AAV Gene Therapy in Ocular Diseases

The human eye, a masterpiece of biological engineering, orchestrates the intricate dance of light and neural signals that paints our world in vibrant detail. However, for millions worldwide, this precious gift is dimmed by inherited and acquired ocular diseases, often leading to irreversible vision loss. Recognizing the need for effective interventions, adeno-associated virus (AAV) vectors have emerged as a cornerstone of gene therapy. Their favorable safety profile, high transduction efficiency, and capacity for sustained transgene expression in target tissues make them particularly well-suited for addressing such debilitating conditions.

Building upon the inherent advantages of AAV vectors, the eye presents a uniquely amenable environment for gene-based interventions. Its immune-privileged status minimizes the risk of rejection, while its compartmentalized anatomy facilitates targeted delivery. Furthermore, the optical accessibility of the eye allows for direct monitoring of therapeutic effects. Consequently, AAV vectors have demonstrated remarkable potential in this context, offering the prospect of long-term therapeutic benefits with a reduced risk of adverse events. Over the past decade, AAV-based gene therapies have successfully transitioned from preclinical research into clinical applications. Since the landmark approval of Luxturna in 2017, AAV-mediated ocular gene therapy has rapidly advanced, with multiple candidates now in late-stage clinical trials.

To further illuminate this promising field, this article provides an in-depth exploration of AAV gene therapy in ocular diseases. We will delve into specific disease indications where AAV therapy is being investigated, provide a concise overview of relevant eye anatomy, detail various AAV injection methods, discuss the crucial role of serotypes and their tropism in targeting specific retinal cells, and outline representative clinical trials, both completed and ongoing, that illustrate the progress and complexities of this rapidly evolving area.

1. Ocular Disease Indications for AAV Gene Therapy

AAV gene therapy targets a spectrum of ocular diseases, ranging from monogenic inherited retinal diseases (IRDs) to complex acquired conditions. Below is a detailed overview of key indications:

Inherited Retinal Diseases (IRDs)

IRDs are a group of rare, genetically heterogeneous disorders caused by mutations in genes critical for retinal function. AAV gene therapy has primarily focused on these conditions due to their monogenic nature and clear therapeutic targets (Figure 1):

• Leber Congenital Amaurosis (LCA): A severe, early-onset retinal dystrophy, LCA results in profound vision loss due to mutations in genes like RPE65, GUCY2D, or CEP290. LCA2 (RPE65-related) has been a flagship target, with Luxturna (voretigene neparvovec) demonstrating significant visual improvement. LCA’s early onset necessitates intervention in pediatric populations, posing unique clinical trial design challenges.
• Retinitis Pigmentosa (RP): This heterogeneous group of disorders, affecting 1 in 4,000 individuals, is caused by mutations in over 80 genes, including RPGR, RHO, and USH2A. RP leads to progressive photoreceptor and retinal pigment epithelium degeneration, causing night blindness and tunnel vision. Gene therapies targeting RPGR (e.g., NCT03116113) aim to restore rod and cone function, though genetic diversity complicates development.
• Choroideremia: Caused by mutations in the CHM gene, choroideremia results in progressive retinal pigment epithelium and photoreceptor loss, primarily in males. Clinical trials (e.g., NCT01461213) have explored AAV2-mediated REP1 expression, but mixed outcomes highlight challenges in achieving sustained efficacy in advanced disease stages.
• Achromatopsia: This cone dysfunction disorder, caused by mutations in genes like CNGA3 or CNGB3, leads to color blindness, photophobia, and reduced visual acuity. AAV therapies (e.g., NCT02935517) aim to restore cone function, with early trials showing partial visual gains.
• X-linked Retinoschisis (XLRS): Resulting from RS1 mutations, XLRS causes retinal splitting and cystic cavities, impairing vision. AAV2-based trials (e.g., NCT02416622) target retinal ganglion cells and photoreceptors, though structural retinal changes pose delivery challenges.
• Leber Hereditary Optic Neuropathy (LHON): A mitochondrial disorder caused by mutations in genes like ND4, LHON affects retinal ganglion cells, leading to optic nerve degeneration and central vision loss. AAV2-mediated ND4 delivery (e.g., NCT02161380) has shown partial visual recovery, particularly in early-stage patients.
• Usher Syndrome: Combining hearing loss and RP, Usher syndrome is caused by mutations in large genes like MYO7A, PCDH15 or USH2A. The large size of these genes exceeds AAV’s cargo capacity, prompting exploration of dual AAV vectors.
• Stargardt Disease: Caused by ABCA4 mutations, Stargardt disease leads to macular degeneration and central vision loss. The large ABCA4 gene necessitates innovative delivery strategies, such as dual AAV.

