Death after High-Dose rAAV9 Gene Therapy in a Patient with Duchenne's Muscular Dystrophy

Anti-fibrotic, muscle-promoting antibody-drug conjugates for the improvement and treatment of DMD

Fibrosis, characterized by the deposition of excess and disorganized extracellular matrix (ECM), is a key pathological hallmark of multiple diseases, including Duchenne muscular dystrophy (DMD). Aiming to inhibit fibrosis progression, we generated an antibody-drug conjugate (ADC) that delivers an innovative small molecule conjugate to inhibit the ECM-modifying enzyme Lysyl oxidase (LOX) specifically in fibrotic lesions by targeting M2 macrophages. Administration of the ADC to mdx mice, the murine model of DMD, results in ADC accumulation in fibrotic muscles without affecting healthy tissues. Long-term ADC treatments of adult mdx mice lead to inhibition of the fibrotic process and to significant improvement of cardiac and skeletal muscle function. Our study demonstrates that targeted inhibition of LOX-dependent fibrotic diseases, such as DMD, facilitates improved outcomes for muscular dystrophies.

AAV vectors trigger DNA damage response-dependent pro-inflammatory signalling in human iPSC-derived CNS models and mouse brain

Adeno-associated viral (AAV) vector-based gene therapy is gaining foothold as treatment for genetic neurological diseases with encouraging clinical results. Nonetheless, dose-dependent adverse events have emerged in recent clinical trials through mechanisms that remain unclear. We have modelled here the impact of AAV transduction in cell models of the human central nervous system (CNS), taking advantage of induced pluripotent stem cells. Our work uncovers vector-induced innate immune mechanisms that contribute to cell death. While empty AAV capsids were well tolerated, the AAV genome triggered p53-dependent DNA damage responses across CNS cell types followed by the induction of inflammatory responses. In addition, transgene expression led to MAVS-dependent activation of type I interferon responses. Formation of DNA damage foci in neurons and gliosis were confirmed in murine striatum upon intraparenchymal AAV injection. Transduction-induced cell death and gliosis could be prevented by inhibiting p53 or by acting downstream on STING- or IL-1R-mediated responses. Together, our work identifies innate immune mechanisms of vector sensing in the CNS that can potentially contribute to AAV-associated neurotoxicity.

Single-cut gene therapy in a one-step generated rhesus monkey model of Duchenne muscular dystrophy

Progress in Duchenne muscular dystrophy (DMD) treatment is hindered by the lack of animal models that closely replicate human pathology and enable the evaluation of therapy efficacy and safety based on these models. To address this need, we optimize the generation of nonhuman primate DMD models, reducing the development time from 6 to 7 years to under 1 year, enabling the rapid generation of DMD monkey models. These models closely mimic human DMD pathology and motor dysfunction, making them suitable for testing gene therapies. Using these models, we develop a single-cut gene therapy strategy that can be directly applied to humans. This treatment restores dystrophin expression, improves pathological features, and enhances motor abilities in DMD monkeys, with effects lasting at least 1.5 years. In conclusion, we achieve the rapid generation of DMD monkey models and demonstrate that our gene therapy approach is effective and holds significant potential for clinical application.

Gene Editing for Duchenne Muscular Dystrophy: From Experimental Models to Emerging Therapies

The CRISPR system has emerged as a ground-breaking gene-editing tool, offering promising therapeutic potential for Duchenne muscular dystrophy (DMD), a severe genetic disorder affecting approximately 1 in 5000 male births globally. DMD is caused by mutations in the dystrophin gene, which encodes a critical membrane-associated protein essential for maintaining muscle structure, function and repair. Patients with DMD experience progressive muscle degeneration, loss of ambulation, respiratory insufficiency, and cardiac failure, with most succumbing to the disease by their third decade of life. Despite the well-characterized genetic basis of DMD, curative treatments- such as exon skipping therapies, micro-dystrophin, and steroids- remain elusive. Recent preclinical studies have demonstrated the promise of CRISPR-based approaches in restoring dystrophin expression across various models, including human cells, murine systems, and large animal models. These advancements highlight the potential of gene editing to fundamentally alter the trajectory of the disease. However, significant challenges persist, including immunogenicity, off-target effects, and limited editing efficiency, which hinder clinical translation. This review provides a comprehensive analysis of the latest developments in CRISPR-based therapeutic strategies for DMD. It emphasizes the need for further innovation in gene-editing technologies, delivery systems, and rigorous safety evaluations to overcome current barriers and harness the full potential of CRISPR/Cas as a durable and effective treatment for DMD.

Current trends in gene therapy to treat inherited disorders of the brain

Gene therapy development, re-engineering, and application to patients hold promise to revolutionize medicine, including therapies for disorders of the brain. Advances in delivery modalities, expression regulation, and improving safety profiles are of critical importance. Additionally, each inherited disorder has its own unique characteristics as to regions and cell types impacted and the temporal dynamics of that impact that are essential for the design of therapeutic design strategies. Here, we review the current state of the art in gene therapies for inherited brain disorders, summarizing key considerations for vector delivery, gene addition, gene silencing, gene editing, and epigenetic editing. We provide examples from animal models, human cell lines, and, where possible, clinical trials. This review also highlights the various tools available to researchers for basic research questions and discusses our views on the current limitations in the field.

The road toward AAV-mediated gene therapy of Duchenne muscular dystrophy

Forty years after the dystrophin gene was cloned, significant progress has been made in developing gene therapy approaches for Duchenne muscular dystrophy (DMD). The disorder has presented numerous challenges, including the enormous size of the gene (2.2 MB), the need to target muscles body wide, and immunogenic issues against both vectors and dystrophin. Among human genetic disorders, DMD is relatively common, and the genetics are complicated since one-third of all cases arise from a spontaneous new mutation, resulting in thousands of independent lesions throughout the locus. Many approaches have been pursued in the goal of finding an effective therapy, including exon skipping, nonsense codon suppression, upregulation of surrogate genes, gene replacement, and gene editing. Here, we focus specifically on methods using AAV vectors, as these approaches have been tested in numerous clinical trials and are able to target muscles systemically. We discuss early advances to understand the structure of dystrophin, which are crucial for the design of effective DMD gene therapies. Included is a summary of efforts to deliver micro-, mini-, and full-length dystrophins to muscles. Finally, we review current approaches to adapt gene editing to the enormous DMD gene with prospects for improved therapies using all these methods.

Is Duchenne gene therapy a suitable treatment despite its immunogenic class effect?

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a severe X-linked disorder characterized by progressive muscle weakness and eventual death due to cardiomyopathy or respiratory complications. Currently, there is no cure for DMD, with standard treatments primarily focusing on symptom management. Using immunosuppressive measures and optimized vector designs allows for gene therapies to better address the genetic cause of the disease.

AREAS COVERED

This review evaluates the efficacy and safety of emerging DMD gene therapies as of 2024. It also discusses the potential of utrophin upregulation, gene editing, and truncated dystrophin as therapeutic strategies. It highlights safety concerns associated with these therapies, including adverse events and patient deaths. A comprehensive overview of developments covers topics such as CRISPR-Cas9 therapies, micro-dystrophin, and the potential delivery of full-length dystrophin.

