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PubMed2026

Standardisation in the Analytical Characterization of Adeno-Associated Virus (AAV) Vectors.

Adeno-associated virus (AAV) has become a leading vector for in vivo gene therapy, with eight products currently holding marketing authorization. As the field rapidly evolves, the need for robust analytical methods to characterize critical quality attributes (CQAs)-including capsid titer, genome titer, capsid content (empty/full ratio), identity, and purity-continues to grow. Reference Standard Materials (RSMs) play a pivotal role by providing well-characterized, standardized AAV batches that serve as universal benchmarks. RSMs facilitate the validation of emerging analytical technologies, ensure the accuracy and reproducibility of routine assays, and enable inter-laboratory comparability. However, developing universal AAV RSMs is fundamentally constrained by the complex biology, diversity of serotypes, vector genomes, and engineered capsid variants, necessitating serotype-specific and application-specific standards. Recent advances, including the release of pharmacopeial AAV8 reference standards characterized by multiple orthogonal methods, represent meaningful progress toward measurement harmonisation. This review addresses the critical need for RSMs in AAV gene therapy, evaluates the currently available pharmacopeial and commercial standards, and outlines practical strategies for in-house RSM development. Establishing robust, serotype-specific AAV RSMs and harmonised standard operating protocols (SOPs) are essential for advancing AAV gene therapy and ensuring accuracy, reproducibility, and safety across research, development, and clinical manufacturing.

Dependovirus↗

PubMed2024

Chemical approaches to probe and engineer AAV vectors.

Adeno-associated virus (AAV) has emerged as the most promising vector for in vivo human gene therapy, with several therapeutic approvals in the last few years and countless more under development. Underlying this remarkable success are several attractive features that AAV offers, including lack of pathogenicity, low immunogenicity, long-term gene expression without genomic integration, the ability to infect both dividing and non-dividing cells, etc. However, the commonly used wild-type AAV capsids in therapeutic development present significant challenges, including inadequate tissue specificity and the need for large doses to attain therapeutic effectiveness, raising safety concerns. Additionally, significant preexisting adaptive immunity against most natural capsids, and the development of such anti-capsid immunity after the first treatment, represent major challenges. Strategies to engineer the AAV capsid are critically needed to address these challenges and unlock the full promise of AAV gene therapy. Chemical modification of the AAV capsid has recently emerged as a powerful new approach to engineer its properties. Unlike genetic strategies, which can be more disruptive to the delicate capsid assembly and packaging processes, "late-stage" chemical modification of the assembled capsid-whether at natural amino acid residues or site-specifically installed noncanonical amino acid residues-often enables a versatile approach to introducing new properties to the capsid. This review summarizes the significant recent progress in AAV capsid engineering strategies, with a particular focus on chemical modifications in advancing the next generation of AAV-based gene therapies.

Dependovirus↗

PubMed2026

Impact of transfection optimization on adeno-associated virus purification performance and vector quality.

Recombinant adeno-associated virus (rAAV) has shown great promise as a viral vector for gene therapy. However, efficient manufacture of high-quality rAAV to meet clinical demands remains challenging. Here, we optimized rAAV production via a design of experiments (DoE) approach to evaluate the effects of five transfection parameters on vector genome titer, full particle ratio (FE ratio), and viral protein (VP) stoichiometry. The DoE model showed that no single set of transfection conditions could maximize all three responses simultaneously. Subsequently, the materials from DoE-optimized transfections were purified by affinity chromatography followed by anion exchange chromatography (AEX). We observed that AEX recovery declined when capsid loading was high, a situation caused by the combination of high titer with low FE ratio, reducing some of the gains in titer achieved by transfection optimization. Furthermore, AEX had limited capacity to enrich full particles from materials with a very low initial FE ratio. Finally, materials from DoE-optimized transfections showed improved transduction efficiency, which was associated with the ratios of VP1 and VP2 to total VP in the capsid. Overall, this study demonstrates that transfection-derived quality attributes affect purification outcomes and overall vector quality. Our findings highlight the necessity of strategically balancing multiple quality attributes during transfection optimization and provide insights for integrated upstream transfection and downstream purification development.

Adeno-associated virus↗

PubMed2026

In Vivo Genome Editing Approach to Disrupt Hydroxyacid Oxidase 1 for the Treatment of Primary Hyperoxaluria Type 1.

