Scientists say they have created viable embryonic stem cell lines without destroying any embryos - a development that could clear ethical barriers that have sharply restricted federal funding for the controversial research.
Two separate techniques were demonstrated in mice, and researchers are optimistic the processes could be replicated with human cells. The new methods were published online Sunday by the journal Nature.
Scientists and ethicists said the approaches offer a potential compromise with social conservatives who see embryonic stem cell research as an untenable trade-off that amounts to destroying life to create medical cures.
Dr. William Hurlbut, an influential member of the President's Council on Bioethics, said he has persuaded several religious and conservative philosophers that at least one of the new approaches is morally sound.
Protection of human embryos has been the guiding principle behind President Bush's stem-cell funding policy.
One of the new approaches is based on a routine procedure used by fertility clinics to look for genetic defects in embryos.
Dr. Robert Lanza, medical director for Worcester, Mass.-based Advanced Cell Technology Inc. and an author of one of the papers, extracted a cell from a mouse embryo that developed into an eight-cell bundle.
After removing the cell, called a blastomere, Lanza's team surrounded it with embryonic stem cells from the Bush-approved lines, allowing it to pick up the appropriate biochemical cues to start behaving like one of them.
Using 125 blastomeres, they were able to create five cell lines that tests found had the same properties as embryonic stem cells.
When the seven-cell embryos were implanted into surrogate mothers, they resulted in live births 49 percent of the time, virtually the same as for regular eight-cell embryos.
Human stem cell lines could be created using single cells extracted for genetic diagnosis at in vitro fertilization clinics, Lanza said.
In a laboratory dish, the extracted cell would be allowed to divide into two. One cell could be screened for genetic defects and the other used to create stem cells, he said.
The other approach, developed by Massachusetts Institute of Technology biologist Dr. Rudolph Jaenisch, relies on deactivating a gene needed to implant an embryo into a uterus.
Jaenisch altered mouse DNA and inserted it into an egg whose own DNA had been removed using a common stem-cell procedure called nuclear transfer.
Because the resulting embryo could not attach to the uterus, it would have no chance to develop into a healthy baby, thus avoiding any ethical quandary. Hurlbut, the presidential adviser, strongly backs this approach.
After the DNA insertion, the egg was prompted to begin developing and stem cells were harvested a few days later.
To complete the experiment, the researchers turned the silenced gene back on. The resulting stem cells demonstrated the same abilities as traditional embryonic stem cells.