But obtaining human embryonic stem cells has been controversial, because until now it required the destruction of living embryos.

In the current technology, embryonic stem cells are derived by extracting a mass of cells from an embryo.

Since an early embryo is made of only a few cellsabout eight to tentaking enough to create viable cultures kills the embryo.

"Many people, including [U.S.] President Bush, are concerned about destroying life in order to save life," Lanza said.

U.S. law currently prohibits the use of federal funds for research in which a human embryo is destroyed.

Colony of Stem Cells

Last year Lanza's team showed that it's possible to remove a single cell from a mouse embryo without destroying the embryo.

Through various manipulations, the team grew that cell into a colony of mouse embryonic stem cells.

The extraction procedure is similar to that used during in vitro fertilization to remove a single cell for preimplantation genetic diagnosis (PGD).

PGD is a very early form of diagnosis that tests a human embryo for genetic abnormalities before it is implanted in a woman's uterus.

"This is a relatively simple biopsy procedure that has been used to generate over 2,000 healthy babies," Lanza said.

(See 3-D illustrations of a fetus growing in the womb.)

Using spare human embryos from in vitro fertilization for their most recent study, the scientists used a tiny pipette to extract one cell from each embryo and then grew each cell in a hormone-laden culture.

Just like in the case of PGD tests, embryos with only one cell removed would have survived and gone on to grow into fetuses. To get the most from their samples, however, Lanza's team took several cells from each embryo, destroying the embryos in the process.

From a total of 91 cells taken from 16 embryos, Lanza said his team "obtained two stable human embryonic stem cell lines, which have been growing over eight months at this point."

He says the new stem cell lines behave exactly like conventional embryonic stem cells.

"The resulting cells could be used for genetic testing as well as to create stem cells without affecting the subsequent chances of [the embryos developing into children]," Lanza said.

Ethical Quandary Resolved?

Ronald M. Green, director of the Ethics Institute at Dartmouth College in Hanover, New Hampshire, says the research directly addresses the ethical concerns that many people have about stem cell research.

"It is very, very unusual for scientific research to resolve an ethical quandary, and this is one of those rare instances," Green said. "I do believe it solves the ethical problems."

(Explore the stem cell debate in National Geographic magazine: see photos, take a poll, and join the forum.)

Scientists hope the results will soon lead to the release of U.S. federal funding for embryonic stem cell research.

"This could conform to both the ethical and maybe even the legal thinking that has motivated the [U.S.] President to oppose this," Green said.

"I hope he sees this as an opportunity consistent with his values."

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embryonic stem cells - National Geographic News