By Ron Winslow

Doctors at Yale University have successfully implanted a biodegradablescaffold seeded with a four-year-old girls own bone-marrowcells to help treat a serious heart defect, as WSJs Heartbeat column describes.

The tube about three inches long is made of polyester material similar to that used in the manufacture of dissolvable sutures. Six months after Angela Irizarrys surgery, it had disappeared, replaced by a bioengineered conduit that acts like a normal blood vessel.

The vanishing act for the scaffold was expected, but what happens to the cells, including stem cells, that spawned the new vessel?

Much to the researchers surprise, says Chris Breuer, the Yale pediatric surgeon leading the experimental tissue-engineering project, the cells go away too.

Stem cells and certain other bone-marrow cells have building-block properties that make them the foundation for more specialized cells that grow into the bodys various tissues and structures. Researchers have long believed that stem cells transplanted into heart tissue, for instance, would be a primary component of whatever new tissue that grew as a result.

A lot of people think that when you put cells in, they turn into whatever cells you want them to turn into, Breuer tells the Health Blog. Weve clearly shown that doesnt happen in our graft.

Indeed, in experiments performed to learn how the tubes morphed into blood vessels, Breuer and his colleagues transplanted their scaffold seeded with human cells into mice bred with deficient immune systems to prevent rejection of the cells. Within a few days, the human cellswere gone, replaced within the scaffold by mouse cells, including cells characteristic of those that line the inner wall of blood vessels.

Initially, I refused to believe it, Breuer says. I redid the experiment three different ways and saw the same thing every time.

The upshot: Transplanted cells that have a quality of stem cells dont buildnew parts themselves, he says.They cause the body to induce regeneration.

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In Treatment of Child’s Heart Defect, Doctors Find a Stem-Cell Surprise