(+) and CD8(+) lymphocyte subsets without prior stimulation. Detailed analysis indicated that the lentiviral vectors containing the EF1 alpha or PGK ubiquitous promoter can transduce unstimulated PBL and achieve low-level transgene expression in the absence of any T-cell activation. However, T-cell activation subsequent to the transduction of unstimulated PBL is required for high-level transgene expression. Transduced PBL expressing transgene delivered by the lentiviral vectors still preserved resting and naïve cell phenotypes. Taken together, prior T cell stimulation and HIV-1 accessory proteins are dispensable for lentivirus-mediated gene transfer into resting naïve and memory T lymphocytes. These results will have significant implications for the study of T-cell biology and for the improvement of clinical gene therapies of acquired immune deficiency syndrome (AIDS) and cancer.

Targeting the cell cycle machinery for the treatment of cardiovascular disease

Cardiovascular disease represents a major clinical problem affecting a significant proportion of the world's population and remains the main cause of death in the UK. The majority of therapies currently available for the treatment of cardiovascular disease do not cure the problem but merely treat the symptoms. Furthermore, many cardioactive drugs have serious side effects and have narrow therapeutic windows that can limit their usefulness in the clinic. Thus, the development of more selective and highly effective therapeutic strategies that could cure specific cardiovascular diseases would be of enormous benefit both to the patient and to those countries where healthcare systems are responsible for an increasing number of patients. In this review, we discuss the evidence that suggests that targeting the cell cycle machinery in cardiovascular cells provides a novel strategy for the treatment of certain cardiovascular diseases. Those cell cycle molecules that are important for regulating terminal differentiation of cardiac myocytes and whether they can be targeted to reinitiate cell division and myocardial repair will be discussed as will the molecules that control vascular smooth muscle cell (VSMC) and endothelial cell proliferation in disorders such as atherosclerosis and restenosis. The main approaches currently used to target the cell cycle machinery in cardiovascular disease have employed gene therapy techniques. We will overview the different methods and routes of gene delivery to the cardiovascular system and describe possible future drug therapies for these disorders. Although the majority of the published data comes from animal studies, there are several instances where potential therapies have moved into the clinical setting with promising results.

Comparison of three retroviral vector systems for transduction of nonobese diabetic/severe combined immunodeficiency mice repopulating human CD34+ cord blood cells

The use of recombinant vectors based on wild-type viruses that are absent in humans and are not associated with any disease in their natural animal hosts or in accidentally infected humans would add an additional level of safety for human somatic gene therapy approaches. These criteria are fulfilled by foamy viruses (FVs), a family of complex retroviruses whose members are widely found among mammals and are apathogenic in all hosts. Here, we show by comparison of identically designed vector constructs that recombinant retroviral vectors based on FVs were as efficient as lentiviral vectors in transducing nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice repopulating human CD34(+) cord blood (CB) cells. The FV vector was able to achieve gene transfer levels up to 84% of engrafted human cells in a short overnight transduction protocol. In contrast, without prestimulation of the target cells, a human immunodeficiency virus type 1 (HIV-1)-based lentiviral vector pseudotyped with gibbon ape leukemia virus envelope (GALV Env) was nearly as inefficient as murine leukemia virus (MLV)-based oncoretroviral vectors in transducing NOD/SCID repopulating cells. The same HIV vector pseudotyped with the vesicular stomatitis virus glycoprotein G (VSV-G) achieved high marking efficiency. Clonality analysis of bone marrow samples showed oligoclonal hematopoiesis with single to multiple insertions per cell, both for FV and HIV vectors. These data demonstrate that vectors based on FVs warrant further investigation and development for medical use.

Efficient transduction of primary human B lymphocytes and nondividing myeloma B cells with HIV-1-derived lentiviral vectors

We studied the transduction of primary human B lymphocytes and myeloma cells with lentiviral vectors. In peripheral blood B cells that had been activated with helper T cells (murine thymoma EL-4 B5) and cytokines, multiply attenuated HIV-1-derived vectors pseudotyped with vesicular stomatitis virus (VSV) G-envelope protein achieved the expression of green fluorescence protein (GFP) in 27% +/- 12% (mean +/- 1 SD; median, 27%) of B cells in different experiments. When compared in parallel cultures, the transducibility of B cells from different donors exhibited little variation. The human cytomegalovirus (CMV) promoter gave 4- to 6-fold higher GFP expression than did the human elongation factor-1alpha promoter. A murine retroviral vector pseudotyped with VSV G protein proved inefficient even in mitotically active primary B cells. B cells freshly stimulated with Epstein-Barr virus were also transducible by HIV vectors (24% +/- 9%), but B cells activated with CD40 ligand and cytokines resisted transduction. Thus, different culture systems gave different results. Freshly isolated, nondividing myeloma cells were efficiently transduced by HIV vectors; for 6 myelomas the range was 14% to 77% (median, 28%) GFP(+) cells. HIV vectors with a mutant integrase led to no significant GFP signal in primary B or myeloma cells, suggesting that vector integration was required for high transduction. In conclusion, HIV vectors are promising tools for studies of gene functions in primary human B cells and myeloma cells for the purposes of research and the development of gene therapies.