Acquired Retinal Diseases

Acquired diseases, driven by multifactorial etiologies, are increasingly targeted by AAV therapies to deliver therapeutic proteins rather than gene replacement:

• Age-Related Macular Degeneration (AMD): Wet AMD, characterized by choroidal neovascularization (CNV), is a leading cause of blindness in the elderly. Current treatments require frequent anti-vascular endothelial growth factor (anti-VEGF) injections. AAV therapies like RGX-314 (NCT04514653) aim to provide sustained anti-VEGF expression, reducing injection frequency.
• Diabetic Retinopathy (DR): A complication of diabetes, DR involves vascular leakage and retinal ischemia. AAV-based anti-angiogenic therapies (e.g., NCT04567550) target vascular abnormalities to halt progression.
• Glaucoma: Characterized by retinal ganglion cells loss and optic nerve damage, glaucoma is a leading cause of irreversible blindness. AAV therapies delivering neuroprotective factors like ciliary neurotrophic factor (CNTF) aim to preserve retinal ganglion cells.

IRDs benefit from gene replacement strategies, but acquired diseases require sustained expression of therapeutic proteins, posing challenges in vector design and long-term efficacy. The genetic complexity and variable progression of acquired diseases complicate trial design compared to monogenic IRDs.

Fig 1. AAV therapy targets a spectrum of ocular diseases. 

2. Eye Anatomy and Relevant Gene Targets

The eye’s compartmentalized anatomy facilitates precise AAV delivery, enhancing therapeutic efficacy and safety. Its immune-privileged status further supports gene therapy by minimizing inflammatory responses. Below is a detailed examination of relevant anatomical structures:

• Cornea and Anterior Chamber: The cornea, a transparent avascular tissue, and the aqueous humor-filled anterior chamber are relevant for diseases like corneal dystrophies and glaucoma. Intra-cameral or intra-stromal injections target corneal endothelial cells or trabecular meshwork.
• Vitreous Humor: This gel-like substance fills the posterior chamber and serves as the medium for intravitreal injections, targeting inner retinal layers (e.g., Müller glia).
• Retina: The retina’s multilayered structure is central to most AAV therapies:

  • Retinal Pigment Epithelium (RPE): A monolayer supporting photoreceptors, the RPE is critical in LCA, choroideremia, and Stargardt disease. It is efficiently transduced via subretinal injection.
  • Photoreceptors (Rods and Cones): These light-sensing cells are primary targets in RP, achromatopsia, and LCA. Their outer segment turnover requires sustained transgene expression.
  • Retinal Ganglion Cells (RGCs): Located in the inner retina, RGCs transmit visual signals to the brain and are targeted in LHON and glaucoma.
  • Müller Glia and Amacrine Cells: These support cells are transduced by certain AAV serotypes, influencing retinal homeostasis.

• Choroid and Sclera: The vascular choroid and fibrous sclera are relevant for wet AMD and uveitis, accessible via suprachoroidal injections.
• Optic Nerve: Affected in LHON, the optic nerve’s axonal structure poses delivery challenges.

The gene targets for AAV-based therapies in ocular diseases are intricately tied to the eye’s anatomical structures, particularly the retina (Figure 2), where most therapeutic interventions are focused due to its layered organization and accessibility. As mentioned earlier, RPE65, targeted in LCA, encodes a protein in the RPE, a monolayer beneath the retina that supports photoreceptors by recycling visual pigments. In RP, RPGR and RHO mutations affect the photoreceptor layer—RPGR is critical for protein transport in rod and cone outer segments, while RHO encodes rhodopsin, essential for rod phototransduction—causing progressive photoreceptor death and retinal thinning. CHM in choroideremia, expressed in the RPE and choroid (a vascular layer beneath the RPE), leads to degeneration of both RPE and photoreceptors when mutated. For wet AMD, it is critical to deliver transgenes to the subretinal or suprachoroidal space to inhibit neovascularization in the choroid. RS1, targeted in XLRS, encodes retinoschisin, a protein maintaining retinal architecture; its mutation causes splitting within the inner retinal layers, including the ganglion cell and inner nuclear layers, disrupting signal transmission. Lastly, ND4 in LHON is a mitochondrial gene critical for RGC function; AAV delivery to the inner retina aims to restore mitochondrial activity, preserving optic nerve integrity and central vision. These targets underscore the need for precise delivery methods—like subretinal injections for RPE and photoreceptors or intravitreal injections for RGCs—to address the specific anatomical layers affected by each disease. Each of these targets is carefully selected based on its expression within specific eye compartments, allowing precise intervention while minimizing off-target effects in AAV gene therapy.

