Controversial Chimera Research Continues

Chimera Crop

The shortage of human organs available for transplantation in the U.S. and around the world has led scientists to consider how to grow them in animals to be harvested later for transplants.

One approach that scientists have been investigating is the generation of human-animal chimeras, which are made possible because of advances in stem cell technologies. Using this approach, scientists add human pluripotent stem cells to animal embryos and track the human cells to better understand how they contribute to the growing embryo. The objective is to use the human cells to help produce particular organs that are needed for transplantation in human patients.

In the past, researchers combined human cells with mouse and pig embryos. In doing so, however, they found that human cells did not contribute greatly to the overall composition of the chimeras, possibly due to the evolutionary distances between humans and these animals.

In a new study, scientists combined human stem cells with embryos of macaque monkeys (shown in image above), which are more closely related to humans, and followed the cells in these chimeras for up to 20 days to see if they would have a greater presence. Human cells were present in greater numbers in these embryos, but, at most, they contributed to about 7% of the cells present in various layers within the embryos.

Stem cell biologists recognize that the number of human cells in the chimeric embryos is low. However, they want to continue research in this area to learn how to make human cells integrate directly into specific organs, as well as how to make the human cells more competitive in general, to advance their goal of producing organs available for transplantation.

While none of the chimeric human-animal organisms were brought to term in these experiments, NAVS has serious objections to the concept of creating human-animal chimeras. Presumptions and overconfidence by the scientific community about the promise of chimera research should not outweigh the cost of this dangerous experimentation. Just because scientists can do this research does mean they should.

We can’t ignore the possibility that human cells will be present in organs and tissues that the researchers hadn’t anticipated. If human cells end up in the brain of the chimeric animal, for instance, there is the possibility that the hybrid animal could acquire human mental cognition and consciousness, which raises serious bioethical issues. Chimera research also exploits animals and can potentially cause significant animal suffering. And, of course, should the chimera experiments prove “successful,” the animals would be killed to harvest their organs.

There is no question that the shortage of human organs available for transplantation is a pressing issue. However, the creation of chimeric animals is not the best answer. A better solution is to modify existing organ donation programs to presume the intent to donate organs with the option to opt out. Not only is this approach more cost-effective, it spares both human and animal suffering.


Source: “Human-Monkey Chimeras Shed Light on Development,” The Scientist, April 15, 2021
Image: Weizhi Ji/Kunming University of Science and Technology