Gene Therapy Platform Harnesses Brain's Glymphatic System for Targeted Delivery

Researchers have developed a gene therapy platform that uses the brain's glymphatic system to deliver therapeutic genes to glial cells throughout the brain, bypassing the blood–brain barrier for safer, more effective treatments. The new study describes a strategy that distributes engineered viral vectors throughout the brain via the brain's own glymphatic transport system. The approach addresses two major challenges in neurological medicine—reaching therapeutic targets behind the blood–brain barrier and limiting unwanted effects elsewhere in the body—and could pave the way for new treatments for diseases including multiple sclerosis, Huntington's disease, and rare childhood white matter disorders. The study appears in Nature Biotechnology.

The platform pairs specially engineered adeno-associated viruses (AAVs) with a delivery strategy that harnesses the brain's natural fluid transport pathways. Together, these innovations enabled researchers to deliver therapeutic genes broadly throughout the brain, preferentially targeting human glial cells while minimizing exposure to other cell types and organs. "Gene delivery to the brain has always faced two major obstacles," said the study's lead author, co-director of the University of Rochester Medicine Center for Translational Neuromedicine. "You need a way to get therapies into the brain selectively and efficiently, and you need vectors that can deliver those therapies to the right cells once they get there. This work addresses both challenges simultaneously."

The researchers engineered a library of modified AAV5 viral vectors, each containing small changes to its outer protein shell, or capsid, which determines the types of cells a virus can infect. The team screened the vectors in mice whose brains had been transplanted with human glial progenitor cells. Using a genetic tracking system, the researchers identified the viral variants that most effectively infected the human glial cells in the environment of the living brain. "Human cells display different molecular signatures than mouse cells, and cells behave differently in the brain than they do in a dish," said the lead author. "By selecting vectors under biologically relevant conditions, we were able to identify candidates with a strong preference for human glia." The resulting vectors preferentially targeted human glial progenitor cells and their descendants, including astrocytes and oligodendrocytes, while showing limited infection of peripheral tissues.

Developing the right vector solved only half the problem. The team also needed a better way to distribute those vectors throughout the brain. To do so, they turned to the glymphatic system, a network of fluid-filled pathways that circulates cerebrospinal fluid through the brain to clear metabolic waste. This system was first described by a University of Rochester Medicine neuroscientist, who worked with the team to design a strategy to co-opt the glymphatic pathways for viral delivery. The researchers delivered the engineered AAVs into the cisterna magna, a fluid-filled compartment at the base of the brain, while using hypertonic treatment to enhance fluid uptake into the glymphatic network. The approach enabled the vectors to spread broadly through the brain tissue, while largely circumventing the blood–brain barrier. Because the vectors were concentrated in the brain, the strategy also reduced exposure to peripheral organs such as the liver, a common source of toxicity in conventional systemic gene therapy approaches.

"The glymphatic system is changing the way we think about brain drug delivery," said the lead author. "Rather than trying to force therapies across the blood–brain barrier from the bloodstream, we can use the brain's own transport pathways to distribute them more effectively where they are needed." This work builds on a longstanding focus on glial cells—the support cells of the nervous system that help maintain brain function, produce myelin, and regulate neuronal health. In Huntington's disease, for example, the team previously found that healthy human glial progenitor cells could outcompete and replace diseased cells in the brain, highlighting the therapeutic potential of targeting glia. "Over the last decade, we've learned that many neurological disorders involve glial dysfunction as a major driver of disease," the lead author said.