Translating Sleeping Beauty transposition into cellular therapies: victories and challenges

Construction of a Set of Novel Transposon Vectors for Efficient Silencing of Protein and lncRNA Genes via CRISPR Interference

In recent years, CRISPR interference (CRISPRi) technology of gene silencing has emerged as a promising alternative to RNA interference (RNAi) surpassing the latter in terms of efficiency and accuracy. Here, we describe the construction of a set of transposon vectors suitable for constitutive or tetracycline (doxycycline)-inducible silencing of genes of interest via CRISPRi method and conferring three different antibiotic resistances, using vectors available via Addgene repository. We have analyzed the performance of the new vectors in the silencing of mouse Adam10 and human lncRNA, NORAD. The empty vector variants can be used to efficiently silence any genes of interest.

Targeted delivery of a PD-1-blocking scFv by CD133-specific CAR-T cells using nonviral Sleeping Beauty transposition shows enhanced antitumour efficacy for advanced hepatocellular carcinoma

BACKGROUND

CD133 is considered a marker for cancer stem cells (CSCs) in several types of tumours, including hepatocellular carcinoma (HCC). Chimeric antigen receptor-specific T (CAR-T) cells targeting CD133-positive CSCs have emerged as a tool for the clinical treatment of HCC, but immunogenicity, the high cost of clinical-grade recombinant viral vectors and potential insertional mutagenesis limit their clinical application.

METHODS

CD133-specific CAR-T cells secreting PD-1 blocking scFv (CD133 CAR-T and PD-1 s cells) were constructed using a sleeping beauty transposon system from minicircle technology, and the antitumour efficacy of CD133 CAR-T and PD-1 s cells was analysed in vitro and in vivo.

RESULTS

A univariate analysis showed that CD133 expression in male patients at the late stage (II and III) was significantly associated with worse progression-free survival (PFS) (P = 0.0057) and overall survival (OS) (P = 0.015), and a multivariate analysis showed a trend toward worse OS (P = 0.041). Male patients with advanced HCC exhibited an approximately 20-fold higher PD-L1 combined positive score (CPS) compared with those with HCC at an early stage. We successfully generated CD133 CAR-T and PD-1 s cells that could secrete PD-1 blocking scFv based on a sleeping beauty system involving minicircle vectors. CD133 CAR-T and PD-1 s cells exhibited significant antitumour activity against HCC in vitro and in xenograft mouse models. Thus, CD133 CAR-T and PD-1 s cells may be a therapeutically tractable strategy for targeting CD133-positive CSCs in male patients with advanced HCC.

CONCLUSIONS

Our study provides a nonviral strategy for constructing CAR-T cells that could also secrete checkpoint blockade inhibitors based on a Sleeping Beauty system from minicircle vectors and revealed a potential benefit of this strategy for male patients with advanced HCC and high CD133 expression (median immunohistochemistry score > 2.284).

Challenges and new technologies in adoptive cell therapy

Adoptive cell therapies (ACTs) have existed for decades. From the initial infusion of tumor-infiltrating lymphocytes to the subsequent specific enhanced T cell receptor (TCR)-T and chimeric antigen receptor (CAR)-T cell therapies, many novel strategies for cancer treatment have been developed. Owing to its promising outcomes, CAR-T cell therapy has revolutionized the field of ACTs, particularly for hematologic malignancies. Despite these advances, CAR-T cell therapy still has limitations in both autologous and allogeneic settings, including practicality and toxicity issues. To overcome these challenges, researchers have focused on the application of CAR engineering technology to other types of immune cell engineering. Consequently, several new cell therapies based on CAR technology have been developed, including CAR-NK, CAR-macrophage, CAR-γδT, and CAR-NKT. In this review, we describe the development, advantages, and possible challenges of the aforementioned ACTs and discuss current strategies aimed at maximizing the therapeutic potential of ACTs. We also provide an overview of the various gene transduction strategies employed in immunotherapy given their importance in immune cell engineering. Furthermore, we discuss the possibility that strategies capable of creating a positive feedback immune circuit, as healthy immune systems do, could address the flaw of a single type of ACT, and thus serve as key players in future cancer immunotherapy.

Enhanced Biosafety of the Sleeping Beauty Transposon System by Using mRNA as Source of Transposase to Efficiently and Stably Transfect Retinal Pigment Epithelial Cells

Neovascular age-related macular degeneration (nvAMD) is characterized by choroidal neovascularization (CNV), which leads to retinal pigment epithelial (RPE) cell and photoreceptor degeneration and blindness if untreated. Since blood vessel growth is mediated by endothelial cell growth factors, including vascular endothelial growth factor (VEGF), treatment consists of repeated, often monthly, intravitreal injections of anti-angiogenic biopharmaceuticals. Frequent injections are costly and present logistic difficulties; therefore, our laboratories are developing a cell-based gene therapy based on autologous RPE cells transfected ex vivo with the pigment epithelium derived factor (PEDF), which is the most potent natural antagonist of VEGF. Gene delivery and long-term expression of the transgene are enabled by the use of the non-viral Sleeping Beauty (SB100X) transposon system that is introduced into the cells by electroporation. The transposase may have a cytotoxic effect and a low risk of remobilization of the transposon if supplied in the form of DNA. Here, we investigated the use of the SB100X transposase delivered as mRNA and showed that ARPE-19 cells as well as primary human RPE cells were successfully transfected with the Venus or the PEDF gene, followed by stable transgene expression. In human RPE cells, secretion of recombinant PEDF could be detected in cell culture up to one year. Non-viral ex vivo transfection using SB100X-mRNA in combination with electroporation increases the biosafety of our gene therapeutic approach to treat nvAMD while ensuring high transfection efficiency and long-term transgene expression in RPE cells.

Early Subcellular Hepatocellular Alterations in Mice Post Hydrodynamic Transfection: An Explorative Study

Hydrodynamic transfection (HT) or hydrodynamic tail vein injection (HTVi) is among the leading technique that is used to deliver plasmid genes mainly into the liver of live mice or rats. The DNA constructs are composed of coupled plasmids, while one contains the gene of interest that stably integrate into the hepatocyte genome with help of the other consisting sleeping beauty transposase system. The rapid injection of a large volume of DNA-solution through the tail vein induces an acute cardiac congestion that refluxed into the liver, mainly in acinus zone 3, also found through our EM study. Although, HT mediated hydrodynamic force can permeabilizes the fenestrated sinusoidal endothelium of liver, but the mechanism of plasmid incorporation into the hepatocytes remains unclear. Therefore, in the present study, we have hydrodynamically injected 2 mL volume of empty plasmid (transposon vector) or saline solution (control) into the tail vein of anesthetized C57BL/6J/129Sv mice. Liver tissue was resected at different time points from two animal group conditions, i.e., one time point per animal (1, 5, 10-20, 60 min or 24 and 48 hrs after HT) or multiple time points per animal (0, 1, 2, 5, 10, 20 min) and quickly fixed with buffered 4% osmium tetroxide. The tissues fed with only saline solution was also resected and fixed in the similar way. EM evaluation from the liver ultrathin sections reveals that swiftly after 1 min, the hepatocytes near to the central venule in the acinus zone 3 shows cytoplasmic membrane-bound vesicles. Such vesicles increased in both numbers and size to vacuoles and precisely often found in the proximity to the nucleus. Further, EM affirm these vacuoles are also optically empty and do not contain any electron dense material. Although, some of the other hepatocytes reveals sign of cell damage including swollen mitochondria, dilated endoplasmic reticulum, Golgi apparatus and disrupted plasma membrane, but most of the hepatocytes appeared normal. The ultrastructural findings in the mice injected with empty vector or saline injected control mice were similar. Therefore, we have interpreted the vacuole formation as nonspecific endocytosis without specific interactions at the plasma membrane.

