Human-animal hybrids are to be developed in embryo form in Japan after the government approved controversial stem-cell research.
Human cells will be grown in rat and mouse embryos, then brought to term in a surrogate animal, as part of experiments set to be carried out at the University of Tokyo.
Supporters say the work – led by renowned geneticist Hiromitsu Nakauchi – could be a vital first step towards eventually growing organs that can then be transplanted into people in need.
But opponents have raised concerns that scientists are playing God.
They worry the human cells could stray beyond the targeted organs into other areas of the animal, effectively creating a creature that is part animal, part person.
For that reason, such prolonged experimentation has been effectively banned or gone unfinanced across the world in recent years.
In Japan itself, scientists were forbidden from going beyond a 14-day growth period. But those laws were relaxed in March when the country’s education and science ministry issued new guidelines saying such creations could now be brought to term.
Now, Dr Nakauchi’s application to experiment is the first to be approved under that new framework.
"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," he told the Asahi Shimbun newspaper.
He added that he planned to proceed slowly, and will not attempt to bring any hybrid embryos to term for some years, rather growing the hybrid mouse embryos to 14.5 days, when the animal’s organs are mostly formed, and the hybrid rat embryos to 15.5 days.
Such caution was welcomed by bioethicists in the country.
“It is good to proceed with caution,” said Tetsuya Ishii, science-policy researcher at Hokkaido University in Sapporo. “It will make it possible to have a dialogue with the public, which is feeling anxious and has concerns.”
