South Korean scientists have dramatically sped up the creation of human embryonic stem cells (search), growing 11 new batches that for the first time were a genetic match for injured or sick patients.

It is a major advancement in the quest to grow patients' own replacement tissue to treat diseases.

The same scientists last year were the first to clone a human embryo. Now they have improved, by more than tenfold, their efficiency at culling these master cells, thus making pursuit of therapeutic cloning more practical.

"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 Korean lab in analyzing its data, which was being published Friday in the journal Science.

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

This research is not cloning to make babies. Instead, scientists create test-tube embryos to supply stem cells — the building blocks which give rise to every tissue in the body — that are a genetic match for a particular patient and thus won't be rejected by the immune system.

If scientists could harness the regenerative power of those stem cells, they might be able to repair damage from spinal cord injuries, diabetes (search), Parkinson's and other diseases.

Stem cells also can come from embryos left over in fertility clinics. But these cells would not be a genetic match for any patient.

Any potential therapy is years away from being tested in people. But the new research marks several advances:

_Last year's cloned stem cells were from one healthy woman. This time, the Seoul scientists created stem cells that were genetic matches to each of 11 patients — male and female, as young as age 2 and as old as 56, suffering either spinal cord injuries, diabetes or a genetic immune disease.

_Last year, it took attempts with 242 donated human eggs to grow one batch of stem cells. This time, it took an average of 17 eggs per batch and 14 eggs if they were from women younger than 30.

_The researchers eliminated use of mouse "feeder cells" that, until now, have been used to nourish human stem-cell lines, easing concerns about animal contamination.

The research also will add to political sparring over whether to expand government-funded stem cell research in the United States.

Because culling stem cells destroys the days-old embryo harboring the cells, President Bush in 2001 banned federally funded research on all but a few old embryonic stem-cell lines. A vote on whether to ease those restrictions could come in the House as early as next week.

The South Korean research, funded by the South Korean government, spotlights the frustration that many U.S. scientists feel at being left behind.

"It's just going to highlight the tragedy of our current situation in America where there are technologies that are promising that are not being pursued by talented American scientists because of ideologic constraints," said Dr. Janet Rowley of the University of Chicago. The genetics specialist helped write recent national ethics guidelines on stem-cell research.

The lead South Korean researcher, Hwang Woo-suk of Seoul National University, said in a telephone interview, "Therapeutic cloning has tremendous, tremendous healing potential, but we have to open so many doors before human trials."

More immediately, the research will allow scientists to watch the very earliest origins of diseases such as Alzheimer's form inside an actual patient's cloned, living cells, said neuroscientist Fred Gage of the Salk Institute for Biological Studies in San Diego. That could point to new ways to prevent and treat illness, said Gage, who plans to perform some of that work.

The Seoul researchers collected eggs that were donated by 18 unpaid volunteers and removed the gene-containing nucleus from them.

The scientists inserted into those eggs DNA from skin cells of the 11 patients and chemically jump-started cellular division. Thirty-one blastocysts — early-stage embryos of 100 or so cells each — successfully grew. From those, the scientists harvested 11 stem cell lines.

Each is a genetic match to the patient who had donated a skin snippet, and each can form other tissues, such as brain cells or bone cells. Next, the scientists must learn how to control that cell development.

The work means there may be more demand for donated eggs for medical research. Women considering doing so must understand they get no benefit and face some risk, said Stanford University bioethicists David Magnus and Mildred Cho.

The advances do not mean it is time to try reproductive cloning, Hwang said. That, he said, "is unsafe and unethical," noting that animal studies show more failures than successes. "Biologically, it may be impossible."