Primary hyperoxaluria type 1 (PH1) is a rare autosomal recessive disorder that leads to kidney and liver failure. PH1 is caused by a mutation in the alanine glyoxylate aminotransferase (AGXT) gene, which encodes a key metabolic enzyme that converts glyoxylate to glycine in the liver. Inability to metabolize glyoxylate leads to oxalate overproduction, yielding insoluble calcium oxalate crystals; accumulation of these crystals leads to progressive organ failure. Here, we used a novel, minimally disruptive genome-editing approach to disrupt the mechanism of action of hydroxyacid oxidase 1 (HAO1), an upstream enzyme in the glyoxylate metabolic pathway. Successful gene editing and disruption of the HAO1 gene is expected to increase levels of glycolate, a harmless intermediate of the glycine metabolic pathway, thereby preventing the formation of calcium oxalate crystals. We intravenously administered an adeno-associated virus (AAV) vector expressing the M1HAO1 meganuclease to both wild-type and Agxt-/- mice, a mouse model of PH1. We observed >30% editing of HAO1 in Agxt-/- mice, correlating with a dose-dependent increase in serum glycolate levels. At the highest dose tested, urine glycolate levels increased by 79%, with a concomitant 75% decrease in urine oxalate levels. We also evaluated in vivo targeting in rhesus macaques injected with AAV expressing two different versions of the HAO1 meganuclease. Dose-dependent editing of hepatic DNA and RNA was achieved, and serum glycolate levels changed in a manner consistent with successful liver editing; additionally, the treatment was well tolerated. Our results indicate that AAV-delivered meganucleases can effectively target HAO1 in mice and nonhuman primates to achieve high levels of HAO1 gene editing. Moreover, increased glycolate levels in serum indicate that this intervention significantly impacts the HAO1-mediated glycolate-to-glyoxylate pathway. These data suggest that this approach may represent an effective treatment for PH1.

Hyperoxaluria, Primary↗

PubMed2024

Split intein-mediated protein trans-splicing to express large dystrophins.

Gene replacement using adeno-associated virus (AAV) vectors is a promising therapeutic approach for many diseases1,2. However, this therapeutic modality is challenged by the packaging capacity of AAVs (approximately 4.7 kilobases)3, limiting its application for disorders involving large coding sequences, such as Duchenne muscular dystrophy, with a 14 kilobase messenger RNA. Here we developed a new method for expressing large dystrophins by utilizing the protein trans-splicing mechanism mediated by split inteins. We identified several split intein pairs that efficiently join two or three fragments to generate a large midi-dystrophin or the full-length protein. We show that delivery of two or three AAVs into dystrophic mice results in robust expression of large dystrophins and significant physiological improvements compared with micro-dystrophins. Moreover, using the potent myotropic AAVMYO4, we demonstrate that low total doses (2 × 1013 viral genomes per kg) are sufficient to express large dystrophins in striated muscles body-wide with significant physiological corrections in dystrophic mice. Our data show a clear functional superiority of large dystrophins over micro-dystrophins that are being tested in clinical trials. This method could benefit many patients with Duchenne or Becker muscular dystrophy, regardless of genotype, and could be adapted to numerous other disorders caused by mutations in large genes that exceed the AAV capacity.

Animals↗

PubMed2026

MADCAP: isolation of novel nAb-naïve AAV capsids from metagenomic data.

UNLABELLED: Gene therapy using adeno-associated virus (AAV) vectors offers promising treatment for genetic disorders, but significant limitations restrict clinical application. Current AAV serotypes exhibit strong liver tropism and require high doses for extra-hepatic targeting, and pre-existing antibodies (NAbs) exclude up to 50% of potential patients. Evolutionarily distant isolates can evade neutralization but typically transduce human tissues poorly and require extensive engineering. We developed MADCAP (Metagenomic AAV Discovery and Capsid Annotation Pipeline) to systematically mine metagenomic data for functional, clinically relevant AAV capsids. We hypothesized that these sources might contain capsids that do not circulate widely in humans, can transduce human cells, and avoid neutralization. We screened 4.2 million metagenomic samples and identified 139 novel AAV capsid isolates which were tested for viral capsid assembly, viability, neutralization evasion, and tissue transduction in non-human primates. While natural serotypes (AAV1, AAV2, AAV9) were neutralized at low dilutions of pooled human immunoglobulin (IVIG), 68% of tested MADCAP capsids exhibited minimal to undetectable neutralization even at supra-physiological IVIG concentrations. Systemically delivered MADCAP capsids effectively transduced multiple clinically relevant tissues in non-human primates. Two capsids, MC46 and MC55, demonstrated improved CNS tropism compared to AAV9 while maintaining comparable production yields. In passive transfer studies, MC46 retained full transduction efficiency in the presence of human antibodies, while AAV9 transduction was completely lost. This work establishes metagenomic mining as a powerful tool for accelerating AAV capsid discovery, identifying isolates with favorable tissue tropisms and resistance to broadly neutralizing antibodies. IMPORTANCE: This work provides proof of concept that potentially clinically relevant AAVs can be isolated from metagenomic data. Our findings lay the groundwork for accelerated discovery of AAV capsids which could potentially increase the accessibility and effectiveness of AAV gene therapy.

