Breaking the Species Barrier
Despite all the obstacles, a few cross-species transplants have actually worked, at least for a time:

• In 1963, several people received chimpanzee kidneys. The kidneys were rejected, but no faster than human kidneys were rejected at that time (this was before good anti-rejection drugs were available).
• Hearts transplanted from cynomolgus monkeys into baboons have survived an average of 6 months -- perhaps long enough to justify testing primate hearts as a "bridge" until a human heart is available.
• And pig livers saved the life of a man with liver disease.
• Pig skin is used for skin grafts.
• Various hormones and enzymes -- including insulin and clotting factor -- were or still are routinely purified from animals for use in people.