Viral vector from duck may enable gene therapy redosing in Pompe
Work already underway to move technology toward potential clinical use
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A viral vector engineered from a duck virus, called AAV.div3A, may offer a way to safely give patients more than one dose of gene therapyaccording to a study.
This is something that is largely impossible today, yet critical for diseases requiring early treatment and that may need additional doses over time, such as Pompe disease,
The new approach avoided the immune attacks that normally make redosing ineffective and unsafe, and allowed a second dose of gene therapy to successfully deliver its genetic cargo in a mouse model of Pompe disease.
These findings suggest these vectors may offer a promising platform for future gene therapy approaches, researchers noted, adding that work is already underway to further develop the technology toward potential clinical use.
The study, “Complete neutralizing antibody evasion by serodivergent non-mammalian AAVs enables gene therapy redosing,” was published in Cell Reports Medicine.
AAV-based gene therapy for Pompe faces major limitations
Gene therapy is being explored as a promising treatment for a range of disorders with a known genetic cause, including Pompe disease. Such treatment often uses adeno-associated viruses (AAVs) that naturally infect humans or other primates but have been modified to act as harmless carriers of a therapeutic gene into the body’s cells.
In Pompe, gene therapies are designed to deliver a healthy copy of the GAA gene to restore the activity of acid alpha-glucosidase (GAA), the enzyme that’s lacking in people with the disorder.
AAV-based gene therapies, however, still face major limitations, as many patients are unable to receive them, and for those who can, the treatment is typically administered only once.
This is because the immune system produces antibodies that recognize and destroy the viral vector used to deliver the gene before it reaches its target cells. These AAV-targeting antibodies may already be present due to natural exposure to AVVs earlier in life, preventing some patients from receiving the therapy at all. They can also appear after a first dose of treatment.
This limitation is particularly important for diseases such as Pompe, where treatment may begin in infancy or early childhood, and additional doses may be needed as patients grow.
Researchers focused on non-mammalian viruses
In light of these challenges, a team of researchers from Duke University set out to find a different type of AAV — one that the human immune system would not recognize — with the goal of widening access to gene therapy and making redosing possible.
They focused on non-mammalian Dependoparvoviruses, a group of AAVs found in birds, reptiles, and other species. Because these viruses are evolutionarily distant from AAVs that infect mammals, including humans, people are far less likely to carry antibodies against them.
To identify the best candidates, the researchers built a library of 80 engineered viral vectors, each based on a non-mammalian AAV but modified to include a small portion from a human-compatible AAV so it could enter human or mouse cells.
When these vectors were screened for their ability to reach cells and deliver their genetic cargo, one candidate clearly stood out: a vector derived from a Muscovy duck virus, which the researchers named AAV.div3A.
AAV.div3A delivered genes effectively in multiple cell models and across different mouse tissues. But its most important feature was its ability to evade existing antibodies.
Duck virus could offer key advantages
In lab experiments, when exposed to blood samples from mice, non-human primates, or human donors containing antibodies against commonly used vectors such as AAV8 and AAV9, none of the antibodies recognized or attacked AAV.div3A.
These findings suggested that AAV.div3A could offer two key advantages: It could work in patients with preexisting immunity and support effective redosing after initial treatment.
To test this, the researchers treated mice that already had antibodies against AAV9 with an AAV9 vector carrying a reporter gene — a harmless test gene that produces a measurable signal. As expected, using AAV9 almost gave no signal. However, when the same reporter gene was delivered using AAV.div3A, the signal was observed across multiple tissues.
Because Pompe disease mainly affects muscle tissue — including the heart and the diaphragm, the major muscle involved in breathing — effective therapy requires strong gene delivery to these tissues. For this reason, the researchers modified the surface of AAV.div3A to create several variants with different tissue preferences.
Overall, our work leverages untapped dependoparvoviral diversity to overcome pre-existing and vector-induced immunity, enabling expansion of patient eligibility and effective redosing.
One version, called AAV.div3A-M1, showed a strong ability to target the heart and diaphragm while reducing delivery to the liver. This is useful because the liver often absorbs a significant portion of the vector, which can limit the amount that effectively reaches target cells.
In a Pompe model, mice were initially administered a dose of an AAV9-based gene therapy that delivered the healthy GAA gene. Four weeks later, as expected, a second dose produced almost no gene activity due to the immune response triggered by the first dose.
But when mice were redosed using AAV.div3A or the muscle-targeted AAV.div3A-M1, GAA enzyme levels increased significantly, with the largest gains seen in the heart and diaphragm.
Treatment with AAV.div3A-M1 provided the greatest benefit. Compared with a single dose of AAV9, redosing with this variant increased GAA levels ninefold in the diaphragm and sevenfold in the heart, with more modest increases seen in the liver.
“Overall, our work leverages untapped dependoparvoviral diversity to overcome pre-existing and vector-induced immunity, enabling expansion of patient eligibility and effective redosing,” the researchers concluded.
