Gene therapy as a new treatment option for inherited monogenic diseases

Oligodendrocytes, the Forgotten Target of Gene Therapy

If the billions of oligodendrocytes (OLs) populating the central nervous system (CNS) of patients could express their feelings, they would undoubtedly tell gene therapists about their frustration with the other neural cell populations, neurons, microglia, or astrocytes, which have been the favorite targets of gene transfer experiments. This review questions why OLs have been left out of most gene therapy attempts. The first explanation is that the pathogenic role of OLs is still discussed in most CNS diseases. Another reason is that the so-called ubiquitous CAG, CBA, CBh, or CMV promoters-widely used in gene therapy studies-are unable or poorly able to activate the transcription of episomal transgene copies brought by adeno-associated virus (AAV) vectors in OLs. Accordingly, transgene expression in OLs has either not been found or not been evaluated in most gene therapy studies in rodents or non-human primates. The aims of the current review are to give OLs their rightful place among the neural cells that future gene therapy could target and to encourage researchers to test the effect of OL transduction in various CNS diseases.

Combination of MAR and intron increase transgene expression of episomal vectors in CHO cells

Previous work has shown that the EF-1α promoter of episomal vectors maintains high-level transgene expression in stably transfected Chinese hamster ovary (CHO) cells. However, the transgene expression levels need to be further increased. Here, we first incorporated matrix attachment regions (MARs), ubiquitous chromatin opening element (UCOE), stabilizing anti repressor elements 40 (STAR 40) elements into episomal vector at different sites and orientations, and systemically assessed their effects on transgene expression in transfected CHO-K1 cells. Results showed that enhanced green fluorescent protein (eGFP) expression levels increased remarkably when MAR X-29 was inserted upstream of the promoter, followed by the insertion of MAR1 downstream of the poly A, and the orientation had no significant effect. Moreover, MAR X-29 combined with human cytomegalovirus intron (hCMVI) yielded the highest transgene expression levels (4.52-fold). Transgene expression levels were not exclusively dependent on transgene copy numbers and were not related to the mRNA expression level. In addition, vector with MAR X-29+hCMVI can induce herpes simplex virus thymidine kinase (HSV-TK) protein expression, and the HSV-TK protein showed a cell-killing effect and an obvious bystander effect on HCT116 cells. In conclusion, the combination of MAR X-29 and hCMV intron can achieve high efficiency transgene expression mediated by episomal vectors in CHO-K1 cells.

Gene therapy for inherited metabolic diseases

Over the last two decades, gene therapy has been successfully translated to many rare diseases. The number of clinical trials is rapidly expanding and some gene therapy products have now received market authorisation in the western world. Inherited metabolic diseases (IMD) are orphan diseases frequently associated with a severe debilitating phenotype with limited therapeutic perspective. Gene therapy is progressively becoming a disease-changing therapeutic option for these patients. In this review, we aim to summarise the development of this emerging field detailing the main gene therapy strategies, routes of administration, viral and non-viral vectors and gene editing tools. We discuss the respective advantages and pitfalls of these gene therapy strategies and review their application in IMD, providing examples of clinical trials with lentiviral or adeno-associated viral gene therapy vectors in rare diseases. The rapid development of the field and implementation of gene therapy as a realistic therapeutic option for various IMD in a short term also require a good knowledge and understanding of these technologies from physicians to counsel the patients at best.

Improvement of DNA Vector Delivery of DOTAP Lipoplexes by Short-Chain Aminolipids

Cellular delivery of DNA vectors for the expression of therapeutic proteins is a promising approach to treat monogenic disorders or cancer. Significant efforts in a preclinical and clinical setting have been made to develop potent nonviral gene delivery systems based on lipoplexes composed of permanently cationic lipids. However, transfection efficiency and tolerability of such systems are in most cases not satisfactory. Here, we present a one-pot combinatorial method based on double-reductive amination for the synthesis of short-chain aminolipids. These lipids can be used to maximize the DNA vector delivery when combined with the cationic lipid 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). We incorporated various aminolipids into such lipoplexes to complex minicircle DNA and screened these systems in a human liver-derived cell line (HuH7) for gene expression and cytotoxicity. The lead aminolipid AL-A12 showed twofold enhanced gene delivery and reduced toxicity compared to the native DOTAP:cholesterol lipoplexes. Moreover, AL-A12-containing lipoplexes enabled enhanced transgene expression in vivo in the zebrafish embryo model.

