Japan Ministry grants permission for historic human-animal hybrid experiments

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Stem cell biologist Hiromitsu Nakauchi hopes the project will one day enable scientists to grow custom human organs in sheep and pigs.

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The Japanese Ministry have confirmed that they will allow work to begin on a project that will include implanting human cell-infused embryos into rodents.

Last year, the country passed controversial legislation that allowed scientists to not only implant hybrid embryos into animals, but to bring them to term.

Rather than introduce a new animal-human species into the world, the end goal of these early stage experiments is to grow viable human transplant organs in animals.    

"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," University of Tokyo stem cell biologist Hiromitsu Nakauchi told The Asahi Shimbun.

Nakauchi and his team are attempting to harvest a pancreas that contains human cells in mice; growing the embryo to 15.5 days - almost fully to term. 

Human induced pluripotent stem (iPS) cells will be placed in fertilised embryos of rodents which will then be placed in the wombs of the animal subject to grow.

If the scientists are successful in growing a human-suitable pancreas in a rodent’s foetus they will then ask permission to progress to pigs. 

The Japanese Government has stipulated that an embryo with a brain consisting of more than 30 per cent human cells must be destroyed.

The revised guidelines come after a previous ban on such projects for fear it could result in the birth of a creature that contains both animal and human genes.

Despite the public concern for experiments of such a nature to deviate into sci-fi, Nakauchi says the reality of such a being making its way into the world is highly unlikely.

“The number of human cells grown in the bodies of sheep is extremely small, like one in thousands or one in tens of thousands,” he said. 

At that level, an animal with a human face will never be born.

Nakauchi has previously conducted experiments at Stanford University in the US that involved placing human iPS cells into the fertilised eggs of sheep and transplanting those embryos into the wombs of sheep. 

Ethical concerns

In September 2015, the U.S. National Institutes of Health abruptly announced a moratorium on funding studies related to human stem cells being implanted in animal embryos.

Jiro Nudeshima, a life science specialist, told The Asahi Shimbun that not only will the experiments on rats be of little use to human development because of the extreme difference is anatomy but they also pose ethical questions.

“It is problematic, both ethically and from a safety aspect, to place human iPS cells, which are still capable of transforming into all types of cells, into the fertilised eggs of rats and mice," he said.

“If the goal of such studies is to discover a therapeutic application for humans, experiments on rats and mice are unlikely to produce a useful result because the size of the organ will not be sufficient and the result will be a far cry from humans anatomically.”

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