Are Chimeras For Human Organs a Chimera?
The word "chimera" originally referred to a creature in Greek mythology. It had a lion's head and body, a goat's head growing out of its back, a serpent's tail, and it breathed fire. Also, it was female. Seeing a chimera was generally regarded as a bad omen, leading to earthquakes or famines.
The other use of the word, as in "the chimera of peace in the Middle East" is to mean something that's probably never going to happen. Recent experiments at the Salk Institute and elsewhere show that while mice may be able to grow organs for transplantation into sick rats, the hope that pigs may be able to grow human organs for transplants have receded into the future, and may never be realized. What I'd like to know is, should we even be doing this stuff at all?
First, the background.
Human organ transplants from either cadavers or live donors are plagued by the problem of rejection. The body recognizes foreign tissue and mounts an attack on it, leading to complications in organ transplants such as graft-versus-host disease, which can ultimately lead to the failure of the transplanted organ and other chronic and acute problems. So medical researchers would like to develop replacement organs from the patient's own body using the patient's own adult stem cells, which can be potentially made to become a wide variety of organs. The problem is that for a desired organ such as a pancreas to develop from stem cells, it needs to be in an embryo, or an embryo-like environment that is similar enough to a human embryo to encourage the proper development and growth.
Pigs turn out to be one of the closest animals to humans physiologically, in terms of weight, size of organs, and other factors. So Juan Carlos Izpisúa Belmonte and Jun Wu of San Diego's Salk Institute inserted adult human stem cells in 2000 pig embryos and implanted the embryos in a number of female pigs. The yield wasn't very good—only 186 embryos lived as long as a month, at which time the pigs were "sacrificed." Many of the modified pig embryos were smaller than normal, and the human stem cells that survived were mostly just scattered around in the embryos rather than forming specific human organs. Wu views this setback as temporary, calling it "a technical problem that can be tackled in a targeted and rational way."
At a recent workshop sponsored by the U. S. National Institutes of Health (NIH), that federal agency reviewed the ethics of chimera research and said it would reconsider its current ban on federal funding of such work. But it is not clear now that a new administration has taken charge whether the ban will be lifted or not. The Salk Institute researchers got around the ban by using private funds for their research.
It's easy to think of arguments against chimera experiments involving human cells. The NIH people seem especially worried about the brain of a pig getting human brain cells, or the germ line (eggs and sperm) of a pig receiving human DNA. The thought that a candidate for transformation into pork chops has a family tree that includes your Uncle Jack is indeed a disquieting notion. And what about a human brain growing in a pig's body? Would that make the pig-chimera human? Obviously, to answer this question requires that one have a robust definition of what it means to be human. And it's not clear to me that the NIH has such a definition, at least not one that can be coherently defended.
If possession of a human brain is all you need to be human, U. S. law currently allows humans to be aborted up to nearly the time of birth, under some circumstances. While the question of human-chimera research does not at first seem relevant to the issue of abortion, both issues involve treating living beings as instruments of someone's will.
Bioethicist Leon Kass used the phrase "the wisdom of repugnance" to describe certain reactions that people have which cannot necessarily be articulated into finely honed arguments, but which nevertheless deserve attention. A more pungent term for the same idea is "yuck factor." If the idea of growing a human brain inside a pig's body fills us with revulsion, maybe we should pay attention to the revulsion even if we can't say exactly why we are revolted.
Proponents of animal rights are probably not rejoicing over the prospect of pigs that grow human organs either. Their reasons are different in some ways, but go back to the question of whether living beings—human or animal—should be used as instruments for another's will. There is near-universal agreement that one human should not use another as an instrument, a sentiment that goes back at least to Kant. But there is disagreement about whether humans can use other animals as instruments, a practice that also has a long-standing tradition in favor of it.
For now, the debate about human chimeras is largely still academic, as it appears that pigs are not yet a good candidate for this sort of thing. Maybe they'll try monkeys next, but that raises the same sort of issues as experiments with pigs.
God gave us human beings minds that are capable of devising plans for great good and also for great evil. Most religious traditions hold that people also have a moral sense that gives rise to such things as the yuck factor, and that we ignore this sense at our peril. It's probably a good thing that the NIH has refrained from supporting human chimera research, but obviously that hasn't stopped its progress. If someone told me I had a fatal disease that could be cured with a transplant from a specially grown pig, or monkey, I don't know what I would decide. But I'm not sure we should even contemplate asking people to make such a decision, especially if, in the process, we risk creating monstrosities who might be human and might not be. And only the chimera would know for sure.
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