Human admixed embryos
Human admixed embryos are those that contain human and animal matter. The most common type is a cytoplasmic hybrid embryo, which is created by adding the nucleus from a mature human cell (such as a skin cell) to an animal egg cell emptied of its nucleus, via a process called somatic cell nuclear transfer.
Genetically speaking, cytoplasmic hybrid embryos are 99.9 per cent human. The other 0.1 per cent is mitochondrial DNA from the animal egg.
The ability to obtain human eggs - from which embryonic stem cells are currently derived - is very limited and raises ethical issues. Creating hybrid embryos could provide a means to overcome this limited supply, for the purposes of research only.
Currently, two groups in the UK have been granted licences to create cytoplasmic hybrid embryos for research.
Dr Stephen Minger from King's College London and colleagues have been granted a licence to create hybrid embryos using adult skin cells from patients with genetic neurodegenerative disorders such as Alzheimer's, Parkinson's and spinal muscular atrophy. The researchers plan to create stem cell lines containing the same genetic mutations as seen in the patients with the disorders.
At Newcastle University, Dr Lyle Armstrong and colleagues will create cytoplasmic hybrid embryos to study how the nucleus is reprogrammed during embryonic development. They also plan to develop stem cell lines from these embryos and compare them to those derived from embryos created during IVF.
Research using other types of human admixed embryos may also help to improve our understanding of stem cells, gene function and embryo development. These other kinds include:
- true hybrids - embryos created with human eggs and animal sperm, or with animal eggs and human sperm
- transgenic human embryos - human embryos into which animal DNA has been added
- chimeric human embryos - human embryos into which one or more animal cells have been added.
As with cytoplasmic hybrid embryos, these human admixed embryos will not be allowed to develop beyond 14 days, it will be prohibited to implant them into humans or animals, and their use will be regulated by the Human Fertilisation and Embryology Authority.
Image: The nucleus (containing the DNA) being removed from an animal egg cell with a glass needle. The empty egg will act as an incubator for the human DNA.
