Gene Therapy Successfully Alleviates Blindness
March 30, 2012 § Leave a comment
Scientists from the Perelman School of Medicine at the University of Pennsylvania have found that gene therapy can help improve vision for those with hereditary blindness. The patients had Leber Congenital Amaurosis (LCA), a retinal infection that causes blindness to increase with age. LCA is a group of hereditary retinal diseases in which gene mutation impairs production of an enzyme essential to light receptors in the retina.
The researchers injected patients with a vector, a genetically engineered adeno-associated virus, which carries a normal version of a gene called RPE65, that is mutated in one form of LCA. The team had previously conducted this type of gene therapy in a clinical trial, administering the gene to 12 patients with LCA. They inserted the genes into the worse eye of patients. In the current study, the genes were inserted into the other eye of the same patients.
Both the clinical trial and the current study were sponsored by the Center for Cellular and Molecular Therapeutics (CCMT) at The Children’s Hospital of Philadelphia. They also sponsored the manufacturing of the vector used to carry the corrective gene.
The research team first conducted the experiment on animals. Readministering treatment in the second eye was shown to be safe and effective. These results were encouraging, but researchers were worried that readministering the gene in the untreated eye would generate a vaccine-like immune response, causing inflammation and reducing the initial benefits in the untreated eye. They were afraid the patients’ immune systems would kick in with repeated exposure because the eye is “immune-privileged.” Regardless, tests had to be performed on that specific area in order to anticipate results.
Once the experiment was conducted, the patients’ visions improved. Study co-leader Jean Bennett, M.D. Ph.D., reported in the study’s publication in Science Translational Medicine that, “Patients have told us how their lives changed since receiving gene therapy.” Also, F.M. Kirby, ophthalmology professor at the University of Pennsylvania, said, “They are able to walk around at night, go shopping for groceries and recognize people’s faces – all things they couldn’t do before. At the same time, we were able to objectively measure improvements in light sensitivity, side vision and other visual functions.”
Neuroimaging results support these findings. Brain signals were monitored while patients were exposed to a dimly flickering checkerboard pattern. When the pattern was flashed in front of the patient’s recently treated eye, the brain area responsible for vision lit up during fMRI, evidence that the patient’s brain was responding to the eye’s sensitivity to dim light.
There were no adverse effects and no immune responses. In fact, there was an unanticipated benefit – fMRI results also showed improved brain responses in the first eye. This is most likely due to the fact that after both eyes were treated with the same gene injection, they were better able to coordinate with each other. Bennet also suggests that children subjects may reap more benefit from the therapy because their retinas have not degenerated to the degree to those of adults.
These findings bode well, but before treating retinal disease with gene therapy can be considered safe for humans, the research team suggests further research is required. This would entail follow-up studies, performed over longer periods of time and with additional subjects.
Kreeger, Karen. (2012, February 8). Gene Therapy for Inherited Blindness Succeeds in Patients’ Other Eye. http://neurosciencenews.com/gene-therapy-inherited-blindness-lca/