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Schumann GG, Fuchs NV, Tristán-Ramos P, Sebe A, Ivics Z, Heras SR. The impact of transposable element activity on therapeutically relevant human stem cells. Mob DNA 2019; 10:9. [PMID: 30899334 PMCID: PMC6408843 DOI: 10.1186/s13100-019-0151-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 02/27/2019] [Indexed: 12/11/2022] Open
Abstract
Human stem cells harbor significant potential for basic and clinical translational research as well as regenerative medicine. Currently ~ 3000 adult and ~ 30 pluripotent stem cell-based, interventional clinical trials are ongoing worldwide, and numbers are increasing continuously. Although stem cells are promising cell sources to treat a wide range of human diseases, there are also concerns regarding potential risks associated with their clinical use, including genomic instability and tumorigenesis concerns. Thus, a deeper understanding of the factors and molecular mechanisms contributing to stem cell genome stability are a prerequisite to harnessing their therapeutic potential for degenerative diseases. Chemical and physical factors are known to influence the stability of stem cell genomes, together with random mutations and Copy Number Variants (CNVs) that accumulated in cultured human stem cells. Here we review the activity of endogenous transposable elements (TEs) in human multipotent and pluripotent stem cells, and the consequences of their mobility for genomic integrity and host gene expression. We describe transcriptional and post-transcriptional mechanisms antagonizing the spread of TEs in the human genome, and highlight those that are more prevalent in multipotent and pluripotent stem cells. Notably, TEs do not only represent a source of mutations/CNVs in genomes, but are also often harnessed as tools to engineer the stem cell genome; thus, we also describe and discuss the most widely applied transposon-based tools and highlight the most relevant areas of their biomedical applications in stem cells. Taken together, this review will contribute to the assessment of the risk that endogenous TE activity and the application of genetically engineered TEs constitute for the biosafety of stem cells to be used for substitutive and regenerative cell therapies.
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Affiliation(s)
- Gerald G Schumann
- 1Division of Medical Biotechnology, Paul-Ehrlich-Institut, Paul-Ehrlich-Str.51-59, 63225 Langen, Germany
| | - Nina V Fuchs
- 2Host-Pathogen Interactions, Paul-Ehrlich-Institut, Paul-Ehrlich-Str. 51-59, 63225 Langen, Germany
| | - Pablo Tristán-Ramos
- 3GENYO. Centre for Genomics and Oncological Research, Pfizer/University of Granada/Andalusian Regional Government, PTS Granada-Avenida de la Ilustración, 114, 18016 Granada, Spain.,4Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, University of Granada, Campus Universitario de Cartuja, 18071 Granada, Spain
| | - Attila Sebe
- 1Division of Medical Biotechnology, Paul-Ehrlich-Institut, Paul-Ehrlich-Str.51-59, 63225 Langen, Germany
| | - Zoltán Ivics
- 1Division of Medical Biotechnology, Paul-Ehrlich-Institut, Paul-Ehrlich-Str.51-59, 63225 Langen, Germany
| | - Sara R Heras
- 3GENYO. Centre for Genomics and Oncological Research, Pfizer/University of Granada/Andalusian Regional Government, PTS Granada-Avenida de la Ilustración, 114, 18016 Granada, Spain.,4Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, University of Granada, Campus Universitario de Cartuja, 18071 Granada, Spain
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Pereira GC, Sanchez L, Schaughency PM, Rubio-Roldán A, Choi JA, Planet E, Batra R, Turelli P, Trono D, Ostrow LW, Ravits J, Kazazian HH, Wheelan SJ, Heras SR, Mayer J, García-Pérez JL, Goodier JL. Properties of LINE-1 proteins and repeat element expression in the context of amyotrophic lateral sclerosis. Mob DNA 2018; 9:35. [PMID: 30564290 PMCID: PMC6295051 DOI: 10.1186/s13100-018-0138-z] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2018] [Accepted: 11/15/2018] [Indexed: 02/07/2023] Open
Abstract
BACKGROUND Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving loss of motor neurons and having no known cure and uncertain etiology. Several studies have drawn connections between altered retrotransposon expression and ALS. Certain features of the LINE-1 (L1) retrotransposon-encoded ORF1 protein (ORF1p) are analogous to those of neurodegeneration-associated RNA-binding proteins, including formation of cytoplasmic aggregates. In this study we explore these features and consider possible links between L1 expression and ALS. RESULTS We first considered factors that modulate aggregation and subcellular distribution of LINE-1 ORF1p, including nuclear localization. Changes to some ORF1p amino acid residues alter both retrotransposition efficiency and protein aggregation dynamics, and we found that one such polymorphism is present in endogenous L1s abundant in the human genome. We failed, however, to identify CRM1-mediated nuclear export signals in ORF1p nor strict involvement of cell cycle in endogenous ORF1p nuclear localization in human 2102Ep germline teratocarcinoma cells. Some proteins linked with ALS bind and colocalize with L1 ORF1p ribonucleoprotein particles in cytoplasmic RNA granules. Increased expression of several ALS-associated proteins, including TAR DNA Binding Protein (TDP-43), strongly limits cell culture retrotransposition, while some disease-related mutations modify these effects. Using quantitative reverse transcription PCR (RT-qPCR) of ALS tissues and reanalysis of publicly available RNA-Seq datasets, we asked if changes in expression of retrotransposons are associated with ALS. We found minimal altered expression in sporadic ALS tissues but confirmed a previous report of differential expression of many repeat subfamilies in C9orf72 gene-mutated ALS patients. CONCLUSIONS Here we extended understanding of the subcellular localization dynamics of the aggregation-prone LINE-1 ORF1p RNA-binding protein. However, we failed to find compelling evidence for misregulation of LINE-1 retrotransposons in sporadic ALS nor a clear effect of ALS-associated TDP-43 protein on L1 expression. In sum, our study reveals that the interplay of active retrotransposons and the molecular features of ALS are more complex than anticipated. Thus, the potential consequences of altered retrotransposon activity for ALS and other neurodegenerative disorders are worthy of continued investigation.
