In mammals, hearing loss is usually due to damage to the sound-sensing hair cells in the inner ear.
Originally, the hair cells were thought to be irreplaceable, but research in mice has shown that the supporting cells that provide structural support to the hair cells can turn into hair cells. If this technology can be applied in older animals, then it might provide a way to stimulate hair cell replacement in adults and treatments for deafness as a result of hair cell loss.
According to Albert Edge of the Harvard Medical School and Massachusetts Eye and Ear Infirmary, hair cell replacement definitely occurs, but does so as rather low levels. According to Edge: “The finding that newborn hair cells regenerate spontaneously is novel.”
Earlier work has shown that inhibition of the Notch signaling pathway increases the formation of new hair cells not from remaining hair cells but from nearby supporting cells that express a cell-surface protein called Lgr5.
When Edge and his team used small molecules to inhibit the Notch signaling pathway, even more support cells differentiated into hair cells, and the Lgr-5-expressing cells were the only supporting cells that differentiated under these conditions.
By combining these new findings about Lgr-5-expressing cells with the previous finding that Notch inhibition can regenerate hair cells, scientists should be able to design new hair cell regeneration strategies to treat hearing loss and deafness.
In the United States, about 15% of children suffer from low or high frequency hearing loss. Sensorineural hearing loss is the most common type of hearing loss, especially at high frequencies. Acquired sensorineural hearing loss results from damage to hair cells in the inner ear (cochlea) and can be caused by illness, medication, noise exposure, birth injury or head trauma. Because the ability to hear affects language development, hearing impairments can lead to poor academic and social development.
This particular study is a Phase I clinical trial, which will determine the safety and efficacy of using cord blood stem cells in children to improve inner ear function, and speech and language development.
In this study, the research group will follow 10 children who range in age from 6 weeks to 6 years, who have been diagnosed with acquired hearing loss for less than 18 months and who have had their own umbilical cord blood processed and stored.
Unfortunately, children who have a known genetic cause of deafness are ineligible for study participation. Patients will receive one intravenous infusion of their own umbilical cord blood stem cells. All patients will be tested at 1 month after the infusion, 6 months, and 1 year post-treatment.
As usual, this clinical trial is inspired by positive results in preclinical tests in laboratory animals.