South Korean researchers who stunned the world last year by becoming the first to clone human embryos have made their technique more efficient. Their purpose is to create embryos as a source for human stem cells for use in treating disease and injury. They have isolated several new stem cell lines from their latest embryo crop compared to only one line last year.

Researchers at Seoul National University report in the journal Science that they cloned the human embryos in the same manner as last year, by transferring the nucleus of skin cells into donated human eggs whose nucleus had been removed. The embryo clones artificially fertilized this way grew into a clump of cells in laboratory dishes genetically matched to the skin cell donors, who all had some disease or injury.

The scientists then removed stem cells from each embryo, showing they established several new stem cell lines. These are the basic, undifferentiated cells that can develop into any kind of tissue and are believed to have the potential to treat many illnesses.

The fact that the stem cells were genetically matched to the individual skin cell donors means that science has the potential to offer them specifically tailored therapies if they can be safely transplanted into their disease or injury sites.

"This brings us much closer to the day when clinical grade stem cells might be available," explained  University of Pittsburgh reproductive biologist Gerald Schatten, who advised the Korean laboratory on data analysis and preparation of their English-language paper.

"This year's announcement represents a stunning, spectacular set of breakthroughs in just one year," he said.

When the Korean researchers performed the procedure last year, they were able to create only one human stem cell line from the eggs of 16 women. That was a breakthrough in itself because human stem cells before then had been taken only from embryos obtained by conventional fertilization.

Nevertheless, last year's single stem cell line was the product of introducing skin cell nuclei from a healthy woman into her own eggs. This left the question of whether the process could be successful when implanting the nucleus of cells from a person of any gender, age, and health status into the egg of an unrelated donor.

The latest experiment shows that it can work. Gerald Schatten says the scientists used 18 egg donors and harvested stem cells from embryos grown from 11 diseased male and female skin cell donors ranging in age from two to 56.

"This year, their efficiencies have gone up between 10 to 16 times greater," he said. "Regardless of age, regardless of sex, regardless of infirmity, they have been able to establish stem cells that promise incredible breakthroughs in medicine and science."

The Seoul researchers believe this year's outcome occurred largely because they nourished the skin cells in the laboratory dish with specially-grown human cells instead of the more traditional method of feeding them with mouse cell nutrients. This avoids the possibility of introducing mouse diseases into the human cells, but Mr. Schatten says it appears to have another benefit.

"Maybe there are special factors that human cells have to feed human cells that mouse cells just cannot have to feed human cells," explained Mr. Schatten.

But the Korean stem cell success this year and last has caused several U.S. groups to fear that the work is a blueprint someone will copy to clone a baby. They are renewing their calls for laws to prevent this.

South Korea has such a law and regulations requiring the strict monitoring of stem cell research to ensure no human is created by cloning. Similar legislation has stalled in the United States because some lawmakers, such as Republican party Senator Sam Brownback, insist it ban not only the creation of cloned infants but also the making of cloned embryos for research.

"There is only one type of cloning, and when successful always results in the creation of a human," he said. "I, along with the President and the vast majority of Americans, do not believe that we should create a human life just to destroy it."

Many others, including Gerald Schatten, argue that banning embryo cloning for stem cell research prevents scientific inquiry they believe would dramatically improve disease treatments. They say allowing it would not weaken measures to prevent cloning people.

"Human reproductive cloning is unsafe, unethical, and ought to be illegal everywhere," he said.

While the debate rages in the United States, Bush administration policy bans scientists funded by the U.S. government from conducting research on human embryo stem cell colonies created after August, 2001, when President Bush introduced the regulation.