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Some Pigs!

After successfully cloning five piglets earlier this month, researchers hope to create a human-compatible pig within a year and say they want to start clinical trials within four years.

The piglets were delivered March 5 at the Virginia-Maryland College of Veterinary Medicine at Virginia Tech.

But the day after the cloning success was announced, there was widespread debate about the ethics of cloning, reported CBS News Correspondent Richard Roth.

Ethicists are urging caution, however, about this latest advance until questions are explored about what diseases the brave new world of transplanting animal organs into people may yield.

"The main ethical concern is the possibility - we don't know how likely - but the possibility of establishing a whole new source of infectious disease," ethicist Dr. Thomas Murray said.

Advancing technology suggests human cloning is moving well within the realm of scientific possibility. And another question being raised is, whether there is a difference between producing livestock for food and raising it so living organs can be harvested for human use?

"I'm against cloning humans," Dr. David Ayares of PPL Therapeutics told CBS News Wednesday morning. "We're focused on using cloned animals for therapeutic purposes."

"I can't think of any reason for cloning humans," he said. "I can think of a good reason for using animals for agricultural purposes, for saving lives."

Dubbed "Dolly the sheep's" cousins, the female piglets were pronounced healthy, all normal weight, after a caesarian section delivery.

The technique used to clone them was similar to the way Dolly the sheep was created in 1996. The piglets' birth was less an achievement in the science of cloning and more an advance in the search for a supply of human-ready, transplantable animal organs.

"We've shown that we can create identical copies of pigs using a process called nuclear transfer, or cloning," Ayares said. "This has the potential in the near term to solve the worldwide organ shortage crisis."

With 70,000 Americans waiting for organs every year and only 10,000 donating, even the skeptical admit advances in this field cannot come quickly enough.

Though monkeys are human's closest relatives, pigs have been singled out as ideal donors because they are widely available and their organs are roughly the same size as those of humans.

While pig heart valves are already widely used in human heart surgeries, however, wide use of pig organs won't be possible until the organs are genetically altered to prevent human rejection.

Cloning is a first step to making human-ready pigs. As Dr. Charles Miller of the Mt. Sinai School of Medicine explained, "Cloning of pigs, if it's really reproducable, mamake it easier to genetically engineer pigs and make them more abundant in supply."

PPL Therapeutics, which cloned Dolly three years ago, said the five piglets were cloned from an adult sow using a slightly different technique than the one that produced Dolly.

Independent tests of the DNA of the piglets - named Millie, Christa, Alexis, Carrel and Dotcom - confirmed they were clones of the sow, the company said.

Transplantation of genetically altered pig organs could be tested on humans in four years, and analysts believe the market for them could be worth $6 billion, PPL said.

PPL scientists plan to try to "knock out" a gene responsible for incorporating in pig cells a sugar group recognized by the human immune system as foreign. The gene triggers an immune response in the human body, prompting it to reject the organ.

Three new genes would then be introduced into the pig cells, and the transplant patient would receive a blood transfusion containing modified cells taken from the pig supplying the organ. Scientists hope this process will reduce long-term rejection of the transplanted organ.

"All the known technical hurdles have been overcome," said Ron James, managing director of PPL Therapeutics. "It is now a case of combining the various strategies into one male and one female pig and breeding from these."

The idea of using animal organs for transplant, known as xenotransplantation, is controversial because some believe illnesses could cross from pigs to humans.

But scientists are excited by the prospect of using animal organs for transplant because of the shortage of human organs. Many people die while waiting for a transplant and experts hope that pigs will be able to provide a steady supply of organs.

PPL Therapeutics said genetically altered pig organs are the only near-term solution to solving the worldwide organ shortage crisis.

All of the research was conducted and funded by PPL Therapeutics, said Ayares, PPL's vice president of research.

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