“Most causes of hearing loss—whether it is congenital hearing loss from some sort of genetic defect or acquired hearing loss from chronic noise exposure or powerful antibiotics or chemotherapy—generally those patients have a hair-cell-based hearing loss,” says Daniel Lee, a surgeon at the Massachusetts Eye and Ear Infirmary in Boston…
“Over time, after you lose the ability to hear due to hair-cell loss, the neurons get pruned back due to lack of activity,” he says.
To address the loss of these cells, [researchers] devised a method to turn human embryonic stem cells into ear-cell progenitors, cells that can then be transplanted into the inner ear, where they further differentiate into auditory neurons. The researchers demonstrated that the transplanted cells could transmit sound signals into the brain.
…The ultimate goal of stem-cell therapy is to replace both the hair cells and the neurons, says Rivolta, but the procedure is much more difficult for the hair cells. “We are still lacking a surgical technique to deliver the cells in the right place without damaging the ear. Moreover, the cells would need to graft in a perfect arrangement, at a correct angle,” he says.