Imagine pigs with human hearts or mice whose brains have a spark of human intelligence. Scientists are cultivating a flock of such experimental creations, called chimeras, by injecting potent human cells into mice, rats, pigs and cows. They hope the new combinations might one day be used to grow human organs for transplants, study human illnesses or to test new drugs.
In the latest advance, researchers in the U.S. and China announced earlier this month that they made embryos that combined human and monkey cells for the first time. So far, these human-monkey chimeras (pronounced ky-meer-uhs) are no more than bundles of budding cells in a lab dish, but the implications are far-reaching, ethics experts say. The use of primates so closely related to humans raises concerns about unintended consequences, animal welfare and the moral status of hybrid embryos, even if the scientific value of the work may be quite high.
“There were lots of breakthroughs in this experiment,” says bioethicist Nita Farahany of Duke University. “A remarkable step has been taken scientifically that raises urgent issues of public concern. We need to figure out what the right pathway forward is to help guide responsible progress.”