First, primates are hard to raise in large numbers, for they reproduce slowly and take many years to mature, so it would be difficult to breed the numbers needed to meet the demand for organs. Second, because they are so closely related to humans, they may carry bacteria and viruses that can easily infect humans. HIV, the virus that cause AIDS, for example, is thought to be a monkey virus that jumped to humans. And finally many people feel it would be unethical to raise such highly intelligent and social animals only to kill them for their organs. They breed quickly, and we have extensive experience in raising them in large numbers.
Fewer people are likely to have ethical qualms about using pigs as a source for organs.
Within minutes of transplantation, antibodies and defensive proteins found in the blood attack the blood vessels within the transplanted pig organ, causing clotting which chokes off blood flow, quickly killing the organ. A number of strategies have been devised to try to prevent hyperacute rejection, Lechler says, some of which will be tested in humans in the next few years. One strategy is to find a way to soak up the antibodies that attack the pig cells. One way to do this would be to run the blood of a pig organ recipient through a filterlike device that contains molecules similar to those found on the surface of pig cells. As the patients blood passed through the filter, the anti-pig antibodies would bind to the filter and so be removed.