AAV↗

PubMed2026

YAP Promotes Microtubule Growth to Facilitate Sarcomere Disassembly in Adult Cardiomyocytes.

BACKGROUND: Mature mammalian cardiomyocytes (CMs) develop compact sarcomeric structures that inhibit proliferation. Consequently, CMs must dedifferentiate to a fetus-like state, which is accompanied by sarcomere disassembly, to enable successful cytokinesis. However, the regulation and coordination of CM dedifferentiation, cell cycle progression, and sarcomere reorganization remain unclear. METHODS: We generated adenovirus and adeno-associated virus (MyoAAV) vectors expressing YAP5SA and YAP5SA-S94A under Xon control for LMI070-inducible protein expression. We also developed MyoAAV-cTnT-Tuba1b-shRNA-miR30 for cardiomyocyte-specific knockdown of Tuba1b. These tools were used to investigate CM dedifferentiation and proliferation and sarcomere disassembly. We also performed Cleavage Under Targets and Release Using Nuclease to map the genome-wide binding sites of YAP5SA and YAP5SA-S94A in combination with RNA sequencing to identify YAP target genes. In addition, time-course live-imaging analysis was used to evaluate microtubule and sarcomere dynamics in adult CMs. RESULTS: We show that microtubule expression and network density decline with cardiac maturation. Overexpression of YAP5SA, a constitutively active YAP mutant, promotes microtubule growth by stabilizing microtubule dynamics, leading to CM dedifferentiation, cell cycle re-entry, and sarcomere disassembly. In contrast, colchicine blocks these processes and significantly attenuates YAP-induced cardiac regeneration. Live imaging reveals a distinct mode of sarcomere disassembly driven by enhanced microtubule polymerization, wherein microtubule plus-ends directly interact with α-actinin and displace α-actinin fragments, thereby facilitating sarcomere breakdown. Furthermore, the YAP5SA-S94A mutation, which disrupts the YAP and TEA domain interaction, significantly reduces YAP5SA-induced microtubule growth, sarcomere disassembly, and cell cycle activity. Mechanistically, cleavage under targets and release using nuclease combined with RNA sequencing identified direct YAP targets, including Ajuba and Tuba1b, which are critical for microtubule growth. CM-specific knockdown of Tuba1b attenuates YAP-driven sarcomere disassembly. CONCLUSIONS: These findings identify microtubule networks as an essential regulator modulating CM dedifferentiation and sarcomere reorganization, which is critical for CM cytokinesis and cardiac regenerative repair.

Animals↗

PubMed2025

Enhancing AAV9-UFμDys1 Gene Therapy Efficacy Through Immunosuppression in Mice with Pre-Existing Immunity and Enabling Redosing Strategies for Duchenne Muscular Dystrophy.

