In 2019, Japan lifted a moratorium on human-animal chimera embryo (HACE) research. This lift permitted Japanese researchers to grow organs in animals by mixing human and animal cells in animal embryos. It also followed a study by CiRA researchers in 2017 that examined the attitudes of the Japanese public towards HACE research (Sawai et al., 2017).

Following that work, the same group has teamed with a U.S. research group led by Dr. Walter C. Low at the University of Minnesota to survey 430 members of the U.S. population between 2018-2020. The new study finds that the U.S. public is more tolerant than the Japanese public of HACE research, encouraging the authors to write forthright that the United States National Institute of Health (NIH), the main body funding and regulating health-related research in the country, should, like Japan, lift its moratorium on HACE research.

The survey used in the new study was the same as the one used in Japan and asked opinions on three incremental types of HACE research. In the first, human stem cells would be injected into pig embryos. In this hypothetical research, scientists could observe how the human cells grow in an (albeit animal) embryo. In the second, the embryo would be transplanted into a pig, which would give birth to a piglet that had a pancreas made of only human cells. By observing the piglet grow, this research could also clarify pancreas development. In the third and final iteration, the human pancreas would be used for transplantation surgery in patients.

Approximately one of every five people surveyed in the U.S. refused any of the suggested types of research, whereas three out of five felt no prohibitions were needed. In contrast, while one of every five people rejected all the proposed types of research in the Japanese survey too, only two out of five found the transplantation of the pancreas into human patients acceptable.

A further breakdown of different groups revealed some interesting results.

Although strong religious views are stereotyped as an obstacle against human embryo research, those views did not come into play for HACE research, in which the embryos are animal-derived. In fact, religious views were quite consistent with the overall U.S. population (55% vs. 59% approving of all three types). In contrast, the one population that expressed by far the greatest hesitation were people opposed to animal research in general. Only 40% approved of transplantation, which resembles the tolerance in the total Japanese population. Moreover, two out of every five people who opposed animal research in general rejected all types of HACE research, doubling the overall rates of the overall U.S. and Japanese populations.

Although the survey focused specifically on HACE research towards the pancreas, it also asked respondents to consider if the HACE resulted in human cells developing in other organs of the animal. Tolerance varied with organ but trended consistently with Japanese opinions. The least tolerance for human cells mixing was toward the brain and sperm/eggs.

The reasons were not explicitly stated in the survey, but CiRA Prof. Misao Fujita, who led the research on the Japanese side, said that her team's research has led to some theories.

"For the brain, people may be worried that the animals will develop human-like consciousness. As for sperm and egg, they may worry that the animal can pass its human genes to offspring," she says.

Overall, the authors' conclusions are unequivocal. "It is clear that, compared with Japan, there is wide acceptance of HACE research. The NIH should lift its moratorium and replace it with strict guidelines for ethically sound research," they write.

• doi: 10.1016/j.stemcr.2020.08.018