The Ethics of ‘Human Admixed Embryos’: Concerns and Responses

By Loane Skene, Professor of Law, University of Melbourne and Julian Savulescu,  Uehiro Chair in Practical Ethics and Director Uehiro Centre for Practical Ethics, University of Oxford

The Human Fertilisation and Embryology Authority (HFEA) Bill, currently before the UK Parliament, will, if passed, permit HFEA to license the creation for research of embryos that combine human and animal genetic material (called, in the Bill, ‘human admixed embryos’). These embryos include cybrids which are formed by inserting the nucleus of a human body cell into an animal egg that has had its nucleus removed. Cybrids would produce embryonic stem cells that are 99.9% human. The Bill would also permit other types of embryos to be formed from human and animal genetic material that would be up to half animal. This post explains why scientists want to create human admixed embryos. It then outlines some ethical concerns about the creation of these embryos and responses that may be made to those concerns.

Why do scientists want to create human admixed embryos?

Scientists want to create embryos with disease mutations to see how the mutations affect the development of early embryos and what might be done to control them.  By deriving stem cells from these embryos, they will have a constant supply of cells to study after the embryo has been destroyed (which must happen within 14 days). In time, this research may lead to the development of treatments for human diseases, such as diabetes, cancer, Parkinson’s disease, Alzheimer’s disease and motor neurone disease. One day, embryonic stem cells might be induced to develop into other types of cells, like nerve cells, muscle cells and heart cells, to treat people with spinal injuries or diseases affecting particular parts of the body. The new cells should not be rejected by the patient’s body, like donated stem cells such as  bone marrow, as they would be ‘matched’ to the patient. Treatment with a patient’s own cells is more likely to be successful and patients would not have to take immuno-suppressive drugs for the rest of their lives.

Current law

The current law in the UK allows scientists to create embryonic stem cells ‘matched’ to a particular person by using the nucleus of a bodycell from that person and inserting it into a donated human egg. However, there are relatively donated human eggs available for research.  If animal eggs can be used, there will be far more eggs available that are ‘matched’ to people with genetic diseases

Concerns and responses

1. It isn’t necessary to create human admixed embryos. Scientists can do research on adult stem cells (like bone marrow) or on stem cells derived from skin cells that have been induced to develop into stem cells without creating an embryo (Professor Yamanka’s technique).

It is true that other methods of deriving human stem cells are being developed. However, that does not mean that other research should be stopped. We do not know where each branch of research will lead. Even if one line of research is promising, other research is still necessary. We don’t stop a horse race because one horse is well ahead. Who knows what will happen before the end of the race?

2. Research on human/animal cells won’t be useful for human treatment as the  cells are not wholly human cells.

Scientists will be able to learn from studying the early development of human admixed embryos and cells derived from them. They will also be able to practise the technical skills in handling embryos that they need for IVF treatment and research.

3. It would not be safe to treat human patients with stem cells that contain animal DNA.

Human admixed embryos and cells derived from them will be used only for research. It will be many years, if ever, before human patients are treated with these cells and that would not be done without extensive safety tests and ethical scrutiny.

4. Treatment with cells containing animal DNA would not be effective in treating people so it is pointless to do research aiming to develop such treatment.

It is true that such treatments may not work. The new cells may not be stable or they may cause teratomas to develop, or have other consequences that we cannot predict. However, the main aim of the research is to learn about cellular development and to develop new diagnostic tools and drugs. No treatment could be attempted on human patients until its effectiveness and safety is established. We should not require scientists to prove at the outset where their research will lead.   

4. Animals may suffer if their eggs can be used to make these embryos for research.

If this research is allowed, the animal eggs will be obtained from ovarian tissue removed after death at an abattoir. Some people object to the meat industry, but most people eat meat and accept that research may be undertaken on animals to benefit human health, provided the research is necessary, scientifically and ethically justifiable, and subject to strict regulatory controls. Results from this research might be used one day by vets to benefit the health of animals.

5. Creating human admixed embryos is an affront to human dignity; it is ‘against Nature’.

Human genes have been introduced into animals for more than 25 years. Laboratory mice are bred with genes for human conditions to be studied in research.  Cows and goats with human genes produce biological substances for human patients in their milk, such as blood clotting factors.  Human insulin was first produced by inserting human DNA into e-coli cells and allowing them to reproduce.  People may regard human admixed embryos differently from mature animals with some human genes, but it would be a criminal offence to allow these embryos to develop for more than 14 days. They will never be human-animal creatures

6. It is wrong to create an embryo with the intention of destroying it.

Even if human admixed embryos were regarded as human embryos, there is no reason why they should not be used in research.  We allow research on donated human embryos and embryos formed from donated human eggs. This type of research could be reduced if human admixed embryos were used in research.

7. Allowing this research would be the first step on a slippery slope. The next step could be allowing the embryos to develop for more than 14 days and even into live born creatures.

If the creation of human admixed embryos is allowed, it will remain subject to stringent regulation. Any changes to the law would have to go though the parliamentary process. It is very unlikely that the 14-day limit would be changed because there is a physical reason for it. That is when the ‘primitive streak’ starts to develop – the beginning of the nervous system. That is the earliest point at which an embryo might feel pain, although even then, the embryo is only the size of a full stop.


In short, research on human admixed embryos may provide valuable knowledge about the nature and causes of disease and help develop new diagnostic methods and treatments. Many concerns expressed about the creation of human admixed embryos can be met by strict regulatory controls.  In particular, the law prohibits the development of any research embryos for more than 14 days and prevents them being implanted in a woman or an animal. The research is allowed only under licence.

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