Significant progress has been made in gene therapy for Duchenne muscular dystrophy (DMD), a severe genetic disorder primarily affecting pediatric patients. However, the immune responses triggered by high-dose systemic delivery of adeno-associated virus (AAV) vectors remain a major challenge. These responses include the generation of long-lasting anti-capsid antibodies and potential immunity against the therapeutic transgene, rendering gene therapy ineffective. In addition, pre-existing anti-AAV antibodies exclude patients from eligibility for treatment. To address these limitations, we have developed an immunosuppression (IMS) strategy aimed at mitigating immune responses to the AAV capsid while enhancing microdystrophin expression. Using an optimized expression cassette (AAV9-UFµDys1) for sustained microdystrophin expression in striated muscle and heart, we observed a 40% improvement in muscle force compared with animals receiving a GFP-encoding control AAV9 vector. In mdx mice, a single-dose IMS regimen significantly increased microdystrophin expression in cardiac and skeletal tissues and repeat dosing further enhanced expression, an effect not observed in non-IMS-treated mdx mice. To model pre-existing immunity, we immune-challenged wild-type mice with empty AAV9 capsids and tracked antibody responses over time. The IMS regimen effectively reduced total anti-AAV antibody levels and increased microdystrophin expression in UFµDys1-treated mice. These findings highlight the potential of IMS to minimize immune barriers, facilitate repeat AAV administration, and expand the therapeutic window for DMD gene therapy. Our results support the further development of AAV-mediated approaches using either microdystrophin-expressing vectors or next-generation systems delivering full-length or near-full-length dystrophin.

Animals↗

PubMed2024

Adeno-Associated Virus Engineering and Load Strategy for Tropism Modification, Immune Evasion and Enhanced Transgene Expression.

Gene therapy aims to add, replace or turn off genes to help treat disease. To date, the US Food and Drug Administration (FDA) has approved 14 gene therapy products. With the increasing interest in gene therapy, feasible gene delivery vectors are necessary for inserting new genes into cells. There are different kinds of gene delivery vectors including viral vectors like lentivirus, adenovirus, retrovirus, adeno-associated virus et al, and non-viral vectors like naked DNA, lipid vectors, polymer nanoparticles, exosomes et al, with viruses being the most commonly used. Among them, the most concerned vector is adeno-associated virus (AAV) because of its safety, natural ability to efficiently deliver gene into cells and sustained transgene expression in multiple tissues. In addition, the AAV genome can be engineered to generate recombinant AAV (rAAV) containing transgene sequences of interest and has been proven to be a safe gene vector. Recently, rAAV vectors have been approved for the treatment of various rare diseases. Despite these approvals, some major limitations of rAAV remain, namely nonspecific tissue targeting and host immune response. Additional problems include neutralizing antibodies that block transgene delivery, a finite transgene packaging capacity, high viral titer used for per dose and high cost. To deal with these challenges, several techniques have been developed. Based on differences in engineering methods, this review proposes three strategies: gene engineering-based capsid modification (capsid modification), capsid surface tethering through chemical conjugation (surface tethering), and other formulations loaded with AAV (virus load). In addition, the major advantages and limitations encountered in rAAV engineering strategies are summarized.

Dependovirus↗

PubMed2014

Engineering adeno-associated viruses for clinical gene therapy.

Clinical gene therapy has been increasingly successful owing both to an enhanced molecular understanding of human disease and to progressively improving gene delivery technologies. Among these technologies, delivery vectors based on adeno-associated viruses (AAVs) have emerged as safe and effective and, in one recent case, have led to regulatory approval. Although shortcomings in viral vector properties will render extension of such successes to many other human diseases challenging, new approaches to engineer and improve AAV vectors and their genetic cargo are increasingly helping to overcome these barriers.

Capsid↗

PubMed2025

Pentatricopeptide repeat protein targeting CUG repeat RNA ameliorates RNA toxicity in a myotonic dystrophy type 1 mouse model.

Myotonic dystrophy type 1 (DM1) is an autosomal dominant multisystemic disorder caused by the expansion of a CTG-triplet repeat in the 3' untranslated region of the dystrophia myotonica protein kinase (DMPK) gene. It results in the transcription of toxic RNAs that contain expanded CUG repeats (CUGexp). Splicing factors, such as muscleblind-like 1 (MBNL1), are sequestered by CUGexp, thereby disrupting the normal splicing program that is essential for various cellular functions. Pentatricopeptide repeat (PPR) proteins, originally found in plants, regulate RNA in organelles by binding in a sequence-specific manner. Here, we designed PPR proteins that specifically bind to the hexamer of CUG repeat RNAs (CUG-PPRs) and showed that CUG-PPR1 could ameliorate RNA toxicity induced by CUGexp in cell models of DM1. A single systemic recombinant adeno-associated virus (AAV9) vector-mediated gene delivery of CUG-PPR1 demonstrated long-term therapeutic effects on myotonia and restored splicing activity in a mouse model of DM1. These results highlight the potential of PPR molecules to target pathogenic RNA sequences in DM1 and potentially other RNA-mediated disorders.

