Japan Green Lights Human-Animal Embryo Experiments

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By Tarik Johnson

A Japanese stem-cell scientist will soon have the approval to begin his experiments to grow human organs in animals. Hiromitsu Nakauchi, the leader of research teams in Stanford and Tokyo University has been working for a decade on growing human cells in mice and rat embryos and then transplanting those embryos into surrogate animals. The ultimate goal of the study is to produce animals with organs made of human cells that could be transplanted into humans.

On July 24th, a committee of members from the Ministry of Education, Culture, Sports, Science and Technology granted permission to University of Tokyo researchers to conduct a study to create human pancreas in rodents by using human induced pluripotent stem (iPS) cells. “Finally, we are in a position to start serious studies in this field after 10 years of preparation. We don’t expect to create human organs immediately, but this allows us to advance our research based upon the know-how we have gained up to this point,” said Nakauchi.

Before March, Japan, like many other countries, explicitly prohibited the growth of animal embryos containing human cells beyond fourteen days or the transplant of such embryos into a surrogate uterus. Governments were worried such studies could lead to the birth of creatures that involve a mix of animal and human genes. However after adjusting guidelines following consultations with experts that started in 2012, the creation of human–animal embryos that can be transplanted into surrogate animals and brought to term was sanctioned. “It is good to proceed stepwise with caution, which will make it possible to have a dialogue with the public, which is feeling anxious and has concerns,” says science-policy researcher Tetsuya Ishii of Hokkaido University in Sapporo, Japan.

According to Nature, some bioethicists are concerned about the possibility that human cells might stray beyond development of the targeted organ, travel to the developing animal’s brain and potentially affect its cognition. Nakauchi responded to the concerns saying, “We are trying to do targeted organ generation, so the cells go only to the pancreas.” If they detect that human cells exceed more than thirty percent of the brains of the rodent embryos, they will suspend the experiment.

The details of the procedure go like this: first the animal must be genetically altered so that it cannot grow a normal pancreas. Then iPS cells are introduced into the embryos. iPS cells are obtained by reprogramming human cells to revert to an embryonic-like state from which they can form other cell types. Finally, the theory is the stem cells will develop into a pancreas composed mainly of human cells as the embryo develops.

In 2017, Nakauchi and his colleagues reported a rat that was unable to produce a pancreas received an injection of mouse iPS cells into the embryo. The rat formed a pancreas made entirely of mouse cells. Nakauchi and his team transplanted that pancreas back into a mouse that was engineered to have diabetes. The rat-produced organ was able to control blood sugar levels, effectively curing the mouse of diabetes. Final approval from the ministry is expected next month.

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