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Affiliation(s)
- Gavin C. Pereira
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Laura Sanchez
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
| | - Paul M. Schaughency
- Oncology Center-Cancer Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Alejandro Rubio-Roldán
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
| | - Jungbin A. Choi
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Evarist Planet
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Ranjan Batra
- Department of Neurosciences, School of Medicine, University of California at San Diego, San Diego, California USA
| | - Priscilla Turelli
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Didier Trono
- School of Life Sciences, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Lyle W. Ostrow
- Neuromuscular Division, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - John Ravits
- Department of Neurosciences, School of Medicine, University of California at San Diego, San Diego, California USA
| | - Haig H. Kazazian
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Sarah J. Wheelan
- Oncology Center-Cancer Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
| | - Sara R. Heras
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
- Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, University of Granada, Granada, Spain
| | - Jens Mayer
- Department of Human Genetics, Medical Faculty, University of Saarland, Homburg/Saar, Germany
| | - Jose Luis García-Pérez
- GENYO. Centre for Genomics and Oncological Research: Pfizer, University of Granada, Andalusian Regional Government, Granada, Spain
- MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine (IGMM), University of Edinburgh, Western General Hospital, Edinburgh, UK
| | - John L. Goodier
- McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland USA
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3
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Labanieh L, Majzner RG, Mackall CL. Programming CAR-T cells to kill cancer. Nat Biomed Eng 2018; 2:377-391. [PMID: 31011197 DOI: 10.1038/s41551-018-0235-9] [Citation(s) in RCA: 218] [Impact Index Per Article: 36.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2017] [Accepted: 04/09/2018] [Indexed: 02/06/2023]
Abstract
T cells engineered to express chimeric antigen receptors (CARs) that are specific for tumour antigens have led to high complete response rates in patients with haematologic malignancies. Despite this early success, major challenges to the broad application of CAR-T cells as cancer therapies remain, including treatment-associated toxicities and cancer relapse with antigen-negative tumours. Targeting solid tumours with CAR-T cells poses additional obstacles because of the paucity of tumour-specific antigens and the immunosuppressive effects of the tumour microenvironment. To overcome these challenges, T cells can be programmed with genetic modules that increase their therapeutic potency and specificity. In this Review Article, we survey major advances in the engineering of next-generation CAR-T therapies for haematologic cancers and solid cancers, with particular emphasis on strategies for the control of CAR specificity and activity and on approaches for improving CAR-T-cell persistence and overcoming immunosuppression. We also lay out a roadmap for the development of off-the-shelf CAR-T cells.
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Affiliation(s)
- Louai Labanieh
- Department of Bioengineering, Stanford University, Stanford, CA, USA
| | - Robbie G Majzner
- Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA
| | - Crystal L Mackall
- Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA. .,Stanford Cancer Institute, Stanford University School of Medicine, Stanford, CA, USA. .,Department of Medicine, Stanford University School of Medicine, Stanford, CA, USA.
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4
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Tipanee J, VandenDriessche T, Chuah MK. Transposons: Moving Forward from Preclinical Studies to Clinical Trials. Hum Gene Ther 2017; 28:1087-1104. [DOI: 10.1089/hum.2017.128] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Affiliation(s)
- Jaitip Tipanee
- Department of Gene Therapy and Regenerative Medicine, Free University of Brussels (VUB), Brussels, Belgium
| | - Thierry VandenDriessche
- Department of Gene Therapy and Regenerative Medicine, Free University of Brussels (VUB), Brussels, Belgium
- Center for Molecular and Vascular Biology, Department of Cardiovascular Sciences, University of Leuven, Leuven, Belgium
| | - Marinee K. Chuah
- Department of Gene Therapy and Regenerative Medicine, Free University of Brussels (VUB), Brussels, Belgium
- Center for Molecular and Vascular Biology, Department of Cardiovascular Sciences, University of Leuven, Leuven, Belgium
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5
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Macia A, Widmann TJ, Heras SR, Ayllon V, Sanchez L, Benkaddour-Boumzaouad M, Muñoz-Lopez M, Rubio A, Amador-Cubero S, Blanco-Jimenez E, Garcia-Castro J, Menendez P, Ng P, Muotri AR, Goodier JL, Garcia-Perez JL. Engineered LINE-1 retrotransposition in nondividing human neurons. Genome Res 2016; 27:335-348. [PMID: 27965292 PMCID: PMC5340962 DOI: 10.1101/gr.206805.116] [Citation(s) in RCA: 107] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2016] [Accepted: 12/01/2016] [Indexed: 12/21/2022]
Abstract
Half the human genome is made of transposable elements (TEs), whose ongoing activity continues to impact our genome. LINE-1 (or L1) is an autonomous non-LTR retrotransposon in the human genome, comprising 17% of its genomic mass and containing an average of 80-100 active L1s per average genome that provide a source of inter-individual variation. New LINE-1 insertions are thought to accumulate mostly during human embryogenesis. Surprisingly, the activity of L1s can further impact the somatic human brain genome. However, it is currently unknown whether L1 can retrotranspose in other somatic healthy tissues or if L1 mobilization is restricted to neuronal precursor cells (NPCs) in the human brain. Here, we took advantage of an engineered L1 retrotransposition assay to analyze L1 mobilization rates in human mesenchymal (MSCs) and hematopoietic (HSCs) somatic stem cells. Notably, we have observed that L1 expression and engineered retrotransposition is much lower in both MSCs and HSCs when compared to NPCs. Remarkably, we have further demonstrated for the first time that engineered L1s can retrotranspose efficiently in mature nondividing neuronal cells. Thus, these findings suggest that the degree of somatic mosaicism and the impact of L1 retrotransposition in the human brain is likely much higher than previously thought.
