Scientists create synthetic human embryos in landmark study

Scientists have created the most realistic models of human embryos yet using stem cells, and then grown them outside the womb to the equivalent of 14 days’ development.

Dr Jacob Hanna from Israel's Weizmann Institute of Science. Picture: AFP

Scientists have created the most realistic models of human embryos yet using stem cells, and then grown them outside the womb to the equivalent of 14 days’ development.

The “synthetic” embryos were made without sperm or an egg but contain all key features and cell types seen in developing humans.

They were able to self-organise and develop from a clump of 120 cells, mirroring an embryo at a week’s development, to 2500 cells a week later. When scientists took secretions from the cells and put them to a pregnancy test, it came out positive.

The advance, which comes after the announcement of the creation of similar but less complete synthetic embryos in June, will raise further ethical questions, although the team behind the finding, announced in the journal Nature, stressed it was impossible for the creation to develop into a full pregnancy.

Jacob Hanna, of the Weizmann Institute of Science in Israel, said the aim was purely to advance understanding of embry­onic development. “The drama is in the first month; the remaining eight months of pregnancy are mainly lots of growth,” Dr Hanna said. “That first month is still largely a black box.”

It is hard to follow what happens in the first few days after fertilisation, in part because of ethi­cal problems dealing with human embryos. Learning about this period could help with spotting and treating developmental diseases and preventing miscarriage.

The model embryo was created by taking stem cells, derived from adult skin cells, and coaxing them to develop into different specialisms. Some were left as they were, to become the embryo.

Others were treated with chemicals to activate specific genes that would help them to form the structures that support the embryo, including the placenta and yolk sac.

Then they let the cells develop by themselves.

The Times