The South Korean scientists who last year cloned the world's first human embryo have surmounted another hurdle in stem-cell research, reporting yesterday that they have created 11 new embryonic stem-cell lines that are matched genetically to injured or sick patients.

The development marks a significant advance in therapeutic cloning, the fast-paced but controversial field that aims to make customized heart tissues for heart-attack patients, nerves for patients with spinal-cord injuries and a host of other laboratory-grown spare parts genetically tailored to patients who need them.

"I didn't think they would be at this stage for decades, let alone within a year," said Dr. Gerald Schatten of the University of Pittsburgh. He acted as an adviser to the South Korean team.

"This paper will be of major impact," said stem-cell researcher Dr. Rudolph Jaenisch of the Whitehead Institute for Biomedical Research in Cambridge, Mass. "The argument that it will not work in humans will not be tenable after this."

The single previous claim that stem cells had been derived from a cloned human embryo, reported last year by the same team at Seoul National University's College of Veterinary Medicine, left some scientists doubting the results. Moreover, the process appeared hopelessly inefficient, requiring almost 250 eggs extracted from women to produce one cloned embryo with its precious cache of stem cells.

In the new experiments, reported in the online edition of the journal Science and funded entirely by South Korea, the team needed only 17 eggs on average to make each batch of stem cells. That means a single procedure of the sort used routinely in fertility clinics is now adequate to produce a colony of personalized cells with the potential to treat a wide spectrum of diseases.

If therapeutic cloning can be achieved with the same efficiency as such a widely accepted medical procedure, it will undercut an ethics argument against it: that it would require egg donations by countless women — at some risk — to make enough embryos and stem cells to be medically useful.

"I think this paper will have enormous impact on the political discussion," Jaenisch said.

The researchers also insisted that their progress will not make things easier for anyone attempting to clone a baby, which they think is impossible.

"Reproductive cloning is not our goal," said Woo Suk Hwang, who led the research. "Reproductive cloning is unsafe and unethical, and so it shouldn't be done in any country."

Escalating battle

The report comes at a delicate time in the escalating U.S. battle over funding of embryonic stem-cell research. Because culling stem cells destroys embryos, President Bush in 2001 banned federally funded research on all but a few old lines. The House is expected to vote by the end of the month on legislation that would loosen those restrictions.

That legislation would not allow funding of cloning research like that done in South Korea — a kind of research the House has twice voted to ban and over which the Senate has deadlocked for years. Rather, it would facilitate the less-contentious use of frozen embryos about to be discarded by fertility clinics.

Several countries, including South Korea, Singapore and Britain, have given their blessings to research on cloned human embryos, and promulgated ethics rules for such work.

A cloned embryo is made from a single cell — often a skin cell — taken from the person or animal to be cloned. The cell then is fused to an egg from a donor.

In the latest experiments, the team started with 185 eggs donated by 18 unpaid women. The women underwent a monthlong series of hormone shots followed by the extraction of about a dozen ripened eggs from their ovaries.

Each egg had its DNA removed and then was fused to a single skin cell taken from one of 11 patients, then allowed to grow into an early embryo. The patients, ages 2 to 56, had either a spinal-cord injury, diabetes or an inborn disease of the immune system.

Of those 185 attempts, 31 grew into embryos in laboratory dishes. The team extracted stem cells from 11 of them. Each of the resulting colonies of stem cells is a genetic and immunological match to the patient who supplied the original skin cell.

The overall efficiency was about one cell line for every 17 eggs. The procedure was even more efficient with eggs from the youngest donors. For eggs retrieved from women younger than 30, one cell line was obtained for every 14 eggs.

In another major advance, the South Koreans said they are cultivating the stem-cell lines in dishes without any animal cells. Most other human embryonic stem-cell lines have been grown on mouse cells, which secrete a cocktail of hormones that support the growth of finicky stem cells.

By growing the stem cells on a bed of human-support cells instead of mouse cells, the team does not have to worry that animal viruses or other contaminants may prevent transplanting the stem cells, or tissue grown from them, into patients.

"We want to find a way to cure devastating diseases, and one of the big points of our research is patients (now) have immune-matched, cloned, embryonic stem cells," Hwang said.

The team is working to transform the cells into kinds of tissues — a process at which scientists are becoming increasingly adept — but has no current plans to put them into patients, Hwang said.

Several experts said they were extremely impressed and predicted that the first therapeutic-cloning treatment would come more quickly than they had imagined.

"They have increased the efficiency tenfold over what their paper was a year ago, and this is very important," said John Gearhart, a stem-cell researcher at Johns Hopkins University. "It's kind of remarkable. It tells you how quickly things are moving."

Others voiced concerns.

"You're placing the woman at risk to create an embryo that has a 100 percent risk of death, to attempt to treat patients who themselves will face significant risks," said Richard Doerflinger, deputy director of pro-life activities at the U.S. Conference of Catholic Bishops.

"To say something was initially impossible but is now possible is not enough," he said. "We have to make moral decisions about whether we should do this."

Compiled from The Washington Post, the Los Angeles Times, The Associated Press and Newsday.