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Organoids and microphysiological systems: Promising models for accelerating AAV gene therapy studies.

The FDA has predicted that at least 10-20 gene therapy products will be approved by 2025. The surge in the development of such therapies can be attributed to the advent of safe and effective gene delivery vectors such as adeno-associated virus (AAV). The enormous potential of AAV has been demonstrated by its use in over 100 clinical trials and the FDA's approval of two AAV-based gene therapy products. Despite its demonstrated success in some clinical settings, AAV-based gene therapy is still plagued by issues related to host immunity, and recent studies have suggested that AAV vectors may actually integrate into the host cell genome, raising concerns over the potential for genotoxicity. To better understand these issues and develop means to overcome them, preclinical model systems that accurately recapitulate human physiology are needed. The objective of this review is to provide a brief overview of AAV gene therapy and its current hurdles, to discuss how 3D organoids, microphysiological systems, and body-on-a-chip platforms could serve as powerful models that could be adopted in the preclinical stage, and to provide some examples of the successful application of these models to answer critical questions regarding AAV biology and toxicity that could not have been answered using current animal models. Finally, technical considerations while adopting these models to study AAV gene therapy are also discussed.

Animals

Factor IX Padua AAV gene therapy in adolescents with hemophilia B: a phase 1 trial.

Adeno-associated virus (AAV)-mediated factor IX Padua gene therapy has demonstrated good safety and efficacy in adult patients with hemophilia B, but its safety and efficacy in adolescent patients with hemophilia B remain unknown. Here we report a multicenter, single-arm, phase 1 study involving 11 adolescent participants (aged 12-18 years) with severe or moderately severe hemophilia B (factor IX coagulant activity (FIX:C) ≤2 IU dl-1) in China. All of them received the AAV gene therapy BBM-H901 at a dose of 5 × 1012 vector genomes per kilogram of body weight and were then enrolled in a 52-week follow-up. The primary endpoint was safety. No dose-limiting toxicity was observed throughout the study. The most common adverse events included elevation of white blood cell count, elevation of neutrophil count and rash associated with corticosteroid use. One serious adverse event and two grade 3 adverse events occurred. Abnormal liver function was observed in one participant, with elevated alanine aminotransferase (197.0 U l-1) and aspartate aminotransferase (75.0 U l-1) levels, which returned to normal 4 weeks after immunosuppression therapy. The key secondary endpoints included the mean (s.d.) FIX:C at week 52 following infusion, which was 41.8 (30.1) IU dl-1 (one-stage SynthASil method), and the mean annualized bleeding rate, which decreased from 13.9 to 0.5. In this study, we show that the gene therapy drug BBM-H901 for hemophilia B is safe in adolescent patients, providing initial insights into its efficacy. ClinicalTrials.gov identifier: NCT05709288 .

Journal Article

AAV gene therapy for autosomal recessive deafness 9: a single-arm trial.

Gene therapy for congenital deafness has shown promising results in children but lacks data in older populations. We conducted a single-arm trial of adeno-associated virus (AAV)-OTOF gene therapy using the Anc80L65 capsid in ten participants with autosomal recessive deafness 9 aged 1.5 to 23.9 years at five sites in China. The primary endpoints were safety and tolerability within 5 years, and secondary endpoints assessed auditory function. Initial findings from the ten patients with 6-12 months of follow-up, including one patient who received two injections, revealed that the therapy was well tolerated, with 162 grade I/II adverse events. Decreased neutrophil percentage was the most common event (16 of 162). All ten participants had at least 6 months of follow-up and improved their pure-tone-average hearing level from baseline 106 ± 9 (mean ± s.d.) to 52 ± 30 decibels (dB). Other secondary endpoints showed similar improvements, including the average click auditory brainstem response (ABR) threshold, the tone-burst ABR threshold and the auditory steady-state response (101 ± 1 to 48 ± 26 dB, 91 ± 4 to 57 ± 19 dB and 80 ± 14 to 64 ± 21 dB, respectively). Post hoc analyses were conducted to evaluate the timecourse and factors contributing to the hearing improvement. Therapeutic effect was rapid, taking 1 month to achieve most of the overall hearing improvement. On an individual level, click and tone-burst ABR thresholds, but not the auditory steady-state response, reliably predicted the behavioral pure-tone-average thresholds after 4 months (R2 = 0.68, 0.73 and 0.17, respectively). An age-dependent therapeutic effect was observed, with optimal outcomes in 5- to 8-year-olds. These preliminary results show that AAV-OTOF was safe and well tolerated in patients ranging from toddlerhood to adulthood. The trial remains ongoing and requires extended follow-up to confirm the long-term safety and efficacy. ClinicalTrials.gov registration: NCT05901480 .

