A New Use for Liver
As Jeff Getty awaits the results of the baboon-cell transplant, at least one man is alive courtesy of pig liver. Five pig livers, to be exact.
His problem (see Treatment of hepatic failure) was a case of acute liver disease caused by the hepatitis B virus. When the man arrived at Duke University Medical Center in November, 1992 he was near death.
Liver disease can be extremely serious since the organ has so many chemical jobs:
- it makes bile, which is used in digestion,
- it makes proteins and immune cells, and
- it filters and breaks down toxic chemicals from the blood.
The liver is so complex, in fact, that nobody's been able to invent an artificial substitute, and patients with liver failure can slip into a coma and die within days. Thus, the Duke University medical team wanted to find a way to tide the patient over until they could find a human liver to transplant. They used livers from pigs which had been genetically manipulated to slow or prevent attack from the complement component of the immune system.
Why Swine?
virus that could infect humanity with a new disease.
Human complement regulatory proteins...), researchers transplanted hearts from genetically altered pigs into baboons. Using a new technique to control the complement system, they got the hearts to survive from 3 to 20 hours. In contrast, an unengineered pig heart would last only an hour or less -- the complement system attack is that fast, furious, and effective.
Although the pig-to-baboon experiment is being hailed as a breakthrough, controlling the complement attack is only the first step in xenotransplantation, warns John Fabre of the University of London (see Nudging xenotransplantion towards humans. "What lies beyond this time is largely unknown, but there are at least two additional barriers to cross," Fabre wrote. "...Virtually every cell surface protein" on the surface of the pig blood vessels (and other cells) would be a "potential target for human antibodies."
Furthermore, there are questions about how effectively pig liver will perform the tasks of a human liver, Fabre wrote. And because the liver is so metabolically active, the foreign proteins it produces could set off further compatibility problems.
