The new advance holds great promise for people with hearing loss, but scientists won't know for years whether a similar treatment would really work in humans

In a promising early study, researchers from the U.K. restored hearing in deaf gerbils by using human embryonic stem cells. It’s an encouraging finding for some of the millions of people who suffer from hearing disorders.

“We have the proof of concept that we can use human embryonic stem cells to repair the damaged ear,” lead author Marcelo Rivolta, a stem cell biologist at the University of Sheffield, in England, told Nature News. “More work needs to be done, but now we know it’s possible.” The study was published in the journal Nature.

Hearing loss is typically caused by disruptions in the connection between the hair cells of the inner ear and the brain. Hair cells turn sounds into electrical signals, which are then carried by auditory neurons to the brain. In the new research, the researchers studied gerbils with damage to the auditory nerves and attempted to replace these cells with human embryonic stem cells.

(MORE: Study: Why Deafness May Improve Vision)

Stem cells can be coaxed into any type of cell in the body, and while they have been turned into auditory nerve cells before, this is the first study to show that such transplanted cells can actually restore hearing.

For the study, researchers used a chemical called ouabain to damage the auditory nerves of gerbils. Then, scientists injected stem cells that had been nurtured into immature nerve cells into the deafened ears of 18 gerbils; eight animals received no treatment. Ten weeks later, hearing in the animals that received the stem cells had improved by 46%, as measured by the brain stem’s response to sound. There was a range of improvement, with some gerbils regaining nearly full hearing and others progressing less, but on average, the animals’ hearing was improved “to the level that a person would be able to engage in conversation in a busy environment,” according to CNN.

Rivolta’s team also used stem cells to make progenitors of inner ear hair cells, which may also be able to treat more cases of hearing loss, but the researchers have yet to test these cells in studies.

(MORE: Scientists Turn Human Skin Cells Into Healthy Heart Cells)

It will be many years before scientists know whether the advance can benefit humans. “The next goals of any protocol are to gain higher levels of efficiency and reproducibility, determine protocol safety and confirm that transplantation leads to prolonged recovery,” Stefan Heller, a stem cell researcher from Stanford, who is also working on turning stem cells into hair cells, told Nature News. “Then we can think about patients.”