Humans

A compact GAD67 promoter enables inhibitory neuron-targeted AAV gene therapy for seizure suppression.

Epilepsy arises from disruption of excitation-inhibition (E/I) balance, typically due to excessive excitatory activity. Despite available therapies, a substantial proportion of patients remain treatment resistant. Enhancing inhibitory neuron activity via gene therapy can restore E/I balance and may therefore provide a therapeutic strategy for treatment-resistant epilepsy. Here, we developed a compact 410-bp glutamic acid decarboxylase 67 promoter (cmGAD67) that enables strong, selective transgene expression in inhibitory neurons while preserving adeno-associated virus (AAV) packaging capacity. Systemic delivery of AAV vectors carrying cmGAD67 preferentially targeted parvalbumin interneurons and enabled efficient circuit modulation. To evaluate therapeutic potential, we expressed glutamic acid decarboxylase 65 (GAD65) under the control of cmGAD67 (AAV-GAD65). AAV-GAD65 suppressed abnormal delta oscillations, reduced seizure-like activity, normalized anxiety-like behavior, and improved survival in seizure models. Biochemical analyses confirmed increased GABA levels in the cortex and hippocampus, linking functional improvements to enhanced inhibitory neurotransmitter synthesis. Together, these findings establish the cmGAD67 promoter as a versatile platform for inhibitory neuron-targeted AAV gene delivery and identify AAV-GAD65 as a promising strategy for seizure control and disorders associated with E/I imbalance.

Glutamate Decarboxylase

AAV gene therapy for hereditary spastic paraplegia type 50: a phase 1 trial in a single patient.

There are more than 10,000 individual rare diseases and most are without therapy. Personalized genetic therapy represents one promising approach for their treatment. We present a road map for individualized treatment of an ultra-rare disease by establishing a gene replacement therapy developed for a single patient with hereditary spastic paraplegia type 50 (SPG50). Through a multicenter collaboration, an adeno-associated virus-based gene therapy product carrying the AP4M1 gene was created and successfully administered intrathecally to a 4-year-old patient within 3 years of diagnosis as part of a single-patient phase 1 trial. Primary endpoints were safety and tolerability, and secondary endpoints evaluated efficacy. At 12 months after dosing, the therapy was well tolerated. No serious adverse events were observed, with minor events, including transient neutropenia and Clostridioides difficile gastroenteritis, experienced but resolved. Preliminary efficacy measures suggest a stabilization of the disease course. Longer follow-up is needed to confirm the safety and provide additional insights on the efficacy of the therapy. Overall, this report supports the safety of gene therapy for SPG50 and provides insights into precision therapy development for rare diseases. Clinical trial registration: NCT06069687 .

Humans

Perspective on Adeno-Associated Virus Capsid Modification for Duchenne Muscular Dystrophy Gene Therapy.

Duchenne muscular dystrophy (DMD) is a X-linked, progressive childhood myopathy caused by mutations in the dystrophin gene, one of the largest genes in the genome. It is characterized by skeletal and cardiac muscle degeneration and dysfunction leading to cardiac and/or respiratory failure. Adeno-associated virus (AAV) is a highly promising gene therapy vector. AAV gene therapy has resulted in unprecedented clinical success for treating several inherited diseases. However, AAV gene therapy for DMD remains a significant challenge. Hurdles for AAV-mediated DMD gene therapy include the difficulty to package the full-length dystrophin coding sequence in an AAV vector, the necessity for whole-body gene delivery, the immune response to dystrophin and AAV capsid, and the species-specific barriers to translate from animal models to human patients. Capsid engineering aims at improving viral vector properties by rational design and/or forced evolution. In this review, we discuss how to use the state-of-the-art AAV capsid engineering technologies to overcome hurdles in AAV-based DMD gene therapy.

Animals

Decoding Nonlinearities in AAV-Based Gene Therapy Using PBPK Modelling.

