The aim of the study was to show that a type of cloning, known as therapeutic cloning, could be used to generate embryonic stem cells, which have the potential to become any cell type in the body and thus could be used to regenerate diseased or damaged tissue.
Opponents to cloning, however, object to the technology because it requires the destruction of a human embryo to obtain the stem cells.
The new study "is a proof of principle for therapeutic cloning," said co-author Jose Cibelli, a professor of animal biotechnology at Michigan State University in East Lansing.
President Bush's 2001 mandate prohibits federal funding for this kind of research in the United States and Cibelli was careful to note it was done entirely in South Korea by a team of 14 researchers.
"It's a major medical milestone," Dr. Robert Lanza, a cloning expert and vice president of medical and scientific development at Advanced Cell Technology in Worcester, Mass., a biotech company that seeks to use cloning to generate medical therapies.
"It represents a major advance in stem cell research, which offers hope to millions of patients suffering from a long list of diseases," Lanza told United Press International. "I think it could help spur a medical revolution as important as antibiotics and vaccines."
Therapeutic cloning differs from reproductive cloning in that it aims to produce embryonic stem cells that are genetically identical to a patient's own cells. Having genetically matched stem cells would allow for producing tissues, such as brain or heart, that could be transplanted into the body, and which the immune system would not reject.
A major problem with transplanting organs, such as hearts, from one person to another is the immune system views the tissue as foreign and often tries to reject it in a potentially life-threatening reaction.
Scientists have cloned a variety of species from mice to horses but cloning humans has proven elusive because of both ethical and technical barriers.
The only previous documented attempt was in 2001 by Advanced Cell Technology. ACT's cloned cells only reached the four to six cell stage -- too early to obtain embryonic stem cells -- before dying.
A study with primate cells that came out last year suggested it might be impossible to clone humans but the new study, which appears in the Feb. 13 issue of Science, puts those questions to rest and shows it is technically possible to clone humans.
That raises concerns that rogue groups, such as the Raelians, could use the technology to reproduce humans. Chief study researcher Woo Suk Hwang, of Seoul National University in Korea, told a news conference in Seattle at the American Association for the Advancement of Science meeting Thursday the technique is difficult, even in the hands of skilled researchers, and noted his team was only able to clone females.
"In my humble opinion, it is not so easy a technology to replicate," Hwang said.
Lanza was adamant, however, the research increases the need for a ban on reproductive cloning.
Wednesday another non-mainstream group, Clonaid, which claims to have cloned as many as five babies, said it had cloned another child in Australia. None of these claims have been scientifically substantiated.
"Now that the methodology is publicly available ... it is absolutely imperative that we pass laws worldwide to prevent the technology from being abused for reproductive cloning purposes," Lanza told UPI. "We need to get past all the political and religious squabbling, and outlaw human reproductive cloning, a position almost every country and scientist agrees with."
Donald Kennedy, Science's editor-in-chief, told the news conference the accomplishment "extraordinary" and said it has important long-range therapeutic applications.
In the experiment, the South Korean researchers extracted the nucleus or DNA material from a cell known as a cumulus cell and placed it in egg cells in which the nucleus had been removed.
The researchers noted that ethical procedures were carefully followed, including getting the study approved by a committee on human subject research protections, and emphasizing women who donated cells did so voluntarily and without financial payment.
Using various chemicals in a lab dish, the researchers stimulated the resultant egg cell to begin dividing just as it would in a normal pregnancy. From the 30 that reached the blastocyst stage, a ball of 32 cells or more, the researchers obtained one embryonic stem cell line. These cells, which were a genetic match to the woman who donated the initial cells, showed evidence of being capable of giving rise to all the cell types in the body, including muscle, bone, cartilage and brain.
"The question is when are we going to see this coming into the clinic" to be used as treatments in human patients, Cibelli said. "That's going to be a long time" because limited funding for cloning and embryonic stem cell research in the United States -- the largest funding source by far of biomedical research -- will slow the speed of progress.
"I would say five years but that's the same thing as saying I don't know," Cibelli said.
Other experts said the study already is generating enthusiasm about the prospects of therapeutic cloning, which may help propel the field along.
"Anytime a technical barrier is passed, lots of people get emboldened to jump into the field," Dr. George Daley, a stem cell biologist at Children's Hospital in Boston, told UPI. "Already my post-docs have come to me and said, 'Why don't we start doing with human cells what we're doing with mouse cells right now?'"
Creating new lines of human embryonic stem cells using federal funding would not be permissible under Bush's decree, issued in August of 2001, which limits government-funded research to lines of embryonic stem cells already in existence. In addition to cloning, new lines of embryonic stem cells could be obtained from surplus eggs from in vitro fertilization clinics.
There are no U.S. regulations that would bar the creation of new stem cell lines using private funding.
"There are real advantages to doing experiments on human cells," Daley said. "And it makes the work more likely to have meaningful clinical applications, which puts us that much closer to be ready to treat a patient."
Arthur Caplan, director of the Center for Bioethics at the University of Pennsylvania in Philadelphia, said the research is likely to stir up the debate on both side of the issue, among those who oppose it and those who think it could lead to medical breakthroughs.
"Each will find reason to renew their attention to this issue," Caplan said.
Richard Doerflinger, deputy director of abortion opposition activities for the U.S. Conference of Catholic Bishops, told UPI the advance increases the urgency with which Congress, particularly the Senate, should enact a ban on any form of cloning.
The House has twice passed a total ban on cloning, a view endorsed by Bush, but the measure has stalled in the Senate because some senators, such as Arlen Specter, R-Pa., want to permit therapeutic cloning.
Doerflinger noted that although cloned embryonic stem cells were obtained in the study, there still was no evidence these would prove therapeutically beneficial. He added even if future studies showed this technique could lead to medical treatments, his group still would oppose it.
"If this is fundamentally wrong, there's no benefit that could outweigh that," Doerflinger said.
Most stem cell scientists, on the other hand, think cloning studies in animals offer persuasive evidence that this technique could be used to generate cells to replace damaged and diseased tissue. A study in mice last year, for example, showed cloning could be used to alleviate symptoms of Parkinson's disease.
Caplan noted, however, the debate over whether to allow cloning research may be moot because the new study is demonstrative of the fact it is going forward in other countries, including Singapore and Britain.
"So the debate about cloned embryo research is not whether it's going to happen but where," he said. "(The study) may also give some states stimulus to pass legislature supporting (cloning)."
California and New Jersey have passed legislation allowing human cloning and Delaware and Massachusetts soon may follow suit, he said.
Daley and Lanza said, however, without the vast funding the U.S. government can offer, progress in this research will lag.
A number of private patient groups have raised money "but they can't fill the shoes of the government," Lanza said. "It's very unfortunate ... because this work could've been done as long as three years ago" if the United States government had put its tremendous resources behind it.
Lanza blamed the funding limitations on "various evangelical groups and Catholics," and said they are unfairly denying potential medical treatments to people who could benefit from them.
"How would they feel if their child needed a lifesaving blood transfusion and the Jehovah's witnesses said, 'No, you can't do that because we object to it'"? he said.
UPI's Science and Technology Editor Phil Berardelli contributed to this story from Seattle.
Steve Mitchell is UPI's Medical Correspondent. E-mail email@example.com