Muscle-directed gene therapy corrects Pompe disease and uncovers species-specific GAA immunogenicity

Gene therapy for genetic diseases: challenges and future directions

Genetic diseases constitute the majority of rare human diseases, resulting from abnormalities in an individual's genetic composition. Traditional treatments offer limited relief for these challenging conditions. In contrast, the rapid advancement of gene therapy presents significant advantages by directly addressing the underlying causes of genetic diseases, thereby providing the potential for precision treatment and the possibility of curing these disorders. This review aims to delineate the mechanisms and outcomes of current gene therapy approaches in clinical applications across various genetic diseases affecting different body systems. Additionally, genetic muscular disorders will be examined as a case study to investigate innovative strategies of novel therapeutic approaches, including gene replacement, gene suppression, gene supplementation, and gene editing, along with their associated advantages and limitations at both clinical and preclinical levels. Finally, this review emphasizes the existing challenges of gene therapy, such as vector packaging limitations, immunotoxicity, therapy specificity, and the subcellular localization and immunogenicity of therapeutic cargos, while discussing potential optimization directions for future research. Achieving delivery specificity, as well as long-term effectiveness and safety, will be crucial for the future development of gene therapies targeting genetic diseases.

Unveiling the Future of Cardiac Care: A Review of Gene Therapy in Cardiomyopathies

For years, the treatment of many cardiomyopathies has been solely focused on symptom management. However, cardiomyopathies have a genetic substrate, and directing therapy towards the pathophysiology rather than the epiphenomenon of the disease may be a winning strategy. Gene therapy involves the insertion of genes or the modification of existing ones and their regulatory elements through strategies like gene replacement and gene editing. Recently, gene therapy for cardiac amyloidosis and Duchenne muscular dystrophy has received approval, and important clinical trials are currently evaluating gene therapy methods for rare heart diseases like Friedreich's Ataxia, Danon disease, Fabry disease, and Pompe Disease. Furthermore, favorable results have been noted in animal studies receiving gene therapy for hypertrophic, dilated, and arrhythmogenic cardiomyopathy. This review discusses gene therapy methods, ongoing clinical trials, and future goals in this area.

Neuropathological Findings in Nonclinical Species Following Administration of Adeno-Associated Virus (AAV)-Based Gene Therapy Vectors

Adeno-associated virus (AAV) gene therapy vectors are an accepted platform for treating severe neurological diseases. Test article (TA)-related and procedure-related neuropathological effects following administration of AAV-based vectors are observed in the central nervous system (CNS) and peripheral nervous system (PNS). Leukocyte accumulation (mononuclear cell infiltration > inflammation) may occur in brain, spinal cord, spinal nerve roots (SNRs), sensory and autonomic ganglia, and rarely nerves. Leukocyte accumulation may be associated with neuron necrosis (sensory ganglia > CNS) and/or glial changes (microgliosis and/or astrocytosis in the CNS, increased satellite glial cellularity in ganglia and/or Schwann cellularity in nerves). Axonal degeneration secondary to neuronal injury may occur in the SNR (dorsal > ventral), spinal cord (dorsal and occasionally lateral funiculi), and brainstem centrally and in nerves peripherally. Patterns of AAV-associated microscopic findings in the CNS and PNS differ for TAs administered into brain parenchyma (where tissue at the injection site is affected most) versus TAs delivered into cerebrospinal fluid (CSF) or systemically (which primarily impacts sensory ganglion neurons and their processes in SNR and spinal cord). Changes related to the TA and procedure may overlap. While often interpreted as adverse, AAV-associated neuronal necrosis and axonal degeneration of limited severity generally do not preclude clinical testing.

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.