The objective of this research was to develop a physiologically based pharmacokinetic (PBPK) model for AAV-based gene therapy, which can capture the nonlinearity observed in both viral vector and transgene product pharmacokinetics (PK) across a wide range of doses, while accounting for the effect of immunogenicity. To develop the PBPK model, previously published PK data generated in mice using AAV8 vector containing the transgene for a non-binding monoclonal antibody was used. Immunocompetent mice were administered with AAV at a wide range of doses (1E8, 1E9, 5E9, 1E10, 2E10, 1E11, 2E11, 1E12, and 1E13vg per mouse), and the PK of transgene and transgene product (i.e., antibody) in plasma and/or tissue was collected. The nonlinearity in transgene product concentrations was characterized using a saturable production process and a concentration-dependent antibody elimination rate was used to characterize the effect of anti-drug antibody (ADA) on transgene product. The model successfully described the PK of both the vector and the transgene product across all dose levels and accurately captured the sigmoidal dose-exposure-response relationship for AAV. Notably, the model described a dose-dependent ADA response, with the high dose group exhibiting an earlier onset and faster rate of transgene product elimination. Lower dose group showed delayed onset and minimal ADA-mediated elimination of transgene product. Overall, the PBPK model presented here effectively characterizes vector and transgene product kinetics in mice and demonstrates utility in preclinical-to-clinical translation and dose optimization of AAV-based gene therapies.

Animals

In Silico Reconstruction of the Viral Evolutionary Lineage Yields a Potent Gene Therapy Vector.

Adeno-associated virus (AAV) vectors have emerged as a gene-delivery platform with demonstrated safety and efficacy in a handful of clinical trials for monogenic disorders. However, limitations of the current generation vectors often prevent broader application of AAV gene therapy. Efforts to engineer AAV vectors have been hampered by a limited understanding of the structure-function relationship of the complex multimeric icosahedral architecture of the particle. To develop additional reagents pertinent to further our insight into AAVs, we inferred evolutionary intermediates of the viral capsid using ancestral sequence reconstruction. In-silico-derived sequences were synthesized de novo and characterized for biological properties relevant to clinical applications. This effort led to the generation of nine functional putative ancestral AAVs and the identification of Anc80, the predicted ancestor of the widely studied AAV serotypes 1, 2, 8, and 9, as a highly potent in vivo gene therapy vector for targeting liver, muscle, and retina.

Dependovirus

Evaluation of early prophylactic corticosteroid administration on early safety and efficacy outcomes of adeno-associated virus gene therapy in the hemophilia dog model.

BACKGROUND: Prior to commercial withdrawal, adeno-associated virus (AAV) gene therapy was approved for the treatment of adults with severe hemophilia A. Mechanisms underlying variability, durability, and liver transaminitis are largely uncharacterized. OBJECTIVES: To evaluate the effects of prophylactic corticosteroid administration on AAV gene therapy outcomes in dogs with severe hemophilia A. METHODS: Seven dogs with hemophilia A received 6e13 vector genomes/kg of AAV5-canine factor (F)VIII. Four dogs received oral prednisolone (1 mg/kg/day) starting 3 hours preinfusion with dose-tapering over 6 weeks; three control dogs received no corticosteroids. Percutaneous liver biopsies were performed on detection of alanine aminotransferase (ALT) >2-fold the upper limit of normal. RESULTS: All dogs expressed therapeutic FVIII:C (8.7-56.1%), improved whole blood clot time, and decreased bleeding rates (pre = 6.11 vs post = 1.42 bleeds/year, P = .016) over 2 years post-AAV5-canine FVIII. Corticosteroid-treated dogs demonstrated a modest increase in mean FVIII:C at 2 years by chromogenic substrate assay (39.1%) compared with controls (29.5%), driven by one female with markedly elevated FVIII:C from day 54 onward. When analyzed by sex, all female dogs exhibited increased mean FVIII:C chromogenic substrate assay at 2 years (49.3%) compared with males (9.1%), regardless of prophylactic corticosteroid use. Prophylactic corticosteroids did not impact transient posttreatment elevations of proinflammatory cytokines, anti-AAV antibody formation, or ALT levels. One corticosteroid-treated dog experienced ALT > 4.3-fold the upper limit of normal at 18 weeks without impacting long-term FVIII:C expression. A liver biopsy showed diffuse, minimal periportal lymphocyte and neutrophil infiltration, consistent with nonspecific minimal hepatitis. CONCLUSIONS: Prophylactic corticosteroids were not clearly associated with increased transgene expression in dogs with hemophilia A.

adeno-associated virus

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

Long-Term Correction of Murine Glycogen Storage Disease Type III by AAV-Mediated Gene Therapy Using an Immunotolerizing Dual Promoter to Express Bacterial Pullulanase.

