Perhaps the bigger question rests on how embryo-like these stem-cell-derived structures are. For some scientists, it’s a catch-22 situation. If the blastoids look too much like embryos, then many believe research with them should be restricted in the same way that we control work on human embryos.
But if they don’t look enough like embryos, then there’s no point in using them for research, says Chuva de Sousa Lopes. “At the moment, it’s so difficult to understand how close they are, or how different they are,” she says.
Scientists tend to look at the size and shape of the structures, and which genes their cells express, to work out how similar they are to typical embryos. But there are other important aspects to consider.
“We first need to agree on what an embryo is,” says Naomi Moris, a developmental biologist at the Crick Institute in London. “Is it the thing that is only generated from the fusion of a sperm and an egg? Is it something to do with the cell types it possesses, or the [shape] of the structure?”
Perhaps it’s more to do with the structure’s potential. A human embryo could go on to form a person. Human blastoids can’t develop into people. Yet.
As the technology advances, it is looking increasingly likely that one day, stem-cell-derived embryos will be able to develop into living animals. “Theoretically, if you have all the right cell types … they could go further,” says Rossant. “Never say never.”
However we define blastoids and other embryo-like structures, now is the time to start regulating how we grow and study them. Rossant is one of the many scientists I spoke to who agree that, given how embryo-like these structures are looking, they should probably be subject to the same rules and regulations that cover research on normal embryos.
“The big risk is … if we had one rogue player that went really fast [with human cells], and developed something that caused a public backlash,” says Moris.