A new hybrid system capable of efficient lentiviral vector production and stable gene transfer mediated by a single helper-dependent adenoviral vector

To achieve efficient and sustained gene expression, we developed a new lentivirus/adenovirus hybrid vector (LA vector) that encodes sequences required for production of a human immunodeficiency virus-based lentiviral vector (i.e., a lentiviral vector, a gag/pol/rev expression cassette, a tetracycline-inducible envelope cassette, and the tetracycline-inducible transcriptional activator cassette) in a single helper-dependent adenovirus vector backbone. Via either transfection or infection, human cell lines transduced with the LA vector produced a lentiviral vector in a doxycycline-dependent manner at titers up to 10(5) to 10(6) green fluorescent protein transducing units per ml, which are comparable to the titers obtained by conventional multiple plasmid transfection methods. Efficient spread and persistent expression of the transgene were observed in cells maintained in long-term culture that had been infected with the LA vector. Furthermore, when cocultured with adherent cells infected with the LA vector, the human T-cell leukemia cell line was successfully transduced with a marker gene. This LA vector possesses the advantages of efficient gene transfer from an adenoviral vector and stable integration from a lentiviral vector; therefore, it might have potential for a variety of gene therapy applications.

Mapping of the bovine immunodeficiency virus packaging signal and RRE and incorporation into a minimal gene transfer vector

Gene transfer systems based on lentiviruses have emerged as promising gene delivery vehicles for human gene therapy due to their ability to efficiently transduce nondividing target cells. Both primate and nonprimate lentiviruses have been used for construction of lentiviral vectors. An early generation of gene transfer system based on bovine immunodeficiency virus (BIV) has been developed (R. D. Berkowitz, H. Ilves, W. Y. Lin, K. Eckert, A. Coward, S. Tamaki, G. Veres, and I. Plavec, 2001, J. Virol. 75, 3371-3382). In this study, we mapped the BIV Rev response element (RRE) to 312 bp of the Env coding region. Furthermore, we compared transduction efficiencies of vectors containing different portions of the BIV Gag coding region and found that the first 104 bp of gag contains a functional part of the BIV packaging signal. These findings enabled the generation of a minimal BIV-based lentiviral vector. The minimal transfer vector construct consists of a self-inactivating long terminal repeats (LTR), minimal packaging sequence, putative central polypurine tract, minimal RRE, an internal promoter driving the gene of interest, and a woodchuck hepatitis posttranscriptional regulatory element. In addition, we constructed a BIV packaging construct containing gag/pol, minimal Rev/RRE, and the accessory gene vpy. The regulatory gene tat and the accessory genes vif and vpw have been inactivated or truncated. The current system has significantly reduced regions of homologies between the transfer vector and the packaging constructs. The vectors generated from this system achieved a titer of greater than 1 x 10(6) transducing units per milliliter and are fully functional as indicated by their ability to efficiently transduce both dividing and nondividing cells. These modifications should provide improved safety features for the BIV-based gene transfer system.

Advanced modular self-inactivating lentiviral expression vectors for multigene interventions in mammalian cells and in vivo transduction

In recent years, lentiviral expression systems have gained an unmatched reputation among the gene therapy community for their ability to deliver therapeutic transgenes into a wide variety of difficult-to-transfect/transduce target tissues (brain, hematopoietic system, liver, lung, retina) without eliciting significant humoral immune responses. We have cloned a construction kit-like self-inactivating lentiviral expression vector family which is compatible to state-of-the-art packaging and pseudotyping technologies and contains, besides essential cis-acting lentiviral sequences, (i) unparalleled polylinkers with up to 29 unique sites for restriction endonucleases, many of which recognize 8 bp motifs, (ii) strong promoters derived from the human cytomegalovirus immediate-early promoter (P(hCMV)) or the human elongation factor 1alpha (P(hEF1)(alpha)), (iii) P(hCMV-) or P(PGK-) (phosphoglycerate kinase promoter) driven G418 resistance markers or fluorescent protein-based expression tracers and (iv) tricistronic expression cassettes for coordinated expression of up to three transgenes. In addition, we have designed a size-optimized series of highly modular lentiviral expression vectors (pLenti Module) which contain, besides the extensive central polylinker, unique restriction sites flanking any of the 5'U3, R-U5-psi+-SD, cPPT-RRE-SA and 3'LTR(DeltaU3) modules or placed within the 5'U3 (-78 bp) and 3'LTR(DeltaU3) (8666 bp). pLentiModule enables straightforward cassette-type module swapping between lentiviral expression vector family members and facilitates the design of Tat-independent (replacement of 5'LTR by heterologous promoter elements), regulated and self-excisable proviruses (insertion of responsive operators or LoxP in the 3'LTR(DeltaU3) element). We have validated our lentiviral expression vectors by transduction of a variety of insect, chicken, murine and human cell lines as well as adult rat cardiomyocytes, rat hippocampal slices and chicken embryos. The novel multi-purpose construction kit-like vector series described here is compatible with itself as well as many other (non-viral) mammalian expression vectors for straightforward exchange of key components (e.g. promoters, LTRs, resistance genes) and will assist the gene therapy and tissue engineering communities in developing lentiviral expression vectors tailored for optimal treatment of prominent human diseases.

