The work targets a leading delivery method for the therapies, adeno-associated virus (AAV), and recently was published in the journal by UofL’s Maureen A. McCall and her colleagues from Harvard University and its Wyss Institute.

AAV is used in treating a number of conditions, including the retinal diseases McCall studies at UofL. However, it also has been known to cause serious side effects, such as elevated immune response and inflammation.

“It’s a real problem since there’s no real control,” said McCall, the Kentucky Lions Eye Research Endowed Chair and a professor in the Departments of Ophthalmology and Visual Sciences and Anatomical Sciences and Neurobiology. “Even with the best-laid plans, you see some inflammatory retinal response, and the amount can vary widely, including dangerous levels.”

The new research focuses on the role of the viral capsid, a component in AAV that’s believed to cause this response. Parts of the viral capsid interact with a protein known as Toll-like receptor 9 (TLR9), which senses foreign DNA in the body. TLR9 triggers the immune response, which causes inflammation and can reduce or eliminate the therapy’s effects.

“So, the hypothesis was that if you could change that capsid code and mask it from the Toll-like receptor, that you could build a better delivery tool,” McCall said.

The idea is to “cloak” the deleterious part of the capsid with a series of synthetic DNA “inflammation-inhibiting oligonucleotide” sequences meant to stop TLR9’s reaction. In mouse models, the researchers saw a 95% reduction in inflammation.

In many cases, gene therapies for optical diseases are delivered through the retina since the blood-retina barrier helps to mitigate some of the immune response. Ying Kai Chan, a former postdoctoral fellow in George Church’s group at the Wyss Institute, reached out to McCall in 2018 to partner on this work because of her research expertise and the experience of her UofL colleagues with these injections, especially Wei Wang, assistant professor of ophthalmology.

McCall’s work at UofL specifically focuses on the use of gene therapies to treat retinal diseases, including retinitis pigmentosa and other conditions that eventually can cause blindness. For some of these conditions, there is no known cure and many therapies are still in development and clinical trials. McCall said eliminating side effects associated with AAV delivery gets researchers one step closer to successful treatment.

“Solving this key problem with delivery is huge,” she said. “These therapies show promise in significantly increasing people’s quality of life. My hope is that one day we can use these therapies to slow – or even stop – the progression of these diseases and restore sight.”

In mice models with genetic mutations similar to humans with night blindness, scientists used adeno-associated viruses to reintroduce the protein into cells in the retina, the specialized tissue at the back of the eye that detects light and triggers impulses through the optic nerve to the brain, where a visual image is formed.

The research, led by scientists at the University of Louisville with collaborators from the Medical College of Wisconsin, recently was published by . Grants from the National Institutes of Health, Research to Prevent Blindness and the Foundation Fighting Blindness funded the research.

“Individual genes that everybody expresses are critical to making sure vision works correctly, and in their absence, some people will have night blindness,” said Ron Gregg, PhD, professor and chair of the Department of Biochemistry and Molecular Genetics at the UofL School of Medicine. “Our research shows that if you replace the missing protein using a gene therapy approach, you can restore visual function.”

Humans are adept at seeing in low light, but genetic mutations can disrupt that function, causing total night blindness. 

Proteins located on the surface of photoreceptors, which are cells in the retina that detect light, ensure that visual signals pass from the two types of photoreceptors – cones and rods – to retinal bipolar cells. This is a crucial step in the transmission of visual information from the eyes to the brain. Genetic mutations disrupt the signal transfer between photoreceptors and retinal bipolar cells, impairing vision.

People with congenital stationary night blindness also have other vision problems, including severe myopia, involuntary eye movements and eyes that do not look in the same direction. These secondary affects are more debilitating than night blindness itself, Gregg said.

The next phase of research requires testing on a large animal model with eyes similar to humans.