Stem Cell Cure for Deafness: FDA Approves U.S. Clinical Trial

Hearing loss stem cell therapy to be tested in U.S. clinical trial. Researchers in the United States have begun a groundbreaking trial to test if stem cells from cord blood can reverse hearing loss in infants and toddlers whose inner ears have been damaged, and the Food and Drug Administration has approved the phase I study.

This means a cord blood stem cell treatment for some forms of deafness is closer to becoming a reality—but not quite there yet.

Phase I clinical studies mean that an experimental treatment is in midstream: it’s hurdled animal studies and is now being tested for the first time on humans to determine, first, if it’s safe. This phase I trial follows promising studies on mice that showed cord blood stem cell transplants were able to rebuild the structures of the inner ear. It also follows some anecdotal evidence that the treatment works for infants with hearing loss.

The clinical trial at Children’s Memorial Hermann Hospital in Houston, Texas is that first step toward using cord blood transplants to treat infants and toddlers with post-birth sensorineural hearing loss.

For the trial, doctors at the Houston, Texas hospital are recruiting 10 infants and toddlers with sensorineural hearing loss, six weeks to 18 months old. The therapy involves transfusing the baby’s own stem cells from umbilical cord blood, harvested after the baby’s birth, then saved up by parents in a cord blood bank.

“We’re looking more at the ones that suffer an injury around birth or shortly after birth,” says Dr. Samer Fakhri, a specialist in head and neck surgery who received his medical training at Canada’s McGill University but who now leads the cord blood trial in Texas.

In the inner ear, the snail shell-shaped cochlea contains “hair cells” that gather electrical signals, which then are transferred to the brain and perceived as sound. Sensorineural hearing impairment happens when these critical structures in the inner ear or the nerve pathways between the inner ear and the brain are damaged.

Critical window for speech, language
Such injuries to the inner ear can be caused by viral infections and even some medications, says Dr. Fakhri. Meningitis is a common cause, he adds, as well as oxygen deprivation, head injury, strong doses of antibiotics or loud noises.

“If they lose hearing at four or five weeks due to a viral infection, we know that there’s a tremendous impact,” he says.

A child with this kind of hearing loss can suffer significant impairment, Dr. Fakhri explains. “You may hear parts of sounds. You may not hear the sounds at all, or you may hear very faint sounds.”

Sadly, for people who lose hearing this early, the development of speech, language and normal socialization are also impaired. “There’s a lot of research that has been done in child development that has determined that there’s really a critical window for children to develop speech, language and social development, and it’s probably in the first 18 months,” observed Dr. Fakhri.

Sensorineural hearing loss affects about six in every 1,000 children, but there’s still no available medical treatment. Instead, the ability of damaged ear tissues is simply boosted with hearing aids or cochlear implants.

But “stem cell therapy may potentially repair the damaged structures of the inner ear and restore normal hearing,” Dr. Fakhri tells the Agence France-Presse (AFP). “We are at the initial stages of this process and the results are looking promising,” he adds.

Cord blood
When a baby is born, some blood remains in the blood vessels of the placenta and the portion of the umbilical cord that remains attached to it after the cord is cut.

This blood, called “cord blood,” is no longer needed by the baby and in recent years, has been harvested—with the permission of birth mothers—to produce stem cells products called hematopoietic progenitor cells.

After being collected, cord blood is isolated, processed, frozen and stored in a cord blood bank for future use. The banks are regulated by the FDA.

For some time now, private cord blood banks have been urging expecting parents to bank their umbilical cord blood and reserve it for personal use as a way to protect members of their family.

But this procedure is expensive—and remains controversial among pediatricians. In fact, the American Academy of Pediatrics in 2007 issued guidelines that discouraged banking for personal use, saying the claims of private cord blood banks were “unsubstantiated.” But the pediatricians’ group says cord blood banking was to be “encouraged” if it’s to be stored in a bank for public use.

Still, many researches on cord blood stem cell therapies to treat kidney and lung disease, juvenile diabetes, cerebral palsy and even some types of brain injury are underway in the U.S. and in other parts of the world.

Repairing hearing loss
European scientists first tested stem cell transfusion to treat partial deafness in 2008, on lab mice with induced sensorineural hearing loss. They transfused human cord blood into the mice with damaged hearing, then examined the treated animals about two months later. They found that “inner ear organization and structure were basically restored,” Dr. Fakhri says.

“That was such a dramatic result,” he enthuses, saying the study “was a proof of concept.” But he concedes that while there are a couple of theories, the exact role of stem cells in the repair of damaged tissue in the mice still isn’t known.

Initially, scientists believed that because stem cells can give rise to many different types of cells in the body, they repaired hearing loss by regenerating lost hair cells. But more recently, scientists theorize that stem cells may go to the site of injury and set off the body’s innate repair mechanisms. “In that sense, they play more of a supporting role,” explains Dr. Fakhri.

Still speculative
But some doctors believe that the idea that stem cells restore damaged hearing in humans is still speculative.

“This study is really very, very preliminary,” said Dr. Robert Harrison, a professor of head and neck surgery at the University of Toronto and a director of the Hearing Foundation of Canada.

“That’s the safety issue,” he says, pointing out that the phase I clinical study must first ensure the stem cells don’t harm patients. Figuring out if they actually work to repair structures in the ear will be tested subsequently in the next trials, he says.

“We’re a long way from looking at the possible therapeutic value of this in terms of restoring some sort of hearing,” says Dr. Harrison tells the Winnipeg Free Press. “It’s a very theoretical concept, and in my opinion it’s not going to happen soon,” he adds.

Some success
But for one person, at least, the stem cell therapy seems to be working.

Two-year-old Finn McGrath suffered hearing loss and brain damage after being deprived of oxygen during a prolonged and complicated delivery, according to his mother, Laura.

Finn suffered organ failure, breathing problems, and his cerebral palsy left him unable to roll, crawl or walk, hold his head up, talk or eat. His hair cells were also damaged, and he sustained hearing loss.

“His doctors told us he was at high risk for cerebral palsy, vision issues, hearing problems and mental retardation,” she tells AFP in an interview.

Searching online for ways to improve his condition, his parents came upon studies using cord blood to help children with cerebral palsy and other disorders.

Thankfully, before Finn was born, the McGraths had arranged to bank his umbilical cord blood with a private bank, a procedure that costs around US$2,000 including storage fees.

Having banked his cord blood, Finn’s parents enrolled him in cord blood trial for cerebral palsy in North Carolina. Finn received his first transplant in November 2009 when he was about seven weeks old and a second one in May 2009.

It was after the two transfusions when his parents began to notice a change: According to Finn’s mother, nighttime noises, like an alarm on his food pump or the sound of ripping medical tape, would startle him awake.

“He started vocalizing sounds and we could tell that he was anticipating things that we would say. Like, if he had heard a story a number of times or a song, he would smile like he recognized the song or the story,” she tells AFP.

In September 2010, Finn had a third infusion when he was one year old. Four months later, an otoacoustic emissions test (OAE), which plays a sound and picks up vibrations in the cochlea and hair cells, came back normal.

While Laura concedes the early hearing tests that showed hearing loss weren’t the same—and thus not comparable—to the tests that showed a positive result, she says she believes the cord blood transfusions may have helped.

“All I can tell you is anecdotally he wasn’t able to hear for probably the first three or four months of his life, and then when he was about six to eight months old, he started hearing.”

She also merits the stem cell transfusion for Finn’s normal cognition, lack of seizures and good vision. “I don’t know how much worse off he would have been without the stem cell transfusion,” she says. “We remain hopeful that he will continue to improve.”

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