A human immunodeficiency virus type 1 pol gene-derived sequence (cPPT/CTS) increases the efficiency of transduction of human nondividing monocytes and T lymphocytes by lentiviral vectors

We have investigated the capacity of two human immunodeficiency virus type 1-derived lentivectors, differing in the presence of a 118-bp pol fragment containing the cPPT/CTS element, to transduce human normal primary cells of different hematopoietic lineages. Infection of resting monocytes with a high multiplicity of infection (MOI > 10) revealed that the lentivirus carrying the pol fragment (cPPT) is effective, transducing 75% of cells compared with 36% for the no-cPPT vector. Even at low MOIs (< or =1) the cPPT vector still shows a better transduction efficiency than the no-cPPT vector. Moreover, transduction does not require dendritic cell differentiation. In contrast, infection of nonactivated T lymphocytes showed that both vectors, tested at high MOIs, can transduce a small, although measurable, percentage of cells (up to 10%), which may correspond to G(1a) "activated" cells as detected by simultaneous staining of DNA and RNA, in our cultures in the presence of medium alone. Furthermore, we show that the sole addition of interleukin 2 or interleukin 15 represents a full proliferative signal under our conditions and permits high transduction efficiency (up to 30% with the cPPT vector and 15% with the no-cPPT vector). Still higher transduction of T lymphocytes can be achieved after stimulation with phytohemagglutinin and interleukin 2 (up to 78% with the cPPT vector vs. 42% with the no-cPPT vector). Finally, both viruses do not transduce either resting or proliferating tonsillar B lymphocytes.

Highly efficient retroviral gene transfer into immortalized CD34(-) cells and organ distribution after transplantation into NOD/SCID mice

BACKGROUND

CD34(-) stem cells are apparently the earliest progenitors of hematopoiesis and mesenchymal tissues. The majority of those progeny rests in the BM as fibroblast-like cells, but can also circulate the peripheral blood. Nevertheless, CD34(-), fibroblast-like cells can be isolated from BM aspirates and PBMC, mediated by their ability to adhere to the plastic surface of tissue culture flasks. In standard colony assays, CD34(-), fibroblast-like cells produce a significant number of colony-forming-units (CFUs), mainly CFU-F (fibroblast).

METHODS

Despite advanced cell-culture techniques and the application of various growth factors, the life span of those multipotent stem cells is limited. Therefore, we immortalized and cloned fibroblast-like, CD34(-) stem cells and used retroviral constructs containing the green-fluorescence protein (GFP) to determine the gene-transfer efficiency and their use for gene marking prior to transplantation into NOD/SCID mice.

RESULTS

We could demonstrate a highly efficient retroviral gene transfer into those immortalized CD34(-), fibroblast-like hematopoietic cells (up to 95% transduced cells), maintaining their ability to produce CFUs, as well as a distinct organ distribution after transplantation into the recipient animals, functioning as SCID-repopulating cells (SRC). Transplanted cells could be detected in the BM, as well as other parenchymal organs, such as the lung, liver, skin, small intestine and brain.

DISCUSSION

CD34(-), fibroblast-like progenitor cells can give rise to hematopoietic progeny, but also home to mesenchymal organ sites in recipient animals. There is increasing evidence that pluripotent CD34(-) stem cells can be isolated from various sources and still maintain their capabilities to generate progeny of different tissues. This could be a promising approach to using peripheral-blood derived stem cells for cellreplacement therapy and tissue engineering.

Sustained transduction of ocular cells with a bovine immunodeficiency viral vector

Human immunodeficiency viral (HIV) vectors mediate long-term transduction of many types of nondividing cells in vivo. Bovine immunodeficiency virus (BIV) is a lentivirus that shares many characteristics with HIV, but does not cause human disease. In this study, we investigated the potential of BIV vectors for ocular gene therapy. An enhanced green fluorescent protein (eGFP)-encoding reporter gene was packaged in recombinant BIV vector (BIV.eGFP). Adult C57BL/6 mice were given an intravitreous (5 x 10(4) or 5 x 10(5) transducing units [TU]) or subretinal (5 x 10(5) TU) injection of BIV.eGFP and then GFP expression was assessed at several time points. In vivo examinations of mice showed that subretinal injection of BIV.eGFP resulted in strong expression of GFP from the first examination at 1 week through the final examination at 20 weeks. Only a few mice that received intravitreous injection of BIV.eGFP showed GFP expression by ocular examinations until 11-12 weeks, when most showed small areas of expression. Postmortem examinations showed prominent GFP expression in retinal pigmented epithelial (RPE) cells throughout the region of subretinal injection of vector, although occasional negatively staining RPE cells were scattered among the much more numerous, brilliantly staining cells. Ciliary epithelial cells frequently expressed GFP, as did occasional Müller cells and rarely other retinal cells. The expression was stable from the first time point (2 weeks) to the last (20 weeks). Postmortem examination of eyes given an intravitreous injection of BIV.eGFP showed transduction of cells in the corneal endothelium and a few scattered retinal cells. There was no evidence of inflammation or toxicity in any eyes. These data show that BIV vectors mediate rapid and sustained transduction of RPE cells, suggesting that they may be useful for ocular gene therapy targeting RPE cells.

