Blood Carries Stem Cells to Brain

Patchwork. Neural stem cells can specialize into cells (green) that fix myelin, which is critical for nerve signals.

Injecting adult neural stem cells into the bloodstream of mice eases the debilitating symptoms of a disease similar to multiple sclerosis (MS). Although any application for humans is uncertain, scientists are intrigued by the possibility of simply delivering these cells via the bloodstream, rather than into the brain.

MS prompts the body's immune system to attack the myelin sheaths that help guide signals between neurons. Without sufficient myelin, patients develop brain lesions, have trouble walking, and suffer fatigue. Today, drugs that suppress the immune system are the treatment of choice, but researchers are also experimenting with stem cells and other cell types to rebuild the myelin sheath. Injected right into a lesion, such cells can fix the problem. The trouble is that patients tend to have many lesions, rendering direct injection impracticable.

Neurologist Gianvito Martino and his colleagues at San Raffaele Hospital in Milan, Italy, wanted to know whether adult neural stem cells could migrate to multiple brain lesions. To find out, they gave these cells to mice suffering from experimental autoimmune encephalomyelitis, a disease that closely resembles MS. Injected into either the bloodstream or spinal fluid, the stem cells found their way to the damaged areas where they turned into the more specialized oligodendrocytes cells and rebuilt the myelin sheaths. Forty-five days after injection, treated mice could walk again, the scientists report in the 17 April issue of Nature. The successful repair of myelin by intravenously injected neuronal stem cells could be a big step toward an improved therapy for humans, says Martino.

“The notion that you can target not just focal lesions but disseminated lesions using this type of delivery system is very powerful,” says Ian Duncan, a neuroscientist at the University of Wisconsin, Madison. “That's what I think the real take-home message would be.”

Related sites
Gianvito Martino's home page
Ian Duncan's home page

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