A High-Capacity Adenoviral Hybrid Vector System Utilizing the Hyperactive Sleeping Beauty Transposase SB100X for Enhanced Integration

Auto-expansion of in vivo HDAd-transduced hematopoietic stem cells by constitutive expression of tHMGA2

We developed an in vivo hematopoietic stem cell (HSC) gene therapy approach that does not require cell transplantation. To achieve therapeutically relevant numbers of corrected cells, we constructed HSC-tropic HDAd5/35++ vectors expressing a 3' UTR truncated HMGA2 gene and a GFP reporter gene. A SB100x transposase vector mediated random integration of the tHMGA2/GFP transgene cassette. HSCs in mice were mobilized by subcutaneous injections of G-CSF and AMD3100/Plerixafor and intravenously injected with the integrating tHMGA2/GFP vector. This resulted in a slow but progressive, competitive expansion of GFP+ PBMCs, reaching about 50% by week 44 with further expansion in secondary recipients. Expansion occurred at the level of HSCs as well as at the levels of myeloid, lymphoid, and erythroid progenitors within the bone marrow and spleen. Importantly, based on genome-wide integration site analyses, expansion was polyclonal, without any signs of clonal dominance. Whole-exome sequencing did not show significant differences in the genomic instability indices between tHGMGA2/GFP mice and untreated control mice. Auto-expansion by tHMGA2 was validated in humanized mice. This is the first demonstration that simple injections of mobilization drugs and HDAd vectors can trigger auto-expansion of in vivo transduced HSCs resulting in transgene-marking rates that, theoretically, are curative for hemoglobinopathies.

Passer, a highly active transposon from a fish genome, as a potential new robust genetic manipulation tool

The discovery of new, active DNA transposons can expand the range of genetic tools and provide more options for genomic manipulation. In this study, a bioinformatics analysis suggested that Passer (PS) transposons, which are members of the pogo superfamily, show signs of recent and current activity in animals and may be active in some species. Cell-based transposition assays revealed that the native PS transposases from Gasterosteus aculeatus and Danio rerio displayed very high activity in human cells relative to the Sleeping Beauty transposon. A typical overproduction inhibition phenomenon was observed for PS, and transposition capacity was decreased by ∼12% with each kilobase increase in the insertion size. Furthermore, PS exhibited a pronounced integration preference for genes and their transcriptional regulatory regions. We further show that two domesticated human proteins derived from PS transposases have lost their transposition activity. Overall, PS may represent an alternative with a potentially efficient genetic manipulation tool for transgenesis and mutagenesis applications.

The Past, Present, and Future of Non-Viral CAR T Cells

Adoptive transfer of chimeric antigen receptor (CAR) T lymphocytes is a powerful technology that has revolutionized the way we conceive immunotherapy. The impressive clinical results of complete and prolonged response in refractory and relapsed diseases have shifted the landscape of treatment for hematological malignancies, particularly those of lymphoid origin, and opens up new possibilities for the treatment of solid neoplasms. However, the widening use of cell therapy is hampered by the accessibility to viral vectors that are commonly used for T cell transfection. In the era of messenger RNA (mRNA) vaccines and CRISPR/Cas (clustered regularly interspaced short palindromic repeat-CRISPR-associated) precise genome editing, novel and virus-free methods for T cell engineering are emerging as a more versatile, flexible, and sustainable alternative for next-generation CAR T cell manufacturing. Here, we discuss how the use of non-viral vectors can address some of the limitations of the viral methods of gene transfer and allow us to deliver genetic information in a stable, effective and straightforward manner. In particular, we address the main transposon systems such as Sleeping Beauty (SB) and piggyBac (PB), the utilization of mRNA, and innovative approaches of nanotechnology like Lipid-based and Polymer-based DNA nanocarriers and nanovectors. We also describe the most relevant preclinical data that have recently led to the use of non-viral gene therapy in emerging clinical trials, and the related safety and efficacy aspects. We will also provide practical considerations for future trials to enable successful and safe cell therapy with non-viral methods for CAR T cell generation.

