Stem cells for human inner-ear therapy
It is difficult to predict how stem-cell-based therapy will be
translated into clinical practice. In addition to inner-ear
cells that are derived from ES cells [4], neural stem cells [5]
Figure 2. The mammalian organ of Corti before and after hair-cell loss and a
speculative visualization of potential regeneration of hair cells. (a) A cross-section
of the normal organ of Corti usually bears a single inner hair cell and three outer
hair cells. All hair cells are depicted in green. (b) After hair-cell loss, the organ of
Corti undergoes morphological rearrangement. In some cases, the remaining cells
accrue to reseal the epithelium; often the cells lose their morphological features
and adopt a basic epithelial organization, as depicted here. (c) Hypothetical view of
a regenerated sensory epithelium in place of the degenerated organ of Corti. New
hair cells (green) can either be reseeded by the integration of progenitor cells or
they can differentiate, following suitable stimulation, by direct regeneration from
the cells that remain after hair-cell loss.
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(a)
(b)
(c)
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and adult inner-ear stem cells [3], other sources of cells for
inner-ear regeneration could include tissue from organ
donors or from animals. Organ donors have been used as a
source for pancreatic islets for the treatment of diabetes by
cell therapy [57], in which the long-term acceptance of
functioning grafts has been possible by using a combination
of anti-rejection drugs. Cells are more readily
obtained from animal donors, and animal cells have been
used in other experimental therapies, such as fetal pig
dopaminergic neurons for Parkinson’s disease [58] and
porcine islets for diabetes [59,60]. This could be a route for
therapeutic cell transplantation, but the immune rejection
barrier, which includes both the acquired and the innate
immune responses (natural antibodies and natural killer
cells) that recognize and kill cells used for xenotransplantation
[61,62], must be overcome.