Parkinson's transplant therapy faces setback
Fetal tissue trial raises stem
cell questions.
28 August 2003
ERIKA CHECK
This story is from the News section of the journal
Nature
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| Parkinson's disease
destroys dopamine-producing brain cells. |
| © GettyImages |
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An experimental technique that uses transplanted fetal
tissue to treat Parkinson's disease is not yet ready
for widespread use, according to a study published online
last week.
In the study, surgeons transplanted nerve tissue from
aborted fetuses into the brains of patients with Parkinson's
disease. The disease destroys neurons that produce the
chemical dopamine, which is required for normal brain
function. The transplanted tissue is intended to replace
these damaged cells.
But the average condition of the 23 patients who received
the treatment did not improve significantly compared
with a group of 11 who did not have it. The researchers,
led by Warren Olanow of the Mount Sinai School of Medicine
in New York, measured whether the treatment affected
the symptoms of the disease, such as muscle tremors,
speech and mental abilities1.
An earlier trial, led by Curt Freed of the University
of Colorado Health Sciences Center in Denver, also found
that patients did not benefit as a group from fetal
tissue transplants2. And
both trials found that the procedure caused some patients
to suffer jerky involuntary movements, or dyskinesias,
as a side effect. More than half of the patients in
the latest trial had dyskinesias, compared with 15%
of those in the earlier trial.
The results may have implications for other research
using aborted fetal tissue — and, perhaps, for
future therapies that might use laboratory-grown stem
cells to replace defective tissue. Some researchers
fear that the negative results will reduce support for
the politically controversial stem-cell therapies.
Researchers say that previous trials of fetal cell
transplants for Parkinson's disease have been encouraging,
as they have worked in some patients. But they feel
that they cannot proceed with the technique until they
work out how to prevent dyskinesias. "Unless we resolve
this, it will have a tremendous negative impact on this
and other issues in stem-cell research," Olanow says.
After Freed's study, scientists thought that the dyskinesias
were caused by overactive neurons. But Olanow found
hints that the opposite is true — poorly functioning
transplants could be the cause. Olanow and others say
that it is crucial to define what makes the transplants
function well. Work with neurons grown from stem cells
could offer clues, they add, because such lab-derived
cells would contain fewer impurities than fetal tissue.
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Unless we resolve this,
it will have a tremendous negative
impact on stem-cell research
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Warren Olanow
Mount Sinai
School of Medicine
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Another question raised by the latest trial is whether
the transplants are being inactivated by the immune
system. Olanow's team found some evidence to suggest
that an immunological reaction is destroying or disabling
the tissue grafts. Such evidence had not been found
in previous trials.
Neurologist Olle Lindvall of the University of Lund
in Sweden, who is leading a 15-year study of fetal transplants
for Parkinson's disease, remains strongly supportive
of the transplant idea. But he agrees that the trials
raise a number of questions that must be answered by
lab work before further clinical trials are done.
"Everyone agrees that we don't yet have a method that
would make fetal cell transplants competitive as a clinical
treatment," he says.
Erica Check is Washington Biological Sciences correspondent
for the journal Nature
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