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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. D. Gearhart,

of

s Hopkins University in Baltimore, land. 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 s 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 s 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