Martin Bobrow welcomes the prospect

Stem cells are unspecialised cells that can self-renew and differentiate into specialised cell types. Understanding their nature and potential is an important field of research that many believe could open new avenues for the treatment of human disease and injury.
Studying stem cells could help shed light on disorders that underlie many diseases, ranging from developmental abnormalities in young children to some cases of degenerative disease, infertility, stroke and cancer. Learning how to control stem cell development could allow the production of specialised cells to treat conditions in which such cells are lost, such as childhood diabetes and Parkinson’s disease. The ability to generate specialised tissues in culture, or in animal models, could also facilitate the development and testing of new drugs before they are used in patients.
Ultimately, understanding how adult cells can be reprogrammed to become stem cells offers the potential for a step-change in treating human disease. Potentially, it allows transplantation of cells and tissues containing a patient’s own DNA, thus avoiding problems of tissue rejection.
 
Human embryonic stem cells
Research into tissue-specific stem cells found in umbilical cord blood and several adult tissues is important and should continue. However, human embryonic stem cells, derived from very early human embryos, could provide a uniquely flexible range of research possibilities and, eventually, potential treatments.
If the full opportunities for disease modelling, drug discovery or individualised stem cell therapy are to be realised, researchers need to control the genetic composition of derived human embryonic stem cells. Somatic Cell Nuclear Transfer (SCNT) offers a way to do this. It entails transferring the nucleus from an adult cell into an oocyte (or unfertilised egg) from which the nucleus has been removed. However, few human eggs are donated for SCNT because patients undergoing fertility treatment need them, and the donation procedure is invasive.

Inter-species embryos
A recent report by the Academy of Medical Sciences describes proposals by scientists to overcome this shortage.1 The idea is to make a specific type of inter-species embryo (cytoplasmic hybrid embryos) by SCNT, involving human nuclei and animal oocytes (cow or rabbit). 
The report describes this work in the context of the long history of research on inter-species constructs. For example, mouse-human hybrid cell lines were the basis for early mapping studies on human genes in the 1970s, eventually leading to the successful Human Genome Project; animal cells have been widely used to produce human therapeutic proteins; and transgenic mice expressing human genes have led to key insights into understanding and treating diseases ranging from Alzheimer’s disease to cancer.
No insurmountable ethical or safety issues have emerged over three decades of this research.
 
UK regulation
The current revision of UK legislation around human embryos offers an important opportunity to consider the future research potential of inter-species embryos in their full scientific, ethical and social context.
We appreciate the sincerely held beliefs of those who consider all research involving human embryos to be inherently unethical. However, UK legislation currently permits licensed research on human embryos subject to defined limits. These are that the creation and use of human embryos for research can only proceed under licence from the Human Fertilisation & Embryology Authority (HFEA); human embryos used for research should not be re-implanted into a woman or animal; and human embryos used for research should not be developed beyond 14 days in vitro. It is our considered view that research on human inter-species embryos should proceed under a similar framework of regulatory control.

Future challenges
The central issue of our report was the creation of human embryos incorporating some non-human material, currently regulated by the HFEA. However, as described above, researchers have for years used transgenic non-human embryos and animals, which are regulated by the Home Office. In the future, the transfer of human embryonic stem cells, or increasing amounts of human genetic material, into non-human animals and embryos is likely to present increasing regulatory and ethical challenges.
Further consideration will need to be given to the interfaces between the regulation of animal research, human embryo research and human embryonic stem cell lines.
The Academy of Medical Sciences will be undertaking further work on this issue, to include a significant component of public engagement, which we hope will inform future debate.

1. See www.acmedsci.ac.uk/publications 
 

Professor Martin Bobrow CBE FRS FMedSci is Emeritus Professor of Medical Genetics, at the University of Cambridge. He was the Chair of an Academy of Medical Sciences Working Group on inter-species embryos