Mitigating Serious Adverse Events in Gene Therapy with AAV Vectors: Vector Dose and Immunosuppression

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.

Progress and Challenges in the Treatment of Fabry Disease

Fabry disease is a rare but life-threatening, X-linked, inherited lysosomal storage disorder in which globotriaosylceramide is insufficiently metabolized because of reduced α-galactosidase A activity. Cellular globotriaosylceramide accumulation causes a multisystemic disease, which, if left untreated, reduces life expectancy in female and male individuals by around 10 and 20 years, respectively, leading to progressive renal failure, hypertrophic cardiomyopathy, cardiac arrhythmia, and premature cerebral infarction. The method of choice for confirming the diagnosis is the determination of reduced α-galactosidase A activity in leukocytes in male individuals and the molecular genetic detection of a disease-causing mutation in female individuals. Current approved treatment includes enzyme replacement therapy (agalsidase alfa [0.2 mg/kg body weight], agalsidase beta or pegunigalsidase alfa [both 1.0 mg/kg body weight]) every other week intravenously or, if a responding ('amenable') α-galactosidase A mutation is present, oral pharmacological chaperone therapy (migalastat 123 mg, every other day). Future therapeutic options may include substrate reduction therapy, gene therapy, messenger RNA therapy, and/or vesicle-packaged enzyme replacement therapy. This review presents current and future treatment options with advantages and disadvantages of the different treatment options.

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.

Advances in the study and treatment of genetic cardiomyopathies

Cardiomyopathies are primary disorders of the heart muscle. Three key phenotypes have been defined, based on morphology and arrhythmia burden: hypertrophic cardiomyopathy (HCM), with thickened heart muscle and diastolic dysfunction; dilated cardiomyopathy (DCM), with left ventricular enlargement and systolic dysfunction; and arrhythmogenic cardiomyopathy (ACM), with right, left, or biventricular involvement and arrhythmias out of proportion to systolic dysfunction. Genetic discoveries of the molecular basis of disease are paving the way for greater precision in diagnosis and management and revealing mechanisms that account for distinguishing clinical features. This deeper understanding has propelled the development of new treatments for cardiomyopathies: disease-specific, mechanistically based medicines that counteract pathophysiology, and emergent gene therapies that aim to intercept disease progression and restore cardiac physiology. Together, these discoveries have advanced fundamental insights into cardiac biology and herald a new era for patients with cardiomyopathy.

Cancer vaccines: an update on recent achievements and prospects for cancer therapy

Decades of basic and translational research have led to a momentum shift in dissecting the relationship between immune cells and cancer. This culminated in the emergence of breakthrough immunotherapies that paved the way for oncologists to manage certain hard-to-treat cancers. The application of high-throughput techniques of genomics, transcriptomics, and proteomics was conclusive in making and expediting the manufacturing process of cancer vaccines. Using the latest research technologies has also enabled scientists to interpret complex and multiomics data of the tumour mutanome, thus identifying new tumour-specific antigens to design new generations of cancer vaccines with high specificity and long-term efficacy. Furthermore, combinatorial regimens of cancer vaccines with immune checkpoint inhibitors have offered new therapeutic approaches and demonstrated impressive efficacy in cancer patients over the last few years. In the present review, we summarize the current state of cancer vaccines, including their potential therapeutic effects and the limitations that hinder their effectiveness. We highlight the current efforts to mitigate these limitations and highlight ongoing clinical trials. Finally, a special focus will be given to the latest milestones expected to transform the landscape of cancer therapy and nurture hope among cancer patients.

Preclinical evaluation of NG101, a potential AAV gene therapy for wet age-related macular degeneration

