Rapid progress in research involving miniature human brains grown in a dish has led to a host of ethical concerns, particularly when these human brain cells are transplanted into nonhuman animals. A new paper evaluates the potential risks of creating “humanized” animals, while providing a pathway for scientists to move forward in this important area.
Neuroscientist Isaac Chen from the Perelman School of Medicine at the University of Pennsylvania, along with his colleagues, has written a timely Perspective paper published today in the science journal Cell Stem Cell. The paper was prompted by recent breakthroughs involving the transplantation of human brain organoids into rodents—a practice that’s led to concerns about the “humanization” of lab animals.
In their paper, the authors evaluate the current limits of this biotechnology and the potential risks involved, while also looking ahead to the future. Chen and his colleagues don’t believe anything needs to be done right now to limit these sorts of experiments, but that could change once scientists start to enhance certain types of brain functions in chimeric animals, that is, animals endowed with human attributes, in this case human brain cells.
In the future, the authors said, scientists will need to be wary of inducing robust levels of consciousness in chimeric animals and even stand-alone brain organoids, similar to the sci-fi image of a conscious brain in a vat.
Cross-section of a brain organoid.
Image: Trujillo et al., 2019, Cell Stem Cell
Human brain organoids are proving to be remarkably useful. Made from human stem cells, brain organoids are tiny clumps of neural cells which scientists can use in their research.
To be clear, pea-sized organoids are far too basic to induce traits like consciousness, feelings, or any semblance of awareness, but because they consist of living human brain cells, scientists can use them to study brain development, cognitive disorders, and the way certain diseases affect the brain, among other things. And in fact, during the opening stages of the Zika outbreak, brain organoids were used to study how the virus infiltrates brain cells.
The use of brain organoids in this way is largely uncontroversial, but recent research involving the transplantation of human brain cells into rodent brains is leading to some serious ethical concerns, specifically the claim that scientists are creating part-human animals.
Anders Sandberg, a researcher at the University of Oxford’s Future of Humanity Institute, said scientists are not yet able to generate full-sized brains due to the lack of blood vessels, supporting structure, and other elements required to build a fully functioning brain. But that’s where lab animals can come in handy.
“Making organoids of human brain cells is obviously interesting both for regenerating brain damage and for research,” explained Sandberg, who’s not affiliated with the new paper. “They do gain some structure, even though it is not like a full brain or even part of a brain. One way of getting around the problem of the lack of blood vessels in a petri dish is to implant them in an animal,” he said. “But it’s at this point when people start to get a bit nervous.”
The concern, of course, is that the human neural cells, when transplanted into a nonhuman animal, say a mouse or rat, will somehow endow the creature with human-like traits, such as greater intelligence, more complex emotions, and so on.
