Bioethics: Xenotransplants
Ethics of Transplanting Organs from Animals to Humans
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Should we develop technologies which would allow us to use the organs of other animals in human beings? There are arguments both for and against, but most people really aren't very aware of them. This is unfortunate, because the time when it will be possible to perform such transplants is fast approaching. The first xenotransplants were failures, but things might change radically before we know it, and we need to be equipped to handle the debate.
There are very good reasons for taking seriously the idea of using organs from other animals. The biggest of these is the fact that almost all of the major problems involved with human-to-human transplants would be eliminated, including the ethical dilemmas which go along with them.
We wouldn't need to wait until a person is nearly dead before doing a transplant - the surgery could be done earlier when the patient is healthier and has a better chance of surviving. We don't need to wait until another person has died to find an organ, meaning we don't need to debate when someone has "really" died and when removing their organs is acceptable. The transplanted organs do not have to travel several hours from person to person, which means that they will be fresher and healthier.
The quality of the organs can be higher - the animals would be raised in the cleanest, best conditions possible, while most human donors may not have taken the best care of themselves. Organs will be more plentiful, eliminating concerns about availability and even eliminating some of the cost. Organs for infants would become available, saving even more human lives. These are all huge considerations, and they are only the tip of the iceberg concerning the possible benefits.
Given all of these wonderful things, is it a realistic possibility to use the organs from other animals? There have been attempts to use primate organs, but those haven't worked out so well. One would think that primate organs would be the best candidates, and for a number of different reasons that might be true. However, primates are difficult, time consuming, and costly to raise. Moreover, being primates, people are uncomfortable with killing them for organs.
The same is not true of pigs - pigs breed quickly, grow quickly, and are already consumed for food in large quantities. Moreover, their physiology is close to human physiology, thus they are among the best candidates for non-human organs in large quantities and good quality.
There is just one problem: if you attach a pig's organ to a human blood system, you can actually watch the organ be destroyed right before your eyes. Within a few minutes the organ may become unusable, and it never lasts for more than a few hours. But why?
It is a strange fact of nature that the blood vessels in pigs are lined with a complex molecule known as GAL - something which is also contained on the surface of a great many bacteria and viruses. Other animals have this, but primates like humans don't, which means that our immune systems are essentially wired to destroy GAL-containing organs in a process known as hyperacute rejection.
Because of this, it has been a major goal of scientists to find a way to genetically engineer pigs so that the GAL molecule is eliminated or replaced. This, then, would end the problem of hyperacute rejection and move us back to the problem of chronic rejection, something which already exists with human transplants and which we can handle to some degree.
That goal has very nearly been achieved. Two different companies have announced that they have produced litters of cloned miniature pigs lacking one copy of a gene that produces the GAL molecules. According to them, pigs with transplantable organs could exist within seven years.
The risks, however, are considerable. The worst-case scenario is the creation of a new plague which could wipe out a significant portion of the human population. No, this is not an unrealistic possibility. There are large numbers of diseases which affect other animals and not humans, but that may change if we start putting their organs in our bodies.
One example of a disease which jumps from animals to humans is the well-known influenza virus. Most new strains of the flu originate in the Far East where large numbers of people live in close, unsanitary conditions with pigs and chickens. In 1998, authorities in Hong Kong had thousands of chickens killed to prevent the spread of a fatal flu virus designated H5N1, which started out killing poultry but then began killing people. Fortunately, it only infected those who came into direct contact with diseased animals; but if it had been transmittable through coughs and sneezes, it might have become a pandemic killing tens of millions around the world.
Pigs raised for their organs may be protected from flu viruses, but that won't protect humans. All pig cells carry a known retrovirus known as Porcine Endogenous Retrovirus, or PERV. It is harmless to them, but no one knows what it might do to humans (although it has been shown that it can infect human cells). Retroviruses like this can incorporate themselves into a host's DNA, meaning that once a host has it, it is impossible to eliminate it entirely, and that is the case with this one. This is not something which can be eliminated in the same way GAL-producing genes have been.
If the term "retrovirus" sounds familiar, it might help to remember another retrovirus which seems to have made a jump from animals to humans: AIDS.
So what will happen if PERV is introduced into human bodies? Could it mutate into something which would directly infect humans - including humans who have not received transplants? Yes, that is possible. Could it mutate into something which is not netural, as with pigs, but which is instead harmful? Yes, that is possible.
We just don't know what will happen. We can't. So what do we do? We could save hundreds of thousands of lives if we are able to use pig organs in xenotransplants, that is pretty certain. We could kill millions the same way, however. How do we weigh the risks? How do we balance the interests of those who would be saved against those who might die?
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