Age-related macular degeneration (AMD) is a leading cause of vision loss in individuals over the age of 55. Approximately 10%-15% of AMD patients develop choroidal neovascularization (CNV), leading to wet AMD (wAMD), which accounts for nearly 90% of AMD-related blindness. Inhibition of vascular endothelial growth factor (VEGF) is the standard treatment for wAMD. However, the frequent administration of the current treatment imposes a significant burden on wAMD patients. Therefore, there is an unmet need for treatments that require less-frequent administration. Here, we present findings on the safety and efficacy of NG101, a recombinant adeno-associated virus (rAAV) vector encoding aflibercept, an anti-VEGF agent, for wAMD therapy. A single subretinal injection of NG101 effectively reduced CNV lesion leakage and size at doses as low as 1 × 106 in mouse and 3 × 109 viral genomes per eye in cynomolgus monkeys. In cynomolgus monkeys, NG101-derived aflibercept expression in ocular tissues persisted for 1 year post-injection, indicating sustained therapeutic potential. Biodistribution analysis revealed that NG101 was primarily localized in ocular tissues. Only mild and transient ocular inflammatory responses were observed. Overall, these findings suggest that NG101, with its efficacy at low doses and sustained expression, is a promising therapeutic candidate for wAMD.

Exploring delivery systems for targeted nanotechnology-based gene therapy in the inner ear

Hearing loss places a significant burden on our aging population. However, there has only been limited progress in developing therapeutic techniques to effectively mediate this condition. This review will outline several of the most commonly utilized practices for the treatment of sensorineural hearing loss before exploring more novel techniques currently being investigated via both in vitro and in vivo research. This review will place particular emphasis on novel gene-delivery technologies. Primarily, it will focus on techniques used to deliver genes that have been shown to encourage the proliferation and differentiation of sensory cells within the inner ear and how these technologies may be translated into providing clinically useful results for patients.

Stimulus-Responsive Nanodelivery and Release Systems for Cancer Gene Therapy: Efficacy Improvement Strategies

Introduction of exogenous genes into target cells to overcome various tumor diseases caused by genetic defects or abnormalities and gene therapy, a new treatment method, provides a promising strategy for tumor treatment. Over the past decade, gene therapy has made exciting progress; however, it still faces the challenge of low nucleic acid delivery and release efficiencies. The emergence of nonviral vectors, primarily nanodelivery and release systems (NDRS), has resulted in a historic breakthrough in the application of gene therapy. NDRS, especially stimulus-responsive NDRS that can respond in a timely manner to changes in the internal and external microenvironment (eg, low pH, high concentration of glutathione/reactive oxygen species, overexpressed enzymes, temperature, light, ultrasound, and magnetic field), has shown excellent loading and release advantages in the precision and efficiency of tumor gene therapy and has been widely applied. The only disadvantage is that poor transfection efficiency limits the in-depth application of gene therapy in clinical practice, owing to the presence of biological barriers in the body. Therefore, this review first introduces the development history of gene therapy, the current obstacles faced by gene delivery, strategies to overcome these obstacles, and conventional vectors, and then focuses on the latest research progress in various stimulus-responsive NDRS for improving gene delivery efficiency. Finally, the future challenges and prospects that stimulus-responsive NDRS may face in clinical application and transformation are discussed to provide references for enhancing in-depth research on tumor gene therapy.

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.

White-to-Beige and Back: Adipocyte Conversion and Transcriptional Reprogramming

Obesity has become a pandemic, as currently more than half a billion people worldwide are obese. The etiology of obesity is multifactorial, and combines a contribution of hereditary and behavioral factors, such as nutritional inadequacy, along with the influences of environment and reduced physical activity. Two types of adipose tissue widely known are white and brown. While white adipose tissue functions predominantly as a key energy storage, brown adipose tissue has a greater mass of mitochondria and expresses the uncoupling protein 1 (UCP1) gene, which allows thermogenesis and rapid catabolism. Even though white and brown adipocytes are of different origin, activation of the brown adipocyte differentiation program in white adipose tissue cells forces them to transdifferentiate into "beige" adipocytes, characterized by thermogenesis and intensive lipolysis. Nowadays, researchers in the field of small molecule medicinal chemistry and gene therapy are making efforts to develop new drugs that effectively overcome insulin resistance and counteract obesity. Here, we discuss various aspects of white-to-beige conversion, adipose tissue catabolic re-activation, and non-shivering thermogenesis.

