AND NOW … Animal-Human Chimeras: Japan Plans To Lift Ban On Growing Human Organs In Animals

Ban on growing human organs in animals to be lifted (The Asahi Shimbun, June 19, 2013):

The government plans to lift a ban on basic scientific research to grow human internal organs in the bodies of other animals for potential use in transplants, raising concerns about compromising the dignity of human beings.

The proposed policy change was presented June 18 during a meeting of an expert panel under the government’s Council for Science and Technology Policy. It will open the door, for example, to experiments to engineer human pancreases and livers in pigs and other animals. Such tests will utilize advanced biotechnology such as induced pluripotent stem (iPS) cells.

But the envisioned creation of animal-human chimeras, which have both human and nonhuman cells, could blur the boundary of humans and nonhumans.

A typical research program would use a fertilized pig egg, genetically modified to inhibit the formation of a pancreas, and grow it into an embryo. Injection of human iPS cells would turn it into an animal-human chimeric embryo.

Returning it into a pig uterus could result in the birth of a piglet with a human pancreas. Porcine internal organs are about the same size as their human counterparts and could therefore be transplanted into humans.

There are high expectations for regenerative medicine applications of iPS cells, which have the potential to develop into cells of different internal organs. However, it remains difficult to engineer the complicated, three-dimensional structures of internal organs from such cells.

The use of animal-human chimeric embryos is considered more suited to the purpose because it would allow the desired internal organs to be grown in animal bodies.

Advances have been made in relevant basic research. A group of scientists from the University of Tokyo and other research institutions said in February they had engineered a porcine pancreas in another pig.

A law-based guideline against human cloning, formulated in 2001, allows animal-human chimeric embryos to be engineered only as part of basic research for the creation of transplant-use internal organs. But such embryos can be grown only in labs up to 14 days and cannot be returned into human or other animal uteri.

The expert panel under the Council for Science and Technology Policy has discussed possible revisions to that guideline. During the June 18 meeting, the panel approved returning animal-human chimeric embryos into animal uteri. The science ministry will be responsible for hammering out the specific amendments to the guideline.

But the expert panel said more discussions were necessary regarding the conditions under which giving birth to such embryos would be approved.

The panel also said there should be measures to protect the dignity of humans. It said certain restrictions should be imposed on studies that use primates and on studies to engineer human brain cells and generative cells.

In the United States, a National Institutes of Health guideline bans the transplant of animal-human chimeric embryos into primates. A recommendation in Britain said experiments that involve “substantial functional modification of the nonhuman primate brain” should “not, for now, be licensed.”

At least one panel member said Japan should follow in the footsteps of the United States and Britain to regulate research for engineering human brain cells.

Relevant research is still in a basic stage and many technological challenges stand in the way of clinical application. It remains unknown whether internal organs can really be grown from embryos in animal bodies.

The engineering of chimeric animals has been a common practice in basic biological studies, but it was only last year that a group of U.S. scientists said that they created the world’s first chimeric monkeys.

There are also concerns about safety, including the potential risk of unknown viruses in animal cells becoming activated and infectious once they are in human cells.


(This article was compiled from reports by Kayoko Geji and Shigeko Segawa.)

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