Figure 2. Retinal disease genes and therapy targets.

3. AAV Injection Methods

The route of AAV administration determines the target cells, transduction efficiency, and therapeutic outcomes. Each method balances accessibility, safety, and efficacy, influenced by vector tropism and anatomical barriers (Figure 3). Below is a detailed analysis:

• Subretinal Injection (SRI):

  • Description: AAV is injected into the potential space between the RPE and photoreceptors via a surgical procedure, inducing temporary retinal detachment.
  • Target Cells: Efficiently transduces RPE and photoreceptors, ideal for LCA, RP, and choroideremia.
  • Advantages: High transduction efficiency, evasion of humoral immunity due to immune privilege, and precise targeting of outer retinal layers.
  • Challenges: Retinal detachment can trigger microglial activation, photoreceptor apoptosis, and inflammation, particularly in degenerated retinas. Serious adverse events, such as vision loss, have been reported in choroideremia trials. The procedure requires specialized surgical expertise.

• Intravitreal Injection (IVT):

  • Description: AAV is injected into the vitreous humor, a less invasive method accessible via outpatient procedures.
  • Target Cells: Primarily transduces RGCs, Müller glia, and amacrine cells; limited penetration to outer retina (photoreceptors, RPE) due to the ILM and extracellular matrix barriers.
  • Advantages: Simpler procedure, broader vector distribution in the vitreous, and suitability for inner retinal diseases like LHON.
  • Challenges: Higher immunogenicity, with NAbs reducing efficacy, especially in contralateral eye injections. Novel capsids (e.g., AAV2.7m8, AAV2.GL) aim to enhance outer retina transduction via IVT.

• Suprachoroidal Injection:

  • Description: AAV is delivered into the suprachoroidal space between the sclera and choroid using microneedles or catheters.
  • Target Cells: RPE, photoreceptors, and choroidal cells, suitable for wet AMD, DR, and uveitis.
  • Advantages: Less invasive than SRI, potentially lower immunogenicity than IVT, and broader distribution across the posterior segment.
  • Challenges: Limited clinical data; transduction efficiency varies by serotype (e.g., AAV8, AAVv128 show promise). Long-term safety remains under investigation.

• Other Routes:

  • Intra-cameral Injection: Targets anterior chamber cells for glaucoma or corneal dystrophies, transducing trabecular meshwork or corneal endothelium.
  • Sub-inner Limiting Membrane Injection: An emerging method to target inner retinal layers, bypassing ILM barriers.
  • Sub-tenon Injection: Used for broader ocular distribution, though less common in AAV therapy.

SRI remains the gold standard for outer retina diseases due to its high transduction efficiency, but its invasiveness drives exploration of IVT and suprachoroidal approaches. The choice of route must consider disease stage, target cell type, and patient-specific factors, such as retinal integrity.

Fig 3. Injection routes for ophthalmic gene therapy. 

4. AAV Serotypes and Eye Tropism

AAV serotypes are critical in ocular gene therapy due to their capsid-driven tropism, which dictates their ability to transduce specific cell types in the eye. AAV2, widely used in therapies like Luxturna, effectively targets RPE and RGCs, but its photoreceptor transduction is limited when delivered intravitreally, prompting the use of subretinal injections for better efficacy in diseases like LCA (Table 1). AAV8 and AAV9 excel at transducing photoreceptors and RPE, making them suitable for conditions such as RP and wet AMD, with AAV8 powering RGX-314 for sustained anti-VEGF expression. Engineered variants like AAV2.7m8 enhance photoreceptor targeting. AAV5 also transduces photoreceptors and RPE, while AAV4 preferentially targets Müller glia, offering potential for supportive retinal therapies. The choice of serotype and delivery route—SRI for outer retinal cells, IVT for inner retinal cells—must align with the target cell type.

Table 1. AAV serotypes and tissue tropism.

