Synthetic embryos were implanted into monkey wombs

But within 20 days of the transfer, the monkey blastoids stopped growing and appeared to separate, say Liu and his colleagues, who published their findings in the journal Cell Stem Cell. This suggests that blastoids are still not perfect replicas of normal embryos, says Alfonso Martinez Arias, a developmental biologist at Pompeu Fabra University in Barcelona, ​​Spain. For now, “it’s clearly not working,” he says.

This could be because a typical embryo is generated from an egg, which is then fertilized by sperm. A blastoid made from stem cells may express genes in the same way as a normal embryo, but it may be missing something crucial that normally comes from an egg, says Martinez Arias.

There is also a chance that the team would have seen more progress if the experiment had been done on more monkeys. After all, of the 484 blastoids that were developing on day seven, only five survived day 17. And getting an embryo to implant in the uterus is tricky business, says Chuva de Sousa Lopes. “Even when you’re doing IVF on a man, that’s one of the bottlenecks to getting pregnant,” she says. “Maybe if you did that with 100 monkeys, you’d have two that got even more pregnant.”

However, the lives of monkeys are precious, says Martinez Arias, and such large-scale experiments would likely not be considered ethical.

A model embryo

None of this means that blastoids aren’t useful. They still provide a good model of what happens in the early stages of embryonic development in monkeys and potentially in humans.

Researchers hope monkey blastoids will help us learn more about human embryos. We know very little about how the union of sperm and egg ultimately leads to the development of our organs and nervous systems – and why things can sometimes go wrong. Scientists are generally not allowed to study human embryos in a laboratory beyond 14 days after fertilization. And recently released international guidelines emphasize that human blastoids should never be implanted in a person or any other animal.

“We want to understand human development, and it’s not safe to transfer human blastoids (into people),” Rivron says. “We have to find an alternative. And non-human primates are the closest relatives of humans.

Scientists hope this type of research can tell us more about human pregnancy, including why some people have trouble conceiving and why some miscarriages occur. Because scientists could generate an infinite number of blastoids, they wouldn’t need to rely on animals as embryo donors. And they could test drugs on hundreds or thousands of blastoids in hopes of discovering ways to improve IVF, says Naomi Moris, who studies embryonic development at the Crick Institute in London.