Japan Relaxes Rules on Human-Animal Chimeras


Japanese regulators have effectively given the green light to research involving human-animal chimera embryos, which are created by implanting human pluripotent stem cells into animals in early development. The country previously permitted such research but required that the embryos be destroyed after 14 days. Revised guidelines, issued in early March, remove even this restriction.


A group of Japanese bioethicists at the Kyoto University have raised ethical concerns about the new policy. In a letter published in Cell Stem Cell, they point out that the guidelines would allow researchers to create chimeras with human cells populating animal brains—something that concerns the Japanese public. They also do not explicitly prohibit chimera embryos made from human and nonhuman primate cells, which could take experiments into ethically uncharted territory.


Invasive research on great apes isn’t allowed in Japan, notes Misao Fujita, a professor of bioethics at Kyoto University and a coauthor of the new letter. But scientists could theoretically produce chimeras made from human and monkey cells, as long as they can justify there’s “sufficient scientific rationale” for the research, according to the paper. Some US scientists have recently argued that human-primate chimeras could serve as better models of neurological and psychiatric disease than current monkey models. Japanese researchers may someday follow suit, Fujita and her colleagues warn.


Dr Fujita and her colleagues recently conducted a survey which found that the Japanese tend to support the general idea of creating human-animal chimeric embryos with human induced pluripotent stem cells (iPSCs). However, they’re worried about the prospect of human cells contributing to animal brains, or in germ cells that lead to progeny—much more so than if they were only present in heart, blood, or liver tissue.


“The biggest concerns, based on our surveys, is [the] concern that animals could become ‘humanized,’” writes Fujita to The Scientistin an email. “It seems people are concerned that the boundary between humans and animals could become blurred.” The group of bioethicists recommends that the government undertake public ethical debates before researchers pursue projects that involve chimeric animals with humanized brains or human gametes.


On the same day the new guidelines were issued, stem cell pioneer Hiromitsu Nakauchi’s laboratory at the University of Tokyo announced plans for a research project aiming to grow a human pancreas inside a pig, according to Jiji Press. His team had previously succeeded in generating a rat pancreas from a mouse, and growing a pancreas from one species of pig from an embryo of another pig species. For the new research, Nakauchi’s team will first have to apply for approval by the university’s ethics committee as well as the Japanese government’s special committee for research ethics.

The Scientist. April 4. Cell Stem Cell. April 4.

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