Table 1.

Research policies on human-animal chimeric embryos and chimeric animals

Country	Policies and recommendations
France	French law stipulates that creating a chimeric human embryo is forbidden. The law clearly forbids the introduction of allogeneic or xenogeneic cells into a human embryo; however, it is unclear whether it also bans the introduction of human cells into animal embryos. We discussed this uncertainty elsewhere [47].
UK	The Human Fertilization and Embryology Act 1990, as amended by the Human Fertilization and Embryology Act 2008, applies to embryos that are either entirely or predominantly human or equally human and animal. It does not forbid the creation of animal chimeras by grafting human embryonic cells or embryonic cell lines into animals. However, transferring a human admixed embryo, which would be predominantly human, into an animal foster “mother” is forbidden. Of note, the definition of “predominantly human” is a crucial point, although admittedly difficult to resolve (http://www.acmedsci.ac.uk/download.php?f=file&i=13666).
Germany	The German law forbids combining a human embryo with animal cells, but not the introduction of human cells into an animal embryo. The German Ethics Council (Deutscher Ethikrat) published an opinion paper in September 2011 on the use of human–animal mixtures in research [48]. This paper highlighted the importance of finding a balance between expected medical benefits, respect of the animal welfare, and, overall, the need for an interdisciplinary scientific discussion on this subject (www.ethikrat.org/files/opinion-human-animal-mixtures-in-research.pdf).
USA	Federal US laws do not rule this issue. Nonetheless, in 2005, “the U.S. National Research Council and the Institute of Medicine recommended limits on such research, among them that no human stem cells be added to primate embryos and that animal-human chimeras not be allowed to breed” [32].
Japan	The Japanese law currently limits research on human–animal chimeric embryos by not allowing the development of such embryos beyond the appearance of the primitive streak (maximum 14 days post fertilization) and their transfer into an animal uterus. Recently, the Japanese Expert Panel on Bioethics [49] supported the idea of creating a human––animal chimera and proposed that the Japanese research regulation “should be capable of responding flexibly to the advances in research”.