BACKGROUND: We recently reported an innovative gene therapy approach for GSD III using a recombinant adeno-associated virus serotype 9 vector (AAV9-Dual-Pull) expressing a bacterial debranching enzyme (pullulanase) driven by a tandem dual promoter that consists of an immunotolerizing liver-specific promoter (LSP) and the ubiquitous CMV enhance/chicken β-actin (CB) promoter. In this follow-up study, we evaluated the long-term efficacy of this gene therapy in GSD IIIa mice. METHODS: Three-month-old GSD IIIa mice were intravenously injected with AAV9-LSP-Pull or AAV9-Dual-Pull at the same dose (2.5 × 1013 vg/kg). Tissues were collected after 9 months for AAV genome quantification, pullulanase expression determination, and glycogen content measurement. Liver and muscle enzymes in plasma and disease biomarker in urine were analyzed at multiple time points to examine the correction of liver and muscle damage. Behavioral tests were performed during the course of AAV treatment to evaluate the improvement of muscle function. RESULTS: The AAV-Dual-Pull treatment led to persistent pullulanase expression and effective glycogen reduction in the liver, heart, and skeletal muscle, accompanied by the reversal of liver fibrosis, decrease of plasma enzyme activities, and long-term improvement of muscle function. The AAV-LSP-Pull treatment showed a better therapeutic efficacy in the liver but had no effect on the cardiac and skeletal muscles. CONCLUSION: Our results demonstrated the long-term efficacy and safety of systemic AAV9-Dual-Pull delivery in GSD IIIa mice. Future studies will test this gene therapy approach in GSD IIIa dogs prior to the clinical translation to GSD III patients.

AAV gene therapy

Proteomics-based evaluation of AAV dystrophin gene therapy outcomes in mdx skeletal muscle.

Duchenne muscular dystrophy (DMD) is a fatal genetic muscle-wasting disease characterized by loss of dystrophin protein. Therapeutic attempts to restore a functional copy of dystrophin to striated muscle are under active development, and many utilize adeno-associated viral (AAV) vectors. However, the limited cargo capacity of AAVs precludes delivery of full-length dystrophin, a 427 kDa protein, to target tissues. Recently, we developed a method to express large dystrophin constructs using the protein trans-splicing mechanism mediated by split inteins and myotropic AAV vectors. The efficacy of this approach to restore muscle function in mdx4cv mice was previously assessed using histology, dystrophin immunolabeling, and Western blotting. Here, we expand our molecular characterization of dystrophin constructs with variable lengths using a mass spectrometry-based proteomics approach, providing insight into unique protein expression profiles in skeletal muscles of wild-type, dystrophic mdx4cv, and AAV-treated mdx4cv mice. Our data reveal several affected cellular processes in mdx4cv skeletal muscles with changes in the expression profiles of key proteins to muscle homeostasis, whereas successful expression of dystrophin constructs results in an intermediate to complete restoration. This study highlights several biomarkers that could be used in future preclinical or clinical studies to evaluate the effectiveness of therapeutic strategies.

Animals

Assessment of systemic AAV-microdystrophin gene therapy in the GRMD model of Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD) is a progressive muscle wasting disease caused by the absence of dystrophin, a membrane-stabilizing protein encoded by the DMD gene. Although mouse models of DMD provide insight into the potential of a corrective therapy, data from genetically homologous large animals, such as the dystrophin-deficient golden retriever muscular dystrophy (GRMD) model, may more readily translate to humans. To evaluate the clinical translatability of an adeno-associated virus serotype 9 vector (AAV9)-microdystrophin (μDys5) construct, we performed a blinded, placebo-controlled study in which 12 GRMD dogs were divided among four dose groups [control, 1 × 1013 vector genomes per kilogram (vg/kg), 1 × 1014 vg/kg, and 2 × 1014 vg/kg; n = 3 each], treated intravenously at 3 months of age with a canine codon-optimized microdystrophin construct, rAAV9-CK8e-c-μDys5, and followed for 90 days after dosing. All dogs received prednisone (1 milligram/kilogram) for a total of 5 weeks from day -7 through day 28. We observed dose-dependent increases in tissue vector genome copy numbers; μDys5 protein in multiple appendicular muscles, the diaphragm, and heart; limb and respiratory muscle functional improvement; and reduction of histopathologic lesions. As expected, given that a truncated dystrophin protein was generated, phenotypic test results and histopathologic lesions did not fully normalize. All administrations were well tolerated, and adverse events were not seen. These data suggest that systemically administered AAV-microdystrophin may be dosed safely and could provide therapeutic benefit for patients with DMD.

Animals

Battling Neurodegenerative Diseases with Adeno-Associated Virus-Based Approaches.