Safe and efficient in vivo hematopoietic stem cell transduction in nonhuman primates using HDAd5/35++ vectors

We tested a new in vivo hematopoietic stem cell (HSC) transduction/selection approach in rhesus macaques using HSC-tropic, integrating, helper-dependent adenovirus vectors (HDAd5/35++) designed for the expression of human γ-globin in red blood cells (RBCs) to treat hemoglobinopathies. We show that HDAd5/35++ vectors preferentially transduce HSCs in vivo after intravenous injection into granulocyte colony-stimulating factor (G-CSF)/AMD3100-mobilized animals and that transduced cells return to the bone marrow and spleen. The approach was well tolerated, and the activation of proinflammatory cytokines that are usually associated with intravenous adenovirus vector injection was successfully blunted by pre-treatment with dexamethasone in combination with interleukin (IL)-1 and IL-6 receptor blockers. Using our MGMT^P140K-based in vivo selection approach, γ-globin⁺ RBCs increased in all animals with levels up to 90%. After selection, the percentage of γ-globin⁺ RBCs declined, most likely due to an immune response against human transgene products. Our biodistribution data indicate that γ-globin⁺ RBCs in the periphery were mostly derived from mobilized HSCs that homed to the spleen. Integration site analysis revealed a polyclonal pattern and no genotoxicity related to transgene integrations. This is the first proof-of-concept study in nonhuman primates to show that in vivo HSC gene therapy could be feasible in humans without the need for high-dose chemotherapy conditioning and HSC transplantation.

In vivo HSC gene therapy for SARS-CoV2 infection using a decoy receptor

While SARS-CoV2 vaccines have shown an unprecedented success, the ongoing emergence of new variants and necessity to adjust vaccines justify the development of alternative prophylaxis and therapy approaches. Hematopoietic stem cell (HSC) gene therapy using a secreted CoV2 decoy receptor protein (sACE2-Ig) would involve a one-time intervention resulting in long-term protection against airway infection, viremia, and extrapulmonary symptoms. We recently developed a technically simple and portable in vivo hematopoietic HSC transduction approach that involves HSC mobilization from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating, helper-dependent adenovirus (HDAd5/35⁺⁺) vector system. Considering the abundance of erythrocytes, in this study, we directed sACE2-Ig expression to erythroid cells using strong β-globin transcriptional regulatory elements. We performed in vivo HSC transduction of CD46-transgenic mice with an HDAd-sACE2-Ig vector. Serum sACE2-Ig levels reached 500–1,300 ng/mL after in vivo selection. At 22 weeks, we used genetically modified HSCs from these mice to substitute the hematopoietic system in human ACE2-transgenic mice, thus creating a model that is susceptible to SARS-CoV2 infection. Upon challenge with a lethal dose of CoV2 (WA-1), sACE2-Ig expressed from erythroid cells of test mice diminishes infection sequelae. Treated mice lost significantly less weight, had less viremia, and displayed reduced cytokine production and lung pathology. The second objective of this study was to assess the safety of in vivo HSC transduction and long-term sACE2-Ig expression in a rhesus macaque. With appropriate cytokine prophylaxis, intravenous injection of HDAd-sACE2-Ig into the mobilized animal was well tolerated. In vivo transduced HSCs preferentially localized to and survived in the spleen. sACE2-Ig expressed from erythroid cells did not affect erythropoiesis and the function of erythrocytes. While these pilot studies are promising, the antiviral efficacy of the approach has to be improved, for example, by using of decoy receptors with enhanced neutralizing capacity and/or expression of multiple antiviral effector proteins.

