Transplantation of monkey embryonic stem cells [

The replenishment of missing neurons in the brain
as a treatment for
Parkinson disease reached the stage of human
trials over 15 years ago,
however the field is still in its infancy.
Researchers from Kyoto
University have now shown that dopamine-producing
neurons (DA neurons)
generated from monkey embryonic stem cells and
transplanted into areas of
the brain where these neurons have degenerated in
a monkey model of
Parkinson disease, can reverse parkinsonism.
Their results appear in the
January 3 issue of the Journal of Clinical
Investigation.

Studies of animal models of Parkinson disease as
well as clinical
investigations, have shown that transplantation
of fetal DA neurons can
relieve the symptoms this disease. However the
technical and ethical
difficulties in obtaining sufficient and
appropriate donor fetal brain
tissue have limited the application of this
therapy.

These researchers previously demonstrated that
mouse embryonic stem cells
can differentiate into neurons when cultured
under specific conditions.
These same culture conditions, technically simple
and efficient, were
recently applied to primate embryonic stem cells
and resulted in the
generation of large numbers of DA neurons. In
their current JCI study, Jun
Takahashi and colleagues generated neurons from
monkey embryonic stem
cells and exposed these cells to FGF20, a growth
factor that is produced
exclusively in the area of the brain affected by
Parkinson disease and is
reported to have a protective effect on DA
neurons. The authors observed
increased DA neuron development and subsequently
transplanted these
neurons into monkeys treated with an agent called
MPTP, which is
considered a primate model for Parkinson disease.
These transplanted cells
were able to function as DA neurons and
diminished Parkinsonian symptoms.

In an accompanying commentary, J. William
Langston from the Parkinson's
Institute, California, describes this study as a
milestone in the
development of stem cell technology but cautions
that while the
observations are encouraging, the reported number
of surviving DA neurons
was very low, only 1–3% of the cells surviving,
well below the estimated
number of DA neurons that survive after fetal
cell transplants
(approximately 10%). While this may be a
difference observed between
transplantation in monkeys and humans, Langston
stresses that it may be
necessary for far more DA neurons to survive and
for that survival to be
long lasting in order to render this approach as
a useful therapy in
humans.

Langston highlights that "clearly the study
reported here will advance
research aimed at validating the use of stem
cells to treat
neurodegenerative disease" and this is most
welcome particularly as
investigators face yet another presidential
moratorium endeavoring to
limit the number of human stem cell lines that
can be used for future
research and treatment.