NEW YORK -- A new brain implant therapy for Parkinson's disease
that doesn't rely on human or animal fetal tissue has shown such
promising early results in monkeys that researchers plan to try it
soon in humans.
In seven monkeys with a drug-induced form of Parkinson's, the
cell implants resulted in an improvement in each animal that varied
from 44 percent to 90 percent within three months.
Richard C. Allen of Titan Pharmaceuticals Inc., which developed
the therapy, said last week he believes it can bring about
``long-term, significant restoration of function'' using implants
of ``readily available human cells'' that could be stored frozen
and used as an off-the-shelf product.
The cells are dopamine-producing cells that form a pigmented
layer in the retina of the human eye. Why retina cells produce
dopamine, the substance lacking in Parkinson's, is not known. The
cells can be obtained from donor eyes at organ banks and then grown
and multiplied in the lab. For implanting, the cells are deposited
on the surface of tiny gelatin spheres -- they are barely visible to
the naked eye -- and hundreds of thousands of spheres are injected
into the patient's brain. The cell product is called Spheramine.
One donor eye could provide enough cells to perform thousands of
implants, said Allen. And, unlike implants of human or animal fetal
cells, the Spheramine cells are not attacked by immune cells in the
brain. Exactly why that is hasn't been determined for certain, said
Allen.
The Spheramine results were presented at a recent meeting here
of companies developing tissue engineering and ``regenerative
medicine'' products. The meeting was sponsored by TechVest LLC, an
investment research firm.
The Spheramine clinical trials will be carried out at Emory
University School of Medicine in Atlanta. Dr. Ray Watts, an Emory
neurologist, said Friday that the animal studies, in which he is
involved, have shown a ``very prominent'' improvement. He said it
is too soon to predict the eventual role of Spheramine in
Parkinson's disease.
More than 500,000 people in America have Parkinson's, including
US Attorney General Janet Reno and actor Michael J. Fox.
The disease results from the death of brain cells that produce
dopamine, a key chemical messenger needed for smooth and
coordinated movement. Symptoms usually begin in middle age or
beyond: they include tremors of the hands and, as the disease
progresses, slowed movement, balance and gait difficulties, rigid
extremities, and profound disability.
Medication that provides dopamine to the brain can keep symptoms
under control for a few years, but eventually the drugs lose much
of their effect. In the 1990s, surgeons have experimented with
implanting dopamine-producing nerve cells into the brain, in hopes
the nerves would take root and pump out a constant supply of
dopamine.
This strategy requires fetal cells that can adapt to their new
environment. Implants of human fetal cells are likely to have a
limited role because they present ethical issues, and because
aborted fetuses would not provide a large enough supply for the
expected demand.
Recently, implants have been carried out with fetal pig cells. A
Charlestown company, Diacrin, Inc., has been developing the pig
system and its president and CEO, Thomas H. Fraser, reported on its
progress at the tissue engineering conference.
Fraser said that in a study of 11 implant patients who got a low
dose of pig cells there was an average of 20 percent improvement in
symptoms. Three patients have had ``spectacular recoveries,'' he
said, while three remained at their pre-treatment level of
disability, and the other five were ``somewhere in between.''
It takes about 16 fetal pigs to provide enough nerve cells for a
transplant, Fraser said. The cells have to be used almost
immediately. By contrast, the Spheramine system allows cells to be
frozen and kept indefinitely, and does not require raising large
animals, as the Diacrin effort does.
Watts, at Emory, is involved in research for Diacrin as well as
the Spheramine experiments. At this point, he said, ``I don't think
you can say yet whether one is more effective or more promising
than the other.''