Gene Therapy Potential for Genetic Disorders of Surfactant Dysfunction

Pulmonary surfactant is critically important to prevent atelectasis by lowering the surface tension of the alveolar lining liquid. While respiratory distress syndrome (RDS) is common in premature infants, severe RDS in term and late preterm infants suggests an underlying genetic etiology. Pathogenic variants in the genes encoding key components of pulmonary surfactant including surfactant protein B (SP-B, SFTPB gene), surfactant protein C (SP-C, SFTPC gene), and the ATP-Binding Cassette transporter A3 (ABCA3, ABCA3 gene) result in severe neonatal RDS or childhood interstitial lung disease (chILD). These proteins play essential roles in pulmonary surfactant biogenesis and are expressed in alveolar epithelial type II cells (AEC2), the progenitor cell of the alveolar epithelium. SP-B deficiency most commonly presents in the neonatal period with severe RDS and requires lung transplantation for survival. SFTPC mutations act in an autosomal dominant fashion and more commonly presents with chILD or idiopathic pulmonary fibrosis than neonatal RDS. ABCA3 deficiency often presents as neonatal RDS or chILD. Gene therapy is a promising option to treat monogenic lung diseases. Successes and challenges in developing gene therapies for genetic disorders of surfactant dysfunction include viral vector design and tropism for target cell types. In this review, we explore adeno-associated virus (AAV), lentiviral, and adenoviral (Ad)-based vectors as delivery vehicles. Both gene addition and gene editing strategies are compared to best design treatments for lung diseases resulting from pathogenic variants in the SFTPB, SFTPC, and ABCA3 genes.

Contemporary Transposon Tools: A Review and Guide through Mechanisms and Applications of Sleeping Beauty, piggyBac and Tol2 for Genome Engineering

Transposons are mobile genetic elements evolved to execute highly efficient integration of their genes into the genomes of their host cells. These natural DNA transfer vehicles have been harnessed as experimental tools for stably introducing a wide variety of foreign DNA sequences, including selectable marker genes, reporters, shRNA expression cassettes, mutagenic gene trap cassettes, and therapeutic gene constructs into the genomes of target cells in a regulated and highly efficient manner. Given that transposon components are typically supplied as naked nucleic acids (DNA and RNA) or recombinant protein, their use is simple, safe, and economically competitive. Thus, transposons enable several avenues for genome manipulations in vertebrates, including transgenesis for the generation of transgenic cells in tissue culture comprising the generation of pluripotent stem cells, the production of germline-transgenic animals for basic and applied research, forward genetic screens for functional gene annotation in model species and therapy of genetic disorders in humans. This review describes the molecular mechanisms involved in transposition reactions of the three most widely used transposon systems currently available (Sleeping Beauty, piggyBac, and Tol2), and discusses the various parameters and considerations pertinent to their experimental use, highlighting the state-of-the-art in transposon technology in diverse genetic applications.

Single-dose MGTA-145/plerixafor leads to efficient mobilization and in vivo transduction of HSCs with thalassemia correction in mice

We have developed an in vivo hemopoietic stem cell (HSC) gene therapy approach without the need for myelosuppressive conditioning and autologous HSC transplantation. It involves HSC mobilization and IV injection of a helper-dependent adenovirus HDAd5/35++ vector system. The current mobilization regimen consists of granulocyte colony-stimulating factor (G-CSF) injections over a 4-day period, followed by the administration of plerixafor/AMD3100. We tested a simpler, 2-hour, G-CSF-free mobilization regimen using truncated GRO-β (MGTA-145; a CXCR2 agonist) and plerixafor in the context of in vivo HSC transduction in mice. The MGTA-145+plerixafor combination resulted in robust mobilization of HSCs. Importantly, compared with G-CSF+plerixafor, MGTA-145+plerixafor led to significantly less leukocytosis and no elevation of serum interleukin-6 levels and was thus likely to be less toxic. With both mobilization regimens, after in vivo selection with O6-benzylguanine (O6BG)/BCNU, stable GFP marking was achieved in >90% of peripheral blood mononuclear cells. Genome-wide analysis showed random, multiclonal vector integration. In vivo HSC transduction after mobilization with MGTA-145+plerixafor in a mouse model for thalassemia resulted in >95% human γ-globin+ erythrocytes at a level of 36% of mouse β-globin. Phenotypic analyses showed a complete correction of thalassemia. The γ-globin marking percentage and level were maintained in secondary recipients, further demonstrating that MGTA145+plerixafor mobilizes long-term repopulating HSCs. Our study indicates that brief exposure to MGTA-145+plerixafor may be advantageous as a mobilization regimen for in vivo HSC gene therapy applications across diseases, including thalassemia and sickle cell disease.

