A gene therapy treatment in monkeys may pave the way to curing the blind. Treating blindness has always been an appealing target for gene therapy due to the eye being one of the few sites in the body endowed with the ability to tolerate foreign substances without eliciting an inflammatory immune response.
Although gene therapy has been used to partially restore sight in people who are blind from defects in the pigmented layer of the eye, providing the same treatment for those who are blind through loss of photoreceptor cells – the cells that respond to light – has proven a greater challenge.
To find out whether it would be possible to deliver genes that would eventually restore photoreceptor cells, Luk Vandenberghe at the University of Pennsylvania in Philadelphia, and colleagues used two adeno-associated viruses, called AAV2 and AAV8, to deliver genes into monkey retinas.
The viruses were marked with a green fluorescent protein, visible here in the photos of the monkey retinas after injection. By monitoring the green markers, the researchers were able to assess the minimum dose at which the viruses could deliver working genes into the retinal cells. A dose of AAV8 performed best, presenting an important step in using gene therapy to treat and restore photoreceptor cells in humans.