I was very excited to learn here at ARVO that two early-stage gene therapy clinical trials – one for choroideremia taking place in the U.K., the other for autosomal recessive retinitis pigmentosa (arRP) caused by MERTK mutations underway in Saudi Arabia – are proceeding well thus far. It is important to keep in mind that safety is the primary focus in these Phase I studies.
Dr. Emad Abboud, from the King Khaled Eye Specialist Hospital in Riyadh, reported that three patients, all in their thirties, have been treated with the MERTK gene therapy. The treatment uses an adeno-associated virus 2 (AAV2) – similar to the AAV2 used in landmark vision-restoring gene therapy clinical trials for Leber congenital amaurosis – to deliver copies of the therapeutic gene to retinal pigment epithelial cells in the retina.
Thus far, the MERTK treatment has been safe in all three patients. The two patients who received the treatment in 2011 have reported that they are seeing better with their treated eye and can read more lines on an eye chart than they could before the treatment. One woman said, “I see with the operated eye many things in the kitchen that I couldn’t see before.” The third patient, treated in April 2012, has not had his vision tested since receiving the therapy.
This study is being performed in collaboration with Dr. Kang Zhang at the University of California, San Diego.
Dr. Robert MacLaren, who is conducting the choroideremia gene therapy clinical trial at Moorfields Eye Hospital in London and Oxford Eye Hospital in Oxford, said that six people have been treated thus far with no adverse effects. This therapy also uses an AAV2 to get copies of the healthy gene into the retinal cells.
Dr. MacLaren notes that all six patients entered the trial with relatively good vision, and the goal is to demonstrate that the treatment prevents vision loss. He estimates that it will take at least two years to determine if the patients’ treated retinas have less degeneration, and better vision, than their untreated retinas.
We need to keep in mind that these are very early results for just a handful of patients. Cautious optimism is in order. Not every treatment that enters a clinical trial will be a home run. But the progress is exciting, and we couldn’t have a better group of researchers on the front lines working to get these treatments out to the people who need them.
By the way, the Foundation funded critical lab studies that made both the choroideremia and MERTK gene therapy clinical trials possible.