Molecular and Functional Characterization of BDNF-Overexpressing Human Retinal Pigment Epithelial Cells Established by Sleeping Beauty Transposon-Mediated Gene Transfer

More and more patients suffer from multifactorial neurodegenerative diseases, such as age-related macular degeneration (AMD). However, their pathological mechanisms are still poorly understood, which complicates the development of effective therapies. To improve treatment of multifactorial diseases, cell-based gene therapy can be used to increase the expression of therapeutic factors. To date, there is no approved therapy for dry AMD, including late-stage geographic atrophy. We present a treatment option for dry AMD that transfers the brain-derived neurotrophic factor (BDNF) gene into retinal pigment epithelial (RPE) cells by electroporation using the plasmid-based Sleeping Beauty (SB) transposon system. ARPE-19 cells and primary human RPE cells were co-transfected with two plasmids encoding the SB100X transposase and the transposon carrying a BDNF transcription cassette. We demonstrated efficient expression and secretion of BDNF in both RPE cell types, which were further increased in ARPE-19 cell cultures exposed to hydrogen peroxide. BDNF-transfected cells exhibited lower apoptosis rates and stimulated neurite outgrowth in human SH-SY5Y cells. This study is an important step in the development of a cell-based BDNF gene therapy that could be applied as an advanced therapy medicinal product to treat dry AMD or other degenerative retinal diseases.

Advances and challenges of CAR T therapy and suitability of animal models (Review)

Chimeric antigen receptors (CARs) recently gained momentum in cancer treatment due to their ability to promote T-cell mediated responses to a specific tumor-associated antigen. CARs are part of the adoptive cell transfer (ACT) strategies that utilize patients' T lymphocytes, genetically engineered to kill cancer cells. However, despite the therapy's success against blood-related malignancies, treating solid tumors has not reached its fullest potential yet. The reasons include the complex suppressive tumor microenvironment, mutations on cancer cells' target receptors, lethal side-effects, restricted trafficking into the tumor, suboptimal persistence in vivo and the lack of animal models that faithfully resemble human tumor's immunological responses. Currently, rodent models are used to investigate the safety and efficacy of CAR therapies. However, these models are limited in representing the human disease faithfully, fail to predict the adverse treatment events and overestimate the efficacy of the therapy. On the other hand, spontaneously developed tumors in dogs are more suited in CAR research and their efficacy has been demonstrated in a number of diseases, including lymphoma, osteosarcoma and mammary tumors. The present review discusses the design and evolution of CARs, challenges of CAR in solid tumors, human and canine clinical trials and advantages of the canine model.

Chimeric Antigen Receptor T-Cells: An Overview of Concepts, Applications, Limitations, and Proposed Solutions

Adaptive immunity, orchestrated by B-cells and T-cells, plays a crucial role in protecting the body from pathogenic invaders and can be used as tools to enhance the body's defense mechanisms against cancer by genetically engineering these immune cells. Several strategies have been identified for cancer treatment and evaluated for their efficacy against other diseases such as autoimmune and infectious diseases. One of the most advanced technologies is chimeric antigen receptor (CAR) T-cell therapy, a pioneering therapy in the oncology field. Successful clinical trials have resulted in the approval of six CAR-T cell products by the Food and Drug Administration for the treatment of hematological malignancies. However, there have been various obstacles that limit the use of CAR T-cell therapy as the first line of defense mechanism against cancer. Various innovative CAR-T cell therapeutic designs have been evaluated in preclinical and clinical trial settings and have demonstrated much potential for development. Such trials testing the suitability of CARs against solid tumors and HIV are showing promising results. In addition, new solutions have been proposed to overcome the limitations of this therapy. This review provides an overview of the current knowledge regarding this novel technology, including CAR T-cell structure, different applications, limitations, and proposed solutions.

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.

Minicircles for CAR T Cell Production by Sleeping Beauty Transposition: A Technological Overview

Development and application of chimeric antigen receptor (CAR) T cell therapy has led to a breakthrough in the treatment of hematologic malignancies. In 2017, the FDA approved the first commercialized CD19-specific CAR T cell products for treatment of patients with B-cell malignancies. This success increased the desire to broaden the availability of CAR T cells to a larger patient cohort with hematological but also solid tumors. A critical factor of CAR T cell production is the stable and efficient delivery of the CAR transgene into T cells. This gene transfer is conventionally achieved by viral vectors. However, viral gene transfer is not conducive to affordable, scalable, and timely manufacturing of CAR T cell products. Thus, there is a necessity for developing alternative nonviral engineering platforms, which are more cost-effective, less complex to handle and which provide the scalability requirement for a globally available therapy.One alternative method for engineering of T cells is the nonviral gene transfer by Sleeping Beauty (SB) transposition. Electroporation with two nucleic acids is sufficient to achieve stable CAR transfer into T cells. One of these vectors has to encode the gene of interest, which is the CAR , the second one a recombinase called SB transposase, the enzyme that catalyzes integration of the transgene into the host cell genome. As nucleic acids are easy to produce and handle SB gene transfer has the potential to provide scalability, cost-effectiveness, and feasibility for widespread use of CAR T cell therapies.Nevertheless, the electroporation of two large-size plasmid vectors into T cells leads to high T cell toxicity and low gene transfer rates and has hindered the prevalent clinical application of the SB system. To circumvent these limitations, conventional plasmid vectors can be replaced by minimal-size vectors called minicircles (MC ). MCs are DNA vectors that lack the plasmid backbone, which is relevant for propagation in bacteria, but has no function in a human cell. Thus, their size is drastically reduced compared to conventional plasmids. It has been demonstrated that MC-mediated SB CAR transposition into T cells enhances their viability and gene transfer rate enabling the production of therapeutic doses of CAR T cells. These improvements make CAR SB transposition from MC vectors a promising alternative for engineering of clinical grade CAR T cells.

A Novel off-the-Shelf Trastuzumab-Armed NK Cell Therapy (ACE1702) Using Antibody-Cell-Conjugation Technology

Simple Summary

Chimeric antigen receptor T cell therapy has shown its potency against hematologic malignancies in autologous settings but also limited success against solid tumors with severe adverse events, including fatal cases of cytokine releasing syndrome. The aim of this research is to develop a novel off-the-shelf natural killer cell therapy against HER2-expressing cancers using Antibody-Cell Conjugation (ACC) technology and the endogenous CD16-expressing oNK cell line. ACE1702, trastuzumab-armed oNK cells with γ irradiation and cryopreservation, present superior in vitro and in vivo potency against HER2-expressing cancer cells and shows no tumorigenic potential, indicating the clinical application fighting HER2-expressing solid tumors. These findings suggest that ACC technology can be applied to allogeneic immune cells to provide off-the-shelf therapies for cancer patients.

Abstract

Natural killer (NK) cells harbor efficient cytotoxicity against tumor cells without causing life-threatening cytokine release syndrome (CRS) or graft-versus-host disease (GvHD). When compared to chimeric antigen receptor (CAR) technology, Antibody-Cell Conjugation (ACC) technology has been developed to provide an efficient platform to arm immune cells with cancer-targeting antibodies to recognize and attack cancer cells. Recently, we established an endogenous CD16-expressing oNK cell line (oNK) with a favorable expression pattern of NK activation/inhibitory receptors. In this study, we applied ACC platform to conjugate oNK with trastuzumab and an anti-human epidermal growth factor receptor 2 (HER2) antibody. Trastuzumab-conjugated oNK, ACE-oNK-HER2, executed in vitro and in vivo cytotoxicity against HER2-expressing cancer cells and secretion of IFNγ. The irradiated and cryopreserved ACE-oNK-HER2, designated as ACE1702, retained superior HER2-specific in vitro and in vivo potency with no tumorigenic potential. In conclusion, this study provides the evidence to support the potential clinical application of ACE1702 as a novel off-the-shelf NK cell therapy against HER2-expressing solid tumors.