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Affiliation(s)
- Angela Macia
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Thomas J Widmann
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Sara R Heras
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Veronica Ayllon
- Department of Oncology, GENYO, Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Laura Sanchez
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Meriem Benkaddour-Boumzaouad
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Martin Muñoz-Lopez
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Alejandro Rubio
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Suyapa Amador-Cubero
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | - Eva Blanco-Jimenez
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain
| | | | - Pablo Menendez
- Department of Oncology, GENYO, Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain.,Josep Carreras Leukemia Research Institute, Department of Biomedicine, School of Medicine, University of Barcelona, Instituciò Catalana Recerca Estudis Avançats (ICREA), 08036 Barcelona, Spain
| | - Philip Ng
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Alysson R Muotri
- Department of Pediatrics/Rady Children's Hospital San Diego, University of California San Diego, La Jolla, California 92093, USA
| | - John L Goodier
- McKusick-Nathans Institute for Genetic Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
| | - Jose L Garcia-Perez
- Department of Genomic Medicine and Centre for Genomics and Oncology (Pfizer-University of Granada and Andalusian Regional Government), PTS Granada, 18016 Granada, Spain.,Medical Research Council Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
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6
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Smith RP, Riordan JD, Feddersen CR, Dupuy AJ. A Hybrid Adenoviral Vector System Achieves Efficient Long-Term Gene Expression in the Liver via piggyBac Transposition. Hum Gene Ther 2016; 26:377-85. [PMID: 25808258 DOI: 10.1089/hum.2014.123] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Much research has gone into the development of hybrid gene delivery systems that combine the broad tropism and efficient transduction of adenoviral vectors with the ability to achieve stable expression of cargo genes. In addition to gene therapy applications, such a system has considerable advantages for studies of gene function in vivo, permitting fine-tuned genetic manipulation with higher throughput than can be achieved using standard transgenic and DNA targeting techniques. Existing strategies are limited, however, by low integration efficiencies, small cargo capacity, and/or a dependence on target cell division. The utility of this approach could be enhanced by a system that provides all of the following: (1) efficient delivery, (2) stable expression in a high percentage of target cells (whether mitotic or not), (3) large cargo capacity, (4) flexibility to use with a wide range of additional experimental conditions, and (5) simple experimental technique. Here we report the initial characterization of a hybrid system that meets these criteria by utilizing piggyBac (PB) transposition to achieve genomic integration from adenoviral vectors. We demonstrate stable expression of an adenovirus (Ad)-PB-delivered reporter gene in ∼20-40% of hepatocytes following standard tail vein injection. Its high efficiency and flexibility relative to existing hybrid adenoviral gene delivery approaches indicate a considerable potential utility of the Ad-PB system for therapeutic gene delivery and in vivo studies of gene function.
