John Brigande, who hears nothing out of his left ear and only poorly out of his right, has revealed that his experimental gene therapy has been found to generate the type of cells that are damaged or missing in deaf animals.
He revealed that when mice embryos were injected with a key developmental gene during a study, it led to the production of ear cells that convey sounds to the brain.
"That is sort of the major achievement or milestone that we all had to reach," New Scientist magazine quoted Stanford University cell biologist Stefan Heller, who was not involved in the study, as saying.
Brigande, however, insists that his advance represents only an incremental step in the search for a treatment to human hearing loss.
"We're really far away from a cure for deafness," says Brigande, who began losing his own hearing aged 10.
While speaking to the magazine with the aid of a closed captioning program, he said: "I'd like to hear, and I would love to be a member of the research team or community that does define an efficacious therapy, but I think it needs to be approached with enormous caution."
Hearing loss is generally caused by damage to the cochlea's "hair" cells, which convert the air vibrations of sound into the electric currents used by the brain. Loud sounds, antibiotic drugs and gene mutations can all deaden such cells.
During the study, Brigande's team focused on birthing new hair cells, not restoring hearing, in mice that could hear.
The researchers achieved that feat by injecting mice embryos with a gene called Atoh1, as well as a gene that produced a fluorescent protein.
Newborn mice that received the gene therapy grew fluorescent green hair cells in precisely the right location in their cochleae, according to the team, and the cells made connections to nerve fibres that travel to the brain.
Working with his colleague Anthony Ricci, Brigand also proved that the cells worked, converting movements into electrical nerve pulses.
He, however, warned that the cells were tested just a few days after birth, and they could have stopped working not long after.
The researcher said that he and his colleagues were planning to test the same approach in mice born without working hair cells.
The understanding gained from the ability to tweak the developing mouse cochleae might eventually allow researchers to figure out how to treat deafness with drugs, not untested and controversial therapies such as genes and stem cells.
"I think it's potentially achievable one day," Brigande says.
The study has been published in the journal Nature.