A virus has been harnessed to turn the eye into a drug factory to treat a major cause of vision loss: age-related macular degeneration (AMD).
Scientists used a harmless virus to deliver the gene to the eye, where it directs it to produce and supply a substance that preserves vision.
And this breakthrough could lead to new treatments that are less troublesome than AMD. This condition occurs when the macula, the part of the retina at the back of the eye involved in acute central vision, is damaged.
People with this condition lose their central vision - they can see a clock but can't tell the time, for example, and lose the ability to recognize people's faces. It's usually diagnosed by a routine eye exam, and the first signs often appear in people in their 50s and 60s. The cause is unknown, although it is linked to smoking, high blood pressure, obesity and a family history of the condition.
There are two types of AMD: dry and wet. Dehydration is the most common form - the result of a buildup of an oily substance called drusen at the back of the eye. The wet type is caused by vascular endothelial growth factor (VEGF), a compound that stimulates the growth of new blood vessels needed for healing, such as after an injury.
Wet AMD causes abnormal blood vessels to grow under the retina.
While dry AMD usually develops slowly, over many years in some cases, the wet form can start and get worse within weeks, even days.
And there are ways to deal with wet AMD — prompt treatment is vital to prevent further damage — but they can be stressful.
Medications including aflibercept, a protein that blocks the action of VEGF, must be injected into the eye for life. This should be done frequently, once a month.
These treatments can be painful and cause bruising around the eyes (including rare complications such as cataracts and infection). And nearly half of patients stop treatment within two years, according to a 2021 review in the Journal of Ophthalmology.
The new treatment, known as ADVM-022, involves only one injection, possibly every three years.
Developed by the US-based company Adverum, it is a form of gene therapy. It involves injecting a virus containing the genetic code for making aflibercept into the eye. The virus acts as a means of transferring genes to the eye.
The genetic code then directs the cells in the eye to make the protein, which allows the eye to repair itself.
Data from an ongoing US trial, reported at the annual conference of the American Academy of Ophthalmology, showed a 93% reduction in harmful fluid levels in the eye after injection.
Another trial involving 36 patients in 14 hospitals in the United States is looking at the treatment of a different eye condition, diabetic macular edema caused by fluid buildup in the macula, the most common cause of vision loss in people with diabetic retinopathy.
Commenting on the treatment, Gwen Williams, consultant ophthalmologist at Singleton Hospital in Swansea, said: "Wet AMD is a huge public health problem. Gene therapy-based therapies like this are exciting and are at the forefront of scientific understanding. It will be interesting to see the results of the trial."