EXPERT OPINION

The FDA's recent approval of delandistrogene moxeparvovec (Elevidys) underscores the promise of gene replacement therapies for DMD patients. Understanding the mechanisms behind the adverse effects and excluding patients with specific pathogenic variants may enhance the safety profiles of these therapies. CRISPR/Cas9 therapies, while promising, face significant regulatory and safety challenges that hinder their clinical application. Optimal DMD therapies should target both skeletal and cardiac muscles to be effective.

X-linked myotubular myopathy: an untreated treatable disease

INTRODUCTION

X-linked myotubular myopathy (XLMTM) is a life-threatening congenital disorder characterized by severe respiratory and motor impairment. This disease presents significant therapeutic challenges, with various strategies being explored to address its underlying pathology. Among these approaches, gene replacement therapy has demonstrated substantial functional improvements in clinical trials. However, safety issues emerged across different therapeutic approaches, highlighting the need for further research.

AREAS COVERED

This review provides a comprehensive analysis of the data gathered from natural history studies, preclinical models and clinical trials, with a particular focus on gene replacement therapy for XLMTM. The different therapeutic strategies are addressed, including their outcomes and associated safety concerns.

EXPERT OPINION

Despite the encouraging potential of gene therapy for XLMTM, the occurrence of safety challenges emphasizes the urgent need for a more comprehensive understanding of the disease's complex phenotype. Enhancing preclinical models to more accurately mimic the full spectrum of disease manifestations will be crucial for optimizing therapeutic strategies and reducing risks in future clinical applications.

In vivo base editing extends lifespan of a humanized mouse model of prion disease

Prion disease is a fatal neurodegenerative disease caused by the misfolding of prion protein (PrP) encoded by the PRNP gene. While there is currently no cure for the disease, depleting PrP in the brain is an established strategy to prevent or stall templated misfolding of PrP. Here we developed in vivo cytosine and adenine base strategies delivered by adeno-associated viruses to permanently modify the PRNP locus to achieve PrP knockdown in the mouse brain. Systemic injection of dual-adeno-associated virus PHP.eB encoding BE3.9max and single guide RNA installing PRNP R37X resulted in 37% average installation of the desired edit, 50% reduction of PrP in the mouse brain and 52% extension of lifespan in transgenic human PRNP mice inoculated with pathogenic human prion isolates representing the most common sporadic and genetic subtypes of prion disease. We further engineered base editing systems to achieve improved in vivo potency and reduced base editor expression in nontargeting tissues, resulting in 63% average PrP reduction in the mouse brain from a 6.7-fold lower viral dose, with no detected off-target editing of anticipated clinical significance observed in either human cells or mouse tissues. These findings support the potential of in vivo base editing as one-time treatment for prion disease.

The curious case of AAV immunology

Immune responses to adeno-associated virus (AAV) have long been perplexing, from its first discovery to the latest clinical trials of recombinant AAV (rAAV) therapy. Wild-type AAV (wtAAV) does not cause any known disease, making it an ideal vector for gene therapy, as viral vectors retain virus-like properties. Although AAV stimulates only a mild immune response compared with other viruses, it is still recognized by the innate immune system and induces adaptive immune responses. B cell responses against both wtAAV and rAAV are robust and can hinder gene therapy applications and prevent redosing. T cell responses can clear transduced cells or establish tolerance against gene therapy. Immune responses to AAV gene therapy are influenced by many factors. Most clinical immunotoxicities that develop in response to gene therapies have emerged as higher doses of AAV vectors have been utilized and were not properly modeled in preclinical animal studies. Thus, several strategies have been undertaken to reduce or mitigate immune responses to AAV. While we have learned a considerable amount about how the immune system responds to AAV gene therapy since the discovery of AAV virus, it still remains a curious case that requires more investigation to fully understand.

The deLIVERed promises of gene therapy: Past, present, and future of liver-directed gene therapy

Gene therapy has revolutionized modern medicine by offering innovative treatments for genetic and acquired diseases. The liver has been and continues as a prime target for in vivo gene therapy due to its essential biological functions, vascular access to the major target cell (hepatocytes), and relatively immunotolerant environment. Adeno-associated virus (AAV) vectors have become the cornerstone of liver-directed therapies, demonstrating remarkable success in conditions such as hemophilia A and B, with US Food and Drug Administration (FDA)-approved therapies like etranacogene dezaparvovec, Beqvez, and Roctavian marking milestones in the field. Despite these advances, challenges persist, including vector immunogenicity, species-specific barriers, and high manufacturing costs. Innovative strategies, such as capsid engineering, immune modulation, and novel delivery systems, are continuing to address these issues in expanding the scope of therapeutic applications. Some of the challenges with many new therapies result in the discordance between preclinical success and translation into humans. The advent of various genome-editing tools to repair genomic mutations or insert therapeutic DNAs into precise locations in the genome further enhances the potential for a single-dose medicine that will offer durable life-long therapeutic treatments. As advancements accelerate, liver-targeted gene therapy is poised to continue to transform the treatment landscape for both genetic and acquired disorders, for which unmet challenges remain.

Recent advances in therapeutic gene-editing technologies

The advent of gene-editing technologies, particularly CRISPR-based systems, has revolutionized the landscape of biomedical research and gene therapy. Ongoing research in gene editing has led to the rapid iteration of CRISPR technologies, such as base and prime editors, enabling precise nucleotide changes without the need for generating harmful double-strand breaks (DSBs). Furthermore, innovations such as CRISPR fusion systems with DNA recombinases, DNA polymerases, and DNA ligases have expanded the size limitations for edited sequences, opening new avenues for therapeutic development. Beyond the CRISPR system, mobile genetic elements (MGEs) and epigenetic editors are emerging as efficient alternatives for precise large insertions or stable gene manipulation in mammalian cells. These advances collectively set the stage for next-generation gene therapy development. This review highlights recent developments of genetic and epigenetic editing tools and explores preclinical innovations poised to advance the field.

Preclinical development of genome editing to treat Duchenne muscular dystrophy by exon skipping

Duchenne muscular dystrophy (DMD) is caused by loss-of-function mutations to the gene encoding dystrophin. Restoring the reading frame of dystrophin by removing internal out-of-frame exons may address symptoms of DMD. Therefore, the principle of exon skipping has been at the center stage in drug development for Duchenne muscular dystrophy (DMD) over the past two decades. Antisense oligonucleotides (AONs) have proven effective in modulating splicing sites for exon skipping, resulting in the FDA approval of several drugs using this technique in recent years. However, due to the temporary nature of AON, researchers are actively exploring genome editing as a potential long-term, single-administration treatment. The advancements in genome-editing technology over the last decade have boosted this transition. While no clinical trials for exon skipping in DMD via genome editing have been conducted as of this writing, preclinical studies show encouraging results. This review describes the preclinical landscape of genome editing for exon skipping in DMD treatment. Along with highlighting the adaptability of genome editing in exon skipping, this review also describes delivery challenges and outlines future research directions that could set a new stage for enhanced therapeutic development in DMD.

