A cell therapy approach to substitute neural elements in the inner ear

Three different donor tissues were tested for their capacity to survive, integrate and differentiate in the adult inner ear. Surviving embryonic dorsal root ganglion cells were found within the spiral ganglion neuron region and along the auditory nerve fibers. In the presence of exogenous nerve growth factor (NGF), the dorsal root ganglion cells formed extensive growth of neurites that seemed to contact the host neurons. Adult neural stem cells survived relative poorly in the inner ear whereas embryonic stem cells showed a somewhat greater capacity for survival and integration. Overall, the survival rate of implanted tissue was quite low in the cochlea. It is concluded that an inner ear cell therapy approach based on the implantation of exogenous cells will require that important survival factors are identified and supplied. In addition, it is possible that the physical properties of the cochlea, e.g., fluid-filled compartments and very limited space for cell proliferation, are unfavorable, at least in the normal cochlea.