The world's first litter of pigletsmay signal hope for transplants.

March 15, 2000 -- In the last 100 years, the field of organ transplantation has advanced at an astonishing pace. Human-tissue grafting was first performed less than a century ago by the Swiss. In 1950, the first successful kidney transplant occurred at the University of Chicago and was followed by the world's first heart transplant by South African surgeon Christiaan Barnard in 1967. Yesterday, a litter of cloned pigs was unveiled to the world -- an event that already is raising hopes that organ transplants may soon be possible between animals and humans.

"I think this is a big step forward they've made. I applaud it,'' Dr. Fritz Bach of Harvard Medical School, a researcher studying transplantation from animals to people, said yesterday.

The transfer of animal organs to humans, or xenotransplantation, pairs two highly controversial technologies -- cloning and the use of animals to create biological materials for human medicine. The goal of xenotransplantation is not unlike that of "pharming," in which the genetic material of animals is altered to stimulate the growth of certain chemicals. Those chemicals then are extracted for use in human patients. But xenotransplantation takes the idea significantly further.

Cross-species transplants have failed in the past because the human immune system rejects non-human tissue, often with fatal consequences. But pigs, which are one of the animals most physiologically similar to humans, can be genetically engineered to carry human genes that will make their organs appear to the immune system to be human organs.

The technique is extremely expensive and potentially dangerous. Viruses are integrated into pig genes, and scientists do not yet know if people can become infected with those viruses if they receive a pig-organ transplant. Once researchers isolate and remove the viruses, they will have a single model pig that can be cloned repeatedly to create organs for human transplants.

Approximately 66,000 Americans are on the waiting list for organ transplants, according to the Health and Human Services Department. But only about 21,000 transplants occur each year -- primarily due to a shortage of organs.

The firm responsible for the cloned pigs, PPL Therapeutics of Edinburgh, Scotland (the same firm responsible for cloning Dolly the sheep four years ago), says that xenotransplantation could be tested on humans in just four years. The company cites financial analysts who believe the market for solid organs alone could be worth $6 billion.

However, xenotransplantation is not without controversy. The health implications for organ recipients are not fully tested, and patients receiving animal organs could have severe restrictions placed on their lifestyles.

Recommendations published by Britain's Xenotransplantation Interim Regulatory Authority suggest that anyone who receives an animal organ should never have unprotected sex and should never have children because of the public health risk. Opponents of the technology also maintain that any virus that could be transmitted from a pig to a human could spread to the rest of the population easily, noting that HIV was likely a cross-species transfer. In addition, animal-rights activists are outraged that animals are being tested and cloned in order to possibly alleviate human medical conditions.

To some scientists, the ultimate goal of this research is not just to "pharm" animals but to clone the most complex animal in existence -- the human. "There is a global race, if not a stampede, towards it," Dr. Patrick Dixon, a leading expert on cloning, told Reuters. "Scientists are ticking off which species they have cloned, pigs being the latest, leading inevitably towards humans. ... It will be very rewarding for the team which [does] it, and the first cloned baby will be the defining image of the start of the third millennium."

Human cloning may come sooner than the public expects. The first cloned human embryo was produced nearly nine months ago in Massachusetts.

Because the United States bans human cloning, researchers killed the embryo after 12 days. However, many other nations do not regulate cloning as strictly as the United States, and technology developed in America and Britain ultimately may be employed elsewhere to create the first living human clone.

Cloning of Animals Needs Greater Regulation	The Enormous Potential of Animal Cloning