Animals↗

PubMed2026

Adeno-Associated Virus Gene Therapy Translation: Lessons from Early Regulatory Meetings.

The Platform Vector-Gene Therapy (PaVe-GT) program is a National Institutes of Health (NIH) initiative that aims to develop adeno-associated virus (AAV) gene therapies for four monogenic rare diseases, two organic acidemias and two congenital myasthenic syndromes. PaVe-GT's platform-based approach identifies and diminishes redundancies and applies efficiencies in preclinical, clinical, and regulatory activities. The program's hypothesis is that implementing these efficiencies can accelerate clinical trial initiation. Based on its platform-centric experience and public-serving mission, the PaVe-GT program actively shares its scientific and regulatory learnings with the public to benefit the development of similar gene therapy products for rare diseases. PaVe-GT's first investigational AAV gene therapy candidate is AAV serotype 9 human propionyl-CoA carboxylase alpha subunit (AAV9-hPCCA) for propionic acidemia caused by PCCA deficiency, which received initial feedback from the Food and Drug Administration (FDA) in an INitial Targeted Engagement for Regulatory Advice on CBER/Center for Drug Evaluation and Research (CDER) ProducTs (INTERACT) meeting. Upon further product development that took into consideration the FDA's initial advice, the program obtained the Agency's feedback in pre-investigational new drug (IND) (Type B) and Type C meetings. Here, we share our experience from these meetings, including strategy, preparation, pre- and post-meeting feedback from the FDA, and lessons learned during the AAV9-hPCCA regulatory process, which the program plans to apply across the PaVe-GT platform. Topics discussed in the regulatory meetings included animal model and efficacy studies, toxicology study plans, manufacturing of the investigational AAV product, and clinical trial design. The main lessons learned from the pre-IND and Type C meetings for AAV9-hPCCA are: (1) Pharmacology/Toxicology studies in a single rodent species are sufficient for filing an initial IND; (2) FDA feedback guides product quality improvements and early development of a quantitative potency assay; (3) use of biomarkers as potential surrogate endpoints in a future efficacy trial benefits from collection of data in the natural history study and the first-in-human Phase 1/2 study; and (4) evidence from the Phase 1/2 clinical trial could be leveraged to support a license application. Lightly redacted regulatory documents and comprehensive templates developed by the PaVe-GT team are available on the PaVe-GT website.

Dependovirus↗

PubMed2025

BCKDHA-BCKDHB digenic gene therapy restores metabolic homeostasis in two mouse models and a calf with classic maple syrup urine disease.

Classic maple syrup urine disease (MSUD) results from biallelic mutations in genes that encode the branched-chain α-ketoacid dehydrogenase E1α (BCKDHA), E1β (BCKDHB), or dihydrolipoamide branched-chain transacylase (DBT) subunits, which interact to form the mitochondrial BCKDH complex that decarboxylates ketoacid derivatives of leucine, isoleucine, and valine. MSUD is an inborn error of metabolism characterized by recurrent life-threatening neurologic crises and progressive brain injury that can only be managed with an exacting prescription diet or allogeneic liver transplant. To develop a gene replacement therapy for MSUD, we designed a dual-function recombinant adeno-associated virus serotype 9 (rAAV9) vector to deliver codon-optimized BCKDHA and BCKDHB (rAAV9.hA-BiP-hB) to the liver, muscle, heart, and brain. rAAV9.hA-BiP-hB restored coexpression of BCKDHA and BCKDHB as well as BCKDH holoenzyme activity in BCKDHA-/- HEK293T cells and did not perturb physiologic branched-chain amino acid homeostasis in wild-type mice at a systemic dose of 2.7 × 1014 vector genomes per kilogram. In two models of severe MSUD (Bckdha-/- and Bckdhb-/- mice) and a newborn calf homozygous for BCKDHA c.248C>T, one postnatal injection prevented perinatal death, normalized growth, restored coordinated expression of BCKDHA and BCKDHB in the skeletal muscle, liver, heart, and brain, and stabilized MSUD biomarkers in the face of high protein ingestion. In summary, we developed a one-time BCKDHA-BCKDHB systemic dual-gene replacement strategy that holds promise as a therapeutic alternative to prescription diet and liver transplant for treatment of MSUD types 1A and 1B, the two most common forms of MSUD in humans.