Inhibiting EZH2 complements steroid effects in Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a devastating X-linked disorder caused by dystrophin gene mutations. Despite recent advances in understanding the disease etiology and applying emerging treatment methodologies, glucocorticoid derivatives remain the only general therapeutic option that can slow disease development. However, the precise molecular mechanism of glucocorticoid action remains unclear, and there is still need for additional remedies to complement the treatment. Here, using single-nucleus RNA sequencing and spatial transcriptome analyses of human and mouse muscles, we investigated pathogenic features in patients with DMD and palliative effects of glucocorticoids. Our approach further illuminated the importance of proliferating satellite cells and revealed increased activity of a signal transduction pathway involving EZH2 in the patient cells. Subsequent administration of EZH2 inhibitors to Dmd mutant mice resulted in improved muscle phenotype through maintaining the immune-suppressing effect but overriding the muscle weakness and fibrogenic effects exerted by glucocorticoids. Our analysis reveals pathogenic mechanisms that can be readily targeted by extant therapeutic options for DMD.

CRISPR screen reveals modifiers of rAAV production including known rAAV infection genes playing an unexpected role in vector production

Recombinant adeno-associated virus (rAAV) vectors are an effective and well-established tool in the growing gene therapy field, with five U.S. Food and Drug Administration-approved AAV-mediated gene therapies already on the market and numerous more in clinical trials. However, manufacturing rAAV vectors is an expensive, timely, and labor-intensive process that limits the commercial use of AAV-mediated gene therapies. To address this limitation, we screened producer cells for genes that could be targeted to increase rAAV yield. Specifically, we performed a CRISPR-based genome-wide knockout (KO) screen in human embryonic kidney (HEK) 293 cells using an antibody specific to intact AAV2 capsids coupled with flow cytometry to identify genes that modulate rAAV production. We discovered that the KO of a group of heparan sulfate biosynthesis genes previously implicated in rAAV infectivity decreased rAAV production. Additionally, we identified several vesicular trafficking proteins for which KO in HEK 293 cells increased rAAV yields. Our findings provide evidence that host proteins associated with viral infection may have also been co-opted for viral assembly and that the genetic makeup of viral producer cells can be manipulated to increase particle yield.

Recombinant AAV batch profiling by nanopore sequencing elucidates product-related DNA impurities and vector genome length distribution

During production, recombinant adeno-associated virus (rAAV) capsids are equipped with heterogeneous genetic payloads including undesired DNA impurities as well as truncated vector genomes. Comprehensive analysis of encapsidated DNA by long-read next-generation sequencing is destined to guide platform optimization and provide crucial insights into safety of gene therapies. We used nanopore sequencing for in-depth profiling of an rAAV9 batch produced using our proprietary split two-plasmid system in a 50-L bioreactor. We compared three methods for single-strand to double-strand DNA conversion and their impact on the sequencing data. We observed a distinct library size profile but comparable impurity distribution. We contrasted recent nanopore sequencing advancements such as the V14 chemistry and dorado basecalling software with the widespread V9 chemistry and detected a markedly increased read quality. Our data highlight a high vector batch quality with low plasmid-derived and host cell DNA impurities of random origin, critical for mitigating associated safety risks. Finally, we compared nanopore data with orthogonal SMRT sequencing data and observed a higher base quality, but largely similar length and impurity profiles. Taken together, nanopore sequencing is a state-of-the-art method for comprehensive, in-depth rAAV vector batch analysis during all stages of gene therapy development.

Advanced delivery systems for gene editing: A comprehensive review from the GenE-HumDi COST Action Working Group

In the past decade, precise targeting through genome editing has emerged as a promising alternative to traditional therapeutic approaches. Genome editing can be performed using various platforms, where programmable DNA nucleases create permanent genetic changes at specific genomic locations due to their ability to recognize precise DNA sequences. Clinical application of this technology requires the delivery of the editing reagents to transplantable cells ex vivo or to tissues and organs for in vivo approaches, often representing a barrier to achieving the desired editing efficiency and safety. In this review, authored by members of the GenE-HumDi European Cooperation in Science and Technology (COST) Action, we described the plethora of delivery systems available for genome-editing components, including viral and non-viral systems, highlighting their advantages, limitations, and potential application in a clinical setting.

CDC20 protects the heart from doxorubicin-induced cardiotoxicity by modulating CCDC69 degradation

AIMS

Doxorubicin (DOX) is a potent anticancer drug; however, it is associated with significant cardiotoxicity. CDC20 is an E3 ubiquitin ligase that plays a role in cell cycle progression and apoptosis in various types of cancers. The involvement of CDC20 in DOX-induced cardiotoxicity (DIC) is poorly understood. Hence, this study aimed to explore the potential role of CDC20 in the development of DIC and assess whether CDC20 influences the antitumor effects of DOX.

METHODS AND RESULTS

H9C2 cells were treated with DOX, followed by transcriptomic analysis to identify differentially expressed genes. C57BL/6 mice were treated with DOX for 4 weeks after tail vein injection of CDC20 myocardial-specific knockout mice, AAV9-cTNT-(si) CDC20, or intraperitoneal injection of apcin. Cardiac function and pathological changes were evaluated by echocardiography and pathological staining, respectively. The influence of CDC20 on DOX-induced tumor inhibition was assessed in tumor-bearing mice. In vitro analysis involved treating cardiomyocytes with the Ad-CDC20 adenovirus and DOX, followed by proteomic and ubiquitination-related assays to identify potential downstream ubiquitinated CDC20 proteins. Additionally, we investigated the effect of CCDC69 on CDC20-mediated protection against DOX-induced apoptosis using CCDC69 shRNA. Transcriptome analysis revealed that DOX effectively suppressed the expression of CDC20. Cardiomyocyte-specific overexpression of CDC20 in a DOX-induced mouse model of myocardial injury effectively mitigated cardiomyocyte apoptosis, inflammation, fibrosis, and cell atrophy. Our mechanistic investigation revealed that CDC20 attenuates DOX-induced apoptosis by downregulating CCDC69 expression. Moreover, cardiomyocyte-specific overexpression of CDC20 had no effect on the therapeutic efficacy of DOX against tumors.

CONCLUSION

Our findings indicate that CDC20 safeguards the heart against DOX-induced cardiotoxicity by modulating CCDC69 degradation without compromising the antitumor efficacy of DOX.

CRISPR: fundamental principles and implications for anaesthesia

Clustered regularly interspaced short palindromic repeats (CRISPR)-based medical therapies are increasingly gaining regulatory approval worldwide. Consequently, patients receiving CRISPR therapy will come under the care of anaesthesiologists. An understanding of CRISPR, its technological implementations, and the characteristics of patients likely to receive this therapy will be essential to caring for this patient population. However, the role of CRISPR in anaesthesiology extends beyond simply caring for patients with prior CRISPR therapy. CRISPR has multiple direct potential applications in anaesthesia, particularly for managing chronic pain and critical illness. Additionally, given the unique skills anaesthesiologists possess, CRISPR potentially allows new roles for anaesthesiologists in the field of oncology. Consequently, CRISPR technology could enable new domains of anaesthetic practice. This review provides a primer on CRISPR for anaesthesiologists and an overview on how the technology could impact the field.

