by Neil Bauman, Ph.D.
Research into regenerating human hair cells in the inner ear, with the aim of restoring hearing, has been ongoing for a number of years. Researchers have been trying, with varying degrees of success, to get hair cells to regenerate in animals—but there are still many hurdles to overcome. Consequently, human trials appear to still be a number of years away.
However, one method has just leapfrogged the competition and has already begun a Phase I clinical trial. (Note: a Phase I clinical trial is done on a very small group of people [in this case 10] to see if the proposed treatment will be safe and identify any resulting side effects. It’s not till Phase II trials that researchers primarily determine just how effective the treatment will be, although preliminary results hopefully will come out of the Phase I trials.)
This Phase I clinical trial is very limited in scope—just for children between the ages of 6 weeks and 18 months who have an acquired (but not genetic) moderate to profound sensorineural hearing loss since birth, and who have had their umbilical cord blood saved by the Cord Blood Registry.
The idea behind this trial is that there are progenitor stem cells floating around in the umbilical cord blood that researchers want to use in this trial. You see, when some babies are born, doctors extract and save the blood left in a baby’s umbilical cord for use later in the same baby if the baby ever needs it. The fancy name for this is “autologous human umbilical cord blood”. Using the baby’s own blood guarantees that the baby’s immune system won’t reject the blood when it is intravenously injected back into the child at some time in the future.
In this trial, researchers will intravenously inject the stored blood back into the same young child that originally “donated” it. What they expect to happen is that the hemopoietic [hee-moe-poy-ET-ik] stem cells [stem cells that make blood cells] still floating around in this umbilical cord blood will make their way to the inner ear where they will become involved in replacing and repairing any damaged hair cells. The hope is that this will ultimately restore some degree of hearing.
As the clinical trial prospectus states: “Pre-clinical data suggest progenitor cell infusions may enhance intrinsic repair mechanisms in the Organ of Corti which may restore hair cells. This treatment could ultimately lead to hearing improvement. Human umbilical cord blood is an available, autologous, stored progenitor cell population available for potential therapeutic use.” (1)
This clinical trial began earlier this year at the Children’s Memorial Hermann Hospital in Houston, TX, and is estimated to be completed by April of 2015.
Results from previous studies using mice showed that cochlear regeneration occurred. “Our findings show dramatic repair of damage with surprisingly few human-derived cells having migrated to the cochlea,” said Roberto P. Revoltella, MD, PhD, lead author of one such study. “A fraction of circulating hemopoietic stem cells fused with resident cells, generating hybrids, yet the administration of hematopoietic stem cells appeared to be correlated with tissue regeneration and repair as the cochlea in non-transplanted mice remained seriously damaged.” (2)
The mice in these studies had had their hearing damaged by either loud noise or by ototoxic drugs. Interestingly enough, cochlear regeneration was less successful in the group deafened by noise than in the group deafened by ototoxic drugs, implying that damage was more severe when induced by noise. Furthermore, regenerative effects were greater in mice injected with a higher number of hematopoietic stem cells. Researchers also found that regeneration of cochlear tissues improved as time passed. (2)
In another year or two, we should know whether this method of restoring hearing (to some degree or other since it obviously wasn’t 100% in the animal studies) will work on young children.