Early Trials of Gene Therapies for Eye Disease Appear Safe

January 7, 2012 - Gene therapies are a promising approach to treating retinal eye diseases. The first clinical trial of a gene therapy for one type of Leber congenital amaurosis began in 2007; since then more than 30 people have been treated, all with some degree of benefit and without significant side-effects or apparent risk.

This success has prompted a growing interest in gene therapy trials.

Oxford BioMedica is one company working to develop gene therapies for retinal degenerative disease. The company currently has three treatments in early stage human clinical trials:

  • RetinoStat® for wet age-related macular degeneration
  • StarGen™ for Stargardt disease
  • UshStat® for Usher disease type 1B (caused by a mutation in the MY07A gene)

Many readers have been curious about what is happening in these trials, all launched in the past two years.

In each case, the company uses its own specially engineered form of a lentivirus to introduce new genes into the retina of people with retinal disease. Lentivirus is advantageous because of its high efficiency for introducing replacement genes into non-dividing cells, long-term stable expression of the introduced gene, and low tendency to cause an immune response. In the case of the Usher and Stargardt disease trials, this new gene would replace the missing functions of an existing gene that has been damaged by mutation. In the wet AMD trial, the new gene would produce proteins that stop abnormal blood vessel growth from occurring – emulating the actions of wet AMD drugs, without requiring repeated injections of drugs into the eye.

Only small numbers of people have been treated with each of these therapies so far. Nine people in the RetinoStat trial and eight people in the StarGen trial have been monitored for more than a year. In the UshStat trial, three people have now been treated for more than six months. In all cases, there have been no serious adverse reactions to these treatments and no significant inflammation in the treated eye. In the wet AMD trial, it has also been reported that the genes transferred into retinal cells continue to produce new proteins for more than a year.

“Everyone wants to know if these therapies are working, but we don’t yet know this. In these early trials, the purpose is to show that people can receive the treatment without ill effect, and so far, this seems to be the case,” says Dr. Bill Stell, FFB Director of Research Programs. He adds that these particular studies are also trying to find out what is the best dosage.

Each subsequent small group of patients has received a slightly higher dose of the treatment, while scientists watch closely for any signs of complications. “It is important for scientists to know how much they can increase the dose without triggering the immune system or causing other complications.”

Compelling results about treatment outcomes will take time. Stargardt disease and Usher disease both cause vision loss slowly, so it may take an extended period of time to demonstrate whether or not these therapies can protect vision. While the early signs from these trials are hopeful, only larger, longer trials will produce the evidence on which widespread, safe and effective therapies can be based.

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