Translational nanorobotics breaking through biological membranes

In the dynamic realm of translational nanorobotics, the endeavor to develop nanorobots carrying therapeutics in rational in vivo applications necessitates a profound understanding of the biological landscape of the human body and its complexity. Within this landscape, biological membranes stand as critical barriers to the successful delivery of therapeutic cargo to the target site. Their crossing is not only a challenge for nanorobotics but also a pivotal criterion for the clinical success of therapeutic-carrying nanorobots. Nevertheless, despite their urgency, strategies for membrane crossing in translational nanorobotics remain relatively underrepresented in the scientific literature, signaling an opportunity for further research and innovation. This review focuses on nanorobots with various propulsion mechanisms from chemical and physical to hybrid mechanisms, and it identifies and describes four essential biological membranes that represent the barriers needed to be crossed in the therapeutic journey of nanorobots in in vivo applications. First is the entry point into the blood stream, which is the skin or mucosa or intravenous injection; next is the exit from the bloodstream across the endothelium to the target site; further is the entry to the cell through the plasma membrane and, finally, the escape from the lysosome, which otherwise destroys the cargo. The review also discusses design challenges inherent in translating nanorobot technologies to real-world applications and provides a critical overview of documented membrane crossings. The aim is to underscore the need for further interdisciplinary collaborations between chemists, materials scientists and chemical biologists in this vital domain of translational nanorobotics that has the potential to revolutionize the field of precision medicine.

Analysis of Hepatic Lentiviral Vector Transduction: Implications for Preclinical Studies and Clinical Gene Therapy Protocols

Lentiviral vector-transduced T cells were approved by the FDA as gene therapy anti-cancer medications. Little is known about the effects of host genetic variation on the safety and efficacy of the lentiviral vector gene delivery system. To narrow this knowledge gap, we characterized hepatic gene delivery by lentiviral vectors across the Collaborative Cross (CC) mouse genetic reference population. For 24 weeks, we periodically measured hepatic luciferase expression from lentiviral vectors in 41 CC mouse strains. Hepatic and splenic vector copy numbers were determined. We report that the CC mouse strains showed highly diverse outcomes following lentiviral gene delivery. For the first time, a moderate correlation between mouse-strain-specific sleeping patterns and transduction efficiency was observed. We associated two quantitative trait loci (QTLs) with intrastrain variations in transduction phenotypes, which mechanistically relates to the phenomenon of metastable epialleles. An additional QTL was associated with the kinetics of hepatic transgene expression. Genes found in the above QTLs are potential targets for personalized gene therapy protocols. Importantly, we identified two mouse strains that open new directions for characterizing continuous viral vector silencing and HIV latency. Our findings suggest that wide-range patient-specific outcomes of viral vector-based gene therapy should be expected. Thus, novel clinical protocols should be considered for non-fatal diseases.

The latest developments in synthetic approaches to Duchenne muscular dystrophy

INTRODUCTION

Duchenne muscular dystrophy (DMD) is a rare X-linked genetic disorder caused by mutations in the dystrophin gene, leading to an almost complete absence of dystrophin, which is essential for muscle cell structure and function. This resulting muscle deterioration and fibrosis, eventually causes respiratory failure and cardiomyopathy. While there is currently no cure, existing therapies aim to prolong survival and alleviate symptoms.

AREAS COVERED

This paper reviews current and emerging therapies for DMD, focusing on their safety and efficacy. Although corticosteroids remain the standard treatment, newly approved drugs such as exon-skipping therapies, vamorolone, delandistrogene moxeparvovec, and givinostat provide new treatment options. Additionally, future therapies, including gene therapy, stem cell treatments, and anti-fibrotic agents, show promise for clinical application.

EXPERT OPINION

Advancements in DMD treatments have expanded patient options. While gene therapy offers potential for correcting the genetic defect and alleviating symptoms, corticosteroids remain the most cost-effective and well-researched treatment. This is partly due to the lack of compelling long-term safety and efficacy data for gene therapies. The accelerated FDA review process has enabled faster approval of new medications; however many have provided minimal clinical benefit to patients. Despite these challenges, continued drug development and innovative research offer hope to patients.

Thrombotic Microangiopathy Associated with Systemic Adeno-Associated Virus Gene Transfer: Review of Reported Cases

Complement-mediated thrombotic microangiopathy (TMA) in the form of atypical hemolytic uremic syndrome (aHUS) has emerged as an immune complication of systemic adeno-associated virus (AAV) gene transfer that was unforeseen based on nonclinical studies. Understanding this phenomenon in the clinical setting has been limited by incomplete data and a lack of uniform diagnostic and reporting criteria. While apparently rare based on available information, AAV-associated TMA/aHUS can pose a substantial risk to patients including one published fatality. Reported cases were originally limited to pediatric Duchenne muscular dystrophy patients receiving micro- or mini-dystrophin transgenes via AAV9 but have subsequently been reported in both pediatric and adult patients across a range of disorders, transgenes, promoters, and AAV capsid types. This article provides an introduction to the complement system, TMA and aHUS, and anticomplement therapies, then presents clinical reviews of AAV-associated TMA/aHUS cases that have been reported publicly. Finally, exploration of risk factors and current and future mitigation approaches are discussed.

Current and Emerging Issues in Adeno-Associated Virus Vector-Mediated Liver-Directed Gene Therapy

Adeno-associated virus (AAV) vectors have demonstrated safety and efficacy for gene transfer to hepatocytes in preclinical models, in various clinical trials and from a clinical experience with a growing number of approved gene therapy products. Although the exact duration is unknown, the expression of therapeutic genes in hepatocytes remains stable for several years after a single administration of the vector at clinically relevant doses in adult patients with hemophilia and other inherited metabolic disorders. However, clinical applications, especially for diseases requiring high AAV vector doses by intravenous administrations, have raised several concerns. These include the high prevalence of pre-existing immunity against the vector capsid, activation of the complement and the innate immunity with serious life-threatening complications, elevation of liver transaminases, liver growth associated with loss of transgene expression, underlying conditions negatively affecting AAV vector safety and efficacy. Despite these issues, the field is rapidly advancing with a better understanding of vector-host interactions and the development of new strategies to improve liver-directed gene therapy. This review provides an overview of the current and emerging challenges for AAV-mediated liver-directed gene therapy.