CARAMBA: a first-in-human clinical trial with SLAMF7 CAR-T cells prepared by virus-free Sleeping Beauty gene transfer to treat multiple myeloma

Clinical development of chimeric antigen receptor (CAR)-T-cell therapy has been enabled by advances in synthetic biology, genetic engineering, clinical-grade manufacturing, and complex logistics to distribute the drug product to treatment sites. A key ambition of the CARAMBA project is to provide clinical proof-of-concept for virus-free CAR gene transfer using advanced Sleeping Beauty (SB) transposon technology. SB transposition in CAR-T engineering is attractive due to the high rate of stable CAR gene transfer enabled by optimized hyperactive SB100X transposase and transposon combinations, encoded by mRNA and minicircle DNA, respectively, as preferred vector embodiments. This approach bears the potential to facilitate and expedite vector procurement, CAR-T manufacturing and distribution, and the promise to provide a safe, effective, and economically sustainable treatment. As an exemplary and novel target for SB-based CAR-T cells, the CARAMBA consortium has selected the SLAMF7 antigen in multiple myeloma. SLAMF7 CAR-T cells confer potent and consistent anti-myeloma activity in preclinical assays in vitro and in vivo. The CARAMBA clinical trial (Phase-I/IIA; EudraCT: 2019-001264-30) investigates the feasibility, safety, and anti-myeloma efficacy of autologous SLAMF7 CAR-T cells. CARAMBA is the first clinical trial with virus-free CAR-T cells in Europe, and the first clinical trial that uses advanced SB technology worldwide.

CAR T-Cell Production Using Nonviral Approaches

Chimeric antigen receptor T-cells (CAR T-cells) represent a novel and promising approach in cancer immunotherapy. According to the World Health Organization (WHO), the number of oncological patients is steadily growing in developed countries despite immense progress in oncological treatments, and the prognosis of individual patients is still relatively poor. Exceptional results have been recorded for CAR T-cell therapy in patients suffering from B-cell malignancies. This success opens up the possibility of using the same approach for other types of cancers. To date, the most common method for CAR T-cell generation is the use of viral vectors. However, dealing with virus-derived vectors brings possible obstacles in the CAR T-cell manufacturing process owing to strict regulations and high cost demands. Alternative approaches may facilitate further development and the transfer of the method to clinical practice. The most promising substitutes for virus-derived vectors are transposon-derived vectors, most commonly sleeping beauty, which offer great coding capability and a safe integration profile while maintaining a relatively low production cost. This review is aimed at summarizing the state of the art of nonviral approaches in CAR T-cell generation, with a unique perspective on the conditions in clinical applications and current Good Manufacturing Practice. If CAR T-cell therapy is to be routinely used in medical practice, the manufacturing cost and complexity need to be as low as possible, and transposon-based vectors seem to meet these criteria better than viral-based vectors.

Immune cell labelling and tracking: implications for adoptive cell transfer therapies

Background

The understanding of the role of different immune cell subsets that infiltrate tumors can help researchers in developing new targeted immunotherapies to reactivate or reprogram them against cancer. In addition to conventional drugs, new cell-based therapies, like adoptive cell transfer, proved to be successful in humans. Indeed, after the approval of anti-CD19 CAR-T cell therapy, researchers are trying to extend this approach to other cancer or cell types.

Main body

This review focuses on the different approaches to non-invasively monitor the biodistribution, trafficking and fate of immune therapeutic cells, evaluating their efficacy at preclinical and clinical stages. PubMed and Scopus databases were searched for published articles on the imaging of cell tracking in humans and preclinical models.

Conclusion

Labelling specific immune cell subtypes with specific radiopharmaceuticals, contrast agents or optical probes can elucidate new biological mechanisms or predict therapeutic outcome of adoptive cell transfer therapies. To date, no technique is considered the gold standard to image immune cells in adoptive cell transfer therapies.

The Evolution of Gene Therapy in the Treatment of Metabolic Liver Diseases

Monogenic metabolic disorders of hepatic origin number in the hundreds, and for many, liver transplantation remains the only cure. Liver-targeted gene therapy is an attractive treatment modality for many of these conditions, and there have been significant advances at both the preclinical and clinical stages. Viral vectors, including retroviruses, lentiviruses, adenovirus-based vectors, adeno-associated viruses and simian virus 40, have differing safety, efficacy and immunogenic profiles, and several of these have been used in clinical trials with variable success. In this review, we profile viral vectors and non-viral vectors, together with various payloads, including emerging therapies based on RNA, that are entering clinical trials. Genome editing technologies are explored, from earlier to more recent novel approaches that are more efficient, specific and safe in reaching their target sites. The various curative approaches for the multitude of monogenic hepatic metabolic disorders currently at the clinical development stage portend a favorable outlook for this class of genetic disorders.

Innovative CAR-T Cell Therapy for Solid Tumor; Current Duel between CAR-T Spear and Tumor Shield

Novel engineered T cells containing chimeric antigen receptors (CAR-T cells) that combine the benefits of antigen recognition and T cell response have been developed, and their effect in the anti-tumor immunotherapy of patients with relapsed/refractory leukemia has been dramatic. Thus, CAR-T cell immunotherapy is rapidly emerging as a new therapy. However, it has limitations that prevent consistency in therapeutic effects in solid tumors, which accounts for over 90% of all cancer patients. Here, we review the literature regarding various obstacles to CAR-T cell immunotherapy for solid tumors, including those that cause CAR-T cell dysfunction in the immunosuppressive tumor microenvironment, such as reactive oxygen species, pH, O₂, immunosuppressive cells, cytokines, and metabolites, as well as those that impair cell trafficking into the tumor microenvironment. Next-generation CAR-T cell therapy is currently undergoing clinical trials to overcome these challenges. Therefore, novel approaches to address the challenges faced by CAR-T cell immunotherapy in solid tumors are also discussed here.

Dual-use nano-neurotechnology

The chemical and biological nonproliferation regime stands at a watershed moment, when failure seems a real possibility. After the unsuccessful outcome of the 2016 Eighth Review Conference, the future of the Biological and Toxin Weapons Convention is uncertain. As the Chemical Weapons Convention (CWC) approaches its Fourth Review Conference in 2018, it has almost completed removing the huge stocks of chemical weapons, but it now faces the difficult organizational task of moving its focus to preventing the reemergence of chemical weapons at a time when the international security situation appears to be increasingly more difficult and dangerous. In this article, we assess the current and near-term state (5-10 years) and impact of three related areas of science and technology that could be of dual-use concern: targeted delivery of agents to the central nervous system (CNS), particularly by means of nanotechnology; direct impact of nanomaterials on synaptic functions in the CNS; and neuronal circuits in the brain that might be targeted by those with hostile intent. We attempt to assess the implications of our findings, particularly for the consideration of the problem of state-level interest in so-called nonlethal incapacitating chemical agents for law enforcement at the CWC Review Conference in 2018, but also more generally for the longer-term future of the chemical and biological nonproliferation regime.

