Pig to Human Organ Transplants in 5 years (10/11/2006)
Surgical Professor David Sachs has made long strides in xenotransplantation, the process of
transplanting an organ from one species to another. Currently, Professor Sachs is testing
pig kidneys in primates, with hopes of clinical trials on humans within 5 years.
Sachs, director of the Transplantation Biology Research Center at Massachusetts General Hospital is
trying to genetically modify pigs and pig immune tissue so that it isn't rejected by the primate (baboon) immune
system upon implantation. To date the longest any primate has survived has been 83 days, though not
seemingly much, is a considerably longer than the average of 30 days.
Sachs' team has also transplanted a piece of pig tissue, an immune system organ called the thymus, to prime the
baboon for the transplant. The idea is to trick the primate immune system into accepting pig tissue. Currently
immunosuppressants, drugs that slow down or suppress the immune response that can cause organ rejection, are used.
The unfortunate side effect of the suppressants are that they raise the risk of infection. Two of the eight baboons
in Sachs' last transplant experiments died of infections.
Another approach involves transplanting bone marrow cells along with the kidneys and the thymus. This
technique has shown to improve tolerance for the transplanted organs. Scientists, including Sachs' team
are also genetically enhancing the organs by adding human genes for proteins involved in immune regulation
and blood clotting.
The worry is the potential for animal viruses to be passed on to the human hosts. Because pigs are genetically
similar to humans, viruses have an easier time adapting between the two species.
In 1997, British scientists discovered that porcine endogenous retroviruses (PERVs) could infect human cells.
Though there is no evidence that PERVs could be harmful to humans, the fact that they can spread amongst humans is cause for
alarm. If they did ever attack our cells, we might not have the defense mechanisms to fight them off.
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