In Vivo HSC Gene Therapy Using a Bi-modular HDAd5/35++ Vector Cures Sickle Cell Disease in a Mouse Model

We have recently reported that, after in vivo hematopoietic stem cell/progenitor (HSPC) transduction with HDAd5/35++ vectors, SB100x transposase-mediated γ-globin gene addition achieved 10%-15% γ-globin of adult mouse globin, resulting in significant but incomplete phenotypic correction in a thalassemia intermedia mouse model. Furthermore, genome editing of a γ-globin repressor binding site within the γ-globin promoter by CRISPR-Cas9 results in efficient reactivation of endogenous γ-globin. Here, we aimed to combine these two mechanisms to obtain curative levels of γ-globin after in vivo HSPC transduction. We generated a HDAd5/35++ adenovirus vector (HDAd-combo) containing both modules and tested it in vitro and after in vivo HSPC transduction in healthy CD46/β-YAC mice and in a sickle cell disease mouse model (CD46/Townes). Compared to HDAd vectors containing either the γ-globin addition or the CRISPR-Cas9 reactivation units alone, in vivo HSC transduction of CD46/Townes mice with the HDAd-combo resulted in significantly higher γ-globin in red blood cells, reaching 30% of that of adult human α and βS chains and a complete phenotypic correction of sickle cell disease.

Curative in vivo hematopoietic stem cell gene therapy of murine thalassemia using large regulatory elements

Recently, we demonstrated that hematopoietic stem/progenitor cell (HSPC) mobilization followed by intravenous injection of integrating, helper-dependent adenovirus HDAd5/35++ vectors resulted in efficient transduction of long-term repopulating cells and disease amelioration in mouse models after in vivo selection of transduced HSPCs. Acute innate toxicity associated with HDAd5/35++ injection was controlled by appropriate prophylaxis, making this approach feasible for clinical translation. Our ultimate goal is to use this technically simple in vivo HSPC transduction approach for gene therapy of thalassemia major or sickle cell disease. A cure of these diseases requires high expression levels of the therapeutic protein (γ- or β-globin), which is difficult to achieve with lentivirus vectors because of their genome size limitation not allowing larger regulatory elements to be accommodated. Here, we capitalized on the 35 kb insert capacity of HDAd5/35++ vectors to demonstrate that transcriptional regulatory regions of the β-globin locus with a total length of 29 kb can efficiently be transferred into HSPCs. The in vivo HSPC transduction resulted in stable γ-globin levels in erythroid cells that conferred a complete cure of murine thalassemia intermedia. Notably, this was achieved with a minimal in vivo HSPC selection regimen.

Employing large regulatory elements in the context of HDAd5/35++ vectors for in vivo transduction of HSPCs achieved gamma-globin levels in erythroid cells that cured murine thalassemia intermedia.

Genetically modified immune cells targeting tumor antigens

Immunotherapy approaches consisting of genetically modified immune cells have become a promising platform for cancer treatment. Such 'living' therapies targeting tumor antigens have shown success in many cancer patients in the form of durable responses in a growing number of clinical studies. Besides, a large number of ongoing studies have been designed to introduce reliable methods for identification of tumor antigens. In addition, technical and biotechnological developments are being applied to the generation and expansion of genetically modified immune cells. In this review, we summarize and discuss the latest progress and current challenges in the tumor antigen landscape and in the generation of genetically modified immune cells in view of their clinical efficacy, either as monotherapy or combinational therapy.

