How to Build a Body Part

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THE HEART--AND BEYOND. One drawback with all these techniques is that it takes time, usually several weeks, to grow organs using the patient's own cells. Although using these cells sidesteps the rejection problem, time is a luxury many patients, particularly heart patients, can't afford. So Michael Sefton, who directs the tissue-engineering center at the University of Toronto, has proposed building a "heart in a box"--complete with chambers, valves and heart muscles--from cells genetically engineered to block the signal with which the body marshals cells to attack invaders. Sefton envisions spin-offs along the way--like immune-system-resistant replacement valves--to justify the project's $5 billion cost.

Replacement hearts--or even replacement heart parts--are at least a decade off, estimates Kiki Hellman, who monitors tissue-engineering efforts for the FDA. "Any problem that requires lots of cell types 'talking' to one another is really hard," she notes. Bone and cartilage efforts are much closer to fruition, and could be ready for human trials within two years. And what of those magical stem cells that can grow into any organ you happen to need--if the law, and biologists' knowledge, permit? "Using them," says Sefton, "is really the Holy Grail."