261st ENMC International Workshop: Management of safety issues arising following AAV gene therapy. 17th-19th June 2022, Hoofddorp, The Netherlands

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.

An Imperative for Public Sharing of Adverse Events of Gene Therapy Trials

This Viewpoint describes the need for public sharing of adverse events associated with genetic therapies to improve patient safety.

Charcot-Marie-Tooth disease: a review of clinical developments and its management - What's new in 2025?

INTRODUCTION

Charcot-Marie-Tooth disease (CMT) understanding and diagnostic rates are improving. Symptomatic management is still the only option, but many therapeutic approaches are under investigation, some in the clinical trial phase.

AREAS COVERED

Through a comprehensive search in PubMed, the ClinicalTrials.gov website, and the latest abstracts on the topic, the authors review the diagnostic advances and promising treatments, focusing on pharmacological and gene therapy/silencing approaches, and on clinical trial challenges. They also review current CMT management, including rehabilitation, orthotics, and associated symptoms and comorbidities.

EXPERT OPINION

The CMT field is evolving rapidly, with significant advances in genetic diagnosis and disease recognition. International networks and patient organization partnerships are vital for progress, enabling collaboration and large-scale studies. Metabolic neuropathies are relatively easier to target, and interim analysis results from the CMT-SORD trial suggest govorestat may become the first approved CMT drug. Gene therapy shows promise but currently faces safety and targeting challenges; PMP22 silencers for CMT1A are close to being tested in patients. New drugs, such as HDAC6 inhibitors, are also approaching the clinical trial phase, despite existing hurdles. Supportive care, including rehabilitation and orthotics, continues to improve quality of life. There is optimism that within the next decade, approved therapies will reduce disease burden.

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.

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.

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.

A systematic review of immunosuppressive protocols used in AAV gene therapy for monogenic disorders

The emergence of adeno-associated virus (AAV)-based gene therapy has brought hope to patients with severe monogenic disorders. However, immune responses to AAV vectors and transgene products present challenges that require effective immunosuppressive strategies. This systematic review focuses on the immunosuppressive protocols used in 38 clinical trials and 35 real-world studies, considering a range of monogenic diseases, AAV serotypes, and administration routes. The review underscores the need for a deeper understanding of immunosuppressive regimens to enhance the safety and effectiveness of AAV-based gene therapy. Characterizing the immunological responses associated with various gene therapy treatments is crucial for optimizing treatment protocols and ensuring the safety and efficacy of forthcoming gene therapy interventions. Further research and understanding of the impact of immunosuppression on disease, therapy, and route of administration will contribute to the development of more effective and safer gene therapy approaches in the future.

Engineered IgM and IgG cleaving enzymes for mitigating antibody neutralization and complement activation in AAV gene transfer

Systemic dosing of adeno-associated viral (AAV) vectors poses potential risk of adverse side effects including complement activation triggered by anti-capsid immunity. Due to the multifactorial nature of toxicities observed in this setting, a wide spectrum of immune modulatory regimens are being investigated in the clinic. Here, we discover an IgM cleaving enzyme (IceM) that degrades human IgM, a key trigger in the anti-AAV immune cascade. We then engineer a fusion enzyme (IceMG) with dual proteolytic activity against human IgM and IgG. IceMG cleaves B cell surface antigen receptors and inactivates phospholipase gamma signaling in vitro. Importantly, IceMG is more effective at inhibiting complement activation compared with an IgG cleaving enzyme alone. Upon IV dosing, IceMG rapidly and reversibly clears circulating IgM and IgG in macaques. Antisera from these animals treated with IceMG shows decreased ability to neutralize AAV and activate complement. Consistently, pre-conditioning with IceMG restores AAV transduction in mice passively immunized with human antisera. Thus, IgM cleaving enzymes show promise in simultaneously addressing multiple aspects of anti-AAV immunity mediated by B cells, circulating antibodies and complement. These studies have implications for improving safety of AAV gene therapies and possibly broader applications including organ transplantation and autoimmune diseases.

Thrombotic Microangiopathy as an Emerging Complication of Viral Vector-Based Gene Therapy

Gene therapy has brought tremendous hope for patients with severe life-threatening monogenic diseases. Although studies have shown the efficacy of gene therapy, serious adverse events have also emerged, including thrombotic microangiopathy (TMA) following viral vector-based gene therapy. In this review, we briefly summarize the concept of gene therapy, and the immune response triggered by viral vectors. We also discuss the incidence, presentation, and potential underlying mechanisms, including complement activation, of gene therapy-associated TMA. Further studies are needed to better define the pathogenesis of this severe complication of gene therapy, and the optimal measures to prevent it.

Adeno-associated virus as a delivery vector for gene therapy of human diseases

Adeno-associated virus (AAV) has emerged as a pivotal delivery tool in clinical gene therapy owing to its minimal pathogenicity and ability to establish long-term gene expression in different tissues. Recombinant AAV (rAAV) has been engineered for enhanced specificity and developed as a tool for treating various diseases. However, as rAAV is being more widely used as a therapy, the increased demand has created challenges for the existing manufacturing methods. Seven rAAV-based gene therapy products have received regulatory approval, but there continue to be concerns about safely using high-dose viral therapies in humans, including immune responses and adverse effects such as genotoxicity, hepatotoxicity, thrombotic microangiopathy, and neurotoxicity. In this review, we explore AAV biology with an emphasis on current vector engineering strategies and manufacturing technologies. We discuss how rAAVs are being employed in ongoing clinical trials for ocular, neurological, metabolic, hematological, neuromuscular, and cardiovascular diseases as well as cancers. We outline immune responses triggered by rAAV, address associated side effects, and discuss strategies to mitigate these reactions. We hope that discussing recent advancements and current challenges in the field will be a helpful guide for researchers and clinicians navigating the ever-evolving landscape of rAAV-based gene therapy.

Liver-directed gene therapy for inherited metabolic diseases

Gene therapy clinical trials are rapidly expanding for inherited metabolic liver diseases whilst two gene therapy products have now been approved for liver based monogenic disorders. Liver-directed gene therapy has recently become an option for treatment of haemophilias and is likely to become one of the favoured therapeutic strategies for inherited metabolic liver diseases in the near future. In this review, we present the different gene therapy vectors and strategies for liver-targeting, including gene editing. We highlight the current development of viral and nonviral gene therapy for a number of inherited metabolic liver diseases including urea cycle defects, organic acidaemias, Crigler-Najjar disease, Wilson disease, glycogen storage disease Type Ia, phenylketonuria and maple syrup urine disease. We describe the main limitations and open questions for further gene therapy development: immunogenicity, inflammatory response, genotoxicity, gene therapy administration in a fibrotic liver. The follow-up of a constantly growing number of gene therapy treated patients allows better understanding of its benefits and limitations and provides strategies to design safer and more efficacious treatments. Undoubtedly, liver-targeting gene therapy offers a promising avenue for innovative therapies with an unprecedented potential to address the unmet needs of patients suffering from inherited metabolic diseases.