Development of second- and third-generation bovine immunodeficiency virus-based gene transfer systems

Lentivirus-based gene transfer systems have demonstrated their utility in mediating gene transfer to dividing and nondividing cells both in vitro and in vivo. An early-generation gene transfer system developed from bovine immunodeficiency virus (BIV) has been described (Berkowitz et al., J. Virol. 2001;75:3371-3382). In this paper, we describe the development of second-generation (three-plasmid) and third-generation (four-plasmid) BIV-based systems. All accessory genes (vif, vpw, vpy, and tmx) and the regulatory gene tat were deleted or largely truncated from the packaging construct. Furthermore, we split the packaging function into two constructs by expressing Rev in a separate plasmid. Together with our minimal BIV transfer vector construct and a vesicular stomatitis virus G glycoprotein-expressing plasmid, the BIV vectors were generated. The vectors produced by the three- and four-plasmid systems had titers greater than 1 x 10(6) transducing units per milliliter and were fully functional as indicated by their ability to efficiently transduce both dividing and nondividing cells. These results suggest that the accessory genes vif, vpw, vpy, and tmx are dispensable for functional BIV vector development. The modifications made to the packaging constructs improve the safety profile of the vector system. Finally, BIV vectors provide an alternative to human immunodeficiency virus-based gene transfer systems.

Development and characterization of a minimal inducible packaging cell line for simian immunodeficiency virus-based lentiviral vectors

BACKGROUND

Lentiviral vectors allow gene transfer into non-dividing cells. Further development of these vector systems requires stable packaging cell lines that enable adequate safety testing.

METHODS

To generate a packaging cell line for vectors based on simian immunodeficiency virus (SIV), expression plasmids were constructed that contain the codon-optimized gag-pol gene of SIV and the gene for the G protein of vesicular stomatitis virus (VSV-G) under the control of an ponasterone-inducible promoter. Stable cell lines expressing these packaging constructs were established and characterized.

RESULTS

The RT activity and vector titers of cell clones stably transfected with the inducible gag-pol expession plasmid could be induced by ponasterone by more than a factor of 1000. One of these clones was subsequently transfected with the ponasterone-inducible VSV-G expression plasmid to generate packaging cells. Clones of the packaging cells were screened for vector production by infection with an SIV vector and subsequent induction by ponasterone. In the supernatant of selected ponasterone-induced producer clones vector titers of more than 1x10(5) transducing units/ml were obtained. Producer cell clones were stable for at least five months, as tested by vector production.

CONCLUSIONS

The packaging cells described should be suitable for most preclinical applications of SIV-based vectors. By avoiding regions of high homology between the vector and the packaging constructs, the design of the SIV packaging cell line should reduce the risk of transfer of packaging genes to target cells and at the same time provide flexibility with respect to the SIV vector constructs that can be packaged.

In vivo induction of human immunodeficiency virus type 1 entry into nucleus-free cells by CD4 gene transfer to hematopoietic stem cells: a hypothetical possible strategy for therapeutic intervention

As a useful alternative to employing soluble CD4 to inhibit binding of human immunodeficiency virus type 1 (HIV-1) to target cells, the introduction of CD4-bearing erythrocyte has been proposed by two study groups (see Refs. (5,6)). Prominently, Nicolau and colleagues demonstrated that the electroinserted CD4 molecules in the membranes of erythrocytes are capable of mediating HIV-1 entry. The implications of the studies are that inactivation of the integration-dependent retrovirus by the facilitation of entry into the nucleus-free cells, referred to as 'fake host trap' or 'host cell decoy', may be a possible therapeutic approach. Here we expand this concept to include genetic modification of autologous hematopoietic stem cells and review the relevant theoretical basis. Effective application of molecular technologies to induce partial replacement of hematopoiesis may be critical for this strategy.

Biodistribution and toxicity studies of VSVG-pseudotyped lentiviral vector after intravenous administration in mice with the observation of in vivo transduction of bone marrow

Lentiviral vectors can confer high levels of gene transfer and transgene expression in a variety of cell types. However, the biodistribution and toxicity after intravenous administration have not been reported. To address these issues of biodistribution and toxicity, an HIV-1-based vector, HR'cmvGFP, was administered to normal BALB/c mice by tail-vein injection. Nine different organs and bone marrow were evaluated by real-time quantitative PCR (QPCR) assay capable of a broad range of quantitation (5-log fold) to detect as few as one copy of the green fluorescent protein gene (GFP) per 10(5) cells. Four days after vector administration, high levels of transgene and gene expression were observed in liver, spleen, and bone marrow in all animals. By 40 days after injection, GFP levels had decreased in liver and spleen, but bone marrow exhibited a consistently high level of transgene. This finding was consistent with the increase in both GFP frequency and expression levels observed in peripheral blood by fluorescence-activated cell-sorting (FACS) analysis. Between 0 and 1% transgene was detected in all other organs. No significant pathologic lesions were found attributable to vector in any of the tissues examined. The observation of bone marrow transduction after intravenous vector administration suggests the possibility of an in vivo approach to stem cell gene therapy.

Transduction of human NOD/SCID-repopulating cells with both lymphoid and myeloid potential by foamy virus vectors

The efficiency of gene transfer into human hematopoietic stem cells by oncoretroviral vectors is too low for effective gene therapy of most hematologic diseases. Retroviral vectors based on the nonpathogenic foamy viruses (FV) are an alternative gene-transfer system. In this study, human umbilical cord blood CD34(+) cells were transduced with FV vectors by a single 10-h exposure to vector stocks and then injected into sublethally irradiated nonobese diabetic-severe combined immunodeficiency (NOD/SCID) mice. At 5-7 weeks after transplantation, high transgene expression rates were observed in engrafted human hematopoietic cells, including over 60% of clonogenic progenitors. Significant transgene silencing did not occur. We developed an approach for expanding human cell populations derived from transplanted mice to show that multiple SCID repopulating cells (SRCs) had been transduced, including some that were capable of both lymphoid and myeloid differentiation. These findings demonstrate for the first time that human pluripotent (lympho-myeloid) hematopoietic stem cells repopulate NOD/SCID mice and can be efficiently transduced by FV vectors.

