Stanford University team confirms functional recovery after transplanting human iPS cells into mouse brains

When human induced pluripotent stem cells (iPS cells) were transformed into a group of brain nerve cells and transplanted into the brains of newborn mice that had been genetically engineered to lack the cerebral neocortex and the hippocampus, which plays a role in memory, they grew and functioned together, a research team from Stanford University in the US announced in the online edition of the British scientific journal Nature on the 16th.

Although the human brain has not been recreated in mice, it will help elucidate the mechanisms of genetic and neurodegenerative diseases of the brain and develop prevention and treatment methods.

Human iPS cells and embryonic stem cells (ES cells) can be used to create miniature organs such as brains, hearts, livers, and intestines in experimental containers, and are collectively known as "organoids." They are used to elucidate incurable diseases and test new drug candidates, but because they cannot form blood vessels, it is difficult to supply oxygen and nutrients with blood, and they also cannot investigate the functions that cooperate with other tissues.

In 2022, the research team announced that they had conducted an experiment in which human brain organoids were transplanted into the cerebrums of newborn rats. Although they grew and functioned together to some extent, their usefulness was limited because the rat brain grows faster than the human brain. Therefore, in order to secure space for human brain organoids to grow, they created and transplanted newborn mice with almost no neocortex.

There are concerns that such experiments could result in animals with human brains. The research team believes that when conducting experiments using primates, which are similar to humans, discussions between researchers, bioethicists, representatives of patients with incurable diseases, and regulatory authorities are necessary.