Animals↗

PubMed2026

Suppression of AAV-Delivered Transgene Expression Using Artificial MicroRNAs Delivered by an Alternative AAV Serotype.

Adeno-associated virus (AAV) gene transfer vectors mediate long-term expression in nondividing cells, an advantage for treating chronic disorders. However, current platforms lack a way to selectively shut down transgene expression if adverse effects arise. To create an "off switch," we hypothesized that incorporating unique artificial microRNA (amiRNA) target sequences into an AAV expression cassette would allow subsequent suppression of transgene expression using a second AAV vector encoding the cognate amiRNA. We introduced 22-nt sequences absent from human and mouse transcriptomes into the 3' untranslated region (UTR) of a therapeutic AAV cassette. To identify optimal amiRNAs, two tandem copies of each amiRNA were cloned into the 3'UTR of an mCherry reporter gene. In vitro assessment of six amiRNA/target pairs using a dual luciferase assay identified four amiRNAs that efficiently suppressed reporter expression. Cells cotransfected with target site 3 (TS3) and amiRNA-T3B showed the greatest reduction in luciferase activity (80%, p < 0.0001) and were selected for further study. The "off-switch" system was then evaluated using an AAV5 therapeutic vector expressing a recombinant humanized anti-IgE monoclonal antibody (AAV5-TBG-anti-IgE-TS3), designed for long-term suppression of allergen-induced reactions. Co-transfection of HEK293T cells with anti-IgE-TS3 and amiRNA-T3B significantly reduced anti-IgE mRNA and protein levels relative to a control amiRNA (p < 0.0001). In vivo testing in Balb/c mice (n = 5) involved intravenous administration of AAV5-anti-IgE-TS3 (3.2 × 1010 gc), followed 4 weeks later by an AAVrh.10 amiRNA vector (AAVrh.10-TBG-amiRNA-T3B; 1 × 1011 gc). Control mice receiving only the therapeutic vector expressed 18.4 ± 13.8 µg/mL serum anti-IgE at 10 weeks. In contrast, mice receiving the amiRNA "off" vector showed marked suppression of anti-IgE (0.3 ± 0.15 µg/mL, p < 0.0001). These findings provide proof-of-concept that AAV-delivered amiRNAs can selectively switch off transgene expression, offering a strategy to improve the safety of AAV-mediated gene therapies.

Dependovirus↗

PubMed2024

Suppression of CNS APOE4 Expression by miRNAs Delivered by the S2 AAVrh.10 Capsid-Modified AAV Vector.

The homozygous Apolipoprotein E (APOE4) genotype is the major risk factor for the development of early Alzheimer's disease. Genome engineering studies in mouse models of human APOE4-dependent pathology have established that reduction of APOE4 expression can rescue the phenotype. We hypothesized that APOE4 could be suppressed in the CNS of APOE4 homozygotes using adeno-associated virus (AAV) expression of microRNAs (miRNA) designed to hybridize to APOE mRNA. We screened nine different miRNAs targeting APOE following transfection in HEK293T and Huh7 cells. Optimal APOE suppression was obtained with mir2A (targeting coding region nt330-351) and mirN4 (3' untranslated region nt1142-1162). miRNA expression cassettes were designed with two copies of each of these two miRNAs co-expressed with a mCherry transgene. To optimize delivery of these miRNAs, an engineered AAVrh.10 variant was identified from a screen of multiple peptide insertions into capsid loop IV and substitutions in loop VIII. This led to identifying the AAV.S2 capsid with enhanced transduction of both neurons and glia and enhanced distribution in the brain. The engineered capsid was used to deliver the APOE miRNA suppression cassette to the hippocampus of TRE4 mice (human APOE4 knock-in replacement of the murine apoE locus). Two weeks after intra-hippocampus administration, regional expression of miRNA at the injection site was quantified at the mRNA level relative to an endogenous reference. The AAV.S2 capsid provided 2.31 ± 0.37-fold higher expression of miRNA over that provided by AAVrh.10 (p < 0.05). In the targeted region, a single intra-hippocampus AAV.S2 administration suppressed hippocampal APOE4 mRNA levels by 76.5 ± 3.9% compared with 41.3 ± 3.3% with the same cassette delivered by the wildtype AAVrh.10 capsid (p < 0.0001). We conclude that an expression cassette with two different miRNAs targeting APOE4 delivered by the AAV.S2 capsid will generate highly significant suppression of APOE4 in the CNS.