Preferential transduction of human hepatocytes with lentiviral vectors pseudotyped by Sendai virus F protein

One of the major challenges facing gene therapy is the development of vectors targeting specific cell types. Restricting gene delivery to the relevant cell type leads to reduced T-cell responses to transgene products and prolonged gene expression. In this study, we demonstrate that vectors derived from human immunodeficiency virus (HIV) can be pseudotyped with Sendai virus fusion protein F. Such vectors transduced human hepatoma cells and primary human hepatocytes efficiently, but not non-liver cells. Several different approaches were also taken to significantly increase the titer of the pseudotyped vector. These studies may facilitate HIV vector-mediated gene delivery into liver in vivo.

Transduction of interphase cells by avian sarcoma virus

It has been generally believed that oncoretroviruses are dependent on mitosis for efficient nuclear entry of viral DNA. We previously identified a nuclear localization signal in the integrase protein of an oncoretrovirus, avian sarcoma virus (ASV), suggesting an active import mechanism for the integrase-DNA complex (G. Kukolj, R. A. Katz, and A. M. Skalka, Gene 223:157-163, 1998). Here, we have evaluated the requirement for mitosis in nuclear import and integration of ASV DNA. Using a modified ASV encoding a murine leukemia virus amphotropic env gene and a green fluorescent protein (GFP) reporter gene, DNA nuclear import was measured in cell cycle-arrested avian (DF-1) as well as human (HeLa) and mouse cells. The results showed efficient accumulation of nuclear forms of ASV DNA in gamma-irradiation-arrested cells. Efficient transduction of a GFP reporter gene was also observed after infection of cells that were arrested with gamma-irradiation, mitomycin C, nocodazole, or aphidicolin, confirming that nuclear import and integration of ASV DNA can occur in the absence of mitosis. By monitoring GFP expression in individual cells, we also obtained evidence for nuclear import of viral DNA during interphase in cycling cells. Lastly, we observed that ASV can transduce postmitotic mouse neurons. These results support an active nuclear import mechanism for the oncoretrovirus ASV and suggest that this mechanism can operate in both nondividing and dividing cells.

Lentiviral vectors for sustained transgene expression in human bone marrow-derived stromal cells

Bone marrow-derived mesenchymal stromal cells (MSCs) have attracted attention as potential platforms for the systemic delivery of therapeutic proteins in vivo following gene transfer using oncogenic retroviruses. However, the major limitations of this strategy include low levels of gene transfer and a general lack of long-term transgene expression. We have investigated the expression of several transgenes in MSCs following HIV-1 lentiviral vector-mediated gene transfer. Vectors containing a variety of strong promoters driving enhanced green fluorescence protein (EGFP) and coral (Discosoma sp.)-derived red fluorescent protein (DsRed) reporter genes pseudotyped with the vesicular stomatitis virus-G (VSV-G) glycoprotein were able to transduce cultured MSCs with high efficiency. Transduction efficiencies and transgene expression levels in MSCs were found to be higher with lentiviral vectors than with a vector based on the murine stem cell virus pseudotyped with VSV-G. Transgene expression was maintained in culture for at least 5 months. HIV-1-based lentiviral vectors were able to transduce clonogenic mesenchymal progenitor cells, which were capable of maintaining transgene expression by their MSC progeny, over several cell divisions and during differentiation into adipocytes, indicating that terminal adipocyte cell differentiation was unaffected by lentivirus-mediated reporter gene transfer. Collectively these results suggest that lentivirus-mediated gene transfer strategies provide an efficient tool for ex vivo modification of MSCs that does not interfere with differentiation.

Targeted transduction patterns in the mouse brain by lentivirus vectors pseudotyped with VSV, Ebola, Mokola, LCMV, or MuLV envelope proteins

Lentiviral vectors have proven to be promising tools for transduction of central nervous system (CNS) cells in vivo and in vitro. In this study, CNS transduction patterns of lentiviral vectors pseudotyped with envelope glycoproteins from Ebola virus, murine leukemia virus (MuLV), lymphocytic choriomeningitis virus (LCMV), or the rabies-related Mokola virus were compared to a vector pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G). Mokola-, LCMV-, and VSV-G-pseudotyped vectors transduced similar populations, including striatum, thalamus, and white matter. Mokola-pseudotyped vectors were the most efficient of the three. MuLV-pseudotyped lentivirus efficiently transduced striatum and hippocampal dentate gyrus. In contrast, no transduction resulted from injection of Ebola-pseudotyped virus in the CNS. The same pattern was observed in vitro with primary cultured oligodendrocytes. LCMV, MuLV, and Ebola pseudotypes were the most stable. These results demonstrate that targeted transduction in the CNS can be achieved using specific envelope glycoproteins to pseudotype lentiviral vectors, and support the use of Mokola-pseudotyped and MuLV-pseudotyped lentiviral vectors as efficient and stable alternatives to VSV-G-pseudotyped vectors for experiments in the mouse CNS.