Advances in Pompe Disease Treatment: From Enzyme Replacement to Gene Therapy

Pompe disease is a neuromuscular disorder caused by a deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA), hydrolyzing glycogen to glucose. Pathological glycogen storage, the hallmark of the disease, disrupts the metabolism and function of various cell types, especially muscle cells, leading to cardiac, motor, and respiratory dysfunctions. The spectrum of Pompe disease manifestations spans two main forms: classical infantile-onset (IOPD) and late-onset (LOPD). IOPD, caused by almost complete GAA deficiency, presents at birth and leads to premature death by the age of 2 years without treatment. LOPD, less severe due to partial GAA activity, appears in childhood, adolescence, or adulthood with muscle weakness and respiratory problems. Since 2006, enzyme replacement therapy (ERT) has been approved for Pompe disease, offering clinical benefits but not a cure. However, advances in early diagnosis through newborn screening, recognizing disease manifestations, and developing improved treatments are set to enhance Pompe disease care. This article reviews recent progress in ERT and ongoing translational research, including the approval of second-generation ERTs, a clinical trial of in utero ERT, and preclinical development of gene and substrate reduction therapies. Notably, gene therapy using intravenous delivery of adeno-associated virus (AAV) vectors is in phase I/II clinical trials for both LOPD and IOPD. Promising data from LOPD trials indicate that most participants met the criteria to discontinue ERT several months after gene therapy. The advantages and challenges of this approach are discussed. Overall, significant progress is being made towards curative therapies for Pompe disease. While several challenges remain, emerging data are promising and suggest the potential for a once-in-a-lifetime treatment.

Immune remodulation in pediatric inherited metabolic liver diseases

Inherited metabolic liver diseases arise from genetic mutations that lead to disruptions in liver metabolic pathways and are predominantly observed in pediatric populations. The spectrum of genetic metabolic liver disorders is diverse, encompassing a range of conditions associated with aberrations in iron, copper, carbohydrate, lipid, protein, and amino acid metabolism. Historically, research in the domain of genetic metabolic liver diseases has predominantly concentrated on hepatic parenchymal cell alterations. Nevertheless, emerging studies suggest that inherited metabolic liver diseases exert significant influences on the immune microenvironment, both within the liver and systemically. This review endeavors to encapsulate the immunological features of genetic metabolic liver diseases, aiming to expand the horizons of researchers in this discipline, and to elucidate the underlying pathophysiological mechanisms pertinent to hereditary metabolic liver diseases and to propose innovative therapeutic approaches.

Precision Genetic Therapies: Balancing Risk and Benefit in Patients with Heart Failure

PURPOSE OF REVIEW

Precision genetic medicine is evolving at a rapid pace and bears significant implications for clinical cardiology. Herein, we discuss the latest advancements and emerging strategies in gene therapy for cardiomyopathy and heart failure.

RECENT FINDINGS

Elucidating the genetic architecture of heart failure has paved the way for precision therapies in cardiovascular medicine. Recent preclinical studies and early-phase clinical trials have demonstrated encouraging results that support the development of gene therapies for heart failure arising from a variety of etiologies. In addition to the discovery of new therapeutic targets, innovative delivery platforms are being leveraged to improve the safety and efficacy of cardiac gene therapies. Precision genetic therapy represents a potentially safe and effective approach for improving outcomes in patients with heart failure. It holds promise for radically transforming the treatment paradigm for heart failure by directly targeting the underlying etiology. As this new generation of cardiovascular medicines progress to the clinic, it is especially important to carefully evaluate the benefits and risks for patients.

The menace of severe adverse events and deaths associated with viral gene therapy and its potential solution

Over the past decade, in vivo gene replacement therapy has significantly advanced, resulting in market approval of numerous therapeutics predominantly relying on adeno-associated viral vectors (AAV). While viral vectors have undeniably addressed several critical healthcare challenges, their clinical application has unveiled a range of limitations and safety concerns. This review highlights the emerging challenges in the field of gene therapy. At first, we discuss both the role of biological barriers in viral gene therapy with a focus on AAVs, and review current landscape of in vivo human gene therapy. We delineate advantages and disadvantages of AAVs as gene delivery vehicles, mostly from the safety perspective (hepatotoxicity, cardiotoxicity, neurotoxicity, inflammatory responses etc.), and outline the mechanisms of adverse events in response to AAV. Contribution of every aspect of AAV vectors (genomic structure, capsid proteins) and host responses to injected AAV is considered and substantiated by basic, translational and clinical studies. The updated evaluation of recent AAV clinical trials and current medical experience clearly shows the risks of AAVs that sometimes overshadow the hopes for curing a hereditary disease. At last, a set of established and new molecular and nanotechnology tools and approaches are provided as potential solutions for mitigating or eliminating side effects. The increasing number of severe adverse reactions and, sadly deaths, demands decisive actions to resolve the issue of immune responses and extremely high doses of viral vectors used for gene therapy. In response to these challenges, various strategies are under development, including approaches aimed at augmenting characteristics of viral vectors and others focused on creating secure and efficacious non-viral vectors. This comprehensive review offers an overarching perspective on the present state of gene therapy utilizing both viral and non-viral vectors.

