David P. Corey, Ph.D.
Bertarelli Professor of Translational Medical Science
Harvard Medical School
Benjamin P. Kleinstiver, Ph.D.
Assistant Professor of Pathology
Massachusetts General Hospital
Project: In Vivo Correction of a Common Hereditary Deafness Mutation using Prime Editing
Although most hearing loss occurs with aging and is associated with toxic chemicals or noise, some children are born with severe or profound hearing loss that is genetic. Over a hundred different genes are essential for hearing, and inherited mutations in these can produce congenital hearing loss. By far the most common hereditary hearing loss is the disorder DFNB1, caused by mutations in the GJB2 gene. This gene carries the instructions to produce connexin 26, an ion channel that connects the interiors of adjacent cells in the inner ear and that helps create a supportive environment for the specialized cells that sense sound. Of many different mutations in GJB2 that can compromise function, just three are most common; among these is the 35delG mutation in which a single DNA base, a G, is missing.
Two laboratories will bring complementary skills to genetically correct the 35delG mutation in a patient’s own cells. They will first develop a mouse model of the disease and characterize its hearing loss. In parallel, they will use a novel gene editing system called prime editing, which can insert bits of DNA into a cell’s genome—in this case a bit that includes the missing G. The components of the prime editing system will be optimized in vitro. They will then develop viral vectors that can carry these components into cells of the inner ear. A special challenge is that the common AAV vectors used for DNA delivery do not have the capacity for the prime editing system, so the investigators will develop paired vectors that each carry part of the system in a way that allows it to reassemble once in a cell. These AAV vectors, delivered to the inner ear of the deaf mouse model, will be tested for their ability to restore hearing. Finally, the best vectors will be tested in non-human primates, to ensure their ability to edit the GJB2 gene and to ensure lack of toxicity. When optimized, this strategy could be used to treat some of the more than 2000 children per year born with the 35delG mutation in the United States and Europe.