Genetic counseling for the dystrophinopathies-Practice resource of the National Society of Genetic Counselors

The dystrophinopathies encompass the phenotypically variable forms of muscular dystrophy caused by pathogenic variants in the DMD gene. The dystrophinopathies include the most common inherited muscular dystrophy among 46,XY individuals, Duchenne muscular dystrophy, as well as Becker muscular dystrophy and other less common phenotypic variants. With increased access to and utilization of genetic testing in the diagnostic and carrier setting, genetic counselors and clinicians in diverse specialty areas may care for individuals with and carriers of dystrophinopathy. This practice resource was developed as a tool for genetic counselors and other health care professionals to support counseling regarding dystrophinopathies, including diagnosis, health risks and management, psychosocial needs, reproductive options, clinical trials, and treatment. Genetic testing efforts have enabled genotype/phenotype correlation in the dystrophinopathies, but have also revealed unexpected findings, further complicating genetic counseling for this group of conditions. Additionally, the therapeutic landscape for dystrophinopathies has dramatically changed with several FDA-approved therapeutics, an expansive research pathway, and numerous clinical trials. Genotype-phenotype correlations are especially complex and genetic counselors' unique skill sets are useful in exploring and explaining this to families. Given the recent advances in diagnostic testing and therapeutics related to dystrophinopathies, this practice resource is a timely update for genetic counselors and other healthcare professionals involved in the diagnosis and care of individuals with dystrophinopathies.

Analysis of Exon Skipping Applicability for Dysferlinopathies

Exon skipping, mediated through antisense oligonucleotides (ASOs), is a promising approach to exclude pathogenic variants from the DYSF gene and treat dysferlinopathies. Understanding the applicability of various exon skipping strategies in the total patient population, an analysis not previously performed, can help guide researchers in prioritizing therapies with the broadest potential impact. Using data from the UMD-DYSF database, we evaluated all reported pathogenic variants in dysferlinopathy patients for the applicability of single- or double-exon skipping approaches to exclude the pathogenic variants while maintaining the open reading frame. A total of 61 theoretically applicable exon skipping strategies were identified, with the potential to address 90.0% of the pathogenic variants reported-44.6% through single-exon skipping and 45.3% through double-exon skipping. The most broadly applicable targets include exons 28 and 29 (9.0%), exons 27 and 28 (6.7%), and exons 50 and 51 (5.4%). While numerous theoretically applicable strategies were identified, it remains unclear if the truncated proteins produced through each exon skipping strategy will have improved functionality to alleviate patient symptoms. Further preclinical studies and clinical trials will be essential to determine the effectiveness of these therapies, potentially expanding access to disease-modifying treatments for dysferlinopathy patients.

Delivery of genetic medicines for muscular dystrophies

Muscular dystrophies are a group of heterogenic disorders characterized by progressive muscle weakness, the most common of them being Duchenne muscular dystrophy (DMD). Muscular dystrophies are caused by mutations in over 50 distinct genes, and many of them are caused by different genetic mechanisms. Currently, none of these diseases have a cure. However, in recent years, significant progress has been made to correct the underlying genetic cause. The clinical development of adeno-associated viral vector-based therapies has simultaneously produced excitement and disappointment in the research community due to the moderate effect, making it clear that new methods of muscle delivery have to be created. Herein, we review the main characteristics of major muscular dystrophies and outline various muscle-targeted delivery methods being explored for genetic medicines.

Extracellular vesicle-mediated VEGF-A mRNA delivery rescues ischaemic injury with low immunogenicity

BACKGROUND AND AIMS

Lackluster results from recently completed gene therapy clinical trials of VEGF-A delivered by viral vectors have heightened the need to develop alternative delivery strategies. This study aims to demonstrate the pre-clinical efficacy and safety of extracellular vesicles (EVs) loaded with VEGF-A mRNA for the treatment of ischaemic vascular disease.

METHODS

After encapsulation of full-length VEGF-A mRNA into fibroblast-derived EVs via cellular nanoporation (CNP), collected VEGF-A EVs were delivered into mouse models of ischaemic injury. Target tissue delivery was verified by in situ analysis of protein and gene expression. Functional rescue was confirmed by in vivo imaging and histology. The safety of single and serial delivery was demonstrated using immune-based assays.

RESULTS

VEGF-A EVs were generated with high mRNA content using a CNP methodology. VEGF-A EV administration demonstrated expression of exogenous VEGF-A mRNA by in situ RNA hybridization and elevated protein expression by western blot, microscopy, and enzyme-linked immunosorbent assay. Mice treated with human VEGF-A EVs after femoral or coronary artery ligation exhibited heightened neovascularization in ischaemic tissues with increased arterial perfusion and improvement in left ventricular function, respectively. Serial delivery of VEGF-EVs in injured skin showed improved wound healing with repeat administration. Importantly, as compared with adeno-associated viral and lipid nanoparticle VEGF-A gene therapy modalities, murine VEGF-A EV delivery did not trigger innate or adaptive immune responses at the injection site or systemically.

CONCLUSIONS

This study demonstrated that VEGF-A EV therapy offers efficient, dose-dependent VEGF-A protein formation with low immunogenicity, resulting in new vessel formation in murine models of ischaemic vascular disease.

Personalized membrane protein vaccine based on a lipid nanoparticle delivery system prevents postoperative recurrence in colorectal cancer models

While accessing tumor neoantigens and developing effective delivery systems have posed significant challenges in therapeutic oncology vaccines, this study introduces a cost- and time-efficient personalized tumor vaccine demonstrating potent anti-tumor effects in a mouse xenograft model. This vaccine utilizes a lipid nanoparticle (C5 LNP) system loaded with membrane protein antigens (mAg) derived from surgically excised tumor tissue. Its safety and efficacy were validated in a B16-OVA murine model. C5/OVA exhibited significant uptake by dendritic cells (DCs), leading to cross-presentation, maturation, and subsequent initiation of robust cell-mediated and humoral immune responses. This resulted in clear tumor growth suppression and extended survival in the B16-OVA model. Furthermore, the personalized C5/mAg vaccine effectively inhibited tumor growth in a colorectal carcinoma model. When combined with anti-PD-1 therapy, it notably increased complete remission (CR) rates in the CT26 xenograft model. Vaccinated mice demonstrated 100 % resistance to tumor rechallenge, underscoring the vaccine's ability to induce long-term immune memory. This study presents a promising personalized cancer vaccine delivery system with potential for both treatment and prevention of carcinoma in clinical applications. STATEMENT OF SIGNIFICANCE: In this paper, we present a scheme for manufacturing personalized tumor vaccines. The vaccine component consists of lipid nanoparticles (LNPs) designated C5 and membrane protein antigens (mAg) derived from autologous tumor tissue surgically resected from the patient. Our study demonstrates that the personalized mAg-C5 vaccine for colorectal carcinoma significantly inhibits tumor growth. Furthermore, conjugation with anti-PD-1 therapy demonstrably increased the complete remission (CR) rate in the murine CT26 xenograft tumor model. Additionally, mice treated with the C5/mAg vaccine exhibited 100 % resistance to tumor growth in a colon carcinoma rechallenge model, indicating the induction of immune memory by the vaccine. Our research results suggest that the mAg-LNP vaccine is a simple, cost-effective treatment that clinicians can easily and quickly integrate into routine practice.