CAR T Cells for Solid Tumors: New Strategies for Finding, Infiltrating, and Surviving in the Tumor Microenvironment

Chimeric antigen receptor (CAR) T cells, T cells that have been genetically engineered to express a receptor that recognizes a specific antigen, have given rise to breakthroughs in treating hematological malignancies. However, their success in treating solid tumors has been limited. The unique challenges posed to CAR T cell therapy by solid tumors can be described in three steps: finding, entering, and surviving in the tumor. The use of dual CAR designs that recognize multiple antigens at once and local administration of CAR T cells are both strategies that have been used to overcome the hurdle of localization to the tumor. Additionally, the immunosuppressive tumor microenvironment has implications for T cell function in terms of differentiation and exhaustion, and combining CARs with checkpoint blockade or depletion of other suppressive factors in the microenvironment has shown very promising results to mitigate the phenomenon of T cell exhaustion. Finally, identifying and overcoming mechanisms associated with dysfunction in CAR T cells is of vital importance to generating CAR T cells that can proliferate and successfully eliminate tumor cells. The structure and costimulatory domains chosen for the CAR may play an important role in the overall function of CAR T cells in the TME, and “armored” CARs that secrete cytokines and third- and fourth-generation CARs with multiple costimulatory domains offer ways to enhance CAR T cell function.

Innovative Therapy for Alzheimer's Disease-With Focus on Biodelivery of NGF

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder associated with abnormal protein modification, inflammation and memory impairment. Aggregated amyloid beta (Aβ) and phosphorylated tau proteins are medical diagnostic features. Loss of memory in AD has been associated with central cholinergic dysfunction in basal forebrain, from where the cholinergic circuitry projects to cerebral cortex and hippocampus. Various reports link AD progression with declining activity of cholinergic neurons in basal forebrain. The neurotrophic molecule, nerve growth factor (NGF), plays a major role in the maintenance of cholinergic neurons integrity and function, both during development and adulthood. Numerous studies have also shown that NGF contributes to the survival and regeneration of neurons during aging and in age-related diseases such as AD. Changes in neurotrophic signaling pathways are involved in the aging process and contribute to cholinergic and cognitive decline as observed in AD. Further, gradual dysregulation of neurotrophic factors like NGF and brain derived neurotrophic factor (BDNF) have been reported during AD development thus intensifying further research in targeting these factors as disease modifying therapies against AD. Today, there is no cure available for AD and the effects of the symptomatic treatment like cholinesterase inhibitors (ChEIs) and memantine are transient and moderate. Although many AD treatment studies are being carried out, there has not been any breakthrough and new therapies are thus highly needed. Long-term effective therapy for alleviating cognitive impairment is a major unmet need. Discussion and summarizing the new advancements of using NGF as a potential therapeutic implication in AD are important. In summary, the intent of this review is describing available experimental and clinical data related to AD therapy, priming to gain additional facts associated with the importance of NGF for AD treatment, and encapsulated cell biodelivery (ECB) as an efficient tool for NGF delivery.

Evolution-guided evaluation of the inverted terminal repeats of the synthetic transposon Sleeping Beauty

Sleeping Beauty (SB) is a synthetic Tc1/mariner transposon that is widely used for genetic engineering in vertebrates, including humans. Its sequence was derived from a consensus of sequences found in fish species including the Atlantic salmon (Salmo salar). One of the functional components of SB, the transposase enzyme, has been subject to extensive mutagenesis yielding hyperactive protein variants for advanced applications. The second functional component, the transposon inverted terminal repeats (ITRs), has so far not been extensively modified, mainly due to a lack of natural sequence information. Importantly, as genome sequences become available, they can provide a rich source of information for a refined molecular definition of the functional components of these transposons. Here we have mined the Salmo salar genome for a comprehensive set of transposon sequences that were used to build a refined consensus sequence. We synthetically produced the new consensus ITR sequences and used them to build a new transposon, the performance of which has been tested in cell-based transposition assays. The consensus sequence did not support enhanced transposition, suggesting alternative mechanisms responsible for the preferential amplification of these sequence variants in the salmon genome.

Rigidity and flexibility characteristics of DD[E/D]-transposases Mos1 and Sleeping Beauty

DD[E/D]-transposases catalyze the multistep reaction of cut-and-paste DNA transposition. Structurally, several DD[E/D]-transposases have been characterized, revealing a multi-domain structure with the catalytic domain possessing the RNase H-like structural motif that brings three catalytic residues (D, D, and E or D) into close proximity for the catalysis. However, the dynamic behavior of DD[E/D]-transposases during transposition remains poorly understood. Here, we analyze the rigidity and flexibility characteristics of two representative DD[E/D]-transposases Mos1 and Sleeping Beauty (SB) using the minimal distance constraint model (mDCM). We find that the catalytic domain of both transposases is globally rigid, with the notable exception of the clamp loop being flexible in the DNA-unbound form. Within this globally rigid structure, the central β-sheet of the RNase H-like motif is much less rigid in comparison to its surrounding α-helices, forming a cage-like structure. The comparison of the original SB transposase to its hyperactive version SB100X reveals the region where the change in flexibility/rigidity correlates with increased activity. This region is found to be within the RNase H-like structural motif and comprise the loop leading from beta-strand B3 to helix H1, helices H1 and H2, which are located on the same side of the central beta-sheet, and the loop between helix H3 and beta-strand B5. We further identify the RKEN214-217DAVQ mutations of the set of hyperactive mutations within the catalytic domain of SB transposase to be the driving factor that induces change in residue-pair rigidity correlations within SB transposase. Given that a signature RNase H-like structural motif is found in DD[E/D]-transposases and, more broadly, in a large superfamily of polynucleotidyl transferases, our results are relevant to these proteins as well.

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.

Development of a Mouse Model of Prostate Cancer Using the Sleeping Beauty Transposon and Electroporation

The Sleeping Beauty (SB) transposon system is non-viral and uses insertional mutagenesis, resulting in the permanent expression of transferred genes. Although the SB transposon is a useful method for establishing a mouse tumor model, there has been difficulty in using this method to generate tumors in the prostate. In the present study, electroporation was used to enhance the transfection efficiency of the SB transposon. To generate tumors, three constructs (a c-Myc expression cassette, a HRAS (HRas proto-oncogene, GTPase) expression cassette and a shRNA against p53) contained within the SB transposon plasmids were directly injected into the prostate. Electroporation was conducted on the injection site after the injection of the DNA plasmid. Following the tumorigenesis, the tumors were monitored by animal PET imaging and identified by gross observation. After this, the tumors were characterized by using histological and immunohistochemical techniques. The expression of the targeted genes was analyzed by Real-Time qRT-PCR. All mice subjected to the injection were found to have prostate tumors, which was supported by PSA immunohistochemistry. To our knowledge, this is the first demonstration of tumor induction in the mouse prostate using the electroporation-enhanced SB transposon system in combination with c-Myc, HRAS and p53. This model serves as a valuable resource for the future development of SB-induced mouse models of cancer.

Improved molecular platform for the gene therapy of rare diseases by liver protein secretion

Many rare monogenic diseases are treated by protein replacement therapy, in which the missing protein is repetitively administered to the patient. However, in several cases, the missing protein is required at a high and sustained level, which renders protein therapy far from being adequate. As an alternative, a gene therapy treatment ensuring a sustained effectiveness would be particularly valuable. Liver is an optimal organ for the secretion and systemic distribution of a therapeutic transgene product. Cutting edge non-viral gene therapy tools were tested in order to produce a high and sustained level of therapeutic protein secretion by the liver using the hydrodynamic delivery technique. The use of S/MAR matrix attachment region provided a slight, however not statistically significant, increase in the expression of a reporter gene in the liver. We have selected the von Willebrand Factor (vWF) gene as a particularly challenging large gene (8.4 kb) for liver delivery and expression, and also because a high vWF blood concentration is required for disease correction. By using the optimized miniplasmid pFAR free of antibiotic resistance gene together with the Sleeping Beauty transposon and the hyperactive SB100X transposase, we have obtained a sustainable level of vWFblood secretion by the liver, at 65% of physiological level. Our results point to the general use of this plasmid platform using the liver as a protein factory to treat numerous rare disorders by gene therapy.

