The Current Status of the Use of Gene Therapy in Ophthalmology

Four retinal diseases could see genetic therapies sooner rather than later.

IRV ARONS

With the first approval of a gene therapy for treating a genetic disorder in the Western world, the future of gene therapy for treating ocular disorders looks bright. Glybera (alipogene tiparvovec), developed by the Dutch company UniQure, to treat a rare lipoprotein lipase deficiency (LPLD), was approved by the European Medicines Agency last November.¹

Glybera is the first gene therapy treatment approved in Europe, but the fourth worldwide. We have seen two previous approvals in China in the field of oncology, and one approval in Russia for peripheral arterial disease. The most recent approval provides a good time to discuss the status of gene therapy for ocular disorders.

I first learned about gene therapy in November 2010, when I was introduced to a company called RetroSense and its research using gene therapy for the treatment of retinitis pigmentosa and dry AMD. ² Since that first write-up, I have been closely following developments in this exciting field.

So what is gene therapy? How does it work? What are the applications in ophthalmology? Who is involved? What is the current status of the many clinical trials now under way? What does the future hold? Here, I’ll provide answers.

WHAT IS GENE THERAPY AND HOW DOES IT WORK?

Gene therapy is the addition of new genes to a patient’s cells to replace missing or defective copies, to restore or impart a new function to overcome a disease — usually of genetic origin. Researchers typically deliver new genes to cells using modified virus vectors, as viruses have evolved as preferred vectors to deliver genetic materials to cells.

Two decades of experimentation and trials have been undertaken, some of which were hallmarked by catastrophic results. In 1999, for instance, one patient suffering from a metabolic disease died in a gene therapy clinical trial, and regulatory agencies have been cautious since. Now, however, gene therapy is emerging as a viable means of treating ocular diseases.

With regard to ocular gene therapy, Abelson et al. noted:

When other areas of the body receive gene therapy, rejection of viral capsids carrying the payload is a concern. The eye however, experiences reduced chances of vector rejection, just as foreign tissue in the eye experiences extended, if not indefinite survival, where it would be rapidly rejected in other parts of the body.

The eye is also relatively easy to monitor, both for potential side effects and for treatment benefit, with methods such as electroretinography, visual acuity, optical coherence tomography, and perimetry. Ophthalmoscopy and fundus photography also provide an easy way to directly visualize and document therapeutic effects.

Over the past several years, the unlocking of the human genome and the discovery that certain genes, or lack thereof or genetic defects therein, can be the cause of certain diseases has led to the ability to identify genes associated with retinal and other ocular diseases. According to the eyeGene National Ophthalmic Disease Genotyping Network, more than 100 ocular gene types have been identified, and the number increases yearly.⁴

In gene therapy, the companies and research institutions doing the work use a virus that has been stripped of its ability to replicate as the delivery mechanism for the gene of interest. The nonpathogenic virus vector of choice for many applications is a recombinant adeno-associated viral vector (rAAV). The identified gene for the particular disease is loaded onto the virus, and this combination is then delivered to the diseased tissue of interest.

To date, the genes for some 35 ocular disorders have been identified,⁵ and a few of these diseases will be discussed below. (Another source, RetNet,⁵ the Retinal Information Network, lists many more genes that have been mapped and identified, specifically for retinal diseases.)

APPLICATIONS IN OPHTHALMOLOGY AND STATUS OF CLINICAL TRIALS

Table 1 (available online at www.retinalphysician.com) lists the companies and university research centers that I have identified as active in this field. The table also shows the virus vector delivery system and the gene therapy products being utilized, the partners involved, and the specific ophthalmic indications targeted.

In Table 2 (online), I list 17 ophthalmic diseases that are currently either in clinical trials or in preclinical research. Table 3 (online) lists the 16 ongoing and completed clinical trials identified, including the clinical sites and the numbers of patients treated to date. A live link to the clinical trial is included for further access to information about each clinical trial.

The four ocular diseases that have received the most attention are Leber’s congenital amaurosis (LCA), wet AMD, Stargardt disease, and Usher syndrome.

Leber’s Congenital Amaurosis

Leber’s congenital amaurosis is a rare, inherited retinal degenerative disease characterized by severe loss of vision at birth or during the first decade of life. A variety of other eye-related abnormalities, nystagmus, deep-set eyes, and sensitivity to bright light, also occur with this disease. Some patients with LCA also experience central nervous system abnormalities.

In treating LCA, the majority of the work has been focused on RPE65, the RPE-specific 65-kDA protein that is involved in the conversion of all-trans retinol to 11-cis retinal during phototransduction and that has been implicated as a genetic defect in LCA. When loaded onto the AAV2 virus, the product becomes AAV2-RPE65.