Neurodegenerative diseases (NDDs) are most commonly found in adults and remain essentially incurable. Gene therapy using AAV vectors is a rapidly-growing field of experimental medicine that holds promise for the treatment of NDDs. To date, the delivery of a therapeutic gene into target cells via AAV represents a major obstacle in the field. Ideally, transgenes should be delivered into the target cells specifically and efficiently, while promiscuous or off-target gene delivery should be minimized to avoid toxicity. In the pursuit of an ideal vehicle for NDD gene therapy, a broad variety of vector systems have been explored. Here we specifically outline the advantages of adeno-associated virus (AAV)-based vector systems for NDD therapy application. In contrast to many reviews on NDDs that can be found in the literature, this review is rather focused on AAV vector selection and their preclinical testing in experimental and preclinical NDD models. Preclinical and in vitro data reveal the strong potential of AAV for NDD-related diagnostics and therapeutic strategies.

Animals

Reducing the risk of adeno-associated virus (AAV) vector mobilization with AAV type 5 vectors.

Current adeno-associated virus (AAV) gene therapy vectors package a transgene flanked by the terminal repeats (TRs) of AAV type 2 (AAV2). Although these vectors are replication deficient, wild-type (wt) AAV2 prevalent in the human population could lead to replication and packaging of a type 2 TR (TR2)-flanked transgene in trans during superinfection by a helper virus, leading to "mobilization" of the vector genome from treated cells. More importantly, it appears likely that the majority of currently characterized AAV serotypes as well as the majority of new novel isolates are capable of rescuing and replicating AAV2 vector templates. To investigate this possibility, we flanked a green fluorescent protein transgene with type 2 and, the most divergent AAV serotype, type 5 TRs (TR2 or TR5). Consistent with AAV clades, AAV5 specifically replicated TR5 vectors, while AAV2 and AAV6 replicated TR2-flanked vectors. To exploit this specificity, we created a TR5 vector production system for Cap1 to Cap5. Next, we showed that persisting recombinant AAV genomes flanked by TR2s or TR5s were mobilized in vitro after addition of the cognate AAV Rep (as well as Rep6 for TR2) and adenoviral helper. Finally, we showed that a cell line containing a stably integrated wt AAV2 genome resulted in mobilization of a TR2-flanked vector but not a TR5-flanked vector upon adenoviral superinfection. Based on these data and the relative prevalence of wt AAV serotypes in the population, we propose that TR5 vectors have a significantly lower risk of mobilization and should be considered for clinical use.

Animals

Adeno-associated virus (AAV) vectors in cancer gene therapy.

Gene delivery vectors based on adeno-associated virus (AAV) have been utilized in a large number of gene therapy clinical trials, which have demonstrated their strong safety profile and increasingly their therapeutic efficacy for treating monogenic diseases. For cancer applications, AAV vectors have been harnessed for delivery of an extensive repertoire of transgenes to preclinical models and, more recently, clinical trials involving certain cancers. This review describes the applications of AAV vectors to cancer models and presents developments in vector engineering and payload design aimed at tailoring AAV vectors for transduction and treatment of cancer cells. We also discuss the current status of AAV clinical development in oncology and future directions for AAV in this field.

Capsid Proteins

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

Novel photoreceptor-specific promoters for gene therapy in mid- to late-stage retinal degeneration.

Inherited retinal degenerations (IRDs) cause progressive photoreceptor loss, leading to vision impairment. Gene therapy using adeno-associated viral (AAV) vectors holds immense promise for treating these conditions. However, achieving optimal gene expression at mid to late stages of retinal degeneration remains challenging due to scarcity of efficient photoreceptor-specific promoters expressed at these disease stages. This study aimed to identify and validate novel promoters capable of robust and specific transgene expression when ≥50% of photoreceptors are lost. Analysis of transcriptomic data from two naturally occurring canine IRD models, laser capture microdissection of retinal cryosections followed by qPCR, and RNA in situ hybridization identified six promising genes with sustained or upregulated expression in photoreceptors in late-stage disease. Upstream cis-regulatory elements of both canine and human orthologs were identified and characterized using in silico analyses and dual-luciferase assays. Short promoters (≤840 base pairs) derived from GNGT2, IMPG2, and PDE6H genes exhibited robust reporter gene expression in photoreceptors when delivered via AAV to the subretinal space of two non-allelic canine IRD models at mid and late disease stages. These findings provide a strategy to enhance AAV-mediated gene therapy by enabling sustained transgene expression in degenerating retinas, improving treatment outcomes for patients with progressive vision loss.

Retinal Degeneration