For Sharif Tabebordbar, finding a gene therapy for genetic muscle wasting diseases was personal. When he was a teenager, his father was diagnosed with a rare genetic muscle disease that eventually left him unable to walk.
In an interview with the Broad Institute at MIT he said: “I watched my dad get worse and worse each day. It was a huge challenge to do things together as a family – genetic disease is a burden on not only patients but families. I thought: This is very unfair to patients and there’s got to be a way to fix this. That’s been my motivation during the 10 years that I’ve been working in the field of gene therapy.”
That commitment now seems to be paying off. In a study published in the journal Cell, Tabebordar and his team at MIT and Harvard showed how they have developed a new, safer and easier way to deliver genes to help repair wasting muscles.
In earlier treatments targeting genetic muscle diseases, researchers used a virus to help deliver the gene that would correct the problem. However, to be effective they had to use high doses of the gene-carrying virus to ensure it reached as many muscles throughout the body as possible. But this meant that more of the payload often ended up in the liver and that led to severe side effects in some patients, even a few deaths.
The usual delivery method of these gene-correcting therapies is something called an adeno-associated virus (AAV), so Dr. Tabebordar set out to develop a new kind of AAV, one that would be safer for patients and more effective at tackling the muscle wasting.
They started by taking an adeno-associated virus called AAV9 and then set out about tweaking its capsid – that’s the outer shell that helps protect the virus and allows it to attach to another cell and penetrate it to deliver the corrected gene. They called this new viral vector MyoAAV and in tests it quickly showed it had an enhanced ability to deliver genes into cells.
The team showed that it not only was around 10 times more efficient at reaching muscle than other AAVs, but that it also reduces the amount that reaches the liver. This meant that MyoAAV could achieve impressive results in doses up to 250 times lower than those previously used.
In animal studies MyoAAV showed encouraging results in diseases like Duchenne Muscular Dystrophy and X-linked myotubular myopathy. Dr. Amy Wagers, a co-senior author of the study, says they are hopeful it will be equally effective in people.
“All of these results demonstrate the broad applicability of the MyoAAV vectors for delivery to muscle. These vectors work in different disease models and across different ages, strains and species, which demonstrates the robustness of this family of AAVs. We have an enormous amount of information about this class of vectors from which the field can launch many exciting new studies.”