Gene Therapy Uses Synthetic Virus To Cure Deafness

It's only worked on mice so far, but human trials won't be far away. Champion Studio/Shutterstock

Gene-editing is rapidly becoming the solution to some serious problems. Just recently, tinkering around with the genetic architecture of some white blood cells managed to cure two young babies of a deadly form of leukemia.

The latest example of gene-editing doesn’t use the body’s own cells, but something a little more unusual: A synthetic virus. As reported in Nature Biotechnology, it has been used to cure mice of deafness, giving them back near-normal levels of hearing. In follow-up experiments, these mice can now hear noises about the volume of a whisper.

The effectiveness of this treatment suggests that, not in the too distant future, it could be used to give people back their ability to hear the world around them.

The problem with these particular mice was that the very delicate, sound-sensing microscopic hairs inside their ear cavities had been “built” incorrectly. This was because they suffered from Usher syndrome, whereupon the underlying genes had essentially issued corrupted construction blueprints.

content-1486469454-gene-hearing605.jpgThese hairs normally redirect sound throughout the ear canals towards the inner sanctums, where smaller versions of these hairs vibrate back and forth. These vibrations are then converted into electrical signals that the brain can interpret. Without them growing properly in an organized fashion, the mice are rendered deaf – and off-balance.

In order to fix this, the team from Harvard Medical School (HMS), Massachusetts Eye and Ear, and the Boston Children’s Hospital custom-made a virus to go in and fix this genetic defect.

In order to make the procedure safe, and to not cause the mice to fall ill, they chose a modified adeno-associated virus (AAV), an extremely small pathogen that is not known to cause any form of disease, and one which provokes only a minor immune reaction.

The AAV was engineered so that it would specifically infect the region of the ear that included the defective genes. Setting to work, it “injected” its genetic code into the ear cells – a code that contained the correct instructions for manufacturing organized microscopic ear hairs.

Image in text: the AAV, wrapped in protective bubbles made of cell membranes, allowing it to better infect the relevant cells. Cyrille Sage/HMS

“Unlike current approaches in the field, we didn’t change or directly modify the virus,” co-author Casey Maguire, HMS assistant professor of neurology, said in a statement. “Instead, we gave it a vehicle to travel in, making it better capable of navigating the terrain inside the inner ear and accessing previously resistant cells.”

The mice rapidly gained the ability to hear. Six months later, they can still hear whispers – but the team is keen to prove that the effect is long-term, along with the fact that the AAV is safe for infection.

The treatment isn’t the Holy Grail of hearing loss reversal, though. There are hundreds of types of hearing loss, along with a variety of causes.

This gene-editing therapy only affects those with Usher syndrome, and even then, it only works on mice that have just been born – their ears are too developed to be fixed after just 10 days of life.

Still, it’s a remarkable insight into the power of gene-editing. We’ve advanced so far in our scientific endeavors that we are able to cure disabilities that were not long ago debilitating life-sentences, including deafness and blindness, using this and similar techniques.

So although there’s a lot more work to be done, this research certainly sounds like good news to us.

Kirill Kurashov/Shutterstock

[H/T: BBC News]

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