Will McLean believes he’s found a fix for a medical conundrum that many thought could never be solved: hearing loss in humans.

McLean’s research focuses on the cochlea, the spiral-shaped cavity within the inner ear that’s responsible for hearing. At birth, the average human cochlea contains 15,000 hair cells, which detect sound waves and transfer them to the brain. Over time, many of these cells are killed by exposure to loud noise and toxic medications. In mammals, unlike birds, reptiles, and amphibians, they don’t naturally grow back. “The inner ear is one of the least regenerative parts of the body,” McLean says. “That’s why hearing loss is permanent.”

McLean, who holds a PhD from MIT in health science and technology, has spent the last decade trying to change that. His early work showed that the inner ear contains distinct progenitor cells—similar to stem cells but more specific in their capabilities—and that some have the potential to become hair cells, though they cannot divide or differentiate on their own to repair damaged tissue. To resolve this, he and colleagues used insights from regenerative tissues, such as those in the intestine. They exposed damaged cochleas from mice to a combination of drugs that can trigger regeneration in these other organs. Surprisingly, their technique not only caused the progenitor cells to proliferate but also induced them to generate new hair cells—the key to restoring hearing.

On the strength of this discovery, McLean and colleagues established Frequency Therapeutics, a startup working to commercialize what he describes as an entirely new mode of medicine. Frequency’s technique, known as progenitor cell activation, uses a combination of compounds that essentially unlock the body’s ability to heal itself. To date, Frequency has filed 19 patent applications and developed an injectable in-ear therapeutic to combat hearing loss. The treatment has successfully passed human safety trials.

—Jonathan W. Rosen