The Beast?

Scientists injected dozens of human stem cells into developing monkey embryos, and the resulting hybrids survived for up to 20 days in lab dishes.

These human-monkey embryos could someday serve as helpful models for human disease, embryonic development and aging, the study authors noted in a new report, published April 15 in the journal Cell. By zooming in on the interaction of human and animal cells in the embryos, scientists could also learn how to help human cells survive amongst animal cells, potentially advancing the effort to grow human organs in living animal models.

Such studies would offer a window into human biology that would otherwise require experimenting on humans, making such studies currently impossible. Of course, the development of human-animal chimeras — organisms that contain cells from two or more species — raises its own ethical concerns, especially in regard to how long such embryos should be allowed to develop.

In the past, scientists have attempted to incorporate human stem cells into pig and sheep embryos, with the eventual goal of growing human organs in the livestock for use in transplant surgeries, Science Magazine reported. But very few human cells survived the experiments.

The low survival rate could be due to the fact that pigs and sheep aren’t closely related to humans, evolutionarily speaking, senior author Juan Carlos Izpisúa Belmonte, a professor at the Salk Institute for Biological Studies in La Jolla, California, told Live Science in an email. For instance, pigs and humans have been diverging from each other for 90 million years, when they last shared a common ancestor, he said.

Because the researchers used monkeys in the new study, "the evolutionary distance is smaller, and this may account for the greater relative efficiency of integration of human stem cells in the chimera," he told Live Science. New data gathered from the human-monkey embryos could provide hints about how to better grow human cells in more distantly related animals, Izpisúa Belmonte said.

While this line of research could lead to exciting advancements in medical science, there are ethical concerns to address, said Alejandro De Los Angeles, a stem cell biologist at the Yale University School of Medicine, who was not involved in the study.

"One of the main concerns with human-animal chimeras is whether 'humanization' of the chimeras will occur, for example, whether such chimeras acquire human-like cognition," De Los Angeles told Live Science in an email. However, these concerns don't necessarily apply to the new experiment, given that the embryos were only allowed to develop for a limited time and weren't implanted in a uterus, he said. But for future studies, "it will be important to discuss how long experiments should be allowed to go for," he said.
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Originally published on Live Science.


Part-human, part-monkey embryos grown in lab dishes | Live Science