Pigs Stripped of Rejection Gene

LONDON — Scientists announced Thursday that they have cloned piglets lacking both copies of a gene that makes the human immune system reject transplanted organs from pigs.

In the United States, Britain and other countries, organ failure is the major cause of death and disability. With a shortage of human organs for transplant, many die while waiting for them--6,000 last year in the United States.

“Developing another source of organs would have a profound impact on society, so from a practical perspective this is a very important advance,” said Dr. Jeffrey L. Platt, director of transplantation biology at the Mayo Clinic in Rochester, Minn. “And even if it doesn’t solve the problem, it will answer very important questions in the field.”

PPL Therapeutics, the Scottish company that in 1996 helped breed Dolly the sheep, the first cloned mammal, announced that four healthy piglets with both copies of the gene “knocked out” were born July 25 at the company’s U.S. subsidiary in Blacksburg, Va.

A fifth piglet died shortly after birth of unknown causes, it said.

The next step is to transplant pig organs into other animals, such as baboons, to see whether the organs can function in the primates for at least three months. Geoff Cook, chief executive of PPL Therapeutics, said studies testing pig organs in humans could start within two years.

It is unknown whether the elimination of the gene will solve the rejection problem. There could be other aspects of human immune response involved. Another worry is whether the organs could carry harmful pig viruses.