Efficient Non-viral Gene Delivery into Human Hematopoietic Stem Cells by Minicircle Sleeping Beauty Transposon Vectors

The Sleeping Beauty (SB) transposon system is a non-viral gene delivery platform that combines simplicity, inexpensive manufacture, and favorable safety features in the context of human applications. However, efficient correction of hematopoietic stem and progenitor cells (HSPCs) with non-viral vector systems, including SB, demands further refinement of gene delivery techniques. We set out to improve SB gene transfer into hard-to-transfect human CD34⁺ cells by vectorizing the SB system components in the form of minicircles that are devoid of plasmid backbone sequences and are, therefore, significantly reduced in size. As compared to conventional plasmids, delivery of the SB transposon system as minicircle DNA is ∼20 times more efficient, and it is associated with up to a 50% reduction in cellular toxicity in human CD34⁺ cells. Moreover, providing the SB transposase in the form of synthetic mRNA enabled us to further increase the efficacy and biosafety of stable gene delivery into hematopoietic progenitors ex vivo. Genome-wide insertion site profiling revealed a close-to-random distribution of SB transposon integrants, which is characteristically different from gammaretroviral and lentiviral integrations in HSPCs. Transplantation of gene-marked CD34⁺ cells in immunodeficient mice resulted in long-term engraftment and hematopoietic reconstitution, which was most efficient when the SB transposase was supplied as mRNA and nucleofected cells were maintained for 4–8 days in culture before transplantation. Collectively, implementation of minicircle and mRNA technologies allowed us to further refine the SB transposon system in the context of HSPC gene delivery to ultimately meet clinical demands of an efficient and safe non-viral gene therapy protocol.

Transposase-mediated gene modulation in the placenta

The placenta is an organ vital to fetal development as well as the maintenance of a healthy pregnancy and plays a crucial role in developmental programming of the fetus. The mechanisms that link intrauterine milieu, fetal health and disease development later in life are poorly understood. Placenta-specific gene modulation, both by generating transgenic animals as well as by developing methods for in vivo genetic modifications is a growing area of interest as this approach provides the opportunity to investigate the role of particular genes or gene networks in regulating placental function and fetal growth. Furthermore, in vivo placental gene transfer may be adapted to treat humans in the future and could be used as an early intervention strategy for a wide range of pregnancy complications. This review is an overview of transposase-based methods available for both transgenic animal generation and in vivo placental gene modifications with an emphasis on piggyBac-based systems.

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.

Long-Term PEDF Release in Rat Iris and Retinal Epithelial Cells after Sleeping Beauty Transposon-Mediated Gene Delivery

Pigment epithelium derived factor (PEDF) is a potent antiangiogenic, neurotrophic, and neuroprotective molecule that is the endogenous inhibitor of vascular endothelial growth factor (VEGF) in the retina. An ex vivo gene therapy approach based on transgenic overexpression of PEDF in the eye is assumed to rebalance the angiogenic-antiangiogenic milieu of the retina, resulting in growth regression of choroidal blood vessels, the hallmark of neovascular age-related macular degeneration. Here, we show that rat pigment epithelial cells can be efficiently transfected with the PEDF-expressing non-viral hyperactive Sleeping Beauty transposon system delivered in a form free of antibiotic resistance marker miniplasmids. The engineered retinal and iris pigment epithelium cells secrete high (141 ± 13 and 222 ± 14 ng) PEDF levels in 72 hr in vitro. In vivo studies showed cell survival and insert expression during at least 4 months. Transplantation of the engineered cells to the subretinal space of a rat model of choroidal neovascularization reduces almost 50% of the development of new vessels.

Swine IRF3/IRF7 attenuates inflammatory responses through TLR4 signaling pathway

To explore the role of IRF3/IRF7 during inflammatory responses, we investigated the effects of swine IRF3/IRF7 on TLR4 signaling pathway and inflammatory factors expression in porcine kidney epithelial PK15 cell lines. We successfully constructed eukaryotic vectors PB-IRF3 and PB-IRF7, transfected these vectors into PK15 cells and observed GFP under a fluorescence microscope. In addition, RT-PCR was also used to detect transfection efficiency. We found that IRF3/IRF7 was efficiently overexpressed in PK15 cells. Moreover, we evaluated the effects of IRF3/IRF7 on the TLR4 signaling pathway and inflammatory factors by RT-PCR. Transfected cells were treated with lipopolysaccharide (LPS) alone, or in combination with a TBK1 inhibitor (LiCl). We revealed that IRF3/IRF7 enhanced IFNα production, and decreased IL-6 mRNA expression. Blocking the TBK1 pathway, inhibited the changes in IFNα, but not IL-6 mRNA. This illustrated that IRF3/IRF7 enhanced IFNα production through TLR4/TBK1 signaling pathway and played an anti-inflammatory role, while IRF3/IRF7 decreased IL-6 expression independent of the TBK1 pathway. Trends in MyD88, TRAF6, TBK1 and NFκB mRNA variation were similar in all treatments. LPS increased MyD88, TRAF6, TBK1 and NFκB mRNA abundance in PBR3/PBR7 and PBv cells, while LiCl blocked the LPS-mediated effects. The levels of these four factors in PBR3/PBR7 cells were higher than those in PBv. These results demonstrated that IRF3/IRF7 regulated the inflammatory response through the TLR4 signaling pathway. Overexpression of swine IRF3/IRF7 in PK15 cells induced type I interferons production, and attenuated inflammatory responses through TLR4 signaling pathway.

Prolonged Expression of Secreted Enzymes in Dogs After Liver-Directed Delivery of Sleeping Beauty Transposons: Implications for Non-Viral Gene Therapy of Systemic Disease

The non-viral, integrating Sleeping Beauty (SB) transposon system is efficient in treating systemic monogenic disease in mice, including hemophilia A and B caused by deficiency of blood clotting factors and mucopolysaccharidosis types I and VII caused by α-L-iduronidase (IDUA) and β-glucuronidase (GUSB) deficiency, respectively. Modified approaches of the hydrodynamics-based procedure to deliver transposons to the liver in dogs were recently reported. Using the transgenic canine reporter secreted alkaline phosphatase (cSEAP), transgenic protein in the plasma was demonstrated for up to 6 weeks post infusion. This study reports that immunosuppression of dogs with gadolinium chloride (GdCl₃) prolonged the presence of cSEAP in the circulation up to 5.5 months after a single vector infusion. Transgene expression declined gradually but appeared to stabilize after about 2 months at approximately fourfold baseline level. Durability of transgenic protein expression in the plasma was inversely associated with transient increase of liver enzymes alanine transaminase and aspartate transaminase in response to the plasmid delivery procedure, which suggests a deleterious effect of hepatocellular toxicity on transgene expression. GdCl₃ treatment was ineffective for repeat vector infusions. In parallel studies, dogs were infused with potentially therapeutic transposons. Activities of transgenic IDUA and GUSB in plasma peaked at 50-350% of wildtype, but in the absence of immunosuppression lasted only a few days. Transposition was detectable by excision assay only when the most efficient transposase, SB100X, was used. Dogs infused with transposons encoding canine clotting factor IX (cFIX) were treated with GdCl₃ and showed expression profiles similar to those in cSEAP-infused dogs, with expression peaking at 40% wt (2 μg/mL). It is concluded that GdCl₃ can support extended transgene expression after hydrodynamic introduction of SB transposons in dogs, but that alternative regimens will be required to achieve therapeutic levels of transgene products.

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.