High-Capacity Adenoviral Vectors: Expanding the Scope of Gene Therapy

The adaptation of adenoviruses as gene delivery tools has resulted in the development of high-capacity adenoviral vectors (HC-AdVs), also known, helper-dependent or "gutless". Compared with earlier generations (E1/E3-deleted vectors), HC-AdVs retain relevant features such as genetic stability, remarkable efficacy of in vivo transduction, and production at high titers. More importantly, the lack of viral coding sequences in the genomes of HC-AdVs extends the cloning capacity up to 37 Kb, and allows long-term episomal persistence of transgenes in non-dividing cells. These properties open a wide repertoire of therapeutic opportunities in the fields of gene supplementation and gene correction, which have been explored at the preclinical level over the past two decades. During this time, production methods have been optimized to obtain the yield, purity, and reliability required for clinical implementation. Better understanding of inflammatory responses and the implementation of methods to control them have increased the safety of these vectors. We will review the most significant achievements that are turning an interesting research tool into a sound vector platform, which could contribute to overcome current limitations in the gene therapy field.

Targeted Integration and High-Level Transgene Expression in AAVS1 Transgenic Mice after In Vivo HSC Transduction with HDAd5/35++ Vectors

Our goal is the development of in vivo hematopoietic stem cell (HSC) transduction technology with targeted integration. To achieve this, we modified helper-dependent HDAd5/35++ vectors to express a CRISPR/Cas9 specific to the "safe harbor" adeno-associated virus integration site 1 (AAVS1) locus and to provide a donor template for targeted integration through homology-dependent repair. We tested the HDAd-CRISPR + HDAd-donor vector system in AAVS1 transgenic mice using a standard ex vivo HSC gene therapy approach as well as a new in vivo HSC transduction approach that involves HSC mobilization and intravenous HDAd5/35++ injections. In both settings, the majority of treated mice had transgenes (GFP or human γ-globin) integrated into the AAVS1 locus. On average, >60% of peripheral blood cells expressed the transgene after in vivo selection with low-dose O⁶BG/bis-chloroethylnitrosourea (BCNU). Ex vivo and in vivo HSC transduction and selection studies with HDAd-CRISPR + HDAd-globin-donor resulted in stable γ-globin expression at levels that were significantly higher (>20% γ-globin of adult mouse globin) than those achieved in previous studies with a SB100x-transposase-based HDAd5/35++ system that mediates random integration. The ability to achieve therapeutically relevant transgene expression levels after in vivo HSC transduction and selection and targeted integration make our HDAd5/35++-based vector system a new tool in HSC gene therapy.

At the Intersection of Biomaterials and Gene Therapy: Progress in Non-viral Delivery of Nucleic Acids

Biomaterials play a critical role in technologies intended to deliver therapeutic agents in clinical settings. Recent explosion of our understanding of how cells utilize nucleic acids has garnered excitement to develop a range of older (e.g., antisense oligonucleotides, plasmid DNA and transposons) and emerging (e.g., short interfering RNA, messenger RNA and non-coding RNAs) nucleic acid agents for therapy of a wide range of diseases. This review will summarize biomaterials-centered advances to undertake effective utilization of nucleic acids for therapeutic purposes. We first review various types of nucleic acids and their unique abilities to deliver a range of clinical outcomes. Using recent advances in T-cell based therapy as a case in point, we summarize various possibilities for utilizing biomaterials to make an impact in this exciting therapeutic intervention technology, with the belief that this modality will serve as a therapeutic paradigm for other types of cellular therapies in the near future. We subsequently focus on contributions of biomaterials in emerging nucleic acid technologies, specifically focusing on the design of intelligent nanoparticles, deployment of mRNA as an alternative to plasmid DNA, long-acting (integrating) expression systems, and in vitro/in vivo expansion of engineered T-cells. We articulate the role of biomaterials in these emerging nucleic acid technologies in order to enhance the clinical impact of nucleic acids in the near future.

