Chinese experts and netizens expressed strong ethical concerns over Japan's first officially-approved experiment to create animal embryos containing human cells and birth to such embryos, following Japan's reversal of its ban in March.
Japanese scientist Hiromitsu Nakauchi, who leads research teams at the University of Tokyo and Stanford University in California, plans to create human pancreases in rodents by using human induced pluripotent stem (iPS) cells, according to a report by The Asahi Shimbun last week.
Researchers will place human iPS cells into fertilized eggs that do not have the ability to make pancreases to create "animal-human embryos" and transplant the embryos into wombs of rats or mice.
The embryos will be born after full-term pregnancies.
Human-animal hybrid embryos have been made in countries, such as the U.S., but never brought to term, according to Nature magazine.
In 2003, Chinese scientists also used cloning techniques to create more than 100 hybrid embryos by fusing human skin cells with rabbit eggs, which was reported as the first such experiment in the world.
These embryos only developed in laboratory dishes for several days before the scientists destroyed them to retrieve the so-called embryonic stem cells from their interiors.
Human-animal embryo study is a long-standing topic of controversy in life science, owing to ethical concerns, Liu Changqiu, a health law expert and research fellow at the Shanghai Academy of Social Sciences, told the Global Times.
"Scientists and citizens all worry that the study may bring about a new creature, which breaks through human ethical boundaries," Liu explained.
In many countries including China, such experiments are still banned or strictly restricted, Liu noted.
Researchers would monitor the rodents during their first two years of life. If they detect that human cells exceed more than 30 percent of the brains of the rodent embryos, they will suspend the experiment, The Asahi Shimbun reported.
If the study goes well, researchers would go further to grow human organs in pigs and sheep and, eventually, transplant these organs into people, thereby solving a chronic shortage of such organs for transplantation, said the report.
However, Liu warned about risks of contaminating the human gene pool in the future if organs produced through such means are transplanted into human bodies.
Chinese netizens also worried that the study would open Pandora's box.
"What if the study results into an animal that owns both human's wisdom and animal's aggressiveness? Will that be the end of human beings?" an online user commented.
"Study without morality is a kind of crime," said another.
Nakauchi told The Asahi Shimbun that the number of human cells grown in the bodies of animals were extremely small, like one in thousands or one in tens of thousands, making it impossible to bring about an animal with a human face.
The plan was approved by the Japanese Ministry of Education, Culture, Sports, Science and Technology on July 24 after the country lifted a ban on such research in March, The Asahi Shimbun reported.
Japan's new guidelines require researchers take appropriate steps to prevent the birth of an ambiguous creature that could be part human. Regulations also ban the reproduction of animals born through this method.