NMR solution structure of the RED subdomain of the Sleeping Beauty transposase

DNA transposons can be employed for stable gene transfer in vertebrates. The Sleeping Beauty (SB) DNA transposon has been recently adapted for human application and is being evaluated in clinical trials, however its molecular mechanism is not clear. SB transposition is catalyzed by the transposase enzyme, which is a multi-domain protein containing the catalytic and the DNA-binding domains. The DNA-binding domain of the SB transposase contains two structurally independent subdomains, PAI and RED. Recently, the structures of the catalytic domain and the PAI subdomain have been determined, however no structural information on the RED subdomain and its interactions with DNA has been available. Here, we used NMR spectroscopy to determine the solution structure of the RED subdomain and characterize its interactions with the transposon DNA.

Engineering of PEDF-Expressing Primary Pigment Epithelial Cells by the SB Transposon System Delivered by pFAR4 Plasmids

Neovascular age-related macular degeneration (nvAMD) is characterized by choroidal blood vessels growing into the subretinal space, leading to retinal pigment epithelial (RPE) cell degeneration and vision loss. Vessel growth results from an imbalance of pro-angiogenic (e.g., vascular endothelial growth factor [VEGF]) and anti-angiogenic factors (e.g., pigment epithelium-derived factor [PEDF]). Current treatment using intravitreal injections of anti-VEGF antibodies improves vision in about 30% of patients but may be accompanied by side effects and non-compliance. To avoid the difficulties posed by frequent intravitreal injections, we have proposed the transplantation of pigment epithelial cells modified to overexpress human PEDF. Stable transgene integration and expression is ensured by the hyperactive Sleeping Beauty transposon system delivered by pFAR4 miniplasmids, which have a backbone free of antibiotic resistance markers. We demonstrated efficient expression of the PEDF gene and an optimized PEDF cDNA sequence in as few as 5 × 10³ primary cells. At 3 weeks post-transfection, PEDF secretion was significantly elevated and long-term follow-up indicated a more stable secretion by cells transfected with the optimized PEDF transgene. Analysis of transgene insertion sites in human RPE cells showed an almost random genomic distribution. The results represent an important contribution toward a clinical trial aiming at a non-viral gene therapy of nvAMD.

Sleeping Beauty transposition: from biology to applications

Sleeping Beauty (SB) is the first synthetic DNA transposon that was shown to be active in a wide variety of species. Here, we review studies from the last two decades addressing both basic biology and applications of this transposon. We discuss how host-transposon interaction modulates transposition at different steps of the transposition reaction. We also discuss how the transposon was translated for gene delivery and gene discovery purposes. We critically review the system in clinical, pre-clinical and non-clinical settings as a non-viral gene delivery tool in comparison with viral technologies. We also discuss emerging SB-based hybrid vectors aimed at combining the attractive safety features of the transposon with effective viral delivery. The success of the SB-based technology can be fundamentally attributed to being able to insert fairly randomly into genomic regions that allow stable long-term expression of the delivered transgene cassette. SB has emerged as an efficient and economical toolkit for safe and efficient gene delivery for medical applications.

Phase I trials using Sleeping Beauty to generate CD19-specific CAR T cells

BACKGROUND

T cells expressing antigen-specific chimeric antigen receptors (CARs) improve outcomes for CD19-expressing B cell malignancies. We evaluated a human application of T cells that were genetically modified using the Sleeping Beauty (SB) transposon/transposase system to express a CD19-specific CAR.

METHODS

T cells were genetically modified using DNA plasmids from the SB platform to stably express a second-generation CD19-specific CAR and selectively propagated ex vivo with activating and propagating cells (AaPCs) and cytokines. Twenty-six patients with advanced non-Hodgkin lymphoma and acute lymphoblastic leukemia safely underwent hematopoietic stem cell transplantation (HSCT) and infusion of CAR T cells as adjuvant therapy in the autologous (n = 7) or allogeneic settings (n = 19).

RESULTS

SB-mediated genetic transposition and stimulation resulted in 2,200- to 2,500-fold ex vivo expansion of genetically modified T cells, with 84% CAR expression, and without integration hotspots. Following autologous HSCT, the 30-month progression-free and overall survivals were 83% and 100%, respectively. After allogeneic HSCT, the respective 12-month rates were 53% and 63%. No acute or late toxicities and no exacerbation of graft-versus-host disease were observed. Despite a low antigen burden and unsupportive recipient cytokine environment, CAR T cells persisted for an average of 201 days for autologous recipients and 51 days for allogeneic recipients.

CONCLUSIONS

CD19-specific CAR T cells generated with SB and AaPC platforms were safe, and may provide additional cancer control as planned infusions after HSCT. These results support further clinical development of this nonviral gene therapy approach.

TRIAL REGISTRATION

Autologous, NCT00968760; allogeneic, NCT01497184; long-term follow-up, NCT01492036.

FUNDING

National Cancer Institute, private foundations, and institutional funds. Please see Acknowledgments for details.

Enhanced CAR T-cell engineering using non-viral Sleeping Beauty transposition from minicircle vectors

Immunotherapy with T cell modified with gamma-retroviral or lentiviral (LV) vectors to express a chimeric antigen receptor (CAR) has shown remarkable efficacy in clinical trials. However, the potential for insertional mutagenesis and genotoxicity of viral vectors is a safety concern, and their cost and regulatory demands a roadblock for rapid and broad clinical translation. Here, we demonstrate that CAR T cells can be engineered through non-viral Sleeping Beauty (SB) transposition of CAR genes from minimalistic DNA vectors called minicircles (MCs). We analyzed genomic distribution of SB and LV integrations and show that a significantly higher proportion of MC-derived CAR transposons compared with LV integrants had occurred outside of highly expressed and cancer-related genes into genomic safe harbor loci that are not expected to cause mutagenesis or genotoxicity. CD19-CAR T cells engineered with our enhanced SB approach conferred potent reactivity in vitro and eradicated lymphoma in a xenograft model in vivo. Intriguingly, electroporation of SB MCs is substantially more effective and less toxic compared with conventional plasmids, and enables cost-effective rapid preparation of therapeutic CAR T-cell doses. This approach sets a new standard in advanced cellular and gene therapy and will accelerate and increase the availability of CAR T-cell therapy to treat hematologic malignancies.

Genetic Modification of T Cells

Gene transfer technology and its application to human gene therapy greatly expanded in the last decade. One area of investigation that appears particularly promising is the transfer of new genetic material into T cells for the potential treatment of cancer. Herein, we describe several core technologies that now yield high-efficiency gene transfer into primary human T cells. These gene transfer techniques include viral-based gene transfer methods based on modified Retroviridae and non-viral methods such as DNA-based transposons and direct transfer of mRNA by electroporation. Where specific examples are cited, we emphasize the transfer of chimeric antigen receptors (CARs) to T cells, which permits engineered T cells to recognize potential tumor antigens.

Sleeping Beauty Transposition

Sleeping Beauty (SB) is a synthetic transposon that was constructed based on sequences of transpositionally inactive elements isolated from fish genomes. SB is a Tc1/mariner superfamily transposon following a cut-and-paste transpositional reaction, during which the element-encoded transposase interacts with its binding sites in the terminal inverted repeats of the transposon, promotes the assembly of a synaptic complex, catalyzes excision of the element out of its donor site, and integrates the excised transposon into a new location in target DNA. SB transposition is dependent on cellular host factors. Transcriptional control of transposase expression is regulated by the HMG2L1 transcription factor. Synaptic complex assembly is promoted by the HMGB1 protein and regulated by chromatin structure. SB transposition is highly dependent on the nonhomologous end joining (NHEJ) pathway of double-strand DNA break repair that generates a transposon footprint at the excision site. Through its association with the Miz-1 transcription factor, the SB transposase downregulates cyclin D1 expression that results in a slowdown of the cell-cycle in the G1 phase, where NHEJ is preferentially active. Transposon integration occurs at TA dinucleotides in the target DNA, which are duplicated at the flanks of the integrated transposon. SB shows a random genome-wide insertion profile in mammalian cells when launched from episomal vectors and "local hopping" when launched from chromosomal donor sites. Some of the excised transposons undergo a self-destructive autointegration reaction, which can partially explain why longer elements transpose less efficiently. SB became an important molecular tool for transgenesis, insertional mutagenesis, and gene therapy.

