Around 1 in 4000 people suffer from retinitis pigmentosa—a disease in which the retina degenerates, eventually leading to blindness. There is no cure for it, but a collaborative study out of Oxford found that gene therapy might hold the key.
Gene therapy involves modifying a genome to treat a disease—usually by having a virus deliver a gene to the cells where it’s needed. Once the gene is inserted, the cells are able to build the molecule the gene encodes.
For this study, the scientists injected mice with modified viruses. Like humans, mice have eyes containing rods (black and white and night vision cells) and cones (color vision cells), but the mice studied here were special: their cone cells were modified to glow fluorescent green so they could be easily counted.
The retinitis pigmentosa-model mice were at the stage of the disease where their rods were beginning to degenerate, leaving their cones yet untouched. For each mouse, one eye was treated with saline as a control, while the other was injected with a virus carrying a gene to produce human ciliary neurotrophic factor (CNTF)—a protein previously shown to prevent the loss of retinal cells.
CNTF is problematic, however—it’s toxic in certain doses. However, since the scientists had modified the cone cells to glow, they were able to see if the CNTF dose was actually killing cells by counting the cones at various stages. If cone cells began to die, they lowered the dose. Thus, they were able to directly control the gene therapy dose while minimizing toxic effects.
After 24 weeks, cones were preserved in mice with high-dose eyes, while those with low-dose or saline had completely lost all of their cones. The researchers gave the high-dose mice behavioral tests and measured brain blood flow, and confirmed their cones were still functional.
“Our results in this mouse model of retinitis pigmentosa clearly show that CNTF treatment can both give life-long protection to cone photoreceptors and preserve useful vision. While there remains a lot to understand, for example on the role of rods in cone preservation and translation to human retinal anatomy, this is a very promising study,” said author Robert MacLaren, professor at the University of Oxford’s Nuffield Laboratory of Ophthalmology.
“We already know from clinical trials aimed at preventing motor neuron loss in ALS that high-dose systemic treatment with CNTF causes too many adverse reactions to be tolerated by patients. However, our results suggest that directly increasing activity in the class of genes that were upregulated in our high-dose CNTF group has the potential to provide a novel, targeted treatment for retinitis pigmentosa and a range of neurodegenerative diseases.”
(Image credit: University of Oxford)
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