It made big headlines two years ago, even though it wasn't quite ready for prime time. Now researchers say they have made good on the promise of generating stem cells from embryos without destroying the latter in the process.

A team led by researchers from Advanced Cell Technology (ACT) in Worcester, Mass., reports in Cell Stem Cell that it created five new stem cell lines by plucking single cells from embryos in the early blastocyst stage, a grapelike cluster of eight cells called blastomeres. Researchers normally create this kind of stem cell line at a more developed stage from the entire mass of embryonic cells.

The group says the embryos survived the removal of a blastomere or two and grew normally to the 10-cell stage 80 percent of the time, the same rate as untouched IVF (in vitro fertilization) embryos. IVF doctors routinely take single cells from embryos to check for genetic diseases before implanting them in the womb.

"If we base this on objective scientific criteria, there's no evidence that removing a single blastomere harms the embryo," says Robert Lanza, ACT's chief scientific officer. The frozen embryos were set to be discarded by IVF clinics, but donor couples instead consented to their use for research.

It is up in the air whether research on cells created this way qualify for federal funding under current restrictions. But if it does, Lanza says it could double or triple the number of stem cell lines available to researchers in a matter of months.

Lanza and other stem cell researchers, including Atala, applied to the National Institutes of Health last February for a federal grant to compare the potential of stem cells derived from single blastomeres with those isolated from amniotic fluid or other sources. Lanza says they are still waiting for a decision.

"Whether it doesn't harm the embryo, I don't think we're ready to answer that question fully," says stem cell researcher Anthony Atala, directory of the Wake Forest Institute for Regenerative Medicine, who was not part of the study. But if true, "that means you're using embryos that no one has an issue with," he says.

Preliminary findings were widely reported last August as the creation of embryo-safe stem cells, but the embryos in that study had as many as seven cells removed and there was no follow-up to monitor whether they had developed normally, which they probably would not have. They were also grown in close proximity to each other as well as to embryonic stem cells created in the usual way, making it unclear whether the freshly generated embryos could have survived on their own.

Lanza says the team had to pile up plucked cells in that study because they tended to grow into balls of tissue that typically develop into placentas—not fetuses. To get over that hurdle, his group incubated the plucked stem cells for 12 to 24 hours next to their parent embryos, and added a protein to inhibit the formation of the preplacental tissue.

The paper, co-authored by researchers from the University of California, San Francisco, and Wake Forest University School of Medicine in Winston–Salem, N.C., reports success with four of 41 embryos generated and cultured alongside preexisting stem cells, and one of two cultured without other stem cells, compared with a 2 percent success rate in the first study.

President George W. Bush twice vetoed legislation that would have lifted a ban on federal funding for new lines of embryonic stem cells; the measures would have provided federal monies for research on stem cells from frozen embryos at fertility clinics that donors were planning to discard but had consented to hand over to scientists.

The new method would arguably bypass current objections that embryos not be destroyed to make stem cells. And a higher efficiency makes it more practical to use IVF embryos, which number around 400,000 nationwide, according to a 2003 RAND study.

Atala says he will likely begin creating new cell lines from single blastomeres using private funding. He said he had no definite start date or number of new lines in mind. "You could easily create four to five lines a month, if need be," he notes.

Lanza says that so-called induced pluripotent cells (stemlike cells generated directly from skin tissue) may have great potential, but that research on them is only in its early stages. Researchers are still in the dark about many aspects of stem cells, especially how to grow them to replace worn-out tissue in patients.

Studying the real thing, he adds, could give them a big leg up.