Dose-response evaluation of intravenous gene therapy in a symptomatic mouse model of metachromatic leukodystrophy

Metachromatic leukodystrophy (MLD) is a rare, autosomal recessive neurodegenerative disease caused by deficient activity of the lysosomal enzyme arylsulfatase A (ARSA), resulting in sulfatide accumulation and subsequent demyelination and neuronal damage within the central and peripheral nervous systems. Three clinical forms of MLD have been described, based on age at symptom onset. The most frequent and severe forms have an early onset, with the disease progressing rapidly toward severe motor and cognitive regression and ultimately premature death. There are currently no approved therapies for most of these early-onset patients once symptoms are present. Thus, it is crucial to develop new approaches to treat symptomatic patients. Here, we proposed a gene therapy approach based on the intravenous delivery of AAVPHP.eB encoding ARSA. MLD mice were treated at 6 months for a dose-response study and at 9 months to assess late-treatment efficacy. Therapeutic efficacy was evaluated 3 or 6 months after injection. We demonstrated a broad transduction in the central nervous system, a complete correction of sulfatide storage, and a significant improvement in neuroinflammation at low dose and late treatment. Taken together, this work establishes a strong rationale for proposing a phase I/II clinical trial in MLD patients.

Hepatitis after gene therapy, what are the possible causes?

Hepatitis is a common adverse event following gene therapy for haemophilia, often associated with a loss of transgene expression. Investigating the potential causes and implications of this is crucial for the overall success of treatment. Gene therapy trials using adeno-associated virus (AAV) vectors have demonstrated promising results marked by increases in factor FVIII and FIX levels and reductions in episodes of bleeding. However, hepatocellular injury characterised by elevations in alanine aminotransferases (ALT) has been noted. This liver injury is typically transient and asymptomatic, posing challenges in determining its clinical significance. Proposed causes encompass immune-mediated responses, notably T cell cytotoxicity in response to the AAV vector, direct liver injury from the viral capsid or transcribed protein via the unfolded protein response and pre-existing liver conditions. Liver biopsy data conducted years post-gene therapy infusion has shown sinusoidal infiltration without significant inflammation. The overall safety profile of gene therapy remains favourable with no evidence drug-induced liver injury (DILI) based on Hy's Law criteria. Essential pre-therapy monitoring and identifying patients at high risk of liver injury should involve liver function tests and non-invasive fibroscans, while novel blood-based biomarkers are under exploration. Further research is required to comprehend the mechanisms underlying transaminitis, loss of transgene expression and long-term effects on the liver, providing insights for optimising gene therapy for haemophilia.

Gene therapy vector-related myocarditis

Gene therapy is a technique to correct genetic abnormalities, through introduction of a functional gene or through direct genome editing. Adeno-associated virus (AAV)-mediated gene replacement shows promise for targeted therapies in treatment of inherited cardiomyopathies and is the most used approach in clinical trials. However, immune responses from the host to the virus and gene product pose delivery and safety challenges. This review explores the immunological reactions to AAV-based gene therapy, their potential toxic effects, with a focus on myocarditis, and future directions for gene therapy.

Whole-Body Disposition and Physiologically Based Pharmacokinetic Modeling of Adeno-Associated Viruses and the Transgene Product

To facilitate model-informed drug development (MIDD) of adeno-associated virus (AAV) therapy, here we have developed a physiologically based pharmacokinetic (PBPK) model for AAVs following preclinical investigation in mice. After 2E11 Vg/mouse dose of AAV8 and AAV9 encoding a monoclonal antibody (mAb) gene, whole-body disposition of both the vector and the transgene mAb was evaluated over 3 weeks. At steady-state, the following tissue-to-blood (T/B) concentration ratios were found for AAV8/9: ∼50 for liver; ∼10 for heart and muscle; ∼2 for brain, lung, kidney, adipose, and spleen; ≤1 for bone, skin, and pancreas. T/B values for mAb were compared with the antibody biodistribution coefficients, and five different clusters of organs were identified based on their transgene expression profile. All the biodistribution data were used to develop a novel AAV PBPK model that incorporates: (i) whole-body distribution of the vector; (ii) binding, internalization, and intracellular processing of the vector; (iii) transgene expression and secretion; and (iv) whole-body disposition of the secreted transgene product. The model was able to capture systemic and tissue PK of the vector and the transgene-produced mAb reasonably well. Pathway analysis of the PBPK model suggested that liver, muscle, and heart are the main contributors for the secreted transgene mAb. Unprecedented PK data and the novel PBPK model developed here provide the foundation for quantitative systems pharmacology (QSP) investigations of AAV-mediated gene therapies. The PBPK model can also serve as a quantitative tool for preclinical study design and preclinical-to-clinical translation of AAV-based gene therapies.