Inhibition of HIV-1 replication by novel lentiviral vectors expressing transdominant Rev and HIV-1 env antisense

Retroviral vectors expressing transdominant negative mutants of Rev (TdRev) inhibit HIV-1 replication by preventing the nuclear export of unspliced viral transcripts, thus inhibiting the synthesis of Gag-Pol, Env and reducing the levels of genomic RNA available for packaging. Due to these effective mechanisms of inhibition, production of HIV-1-based lentiviral vectors expressing TdRev has been difficult. Here we describe HIV-based vectors in which expression of TdRev is negatively regulated by Rev expression. In these vectors, we maintained the wild-type HIV-1 Tat/Rev exons and intron configuration and its mode of splicing regulation. The second Rev exon was mutated to encode TdRev. Inhibition of TdRev expression by Rev during vector production yields high titer vector preparations. A second vector containing an additional anti-HIV gene (env-antisense) was constructed by flipping a 1.2-kb env fragment contained within the Tat/TdRev intron. SupT1 cells and primary CD4+ lymphocytes transduced with these vectors inhibit HIV-1 replication and show a preferential advantage for survival. Although these vectors are poorly mobilized to secondary target cells by wild-type HIV-1, they reduce the infectivity of the wild-type virions escaping inhibition.

In vivo gene delivery to synovium by lentiviral vectors

The delivery of anti-arthritic genes to the synovial lining of joints is being explored as a strategy for the treatment of rheumatoid arthritis. In this study, we have investigated the use of VSV-G pseudotyped, HIV-1-based lentiviral vectors for gene delivery to articular tissues. Recombinant lentivirus containing a beta-galactosidase/neomycin resistance fusion gene under control of the elongation factor (EF) 1alpha promoter efficiently transduced human and rat synoviocytes and chondrocytes in cell culture. When directly injected into the knees of rats, this vector transduced synovial lining cells, but not other articular tissues such as cartilage. We also constructed a lentiviral vector containing the human interleukin-1 receptor antagonist (IL1RA) cDNA and examined transgene expression in vitro and in vivo following injection into the knee joints of rats. In immunocompetent animals, intra-articular IL1RA expression was high and persisted, at a sharply declining rate, for approximately 20 days. In immunocompromised rats, however, lentivirus-mediated intra-articular expression of human IL1RA was found to persist for at least 6 weeks. Extra-articular expression of the transgene was minimal. These results indicate that lentiviral vectors are capable of efficient in vivo gene transfer to synovium and merit further investigation as a means of providing long-term expression for gene-based treatments of arthritis.

Design of an HIV-1 lentiviral-based gene-trap vector to detect developmentally regulated genes in mammalian cells

The recent development of HIV-1 lentiviral vectors is especially useful for gene transfer because they achieve efficient integration into nondividing cell genomes and successful long-term expression of the transgene. These attributes make the vector useful for gene delivery, mutagenesis, and other applications in mammalian systems. Here we describe two HIV-1-based lentiviral vector derivatives, pZR-1 and pZR-2, that can be used in gene-trap experiments in mammalian cells in vitro and in vivo. Each lentiviral gene-trap vector contains a reporter gene, either beta-lactamase or enhanced green fluorescent protein (EGFP), that is inserted into the U3 region of the 3' long terminal repeat. Both of the trap vectors readily integrate into the host genome by using a convenient infection technique. Appropriate insertion of the vector into genes causes EGFP or beta-lactamase expression. This technique should facilitate the rapid enrichment and cloning of the trapped cells and provides an opportunity to select subpopulations of trapped cells based on the subcellular localization of reporter genes. Our findings suggest that the reporter gene is driven by an upstream, cell-specific promoter during cell culture and cell differentiation, which further supports the usefulness of lentivirus-based gene-trap vectors. Lentiviral gene-trap vectors appear to offer a wealth of possibilities for the study of cell differentiation and lineage commitment, as well as for the discovery of new genes.

In vivo assessment of gene delivery to keratinocytes by lentiviral vectors

For skin gene therapy, introduction of a desired gene into keratinocyte progenitor or stem cells could overcome the problem of achieving persistent gene expression in a significant percentage of keratinocytes. Although keratinocyte stem cells have not yet been completely characterized and purified for gene targeting purposes, lentiviral vectors may be superior to retroviral vectors at gene introduction into these stem cells, which are believed to divide and cycle slowly. Our initial in vitro studies demonstrate that lentiviral vectors are able to efficiently transduce nondividing keratinocytes, unlike retroviral vectors, and do not require the lentiviral accessory genes for keratinocyte transduction. When lentiviral vectors expressing green fluorescent protein (GFP) were directly injected into the dermis of human skin grafted onto immunocompromised mice, transduction of dividing basal and nondividing suprabasal keratinocytes could be demonstrated, which was not the case when control retroviral vectors were used. However, flow cytometry analysis demonstrated low transduction efficiency, and histological analysis at later time points provided no evidence for progenitor cell targeting. In an alternative in vivo method, human keratinocytes were transduced in tissue culture (ex vivo) with either lentiviral or retroviral vectors and grafted as skin equivalents onto immunocompromised mice. GFP expression was analyzed in these human skin grafts after several cycles of epidermal turnover, and both the lentiviral and retroviral vector-transduced grafts had similar percentages of GFP-expressing keratinocytes. This ex vivo grafting study provides a good in vivo assessment of gene introduction into progenitor cells and suggests that lentiviral vectors are not necessarily superior to retroviral vectors at introducing genes into keratinocyte progenitor cells during in vitro culture.