Report on the 6th Ottawa International Conference on Neuromuscular Disease & Biology - September 7-9, 2023, Ottawa, Canada

The 6th Ottawa International Conference in Neuromuscular Disease and Biology was held on September 7-9, 2023 in Ottawa, Canada. The goal of the conference was to assemble international experts in fundamental science, translational medicine and clinical neuromuscular disease research. Speakers provided attendees with updates on a wide range of topics related to neuromuscular disease and biology, including methods to identify novel diseases, recent developments in muscle, motor neuron and stem cell biology, expanded disease pathogenesis of known diseases, and exciting advances in therapy development. A summary of the major topics and results presented by these speakers is provided.

Effective Reduction of Transgene-Specific Immune Response With rAAV Vectors Co-Expressing miRNA-UL112-5p or ERAP1 shRNA

Recombinant adeno-associated virus (rAAV) has emerged as one of the best gene delivery vectors for human gene therapy in vivo. However, the clinical efficacy of rAAV gene therapy is often hindered by the host immune response against its transgene products. Endoplasmic reticulum aminopeptidase 1 (ERAP1) is specialised to process peptides presented by class I molecules of major histocompatibility complex. Therefore, we hypothesise that modulation of the ERAP1 activity in rAAV transduced cells may be favoured to evade immune response against transgene products. In this study, we incorporated either miRNA-UL112-5p or ERAP1 shRNA into rAAV vectors expressing full-length ovalbumin (OVA) as a model antigen, and evaluated their effects for antigen presentation, cellular and humour immune response induced by OVA expression. The results indicated that silencing ERAP1 using miR-UL112-5p or ERAP1 shRNA did not affect the expression of OVA in cells, but inhibited the processing and presentation of OVA antigen peptide SIINFEKL in antigen presenting cells (APCs). Moreover, the rAAV vector co-expressing ERAP1 shRNA maintains stable and high expression of OVA in vivo, while simultaneously suppressing the humoral immunity of OVA. In addition, experimental results demonstrated that rAAV vectors incorporated ERAP1 shRNA efficiently repress costimulatory signals in dendritic cells (DCs), significantly attenuated the cytotoxic T-cell response, allowed for sustained transgene expression and reduced clearance of transduced muscle cells in mice. Moreover, our study suggested that the incorporation of miRNA-UL112-5p or ERAP1 shRNA into rAAV vectors effectively reduced transgene products induced immune response. The proposed method may potentially be applied in clinics to deliver therapeutic proteins safely and efficiently.

Challenges in Cardiomyopathy Gene Therapy Clinical Trial Design

Gene therapy has emerged as a possible treatment for progressive, debilitating Mendelian cardiomyopathies with limited therapeutic options. This paper arises from discussions at the 2023 Cardiovascular Clinical Trialists Forum and highlights several challenges relevant to gene therapy clinical trials, including low prevalence and high phenotypic heterogeneity of Mendelian cardiomyopathies, outcome selection complexities and resulting regulatory uncertainty, and immune responses to the adeno-associated viral vectors that are being used in ongoing studies. Avenues to address these challenges such as natural history studies, external controls, novel regulatory pathways, and immunosuppression are discussed. Relevant cases of recent therapy approvals are highlighted. Ultimately, this work aims to broadly frame discussions on and provide potential future avenues for clinical trial design for rare cardiomyopathy gene therapies.

Optimizing DMD management in Asia: Current challenges and future directions

BACKGROUND

Since 1970, advances in Duchenne muscular dystrophy (DMD) management have significantly extended the patients' life expectancy. However, DMD remains universally fatal.

OBJECTIVE

To understand the current DMD management standards and practices in Asia and to evaluate inconsistencies, unmet needs, and future directions for DMD patient management in the region.

METHODS

Clinical experts from Hong Kong, Singapore, and Taiwan convened in September 2023 to discuss DMD diagnosis, assessment, treatment, and management best practices. A pre-meeting survey was also administered to explore professional perspectives and practices and refine the discussion focus.

RESULTS

Genetic profiling has become the pivotal diagnostic tool and has been universally adopted by experts. Steroid therapy is recognized as the cornerstone of DMD care. However, there are various opinions regarding the timing of its initiation and whether it should be continued after the loss of ambulation. Gene therapy has the potential to significantly improve outcomes in patients with DMD. However, its adoption is hampered by high costs, the potential for serious adverse events, and difficulties with patient selection. Governments and manufacturers must work together to improve its affordability. Establishing a centralized DMD registry garnered strong support from the experts as it promised to provide insights into unique DMD subtypes, standardize treatment protocols, and facilitate the conduct of clinical trials. Furthermore, the introduction of gene therapy has highlighted the need for generating long-term safety and effectiveness data in patients with DMD. Lastly, a centralized patient registry can be used to inform policy decisions.

CONCLUSIONS

DMD care in Asia is characterized by substantial heterogeneity, with financial and reimbursement issues playing a major role in management decisions. A centralized patient registry has the potential to address these concerns by providing a valuable source of information.

The state-of-the-art of N-of-1 therapies and the IRDiRC N-of-1 development roadmap

In recent years, a small number of people with rare diseases caused by unique genetic variants have been treated with therapies developed specifically for them. This pioneering field of genetic N-of-1 therapies is evolving rapidly, giving hope for the individualized treatment of people living with very rare diseases. In this Review, we outline the concept of N-of-1 individualized therapies, focusing on genetic therapies, and illustrate advances and challenges in the field using cases for which therapies have been successfully developed. We discuss why the traditional drug development and reimbursement pathway is not fit for purpose in this field, and outline the pragmatic, regulatory and ethical challenges this poses for future access to N-of-1 therapies. Finally, we provide a roadmap for N-of-1 individualized therapy development.

Identification of a novel neutralization epitope in rhesus AAVs

Adeno-associated viruses (AAVs) are popular gene therapy delivery vectors, but their application can be limited by anti-vector immunity. Both preexisting neutralizing antibodies (NAbs) and post-administration NAbs can limit transgene expression and reduce the clinical utility of AAVs. The development of novel AAVs will advance our understanding of AAV immunity and may also have practical applications. In this study, we identified five novel AAV capsids from rhesus macaques. RhAAV4282 exhibited 91.4% capsid sequence similarity with AAV7 and showed similar tissue tropism with slightly diminished overall signal. Despite this sequence homology, RhAAV4282 and AAV7 showed limited cross-neutralization. We determined a cryo-EM structure of the RhAAV4282 capsid at 2.57 Å resolution and identified a small segment within the hypervariable region IV, involving seven amino acids that formed a shortened external loop in RhAAV4282 compared with AAV7. We generated RhAAV4282 and AAV7 mutants that involved swaps of this region and showed that this region partially determined neutralization phenotype. We termed this region the hypervariable region IV neutralizing epitope (HRNE). Our data suggests that modification of the HRNE can lead to AAVs with altered neutralization profiles.

