Has the Next Generation of Gene Therapy Arrived?

Researchers crack the code to deliver dual gene therapy in preclinical studies – with promises of wider applications.

In a gene therapy breakthrough, a Nationwide Children’s Hospital researcher has successfully used an adeno-associated virus (AAV) to introduce two genes into cells with a single vector. Paul Martin, PhD, created a new dual gene vector approach for his research to treat GNE myopathy, a rare form of muscular dystrophy, and forms of limb girdle muscular dystrophy (LGMD). Using AAV, Dr. Martin combined two gene therapies in a coordinated package. Each gene is intended to serve a different function:

1. Stop the disease from progressing.
2. Reverse the existing disease symptoms.

In animal models that received the dual gene therapy, the muscle booster gene built new muscle mass and strength, allowing mice with disease to return to normal walking.

“I was shocked at how not only could we improve walking with these treatments, but we could completely normalize walking. I hadn’t seen that before with single gene therapies unless they were given before disease symptoms had ever occurred,” says Dr. Martin, a principal investigator in the Center for Gene Therapy at the Abigail Wexner Research Institute at Nationwide Children’s.

Building on Single Gene Therapy Results for Muscular Dystrophy

Dr. Martin and his team have been working on single gene therapies for a long time, but they recognize that approach only promises to halt the disease – requiring early intervention. They were motivated to look for approaches that also offer the opportunity for restoration of function. This would help those whose disease has already progressed by the time of diagnosis, such as GNE myopathy and LGMD.

In gene replacement therapy, scientists put a correct gene into a patient instead of a mutated one. Existing gene therapy for muscular dystrophy can be very effective in treating a child early in the disease process but has lower levels of efficacy as the disease progresses. “It’s a good preventative therapy, but it’s not restorative,” says Dr. Martin.

Developing Dual Gene Therapy

Dr. Martin knew they needed to do more for older children and adults whose GNE myopathy or LGMD had already progressed. “What we have learned from studies on other neuromuscular disorders is that if you treat a child early in the disease process, you can have a profound effect on whether their disease progresses, but if you treat a child after the disease is already severe, these preventative therapies may not work very well, if at all,” says Dr. Martin.

The results were foundational to Dr. Martin’s work moving forward. “We needed a new approach to gene therapy for these degenerative muscle diseases –– one that would have a second component that would be regenerative and not just a gene replacement that just stops the disease at the point it already is,” he says.

Dr. Martin and his team tested existing muscle-building therapies to serve as a restorative gene. The mutated genes in GNE myopathy and LGMD cause muscle damage, leading to reduced amounts of muscle tissue and causing weakness. By stimulating muscle growth, the researchers could double or even quadruple the size and strength of muscles. Combining the restorative gene with the therapeutic gene could potentially reverse the effects of GNE myopathy and LGMD.

After years of testing the technology, Dr. Martin and his team discovered how to engineer both genes into a single AAV vector. AAV is the gene therapy delivery tool that allows researchers to deliver genes to cells using a viral protein. It has a packaging limit of 4.7 kilobases of DNA, which was enough for the target genes Dr. Martin tested. “As you get to bigger genes, what you can do becomes more limited and then eventually becomes impossible, but the genes for GNE myopathy and many LGMDs are small enough to use this approach,” he says.

Combining the two genes, each driven by a separate promoter, allowed the researchers to amplify the gene expression for both genes tenfold. This led to a more potent therapy. “It isn’t just that we’re doing two things at once. We’re actually engineering them so that they work better than they would have worked if just given on their own,” says Dr. Martin.

Making the Research Translational

Dr. Martin partnered with Gidon Akler, MD, FACMG, to launch Genosera, a new startup with the goal of developing and bringing to market next-generation gene therapies. Dr. Akler is a pediatrician and geneticist who specializes in gene mutations that disproportionately affect the Iranian Jewish community.

There is no existing treatment for GNE myopathy. Finding one is personal for Dr. Akler, who is of Iranian Jewish descent. “I have plenty of friends who have a family member affected by this devastating disease,” he says.

GNE myopathy has a late onset in the 20s and 30s, starting with a foot drop and progressing to upper body weakness. “I have patients and friends who are wheelchair-bound, so it’s very debilitating,” says Dr. Akler.

While the diseases Dr. Martin and Dr. Akler study are rare, their prevalence in the Persian Jewish community is high. As many as one in eight Iranian Jews have the gene mutation for GNE myopathy. “We met with groups of families to share our findings, and this was a very emotional meeting. We’re giving people renewed hope,” says Dr. Akler.

Broader Applications for Dual Gene Therapy

Dr. Martin and Dr. Akler are also studying the applications of dual gene therapy on limb-girdle muscular dystrophy type R9 (LGMDR9) and single gene therapy for lysosomal acid lipase deficiency (LALD), also known as Wolman’s disease. Using the therapy to treat Wolman’s disease may have wider applications for the treatment of fatty liver disease or non-alcoholic steatohepatitis (NASH).

The researchers hope their progress in GNE myopathy and LGMD can be applied to 23 other forms of muscular dystrophy. “We have plenty of proof-of-concept data to suggest this should be successful both in early and in severe disease for multiple disease forms,” says Dr. Martin.

Dual gene therapy also has broader neuromuscular applications for the general population, such as regenerating muscle for seniors suffering from sarcopenia – natural muscle loss that comes with aging. Most people lose a quarter to a third of their muscle mass in their 80s and 90s, increasing the risk of falls and bone fractures.

Combining two genes in one viral vector opens the doors to other dual gene therapy research. “This is the start of the second generation of gene therapy, which is trying to do more than one thing at a time. My hope is this will lead to third, fourth and even fifth generations where additional goals are added on so that many more diseases aren’t just manageable but curable,” says Dr. Martin.

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