Gene transfer into the central nervous system in vivo using a recombinanat lentivirus vector

Gene transfer vectors derived from human immunodeficiency virus (HIV-1) efficiently transduce nondividing cells and may provide for the delivery of their gene products to discrete regions of the brain. We investigated whether stable gene transduction can be achieved in cells of the central nervous system (CNS) in vivo by a potent lentivirus vector. The herpes simplex virus type 1 protein VP22 has been known to facilitate intercellular protein transport and thereby provides an opportunity to increase the effectiveness of therapeutic genes by enhancing the delivery of their protein products. We developed a lentiviral vector construct expressing enhanced green fluorescent protein (EGFP) fused at its N-terminus to the herpes simplex virus VP22. In order to determine expression of the fusion protein in specific cells such as neurons in the CNS, a neuron-specific promoter was also placed into the construct. The viral vectors were injected directly into the striatum and hippocampus of mouse brains. We found that the lentivirus vector efficiently and stably transduced nondividing cells in the CNS with transgene expression for over 3 months. We also show that the delivery of VP22-EGFP fusion protein encoded by the lentivirus was effectively transported between neuronal cells via axons in vivo. Doubly labeled experiments revealed that our lentiviral vector is capable of delivering gene products to neurons and astrocytes in CNS. The data also demonstrate that up to 90% of the CNS cells transduced by our lentiviral vector under the control of the neuronal promoter are neurons.

Lentiviral gene transfer into peripheral blood-derived CD34+ NOD/SCID-repopulating cells

This study reports a lentiviral gene transfer protocol for efficient transduction of adult human peripheral blood (PB)-derived CD34+ NOD/SCID-repopulating cells (SRCs) using vesicular stomatitis virus-G protein (VSV-G)-pseudotyped lentiviruses encoding for enhanced green fluorescence protein (eGFP). Lentiviral stocks were concentrated by anion exchange chromatography, and transduction was performed under serum-free conditions at a multiplicity of infection (MOI) between 3 and 50. Similar transduction efficiencies were achieved in the presence and absence of cytokines. Transduction of PB-derived CD34+ cells at a MOI of 3 resulted in gene transfer efficiencies into SRCs of 9.2% and 12.0% in the absence and presence of cytokines, respectively. Using improved lentiviral vectors, transduction frequency varied between 42.0% (MOI 10) and 36.0% (MOI 50) with multilineage transgene expression within SRC-derived myeloid and lymphoid cells. The protocol described can be adapted for clinical application of lentiviral gene transfer into PB-derived CD34+ cells from adult patients.

Gene therapy: promises and problems

Gene therapy can be broadly defined as the transfer of genetic material to cure a disease or at least to improve the clinical status of a patient. One of the basic concepts of gene therapy is to transform viruses into genetic shuttles, which will deliver the gene of interest into the target cells. Based on the nature of the viral genome, these gene therapy vectors can be divided into RNA and DNA viral vectors. The majority of RNA virus-based vectors have been derived from simple retroviruses like murine leukemia virus. A major shortcoming of these vectors is that they are not able to transduce nondividing cells. This problem may be overcome by the use of novel retroviral vectors derived from lentiviruses, such as human immunodeficiency virus (HIV). The most commonly used DNA virus vectors are based on adenoviruses and adeno-associated viruses. Although the available vector systems are able to deliver genes in vivo into cells, the ideal delivery vehicle has not been found. Thus, the present viral vectors should be used only with great caution in human beings and further progress in vector development is necessary.

Development of lentiviral vectors for antiangiogenic gene delivery

Growth and metastasis of malignant tumors requires angiogenesis. Inhibition of tumor-induced angiogenesis may represent an effective cytostatic strategy. We have constructed recombinant self-inactivating lentiviral vectors expressing angiostatin and endostatin, and have tested their antiangiogenic activities. As VSV-G-pseudotyped lentiviral vectors showed low relative transduction titers on bovine aortic and human umbilical vein endothelial cells, it was difficult to achieve significant inhibition of endothelial cell growth by lentivirus-mediated antiangiogenic gene transfer directly to endothelial cells without concomitant vector-associated cytotoxicity. However, lentivirus vectors could efficiently and stably transduce T24 human bladder cancer cells that are relatively resistant to adenovirus infection due to loss of coxsackievirus-adenovirus receptor expression. Long-term expression and secretion of angiostatin and endostatin from lentivirus-transduced T24 cells resulted in significant inhibition of cellular proliferation on coculture with endothelial cells. This report represents the first use of lentivirus-based vectors to deliver the antiangiogenic factors, angiostatin and endostatin, and suggests the potential utility of antiangiogenic gene therapy with lentiviral vectors for the treatment of cancer.