AAVolve: Concatenated long-read deep sequencing enables whole capsid tracking during shuffled AAV library selection

Gene therapies using recombinant adeno-associated virus (AAV) vectors have demonstrated considerable clinical success in the treatment of genetic disorders. Improved vectors with favorable tropism profiles, decreased immunogenicity, and enhanced manufacturability are poised to further improve the state of gene therapies. Such vectors can be identified through directed evolution, a process of subjecting a diverse capsid library to a selection pressure to identify individual variants with a desired trait. Currently, libraries that involve changes distributed throughout the AAV capsid coding region, such as DNA family shuffled libraries, are largely characterized using low-throughput Sanger sequencing of individual clones. However, improvements in long-read sequencing technologies have increased their applicability to capsid libraries and evaluation of the selection process. Here, we explore the application of Oxford Nanopore Technologies refined by a concatemeric consensus method for initial library characterization and monitoring selection of a shuffled AAV capsid library. Furthermore, we present AAVolve, a bioinformatic pipeline for processing long-read data from AAV-directed evolution experiments. Our approach allows high-throughput characterization of AAV capsids in a streamlined manner, facilitating deeper insights into library composition through multiple rounds of selection, and generalization through training of machine learning models.

Gene Therapy in Cardiovascular Disease: Recent Advances and Future Directions in Science: A Science Advisory From the American Heart Association

Cardiovascular disease remains the foremost cause of morbidity and mortality globally, affecting millions of individuals. Recent discoveries illuminate the substantial role of genetics in cardiovascular disease pathogenesis, encompassing both monogenic and polygenic mechanisms and identifying tangible targets for gene therapies. Innovative strategies have emerged to rectify pathogenic variants that cause monogenic disorders such as hypertrophic, dilated, and arrhythmogenic cardiomyopathies and hypercholesterolemia. These include delivery of exogenous genes to supplement insufficient protein levels caused by pathogenic variants or genome editing to correct, delete, or modify mutant sequences to restore protein function. However, effective delivery of gene therapy to specified cells presents formidable challenges. Viral vectors, notably adeno-associated viruses and nonviral vectors such as lipid and engineered nanoparticles, offer distinct advantages and limitations. Additional risks and obstacles remain, including treatment durability, tissue-specific targeting, vector-associated adverse events, and off-target effects. Addressing these challenges is an ongoing imperative; several clinical gene therapy trials are underway, and many more first-in-human studies are anticipated. This science advisory reviews core concepts of gene therapy, key obstacles, patient risks, and ongoing research endeavors to enable clinicians to understand the complex landscape of this emerging therapy and its remarkable therapeutic potential to benefit cardiovascular disease.

AAV-mediated gene therapies by miniature gene editing tools

The advent of CRISPR-Cas has revolutionized precise gene editing. While pioneering CRISPR nucleases like Cas9 and Cas12 generate targeted DNA double-strand breaks (DSB) for knockout or homology-directed repair, next generation CRISPR technologies enable gene editing without DNA DSB. Base editors directly convert bases, prime editors make diverse alterations, and dead Cas-regulator fusions allow nuanced control of gene expression, avoiding potentially risks like translocations. Meanwhile, the discovery of diminutive Cas12 orthologs and Obligate Mobile Element-Guided Activity (OMEGA) nucleases has overcome cargo limitations of adeno-associated viral vectors, expanding prospects for in vivo therapeutic delivery. Here, we review the ever-evolving landscape of cutting-edge gene editing tools, focusing on miniature Cas12 orthologs and OMEGA effectors amenable to single AAV packaging. We also summarize CRISPR therapies delivered using AAV vectors, discuss challenges such as efficiency and specificity, and look to the future of this transformative field of in vivo gene editing enabled by AAV vectors delivery.

Systemic Treatment of Body-Wide Duchenne Muscular Dystrophy Symptoms

Duchenne muscular dystrophy (DMD) is a fatal X-linked disease that leads to premature death due to the loss of dystrophin. Current strategies predominantly focus on the therapeutic treatment of affected skeletal muscle tissue. However, certain results point to the fact that with successful treatment of skeletal muscle, DMD-exposed latent phenotypes in tissues, such as cardiac and smooth muscle, might lead to adverse effects and even death. Likewise, it is now clear that the absence of dystrophin affects the function of the nervous system, and that this phenotype is more pronounced when shorter dystrophins are absent, in addition to the full-length dystrophin that is present predominantly in the muscle. Here, I focus on the systemic aspects of DMD, highlighting the ubiquitous expression of the dystrophin gene in human tissues. Furthermore, I describe therapeutic strategies that have been tested in the clinic and point to unresolved questions regarding the function of distinct dystrophin isoforms, and the possibility of current therapeutic strategies to tackle phenotypes that relate to their absence.

AAV delivery strategy with mechanical support for safe and efficacious cardiac gene transfer in swine

Adeno-associated virus-based gene therapy is a promising avenue in heart failure treatment, but has shown limited cardiac virus uptake in humans, requiring new approaches for clinical translation. Using a Yorkshire swine ischemic heart failure model, we demonstrate significant improvement in gene uptake with temporary coronary occlusions assisted by mechanical circulatory support. We first show that mechanical support during coronary artery occlusions prevents hemodynamic deterioration (n = 5 female). Subsequent experiments show that coronary artery occlusions during gene delivery improve gene transduction, while adding coronary sinus occlusion (Stop-flow) further improves gene expression up to >1 million-fold relative to conventional intracoronary infusion. Complete survival during and after delivery (n = 10 female, n = 10 male) further indicates safety of the approach. Improved cardiac gene expression correlates with virus uptake without an increase in extra-cardiac expression. Stop-flow delivery of virus-sized gold nanoparticles exhibits enhanced endothelial adherence and uptake, suggesting a mechanism independent of virus biology. Together, utilizing mechanical support for cardiac gene delivery offers a clinically-applicable strategy for heart failure-targeted therapies.

Systemic Toxicity of Recombinant Adeno-Associated Virus Gene Therapy Vectors

Recombinant adeno-associated virus (rAAV) vectors have emerged as a promising tool for gene therapy. However, the systemic administration of rAAV vectors is not without risks, particularly for dose levels >1 × 1014 viral genome per kilogram of body weight (vg/kg). rAAV-associated toxicities can variably manifest either acutely or in a delayed manner. Acute toxicities often present shortly after administration and can include severe immune responses, hepatotoxicity, and thrombotic microangiopathy (TMA). Delayed toxicities, on the other hand, may emerge weeks to months post-treatment, potentially involving chronic liver damage or prolonged immune activation. Thrombotic microangiopathy is often associated with complement activation and endothelial damage. The activation of the complement system can additionally trigger a cascade of inflammatory responses, exacerbating systemic toxicity. While many of these toxicities are reversible with appropriate medical intervention, there have been instances where the adverse effects were severe enough to lead to fatalities. Both human and animal studies have reported these adverse effects, highlighting the critical importance of thorough preclinical testing. However, a differential toxicity profile associated with systemic AAV administration exists between humans and nonhuman primates (NHPs), in which certain toxicities reported in humans are yet to be observed in NHPs, and vice versa. This review aims to explore the recent literature on systemic rAAV toxicities, focusing on dose levels, the role of the complement activation pathway, endothelial injury, TMA, hepatotoxicity, and the bidirectional translational safety profiles from both human and animal studies.

