Snuppy, born to a yellow Labrador retriever, appears to be a normal Afghan puppy, physically as well as genetically identical to the 3-year-old male whose cells were used to clone him.

The point of the feat, they stressed, is not to create duplicates for pet owners but to advance medical and veterinary science. The researchers want to establish lines of embryonic stem cells from dogs to see whether they might lead to safe and effective treatments for diseases that occur in dogs as well as people -- such as heart disease, diabetes, dementia, blood disorders and cancers.

"It's important to work with diverse populations of dogs -- not just inbred mice -- before testing stem cells on people," said Dr. Gerald Schatten, a reproductive expert at the University of Pittsburgh Medical School who co-authored the paper published in the scientific journal Nature.

Stars in Stem Cell Research

Since Dolly the sheep was cloned in 1996, many other animals have followed: mice, rats, cats, cows, goats, pigs, rabbits, a horse, a mule. But cloning a dog has proved stubbornly difficult.

The researchers who pulled it off, though credentialed animal cloners, are better known as stars in stem cell research. Led by veterinarian Woo-Suk Hwang, the team startled the world in February 2004 by announcing it had successfully derived stem cells from a cloned human embryo.

Hwang earlier had created Korea's first cow using in vitro fertilization (1993), its first cloned cow (1999), cloned pigs (2002) and cloned cows resistant to mad cow disease (2003).

The team named its latest achievement Snuppy, for Seoul National University puppy.

Cloning involves removing the gene-bearing nucleus of an egg and replacing it with the nucleus of a cell taken from the animal scientists want to clone. Scientists then chemically jump-start cell division, producing early embryos to be implanted in a female surrogate.

The problem with dog cloning is that, unlike humans, canines don't respond to hormone treatments meant to stimulate ovulation. Nor can scientists force the surrogates to come into heat to carry the cloned embryos.

So the researchers had to carefully monitor the hormones of numerous female dogs so they would know the right time to collect eggs and implant the clones.

After harvesting the eggs, they replaced the eggs' genetic material with the nuclei of cells taken from the ear of an adult Afghan hound, a male.

The 1,095 viable embryos that resulted were transferred into 123 surrogates, resulting in three pregnancies. One fetus miscarried, and two others were carried to term.

One of the clones died of aspiration pneumonia when it was 22 days old. "No major anatomical anomalies were evident post mortem," the researchers wrote.

'Major Breakthrough'

Snuppy, born to a yellow Labrador retriever, appears to be a normal Afghan puppy, physically as well as genetically identical to the 3-year-old male whose cells were used to clone him.

"Prof. Huang is embarking on a major project to develop dog stem cells after nuclear transfer," Schatten said. "But we must first demonstrate (even in just one dog) that nuclear transfer succeeds. This is the major breakthrough."

The researchers admit that the efficiency of dog cloning is still very low: two live births from 123 surrogates.

Nor is it likely to improve much, said Dr. Mark Westhusin, director of the reproductive sciences laboratory at Texas A&M University, who cloned the first cat. He achieved two pregnancies -- one survived 37 days, the other was stillborn -- when he tried to clone a dog.

"You basically have to have hundreds -- if not thousands -- of dogs that you're watching every day for when they're starting to come into heat," he said.

"Then you've got to do hormonal assays to figure out when they're ovulating. And you have to schedule surgery to collect your ova from the ovaduct. And you need other dogs that are basically in synchrony with your donors so you can transfer the embryos into them after you've made them and hope they'll carry them to term."

Terming such work "a nightmare," Westhusin gave up more than two years ago. "Until you can get the eggs to mature in test tubes, you've got to go collect them from the dog. And until you can get them to come into heat when you want, dog cloning is not going to be very practical at all."

Treatments for Incurable Diseases

The Seoul team's success at harvesting stem cells from cloned human embryos represented a first step toward someday taking cells from an ill person and creating individualized treatments for incurable diseases, said Hwang and his colleague Dr. Moon Shin-yong.

Critics fear that the techniques developed in this field -- called therapeutic cloning -- could be used to create cloned babies. The term for that is reproductive cloning, and to prevent it the critics want Congress to ban all human cloning.

A similar outcry may follow the birth of Snuppy, although commercial dog cloning still seems a long way off.

"It is important to keep in mind the huge cost involved in creating the first cloned dog," said Arthur Caplan, a dog fancier and director of bioethics at the University of Pennsylvania. "The failure rate in terms of dead animals and embryos was staggering and it took a huge effort scientifically and practically to get this done.

"Right now, this remarkable breakthrough really demonstrates feasibility and the skill the Korean group has developed in cloning techniques," he added. "The prospect of cloning pet companies or even cloning dogs for research is still far off in the future."

The nation's leading registry of purebred dogs, the American Kennel Club, which could be directly affected if champion dogs could be cloned, said in a statement that its board of directors was reviewing the issues raised by the possibility of registering, breeding or exhibiting cloned dogs.

"There is hardly any animal that generates more interest when it comes to cloning than dogs -- and that includes human beings," Caplan said. "The announcement will surely rekindle the debate about the morality of cloning pet animals since there are many who might choose to do so and not a few entrepreneurs who will want to cash in on that desire."

'Medical Research, Not for Cloning Pets'

Some experts used the announcement as an occasion to reiterate their opposition to reproductive cloning of humans.

Dr. Robert Schenken, president of the American Society for Reproductive Medicine, said the report of successful canine cloning shows "yet again the exciting promise of the technology of somatic cell nuclear transfer," which he said has the potential to develop lifesaving technologies.

"However, it also points out that in dogs as in most species, cloning for reproductive purposes is unsafe," Schenken said.

The cloner of Dolly the sheep, Dr. Ian Wilmut of the University of Edinburgh, congratulated the South Korean team "on another great success" and called for a global ban on human reproductive cloning.

"Successful cloning of an increasing number of species confirms the general impression that it would be possible to clone any mammalian species, including humans, given an optimized method," he said.

Hwang said he agreed with Wilmut. "Our research is medical research, not for cloning pets," he said. "Human reproductive cloning is unsafe, unethical and should be illegal -- just as it is illegal in Korea."