TOKYO -- A research plan to make human pancreases in pigs is to be submitted to the ethics committee of the University of Tokyo by professor Hiromitsu Nakauchi of the prestigious school's Institute of Medical Science, Nakauchi has told the Mainichi Shimbun.

He plans to make the application right after government guidelines to allow research on the making of human organs inside animal bodies are introduced as early as next spring. If approved by the university and the government, it will be the first study of its kind in Japan.

According to Nakauchi, he plans to inject human iPS cells -- induced pluripotent stem cells that can develop into any kind of cells -- into the fertilized eggs of pigs with their pancreas-making genes edited out. This procedure is carried out to make what is called human-animal chimeric embryos, which will then be placed inside the wombs of surrogate pig mothers.

If everything goes well, human pancreases will develop in the places of pig pancreases in the embryos. About 100 days later, shortly before delivery, they will be taken out of the wombs for examination of their pancreases. The researcher will check if the produced human organs are safe for transplant, or if cells that originated in humans have spread to other organs or tissues inside the pigs.

Nakauchi and his fellow researchers made the rat's pancreas inside a mouse in 2010 in a bid to utilize the technology for transplant medicine. The next year, he reported that he made a pig pancreas inside the body of a different pig. In 2017, he and others published the results of a study in which they successfully observed treatment effects on a mouse with diabetes by transplanting parts of mouse pancreases made inside rats.

Japan's existing government guidelines provide that the human-animal chimeric embryo can culture for up to 14 days and ban its transplant into animal wombs. However, the Ministry of Education, Culture, Sports, Science and Technology has reviewed the rules for five years and came up with draft revisions in October this year, which would approve studies to make animals with human organs using the hybrid embryo. The new guidelines would allow such studies for medicine creation or basic research, and ban the transplants of such embryos into humans.

No successful production of human organs inside animals has been carried out so far. Nakauchi said that it took him eight years for his study to be accepted in Japan since the first time he explained what he wanted to do to the government. "I would like to advance the research carefully by checking if human cells get mixed up with (pigs') brains or reproductive cells," said Nakauchi.

(Japanese original by Momoko Suda, Science & Environment News Department)