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Paralyzed mice given stem cells walk again

Study suggests treatment may help repair damaged spinal cords

http://www.msnbc.msn.com/id/9401832/

Updated: 5:50 p.m. ET Sept. 19, 2005

WASHINGTON - Injections of human stem cells seem to directly repair some

of the damage caused by spinal cord injury, according to research that

helped partially paralyzed mice walk again.

The experiment, reported Monday, isn’t the first to show that stem cells

offer tantalizing hope for spinal cord injury — other scientists have

helped mice recover, too.

But the new work went an extra step, suggesting the connections that the

stem cells form to help bridge the damaged spinal cord are key to recovery.

Surprisingly, they didn’t just form new nerve cells. They also formed

cells that create the biological insulation that nerve fibers need to

communicate. A number of neurological diseases, such as multiple

sclerosis, involve loss of that insulation, called myelin.

“The actual cells that we transplanted, the human cells, are the ones

that are making myelin,” explained lead researcher Aileen of

the University of California, Irvine. “We’re extremely excited about

these cells.”

The research is reported in Monday’s issue of Proceedings of the

National Academy of Sciences.

Stem cells are building blocks that turn into different types of tissue.

Embryonic stem cells in particular have made headlines recently, as

scientists attempt to harness them to regenerate damaged organs or other

body parts. They’re essentially a blank slate, able to turn into any

tissue given the right biochemical instructions.

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But they’re not the only type of stem cell. and colleagues used

fetal neural stem cells, a type that are slightly more developed than

embryonic stem cells because they’re destined to make cells for the

central nervous system.

The researchers injured the spinal cords of mice and nine days later

injected some with the human neural stem cells.

Four months later, the treated mice could again step normally with their

hind paws. Mice given no treatment or an injection with an unrelated

cell showed no improvement.

The question was what sparked that improvement. Injections of stem cells

might simply stimulate the body to produce some healing factor, or they

might directly repair damage themselves.

'Striking' improvements

So injected the animals with diphtheria toxin, which kills only

human cells, not mouse cells. The improvements in walking disappeared,

suggesting it was the cells themselves responsible for recovery.

“It was striking,” said.

Finally, the researchers analyzed the actual mouse spinal cords to see

what the human stem cells had turned into. The hope was that they would

make neurons, or nerve cells, and some did.

But the bulk of the injected stem cells formed oligodendrocytes, a

different type of cell that forms myelin, the insulation coating that is

key for nerve fibers to transmit the electrical signals they use to

communicate.

The toxin step was key to ensuring the transplanted cells themselves are

functioning, and all researchers must provide such evidence because

different types of stem cells almost certainly will work by different

mechanisms in different tissues, said Dr. Doug Kerr, a s Hopkins

University neurologist who is performing similar spinal cord research

with embryonic stem cells.

Much more research must be done before testing stem cells in people with

spinal cord injuries, cautioned . One question is how soon after

an injury cells must be administered to have any effect — no one knows

how nine days in a mouse’s life correlates to the post-injury period for

a person. Also, the mice were bred to avoid immune system destruction of

the human cells, and suppressing a person’s immune system because of

similar transplant rejection risk poses big problems.

“The last thing we want to do is take someone who’s living a productive

life — if confined, we all understand that — and make them worse,” said

, who said the work also shows the need to study all types of

stem cells. “The exciting part is the potential is there.”

The research was funded by the nonprofit Reeve Foundation

and the National Institutes of Health. StemCells Inc. of Palo Alto,

Calif., provided the fetal-derived stem cells.

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