One of the leading groups in research into the treatment for LCA has consisted of Jean Bennett, MD, and Albert Maguire, MD, with their ground-breaking work done at the University of Pennsylvania and Children’s Hospital in Philadelphia. Once the gene responsible for Leber’s was identified in the late 1990s, Drs. Bennett and Maguire, who initially worked on this project with Drs. Sam Jacobson, Gus Aguirre, Bill Hauswirth, and Eric Pierce, initiated in 2007 one of the first clinical trials for a retinal degeneration.⁶

Since then, they have undertaken two additional clinical trials and have successfully treated more than a dozen children with Leber’s, with most showing improved vision. They have now treated at least four of these children in their second eye.

A new study, from the Scheie Eye Institute at the University of Pennsylvania,⁷ indicated that although continuing signs of vision improvement in clinical trials were shown following gene therapy treatment, advancing degeneration of affected retinal cells was also seen, both in LCA patients and animal models of the same condition.

“We all hoped that the gene injections cured both components — re-establishing the cycle of vision and also preventing further loss of cells to the second disease component,” said Artur V. Cideciyan, PhD, coinvestigator of the LCA clinical trial at Penn.

However, when the otherwise invisible cell layers of the retina were measured by optical imaging in clinical trial participants serially over many years, the rate of cell loss was the same in treated and untreated regions. In other words, gene therapy improved vision but did not slow or halt the progression of cell loss,” commented Cideciyan.

“These unexpected observations should help to advance the current treatment by making it better and longer lasting,” said Samuel G. Jacobson, MD, PhD, principal investigator of the clinical trial. “Slowing cell loss in different retinal degenerations has been a major research direction long before the current gene therapy trials. Now, the two directions must converge to ensure the longevity of the beneficial visual effects in this form of LCA.”

Other institutions involved in studying Leber’s include Hadassah Medical (Israel), University College London, and the University of Pennsylvania, with support from the NEI, the University of Nantes in France, and Applied Genetic Technologies Corporation (AGTC).

Wet AMD

Another major area of emphasis in gene therapy is treatment of wet AMD. Although anti-VEGF drugs are currently successfully treating wet AMD, the cost and time involved in monthly or semimonthly injections can be troublesome. A one-time treatment — the promise of gene therapy (the “forever fix”⁸) — is attractive.

Several companies are at the forefront of research into the use of gene therapy for wet AMD. These include Genzyme; Avalanche Biotechnologies, working with the Lions Eye Institute of Perth, Australia; and Oxford BioMedica, in partnership with Sanofi.

In wet AMD, VEGF plays a critical role because blockade of VEGF is sufficient to suppress the development of choroidal neovascularization. A variety of antiangiogenic proteins oppose the actions of proangiogenic factors, such as VEGF. Gene transfer to augment expression of these endogenous inhibitors or related engineered proteins is a potential alternative to suppress CNV and avoid frequent intraocular injections. Considerable preclinical and emerging clinical data suggest this approach may be feasible.

The secreted extracellular domain of VEGF receptor-1, sFlt-1, is a naturally occurring protein antagonist of VEGF formed by alternative splicing of the pre-mRNA for the full-length receptor. Intraocular injection of Ad.sFlt-1 strongly suppressed retinal or subretinal neovascularization in mice

Genzyme has developed a VEGF-binding protein that consists of domain 2 of Flt-1 linked to a human immunoglobulin G1 (IgG) heavy chain Fc fragment (sFLT01). Intravitreous injection of AAV2.sFLT01 is being evaluated in a phase 1/2 clinical trial of wet AMD.⁹

At least 17 patients have been treated to date with safety demonstrated, but no visual improvement results have been reported, in keeping with normal clinical trial protocol.

Stargardt Disease

The progressive vision loss associated with Stargardt disease usually starts between the ages of 6 and 12 years plateaus shortly afterward, with rapid reduction in visual acuity.

The gene identified in the treatment of Stargardt disease is ABCA4. This gene produces a protein involved in energy transport to and from photoreceptor cells in the retina. Mutations in the ABCA4 gene produce a dysfunctional protein that cannot perform its transport function. As a result, photoreceptor cells degenerate and vision loss occurs.

Stargardt is being studied by Oxford BioMedica and Sanofi. They have an ongoing phase 1/2a clinical trial under way, in both the United States at the Casey Eye Institute in Seattle and at the Centre Hospitalier Nationale d’Ophthalmologie des Quinz-Vingts in Paris. To date, 12 patients have been treated in cohorts 1 and 2, with cohort 3 under way at dose level 2.

Safety has been demonstrated for up to 12 months, but as is normal procedure in clinical trials, no vision improvement results have yet been reported.

Usher Syndrome 1b

Usher syndrome is a rare inherited condition characterized by both hearing impairment and progressive vision loss and is a leading cause of deaf-blindness. The vision loss is due to retinitis pigmentosa. Balance may also be affected. Symptoms vary from person to person and progress at different rates.

