An international research team, funded in part by the Foundation Fighting Blindness, has used gene therapy to reactivate retinal cells that were previously unresponsive to light. The treatment was delivered to cones, the retinal cells that provide central and daytime vision. Investigators evaluated the gene therapy in two mouse models of retinal degenerative disease, as well as cultures of human retinal tissue. Using a variety of tests, the researchers demonstrated that the treated cells restored functional vision, and that the restoration of vision persisted over a long period of time.
In retinal degenerative diseases such as retinitis pigmentosa, cones stop providing vision before they die and can remain in a compromised state for several years. The gene therapy used to restore vision in the cone-reactivation study leads to the production of a light-sensitive protein called halorhodopsin, which is similar to vision-activating proteins occurring naturally in the retina. The presence of halorhodopsin appears to reactivate the visual cycle, the biochemical process in retinal cells that lead to vision.
An adeno-associated virus (AAV), a therapeutic virus, was used to deliver the treatment to the cones. AAVs are the same delivery mechanism used in landmark gene therapy clinical trials that have restored vision in 28 children and young adults who were virtually blind from Leber congenital amaurosis.
Dr. José-Alain Sahel, one of the cone-reactivation study investigators and director of the Foundation-funded Paris Research Center for the Study of Retina Degenerative Diseases, says that through high-resolution imaging, his team has identified people who may be good candidates for a future clinical trial. He adds that even people who are legally blind might have some cones reactivated and vision restored.
Dr. Sahel also notes that the cone-reactivation treatment has the potential to be even more beneficial if coupled with a therapy that helps protect cones from degeneration. Dr. Sahel and his team are planning a clinical trial of a neuroprotective treatment called rod-derived cone viability factor, or RdCVF, which has shown excellent results for preserving cones in preclinical studies.
The cone-reactivation study was led by Dr. Botond Roska of the Friedrich Miescher Institute for Biomedical Research in Switzerland, and included scientists from several European research institutions. Results of the study were published in the June 24 issue of the journal Science (online edition).