5. The Clinical Trial Landscape

The clinical development landscape for AAV-based ocular gene therapies encompasses a diverse range of ocular conditions, employing varied therapeutic strategies and delivery methods, as exemplified by the trials listed in Table 2, with both successes and setbacks shaping the field. Notably, Luxturna from Spark Therapeutics stands as the only currently approved AAV-based gene therapy for ocular disease, specifically treating RPE65 mutation-associated retinal dystrophy, which includes LCA and RP. In wet AMD, Regenxbio (Abbvie)’s Phase II trial of subretinally delivered RGX-314 (AAV8-VEGF inhibitor) demonstrated positive outcomes in a fellow eye sub-study, reporting significant reductions in anti-VEGF treatment burden at nine months (October 2024). Similarly, 4D Molecular Therapeutics’ Phase I/II PRISM trial (4D-150, proprietary AAV-aflibercept/miRNA) yielded encouraging interim results in 2024, showing a substantial decrease in injection rates with a favorable safety profile over 24 weeks in 30 patients. Building on this momentum, 4DMT initiated the pivotal 4FRONT-1 Phase III trial in March 2025 to further assess 4D-150’s efficacy and safety in wet AMD. In contrast, Adverum Biotechnologies’ Phase II trial of intravitreally delivered ADVM-022 (AAV.7m8-Aflibercept) for DME was terminated due to a dose-limiting toxicity. For inherited retinal diseases, GenSight Biologics’ Phase I/II trial of subretinally delivered GS030-DP (AAV2.7m8-light-sensitive protein) for RP showed promising safety and efficacy signals at one year post-administration in nine patients (reported in 2023). Beacon Therapeutics reported positive 24-month data in 2024 from its Phase I/II trial of subretinally delivered AAV-CNGA3 (AAV8-CNGA3) for achromatopsia and is also advancing its Phase II/III trial of subretinally delivered AAV-RPGR (AAV8-RPGR) for XLRP. For dry AMD, Johnson & Johnson completed its Phase I trial of intravitreally delivered AAVCAGscD59 (AAV2-sCD59) by 2019 and has since initiated a long-term extension study (ongoing as of February 2025) to further evaluate safety and tolerability. However, Biogen’s Phase III trial of subretinally delivered BIIB112 (AAV5-REP1) for choroideremia did not meet its primary endpoint of statistically significant improvement in visual acuity. Similarly, Editas Medicine paused enrollment in its Phase I/II trial of subretinally delivered EDIT-101 (AAV5-CEP290) for LCA in 2022 due to a small responsive patient population and decided not to progress the therapy independently.

Table 2. Representative clinical trials for AAV-based therapy.

6. Conclusion

AAV gene therapy represents a groundbreaking approach to treating ocular diseases, offering hope for patients with conditions that were once considered untreatable. The success of therapies like Luxturna and the progress of numerous clinical trials underscore the potential of AAV vectors to revolutionize ocular therapeutics. The eye’s anatomical advantages, combined with AAV’s safety, versatility, and tropism, have positioned it as a leading platform for both IRDs and acquired diseases like wet AMD. Ongoing efforts, novel capsids, and innovative delivery methods (e.g., suprachoroidal injection) signal a vibrant pipeline, yet challenges remain. Immune responses, cargo size limitations, long-term efficacy, and high costs require urgent attention to ensure equitable access and sustained therapeutic impact. By addressing these hurdles through vector engineering, innovative manufacturing platform and global collaboration, AAV gene therapy can fulfill its promise as a cornerstone of precision ophthalmology.

Reference:

1. Hinsch, V. G., et al. A Comprehensive Review of Clinically Applied Adeno-Associated Virus-Based Gene Therapies for Ocular Disease. Hum Gene Ther. 2025.
2. Castro, B. F. M. AAV-Based Strategies for Treatment of Retinal and Choroidal Vascular Diseases: Advances in Age-Related Macular Degeneration and Diabetic Retinopathy Therapies. BioDrugs. 2024;38(1):73-93.
3. Buck, T. M. Recombinant Adeno-Associated Viral Vectors (rAAV)-Vector Elements in Ocular Gene Therapy Clinical Trials and Transgene Expression and Bioactivity Assays. Int J Mol Sci. 2020;21(12):4197.
4. Banou, L. Ocular Gene Therapy: An Overview of Viral Vectors, Immune Responses, and Future Directions. Yale J Biol Med. 2024;97(4):491-503.
5. Purdy, R. Gene Therapy-Associated Uveitis (GTAU): Understanding and mitigating the adverse immune response in retinal gene therapy. Prog Retin Eye Res. 2025;106:101354.