A Broad Range of Dose Optima Achieve High-level, Long-term Gene Expression After Hydrodynamic Delivery of Sleeping Beauty Transposons Using Hyperactive SB100x Transposase

The Sleeping Beauty (SB) transposon system has been shown to enable long-term gene expression by integrating new sequences into host cell chromosomes. We found that the recently reported SB100x hyperactive transposase conferred a surprisingly high level of long-term expression after hydrodynamic delivery of luciferase-encoding reporter transposons in the mouse. We conducted dose-ranging studies to determine the effect of varying the amount of SB100x transposase-encoding plasmid (pCMV-SB100x) at a set dose of luciferase transposon and of varying the amount of transposon-encoding DNA at a set dose of pCMV-SB100x in hydrodynamically injected mice. Animals were immunosuppressed using cyclophosphamide in order to prevent an antiluciferase immune response. At a set dose of transposon DNA (25 µg), we observed a broad range of pCMV-SB100x doses (0.1–2.5 µg) conferring optimal levels of long-term expression (>10¹¹ photons/second/cm²). At a fixed dose of 0.5 μg of pCMV-SB100x, maximal long-term luciferase expression (>10¹⁰ photons/second/cm²) was achieved at a transposon dose of 5–125 μg. We also found that in the linear range of transposon doses (100 ng), co-delivering the CMV-SB100x sequence on the same plasmid was less effective in achieving long-term expression than delivery on separate plasmids. These results show marked flexibility in the doses of SB transposon plus pCMV-SB100x that achieve maximal SB-mediated gene transfer efficiency and long-term gene expression after hydrodynamic DNA delivery to mouse liver.

Genome-wide Profiling Reveals Remarkable Parallels Between Insertion Site Selection Properties of the MLV Retrovirus and the piggyBac Transposon in Primary Human CD4(+) T Cells

The inherent risks associated with vector insertion in gene therapy need to be carefully assessed. We analyzed the genome-wide distributions of Sleeping Beauty (SB) and piggyBac (PB) transposon insertions as well as MLV retrovirus and HIV lentivirus insertions in human CD4⁺ T cells with respect to a panel of 40 chromatin states. The distribution of SB transposon insertions displayed the least deviation from random, while the PB transposon and the MLV retrovirus showed unexpected parallels across all chromatin states. Both MLV and PB insertions are enriched at transcriptional start sites (TSSs) and co-localize with BRD4-associated sites. We demonstrate physical interaction between the PB transposase and bromodomain and extraterminal domain proteins (including BRD4), suggesting convergent evolution of a tethering mechanism that directs integrating genetic elements into TSSs. We detect unequal biases across the four systems with respect to targeting genes whose deregulation has been previously linked to serious adverse events in gene therapy clinical trials. The SB transposon has the highest theoretical chance of targeting a safe harbor locus in the human genome. The data underscore the significance of vector choice to reduce the mutagenic load on cells in clinical applications.

Minicircle-Based Engineering of Chimeric Antigen Receptor (CAR) T Cells

Plasmid DNA is being used as a pharmaceutical agent in vaccination, as well as a basic substance and starting material in gene and cell therapy, and viral vector production. Since the uncontrolled expression of backbone sequences present in such plasmids and the dissemination of antibiotic resistance genes may have profound detrimental effects, an important goal in vector development was to produce supercoiled DNA lacking bacterial backbone sequences: Minicircle (MC) DNA. The Sleeping Beauty (SB) transposon system is a non-viral gene delivery platform enabling a close-to-random profile of genomic integration. In combination, the MC platform greatly enhances SB transposition and transgene integration resulting in higher numbers of stably modified target cells. We have recently developed a strategy for MC-based SB transposition of chimeric antigen receptor (CAR) transgenes that enable improved transposition rates compared to conventional plasmids and rapid manufacturing of therapeutic CAR T cell doses (Monjezi et al. 2016). This advance enables manufacturing CAR T cells in a virus-free process that relies on SB-mediated transposition from MC DNA to accomplish gene-transfer. Advantages of this approach include a strong safety profile due to the nature of the MC itself and the genomic insertion pattern of MC-derived CAR transposons. In addition, stable transposition and high-level CAR transgene expression, as well as easy and reproducible handling, make MCs a preferred vector source for gene-transfer in advanced cellular and gene therapy. In this chapter, we will review our experience in MC-based CAR T cell engineering and discuss our recent advances in MC manufacturing to accelerate both pre-clinical and clinical implementation.

Antiangiogenic and Neurogenic Activities of Sleeping Beauty-Mediated PEDF-Transfected RPE Cells In Vitro and In Vivo

Pigment epithelium-derived factor (PEDF) is a potent multifunctional protein that inhibits angiogenesis and has neurogenic and neuroprotective properties. Since the wet form of age-related macular degeneration is characterized by choroidal neovascularization (CNV), PEDF would be an ideal candidate to inhibit CNV and support retinal pigment epithelial (RPE) cells. However, its short half-life has precluded its clinical use. To deliver PEDF to the subretinal space, we transfected RPE cells with the PEDF gene using the Sleeping Beauty transposon system. Transfected cells expressed and secreted biologically active recombinant PEDF (rPEDF). In cultures of human umbilical vein endothelial cells, rPEDF reduced VEGF-induced cumulative sprouting by ≥47%, decreased migration by 77%, and increased rate of apoptosis at least 3.4 times. rPEDF induced neurite outgrowth in neuroblastoma cells and protected ganglion and photoreceptor cells in organotypic retinal cultures. In a rat model of CNV, subretinal transplantation of PEDF-transfected cells led to a reduction of the CNV area by 48% 14 days after transplantation and decreased clinical significant lesions by 55% and 40% after 7 and 14 days, respectively. We showed that transplantation of pigment epithelial cells overexpressing PEDF can restore a permissive subretinal environment for RPE and photoreceptor maintenance, while inhibiting choroidal blood vessel growth.

Anti-Tumor Effects after Adoptive Transfer of IL-12 Transposon-Modified Murine Splenocytes in the OT-I-Melanoma Mouse Model

Adoptive transfer of gene modified T cells provides possible immunotherapy for patients with cancers refractory to other treatments. We have previously used the non-viral piggyBac transposon system to gene modify human T cells for potential immunotherapy. However, these previous studies utilized adoptive transfer of modified human T cells to target cancer xenografts in highly immunodeficient (NOD-SCID) mice that do not recapitulate an intact immune system. Currently, only viral vectors have shown efficacy in permanently gene-modifying mouse T cells for immunotherapy applications. Therefore, we sought to determine if piggyBac could effectively gene modify mouse T cells to target cancer cells in a mouse cancer model. We first demonstrated that we could gene modify cells to express murine interleukin-12 (p35/p40 mIL-12), a transgene with proven efficacy in melanoma immunotherapy. The OT-I melanoma mouse model provides a well-established T cell mediated immune response to ovalbumin (OVA) positive B16 melanoma cells. B16/OVA melanoma cells were implanted in wild type C57Bl6 mice. Mouse splenocytes were isolated from C57Bl6 OT-I mice and were gene modified using piggyBac to express luciferase. Adoptive transfer of luciferase-modified OT-I splenocytes demonstrated homing to B16/OVA melanoma tumors in vivo. We next gene-modified OT-I cells to express mIL-12. Adoptive transfer of mIL-12-modified mouse OT-I splenocytes delayed B16/OVA melanoma tumor growth in vivo compared to control OT-I splenocytes and improved mouse survival. Our results demonstrate that the piggyBac transposon system can be used to gene modify splenocytes and mouse T cells for evaluating adoptive immunotherapy strategies in immunocompetent mouse tumor models that may more directly mimic immunotherapy applications in humans.

