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The functional recovery was about 46 percent on average and was evident about four weeks after administering the cells. As well as proving that stem cells can be used to repair damaged hearing, it is hoped the breakthrough, reported in the journal Nature, will lead to new treatments and therapies for people.

The model of hearing loss successfully treated by the scientists is similar to a human condition known as auditory neuropathy, a common form of deafness in which the damage occurs at the level of the cochlear nerve. It is thought to represent up to 15 percent of the population across the world with profound hearing loss.

Human stem cell-derived otic neurons repopulating the cochlea of deaf gerbils. Human cells are labelled green, and the red is a marker of neuronal differentiation. Therefore yellow cells are neurons of human origin. (Credit: University of Sheffield)

“We developed a method to drive human embryonic stem cells to produce both hair cells and neurons, or nerve cells, but we only transplanted the neurons,” says Marcelo Rivolta of the University of Sheffield.

“We then used a technique called auditory brainstem evoked responses (ABR), which measures if the brain can perceive an electrical signal after sound stimulation. The responses of the treated animals were substantially better than those untreated, although the range of improvement was broad. Some subjects did very well, while in others recovery was poor.”

Auditory neuropathy is a type of deafness where the problem lies, not primarily with the hair cells, but in the connection of the hair cells with the brain. Patients can be born with it and there are cases due to a genetic defect where a few responsible genes have already been identified.

However, there is increasing evidence that environmental factors, such as jaundice at birth and noise exposure later in life, play an important role, at least as risk factors.

“We believe this an important step forward. We have now a method to produce human cochlear sensory cells that we could use to develop new drugs and treatments, and to study the function of genes. And more importantly, we have the proof-of-concept that human stem cells could be used to repair the damaged ear,” Rivolta says.

“More research is needed. For instance, we want to understand the long term implications of this treatment and its safety. Moreover, while in auditory neuropathy patients that retain their hair cells the sole application of stem cells could be beneficial; those with more comprehensive damage may need a cochlear implant to compensate for the hair cell deficit. In these patients it is possible that stem cells should be administered in combination with a cochlear implant. It is therefore important to explore this interaction.”

Paul Colville-Nash, Program Manager for stem cell, developmental biology, and regenerative medicine at the Medical Research Council, which co-funded the research, says: “This is promising research that demonstrates further proof-of-concept that stem cells have the potential to treat a range of human diseases that currently have no effective cures.

“While any new treatment is likely to take years to reach the clinic, this study clearly demonstrates that investment in UK stem cell research and regenerative medicine is beginning to bear fruit, and that is very exciting.”

The research was also funded by the UK research charity Action on Hearing Loss.

Source: University of Sheffield