In-Depth Characterization of a Mifepristone-Regulated Expression System for AAV5-Mediated Gene Therapy in the Liver

Gene therapy is being developed for the treatment of inherited diseases, whereby a therapeutic gene is continuously expressed in patients after delivery via viral vectors such as adeno-associated virus (AAV). Depending on the transgene, there could be a limited therapeutic window, and regulating timing and levels of transgene expression is advantageous. To control transgene transcription, the regulatory system GeneSwitch (GS) was evaluated in detail both in vitro and in vivo. The classical two-plasmid mifepristone (MFP)-inducible GS system was put into one plasmid or a single AAV5 vector. Our data demonstrate the inducibility of multiple transgenes and the importance of promoter and regulatory elements within the GS system. Mice injected with AAV5 containing the GS system transiently expressed mRNA and protein after MFP induction. The inducer MFP could be measured in plasma and liver tissue, and assessment of MFP and its metabolites showed rapid clearance from murine plasma. In a head-to-head comparison, our single vector outclassed the classical two-vector GS system. Finally, we show repeated inducibility of the transgene that also translated into a dynamic phenotypic change in mice. Taken together, this in-depth analysis of the GS system shows its applicability for regulated gene therapy.

Progress in biopharmaceutical development

Since its introduction in 1982, biopharmaceutical drugs have revolutionized the treatment of a broad spectrum of diseases and are increasingly used in nearly all branches of medicine. In recent years, the biopharmaceuticals market has developed much faster than the market for all drugs and is believed to have great potential for further dynamic growth because of the tremendous demand for these drugs. Biobetters, which contain altered active pharmaceutical ingredients with enhanced efficacy, will play an important role in the development of biopharmaceuticals. Another significant group of biopharmaceuticals are biosimilars. Their introduction in the European Union and, recently, the Unites States markets will reduce the costs of biopharmaceutical treatment. This review highlights recent progress in the field of biopharmaceutical development and issues concerning the registration of innovative biopharmaceuticals and biosimilars. The leading class of biopharmaceuticals, the current biopharmaceuticals market, and forecasts are also discussed.

Genome editing: a robust technology for human stem cells

Human pluripotent stem cells comprise induced pluripotent and embryonic stem cells, which have tremendous potential for biological and therapeutic applications. The development of efficient technologies for the targeted genome alteration of stem cells in disease models is a prerequisite for utilizing stem cells to their full potential. Genome editing of stem cells is possible with the help of synthetic nucleases that facilitate site-specific modification of a gene of interest. Recent advances in genome editing techniques have improved the efficiency and speed of the development of stem cells for human disease models. Zinc finger nucleases, transcription activator-like effector nucleases, and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated system are powerful tools for editing DNA at specific loci. Here, we discuss recent technological advances in genome editing with site-specific nucleases in human stem cells.

Revisiting APOLT for Metabolic Liver Disease: A New Look at an Old Idea

Even though auxiliary partial orthotopic liver transplantation (APOLT) as a technique was popularized in the late 80s, its role in metabolic liver disease remains controversial. The slow progress in gene therapy research, high incidence of technical complications, and the problem of long term graft atrophy have been roadblocks to its wider application. Better understanding of reciprocal dynamics of portal flow and regeneration between the graft and native liver along with multiple refinements in surgical technique have improved the outcomes of this operation, making it a safe alternative to orthotopic liver transplantation for patients with a wide range of noncirrhotic metabolic liver diseases (NCMLD). The ability to perform APOLT safely has also opened up a range of exciting indications in the setting of NCMLD. This article reviews the current status of APOLT for NCMLD, technical refinements which have improved outcomes and novel indications, which have rekindled fresh interest in this procedure.

