The achievement offers researchers a powerful laboratory model with which to develop therapies for deafness and hearing loss, which affect about nine million people in Britain.
In the longer term the advance could allow scientists to grow replacements for damaged hair cells in the ear, which cause between 60 and 90 percent of cases of hearing loss and also contribute to tinnitus.
The hair cells, in a part of the inner ear called the cochlea, bend in response to vibrations, converting sound waves into electrical signals that are sent on to the brain. Humans have about 15,000 hair cells in each ear. They do not regenerate when damaged.
In the study a team led by Stefan Heller, Professor of Otolaryngology at Stanford University in California, has found a way to coax two types of mouse stem cells to develop into sensory hair cells. Embryonic stem (ES) cells and induced pluripotent stem (IPS) cells, reprogrammed from skin tissue to give them versatile properties, were used to produce hair cells that behaved like the real thing.
"They really looked like they were more or less taken out of the ear," Professor Heller said. The findings published in the journal Cell, suggest that it will be possible to grow thousands of hair cells. These could be used to examine how they are damaged and for testing drug treatments that may protect them or encourage regrowth. The scientists plan to repeat the experiment with human stem cells.
"We are working on applying our protocol to human ES and IPS cells," Professor Heller said. "Human cells are a little more tricky to handle... We expect that generating human hair cells will be feasible, but it will take us a couple of years.
"If this works, we would be able to take, for example, a skin cell from a human patient and convert this cell first into IPS cells, then into inner ear cells. We could then probe and analyse hair cells generated from patients directly to investigate the source of their dysfunction."
Eventually, such cells could potentially be transplanted to reverse hearing loss, though extensive testing would be required. "I expect that the primary use of the cells lies in basic science research, as well as drug screening," Professor Heller said. "I am not saying that (transplants) will be unfeasible, but (they are) certainly not around the corner."
Ralph Holme, Director of biomedical research at the deafness charity RNID, said: "We are very excited about this research. Treatments for the 9 million people in the UK with hearing loss are currently limited to hearing aids and cochlear implants. What we want is a way of developing drugs that can prevent hearing loss or reverse it, and this research opens the door to doing that."
David Corey, Professor of Neurobiology at Harvard University, who was not involved in the research, said: "This gives us real hope that there might be some kind of therapy for regenerating hair cells. It could take a decade or more, but it is a possibility."
