Safety of rAAV2/2- ND4 Gene Therapy for Leber Hereditary Optic Neuropathy

AAV Vector Immunogenicity in Humans: A Long Journey to Successful Gene Transfer

Gene therapy with adeno-associated virus (AAV) vectors has demonstrated safety and long-term efficacy in a number of trials across target organs, including eye, liver, skeletal muscle, and the central nervous system. Since the initial evidence that AAV vectors can elicit capsid T cell responses in humans, which can affect the duration of transgene expression, much progress has been made in understanding and modulating AAV vector immunogenicity. It is now well established that exposure to wild-type AAV results in priming of the immune system against the virus, with development of both humoral and T cell immunity. Aside from the neutralizing effect of antibodies, the impact of pre-existing immunity to AAV on gene transfer is still poorly understood. Herein, we review data emerging from clinical trials across a broad range of gene therapy applications. Common features of immune responses to AAV can be found, suggesting, for example, that vector immunogenicity is dose-dependent, and that innate immunity plays an important role in the outcome of gene transfer. A range of host-specific factors are also likely to be important, and a comprehensive understanding of the mechanisms driving AAV vector immunogenicity in humans will be key to unlocking the full potential of in vivo gene therapy.

Immune Response and Intraocular Inflammation in Patients With Leber Hereditary Optic Neuropathy Treated With Intravitreal Injection of Recombinant Adeno-Associated Virus 2 Carrying the ND4 Gene: A Secondary Analysis of a Phase 1/2 Clinical Trial

Importance

Intravitreal gene therapy is regarded as generally safe with limited mild adverse events, but its systemic effects remain to be investigated.

Objective

To examine the association between immune response and intraocular inflammation after ocular gene therapy with recombinant adeno-associated virus 2 carrying the ND4 gene (rAAV2/2-ND4).

Design, Setting, and Participants

This secondary analysis of an open-label, dose-escalation phase 1/2 randomized clinical trial of rAAV2/2-ND4 included data from February 13, 2014 (first patient visit), to March 30, 2017 (last patient visit at week 96), the first 2 years after injection. Patients older than 15 years with diagnosed ND4 Leber hereditary optic neuropathy (LHON) and visual acuity of at least counting fingers were enrolled in 1 of 5 cohorts. Four dose cohorts of 3 patients each were treated sequentially. An extension cohort of 3 patients received the dose of 9 × 1010 viral genomes per eye.

Interventions

Patients received increasing doses of rAAV2/2-ND4 (9 × 109, 3 × 1010, 9 × 1010, and 1.8 × 1011 viral genomes per eye) as a single unilateral intravitreal injection. Patients were monitored for 96 weeks after injection; ocular examinations were performed regularly, and blood samples were collected for immunologic testing.

Main Outcomes and Measures

A composite ocular inflammation score (OIS) was calculated based on grades of anterior chamber cells and flare, vitreous cells, and haze according to the Standardization of Uveitis Nomenclature. The systemic immune response was quantified by enzyme-linked immunospot (cellular immune response), enzyme-linked immunosorbent assay (IgG titers), and luciferase assay (neutralizing antibody [NAb] titers).

Results

The present analysis included 15 patients (mean [SD] age, 47.9 [17.2] years; 13 men and 2 women) enrolled in the 5 cohorts of the clinical trial. Thirteen patients experienced intraocular inflammation after rAAV2/2-ND4 administration. Mild anterior chamber inflammation and vitritis were reported at all doses, and all cases were responsive to treatment. A maximum OIS of 9.5 was observed in a patient with history of idiopathic uveitis. Overall, OIS was not associated with the viral dose administered. No NAbs against AAV2 were detected in aqueous humor before treatment. Two patients tested positive for cellular immune response against AAV2 at baseline and after treatment. Humoral immune response was not apparently associated with the dose administered or with the immune status of patients at baseline. No association was found between OISs and serum NAb titers.

Conclusions and Relevance

In this study, intravitreal administration of rAAV2/2-ND4 in patients with LHON was safe and well tolerated. Further investigations may shed light into the local immune response to rAAV2/2-ND4 as a potential explanation for the observed intraocular inflammation.

Perspectives on Gene Therapy: Choroideremia Represents a Challenging Model for the Treatment of Other Inherited Retinal Degenerations

Purpose

To report combined viewpoints on ocular gene therapy from a select group of clinician scientists and a patient advocacy group.

Methods

With the support of Randy Wheelock and Dr. Chris Moen from the Choroideremia Research Foundation (CRF), a special interest group at the 2019 Annual meeting of the Association for Research in Vision and Ophthalmology in Vancouver, Canada, shared their knowledge, experience, concepts, and ideas and provided a forum to discuss therapeutic strategies for the treatment of inherited retinal disorders, using experience in choroideremia (CHM) as a model.

Results

A member of the CRF presented the patient perspective and role in clinical trials. Five clinician scientists presented reasons for limited long-term visual improvement in many gene therapy trials, including challenges with dose, incomplete understanding of photoreceptor metabolism, vector delivery, inflammation, and identification of patients likely to benefit from treatment.