Dependovirus↗

PubMed2026

289th ENMC international workshop: assessing and managing emerging AAV related toxicities after gene therapy for neuromuscular disorders, 26 - 28 September 2025, Hoofddorp, The Netherlands.

Adeno-associated virus (AAV) mediated gene therapies has emerged as a potentially transformative treatment approaches for neuromuscular disorders, with two FDA-approved products now in widespread clinical use: onasemnogene abeparvovec (Zolgensma) for spinal muscular atrophy and delandistrogene moxeparvovec-rokl (Elevidys) for Duchenne Muscular Dystrophy. However, severe and occasionally fatal adverse events affecting vital organs, including the blood, liver, muscle, and heart, have emerged in both clinical trials and real-world post marketing settings. The 289th European NeuroMuscular Centre (ENMC) workshop convened 38 participants from patient advocacy groups, industry, and preclinical and clinical research groups to collaboratively review these toxicities, their underlying mechanisms, and potential mitigation and monitoring strategies. Discussions addressed the clinical spectrum and biological drivers of these events, the respective roles of innate and adaptive immunity, the contribution of specific vector characteristics as well as of the specific disease and recipient. The application of risk stratification and immunosuppressive regimens for prevention, monitoring, and management were considered. Emerging toxicities, including capillary leak syndrome, endothelial and dorsal root ganglia injuries, were reviewed alongside corresponding preclinical data from non-human primates. Participants agreed on the need to harmonize standard operating procedures, clinical guidelines, and data-sharing practices, and endorsed collaborative initiatives to proactively address critical gaps and unresolved key questions through a patient-centered framework.

Adaptive immune response↗

PubMed2025

Self-regulating gene therapy ameliorates phenotypes and overcomes gene dosage sensitivity in a mouse model of Rett syndrome.

Conventional methods of gene transfer lead to inconsistent transgene expression within cells. This variability can be problematic, particularly in conditions like Rett syndrome (RTT), a neurological disorder caused by mutations in the MECP2 (methyl-CpG binding protein 2) gene, because overexpression of MECP2 can also cause adverse effects. To address these challenges, we devised a gene regulation system called Expression Attenuation via Construct Tuning (EXACT), which uses a self-contained, microRNA-based feed-forward loop that not only ensures more consistent transgene expression but also protects against excessive expression. Through cell-based screening assays, we demonstrated the ability of the EXACT circuit to modulate the expression of full-length human MeCP2. Compared with a conventional construct, an EXACT-MECP2 construct exhibited a narrower range of cellular protein abundance. Furthermore, the degree of regulation by the EXACT circuit increased with higher transgene doses in vitro and in wild-type mice and mice modeling RTT. On the basis of cellular and in vivo testing, we identified an optimal configuration for the adeno-associated virus serotype 9 (AAV9) construct for self-regulated MECP2 gene therapy, designated NGN-401. Delivery of NGN-401 to neonatal male Mecp2-/y hemizygous mice via intracerebroventricular injection resulted in prolonged survival and amelioration of RTT-like phenotypes compared with vehicle-treated animals. NGN-401 was also well tolerated by female Mecp2+/- mice and healthy juvenile nonhuman primates, in contrast with a conventional construct, which caused toxicity. The results from these studies underpin a first-in-human pediatric trial of NGN-401 in RTT (ClinicalTrials.gov, NCT05898620).

Animals↗

PubMed2026

Interindividual variability in immune response to AAV ocular gene delivery across species impedes immunomonitoring.

Adeno-associated viruses (AAVs) have been used in gene therapy, especially for inherited retinal diseases. Despite their effectiveness in gene transduction, immune responses to the AAV capsid and transgene products have been reported, which can compromise both the efficacy and the safety of AAV-mediated therapies. The eye is regarded as an immune-privileged organ where immune activity is constitutively suppressed. Here, we highlight that immunomonitoring in an ocular gene transfer reveals variable immune responses, whatever the species (human clinical trial, nonhuman primates, mice), the site of injection, the cassette, and the dose. We further explored factors contributing to this variability, investigating the potential correlation among immune parameters in a controlled experimental setting. In a syngeneic murine model after a subretinal injection of AAV, our results highlight an interindividual variability of immune parameters, emphasizing the importance of considering inherent variability among individuals when designing personalized therapies.

Animals↗