Clinical features and genetic analysis of 5 cases of infantile-type glycogen storage disease type II: Case reports

OBJECTIVE

Clinical and genetic mutation analysis was performed on 5 infantile glycogen storage disease type II children in Chinese mainland.

METHODS

Clinical data of 5 children with infantile-type glycogen storage disease type II due to the acidic α-glucosidase (GAA) gene variants diagnosed and treated at Hebei Provincial Children's Hospital from January 2018 to April 2020 were retrospectively analyzed.

RESULTS

Among the 5 cases, 1 was female and 4 were male, and the age at first diagnosis was from 2 months to 7 months. The first symptoms of all 5 cases showed progressive muscle weakness, hypotonia, and motor developmental backwardness, and all of them had abnormally elevated creatine kinase, and the echocardiograms suggested different degrees of myocardial hypertrophy, with ejection fractions ranging from 44% to 67%. Analysis of GAA gene variations: all 5 cases were compound heterozygous, and a total of 12 variant loci were detected, of which c.2024_2026delACA, c.2853G > A, c.1124G > T, c.574G > A, c.2509C > T, and c.2013G > A were new mutations that had not been reported.

FOLLOWUP

All 5 children died before 1 year of age, and the age of death ranged from 7 months to 11.5 months, with a mean survival time of 9.8 months.

CONCLUSION

Peripheral blood GAA gene testing and alpha-glucosidase enzyme activity testing is an effective method for diagnosing this disease.

Best Practices for Development and Validation of Enzymatic Activity Assays to Support Drug Development for Inborn Errors of Metabolism and Biomarker Assessment

Aberrant or dysfunctional cellular enzymes are responsible for a wide range of diseases including cancer, neurodegenerative conditions, and metabolic disorders. Deficiencies in enzyme level or biofunction may lead to intracellular accumulation of substrate to toxic levels and interfere with overall cellular function, ultimately leading to cell damage, disease, and death. Marketed therapeutic interventions for inherited monogenic enzyme deficiency disorders include enzyme replacement therapy and small molecule chaperones. Novel approaches of in vivo gene therapy and ex vivo cell therapy are under clinical evaluation and provide promising opportunities to expand the number of available disease-modifying treatments. To support the development of these different therapeutics, assays to quantify the functional activity of protein enzymes have gained importance in the diagnosis of disease, assessment of pharmacokinetics and pharmacodynamic response, and evaluation of drug efficacy. In this review, we discuss the technical aspects of enzyme activity assays in the bioanalytical context, including assay design and format as well as the unique challenges and considerations associated with assay development, validation, and life cycle management.

Base editing rescues acid α-glucosidase function in infantile-onset Pompe disease patient-derived cells

Infantile-onset Pompe disease (IOPD) results from pathogenic variants in the GAA gene, which encodes acid α-glucosidase. The correction of pathogenic variants through genome editing may be a valuable one-time therapy for PD and improve upon the current standard of care. We performed adenine base editing in human dermal fibroblasts harboring three transition nonsense variants, c.2227C>T (p.Q743∗; IOPD-1), c.2560C>T (p.R854∗; IOPD-2), and c.2608C>T (p.R870∗; IOPD-3). Up to 96% adenine deamination of target variants was observed, with minimal editing across >50 off-target sites. Post-base editing, expressed GAA protein was up to 0.66-fold normal (unaffected fibroblasts), an improvement over affected fibroblasts wherein GAA was undetectable. GAA enzyme activity was between 81.91 ± 13.51 and 129.98 ± 9.33 units/mg protein at 28 days post-transfection, which falls within the normal range (50-200 units/mg protein). LAMP2 protein was significantly decreased in the most robustly edited cell line, IOPD-3, indicating reduced lysosomal burden. Taken together, the findings reported herein demonstrate that base editing results in efficacious adenine deamination, restoration of GAA expression and activity, and reduction in lysosomal burden in the most robustly edited cells. Future work will assess base editing outcomes and the impact on Pompe pathology in two mouse models, Gaa c.2227C>T and Gaa c.2560C>T.