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Affiliation(s)
- Ryan P Smith
- Department of Anatomy and Cell Biology, Roy J. & Lucille A. Carver College of Medicine, University of Iowa , Iowa City, IA 52242
| | - Jesse D Riordan
- Department of Anatomy and Cell Biology, Roy J. & Lucille A. Carver College of Medicine, University of Iowa , Iowa City, IA 52242
| | - Charlotte R Feddersen
- Department of Anatomy and Cell Biology, Roy J. & Lucille A. Carver College of Medicine, University of Iowa , Iowa City, IA 52242
| | - Adam J Dupuy
- Department of Anatomy and Cell Biology, Roy J. & Lucille A. Carver College of Medicine, University of Iowa , Iowa City, IA 52242
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7
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Zhang W, Solanki M, Müther N, Ebel M, Wang J, Sun C, Izsvak Z, Ehrhardt A. Hybrid adeno-associated viral vectors utilizing transposase-mediated somatic integration for stable transgene expression in human cells. PLoS One 2013; 8:e76771. [PMID: 24116154 PMCID: PMC3792901 DOI: 10.1371/journal.pone.0076771] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2013] [Accepted: 08/28/2013] [Indexed: 12/14/2022] Open
Abstract
Recombinant adeno-associated viral (AAV) vectors have been shown to be one of the most promising vectors for therapeutic gene delivery because they can induce efficient and long-term transduction in non-dividing cells with negligible side-effects. However, as AAV vectors mostly remain episomal, vector genomes and transgene expression are lost in dividing cells. Therefore, to stably transduce cells, we developed a novel AAV/transposase hybrid-vector. To facilitate SB-mediated transposition from the rAAV genome, we established a system in which one AAV vector contains the transposon with the gene of interest and the second vector delivers the hyperactive Sleeping Beauty (SB) transposase SB100X. Human cells were infected with the AAV-transposon vector and the transposase was provided in trans either by transient and stable plasmid transfection or by AAV vector transduction. We found that groups which received the hyperactive transposase SB100X showed significantly increased colony forming numbers indicating enhanced integration efficiencies. Furthermore, we found that transgene copy numbers in transduced cells were dose-dependent and that predominantly SB transposase-mediated transposition contributed to stabilization of the transgene. Based on a plasmid rescue strategy and a linear-amplification mediated PCR (LAM-PCR) protocol we analysed the SB100X-mediated integration profile after transposition from the AAV vector. A total of 1840 integration events were identified which revealed a close to random integration profile. In summary, we show for the first time that AAV vectors can serve as template for SB transposase mediated somatic integration. We developed the first prototype of this hybrid-vector system which with further improvements may be explored for treatment of diseases which originate from rapidly dividing cells.
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Affiliation(s)
- Wenli Zhang
- Max von Pettenkofer-Institute, Department of Virology, Ludwig-Maximilians-University Munich, Munich, Germany
- Institute of Virology and Microbiology, Center for Biomedical Education and Research, Department of Human Medicine, Faculty of Health, University Witten/Herdecke, Witten, Germany
| | - Manish Solanki
- Institute of Virology and Microbiology, Center for Biomedical Education and Research, Department of Human Medicine, Faculty of Health, University Witten/Herdecke, Witten, Germany
| | - Nadine Müther
- Max von Pettenkofer-Institute, Department of Virology, Ludwig-Maximilians-University Munich, Munich, Germany
| | - Melanie Ebel
- Institute of Virology and Microbiology, Center for Biomedical Education and Research, Department of Human Medicine, Faculty of Health, University Witten/Herdecke, Witten, Germany
| | - Jichang Wang
- Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - Chuanbo Sun
- Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | | | - Anja Ehrhardt
- Max von Pettenkofer-Institute, Department of Virology, Ludwig-Maximilians-University Munich, Munich, Germany
- Institute of Virology and Microbiology, Center for Biomedical Education and Research, Department of Human Medicine, Faculty of Health, University Witten/Herdecke, Witten, Germany
- * E-mail:
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8
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Huang S, Kamihira M. Development of hybrid viral vectors for gene therapy. Biotechnol Adv 2013; 31:208-23. [DOI: 10.1016/j.biotechadv.2012.10.001] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 09/26/2012] [Accepted: 10/04/2012] [Indexed: 01/23/2023]
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9
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Vetrini F, Ng P. Gene therapy with helper-dependent adenoviral vectors: current advances and future perspectives. Viruses 2010; 2:1886-1917. [PMID: 21994713 PMCID: PMC3186006 DOI: 10.3390/v2091886] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2010] [Revised: 08/26/2010] [Accepted: 08/30/2010] [Indexed: 11/21/2022] Open
Abstract
Recombinant Adenoviral vectors represent one of the best gene transfer platforms due to their ability to efficiently transduce a wide range of quiescent and proliferating cell types from various tissues and species. The activation of an adaptive immune response against the transduced cells is one of the major drawbacks of first generation Adenovirus vectors and has been overcome by the latest generation of recombinant Adenovirus, the Helper-Dependent Adenoviral (HDAd) vectors. HDAds have innovative features including the complete absence of viral coding sequences and the ability to mediate high level transgene expression with negligible chronic toxicity. This review summarizes the many aspects of HDAd biology and structure with a major focus on in vivo gene therapy application and with an emphasis on the unsolved issues that these vectors still presents toward clinical application.
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Affiliation(s)
| | - Philip Ng
- Author to whom correspondence should be addressed; Tel.: +1 7137984158; E-Mail:
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10
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Adenovirus-retrovirus hybrid vectors achieve highly enhanced tumor transduction and antitumor efficacy in vivo. Mol Ther 2010; 19:76-82. [PMID: 20808291 DOI: 10.1038/mt.2010.182] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Murine leukemia virus (MLV)-based replication-competent retrovirus (RCR) vectors have been shown to mediate efficient, selective, and persistent tumor transduction, thereby achieving significant therapeutic benefit in a wide variety of cancer models. To further augment the efficiency of this strategy, we have developed a delivery method employing a gutted adenovirus encoding an RCR vector (AdRCR); thus, tumor cells transduced with the adenoviral vector transiently become RCR vector producer cells in situ. As expected, high-titer AdRCR achieved significantly higher initial transduction levels in human cancer cells both in vitro and in vivo, as compared to the original RCR vector itself. Notably, even at equivalent initial transduction levels, more secondary RCR progeny were produced from AdRCR-transduced cells as compared to RCR-transduced cells, resulting in further acceleration of subsequent RCR replication kinetics. In pre-established tumor models in vivo, prodrug activator gene therapy with high-titer AdRCR could achieve enhanced efficacy compared to RCR alone, in a dose-dependent manner. Thus, AdRCR hybrid vectors offer the advantages of high production titers characteristic of adenovirus and secondary production of RCR in situ, which not only accelerates subsequent vector spread and progressive tumor transduction, but can also significantly enhance the therapeutic efficacy of RCR-mediated prodrug activator gene therapy.
