Japan Changes the Rules

Science Fields

The Japanese government made a first in its history and cracked the doors open to developing human organs in animals. By placing human stem cells called iPS (induced pluripotent stem cells) into modified animal foetuses, it will be possible to cultivate human organs in the bodies of animals. And maybe one day, we will be able to transplant these organs to humans.

The study, led by Hiromitsu Nakauchi of Stanford University, is the first to be approved by the government. Before this, the Japanese government ordered the destruction of animal foetuses carrying human cells after 14 days of development and never allowed implanting these foetuses in the uterus. Laws on this issue vary in each country. For example, while there are no federal restrictions in the US, some countries, such as Japan, do not allow such experiments to last longer than two weeks.

These creatures carrying both human and animal cells are named after the monster chimaera in ancient Greek mythology. Chimaera was a monster that is a combination of a lion, a goat, and a snake. And its name is often attributed to beings possessing the characteristics of several animals.

Experiments involve implanting iPS cells to mouse, rat, or pig embryos that do not have a pancreas. The cells are expected to replace the missing organ. The embryo placed in the uterus is expected to have a functional human pancreas at birth. The pancreas grew in the rat’s body then performs its function successfully when transplanted to a mouse. However, the kidneys grown the same way are not yet able to adapt to their new bodies. Furthermore, because the embryo has been modified, rats carrying mouse stem cells can survive for a very short time after birth.

“It took nearly 10 years, but we are now able to start the experiment,” says Nakauchi, “The study is just about to begin. Do not expect that we are generating human organs in a year or two.”

Besides technological issues, certain ethical rules restrict research. Growing human brains or reproductive cells in animal bodies, and how this will contradict the nature of living things are hot topics of debate. Researchers who are aware of the topic’s sensitivity check the embryos at every stage to monitor whether human cells are formed in the animal’s brain. If not, the experiment proceeds to the next stage. By law, the experiment must be terminated if human cells are detected in more than 30 percent of the brain of experimental animals.

Researchers emphasise that fearful scenarios, such as the emergence of mice with human characteristics, are quite unlikely because the cells of host organisms often dominate the implanted cells. This means that the mouse cells implanted in rat embryos are generally at a disadvantage.

We need more time to grow human organs in pig bodies, but experts say that such state-approved studies can be useful in overcoming the restrictions they face.

This is how we see the progress of technology with great potential for patients in need of organ or tissue transplantation, in the treatment of many diseases.


  • 1. https://medicalxpress.com/news/2019-08-japan-human-animals.html?utm_source=nwletter&utm_medium=email&utm_campaign=daily-nwletter
  • 2. https://www.livescience.com/66071-human-animal-hybrid-embryos.html