Human stem cells restore hearing in gerbil study

NEW YORK (AP) - For the first time, scientists have improved hearing in deaf animals by using human embryonic stem cells, an encouraging step for someday treating people with certain hearing disorders.

"It's a dynamite study (and) a significant leap forward," said one expert familiar with the work, Dr. Lawrence Lustig of the University of California, San Francisco.

The experiment involved an uncommon form of deafness, one that affects fewer than 1 percent to perhaps 15 percent of hearing-impaired people. And the treatment wouldn't necessarily apply to all cases of that disorder. Scientists hope the approach can be expanded to help with more common forms of deafness. But in any case, it will be years before human patients might benefit.

Results of the work, done in gerbils, were reported online Wednesday in the journal Nature by a team led by Dr. Marcelo Rivolta of the University of Sheffield in England.

To make the gerbils deaf in one ear, scientists killed nerve cells that transmit information from the ear to the brain. The experiment was aimed at replacing those cells.

Human embryonic stem cells can be manipulated to produce any type of cell. Using them is controversial because they are initially obtained by destroying embryos. Once recovered, stem cells can be grown and maintained in a lab and the experiment used cells from lab cultures.

The stem cells were used to make immature nerve cells. Those were then transplanted into the deaf ears of 18 gerbils.

Ten weeks later, the rodents' hearing ability had improved by an average of 46 percent, with recovery ranging from modest to almost complete, the researchers reported.

And how did they know the gerbils could hear in their deafened ears? They measured hearing ability by recording the response of the brain stem to sound.

The gerbils were kept on medication to avoid rejecting the human cells, much like people who get transplants of human organs, Rivolta said. But that might not be necessary if the procedure proceeds to people, he said. Scientists may be able to work with stem cells that closely match a patient, or even use a different technology to make the transplanted cells from a patient's own tissue, he said.

Rivolta's team also reported making immature versions of a second kind of inner-ear cell. Transplants of those cells might be able to treat far more cases of hearing loss. But the team has not yet tested these in animals, Rivolta said.

Yehoash Raphael of the University of Michigan, who didn't participate in the work, said it's possible the stem cell transplants worked by stimulating the gerbils' own few remaining nerve cells, rather than creating new ones. But either way, "this is a big step forward in use of stem cells for treating deafness," he said.