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11
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Kubo S, Kataoka M, Tateno C, Yoshizato K, Kawasaki Y, Kimura T, Faure-Kumar E, Palmer DJ, Ng P, Okamura H, Kasahara N. In vivo stable transduction of humanized liver tissue in chimeric mice via high-capacity adenovirus-lentivirus hybrid vector. Hum Gene Ther 2010; 21:40-50. [PMID: 19725756 DOI: 10.1089/hum.2009.027] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
We developed hybrid vectors employing high-capacity adenovirus as a first-stage carrier encoding all the components required for in situ production of a second-stage lentivirus, thereby achieving stable transgene expression in secondary target cells. Such vectors have never previously been tested in normal tissues, because of the scarcity of suitable in vivo systems permissive for second-stage lentivirus assembly. Here we employed a novel murine model in which endogenous liver tissue is extensively reconstituted with engrafted human hepatocytes, and successfully achieved stable transduction by the second-stage lentivirus produced in situ from first-stage adenovirus. This represents the first demonstration of the functionality of adenoviral-lentiviral hybrid vectors in a normal parenchymal organ in vivo.
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Affiliation(s)
- Shuji Kubo
- Division of Digestive Diseases, Department of Medicine, University of California at Los Angeles , Los Angeles, CA 90095, USA.
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12
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Unique functions of repetitive transcriptomes. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2010; 285:115-88. [PMID: 21035099 DOI: 10.1016/b978-0-12-381047-2.00003-7] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Repetitive sequences occupy a huge fraction of essentially every eukaryotic genome. Repetitive sequences cover more than 50% of mammalian genomic DNAs, whereas gene exons and protein-coding sequences occupy only ~3% and 1%, respectively. Numerous genomic repeats include genes themselves. They generally encode "selfish" proteins necessary for the proliferation of transposable elements (TEs) in the host genome. The major part of evolutionary "older" TEs accumulated mutations over time and fails to encode functional proteins. However, repeats have important functions also on the RNA level. Repetitive transcripts may serve as multifunctional RNAs by participating in the antisense regulation of gene activity and by competing with the host-encoded transcripts for cellular factors. In addition, genomic repeats include regulatory sequences like promoters, enhancers, splice sites, polyadenylation signals, and insulators, which actively reshape cellular transcriptomes. TE expression is tightly controlled by the host cells, and some mechanisms of this regulation were recently decoded. Finally, capacity of TEs to proliferate in the host genome led to the development of multiple biotechnological applications.
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13
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Müther N, Noske N, Ehrhardt A. Viral hybrid vectors for somatic integration - are they the better solution? Viruses 2009; 1:1295-324. [PMID: 21994594 PMCID: PMC3185507 DOI: 10.3390/v1031295] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Revised: 12/04/2009] [Accepted: 12/10/2009] [Indexed: 12/18/2022] Open
Abstract
The turbulent history of clinical trials in viral gene therapy has taught us important lessons about vector design and safety issues. Much effort was spent on analyzing genotoxicity after somatic integration of therapeutic DNA into the host genome. Based on these findings major improvements in vector design including the development of viral hybrid vectors for somatic integration have been achieved. This review provides a state-of-the-art overview of available hybrid vectors utilizing viruses for high transduction efficiencies in concert with various integration machineries for random and targeted integration patterns. It discusses advantages but also limitations of each vector system.
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Affiliation(s)
- Nadine Müther
- Max von Pettenkofer-Institut, Department of Virology, Ludwig-Maximilians-Universität Munich, Pettenkoferstr. 9A, 80336 Munich, Germany
| | - Nadja Noske
- Max von Pettenkofer-Institut, Department of Virology, Ludwig-Maximilians-Universität Munich, Pettenkoferstr. 9A, 80336 Munich, Germany
| | - Anja Ehrhardt
- Max von Pettenkofer-Institut, Department of Virology, Ludwig-Maximilians-Universität Munich, Pettenkoferstr. 9A, 80336 Munich, Germany
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14
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The L1 retrotransposition assay: a retrospective and toolkit. Methods 2009; 49:219-26. [PMID: 19398011 DOI: 10.1016/j.ymeth.2009.04.012] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Revised: 03/18/2009] [Accepted: 04/10/2009] [Indexed: 11/23/2022] Open
Abstract
LINE1s (L1s) are a class of mammalian non-LTR (long terminal repeat) retroelements that make up nearly 20% of the human genome. Because of the difficulty of studying the mobilization of endogenous L1s, an exogenous cell culture retrotransposition assay has become integral to research in L1 biology. This assay has allowed for investigation of the mechanism and consequences of mobilization of this retroelement, both in cell lines and in whole animal models. In this paper, we outline the genesis of in vitro retrotransposition systems which led to the development of the L1 retrotransposition assay in the mid-1990s. We then provide a retrospective, describing the many uses and variations of this assay, ending with caveats and predictions for future developments. Finally, we provide detailed protocols on the application of the retrotransposition assay, including lists of constructs available in the L1 research community and cell lines in which this assay has been applied.
