Vision improves in both eyes when gene therapy is administered to only one eye, an international team of researchers has found, whilst treating a rare form of blindness.
The team injected a harmless virus containing the gene into the back of one eye of 37 patients who had vision loss for six to 12 months from a condition called Leber hereditary optic neuropathy (LHON). Nearly two years after treatment, 29 of them had at least some vision improvements in both eyes. Of these, 25 had clinically relevant improvement in their treated eye.
'We expected vision to improve in the eyes treated with the gene therapy vector only. Rather unexpectedly, both eyes improved for 78 percent of patients in the trial following the same trajectory over two years of follow-up,' said lead author Dr Patrick Yu-Wai-Man at the University of Cambridge.
LHON usually affects young men and leads to vision loss. Although there is a lack of effective therapies, it is known to be caused by a mutation in one of the genes inside mitochondria that affects cells of the retina. These cells take up the gene when it is injected into the eye and can then start producing the protein needed to preserve the rest of their retina.
To further investigate why vision improved in both eyes, the team used the gene therapy in three macaque monkeys. After three months, they examined their visual system, which is similar to that of humans, and found all three monkeys had the virus in both their eyes. The virus was also seen in their optic nerves, suggesting that the virus used the optic nerves to travel between the treated and untreated eye.
According to the New Scientist, the discovery has safety implications and raises questions on its effectiveness. Normally, in similar clinical trials, vision would be compared between the treated and untreated eye – something that wasn't possible in this case. Dr Yu-Wai-Man said that future trials may need to compare people given the gene therapy to others who receive a placebo.
Professor Michel Michaelides, an ophthalmologist at University College London and Moorfields Eye Hospital, called the news 'fascinating', telling New Scientist: 'It's an important finding that should be taken into account when designing studies'.
Nevertheless, senior investigator Professor José-Alain Sahel from the University of Pittsburgh is feeling hopeful for these patients who have limited treatment options. He said: 'These patients rapidly lose vision in the course of a few weeks to a couple of months. Our study provides a big hope for treating this blinding disease in young adults.'
The study was published in the journal Science Translational Medicine.