Non-viral therapeutic cell engineering with the Sleeping Beauty transposon system

Widespread treatment of human diseases with gene therapies necessitates the development of gene transfer vectors that integrate genetic information effectively, safely and economically. Indeed, significant efforts have been devoted to engineer novel tools that (i) achieve high-level stable gene transfer at low toxicity to the host cell; (ii) induce low levels of genotoxicity and possess a `safe' integration profile with a high proportion of integrations into safe genomic locations; and (iii) are associated with acceptable cost per treatment, and scalable/exportable vector production to serve large numbers of patients. Two decades after the discovery of the Sleeping Beauty (SB) transposon, it has been transformed into a vector system that is fulfilling these requirements. Here we review recent developments in vectorization of SB as a tool for gene therapy, and highlight clinical development of the SB system towards hematopoietic stem cell gene therapy and cancer immunotherapy.

Recent Advances in Preclinical Developments Using Adenovirus Hybrid Vectors

Adenovirus (Ad)-based vectors are efficient gene-transfer vehicles to deliver foreign DNA into living organisms, offering large cargo capacity and low immunogenicity and genotoxicity. As Ad shows low integration rates of their genomes into host chromosomes, vector-derived gene expression decreases due to continuous cell cycling in regenerating tissues and dividing cell populations. To overcome this hurdle, adenoviral delivery can be combined with mechanisms leading to maintenance of therapeutic DNA and long-term effects of the desired treatment. Several hybrid Ad vectors (AdV) exploiting various strategies for long-term treatment have been developed and characterized. This review summarizes recent developments of preclinical approaches using hybrid AdVs utilizing either the Sleeping Beauty transposase system for somatic integration into host chromosomes or designer nucleases, including transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein-9 nuclease for permanent gene editing. Further options on how to optimize these vectors further are discussed, which may lead to future clinical applications of these versatile gene-therapy tools.

Wide Awake and Ready to Move: 20 Years of Non-Viral Therapeutic Genome Engineering with the Sleeping Beauty Transposon System

Gene therapies will only become a widespread tool in the clinical treatment of human diseases with the advent of gene transfer vectors that integrate genetic information stably, safely, effectively, and economically. Two decades after the discovery of the Sleeping Beauty (SB) transposon, it has been transformed into a vector system that is fulfilling these requirements. SB may well overcome some of the limitations associated with viral gene transfer vectors and transient non-viral gene delivery approaches that are being used in the majority of ongoing clinical trials. The SB system has achieved a high level of stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, representing crucial steps that may permit its clinical use in the near future. This article reviews the most important aspects of SB as a tool for gene therapy, including aspects of its vectorization and genomic integration. As an illustration, the clinical development of the SB system toward gene therapy of age-related macular degeneration and cancer immunotherapy is highlighted.

Preclinical and clinical advances in transposon-based gene therapy

Transposons derived from Sleeping Beauty (SB), piggyBac (PB), or Tol2 typically require cotransfection of transposon DNA with a transposase either as an expression plasmid or mRNA. Consequently, this results in genomic integration of the potentially therapeutic gene into chromosomes of the desired target cells, and thus conferring stable expression. Non-viral transfection methods are typically preferred to deliver the transposon components into the target cells. However, these methods do not match the efficacy typically attained with viral vectors and are sometimes associated with cellular toxicity evoked by the DNA itself. In recent years, the overall transposition efficacy has gradually increased by codon optimization of the transposase, generation of hyperactive transposases, and/or introduction of specific mutations in the transposon terminal repeats. Their versatility enabled the stable genetic engineering in many different primary cell types, including stem/progenitor cells and differentiated cell types. This prompted numerous preclinical proof-of-concept studies in disease models that demonstrated the potential of DNA transposons for ex vivo and in vivo gene therapy. One of the merits of transposon systems relates to their ability to deliver relatively large therapeutic transgenes that cannot readily be accommodated in viral vectors such as full-length dystrophin cDNA. These emerging insights paved the way toward the first transposon-based phase I/II clinical trials to treat hematologic cancer and other diseases. Though encouraging results were obtained, controlled pivotal clinical trials are needed to corroborate the efficacy and safety of transposon-based therapies.