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15
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Meneses-Acosta A, Dormond E, Jacob D, Tom R, Bernier A, Perret S, St-Laurent G, Durocher Y, Gilbert R, Kamen A. Development of a suspension serum-free helper-dependent adenovirus production system and assessment of co-infection conditions. J Virol Methods 2008; 148:106-14. [PMID: 18079009 DOI: 10.1016/j.jviromet.2007.10.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2007] [Revised: 10/20/2007] [Accepted: 10/26/2007] [Indexed: 12/14/2022]
Abstract
Helper-dependent adenovirus (HDAd), deleted in all viral protein-coding sequences has been designed to reduce immune response and favor long-term expression of therapeutic genes in clinical programs. Its production requires co-infection of E1-complementing cells with helper adenovirus (HAd). Significant progresses have been made in the molecular design of HDAd, but large scale production remains a challenge. In this work, a scalable system for HDAd production is designed and evaluated focusing on the co-infection step. A human embryo kidney 293 (293) derived cell line, the 293SF/FLPe was generated to produce efficiently HDAd while restricting the packaging of HAd. This cell line was adapted to grow in suspension and in serum-free medium. Multiplicity of infection (MOI) of HDAd ranging from 0.1 to 50 was evaluated in presence of HAd at a MOI of 5. Optimal MOIs for HDAd amplification were found in the range of 5-10. HAd contamination was only 1%. These results were validated in a 3 L bioreactor under controlled operating conditions where a higher HDAd yield of 2.6 x 10(9) viral particles (VP)/mL or 3.5 x 10(8) infectious units (IU)/mL of HDAd was obtained.
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Affiliation(s)
- Angélica Meneses-Acosta
- Animal Cell Technology Group, Biotechnology Research Institute, National Research Council, 6100 Royalmount Avenue, Montreal, Quebec, Canada H4P 2R2
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16
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Oka K, Chan L. Helper-dependent adenoviral vectors. CURRENT PROTOCOLS IN MOLECULAR BIOLOGY 2008; Chapter 16:Unit 16.24. [PMID: 18265354 DOI: 10.1002/0471142727.mb1624s69] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The helper-dependent adenovirus (HDAd) is a recently developed adenovirus-based vector with an improved safety profile and long-term transgene expression. In this unit, a basic procedure for HDAd production using the Cre-loxP system is presented. Amplification and large-scale production of the vector can be done in both adherent and suspension cell culture systems. Included are protocols for Southern blot analysis to monitor vector amplification, slot blot assay to determine the infectious titer of the purified HDAd, and real-time PCR to detect helper virus contamination in the preparation.
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17
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Kubo S, del Carmen Seleme M, Soifer HS, Perez JLG, Moran JV, Kazazian HH, Kasahara N. L1 retrotransposition in nondividing and primary human somatic cells. Proc Natl Acad Sci U S A 2006; 103:8036-41. [PMID: 16698926 PMCID: PMC1472425 DOI: 10.1073/pnas.0601954103] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Whether long interspersed element-1 (L1 or LINE-1) retrotransposition can occur in quiescent, nondividing, and/or terminally differentiated somatic cells has remained an unanswered fundamental question in human genetics. Here, we used a ubiquitously active phosphoglycerate kinase-1 promoter to drive the expression of a highly active human L1 element from an adenovirus-L1 hybrid vector. This vector system achieved retrotransposition in up to 91% of actively growing immortalized cells, and we demonstrated that L1 retrotransposition can be suppressed by the reverse transcriptase inhibitor 3'-azido-3'-deoxythymidine. This adenovirus vector enabled efficient delivery of the L1 element into differentiated primary human somatic cells and G1/S-arrested cells, resulting in retrotransposition in both cases; however, it was not detected in G0-arrested cells. Thus, these data indicate that L1 retrotransposition can occur in nondividing somatic cells.