The effects of cannabinoids on the kidney

Cannabinoids are a class of drugs derived from the Cannabis plant that are widely used for the treatment of various medical conditions and recreational use. Common examples include Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), spice, and 2-arachidonoylglycerol (2-AG). With more than 100 cannabinoids identified, their influence on the nervous system, role in pain management, and effects due to illicit use have been extensively studied. However, their effects on peripheral organs, such as the kidneys, require further examination. With dramatic rises in use, production, and legalization, it is essential to understand the impact and mechanistic properties of these drugs as they pertain to renal and cardiovascular physiology. The goal of this review is to summarize prior literature on the expression of cannabinoid receptors and how cannabinoids influence renal function. This review first discusses the interaction of the endocannabinoid system (ECS) and renal physiology and pathophysiology. Following, we briefly discuss the role of the ECS in various kidney diseases and the potential therapeutic applications of drugs targeting the cannabinoid system. Lastly, recent studies have identified several detrimental effects of cannabinoids, not only on the kidney but also in contributing to adverse cardiovascular outcomes. Thus, the negative impact of cannabinoids on renal function and the development of various cardiovascular diseases is also discussed.

Next-generation strategies to improve safety and efficacy of adeno-associated virus-based gene therapy for hemophilia: lessons from clinical trials in other gene therapies

Three major directions for the global progress of adeno-associated virus (AAV) vectors for gene therapies (GT) are analyzed: 1) engineering vectors to increase transgene expression; 2) aligning interests of the health system with costs and challenges for the pharmaceutical industry; and 3) refining patient eligibility criteria and endpoint definition. Currently employed AAV vectors may cause toxicity and adverse events. Furthermore, studies in animals do not fully predict risks and clinical benefits of AAV-based GT, and animal models reflecting the heterogeneity of certain clinical settings (e.g., congestive heart failure) are not widely available for improving AAV-based GT. Finally, antisense and gene editing approaches will soon complement gene augmentation strategies for the stable solution of unsolved issues of AAV-based GT. While minimizing toxicity, next-generation AAV vectors should decrease the viral load needed to achieve therapeutic efficacy, be functional in a restricted cellular subset, avoid transgene expression in unwanted cells (e.g., hepatocytes), and escape immune oversight in AAV-based GT. The role of stress-induced apoptosis in the loss of transgene expression in GT should also be explored. Aligning the interests and obligations of the pharmaceutical industry with those of the health system is critical for the success of AAV-based GT. Costs and challenges for the pharmaceutical industry include: a) removing impurities from AAV; b) validating tests to measure treatment efficacy; c) promoting training programs to standardize vector genome delivery; d) collecting long-term follow-up data; and e) maintaining sustainability and cost-effectiveness of AAV-based GT. In rare disorders with small patient numbers (e.g., hemophilia), clear-cut outcomes are mandatory as endpoints of unequivocal efficacy data.

Drug-induced liver injury related to gene therapy: A new challenge to be managed

Gene therapy is being successfully developed for the treatment of several genetic disorders. Various methods of gene transfer have been developed to enable the production of the deficient enzyme or protein. One of the most important is adeno-associated virus vectors, which have been shown to be viable for use in in vivo gene therapy. Several gene therapies have already been approved. They are also promising for acquired diseases. Important examples include gene therapy for haemophilia A and B, X-linked myotubular myopathy, spinal muscular atrophy and several liver diseases such as Criggler-Najjar disease, alpha-1 antitrypsin deficiency and Fabry disease. However, the introduction of a foreign compound into hepatocytes leads to hepatic reactions with heterogeneous phenotypic expression and a wide spectrum of severity, ranging from mild transaminase elevation to acute liver failure. Several mechanisms appear to be involved in liver injury, including an immune response, but also direct toxicity depending on the method of gene transfer. As a result, the incidence, expression and severity of liver injury vary from indication to indication and from patient to patient. Patients treated for haemophilia A are more prone to transaminase elevation than those treated for haemophilia B. Corticosteroids are successfully used to correct liver reactions but also to prevent degradation of the transferred gene and loss of therapeutic activity. The aim of this review is to describe the risk of liver injury according to the indication for gene therapy and the short- and long-term management currently proposed to prevent or correct liver reactions in clinical practice.

Clinical and Translational Landscape of Viral Gene Therapies

Gene therapies hold significant promise for treating previously incurable diseases. A number of gene therapies have already been approved for clinical use. Currently, gene therapies are mostly limited to the use of adeno-associated viruses and the herpes virus. Viral vectors, particularly those derived from human viruses, play a critical role in this therapeutic approach due to their ability to efficiently deliver genetic material to target cells. Despite their advantages, such as stable gene expression and efficient transduction, viral vectors face numerous limitations that hinder their broad application. These limitations include small cloning capacities, immune and inflammatory responses, and risks of insertional mutagenesis. This review explores the current landscape of viral vectors used in gene therapy, discussing the different types of DNA- and RNA-based viral vectors, their characteristics, limitations, and current medical and potential clinical applications. The review also highlights strategies to overcome existing challenges, including optimizing vector design, improving safety profiles, and enhancing transgene expression both using molecular techniques and nanotechnologies, as well as by approved drug formulations.

On RNA-programmable gene modulation as a versatile set of principles targeting muscular dystrophies

The repurposing of RNA-programmable CRISPR systems from genome editing into epigenome editing tools is gaining pace, including in research and development efforts directed at tackling human disorders. This momentum stems from the increasing knowledge regarding the epigenetic factors and networks underlying cell physiology and disease etiology and from the growing realization that genome editing principles involving chromosomal breaks generated by programmable nucleases are prone to unpredictable genetic changes and outcomes. Hence, engineered CRISPR systems are serving as versatile DNA-targeting scaffolds for heterologous and synthetic effector domains that, via locally recruiting transcription factors and chromatin remodeling complexes, seek interfering with loss-of-function and gain-of-function processes underlying recessive and dominant disorders, respectively. Here, after providing an overview about epigenetic drugs and CRISPR-Cas-based activation and interference platforms, we cover the testing of these platforms in the context of molecular therapies for muscular dystrophies. Finally, we examine attributes, obstacles, and deployment opportunities for CRISPR-based epigenetic modulating technologies.

Liver gene transfer for metabolite detoxification in inherited metabolic diseases

Inherited metabolic disorders (IMDs) are a growing group of genetic diseases caused by defects in enzymes that mediate cellular metabolism, often resulting in the accumulation of toxic substrates. The liver is a highly metabolically active organ that hosts several thousands of chemical reactions. As such, it is an organ frequently affected in IMDs. In this article, we review current approaches for liver-directed gene-based therapy aimed at metabolite detoxification in a variety of IMDs. Moreover, we discuss current unresolved challenges in gene-based therapies for IMDs.