Animal-human embryos: monster or marvel?
Text: David Shaw
Hybrid embryos are created by the addition of human stem cells to animal embryos. What ethical issues are involved?
In September 2015 the National Institutes of Health in the United States (NIH) suspended all funding for research involving hybrid embryos. The reason given was that the NIH wanted to consider the ethical issues raised by such research. Now, the NIH has opened a consultation on their plan to again fund research using so-called «chimaera embryos». The type of embryos in question are early-stage animal embryos, normally up to two weeks old. The type of animal can vary, but normally research is conducted on mice, sheep and pigs; only rarely are great apes used. The human stem cells can be obtained either from spare embryos created for reproductive purposes (embryonic stem cells) or directly from humans (induced pluripotent stem cells). These human cells can then be inserted into the animal embryo, affecting its subsequent development.
Why is this research necessary? The NIH has two types of research in mind: adding human cells to animal embryos to affect the growth of particular organs, and also the addition of human stem cells to the brains of more advanced animal fetuses. The latter type of study could be useful for research into neurodegenerative diseases. Hybrid embryo research is important because it allows scientists to study how stem cells change into different cell types, which is fundamental to understanding the development of our bodies and how they interact with disease. Such research could lead to treatments for many types of disease, such as cancer and Alzheimer’s disease. The NIH proposes to permit both these types of research, subject to extra ethical review by an expert panel.
The first ethical issue actually concerns the human stem cells. Some people object to the use of cells obtained from human embryos in research, because they believe that each embryo is a human life that should be respected. However, very few countries actually allow the creation of embryos for this specific purpose; the UK also permits the addition of rabbit mitochondria to human eggs to facilitate fertilization. Most embryonic stem cells used in research are actually derived from existing cell lines, and no (more) embryos need to be destroyed to produce these cells. For many non-religious people, the use of human embryos in research is justified by the potential benefits for people who are affected by disease, both now and in the future. In any case, most hybrid embryos are now created using induced pluripotent cells rather than those derived from embryos.
Some people also object to the use of animals and animal embryos in research. They argue that humans have no right to instrumentalize animals in this way, when doing so causes them pain and suffering. Again, however, most people agree that using animals for research is justified if it yields benefit for humans. Another ethical issue concerns the possibility of creating an animal with human features, such as a pig with a human face, for example, or producing animals that might be intelligent like humans. However, this is a misunderstanding of what is going on in this research: it does not aim to produce actual living animals that are carried to term, but only to conduct research on embryos and sometimes fetuses. There is no prospect of human-looking animals being produced.
One notable exception to this rule is research into using hybrid embryos to produce animals whose organs can be used for transplantation. Scientists in Japan and the United States have succeeded in using stem cells from rats to grow rat organs inside mice embryos. More recently, human organs were grown inside pigs. The next step will be to actually transplant one such organ into a human before beginning clinical trials. The advantage of this approach is that the organ can be grown using a patient’s stem cells so that it will be compatible when transplanted, and the patient will therefore not have to take immunosuppressant drugs. Of course, there is a shortage of organs for transplantation, so any new source of organs is useful. One quirk of the Swiss law on embryonic stem cells is that it does not cover induced pluripotent stem cells derived from humans, meaning that the creation of human organs for transplant inside pigs is accidentally legal, even if no-one is actually doing such research in Switzerland.
The example of growing human organs inside pigs using stem cells brings us on to the last major ethical issue: the so-called «slippery slope». This argument is used in many contexts, including assisted suicide and privatization of healthcare, but in biotechnology it is used to argue that a particular advance is just the first step towards «Frankenstein science» or «playing God». The implication is that if we permit the creation of chimaera embryos, we will soon be allowing everyone to create designer babies and engage in eugenics. Although Switzerland is a very progressive country with regard to assisted dying, its citizens generally seem to have a more conservative attitude with regard to biotechnological advances. At the Institute we recently asked patients about how they perceive synthetic biology, and many were very skeptical about genetic modification until the actual science and potential benefits were explained. Once they understood that many of their fears were misplaced, and that such treatments could be beneficial, their attitudes became more positive. We should not forget that developing treatments to treat sick patients is a fundamentally ethical endeavor.
Fears about chimaera embryos tend to be exaggerated. Scientists who are working with chimaera embryos do not seek to play God, but to help people; each new technology and innovation poses ethical issues, but the answer is to deal with each case as it arises, not to prevent a potentially helpful development because it might at some point lead to a development that might be ethically problematic. The NIH consultation suggests that scientists in the United States will soon be able to seek funding for this important research again. Hopefully some European countries will follow this example.
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