For seven years, scientists have tiptoed through an ethical minefield in their quest to see if unique cells in human embryos might some day be harnessed to treat disease.
Now two independent teams of researchers say they have harvested these cells, called embryonic stem cells, from mice using methods they hope may avoid the ethical morass - if the approaches can be made to work with humans.
Their results, appearing Monday on the website of the journal Nature, follow a study published in August that examined yet a third tack toward harvesting embryonic stem cells in a less controversial way.
Together, these efforts represent a bid to break the stem-cell impasse in the lab rather than in the courts or the halls of Congress.
This broad lab-based approach "is encouraging," says the Rev. Tadeusz Pacholczyk of the National Catholic Bioethics Center in Philadelphia, who holds a doctorate in neuroscience from Yale University. "You're using the power of science to develop a solution that gets around a very grave moral objection."
That objection centers on the most widely used method of harvesting stem cells from embryos, which destroys the embryos that hosted the cells. That method also involves cloning, although scientists insist that it is unethical to try to allow a cloned human embryo to come to term.
Many researchers hold that an embryo at the stem-cell stage does not constitute a human, and so its loss represents a small price to pay in exchange for the potential medical benefits they see in using stems cells. Indeed, they argue that it is unethical to stall or block embryonic stem-cell research.
For those who hold that life begins at conception, however, current harvesting techniques violate the sanctity of human life. Work on stem cells taken from adults, they say, is evidence that embryonic stem cells may be unnecessary for therapeutic use. (Stem-cell researchers say it's too early to know if adult stem cells hold the same potential as embryonic stem cells.)
Enter Alex Meissner and Rudolph Jaenisch, with the Whitehead Institute for Biomedical Research in Cambridge, Mass. They inserted genetic material from adult mice into mouse eggs emptied of their original nucleus. Then they fertilized the eggs, which began to divide and make stem cells. But before they inserted the adult DNA into the original egg, they turned off the gene linked to the process of implanting the embryos in a uterus. Thus, the embryo could not develop much beyond the stem-cell stage.
After the duo extracted the stem cells from the embryos, they removed the switch from the stem cells' genetic material, yielding cells genetically identical to the adults from whom the DNA was originally taken.
Thus, though the embryo was destroyed in the stem-cell harvesting process, it never could latch onto a uterus. This averts the issue of allowing a clone to come to term, says Mr. Meissner. And to some bioethicists, an early-stage embryo that stands no chance of forming anything more advanced lacks a human's ethical or moral standing.
This approach was first proposed by William Hurlbut of Stanford University's program in human biology, who is a member of President Bush's Council on Bioethics. He saw it as a possible way of averting the ethical stalemate over stem-cell research. He acknowledges that he's gratified by the Whitehead team's "proof of concept" results. "We should have started this search for a technical solution a couple of years ago," he says.
Meissner adds, "It gives us one potential idea for how to circumvent the ethical dilemma that has been tearing apart Congress and everyone else."
A second group led by Robert Lanza of Advanced Cell Technology in Worcester, Mass., took a different approach. In essence, his team employed a technique ordinarily used in fertility clinics to gauge the genetic condition of an embryo. When fertilized mouse eggs divided to reach the eight-cell stage, the team removed one cell. The remaining cell cluster could develop normally. The single cell was put in a petri dish with an already established line of stem cells. When the newcomer was removed and allowed to develop further on its own, it formed its own stem-cell line.
Some of these approaches have met with resistance, even from within the stem-cell research community.
In December, three Harvard scientists argued in the New England Journal of Medicine that the approach Dr. Hurlbut proposed - and the Whitehead team later executed - would yield no scientific benefit. Instead, they were concerned that such hunts would divert resources from more mainline embryonic stem-cell work. They added that the approach doesn't solve any ethical dilemma because in their view it incorrectly presumes that the ethical standing of an individual hinges on the action of a single gene.