AAV Immunotoxicity: Implications in Anti-HBV Gene Therapy

Hepatitis B virus (HBV) has afflicted humankind for decades and there is still no treatment that can clear the infection. The development of recombinant adeno-associated virus (rAAV)-based gene therapy for HBV infection has become important in recent years and research has made exciting leaps. Initial studies, mainly using mouse models, showed that rAAVs are non-toxic and induce minimal immune responses. However, several later studies demonstrated rAAV toxicity, which is inextricably associated with immunogenicity. This is a major setback for the progression of rAAV-based therapies toward clinical application. Research aimed at understanding the mechanisms behind rAAV immunity and toxicity has contributed significantly to the inception of approaches to overcoming these challenges. The target tissue, the features of the vector, and the vector dose are some of the determinants of AAV toxicity, with the latter being associated with the most severe adverse events. This review discusses our current understanding of rAAV immunogenicity, toxicity, and approaches to overcoming these hurdles. How this information and current knowledge about HBV biology and immunity can be harnessed in the efforts to design safe and effective anti-HBV rAAVs is discussed.

Redirecting AAV vectors to extrahepatic tissues

Recombinant adeno-associated viral (AAV) vectors are the current benchmark for systemic delivery of gene therapies to multiple organs in vivo. Despite clinical successes, safe and effective gene delivery to extrahepatic tissues has proven challenging due to dose limiting toxicity arising from high liver uptake of AAV vectors. Deeper understanding of AAV structure, receptor biology, and pharmacology has enabled the design and engineering of liver-de-targeted capsids ushering in several new vector candidates. This next generation of AAVs offers significant promise for extrahepatic gene delivery to cardiovascular, musculoskeletal, and neurological tissues with improved safety profiles.

Gene therapy for heart failure and cardiomyopathies

Gene therapy strategies encompass a range of approaches, including gene replacement and gene editing. Gene replacement involves providing a functional copy of a modified gene, while gene editing allows for the correction of existing genetic mutations. Gene therapy has already received approval for treating genetic disorders like Leber's congenital amaurosis and spinal muscular atrophy. Currently, research is being conducted to explore its potential use in cardiology. This review aims to summarize the mechanisms behind different gene therapy strategies, the available delivery systems, the primary risks associated with gene therapy, ongoing clinical trials, and future targets, with a particular emphasis on cardiomyopathies.

Gene therapy and other novel treatment approaches for Charcot-Marie-Tooth disease

There is still no effective drug treatment available for Charcot-Marie-Tooth disease (CMT). Current management relies on rehabilitation therapy, surgery for skeletal deformities, and symptomatic treatment. The challenge is to find disease-modifying therapies. Several approaches, including gene silencing (by means of ASO, siRNA, shRNA, miRNA, CRISPR-Cas9 editing), to counteract the PMP22 gene overexpression in the most frequent CMT1A type are under investigation. PXT3003 is the compound in the most advanced phase for CMT1A, as a second phase-III trial is ongoing. Gene therapy to substitute defective genes (particularly in recessive forms associated with loss-of-function mutations) or insert novel ones (e.g., NT3 gene) are being developed and tested in animal models and in still exceptional cases have reached the clinical trial phase in humans. Novel treatment approaches are also aimed at developing compounds acting on pathways important for different CMT types. Modulation of the neuregulin pathway determining myelin thickness is promising for both hypo-demyelinating and hypermyelinating neuropathies; intervention on Unfolded Protein Response seems effective for rescuing misfolded myelin proteins such as MPZ in CMT1B. HDAC6 inhibitors improved axonal transport and ameliorated phenotypes in different CMT models. Other potential therapeutic strategies include targeting macrophages, lipid metabolism, and Nav1.8 sodium channel in demyelinating CMT and the P2×7 receptor, which regulates calcium influx into Schwann cells, in CMT1A. Further approaches are aimed at correcting metabolic abnormalities, including the accumulation of sorbitol caused by biallelic mutations in the sorbitol dehydrogenase (SORD) gene and of neurotoxic glycosphingolipids in HSN1.