A team of South Korean researchers announced a major advance in human cloning this week, offering a powerful new tool in the war on disease and adding urgency to an international debate over the ethics of cloning technology.
The researchers, who will publish their work today in the online edition of the journal Science, placed genetic material from a Korean volunteer into a human egg cell and coaxed it to develop into a blastocyst, a cluster of about 100 cells that is substantially more advanced than any embryo previously known to have been created in a human cloning experiment.
In another first, the team also extracted embryonic stem cells, powerful cells with the ability to become any other kind of cell, from the cloned blastocyst.
The researchers did not allow the blastocyst to develop further, and stressed that they would not attempt to use the technique to create a cloned baby.
The work, which arguably represents the first successful attempt at human cloning, could have tremendous implications for both science and medicine. In the immediate future, scientists said, the ability to create stem cells this way will give researchers a powerful tool to study a wide range of diseases, from diabetes to Parkinson's. Over the long term, the same type of technique could be used to generate a limitless supply of healthy replacement cells, all genetically identical to a patient in need.
"I would congratulate them on having done a really important experiment," said Douglas Melton, a top stem cell biologist and professor at Harvard University.
But the work, which was led by Woo Suk Hwang of Seoul National University, also plays into a highly charged debate. The ethical questions about human cloning are far from resolved, and many political leaders have called for restraint on the use of lab techniques to create cloned human embryos.
The paper also describes the precise recipe used to perform the cloning, making it easier for fringe scientists to attempt to create a cloned baby -- or for charlatans to claim they are able to do so.
The Bush administration imposed restrictions on human stem cell research in August 2001, barring scientists from using federal funds to work with any embryonic stem cells except those on a list compiled before the announcement. Scientists in the United States could not have used federal money to do the Korean work or to work with the cells that resulted.
Some researchers said the fact that the work was done in Seoul, and not a US research center like Boston or Berkeley, Calif., is a jarring reminder that the government's decision has largely taken American science out of the front lines of a key arena in biology.
"It is very frustrating," said Dr. Irving Weissman, a professor at Stanford University who first isolated stem cells.
In 2001, the Worcester-based company Advanced Cell Technology garnered headlines around the world when it announced that it had created the first cloned human embryo. But scientists later dismissed the claim as unfounded because the egg cells in that experiment divided into just a handful of cells before dying -- not enough to demonstrate that they were reproducing using their new genetic machinery.
The only American coauthor of today's paper, Jose B. Cibelli of Michigan State University, said the Korean team surprised him when they sent him an e-mail last June asking him to critique their work. Cibelli, in his former job as researcher at Advanced Cell Technology, had published the first paper describing an experiment cloning human cells, and he was stunned at the Koreans' work.
Cibelli said the Koreans' cloning technique is similar to Advanced Cell Technology's, but they improved it in several ways, including a gentler method of removing genetic material from the cells, "and that made all the difference." The researchers pointed out that there was a small chance that they were misinterpreting their data, but scientists said the evidence was quite convincing.
"I think they have done it," said Dr. Rudolf Jaenisch, a researcher at the Whitehead Institute for Biomedical Research, who was involved in reviewing the paper for Science and is one of the world's leading specialists on cloning.
The team used a total 242 egg cells from 16 female volunteers. The donors "were fully aware of the scope of our study and signed an informed consent form," they report in the Science paper.
Over the course of several trials, they experimented with different recipes for treating the eggs after they were implanted with genetic material. In the end, they settled on a method that brought 29 percent of the cloned egg cells to the blastocyst stage -- a rate that several scientists said was impressive. All told, the experiment yielded 30 blastocysts.
Within each blastocyst is the "inner cell mass," where embryonic stem cells grow, the beginning of what would eventually develop into all the tissues in the human body. Of the 30 blastocysts, though, the team was able to isolate only one line of stem cells.
Using this technique, or the more refined ones that are sure to follow, scientists will now be able to engineer human embryonic stem cells with virtually any genetic profile they want. For example, they could create an embryonic stem cell with the exact makeup of a patient with type 1 diabetes, explained Melton. They could experiment on these stem cells to discover exactly what goes wrong to cause the disease.
This possibility -- multiplied by countless diseases -- explains the profound excitement in scientific circles at the announcement.
At the same time, all reputable scientists agree that using the technology to attempt to create a baby, a practice known as human reproductive cloning, would be disastrous. Cloned animals have a wide variety of ailments, some quite bizarre, and a cloned baby would almost certainly suffer from enormous medical problems. "It is absolutely imperative that we pass laws worldwide to outlaw human reproductive cloning," said Robert Lanza, medical director for Advanced Cell Technology. "The recipe is out there."
Scott Allen of the Globe staff contributed to this report. Gareth Cook can be reached at email@example.com.