Conclusions

The shared experience of the five clinician scientists indicates that the results of ocular gene therapy for choroideremia have been less successful than for RPE65-related Leber congenital amaurosis. Improvement in vector delivery and developing a better understanding of gene expression in target tissues, treatment dose and side effects, and inflammation, as well as identifying patients who are most likely to benefit without suffering excessive risk, are necessary to advance the development of effective therapies for inherited retinal degenerations.

Translational Relevance

Additional long-term data are required to determine if ocular gene therapy will be sufficient to alter natural progression in choroideremia. Combination therapies may have to be considered, as well as alternative vectors that minimize risk.

Leber's Hereditary Optic Neuropathy as a Promising Disease for Gene Therapy Development

Leber's hereditary optic neuropathy (LHON) is a relatively common, rapidly progressing inherited optic neuropathy wherein LHON-affected eyes undergo optic nerve atrophy due to retinal ganglion cell (RGC) loss. It is a maternally inherited (or sporadic) mitochondrial disorder caused primarily by mutations in genes that encode components of respiratory complex (RC)1 in mitochondria. Mitochondrial deficiency of RC1 compromises ATP production and oxidative stress management in RGCs. The most common LHON-causing mutations are 11778G>A, 3460G>A, and 14484T>C point mutations in MT-ND4, MT-ND1, and MT-ND6. The unusually high mitochondrial load of RGCs makes them particularly sensitive to these mutations. Patients with LHON may be prescribed ubiquinone (a component of RC3) or idebenone, a ubiquinone analogue with enhanced bioavailability to act downstream of RC1. The challenge of accessing the inner mitochondrial membrane with gene therapy for LHON, and other mitochondrial diseases, may be overcome by incorporation of a specific mitochondrion-targeting sequence (MTS) that enables allotropic expression of a nucleus-transcribed ND4 transgene. Because LHON penetrance is incomplete among carriers of the aforementioned mutations, identification of environmental factors, such as heavy smoking, that interact with genetics in the phenotypic expression of LHON may be helpful toward preventing or delaying disease development. LHON has become a model for mitochondrial and neurogenerative diseases owing to it having a clearly identified genetic cause and its early onset and rapid progression characteristics. Hence, LHON studies and genetic treatment advances may inform research of other diseases.

A Missense Mutation in OPA1 Causes Dominant Optic Atrophy in a Chinese Family

Background

To investigate the genetic causes and clinical characteristics of dominant optic atrophy (DOA) in a Chinese family.

Methods

A 5-generation pedigree of 35 family members including 12 individuals affected with DOA was recruited from Shenzhen Eye Hospital, China. Four affected family members and one unaffected family member were selected for whole exome sequencing. Sanger sequencing was used to confirm and screen the identified mutation in 18 members of the family. The disease-causing mutation was identified by bioinformatics analysis and confirmed by segregation analysis. The clinical characteristics of the family members were analyzed.

Results

A heterozygous missense mutation (c.1313A>G, p.D438G) in optic atrophy 1 (OPA1) was identified in 10 individuals affected with DOA in this family. None of the unaffected family members had the mutation. Patients in this family had vision loss since they were children or adolescence. The visual acuity decreased progressively to hand movement, except for one patient (IV-12) who had relatively good vision of 20/30 and 20/28. The fundus typically manifested as optic disc pallor. The visual fields, optical coherence tomography, and visual evoked potential suggested variable degree of abnormality in patients. Patients who had a history of cigarette smoking and alcohol drinking had more severe clinical manifestations.

Conclusions

Our results suggest that the p.D438G mutation in OPA1 causes optic atrophy in this family. The patients who carried the mutation demonstrated heterogeneous clinical manifestations in this family. This is the first report on the c.1313A>G (p.D438G) mutation of OPA1 in a Chinese family affected with DOA.

Neuroprotection in Glaucoma: Towards Clinical Trials and Precision Medicine

Purpose: The eye is currently at the forefront of translational medicine and therapeutics. However, despite advances in technology, primary open-angle glaucoma remains the leading cause of irreversible blindness worldwide. Traditional intraocular pressure (IOP)-lowering therapies are often not sufficient to prevent progression to blindness, even in patients with access to high-quality healthcare. Neuroprotection strategies, which aim to boost the ability of target cells to withstand a pathological insult, have shown significant promise in animal models but none have shown clinically relevant efficacy in human clinical trials to date. We sought to evaluate the current status of neuroprotection clinical trials for glaucoma and identify limitations which have prevented translation of new glaucoma therapies to date.Methods: Literature searches identified English language references. Sources included MEDLINE, EMBASE, the Cochrane Library and Web of Science databases; reference lists of retrieved studies; and internet pages of relevant organisations, meetings and conference proceedings, and clinical trial registries.Results: We discuss six key neuroprotective strategies for glaucoma that have reached the clinical trial stage. Delivery of neurotrophic factors through gene therapy is also progressing towards glaucoma clinical trials. Refinements in trial design and the use of new modalities to define structural and functional endpoints may improve our assessment of disease activity and treatment efficacy. Advances in our understanding of compartmentalised glaucomatous degeneration and continued progress in the molecular profiling of glaucoma patients will enable us to predict individual risk and tailor treatment.Conclusion: New approaches to future glaucoma neuroprotection trials could improve the prospects for new glaucoma therapies. Glaucoma treatment tailored according to an individual's unique risk profile may become increasingly common in the future.

