How could gene therapy change the way we treat age-related macular degeneration?

KEYWORDS:

• Gene therapy
• neovascular age related macular degeneration
• geographic atrophy
• atrophic AMD
• choroidal neovascularization
• anti-VEGF
• adeno-associated virus

1. What is age-related macular degeneration?

Age-related macular degeneration (AMD) is the leading cause of permanent vision loss in individuals over 50 years of age [1]. Advanced AMD can anatomically present as either neovascular (nAMD) or atrophic AMD. nAMD displays characteristic growth of abnormal vasculature that originates from the choroid or retina, resulting in macular neovascularization (MNV).

MNV progression can lead to degeneration of photoreceptors, macular damage, and retinal pigment epithelium disruption [1]. If left untreated, MNV in nAMD can lead to leakage of fluid, lipid, and blood into the outer retina, resulting in irreversible vision loss [1]. Atrophic AMD can progress to geographic atrophy (GA), characterized by atrophy of choriocapillaris, retinal pigment epithelial cells, and macular photoreceptors [1].

1.1. Current treatments

Current FDA-approved treatments of nAMD consist of frequent intravitreal (IVT) anti-vascular endothelial growth factor (anti-VEGF) injections ranging from every 4 to 16 weeks. Anti-VEGF drugs are injected into the vitreous, where they bind to VEGF-A, ultimately inhibiting vascular permeability and angiogenesis [2]. However, IVT treatments, though very safe, can be associated with rare risks such as increased intraocular pressure (IOP), acute endophthalmitis, and intraocular inflammation in a small subset of patients [3]. The frequency of IVT injections also contributes to high patient burden, which may discourage patients from receiving optimal treatments. Most patients do not receive monthly IVT anti-VEGF injections as they can be extended to longer treatment interval, known as the treat-and-extend method. However, various real-world studies have shown that visual acuity outcomes in the real world are inferior to the outcomes seen in clinical trials due to missed visits and injections. There is an unmet need to reduce treatment burden in patients with nAMD and to optimize visual acuity improvements. Various clinical trials are investigating the use of gene therapy to establish an intraocular biofactory of specific proteins as a treatment option for patients suffering from advanced AMD for disease control and to alleviate burden from frequent visits and injections.

2. Gene therapy

There are two common pathways being researched that are associated with treatment for advanced AMD: the VEGF pathway and the complement pathway. The VEGF pathway is targeted for nAMD patients, as treatments target protein inhibition [4]. The complement pathway is targeted to treat patients suffering from GA with treatments inhibiting or modulating the complement cascade [5]. Gene therapy utilizes vectors with specific transgenes to continuously produce a target protein [6]. Gene therapy for nAMD aims to develop an ocular anti-VEGF biofactory to reduce and ultimately eliminate the frequency of anti-VEGF injections [4]. Clinical trials investigating the treatment of GA with gene therapy aims to inhibit or modulate the complement pathway by producing specific, pathway modifying proteins.

A common type of vector used in gene therapy for retinal diseases are adeno-associated viruses (AAV), typically serotypes AAV2 and AAV8 [7]. Through a single injection, the vector transduces target cells, and the therapeutic DNA sequence is expressed in the retinal cells, allowing for the vector to be expressed in the nucleus for a significant time period [8,9]. AAV is a nonpathogenic virus that can infect dividing and nondividing cells, making it a viable option for the delivery of gene therapy in trials [8]. The AAV2 vector is an approved vector for gene therapy and is used for gene therapy treatment of patients with biallelic RPE65 mutation-associated retinal dystrophy.

2.1. Clinical trials for ocular gene therapy

Currently, there are several human clinical trials being performed that utilize the AAV vector for advanced AMD. Clinical trials investigating RGX-314, ADVM-022 and 4D-150 are gene therapy treatments for nAMD while GT005 is a gene therapy treatment for GA. HMR59 is being investigated for both nAMD and GA.

The first RGX-314 gene therapy study, an open-label, phase 1b/2a trial, investigated the safety and tolerability of five doses of surgically administered, subretinal recombinant AAV gene therapy vector encoding a monoclonal antibody fragment that neutralizes VEGF activity (ClinicalTrials.gov Identifier: NCT03066258) [10]. The phase 1b/2a study enrolled 42 patients with a total of 5 dose cohorts; 3 × 10⁹ GC/eye, 1 × 10¹⁰ GC/eye, 6 × 10¹⁰ GC/eye, 1.6 × 10¹¹ GC/eye, 2.5 × 10¹¹ GC/eye [10]. Results from the study demonstrated stable visual acuity and stabilization of anatomy in the higher dose cohorts with greater than 3 years of follow-up. No reports of RGX-314 associated immune responses were documented. Routine post-surgery associated inflammation was seen in the trial and resolved without any sequelae. Retinal pigmentary changes were noticed in majority of the patients in the higher dose cohorts that were related to RGX-314 [11].

