Pigs Cloned for Organ Transplants
by Anita Manning
Two competing groups of scientists have genetically altered and cloned pigs they hope can one day be used to help fill a
desperate need for organ donors.
The bioengineered pigs lack one of a pair of genes that trigger rejection of transplanted tissue in organ recipients.
It's a "very important development" that could resolve a major problem in cross-species transplantation, says Harvard
surgeon David Sachs, director of the Transplantation Biology Research Center at Massachusetts General Hospital. The next step, he says, is to breed the pigs without the
second copy of the gene, a process that could take months.
Pigs are considered good candidates as organ donors because their organs are similar in size and structure to those of humans,
offering hope for an unlimited supply of hearts, kidneys and other organs for transplant.
Research to prevent rejection of transplanted tissues has extended the survival of organs in cross-species transplants from
minutes to months, says Sachs, who was not involved in the research reported this week. Scientists can block the immune system's attack on foreign tissue, he says, but
it always resurges, taking aim at a specific target on the pig cells. That target is created by the gene that now has been knocked out of the high-tech pigs.
More than 71,000 patients are awaiting organ transplants in the USA, donor agencies say. "The reason we're all so
committed to this is that patients are dying every day because they can't get transplants," Sachs says.
The pigs were developed by researchers at the University of Missouri-Columbia working with Immerge BioTherapeutics of
Charlestown, Massachusetts, and another group of researchers at PPL Therapeutics in Blacksburg, Virginia. The development may not resolve all problems involving
animal-to-human organ transplantation, says Randall Prather of the University of Missouri, co-author of a report in today's Science on the birth of four cloned
pigs in September and October. "But we've shown we can do the specific genetic change," he says, so if others are needed, "we can do it."
PPL Therapeutics, which announced
Wednesday the Christmas births of five cloned piglets, says it expects
that tests involving transplants from pigs to humans could begin in four
years.