DeForest Firm Achieves Litter Of Cloned Pigs

Research Targets Tissue Source For Humans

By John Fauber

jfauber@journalsentinel.com

DeForest - A Wisconsin biotech firm said Thursday that it has genetically engineered and cloned a litter of piglets with organs that may resist rapid rejection by the human immune system.

Producing these modified pigs is what many scientists say has been the biggest obstacle to the promise of using pig organs and tissues in people.

"This is a major, major landmark contribution," said Hans Sollinger, head of the University of Wisconsin-Madison organ transplant program. "Xenotransplantation will not happen tomorrow, but at least this will give us a great experimental opportunity."

Sollinger and other UW researchers are trying to develop drugs that can be used to prevent rejection of pig organs.

Infigen Inc. of DeForest said it had produced a litter of three miniature swine in which both copies of a gene that causes rapid human rejection of pig tissue have been inactivated. The Infigen researchers are the second U.S. group to announce the achievement - the cloning of so-called double knockout miniature swine - in the last two months.

Because of a severe shortage of human organs for transplantation, scientists have turned to pigs as a potential source of organs and tissues. Some researchers say that in the coming years, pigs may become a significant, if not the primary, source of such organs.

In the U.S., more than 80,000 people are awaiting an organ transplant. In 2001, about 24,000 transplants were performed, and 6,000 people died waiting for their operations.

Some researchers envision organ farms in which specialized pigs are bred to produce kidneys, hearts and other tissue such as insulin-producing islet cells in the pancreas.

Others say that likely it is years down the road, and the most important issue today is persuading people to become organ donors.

"Seventeen people a day die waiting for an organ transplant," said Anne Paschke, a spokeswoman for the United Network for Organ Sharing.

Still, several groups of researchers have been working to genetically modify and clone pigs that could help meet that demand.

Preventing Rejection

The main stumbling block has been the issue of immune system rejection that occurs in xenotransplantation, or when organs or tissues are transplanted from one species into another.

Because of their size and physiology, miniature swine have long been considered good candidates for human transplantation. The pigs grow to about 180 pounds, about one-fourth the size of regular pigs.

But all pigs are born with two copies of a gene that makes an enzyme that adds a sugar molecule to cell surfaces. Because the sugar, known as alpha-1-galactose, is very similar to a bacterial sugar, human antibodies recognize it as foreign and attack the tissue, resulting in hyperacute rejection of the organ within a matter of minutes.

Working with Immerge BioTherapeutics, a Boston biotech firm, Infigen was able to clone miniature swine with both of those genes deactivated. In addition, they did it on a special type of pig that researchers believe will not transmit a pig virus to humans.

"This is a big step forward," said David Cooper, an associate professor of surgery at Harvard Medical School and head of the xenotransplantation laboratory at Massachusetts General Hospital.

The pig virus, known as porcine endogenous retrovirus, or PERV, has posed a big safety concern for xenotransplantation. In pigs, the virus does not appear to cause symptoms, but it is not known what would happen if the virus were to infect a person after the transplantation of a pig organ. And lab tests suggest that it can infect human cells.

Unlike other viruses that can be eliminated through breeding or raising pigs in a sterile laboratory setting, PERV incorporates itself into the normal genetic makeup of pigs and, as a result, is transferred from parent to offspring.

However, in February 2002, researchers at Infigen's partner, Immerge, published a study in the Journal of Virology showing that miniature swine did not transmit the virus to human cells in laboratory tests.

Infigen now is the second U.S. group to accomplish the cloning of double-knockout miniature swine. Last month, researchers at the University of Missouri-Columbia, also working with Immerge, announced that they had produced one double-knockout miniature swine piglet.

Last August, a U.S. subsidiary of the Scottish firm PPL Therapeutics, the company that cloned Dolly the sheep, announced that it had accomplished the double knockout with the birth of four piglets. However, those animals were commercial swine, considered too big for human transplantation. And commercial swine do not have the added benefit of potential protection from PERV.

"We are closer to actually getting something into a patient," said Walter Simson III, Infigen's chief executive officer.

Infigen's three male piglets were born six weeks ago. One died shortly after birth as the result of complications from taking blood samples. However, the other two are healthy and gaining weight rapidly, company officials said.

The clones are kept together in a special self-enclosed nursery box on a farm north of Madison.

In addition, several more litters of double-knockout miniature swine are expected to be born in the coming months, said Erik Forsberg, Infigen's vice president of development.

Scientist say they now are hopeful that breeding of these two groups of miniature swine and subsequent litters of genetically engineered pigs will produce enough animals to begin transplantation experiments.

The next big step before putting those organs and tissues in people will be to transplant them into non-human primates, most likely baboons, said Harvard's Cooper, co-author of the book "Xeno: The Promise of Transplanting Animal Organs Into Humans." That could take place in the coming months.

If the pig organs used in those experiments perform well, the first human experiment would follow, he said.

Copyright © 2003 Journal Sentinel Inc.

This article posted March 8, 2003.