RNAi-mediated knockdown of MCM7 gene on CML cells and its therapeutic potential for leukemia

MCM7 is one of the subunits of MCM2-7 complex, which is essential to DNA replication licensing and the control of cell cycle progression. It has been demonstrated that MCM7 participates in mRNA transcription and DNA damage regulation as well. MCM7 gene is found to be over-expressed in multiple cancers, but there are few reports about its effect in leukemia. Recent studies have proven that MCM7 expression has a relationship with diagnosis and prognosis, which has led to their potential clinical application as a marker for cancer screening. RNA interference (RNAi) is a biological process in which RNA molecules inhibit gene expression, typically by causing the destruction of specific mRNA molecules. It is a valuable research tool, which is widely used in cell culture and living organisms as well as in medicine recent years. It is indicated that RNAi application for targeting functional carcinogenic molecules, tumor resistance to chemotherapy and radiotherapy is required in cancer treatment. Gene products knockdown by RNAi technology exerts anti-proliferative and pro-apoptotic effects upon cell culture systems, animal models and in clinical trials in the most studies. In the present study, we found that MCM7 highly expressed in K562 cells rather than that in normal neutrophils. Thus, lentivirus-mediated shRNA targeting MCM7 was used to suppress its endogenous expression in K562 cells and develop a novel therapeutic strategy for leukemia.

Gene therapies development: slow progress and promising prospect

Background: In 1989, the concept of human gene therapies has emerged with the first approved human gene therapy trial of Rosenberg et al. Gene therapies are considered as promising therapies applicable to a broad range of diseases. Objective: The objective of this study was to review the descriptive data on gene therapy clinical trials conducted worldwide between 1989 and 2015, and to discuss potential success rates of these trials over time and anticipated market launch in the upcoming years. Methods: A publicly available database, 'Gene Therapy Clinical Trials Worldwide', was used to extract descriptive data on gene therapy clinical trials: (1) number of trials per year between 1989 and 2015; (2) countries; (3) diseases targeted by gene therapies; (4) vectors used for gene delivery; (5) trials status; (6) phases of development. Results: Between 1989 and 2015, 2,335 gene therapy clinical trials have been completed, were ongoing or approved (but not started) worldwide. The number of clinical trials did not increase steadily over time; it reached its highest peak in 2015 (163 trials). Almost 95% of the trials were in early phases of development and 72% were ongoing. The United States undertook 67% of gene therapy clinical trials. The majority of gene therapies clinical trials identified targeted cancer diseases. Conclusion: The first gene therapy was approved in the European Union in 2012, after two decades of dashed expectations. This approval boosted the investment in developing gene therapies. Regulators are creating a specific path for rapid access of those new therapies, providing hope for manufacturers, healthcare professionals, and patients. However, payers are increasingly scrutinizing the additional benefits of the new therapies. Major steps forward are expected in the field of gene therapies in the future.

Non-myeloablative conditioning with busulfan before hematopoietic stem cell transplantation leads to phenotypic correction of murine Bernard-Soulier syndrome

BACKGROUND

Bernard-Soulier syndrome (BSS) is an inherited bleeding disorder characterized by macrothrombocytopenia. Platelet transfusion is used for the management of bleeding, but repeated transfusion often results in alloimmunization. We have recently shown phenotypic correction of murine BSS (GPIbα(null) ) using lethal radiation conditioning followed by hematopoietic lentivirus-mediated gene transfer.

OBJECTIVES

For application of gene therapy to treatment of human patients, it is important to minimize treatment-related side effects. The objective of this study is to model a clinically relevant non-myeloablative hematopoietic stem cell (HSC) transplantation strategy.

METHODS

Using transplantation of bone marrow (BM) HSCs from transgenic mice that express hGPIbα (hGPIbα(tg+/+) ), we sought to (i) determine the percentage of hGPIbα(tg+/+) HSCs required for therapeutic benefit, (ii) evaluate the efficacy of non-myeloablative conditioning using busulfan, and (iii) test the ability of anti-thymocyte globulin (ATG) to prevent/reduce undesirable immune responses.

RESULTS

Transplantation of 10-20% hGPIbα(tg+/+) BM HSCs mixed with GPIbα(null) BM HSCs into irradiated GPIbα(null) mice was sufficient to correct bleeding time (n = 5). Transplantation of hGPIbα(tg+/+) BM HSCs into busulfan-conditioned GPIbα(null) mice corrected bleeding time in 21 of 27 recipients. Antibody response to hGPIbα and immune-mediated thrombocytopenia was documented in eight of 27 recipients, suggesting immunogenicity of hGPIbα in busulfan-conditioned GPIbα(null) mice. However, these antibodies disappeared without treatment within 30 weeks after transplantation. A combination of busulfan plus ATG conditioning successfully prevented antibody development and significantly increased therapeutic engraftment.

CONCLUSION

A conditioning regimen of busulfan in combination with ATG could potentially be used in non-myeloablative autologous gene therapy in human BSS.