Acid α-glucosidase (GAA) activity and glycogen content in muscle biopsy specimens of patients with Pompe disease: A systematic review

Pompe disease is a rare genetic disorder characterized by a deficiency of acid α-glucosidase (GAA), leading to the accumulation of glycogen in various tissues, especially in skeletal muscles. The disease manifests as a large spectrum of phenotypes from infantile-onset Pompe disease (IOPD) to late-onset Pompe disease (LOPD), depending on the age of symptoms onset. Quantifying GAA activity and glycogen content in skeletal muscle provides important information about the disease severity. However, the distribution of GAA and glycogen levels in skeletal muscles from healthy individuals and those impacted by Pompe disease remains poorly understood, and there is currently no universally accepted standard assay for GAA activity measurement. This systematic literature review aims to provide an overview of the available information on GAA activity and glycogen content levels in skeletal muscle biopsies from patients with Pompe disease. A structured review of PubMed and Google Scholar literature (with the latter used to check that no additional publications were identified) was conducted to identify peer-reviewed publications on glycogen storage disease type II [MeSH term] + GAA, protein human (supplementary concept), Pompe, muscle; and muscle, acid alpha-glucosidase. A limit of English language was applied. Results were grouped by methodologies used to quantify GAA activity and glycogen content in skeletal muscle. The search and selection strategy were devised and carried out in line with Preferred Reporting of Items in Systematic Reviews and Meta-Analysis guidelines and documented using a flowchart. Bibliographies of papers included in the analysis were reviewed and applicable publications not already identified in the search were included. Of the 158 articles retrieved, 24 (comprising >100 muscle biopsies from >100 patients) were included in the analysis, with four different assays. Analysis revealed that patients with IOPD exhibited markedly lower GAA activity in skeletal muscles than those with LOPD, regardless of the measurement method employed. Additionally, patients with IOPD had notably higher glycogen content levels in skeletal muscles than those with LOPD. In general, however, it was difficult to fully characterize GAA activity because of the different methods used. The findings underscore the challenges in the interpretation and comparison of the results across studies because of the substantial methodological variations. There is a need to establish standardized reference ranges of GAA activity and glycogen content in healthy individuals and in Pompe disease patients based on globally standardized methods to improve comparability and reliability in assessing this rare disease.

Synergism of dual AAV gene therapy and rapamycin rescues GSDIII phenotype in muscle and liver

Glycogen storage disease type III (GSDIII) is a rare metabolic disorder due to glycogen debranching enzyme (GDE) deficiency. Reduced GDE activity leads to pathological glycogen accumulation responsible for impaired hepatic metabolism and muscle weakness. To date, there is no curative treatment for GSDIII. We previously reported that 2 distinct dual AAV vectors encoding for GDE were needed to correct liver and muscle in a GSDIII mouse model. Here, we evaluated the efficacy of rapamycin in combination with AAV gene therapy. Simultaneous treatment with rapamycin and a potentially novel dual AAV vector expressing GDE in the liver and muscle resulted in a synergic effect demonstrated at biochemical and functional levels. Transcriptomic analysis confirmed synergy and suggested a putative mechanism based on the correction of lysosomal impairment. In GSDIII mice livers, dual AAV gene therapy combined with rapamycin reduced the effect of the immune response to AAV observed in this disease model. These data provide proof of concept of an approach exploiting the combination of gene therapy and rapamycin to improve efficacy and safety and to support clinical translation.

Treatment of infantile-onset Pompe disease in a rat model with muscle-directed AAV gene therapy

OBJECTIVE

Pompe disease (PD) is caused by deficiency of the lysosomal enzyme acid α-glucosidase (GAA), leading to progressive glycogen accumulation and severe myopathy with progressive muscle weakness. In the Infantile-Onset PD (IOPD), death generally occurs <1 year of age. There is no cure for IOPD. Mouse models of PD do not completely reproduce human IOPD severity. Our main objective was to generate the first IOPD rat model to assess an innovative muscle-directed adeno-associated viral (AAV) vector-mediated gene therapy.