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Affiliation(s)
- Shuji Kubo
- *Department of Medicine, UCLA School of Medicine, 675 Charles E. Young Drive South, MRL-1551, Los Angeles, CA 90095-7019
| | - Maria del Carmen Seleme
- Department of Genetics, University of Pennsylvania School of Medicine, 475 Clinical Research Building, 415 Curie Boulevard, Philadelphia, PA 19104-6145
| | - Harris S. Soifer
- Division of Molecular Biology, Beckman Research Institute, City of Hope National Medical Center, 1450 East Duarte Road, Duarte, CA 91010-3011; Departments of
| | | | - John V. Moran
- Human Genetics and
- Internal Medicine, University of Michigan Medical School, 1241 East Catherine Street, Room 4909 Buhl, Ann Arbor, MI 48109-0618
| | - Haig H. Kazazian
- Department of Genetics, University of Pennsylvania School of Medicine, 475 Clinical Research Building, 415 Curie Boulevard, Philadelphia, PA 19104-6145
| | - Noriyuki Kasahara
- *Department of Medicine, UCLA School of Medicine, 675 Charles E. Young Drive South, MRL-1551, Los Angeles, CA 90095-7019
- To whom correspondence should be addressed. E-mail:
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18
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19
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Izsvák Z, Ivics Z. Sleeping beauty transposition: biology and applications for molecular therapy. Mol Ther 2004; 9:147-56. [PMID: 14759798 DOI: 10.1016/j.ymthe.2003.11.009] [Citation(s) in RCA: 165] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2003] [Accepted: 11/20/2003] [Indexed: 11/24/2022] Open
Abstract
Transposable elements can be considered as natural, nonviral gene-delivery vehicles and are valuable and widely used tools for germ-line transgenesis and insertional mutagenesis in invertebrate systems such as flies and worms. Such tools were not available for genome manipulations in vertebrates until recently, when an active element was resurrected from transposon fossils found in fish genomes. This element, the Sleeping Beauty transposon, shows efficient transposition in cells of a wide range of vertebrates, including humans. Sleeping Beauty transposition is a cut-and-paste process, during which the element "jumps" from one DNA molecule to another. Transposon integration into chromosomes provides the basis for long-term, or possibly permanent, transgene expression in transgenic cells and organisms. Thus, the reconstruction of the Sleeping Beauty element generated considerable interest in developing efficient and safe vectors for vertebrate transgenesis as well as for human gene therapy. In this review we summarize our current knowledge of Sleeping Beauty biology and describe the strengths and current limitations of transposon technology for gene therapeutic applications.
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Affiliation(s)
- Zsuzsanna Izsvák
- Max Delbrück Center for Molecular Medicine, D-13092 Berlin, Germany
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20
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Weichenrieder O, Repanas K, Perrakis A. Crystal structure of the targeting endonuclease of the human LINE-1 retrotransposon. Structure 2004; 12:975-86. [PMID: 15274918 DOI: 10.1016/j.str.2004.04.011] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2004] [Revised: 03/30/2004] [Accepted: 04/05/2004] [Indexed: 10/26/2022]
Abstract
The human L1 endonuclease (L1-EN) is encoded by the non-LTR retrotransposon LINE-1 (L1). L1 is responsible for more than 1.5 million retrotransposition events in the history of the human genome, contributing more than a quarter to human genomic DNA (L1 and Alu elements). L1-EN is related to the well-understood human DNA repair endonuclease APE1, and its nicking specificity is a major determinant for retrotransposon integration site selection. The crystal structure of human L1 endonuclease is the first of a retrotransposon-encoded protein and a prototype for retrotransposon-encoded endonucleases involved in target-primed reverse transcription. Structure-based endonuclease alignments reveal a conserved threonine in addition to previously identified invariant residues and suggest that DNA recognition proceeds via the accommodation of an extrahelical nucleotide within a pocket of the enzyme. The present analysis will help to refine phylogenetic and functional relationships among metal-dependent phosphohydrolases and provides a basis for manipulating non-LTR retrotransposon integration site selection.
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Affiliation(s)
- Oliver Weichenrieder
- The Netherlands Cancer Institute, Department of Molecular Carcinogenesis-H2, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
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21
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Farley AH, Luning Prak ET, Kazazian HH. More active human L1 retrotransposons produce longer insertions. Nucleic Acids Res 2004; 32:502-10. [PMID: 14742665 PMCID: PMC373329 DOI: 10.1093/nar/gkh202] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2003] [Revised: 09/18/2003] [Accepted: 12/10/2003] [Indexed: 11/13/2022] Open
Abstract
The vast majority of L1 insertions are 5' truncated and thus inactive. Yet, the mechanism of 5' truncation is unknown. To examine whether the frequency of L1 retrotransposition is directly correlated with the length of genomic L1 insertions, we used a cell culture assay to measure retrotransposition frequency and a PCR-based assay to measure L1 insertion length. We tested five full-length human L1 elements that retrotranspose at different frequencies: LRE3, L1(RP), L1.3, L1.2A and L1.2B. Our data suggest that L1 insertion length correlates with L1 retrotransposition frequency for insertions >1 kb in length. For two elements, L1(RP) and L1.2A, we found that swapping the reverse transcriptase domains had little effect. Instead, we found that genomic insertion length and retrotransposition frequency are substantially affected by amino acid substitutions at positions 363, 1220 and 1259 in ORF2. We suggest that the region containing residues 1220 and 1259 may be important in the binding of ORF2p to L1 RNA to facilitate reverse transcription.
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Affiliation(s)
- Alexander H Farley
- Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, PA, USA
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22
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Largaespada DA. Generating and manipulating transgenic animals using transposable elements. Reprod Biol Endocrinol 2003; 1:80. [PMID: 14613544 PMCID: PMC280724 DOI: 10.1186/1477-7827-1-80] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/15/2003] [Accepted: 11/07/2003] [Indexed: 11/10/2022] Open
Abstract
Transposable elements, or transposons, have played a significant role in the history of biological research. They have had a major influence on the structure of genomes during evolution, they can cause mutations, and their study led to the concept of so-called "selfish DNA". In addition, transposons have been manipulated as useful gene transfer vectors. While primarily restricted to use in invertebrates, prokaryotes, and plants, it is now clear that transposon technology and biology are just as relevant to the study of vertebrate species. Multiple transposons now have been shown to be active in vertebrates and they can be used for germline transgenesis, somatic cell transgenesis/gene therapy, and random germline insertional mutagenesis. The sophistication of these applications and the number of active elements are likely to increase over the next several years. This review covers the vertebrate-active retrotransposons and transposons that have been well studied and adapted for use as gene transfer agents. General considerations and predictions about the future utility of transposon technology are discussed.
