Fertility Journal

Human admixed embryos

One of the most controversial issues in the new Human Fertilisation & Embryology Act centres on the creation of human “admixed embryos” that contain both human and animal genetic material.   These embryos would be created for research purposes in order to obtain stem cells and aid the understanding of disease processes.

What is special about stem cells?

Stem cells have the potential to develop into any type of tissue in the body.  Stem cell research may eventually be a source of new treatments for conditions for which there is currently no specific cure.    These include diseases such as Alzheimer’s, Parkinson’s and motor neurone disease.    Although stem cells can be obtained from adult tissues, the 5-6 day old human embryo (blastocyst) is the richest potential source.   But using human embryos is also very wasteful.   Probably 400 embryos are used before one stem cell line is produced.

What is a human admixed embryo?

This is a term that includes all the variations of embryo that can be created using both human and animal genetic material.     The type of admixed embryo that is likely to be most helpful in the study of human diseases is the cytoplasmic hybrid or “cybrid”.

What is a Cybrid?

This results when the nucleus of a cow’s egg has been removed and replaced with the nucleus from a human skin cell.   Once activated to develop, the resulting embryo will be 99.9% human.  A tiny amount of the animal’s genetic material will remain within the cytoplasm of the egg.

Why is there a need for human –animal hybrid embryos?

Human eggs and embryos for research are in very limited supply.   Couples having IVF use their eggs for their own treatment.  The human embryos used for research therefore tend to be “poor quality” embryos that would normally be discarded and not used for treatment.  Cow eggs on the other hand are plentiful.  Abattoirs are a ready source of supply.

Initially there was very understandable distaste at the thought of creating what would essentially be a potential human being with some cow genes.  Although there has been sustained objection from a number of quarters, widespread public reassurance has been gained following extensive consultation by the Human Fertilisation & Embryology Authority.   It is not permitted to grow human-animal hybrids beyond the 14-day legal limit for research on human embryos.  It is already illegal to transfer any human – animal hybrid into either a human or animal womb.

In 2008, the HFEA  granted licences to create cybrids to  Kings College  and the University of Newcastle.  The University of Newcastle have already been successful in creating cybrids from cow eggs.
The eventual aim is to transfer a human nucleus from an individual with a genetic defect that has caused a neurological disease.   If stem cell lines can be grown, this will increase understanding of the disease processes and permit possible interventions and the opportunity to test new treatments.

Stem cell research is still in its infancy and no source of stem cells should be overlooked for research purposes.   It is important not to create false hopes that cures are going to be found.  For many, the means of using human – animal hybrids justifies the hope of developing treatments for a range of debilitating and lethal conditions.