METHODS

PD rats were generated by CRISPR/Cas9 technology. The novel highly myotropic bioengineered capsid AAVMYO3 and an optimized muscle-specific promoter in conjunction with a transcriptional cis-regulatory element were used to achieve robust Gaa expression in the entire muscular system. Several metabolic, molecular, histopathological, and functional parameters were measured.

RESULTS

PD rats showed early-onset widespread glycogen accumulation, hepato- and cardiomegaly, decreased body and tissue weight, severe impaired muscle function and decreased survival, closely resembling human IOPD. Treatment with AAVMYO3-Gaa vectors resulted in widespread expression of Gaa in muscle throughout the body, normalizing glycogen storage pathology, restoring muscle mass and strength, counteracting cardiomegaly and normalizing survival rate.

CONCLUSIONS

This gene therapy holds great potential to treat glycogen metabolism alterations in IOPD. Moreover, the AAV-mediated approach may be exploited for other inherited muscle diseases, which also are limited by the inefficient widespread delivery of therapeutic transgenes throughout the muscular system.

Applications of Gene Therapy in Cardiomyopathies

Gene therapy is defined by the introduction of new genes or the genetic modification of existing genes and/or their regulatory portions via gene replacement and gene editing strategies, respectively. The genetic material is usually delivered though cardiotropic vectors such as adeno-associated virus 9 or engineered capsids. The enthusiasm for gene therapy has been hampered somewhat by adverse events observed in clinical trials, including dose-dependent immunologic reactions such as hepatotoxicity, acquired hemolytic uremic syndrome and myocarditis. Notably, gene therapy for Duchenne muscular dystrophy has recently been approved and pivotal clinical trials are testing gene therapy approaches in rare myocardial conditions such as Danon disease and Fabry disease. Furthermore, promising results have been shown in animal models of gene therapy in hypertrophic cardiomyopathy and arrhythmogenic cardiomyopathy. This review summarizes the gene therapy techniques, the toxicity risk associated with adeno-associated virus delivery, the ongoing clinical trials, and future targets.

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.

Current avenues of gene therapy in Pompe disease

PURPOSE OF REVIEW

Pompe disease is a rare, inherited, devastating condition that causes progressive weakness, cardiomyopathy and neuromotor disease due to the accumulation of glycogen in striated and smooth muscle, as well as neurons. While enzyme replacement therapy has dramatically changed the outcome of patients with the disease, this strategy has several limitations. Gene therapy in Pompe disease constitutes an attractive approach due to the multisystem aspects of the disease and need to address the central nervous system manifestations. This review highlights the recent work in this field, including methods, progress, shortcomings, and future directions.

RECENT FINDINGS

Recombinant adeno-associated virus (rAAV) and lentiviral vectors (LV) are well studied platforms for gene therapy in Pompe disease. These products can be further adapted for safe and efficient administration with concomitant immunosuppression, with the modification of specific receptors or codon optimization. rAAV has been studied in multiple clinical trials demonstrating safety and tolerability.

SUMMARY

Gene therapy for the treatment of patients with Pompe disease is feasible and offers an opportunity to fully correct the principal pathology leading to cellular glycogen accumulation. Further work is needed to overcome the limitations related to vector production, immunologic reactions and redosing.

A Comprehensive Update on Late-Onset Pompe Disease

Pompe disease (PD) is an autosomal recessive disorder caused by mutations in the GAA gene that lead to a deficiency in the acid alpha-glucosidase enzyme. Two clinical presentations are usually considered, named infantile-onset Pompe disease (IOPD) and late-onset Pompe disease (LOPD), which differ in age of onset, organ involvement, and severity of disease. Assessment of acid alpha-glucosidase activity on a dried blood spot is the first-line screening test, which needs to be confirmed by genetic analysis in case of suspected deficiency. LOPD is a multi-system disease, thus requiring a multidisciplinary approach for efficacious management. Enzyme replacement therapy (ERT), which was introduced over 15 years ago, changes the natural progression of the disease. However, it has limitations, including a reduction in efficacy over time and heterogeneous therapeutic responses among patients. Novel therapeutic approaches, such as gene therapy, are currently under study. We provide a comprehensive review of diagnostic advances in LOPD and a critical discussion about the advantages and limitations of current and future treatments.

