By John Carey and Ellen Licking
Versatile stem cells are biology's answer to a blank canvas on which many wondrous scenes can be painted. Blessed with the ability to become any tissue of the body, they have the potential to restore a failing heart, tame the tremors of Parkinson's, cure diabetes, or treat uncounted other ills.
There's an enormous catch, however. One of the best ways to obtain stem cells is to strip them from a human embryo -- destroying it in the process. It's no surprise, then, that the Bush Administration has banned the use of federal research dollars for work using stem cells created through the destruction of additional embryos, nor that Congress is considering a ban on cloning, which could someday offer a bounteous source of such cells.
But as Congress debates the emotionally and politically charged issues of embryonic stem cells and cloning, science is forging ahead with extraordinary speed. Now come new findings that may offer a way around any restrictions lawmakers impose, while raising even deeper questions for ethicists to ponder.
In late January, scientists at the University of Minnesota revealed that cells from adult bone marrow can match the ability of embryonic stem cells to turn into nerves, muscle, liver, and other specialized tissues. And in the Feb. 1 issue of Science, a team of corporate and academic researchers reports that unfertilized monkey eggs can be induced to provide stem cells with similar amazing potential. If the same process works in humans, "it creates an ethical alternative [to using embryos] that people can be comfortable with," says Kent E. Vrana of Wake Forest University School of Medicine, an author of the Science report.
Some foes of embryo research agree. "Many of us have said we would support stem-cell research that does not result in the destruction of embryos," says C. Ben Mitchell, a senior fellow at the Center for Bioethics & Human Dignity, a Christian-backed nonprofit in Chicago.
Yet ethicists warn that the latest results pose fresh dilemmas. If a stem cell, regardless of its derivation, can be transformed into any type of cell, then it theoretically has the potential to create a human. So, asks Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania, does that make it the functional -- and moral -- equivalent of an embryo?
While politicians and ethicists argue, the science continues to advance. Witness the recent work of Dr. Catherine Verfaillie at the University of Minnesota, who demonstrated the enormous flexibility of certain adult cells. Verfaillie extracted cells from bone marrow, grew them in petri dishes for up to two years, and showed that they could turn into everything from liver and cartilage to brain cells.
The work reported in Science takes a different tack. Researchers at Advanced Cell Technology (ACT) in Worcester, Mass., and several academic centers start with eggs from female monkeys. Bathed in a chemical soup, then zapped with jolts of electricity, the eggs begin developing into embryos, a process known as parthenogenesis.
At ACT, embryos created in this fashion haven't survived for long. But a few have reached the blastocyst stage, consisting of about 100 cells. That's enough for ACT's researchers to extract some of the inner cells and create a long-lived line of stem cells, capable of being transformed into many different types of tissue. "We found hard tissue, smooth muscle, hair follicles, pigmented epithelial cells, and gut cells," says Wake Forest's Vrana. In one experiment, a high proportion became brain cells that produce a chemical called dopamine -- precisely the type of cell that is damaged by Parkinson's disease. "That is spectacular," says Michael D. West, president and CEO of ACT. "No one has seen that before."
The potential is huge. Eventually, scientists may be able to extract an egg from a woman, jolt it down the path toward an embryo, extract stem cells from it, and use them to cure ailments. The cells would have virtually the same genes as the woman's own, so they could be injected back into her without risk of rejection. "We could make anything a woman needed," West says. "Young blood cells or heart cells or neurons -- that is the dream." Males would be trickier, but ultimately possible, he says.
That is, if the procedure can leap all the hurdles: scientific, political, and moral. "Are parthenogenetically created embryos biologically identical to other kinds of embryos?" asks Mitchell. "This is a discussion we need to have." Perhaps tricking unfertilized eggs into becoming embryos for research will prove as morally repugnant to right-to-lifers as using the old-fashioned kind. After all, says biotech foe Jeremy Rifkin, president of the Foundation on Economic Trends, "you are still talking about an embryo." But by the time politicians resolve that question, scientific discoveries are bound, once again, to shift the debate to a whole new level.
Carey and Licking cover science from Washington and New York