Politics & Policy

Of Cybrids, Hybrids, & Chimeras

Learning from the U.K. battle over human-animal hybrids.

In September, Britain’s Human Fertilization and Embryology Authority (HFEA) approved the concept of creating hybrid embryos by merging human cells with animal eggs for research purposes. Essentially a form of cloning, the procedure requires scientists to fuse a normal human body cell with a non-human animal egg — of a cow or a rabbit for instance — stripped of its own nucleus. Once fused, factors remaining in the non-human egg would initiate processes by which an embryonic organism would develop. Whether the non-human source of eggs are remotely genetically related (cow eggs) or proximately related (monkey eggs), the resulting product (called by some a “cybrid”) would, in the opinion of leading experts in mammalian cloning, be essentially human, save for the negligible influence of the non-human genetic material (the mitochondria) found afloat in the enucleated egg.

From such embryos, British researchers want to extract embryonic stem cells. By creating clones from the cells of patients suffering from incurable genetic diseases such as ALS (Lou Gherig’s disease), researchers hope to develop matching lines of stem cells that carry the disease, and to use them to develop therapies. Ian Wilmut, creator of Dolly the Sheep, believes that studying cells derived by the hybrid method cannot be matched by doing similar studies in merely animal models. He points out that these cells could also be used for testing drugs, and for perfecting the cloning technique. Using animal eggs would allow researchers to by-pass ethical concerns regarding the use of human eggs. And under current law in the U.K., the hybrid embryos would be destroyed after 14 days.

As might be expected, the idea of creating human-animal hybrids provoked repugnance in the general public. In response, the HFEA conducted a three month long “consultation,” a mix of polling, town hall style meetings, and debates. This was coupled with months of heavy lobbying by proponents of the technique who claimed at one point that a ban on hybrid cloning “would cost patients’ lives.” According to the HFEA report, once the public was presented with “factual information” most of the respondents “became more at ease with the idea.”

The U.K. human hybrid debate should supply us with several insights about how to revitalize our own intractable national debate over ethical stem cell research. Here are just a few.

The first thing the HFEA had to deal with was the generalized public revulsion at the idea of crossing human DNA with animal eggs. While the yuck factor is at times a useful rule of thumb in moral matters and deserves our careful attention, one must admit that it fails to constitute a sufficient basis for reasonable ethical judgments. Centuries ago, the novel prospect of cutting open and studying human cadavers was met with repugnance and deep moral suspicion; in more recent times, the idea of organ donation met with similar reactions in some quarters. Both were eventually accepted. How many long-accepted medical interventions still cause repugnance? And recent biomedical advances such as the use of porcine heart valves in cardiac patients, the growing of human livers in laboratory animals for study as disease models, or the fusing of non-reproductive cells from human and non-human tissues to study chromosomal behavior — all forms of human-animal chimera formation — while perhaps causing some emotional discomfort are surely morally licit.

On the other hand, if arguably a majority of Americans rejects outright other kinds of human-animal hybrid formation, it is for reasons that go well beyond emotional repugnance. The cross-fertilization of human and non-human egg and sperm, (i.e., the creation of “humanzees”); the grafting of non-human animal stem cells into a human embryo or fetus or vice versa; or bringing about the gestation of a human fetus within a non-human animal womb — all such proposals normally provoke disgust; but if they garner our moral opprobrium, surely it is out of respect for human dignity and not simply because the “yuck” factor has collectively kicked in.

Why, we should ask, do more than a few researchers hold out so remarkably little hope of success for the experiments currently under consideration by the HFEA — to use rabbit or cow eggs to clone human cells? Sir John Gurdon, a pioneer of cloning at Cambridge University, fears these experiments will yield “a lot of genetic abnormality that won’t lead to good quality stem cells”. Neville Cobbe, a geneticist and cell biologist at the University of Edinburgh, writing in the journal Zygon this month, questions the feasibility of modeling these diseases — many of which are late on-set conditions — in embryos when we have only fleeting knowledge of the genes and proteins that cause those diseases. These problems would be further exacerbated by using bovine or murine eggs so distantly related to the human genome. Another leading expert on mammalian cloning, Shoukhrat Mitalipov of Oregon Health and Science University, agrees that “interspecies cloning only works with very close species.” He describes as “very slim” the chances that bovine eggs would reprogram human cells into embryonic stem cells, and points out that several labs have tried these experiments for almost a decade with no success.

This suggests that these scientific proposals are mere test cases to measure the social acceptability of controversial science. But rather than engaging these questions openly, some scientists prefer to do an end-run around public deliberation and force the issue in the laboratory.

The real issue here is the social acceptability of allowing science to cross heretofore inviolable moral boundaries. The British human-animal hybrid debate is a poor proxy for robust moral discussion of the two issues it conceals: the moral licitness of human cloning for research purposes, and the further issue of mingling human and non-human cells in a reproductive manner.

In the U.S., we would do well to continue this debate in earnest, keeping it in the public square where it belongs, while avoiding the pitfalls of investing time, energy and public resources in junk science as a substitute for substantive public moral discourse. While respecting contrary views, I personally believe that as a nation we should reject any form of human-non-human hybrid formation on the same grounds for which I and millions of Americans reject human cloning: human embryos have a privileged moral status and should not be treated as raw material for medical research. There is also a reasonable resistance to creating a market for human eggs and the likely exploitation of women to obtain the eggs.

If cures and therapies are really the name of the game, let’s invest in research that is scientifically promising while purporting to avoid the ethically charged issue of destroying human embryos, such as: the reprogramming of ordinary somatic (body) cells, the procurement of embryonic stem cells from already dead embryos, ways of altering the cloning process so as to avoid the production of human embryos altogether (“altered nuclear transfer”), the derivation of stem cells from umbilical cord blood, and the use of a patient’s own adult stem cells.

I myself believe that embryo-destructive research cannot be morally justified, even if it were to become the source of cures for dreaded diseases. Yes, once upon a time, the ideas of studying human cadavers, and donating organs were deemed an affront to human dignity. And with time this moral objection was judged as groundless. Some today believe opposition to using human embryos for research is another cultural taboo which will also pass with time. I disagree. Neither the carving of cadavers nor the transfer of viable organs requires a willingness to kill a living human individual. Embryo destructive research does just that. It takes the life of a human individual in his or her earliest stage of development. Biomedical science fails humanity when it deliberately destroys human life in the pursuit of trying to cure it.

Rev. Thomas Berg is executive director of the Westchester Institute for Ethics and the Human Person, and member of the ethics committee of New York’s Empire State Stem Cell Board.


The Latest