AAV-mediated delivery of secreted acid α-glucosidase with enhanced uptake corrects neuromuscular pathology in Pompe mice

Gene therapy is under advanced clinical development for several lysosomal storage disorders. Pompe disease, a debilitating neuromuscular illness affecting infants, children, and adults with different severity, is caused by a deficiency of lysosomal glycogen-degrading enzyme acid α-glucosidase (GAA). Here, we demonstrated that adeno-associated virus-mediated (AAV-mediated) systemic gene transfer reversed glycogen storage in all key therapeutic targets - skeletal and cardiac muscles, the diaphragm, and the central nervous system - in both young and severely affected old Gaa-knockout mice. Furthermore, the therapy reversed secondary cellular abnormalities in skeletal muscle, such as those in autophagy and mTORC1/AMPK signaling. We used an AAV9 vector encoding a chimeric human GAA protein with enhanced uptake and secretion to facilitate efficient spread of the expressed protein among multiple target tissues. These results lay the groundwork for a future clinical development strategy in Pompe disease.

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing

Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.

Immune transgene-dependent myocarditis in macaques after systemic administration of adeno-associated virus expressing human acid alpha-glucosidase

Immune responses to human non-self transgenes can present challenges in preclinical studies of adeno-associated virus (AAV) gene therapy candidates in nonhuman primates. Although anti-transgene immune responses are usually mild and non-adverse, they can confound pharmacological readouts and complicate translation of results between species. We developed a gene therapy candidate for Pompe disease consisting of AAVhu68, a clade F AAV closely related to AAV9, that expresses an engineered human acid-alpha glucosidase (hGAA) tagged with an insulin-like growth factor 2 variant (vIGF2) peptide for enhanced cell uptake. Rhesus macaques were administered an intravenous dose of 1x1013 genome copies (GC)/kg, 5x1013 GC/kg, or 1 x 1014 GC/kg of AAVhu68.vIGF2.hGAA. Some unusually severe adaptive immune responses to hGAA presented, albeit with a high degree of variability between animals. Anti-hGAA responses ranged from absent to severe cytotoxic T-cell-mediated myocarditis with elevated troponin I levels. Cardiac toxicity was not dose dependent and affected five out of eleven animals. Upon further investigation, we identified an association between toxicity and a major histocompatibility complex class I haplotype (Mamu-A002.01) in three of these animals. An immunodominant peptide located in the C-terminal region of hGAA was subsequently identified via enzyme-linked immunospot epitope mapping. Another notable observation in this preclinical safety study cohort pertained to the achievement of robust and safe gene transfer upon intravenous administration of 5x1013 GC/kg in one animal with a low pre-existing neutralizing anti-capsid antibodies titer (1:20). Collectively, these findings may have significant implications for gene therapy inclusion criteria.

Enhanced sensitivity of neutralizing antibody detection for different AAV serotypes using HeLa cells with overexpressed AAVR

A cell-based transduction inhibition assay (TI) is widely used in clinical trials to detect neutralizing antibody (NAb) titers against recombinant adeno-associated virus (rAAV), one of the most important criteria to exclude patients in gene therapy. Different cell lines are used in cell-based TI because the rAAV transduction efficiencies vary largely among serotypes. A cell line suitable for TI for most serotypes is highly desirable, especially for those with very low transduction efficiencies in vitro such as rAAV8 and rAAV9. Herein, we report an AAVR-HeLa, a stable cell line with overexpressed AAVR, a newly identified receptor for rAAVs, was established for cell-based TIs. The AAVR expression level in AAVR-HeLa cells was approximately 10-fold higher than in HeLa cells, and was stably transfected after twenty three passages. For all AAV serotypes (AAV1-10), except for AAV4, the transduction efficiencies increased significantly in AAVR-HeLa cells. It was demonstrated that the AAVR enhancement of transduction efficiency was only for rAAV and not for lentiviral and adenoviral vectors. According to the minimal multiplicity of infection (MOIs) for the assay, the NAb detection sensitivity increased at least 10 and 20 fold for AAV8 and AAV9, respectively. The seroprevalence of NAbs were investigated at the 1:30 level as a cutoff value using AAVR-HeLa cells. It was shown that the seropositive rate for AAV2 was 87% in serum samples from 99 adults, followed by lower seropositive rates for AAV5 (7%), AAV8 (7%) and AAV9 (1%). Venn diagram analysis showed the presence of cross-reactivity of NAbs to two or three serotypes in 13 samples (13.1%). However, no patient was found to possess NAbs for all the four serotypes. These results demonstrated that the AAVR-HeLa cell line may be utilized to detect the NAbs through cell-based TI assays for most of AAV serotypes.

