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Scientists clear one hurdle for using stem cells
By Merritt McKinney
NEW YORK, Jan 03 (Reuters Health) - Scientists may have
found a way to overcome some of the obstacles preventing
the use of embryo-derived stem cells, a type of immature
cell
thought to hold great promise in the treatment of
illnesses
such as Parkinson's disease and diabetes.
While the cells can be grown in the laboratory after they
are
collected from embryos, the characteristics of stem cells
make it difficult to move them from the laboratory to the
clinic.
"We can't take the embryonic (stem) cells that we have and
transplant them into anything," said Dr. John D. Gearhart,
of
Johns Hopkins University in Baltimore, Maryland. They will
"just as likely form a tumor as they will differentiate
into some
sort of tissue," he said.
Stem cells never stop dividing, so if the cells were to be
transplanted before they had begun to form more
specialized cells, they might form a tumor instead of
normal
tissue, Gearhart explained.
The key to overcoming this problem is to transplant cells
that
have already specialized somewhat, a process known as
differentiation, according to the Johns Hopkins
researcher.
Differentiated cells are no longer immortal, so they do
not
run the risk of becoming cancerous, Gearhart noted. "Once
a cell commits, it won't become a tumor," he said.
In a report in the January 2nd issue of the Proceedings of
the
National Academy of Sciences, Gearhart and his colleagues
detail their successful efforts to produce cells that can
still
form many different types of cells, but do not carry a
risk of
forming tumors.
The researchers started by coaxing embryonic stem cells to
form clusters of cells known as embryoid bodies. From
these small masses, the scientists then isolated cells
called
embryoid body-derived cells, which they grew in culture
dishes to form different types of cells.
When they analyzed the embryoid body-derived cells, the
researchers detected genes for several different cell
types,
including neurons and blood cells, Gearhart stated.
The fact that the embryoid body-derived cells contain the
genes and other markers for several different cell types
is
intriguing, according to Gearhart. It suggests that the
cells
"share a cluster of genes," he said. If this proves to be
the
case, it may mean that the cells, although more
differentiated
than the earliest of stem cells, may have the capability
to
form different types of tissue depending on where in the
body they are transplanted, Gearhart added.
The researchers also found that, unlike the most immature
stem cells, embryoid-derived cells are not immortal. They
will
divide 70 to 80 times and then die, Gearhart said, which
is
enough to grow tissue but not to form tumors.
The next step, Gearhart pointed out, is to place the cells
in
animals to see whether they can treat disease or heal
spinal
cord injuries. Official results will not be available for
several
months, but preliminary findings look promising, he said.
Gearhart and his colleagues also note that growing
embryoid body-derived cells is much easier and faster than
growing early stem cells. The ease in growing the cells,
as
well as the ability to have a uniform population of the
cells
and the ability to freeze and thaw them--which is
important
for storage--may reduce the number of cells that need to
be
collected from embryos, according to Gearhart.
The research was funded by Geron, Inc. Gearhart and one of
his colleagues, as well as Johns Hopkins, have a financial
interest in the company.
SOURCE: Proceedings of the National Academy of
Sciences 2001;98:113-118.
© 2000, Reuters Health Information Services