How to Build a Body Part

There's a human liver sitting in a lab dish in Madison, Wis. Also a heart, a brain and every bone in the human body--even though the contents of the dish are a few cells too small to be seen without a microscope. But these are stem cells, the most immature human cells ever discovered, taken from embryos before they had decided upon their career path in the body. If scientists could only figure out how to give them just the right kick in just the right direction, each could become a liver, a heart, a brain or a bone. When a team from the University of Wisconsin announced their discovery last fall, doctors around the world looked forward to a new era of medicine--one without organ-donor shortages or the tissue-rejection problems that bedevil transplant patients today.

Doctors also saw obstacles, though. One of them was a U.S. Congress skittish about research on stem cells taken from unwanted human embryos and aborted fetuses. Indeed, last week 70 lawmakers asked in a firmly worded letter that the Federal Government ban all such work.

Yet the era of "grow your own" organs is already upon us, as researchers have sidestepped the stem-cell controversy by making clever use of ordinary cells. Today a machinist in Massachusetts is using his own cells to grow a new thumb after he lost part of his in an accident. A teenager born without half of his chest wall is growing a new cage of bone and cartilage within his chest cavity. Scientists announced last month that bladders, grown from bladder cells in a lab, have been implanted in dogs and are working. Meanwhile, patches of skin, the first "tissue-engineered" organ to be approved by the U.S. Food and Drug Administration, are healing sores and skin ulcers on hundreds of patients across the U.S.

How have scientists managed to do all this without those protean stem cells? Part of the answer is smart engineering. Using materials such as polymers with pores no wider than a toothbrush bristle, researchers have learned to sculpt scaffolds in shapes into which cells can settle. The other part of the answer is just plain cell biology. Scientists have discovered that they don't have to teach old cells new tricks; given the right framework and the right nutrients, cells will organize themselves into real tissues as the scaffolds dissolve. "I'm a great believer in the cells. They're not just lying there, looking stupidly at each other," says Francois Auger, an infectious-disease specialist and builder of artificial blood vessels at Laval University in Quebec City. "They will do the work for you if you treat them right."

FLESH AND BONES. Treating bone cells right is what Charles Vacanti, an anesthesiologist and director of the Center for Tissue Engineering, has been doing at the University of Massachusetts Medical Center in Worcester. When that machinist lopped off the top of his thumb, Vacanti took some of the victim's bone cells, grew them in the lab and then injected them into a piece of coral fashioned into the shape of the missing digit. "Coral's got lots of interconnected channels for the bone cells to grow in," says Vacanti. It also degrades as bone replaces it. The patch was implanted back on the thumb a few months ago. "It looks like he's growing good bone," Vacanti reports. "He could get most of his function back."