Treatment strategies for Leber hereditary optic neuropathy

PURPOSE OF REVIEW

Leber hereditary optic neuropathy (LHON) is the most common primary mitochondrial DNA (mtDNA) disorder in the population and it carries a poor visual prognosis. In this article, we review the development of treatment strategies for LHON, the evidence base and the areas of unmet clinical need.

RECENT FINDINGS

There is accumulating evidence that increasing mitochondrial biogenesis could be an effective strategy for protecting retinal ganglion cells in LHON. A number of clinical trials are currently investigating the efficacy of viral-based gene therapy for patients harbouring the m.11778G>A mtDNA mutation. For female LHON carriers of childbearing age, mitochondrial replacement therapy is being offered to prevent the maternal transmission of pathogenic mtDNA mutations.

SUMMARY

Although disease-modifying treatment options remain limited, a better understanding of the underlying disease mechanisms in LHON is paving the way for complementary neuroprotective and gene therapeutic strategies for this mitochondrial optic nerve disorder.

Gene therapy and the adeno-associated virus in the treatment of genetic and acquired ophthalmic diseases in humans: Trials, future directions and safety considerations

Voretigene neparvovec-rzyl was recently approved for the treatment of Leber congenital amaurosis, and the use of gene therapy for eye disease is attracting even greater interest. The eye has immune privileged status, is easily accessible, requires a reduced dosage of therapy due to its size and is highly compartmentalized, significantly reducing systemic spread. Adeno-associated virus (AAV), with its low pathogenicity, prolonged expression profile and ability to transduce multiple cell types, has become the leading gene therapy vector. Target diseases have moved beyond currently untreatable inherited dystrophies to common, partially treatable acquired conditions such as exudative age-related macular degeneration and glaucoma, but use of the technology in these conditions imposes added obligations for caution in vector design. This review discusses the current status of AAV gene therapy trials in genetic and acquired ocular diseases, and explores new scientific developments, which could help ensure effective and safe use of the therapy in the future.

Current and Emerging Treatment Modalities for Leber's Hereditary Optic Neuropathy: A Review of the Literature

Introduction

The purpose of this review is to present the current and emerging treatment alternatives for Leber’s hereditary optic neuropathy (LHON), emphasizing the most recent use of idebenone and stem cells or gene therapy.

Methods

A comprehensive literature review was performed at the PubMed database regarding the various treatment modalities for LHON.

Results

Treatment modalities for LHON include nutritional supplements, activators of mitochondrial biogenesis, brimonidine, and symptomatic and supportive treatment, but nowadays attention is being paid to idebenone and gene therapy or stem cells.

Conclusion

The treatment of LHON remains challenging, given the nature of the disease and its prognosis.

Leber Hereditary Optic Neuropathy-Light at the End of the Tunnel?

Leber hereditary optic neuropathy (LHON) is an important cause of mitochondrial blindness. The majority of patients harbor one of three mitochondrial DNA (mtDNA) point mutations, m.3460G>A, m.11778G>A, and m.14484T>C, which all affect complex I subunits of the mitochondrial respiratory chain. The loss of retinal ganglion cells in LHON is thought to arise from a combination of impaired mitochondrial oxidative phosphorylation resulting in decreased adenosine triphosphate (ATP) production and increased levels of reactive oxygen species. Treatment options for LHON remain limited, but major advances in mitochondrial neuroprotection, gene therapy, and the prevention of transmission of pathogenic mtDNA mutations will hopefully translate into tangible benefits for patients affected by this condition and their families.

Progress in Gene Therapy to Prevent Retinal Ganglion Cell Loss in Glaucoma and Leber's Hereditary Optic Neuropathy

The eye is at the forefront of the application of gene therapy techniques to medicine. In the United States, a gene therapy treatment for Leber's congenital amaurosis, a rare inherited retinal disease, recently became the first gene therapy to be approved by the FDA for the treatment of disease caused by mutations in a specific gene. Phase III clinical trials of gene therapy for other single-gene defect diseases of the retina and optic nerve are also currently underway. However, for optic nerve diseases not caused by single-gene defects, gene therapy strategies are likely to focus on slowing or preventing neuronal death through the expression of neuroprotective agents. In addition to these strategies, there has also been recent interest in the potential use of precise genome editing techniques to treat ocular disease. This review focuses on recent developments in gene therapy techniques for the treatment of glaucoma and Leber's hereditary optic neuropathy (LHON). We discuss recent successes in clinical trials for the treatment of LHON using gene supplementation therapy, promising neuroprotective strategies that have been employed in animal models of glaucoma and the potential use of genome editing techniques in treating optic nerve disease.