Efficacious results from the phase 1b/2a resulted in the initiation of two pivotal, phase 3 clinical trials for subretinal RGX-314, ATMOSPHERE (ClinicalTrials.gov Identifier: NCT04704921) and ASCENT (ClinicalTrials.gov Identifier: NCT05407636). These studies are currently ongoing and compare two doses of RGX-314 to ranibizumab and aflibercept, respectively.

The phase 2 AAVIATE trial (ClinicalTrials.gov Identifier: NCT04514653) [REGENXBIO], unlike the phase 1b/2a study, involves the suprachoroidal in-clinic delivery of RGX-314, resulting in long-term anti-VEGF expression [12]. As of Q3 2022, 95 patients in 5 dose cohorts have demonstrated tolerability of RGX-314 suprachoroidal delivery [13]. No drug-related serious adverse events occurred. Cases of mild intraocular inflammation (IOI) were reported in cohorts 1 and 2, while cohort 4 saw an increased incidence in mild to moderate inflammation. All IOI cases were resolved following treatment with topical corticosteroids. Patients in the RGX-314 arms demonstrated BCVA and central retinal thickness (CRT) stabilization, along with a meaningful reduction in treatment burden, with the highest reduction in treatment burden seen in Cohort 4 (Dose 3: 1 × 10¹¹ GC/eye). Following RGX-314 administration at the Dose 3 level, patients received a mean of 1.3 injections over 6 months, demonstrating an 84.7% reduction in anti-VEGF treatment burden. 67% of patients in the third dose level received no anti-VEGF injections over 6 months following RGX-314 administration, demonstrating the stable VA and CRT improvements. For patients who are neutralizing antibody (NAb) positive, data from cohorts 2 and 3 suggest no significant difference in VA or safety. This study demonstrates feasibility of suprachoroidal injections to deliver gene therapy.

The OPTIC study (ClinicalTrials.gov Identifier: NCT03748784) [Adverum Biotechnologies] is designed to evaluate the safety and efficacy of ADVM-022 in previously treated patients with nAMD. ADVM-022 delivers an AAV2.7m8 vector carrying a transgene for aflibercept that transduces retinal cells via an in-clinic IVT injection. Two doses were investigated of 6 × 10¹¹ vg and 2 × 10¹¹ vg, with two cohorts for each, with oral prophylactic steroids or topical eye drops post-treatment. Patients demonstrated stable BCVA and improvements in central subfield thickness (CST) over 104 weeks, with +0.2 letters (low dose) and +0.3 letters (high dose), and −55.7 um (low dose) and −95.9 um (high dose) from baseline to last visit [14]. Patients in the high dose arms demonstrated a 98% reduction in annual rates of anti-VEGF injection post-gene therapy, along with an 81% reduction in the low dose arms. ADVM-022 was well tolerated among patients, with mild to moderate inflammation that responded well to topical corticosteroids, but inflammation was recurrent and long-standing in the high dose cohort. There have been no reports of endophthalmitis or vascular occlusions at either dose. Unlike the INFINITY ADVM-022 trial investigating the same gene therapy in diabetic macular edema, there have been no reports of hypotony in the OPTIC study. These positive results led to the phase 2 LUNA (ClinicalTrials.gov Identifier: NCT05536973) which is looking at low 2 × 10¹¹ and even lower 6 × 10¹⁰ with extensive prophylaxis to evaluate the efficacy and safety of ADVM-022 in patients with nAMD.

The 4D-150 clinical trial (ClinicalTrials.gov Identifier: NCT05197270) [4D Molecular Therapeutics] focuses on an IVT injection delivery of an AAV vector, R100, which is designed to deliver dual transgenes targeting VEGF-A by aflibercept and VEGF-C by anti-VEGF-C miRNA expression. The study aims to enroll approximately 65 nAMD patients with primary endpoints investigating safety and tolerability, while secondary endpoints include the need for supplemental aflibercept injections and change in BCVA over time.