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Affiliation(s)
- David A Largaespada
- Department of Genetics, Cell Biology and Development, University of Minnesota Cancer Center, Minneapolis, MN 55455, USA.
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23
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Yant SR, Ehrhardt A, Mikkelsen JG, Meuse L, Pham T, Kay MA. Transposition from a gutless adeno-transposon vector stabilizes transgene expression in vivo. Nat Biotechnol 2002; 20:999-1005. [PMID: 12244327 DOI: 10.1038/nbt738] [Citation(s) in RCA: 150] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2002] [Accepted: 07/16/2002] [Indexed: 11/08/2022]
Abstract
A major limitation of adenovirus-mediated gene therapy for inherited diseases is the instability of transgene expression in vivo, which originates at least in part from the loss of the linear, extrachromosomal vector genomes. Herein we describe the production of a gene-deleted adenovirus-transposon vector that stably maintains virus-encoded transgenes in vivo through integration into host cell chromosomes. This system utilizes a donor transposon vector that undergoes Flp-mediated recombination and excision of its therapeutic payload in the presence of the Flp and Sleeping Beauty recombinases. Systemic in vivo delivery of this system resulted in efficient generation of transposon circles and stable transposase-mediated integration in mouse liver. Somatic integration was sufficient to maintain therapeutic levels of human coagulation Factor IX for more than six months in mice undergoing extensive liver proliferation. These vectors combine the versatility of adenoviral vectors with the integration capabilities of a eukaryotic DNA transposon and should prove useful in the treatment of genetic diseases.
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Affiliation(s)
- Stephen R Yant
- Department of Pediatrics and Genetics, Stanford University School of Medicine, Stanford, CA 94305-5208, USA
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24
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Soifer H, Higo C, Logg CR, Jih LJL, Shichinohe T, Harboe-Schmidt E, Mitani K, Kasahara N. A novel, helper-dependent, adenovirus-retrovirus hybrid vector: stable transduction by a two-stage mechanism. Mol Ther 2002; 5:599-608. [PMID: 11991751 DOI: 10.1006/mthe.2002.0586] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have developed a novel vector system that uses a helper-dependent adenoviral vector as a carrier to deliver a fully functional retrovirus vector. The helper-dependent adenovirus (HDAd) can accommodate large inserts, provide high titers, and infect nondividing as well as dividing cells. However, adenoviral DNA is rarely integrated into the host cell genome, and its episomal expression is transient. Therefore we inserted a replication-competent, ecotropic retrovirus vector containing the green fluorescent protein (GFP) reporter gene as a second-stage component. The well-characterized host species tropism of each vector component provided a stringent biological assay system that demonstrates the two-stage transduction mechanism of the hybrid vector, because the adenovirus stage can efficiently transduce human cells but cannot replicate in murine cells, and conversely, the ecotropic retrovirus stage cannot enter human cells but can efficiently proliferate in murine cells, resulting in permanent integration and progressive spread of reporter gene expression.
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Affiliation(s)
- Harris Soifer
- Institute for Genetic Medicine, University of Southern California, 2250 Alcazar Street, CSC-240, Los Angeles, California 90033, USA
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25
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Abstract
As currently available preventive and therapeutic interventions for hypercholesterolemia are ineffective in a substantial proportion of patients, severe dyslipidemias associated with atherosclerotic vascular disease remain an important target for the development of novel gene therapies. The development of a safe and efficient gene transfer vector has been a major challenge in liver-directed gene therapy, but recently significant progress has been made in this area. Proof-of-principle experiments indicate that the transfer of lipid-modifying genes to the liver is an effective method to restore normal plasma lipids and protect against atherosclerosis. This article summarizes recent developments in liver-directed gene delivery and reviews data on the treatment of dyslipidemias and prevention of atherosclerosis in animals. The evidence presented suggests that some of the approaches taken in animals may be ready for clinical trials in the near future.
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Affiliation(s)
- Kazuhiro Oka
- Department of Molecular & Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
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26
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Abstract
L1 retrotransposons comprise 17% of the human genome. Although most L1s are inactive, some elements remain capable of retrotransposition. L1 elements have a long evolutionary history dating to the beginnings of eukaryotic existence. Although many aspects of their retrotransposition mechanism remain poorly understood, they likely integrate into genomic DNA by a process called target primed reverse transcription. L1s have shaped mammalian genomes through a number of mechanisms. First, they have greatly expanded the genome both by their own retrotransposition and by providing the machinery necessary for the retrotransposition of other mobile elements, such as Alus. Second, they have shuffled non-L1 sequence throughout the genome by a process termed transduction. Third, they have affected gene expression by a number of mechanisms. For instance, they occasionally insert into genes and cause disease both in humans and in mice. L1 elements have proven useful as phylogenetic markers and may find other practical applications in gene discovery following insertional mutagenesis in mice and in the delivery of therapeutic genes.
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Affiliation(s)
- E M Ostertag
- Department of Genetics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.
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