New Strategies in Engineering T-cell Receptor Gene-Modified T cells to More Effectively Target Malignancies

The immune system, T cells in particular, have the ability to target and destroy malignant cells. However, antitumor immune responses induced from the endogenous T-cell repertoire are often insufficient for the eradication of established tumors, as illustrated by the failure of cancer vaccination strategies or checkpoint blockade for most tumors. Genetic modification of T cells to express a defined T-cell receptor (TCR) can provide the means to rapidly generate large numbers of tumor-reactive T cells capable of targeting tumor cells in vivo. However, cell-intrinsic factors as well as immunosuppressive factors in the tumor microenvironment can limit the function of such gene-modified T cells. New strategies currently being developed are refining and enhancing this approach, resulting in cellular therapies that more effectively target tumors and that are less susceptible to tumor immune evasion.

Excision efficiency is not strongly coupled to transgenic rate: cell type-dependent transposition efficiency of sleeping beauty and piggyBac DNA transposons

The Sleeping Beauty (SB) and piggyBac (PB) DNA transposons represent an emerging new gene delivery technology, potentially suitable for human gene therapy applications. Previous studies pointed to important differences between these transposon systems, depending on the cell types examined and the methodologies applied. However, efficiencies cannot always be compared because of differences in applications. In addition, "overproduction inhibition," a phenomenon believed to be a characteristic of DNA transposons, can remarkably reduce the overall transgenic rate, emphasizing the importance of transposase dose applied. Therefore, because of lack of comprehensive analysis, researchers are forced to optimize the technology for their own "in-house" platforms. In this study, we investigated the transposition of several SB (SB11, SB32, SB100X) and PB (mPB and hyPB) variants in various cell types at three levels: comparing the excision efficiency of the reaction by real-time PCR, testing the overall transgenic rate by detecting cells with stable integrations, and determining the average copy number when using different transposon systems and conditions. We concluded that high excision activity is not always followed by a higher transgenic rate, as exemplified by the hyperactive transposases, indicating that the excision and the integration steps of transposition are not strongly coupled as previously thought. In general, all levels of transposition show remarkable differences depending on the transposase used and cell lines examined, being the least efficient in human embryonic stem cells (hESCs). In spite of the comparably low activity in those special cell types, the hyperactive SB100X and hyPB systems could be used in hESCs with similar transgenic efficiency and with reasonably low (2-3) transgene copy numbers, indicating their potential applicability for gene therapy purposes in the future.

Lysosomal storage disease: gene therapy on both sides of the blood-brain barrier

Most lysosomal storage disorders affect the nervous system as well as other tissues and organs of the body. Previously, the complexities of these diseases, particularly in treating neurologic abnormalities, were too great to surmount. However, based on recent developments there are realistic expectations that effective therapies are coming soon. Gene therapy offers the possibility of affordable, comprehensive treatment associated with these diseases currently not provided by standards of care. With a focus on correction of neurologic disease by systemic gene therapy of mucopolysaccharidoses types I and IIIA, we review some of the major recent advances in viral and non-viral vectors, methods of their delivery and strategies leading to correction of both the nervous and somatic tissues as well as evaluation of functional correction of neurologic manifestations in animal models. We discuss two questions: what systemic gene therapy strategies work best for correction of both somatic and neurologic abnormalities in a lysosomal storage disorder and is there evidence that targeting peripheral tissues (e.g., in the liver) has a future for ameliorating neurologic disease in patients?

Manufacture of T cells using the Sleeping Beauty system to enforce expression of a CD19-specific chimeric antigen receptor

T cells can be reprogrammed to redirect specificity to tumor-associated antigens (TAAs) through the enforced expression of chimeric antigen receptors (CARs). The prototypical CAR is a single-chain molecule that docks with TAA expressed on the cell surface and, in contrast to the T-cell receptor complex, recognizes target cells independent of human leukocyte antigen. The bioprocessing to generate CAR(+) T cells has been reduced to clinical practice based on two common steps that are accomplished in compliance with current good manufacturing practice. These are (1) gene transfer to stably integrate the CAR using viral and nonviral approaches and (2) activating the T cells for proliferation by crosslinking CD3 or antigen-driven numeric expansion using activating and propagating cells (AaPCs). Here, we outline our approach to nonviral gene transfer using the Sleeping Beauty system and the selective propagation of CD19-specific CAR(+) T cells on AaPCs.

Cellular immune response against firefly luciferase after sleeping beauty-mediated gene transfer in vivo

The Sleeping Beauty (SB) transposon system has been shown to mediate new gene sequence integration resulting in long-term expression. Here the effectiveness of hyperactive SB100X transposase was tested, and we found that hydrodynamic co-delivery of a firefly luciferase transposon (pT2/CaL) along with SB100X transposase (pCMV-SB100X) resulted in remarkably sustained, high levels of luciferase expression. However, after 4 weeks there was a rapid, animal-by-animal loss of luciferase expression that was not observed in immunodeficient mice. We hypothesized that this sustained, high-level luciferase expression achieved using the SB100X transposase elicits an immune response in pT2/CaL co-administered mice, which was supported by the rapid loss of luciferase expression upon challenge of previously treated animals and in naive animals adoptively transferred with splenocytes from previously treated animals. Specificity of the immune response to luciferase was demonstrated by increased cytokine expression in splenocytes after exposure to luciferase peptide in parallel with MHC I-luciferase peptide tetramer binding. This anti-luciferase immune response observed following continuous, high-level luciferase expression in vivo clearly impacts its use as an in vivo reporter. As both an immunogen and an extremely sensitive reporter, luciferase is also a useful model system for the study of immune responses following in vivo gene transfer and expression.

Treatment of phenylketonuria using minicircle-based naked-DNA gene transfer to murine liver

Host immune response to viral vectors, persistence of nonintegrating vectors, and sustained transgene expression are among the major challenges in gene therapy. To overcome these hurdles, we successfully used minicircle (MC) naked-DNA vectors devoid of any viral or bacterial sequences for the long-term treatment of murine phenylketonuria, a model for a genetic liver defect. MC-DNA vectors expressed the murine phenylalanine hydroxylase (Pah) complementary DNA (cDNA) from a liver-specific promoter coupled to a de novo designed hepatocyte-specific regulatory element, designated P3, which is a cluster of evolutionary conserved transcription factor binding sites. MC-DNA vectors were subsequently delivered to the liver by a single hydrodynamic tail vein (HTV) injection. The MC-DNA vector normalized blood phenylalanine concomitant with reversion of hypopigmentation in a dose-dependent manner for more than 1 year, whereas the corresponding parental plasmid did not result in any phenylalanine clearance. MC vectors persisted in an episomal state in the liver consistent with sustained transgene expression and hepatic PAH enzyme activity without any apparent adverse effects. Moreover, 14-20% of all hepatocytes expressed transgenic PAH, and the expression was observed exclusively in the liver and predominately around pericentral areas of the hepatic lobule, while there was no transgene expression in periportal areas.

CONCLUSION

This study demonstrates that MC technology offers an improved safety profile and has the potential for the genetic treatment of liver diseases.