Stem cell therapy for the treatment of hearing and vestibular loss

Stem cell therapy for the treatment of hearing and vestibular loss. What an existing possibility? But wat is the current situation and is this an option in 2018?

Stem cell therapy for the treatment of hearing and vestibular loss
Stem cells can restore inner ear structures. (Modified from Wikepedia image)

A stem cell is a non-differentiated living cell that has the potential to differentiate into specialised tissue and to produce more stem cells. They are present in all mammals, humans alike.  There are basically two types of stem cells, embryonic stem cells which are isolated from the embryo, as present during early human development, and adult stem cells which are found in adults throughout the body. Stem cells are researched and developed to replace cardiac muscle (like after a heart attack), blood cells (in leukaemia and lymphoma patients) and nerve cells (in Parkinson disease and other neuro-degenerative conditions).

As said, stem cells are found in tissue throughout the human body. In blood, fat, bone marrow, the Organ of Corti and vestibular apparatus of the inner ear, and even the central nervous system. It is nowadays a practice in South Africa to harvest these stem cells immediately after birth from the umbilical cord of babies and to store it for possible later use in life. These are all autologous cells, meaning it comes from the patient itself.

On the other hand, stem cells can also be harvested from embryos, thus from other people/persons and if in an ethical way considered a human being. This is obviously a major ethical issue!

Stem cell therapy for the treatment of hearing and vestibular loss focuses on sensorineural hearing loss due to structural damage in the cochlea or cochlear nerve. It is also utilized to replace damaged vestibular nerve and receptor cells, a promising prospect for patients with bilateral vestibular loss. Common conditions causing these types of sensory loses include presbyacusis (old age changes), ototoxicity, noise induced hearing loss and neuropathy.

Stem cell therapy for the treatment of hearing and vestibular loss
The target cells for stem cell therapy in hearing. Stria vasculararis (1), cochlear nerve (2), hair cells (3) and supporting cells (4). (Modified from Wikipedia image).

The 4 main target cells for stem cell therapy include cells of the stria vascularis, the hair cells, the supporting cells and the spiral ganglion/ nerve cells. It is also postulated that the support cells maintain the ability, with the appropriate signal, to differentiate into hair cells.

There are numerous challenges that need to be addressed before stem cell therapy for the treatment of hearing loss can actually become a viable option. Injecting stem cells into the cochlea may damage residual hearing and elicit an immune response. The high potassium concentration in normal endolymph fluid is highly toxic and is most likely to kill the injected stem cells. It is also not known whether the stem cell will develop into the highly topographic, correctly orientated and frequency specific hair cells as is present in the normal cochlea. The ethical problems surrounding the harvesting of stem cells from embryos was already mentioned.

Stem cell therapy, in conjunction with gene transfer and molecular modification of existing cochlear and vestibular cells is an exciting field with massive potential, unfortunately still in its infant stage. At this time all experiments were conducted in mice, not in humans.

It is not an option, currently, to restore sensorineural hearing and vestibular loss, utilizing stem cells.