The stem cells were no more than a week old when scientists moved them from their slick-walled plastic wells into ones lined with a thin layer of human endometrial tissue. But in that time, the cells had multiplied and transformed, organizing themselves into semi-hollow spheres. Per the instructions of the chemical cocktail in which they’d been steeping, they were trying to turn into embryos.
Video cameras captured what happened next: The balls of cells rotated until they were cavity-side-up, before finally touching down and grabbing onto the endometrial layer, a cellular proxy for a human uterus. Days later, when the scientists dipped paper test strips into the wells, pink lines appeared. Their Petri dishes were pregnant.
“These experiments clearly point out the fact that we are able to model in the dish the first touch between the embryo and the mother,” stem cell biologist Nicolas Rivron told reporters at a press conference.
On Thursday, Rivron and his colleagues at the Institute of Molecular Biotechnology of the Austrian Academy of Sciences in Vienna reported in Nature that they’ve learned to efficiently manufacture realistic models of human embryos from stem cells. These so-called blastoids aren’t the first successful attempt to recapitulate the developmental stage that embryos reach between four and seven days post-fertilization — when they’re a blastocyst made up of about a hundred cells and ready to implant into the walls of the uterus — but they appear to be the most advanced yet.
These synthetic embryos were made by mixing induced pluripotent stem cells with a brew of biochemical signals capable of coaxing them into forming spherical structures that include the beginnings of three distinct cell lineages — outer layers representing the future placenta and amniotic sac, and an inner clump of cells with the potential to develop into a fetus.
“This is a very, very close model of a real, complete human embryo,” said Insoo Hyun, director of research ethics at the Harvard Medical School Center for Bioethics, who was not involved in the study. “It’s probably the closest I’ve seen….”
“At some point we have to ask, ‘when does an embryo model become so good that it functionally becomes an embryo?’” said Hyun. “And for me, that question starts to get raised here.” It’s not that the latest work on blastoids was unethical, he clarified. On the contrary, it met all the guidelines issued by the International Society for Stem Cell Research, which Hyun helped write. The latest version, issued in May, prohibits scientists from transferring blastoids, which contain all the cell types necessary for development, into a human or animal uterus. “It was a really well-done paper, I thought it was kind of stunning actually,” said Hyun. “It just opens up these other questions….”
The above comes from a Dec. 2 story in Stat news.