Screening chimeric GAA variants in preclinical study results in hematopoietic stem cell gene therapy candidate vectors for Pompe disease

Pompe disease is a rare genetic neuromuscular disorder caused by acid α-glucosidase (GAA) deficiency resulting in lysosomal glycogen accumulation and progressive myopathy. Enzyme replacement therapy, the current standard of care, penetrates poorly into the skeletal muscles and the peripheral and central nervous system (CNS), risks recombinant enzyme immunogenicity, and requires high doses and frequent infusions. Lentiviral vector-mediated hematopoietic stem and progenitor cell (HSPC) gene therapy was investigated in a Pompe mouse model using a clinically relevant promoter driving nine engineered GAA coding sequences incorporating distinct peptide tags and codon optimizations. Vectors solely including glycosylation-independent lysosomal targeting tags enhanced secretion and improved reduction of glycogen, myofiber, and CNS vacuolation in key tissues, although GAA enzyme activity and protein was consistently lower compared with native GAA. Genetically modified microglial cells in brains were detected at low levels but provided robust phenotypic correction. Furthermore, an amino acid substitution introduced in the tag reduced insulin receptor-mediated signaling with no evidence of an effect on blood glucose levels in Pompe mice. This study demonstrated the therapeutic potential of lentiviral HSPC gene therapy exploiting optimized GAA tagged coding sequences to reverse Pompe disease pathology in a preclinical mouse model, providing promising vector candidates for further investigation.

Long-term outcomes of very early treated infantile-onset Pompe disease with short-term steroid premedication: experiences from a nationwide newborn screening programme

BACKGROUND

Starting enzyme replacement therapy (ERT) before severe irreversible muscular damage occurs is important in infantile-onset Pompe disease (IOPD). This long-term follow-up study demonstrates our diagnostic and treatment strategies for IOPD and compares our clinical outcomes with those of other medical centres.

METHODS

In this long-term follow-up study, we analysed the outcomes of very early ERT with premedication hydrocortisone in patients with IOPD. Out of 1 228 539 infants screened between 1 January 2010 and 28 February 2021, 33 newborns had confirmed IOPD in Taipei Veterans General Hospital. Twenty-six were regularly treated and monitored at Taipei Veterans General Hospital. Echocardiographic parameters, biomarkers, IgG antibodies against alglucosidase alpha, pulmonary function variables and developmental status were all assessed regularly over an average follow-up duration of 6.18±3.14 years. We compared the long-term treatment outcomes of our patients with those of other research groups.

RESULTS

The average age at ERT initiation was 9.75±3.17 days for patients with classic IOPD. The average of the latest antialglucosidase alpha IgG titre was 669.23±1159.23. All enrolled patients had normal heart sizes, motor milestones, cognitive function and pulmonary function that were near-normal to normal. Compared with patients in other studies, our patients had better outcomes in all aspects.

CONCLUSION

Very early ERT using our rapid diagnostic and treatment strategy enabled our patients with IOPD to have better outcomes than patients in other medical centres.

What's new and what's next for gene therapy in Pompe disease?

INTRODUCTION

Pompe disease is an autosomal recessive disorder caused by a deficiency of acid-α-glucosidase (GAA), an enzyme responsible for hydrolyzing lysosomal glycogen. A lack of GAA leads to accumulation of glycogen in the lysosomes of cardiac, skeletal, and smooth muscle cells, as well as in the central and peripheral nervous system. Enzyme replacement therapy has been the standard of care for 15 years and slows disease progression, particularly in the heart, and improves survival. However, there are limitations of ERT success, which gene therapy can overcome.

AREAS COVERED

Gene therapy offers several advantages including prolonged and consistent GAA expression and correction of skeletal muscle as well as the critical CNS pathology. We provide a systematic review of the preclinical and clinical outcomes of adeno-associated viral mediated gene therapy and alternative gene therapy strategies, highlighting what has been successful.