A Combined In Vivo HSC Transduction/Selection Approach Results in Efficient and Stable Gene Expression in Peripheral Blood Cells in Mice

We recently reported on an in vivo hematopoietic stem cell (HSC) gene therapy approach. It involves the subcutaneous injections of G-CSF/AMD3100 to mobilize HSCs from the bone marrow into the peripheral blood stream and the intravenous injection of an integrating helper-dependent adenovirus vector system. HSCs transduced in the periphery homed back to the bone marrow, where they persisted long-term. However, high transgene marking rates found in primitive bone marrow HSCs were not reflected in peripheral blood cells. Here, we tested small-molecule drugs to achieve selective mobilization and transduction of HSCs. We found more efficient GFP marking in bone marrow HSCs but no increased marking in the peripheral blood cells. We then used an in vivo HSC chemo-selection based on a mutant of the O⁶-methylguanine-DNA methyltransferase (mgmt^P140K) gene that confers resistance to O⁶-BG/BCNU and should give stably transduced HSCs a proliferation stimulus and allow for the selective survival and expansion of progeny cells. Short-term exposure of G-CSF/AMD3100-mobilized, in vivo-transduced mice to relatively low selection drug doses resulted in stable GFP expression in up to 80% of peripheral blood cells. Overall, the further improvement of our in vivo HSC transduction approach creates the basis for a simpler HSC gene therapy.

Gene Therapy with the Sleeping Beauty Transposon System

The widespread clinical implementation of gene therapy requires the ability to stably integrate genetic information through gene transfer vectors in a safe, effective, and economical manner. The latest generation of Sleeping Beauty (SB) transposon vectors fulfills these requirements, and may overcome limitations associated with viral gene transfer vectors and transient nonviral gene delivery approaches that are prevalent in ongoing clinical trials. The SB system enables high-level stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, thereby representing a highly attractive gene transfer strategy for clinical use. Here, we review the most important aspects of using SB for gene therapy, including vectorization as well as genomic integration features. We also illustrate the path to successful clinical implementation by highlighting the application of chimeric antigen receptor (CAR)-modified T cells in cancer immunotherapy.

Going non-viral: the Sleeping Beauty transposon system breaks on through to the clinical side

Molecular medicine has entered a high-tech age that provides curative treatments of complex genetic diseases through genetically engineered cellular medicinal products. Their clinical implementation requires the ability to stably integrate genetic information through gene transfer vectors in a safe, effective and economically viable manner. The latest generation of Sleeping Beauty (SB) transposon vectors fulfills these requirements, and may overcome limitations associated with viral gene transfer vectors and transient non-viral gene delivery approaches that are prevalent in ongoing pre-clinical and translational research. The SB system enables high-level stable gene transfer and sustained transgene expression in multiple primary human somatic cell types, thereby representing a highly attractive gene transfer strategy for clinical use. Here we review several recent refinements of the system, including the development of optimized transposons and hyperactive SB variants, the vectorization of transposase and transposon as mRNA and DNA minicircles (MCs) to enhance performance and facilitate vector production, as well as a detailed understanding of SB's genomic integration and biosafety features. This review also provides a perspective on the regulatory framework for clinical trials of gene delivery with SB, and illustrates the path to successful clinical implementation by using, as examples, gene therapy for age-related macular degeneration (AMD) and the engineering of chimeric antigen receptor (CAR)-modified T cells in cancer immunotherapy.