Bioethics Blogs

Ethical aspects of research with chimera embryos

Vardit Ravitsky highlights a few ethical issues with human-nonhuman chimera research.


Assessing the potential benefits and risks of innovative health research is often a complex task. The higher the stakes, the more daunting such analysis becomes. This is the case with research on human-nonhuman chimera embryos, where human pluripotent stem cells (that can potentially develop into any kind of tissue or organ) are introduced into non-human embryos at a very early stage. These cells can replicate and then specialize, potentially being expressed in any part of the nonhuman animal as it develops, creating an organism that is part human and part nonhuman.

The potential benefits of human-nonhuman chimera research are immense. Such embryos, and the part-human animals that may develop from them, can be used to study human development, shed light on infertility, inform disease models, and test new drugs. If successful, this research might even lead to growing human organs inside nonhuman animals’ bodies that would be compatible with individual patients in need of an organ for transplantation. In light of ongoing organ shortages, chimera research could be a game changer for thousands of patients awaiting life-saving organs.

At the same time, the risks are significant. The effects of pluripotent human stem cells on organs and tissues in the chimeric animal are uncertain. Cells can go ‘off target’ and be expressed in an unintended part of the nonhuman animal’s body. There are, for example, concerns about the possibility that chimeric animals may develop human sperm and eggs, so that if two such animals breed with each other they might produce viable human embryos carried inside non-human animals.

The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.