Topic summary: Chimeras



Published November 2016

A chimera is a single organism with a genetic composition from genetically different zygotes but in which the DNA is never mixed on a chromosomal or intracellular level.¹ Research using animal models containing human cells is not a new phenomenon; for example chimeric animal models with human cells in the brain have been used to study neurological diseases such as Alzheimer’s and Parkinson’s, and human tumour cells are routinely grown in mice to study cancer processes. However, newer forms of stem-cell-based chimera research, which may involve the use of embryos, has raised special concern about the possibility of a human cell contribution to multiple organs and tissues in animals and hence increased human/non-human mixing.

Are there recent scientific, legal or social developments?

There have been multiple recent examples of advances in chimera research including sheep growing partially human livers, and mice with human brain cells that have advanced their learning. In 2013 scientists published work attempting to grow an entirely human pancreas through creation of chimeric pigs.

In May 2008, the House of Commons debated a proposal to ban the creation of human-animal chimera or hybrid embryos for research and came to the decision that they would be permitted, given that they would be destroyed within 14 days. In August 2016 the National Institutes of Health (NIH) in the US proposed changes to their policies on chimeric embryos to expand some of the prohibitions, whilst relaxing others. It also set up a steering committee to look at early embryo research and research where human cells could give rise to a substantial contribution or functional modification to the animal brain.

Are there complex ethical issues?

There are substantial arguments for pursuing research into chimeras given potential benefits which might include curing chronic diseases such as Type 1 diabetes or addressing the shortfall in availability of organs for transplantation. There are currently uncertainties about the effects of human cells on off-target organs and tissues in the chimeric animals, particularly in the nervous system. If the effects of this technology are to include changes in cognition, behaviour or physical appearance of the animal this could raise concern that our manipulation of animals has gone too far. Some worry that in the process of biologically humanising a research animal, scientists may also end up ‘morally humanising’ the resulting chimera, particularly if there is chimerism of the central nervous system. Others have argued that these concerns are overstated; that the appearance of a human-like self-consciousness is highly unlikely and that the presence of human neural matter in a non-human brain is in fact much more likely to create animal suffering and acute biological dysfunction. Questions about how basic animal rights and animal welfare are protected during such research will be important. Animal rights groups have been opposed to chimera research stating that it contributes to the ‘debasement of animals’ whilst others have expressed concern that creating animal-human chimera diminishes the very dignity of being human. Complex ethical issues arise when considering the use of early embryo research involving chimeras, particularly human chimera embryos in which human embryos have animal cells added to them during early development. Many people feel that human embryos have a special status which requires that we give them specific legal protection, over and above that given to animal embryos. A fusion of the two, whichever form that may take, will require fresh consideration.

Is there a potential policy impact?

Regulation of human embryo research is governed by the HFEA in the UK and that of animal embryos by the Home Office. As these technologies advance it is likely that both bodies will be required to update and clarify existing regulation. The current regulation in the UK is not particularly prescriptive but rather sets up authorities to regulate activities.

Is it a subject of public concern?

The media has expressed outcry at the prospect of a ‘humanzee’ and the resulting ethical minefield we would be faced with. Comments posted on the NIH website reveal the extent of public concern with many parties accusing scientists of ‘playing God’ or conducting ‘Frankenstein science’. The HFEA designed a public consultation in 2007 to explore public opinion on hybrid and chimera research and found that the public was finely divided with people generally opposed to such research unless it was tightly regulated and was likely to lead to scientific or medical advancements.

Is the consideration timely?

Given the recent significant progress internationally in chimera research the timing seems appropriate.

Can the Council offer a distinctive contribution?

The Council’s genome editing project proposes to include consideration of xenotransplantation, but there may be larger ethical issues raised by chimeras which may warrant separate consideration. The modification of the nervous system of animals would be a particularly interesting topic to explore, where the Council may be able to provide a unique insight which could influence public policy and regulation.

¹ This is in contrast to a hybrid, which involves crossing two gametes to create a zygote and in which each cell from the hybrid animal contains genetic material from both parent species.

Possible future work topics

This is one of the topics that have been suggested as possible project areas for further investigation by the Council. These topic summaries do not aim for comprehensiveness; rather, they are intended to sign-post some of the key considerations and to provide a starting point for discussion. Each summary includes links to relevant publications on the topic.

Possible future work topics are selected and/or revised regularly, following discussions among members of the Future Work Sub-Group and the Council. This set of topic summaries was published in November 2016.

Previous work

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