Highly efficient targeted transduction of undifferentiated human hematopoietic cells by adenoviral vectors displaying fiber knobs of subgroup B

Human hematopoietic stem cells (HSCs) are poorly transduced by vectors based on adenovirus serotype 5 (Ad5). This is primarily due to the paucity of the coxsackievirus-Ad receptor on these cells. In an attempt to change the tropism of Ad5, we constructed a series of chimeric E1-deleted Ad5 vectors in which the shaft and knob of the capsid fibers were exchanged with those of other Ad serotypes. In all these vectors, the Ad E1 region was replaced by an expression cassette containing the cytomegalovirus immediate-early promoter and the gene for enhanced green fluorescent protein (GFP). Experiments performed in vitro showed an efficient transduction of umbilical cord blood (UCB) monocytes, granulocytes, and their precursors as well as the undifferentiated CD34(+) CD33(-) CD38(-) CD71(-) cells by Ad5 vectors carrying Ad subgroup B-specific fiber chimeras (Ad5FBs). In the latter subpopulation, which comprises less than 1% of the CD34(+) cells and is highly enriched with cells repopulating immunodeficient mice, more than 90% of the cells were GFP(+). Transduction by Ad5FBs of the less primitive fraction within UCB CD34(+) cells was significant lower. Actually, the transduction frequency and GFP level declined gradually with increased expression of the CD33, CD38, and CD71 antigens. Flow cytometric analysis of transduced UCB CD34(+) cells that were cultured for 5 days on an allogeneic human bone marrow stroma layer showed maintenance of the phenotypically defined HSCs at levels similar to those of control cultures. The latter finding indicates that neither the transduction procedure nor the high levels of GFP were toxic for these cells.

Engraftment of NOD/SCID mice with human CD34(+) cells transduced by concentrated oncoretroviral vector particles pseudotyped with the feline endogenous retrovirus (RD114) envelope protein

Oncoretrovirus vectors pseudotyped with the feline endogenous retrovirus (RD114) envelope protein produced by the FLYRD18 packaging cell line have previously been shown to transduce human hematopoietic progenitor cells with a greater efficiency than similar amphotropic envelope-pseudotyped vectors. In this report, we describe the production and efficient concentration of RD114-pseudotyped murine leukemia virus (MLV)-based vectors. Following a single round of centrifugation, vector supernatants were concentrated approximately 200-fold with a 50 to 70% yield. Concentrated vector stocks transduced prestimulated human CD34(+) (hCD34(+)) cells with approximately 69% efficiency (n = 7, standard deviation = 4.4%) using a single addition of vector at a low multiplicity of infection (MOI = 5). Introduction of transduced hCD34(+) cells into irradiated NOD/SCID recipients resulted in multilineage engraftment with long-term transgene expression. These data demonstrate that RD114-pseudotyped MLV-based vectors can be efficiently concentrated to high titers and that hCD34(+) cells transduced with concentrated vector stocks retain in vivo repopulating potential. These results highlight the potential of RD114-pseudotyped oncoretrovirus vectors for future clinical implementation in hematopoietic stem cell gene transfer.

Development of an avian leukosis-sarcoma virus subgroup A pseudotyped lentiviral vector

We are using avian leukosis-sarcoma virus (ALSV) vectors to generate mouse tumor models in transgenic mice expressing TVA, the receptor for subgroup A ALSV. Like other classical retroviruses, ALSV requires cell division to establish a provirus after infection of host cells. In contrast, lentiviral vectors are capable of integrating their viral DNA into the genomes of nondividing cells. With the intention of initiating tumorigenesis in resting, TVA-positive cells, we have developed a system for the preparation of a human immunodeficiency virus type 1 (HIV-1)-based lentiviral vector, pseudotyped with the envelope protein of ALSV subgroup A (EnvA). The HIV(ALSV-A) vector retains the requirement for TVA on the surface of target cells and can be produced at titers of 5 x 10(3) infectious units (IU)/ml. By inserting the central polypurine tract (cPPT) from the HIV-1 pol gene and removing the cytoplasmic tail of EnvA, the pseudotype can be produced at titers approaching 10(5) IU/ml and can be concentrated by ultracentrifugation to titers of 10(7) IU/ml. HIV(ALSV-A) also infects embryonic fibroblasts derived from transgenic mice in which TVA expression is driven by the beta-actin promoter. In addition, this lentivirus pseudotype efficiently infects these fibroblasts after cell cycle arrest, when they are resistant to infection by ALSV vectors. This system may be useful for introducing genes into somatic cells in adult TVA transgenic animals and allows evaluation of the effects of altered gene expression in differentiated cell types in vivo.

Lentivirus administration to rat muscle provides efficient sustained expression of erythropoietin

A lentivirus pseudotyped with vesicular stomatitis virus G protein (VSV-G) encoding rat erythropoietin (EPO) complementary DNA was administered to rat skeletal muscle and red blood cell production was serially monitored. After a single intramuscular injection hematocrit values increased and reached a plateau at about 35 days and were sustained for at least 14 months. Virus doses of 6 x 10(7) infectious units and 6 x 10(6) infectious units produced significantly increased mean hematocrit values of 68.5% +/- 2.1% (P <.001, n = 4) and 52.7% +/- 1.3% (P <.001, n = 3), respectively, over values of control animals receiving normal saline (46.2% +/- 1.5%, n = 2). A polymerase chain reaction (PCR) assay for vector sequences in genomic DNA showed muscle tissue at the site of injection was positive and undetectable in liver, spleen, kidney, and lung. The intramuscular administration of lentivirus provided a dose-responsive, highly efficient and sustained EPO gene delivery, suggesting these vectors may be applied generally to the systemic delivery of proteins such as hormones and clotting factors. (Blood. 2001;98:594-596)