Three forms of Usher syndrome have been identified. Patients with type 1 have severe hearing loss and experience problems with balance, along with RP. Those newborns with type 2 have moderate to severe hearing impairment and symptoms of RP typically start shortly after adolescence. Visual problems progress less rapidly than in Usher type 1, and hearing loss usually remains stable.

Children with type 3, a rarer type, are usually born with good or only mild hearing impairment. Their hearing and vision loss is progressive, starting around puberty. Balance may also be affected.

One of the genes being studied for Usher Syndrome is MY07A, the basis of UshStat in clinical trials by Oxford BioMedica and Sanofi. Their phase 1/2a clinical trial has treated the first cohort of three patients and has received approval to proceed to cohort 2 at dose level 2. This trial is also being conducted at the two locations noted above for Stargardt — Casey Eye and the Centre Hospitalier Nationale. Again, per protocol, no results have yet been released.

In all, as shown in Table 3 (online), more than 80 patients have received ocular gene therapy treatment, and the initial results that have been reported (mostly for LCA) have shown some improvements in vision, along with the safety of the treatment.

REMAINING QUESTIONS

To date, gene therapy in ophthalmology looks promising, in the sense that some vision capacity has been restored, but several questions remain. Will gene therapy deliver the holy grail of the forever fix or something less? And with the first Western approval of a gene therapy treatment (Glybera for LPLD), will ophthalmic therapies be next?

The question of cost also persists. One treatment of Glybera — granted, to treat a very rare disease with a worldwide population of only several hundred — may cost as much as $1.6 million.¹⁰ Nobody expects that any of the proposed ophthalmic treatments will cost that much, as most of the relevant disorders to be treated have populations several orders of magnitude larger than the very rare disease treated by Glybera, although certainly some rarer ocular disorders affect only a few hundred to a few thousand individuals worldwide.

CONCLUSION

In 2012, officials with the Office of Cellular, Tissue and Gene Therapies (OCTGT), Center for Biologics Evaluation and Research of the FDA, stated , “The recent history of gene therapy has been a mixture of promise and disappointment … Despite the setbacks of the past, the OCTGT shares the enthusiasm of the field and is confident that ongoing clinical investigations will lead to commercially available gene therapy products that are safe and effective and advance the public health.”¹¹ RP

REFERENCES

1. Arons I. Gene therapy in ophthalmology update 15: First gene therapy treatment. Irv Arons J. 2012 Nov 6. Available at: http://tinyurl.com/GeneTherapy15. Accessed March 1, 2013.

2. Arons I. The use of gene therapy in treating retinitis pigmentosa and dry AMD. Irv Arons J. 2012 Nov 6. Available at: http://tinyurl.com/GeneTherapy-RP-AMD. Accessed March 1, 2013.

3. Abelson MB, Tzekov RT, Howe A. Gene therapy turns foes into friends. Rev Ophthalmol. 2009 Aug 13. Available at: http://www.revophth.com/content/d/therapeutic_topics/i/1213/c/22855. Accessed March 1, 2013.

4. National Eye Institute. eyeGENE® - National Ophthalmic Disease Genotyping Network: Genes and diseases. Available at: http://www.nei.nih.gov/resources/eyegene/tableforgenes.asp. Accessed March 1, 2013.

5. RetNet. Summaries of genes and loci causing retinal diseases. Available at: https://sph.uth.edu/retnet/sum-dis.htm. Accessed March 1, 2013.

6. Bennett J, Maguire AM. The evolution of retinal gene therapy: from DNA to FDA. Retin Today. 2011 October:55-58.

7. Penn Medicine. Penn study sheds light on the complexity of gene therapy for congenital blindness. Available at: http://www.uphs.upenn.edu/news/News_Releases/2013/01/blindness/. Accessed March 1, 2013.

8. Lewis R. The Forever Fix: Gene Therapy and the Boy Who Saved It. New York, NY; St. Martin’s Press; 2012.

9. Campochiaro PA. Gene transfer for neovascular age-related macular degeneration. Hum Gene Ther. 2011;22:523-529.

10. Whalen J. Gene-therapy approval marks major milestone. Wall St J. 2012 Nov 2. Available at: http://online.wsj.com/article/SB10001424052970203707604578095091940871524.html?KEYWORDS=glybera. Accessed March 1, 2013.

11. Takefman D, Bryan W. The state of gene therapies: the FDA perspective. Mol Ther. 2012;20:877-878.

Table 1. Gene Therapy Companies/Institutions Active in Ophthalmology

Irv Arons August 2012 (Version 13, Aug 9, 2012)

NCT - National Clinical Trial (ClinicalTrials.gov)

Table 2. Gene Therapy in Ophthalmology by Application

Irv Arons May 2012 (Version 4, 5/10/12)

Table 3. Gene Therapy in Ophthalmology - Ongoing Clinical Trial Details

Irv Arons November 2012 (Version 5, November 20, 2012)

NYR - Not yet recruiting
R - Recruiting

1. Reported at ARVO 2012