EXPERT OPINION

Although the preclinical and clinical studies so far have been promising, barriers exist that need to be addressed in gene therapy for Pompe disease. New strategies including novel capsids for better targeting, optimized DNA vectors, and adjuctive therapies will allow for a lower dose, and ameliorate the immune response.

Pompe Disease: a Clinical, Diagnostic, and Therapeutic Overview

Purpose of Review

This review summarizes the clinical presentation and provides an update on the current strategies for diagnosis of Pompe disease. We will review the available treatment options. We examine newly approved treatments as well as upcoming therapies in this condition. We also provide commentary on the unmet needs in clinical management and research for this disease.

Recent Findings

In March 2015, Pompe disease was added to the Recommended Uniform Screening Panel (RUSP) and since then a number of states have added Pompe disease to their slate of diseases for their Newborn Screening (NBS) program. Data emerging from these programs is revising our knowledge of incidence of Pompe disease. In 2021, two randomized controlled trials involving new forms of enzyme replacement therapy (ERT) were completed and one new product is already FDA-approved and on the market, whereas the other product will come up for FDA review in the fall. Neither of the new ERT were shown to be superior to the standard of care product, alglucosidase. The long-term effectiveness of these newer forms of ERT is unclear. Newer versions of the ERT are in development in addition to multiple different strategies of gene therapy to deliver GAA, the gene responsible for producing acid alpha-glucosidase, the defective protein in Pompe Disease. Glycogen substrate reduction is also in development in Pompe disease and other glycogen storage disorders.

Summary

There are significant unmet needs as it relates to clinical care and therapeutics in Pompe disease as well as in research. The currently available treatments lose effectiveness over the long run and do not have penetration into neuronal tissues and inconsistent penetration in certain muscles. More definitive gene therapy and enzyme replacement strategies are currently in development and testing.

Isogenic GAA-KO Murine Muscle Cell Lines Mimicking Severe Pompe Mutations as Preclinical Models for the Screening of Potential Gene Therapy Strategies

Pompe disease (PD) is a rare disorder caused by mutations in the acid alpha-glucosidase (GAA) gene. Most gene therapies (GT) partially rely on the cross-correction of unmodified cells through the uptake of the GAA enzyme secreted by corrected cells. In the present study, we generated isogenic murine GAA-KO cell lines resembling severe mutations from Pompe patients. All of the generated GAA-KO cells lacked GAA activity and presented an increased autophagy and increased glycogen content by means of myotube differentiation as well as the downregulation of mannose 6-phosphate receptors (CI-MPRs), validating them as models for PD. Additionally, different chimeric murine GAA proteins (IFG, IFLG and 2G) were designed with the aim to improve their therapeutic activity. Phenotypic rescue analyses using lentiviral vectors point to IFG chimera as the best candidate in restoring GAA activity, normalising the autophagic marker p62 and surface levels of CI-MPRs. Interestingly, in vivo administration of liver-directed AAVs expressing the chimeras further confirmed the good behaviour of IFG, achieving cross-correction in heart tissue. In summary, we generated different isogenic murine muscle cell lines mimicking the severe PD phenotype, as well as validating their applicability as preclinical models in order to reduce animal experimentation.

Gene Therapy Developments for Pompe Disease

Pompe disease is an inherited neuromuscular disorder caused by deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). The most severe form is infantile-onset Pompe disease, presenting shortly after birth with symptoms of cardiomyopathy, respiratory failure and skeletal muscle weakness. Late-onset Pompe disease is characterized by a slower disease progression, primarily affecting skeletal muscles. Despite recent advancements in enzyme replacement therapy management several limitations remain using this therapeutic approach, including risks of immunogenicity complications, inability to penetrate CNS tissue, and the need for life-long therapy. The next wave of promising single therapy interventions involves gene therapies, which are entering into a clinical translational stage. Both adeno-associated virus (AAV) vectors and lentiviral vector (LV)-mediated hematopoietic stem and progenitor (HSPC) gene therapy have the potential to provide effective therapy for this multisystemic disorder. Optimization of viral vector designs, providing tissue-specific expression and GAA protein modifications to enhance secretion and uptake has resulted in improved preclinical efficacy and safety data. In this review, we highlight gene therapy developments, in particular, AAV and LV HSPC-mediated gene therapy technologies, to potentially address all components of the neuromuscular associated Pompe disease pathology.