In the 1960s, researchers tried transplanting kidneys from chimpanzees to human beings. That effort seems amazing for at least three reasons. First, identifying a suitable candidate for a compatible kidney transplant often means that even close relatives are judged not compatible for a successful transplant. Second, chimpanzees are an endangered species, so it’s not as if a successful Pan troglodytes to Homo sapiens transplant route would have genuinely addressed shortages of human organs. Third, and perhaps most amazing, is that they had some success with this effort. Or at least, success in the form that some transplant recipients lived for months.
Over 110,000 patients are waiting for organ transplants in the United States alone. So the idea of an alternative source for these organs, one that doesn’t depend on either a steady stream of humans who are both compatible and willing to undergo a tremendous personal sacrifice, or compatible humans who conveniently die in conditions that leave them with a healthy heart, or lungs, or liver, has long been attractive. Watching a patient linger, sicken, and die while waiting for a compatible organ is a horror not just for patients, but for doctors, and it’s one they see over and over again.
Writing this week in Science Immunology Megan Sykes and David Sachs of Columbia University Medical Center look at the state of long-running efforts to develop transplants from an animal that may at first not seem like the best possible candidate — Sus domesticus, the domesticated pig.
Pigs have actually been valuable in human health care for a long time. Even though the last common ancestor of pigs and people probably lived about 80 million years ago, pig skin is enough like human skin, pig hearts are enough like human hearts, and several other pig organs enough like human organs that they’re often used medical education and pre-clinical trials. Pig heart valves have been used in human transplants for decades. Also … there are literally a billion of them. Domestic pigs are, thanks to people who already like to transplant parts of pigs directly into their digestive system, the second or third most common large animal on the planet.
Pigs are common, and pig organs are about the right size and right configuration, to replace their human counterparts. Pigs can also be bred in great numbers. Which brings the problem of transplanting them into humans down to the very serious issue of compatibility and rejection. But that’s a serous problem.