The HMR59 clinical trials (NCT03585556) [Janssen Research & Development, LLC] focused on inhibiting formation of the membrane attack complex (MAC) of the complement pathway [14]. The studies involve the delivery of an AAV2 that produced proteins that bind to MAC components (C5b-C9), preventing the MAC from becoming fully functional. In HMR-1001 for GA, 17 eyes diagnosed with atrophic AMD were intravitreally injected the study drug. Dose-limiting toxicity was not observed, and treatment was well tolerated. Four eyes developed mild inflammation, which resolved with topical steroids and pressure-lowering drops in 2 eyes. Patients in the high dose-cohort demonstrated a decreased rate of GA progression compared to historical controls. No eyes converted to nAMD. In HMR-1002, 24 patients with nAMD were injected with the study drug seven days following anti-VEGF treatment. Oral steroids were administered to mitigate adverse effects; however, three patients developed mild inflammation, with resolution following topical and oral steroids. 18% of patients have not required retreatment from month 1 to month 12.

GT005 [Gyroscope Therapeutics Limited] is an AAV2-based gene therapy for patients with GA secondary to AMD that aims to restore homeostasis in the overactive complement system by increasing production of complement factor I (CFI). Endogenous CFI degrades activated C3b and C4b molecules of the complement cascade, which has been implicated in the pathogenesis of atrophic AMD [15]. FOCUS (ClinicalTrials.gov Identifier: NCT03846193) is a phase 1/2 trial that is investigating the safety and efficacy of GT005 in patients with GA secondary to atrophic AMD. 84.6% of patients treated with GT005 demonstrated an average increase in CFI levels compared to baseline (p = 0.002). 16 AEs were associated with the surgical procedure, 12 of which were mild, 4 were moderate. Currently, there are multiple ongoing trials investigating GT005, including the EXPLORE and HORIZON trials (Table 1).

Table 1. Current ocular gene therapy clinical trials with the comparison of age-related macular degeneration type and drug injection method.

Clinical trial	AAV serotype	Age-related macular degeneration type	Method of injection
RGX-314-001	AAV8	nAMD	Subretinal injection
RGX-314-2101 (ATMOSPHERE)	AAV8	nAMD	Subretinal injection
RGX-314-3101 (ASCENT)	AAV8	nAMD	Subretinal injection
RGX-314 (AAVIATE)	AAV8	nAMD	Suprachoroidal injection
ADVM-022-001 (OPTIC)	AAV2.7m8	nAMD	IVT injection
ADVM-022-11 (LUNA)	AAV2.7m8	nAMD	IVT injection
4D-150-C001	AAV – R100	nAMD	IVT injection
HMR-1001	AAV2	GA	IVT injection
HMR-1002	AAV2	nAMD	IVT injection
FOCUS	AAV2	GA	Subretinal injection
EXPLORE	AAV2	GA	Subretinal injection
HORIZON	AAV2	GA	Subretinal injection

nAMD: neovascular age-related macular degeneration; GA: geographic atrophy; IVT: intravitreal; AAV: adeno-associated virus

2.2. Pre-clinical studies of ocular gene therapy

It should be noted that there are many pre-clinical studies regarding gene therapy for treatment of AMD. Many of these studies involve the use of animal retinas, showing combined efficacy [16]. A new discovery of gene therapy, dual acting therapy provides promising results in the treatment of nAMD [17]. New approaches are being researched for potential gene therapy treatments that may change the way physicians treat both types of AMD [18].

2.3. Challenges of gene therapy

The field of gene therapy is rapidly evolving, and is a paradigm shift in the treatment of retinal diseases. As more knowledge is gained about the best vectors, promoters, transgene and delivery, there have been episodes of inflammation with gene therapy especially with intravitreal gene therapy. The goal is to optimize efficacy by determining the lowest dose capable of disease activity control to lower the rates and risk of intraocular inflammation with gene therapy.

The best prophylaxis for patients being treated with gene therapy must be discovered so that the episodes of inflammation are lowered or eliminated. Most patients who have experienced inflammation have had successful management of post-treatment adverse events through steroid therapy, showing that the risk of inflammation is not a setback for retinal gene therapy especially at lower doses.

3. How can gene therapy change the way we treat AMD?

Gene therapy treatments are effective in treating nAMD based on the data seen with RGX-314 and ADVM-022 programs. Gene therapy can present promising results for the treatment of GA, as being evaluated by the GT005 program. Gene therapy can provide a long-term solution for patients who are unable to get frequent injections. With gene therapy, patient burden of frequent injections and follow-up visits can be reduced. More information about the long-term efficacy and safety of gene therapy in patients with nAMD will emerge as the clinical trials mentioned above move to higher phases, but the results are promising in the early stages of these trials.

Declaration of interest

AM Khanani has acted as a consultant and received research funding from RegenXBio, Gyroscope, Adverum and 4DMT. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

Reviewer disclosures

A reviewer on this manuscript has disclosed that they were an investigator on the Gyroscope GT005 clinical trials (Horizon, Explore, Oracle). Peer reviewers on this manuscript have no other relevant financial relationships or otherwise to disclose.

Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.