"Synthetic embryos have formed by themselves up to an advanced stage, from stem cells placed ex utero", summarizes this work published this week in Cell, one of the largest scientific journals in biology. .

Conducted on mice in an Israeli laboratory, under the direction of the Palestinian Jacob Hanna, the experiment resulted in unprecedented success in a field of research that appeared a few years ago.

It involves developing structures close to the embryo in the laboratory, by taking simple cells from an animal and then acting on them without any fertilization procedure.

The main advance dates back to 2018 until then. Researchers, led by Frenchman Nicolas Rivron, had managed to get stem cells to develop into a set close to a very early embryo, a "blastocyst".

But, at this stage, the cells of the embryo have not differentiated and are indistinguishable from what will constitute the future placenta.

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Jacob Hanna's team went further.

She developed structures similar to an eight-day-old mouse embryo, a third of gestation, and at a time when organs are beginning to differentiate.

"drafts" of organs

To do this, the researchers took cells from the skin of the mice, then made them return artificially to the state of stem cells, capable of differentiating again to form different organs.

They placed them in a nutrient bath, continuously agitated and supplied with oxygen to mimic the conditions of a mother's womb as closely as possible.

Result: in a small part of these devices, the cells organized themselves, from the information they contained, to form nascent organs.

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This is an advance never seen, even if it should not be seen either as the secret of artificial life.

In most cases the experiment came to nothing and, even when it succeeded, the result was a whole too badly constituted to be mistaken for a real embryo.

Some scientists are, moreover, uncomfortable with the expression "synthetic embryo".

"These are not embryos", slice with AFP the French researcher Laurent David, specialist in the development of stem cells.

"Until proven otherwise, they do not result in a viable and reproducing individual."

The researcher, who prefers to speak of embryoids, emphasizes in particular that they only present “drafts” of organs.

However, he welcomes "new" and "very convincing" work, which offers the potential to carry out experiments on these imitation embryos to better understand how organs develop.

Hope for the transplant?

Such experiments are crucial to succeed, one day, in cultivating stem cells to form limbs which would then be intended for transplantation without having to take them from a donor.

This is no longer just a theoretical possibility: researchers succeeded several years ago in developing an artificial intestine in the laboratory that could work once implanted in a mouse.

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In humans, such a perspective is still science fiction, although Jacob Hanna believes that his research directly opens the way to such progress.

He also founded a startup, Renewal, to dig this furrow.

Other researchers believe that it is still very early to consider therapeutic advances, even if they readily admit that this research poses an important stone to this building.

But, as such, they also warn that the next and logical step will consist in obtaining similar results from human cells, opening the way to heavy ethical questions about the status to be given to these “embryoids”.

"Even if we are still far from the prospect of synthetic human embryos, it will become essential to engage in broad debates on the legal and ethical implications of such research", summarizes the British researcher James Briscoe, specialist in the development of the embryo, from the organization Science Media Center.

© 2022 AFP