Scientists at the University of Cambridge have successfully grown human “synthetic embryos” in the lab, using stem cells to create embryo-like structures similar to early embryos. These structures are not exactly the same as embryos, as they are made from stem cells grown in the lab and have certain differences to naturally formed embryos. However, they have been grown to a stage equivalent to just past 14 days old, which is the legal limit in the UK for studying natural embryos. This work could help researchers study the causes of early miscarriages and understand how organs develop.
The synthetic embryos have not been wholly synthetically created, as the stem cells came from an embryo originally. Until recently, only synthetic embryos made from animals such as mice and monkeys had been made, but Magdalena Żernicka-Goetz at the University of Cambridge had publicly announced that she was developing human equivalents. On 14 June, she announced that her team had grown the human versions to a stage at which a real embryo would implant into the uterus and start developing some different tissues, including the precursors of cells that go on to form sperm and eggs.
One key advantage of synthetic embryos is that in most countries, natural embryos studied in a dish must be destroyed after 14 days to avoid ethical issues around working with something that could, in some circumstances, grow into a fetus. These rules do not apply to synthetic embryos, so this could let researchers study embryo development for longer, a landmark step towards better understanding organ development and the causes of early miscarriages.
Policymakers may consider making new rules that apply to synthetic embryos. In the UK, scientists have formed a working group along with legal experts, patient representatives, and ethicists to discuss what new rules should apply. The group has submitted recommendations to the UK’s Human Fertilisation and Embryology Authority, which regulates research involving natural embryos and will probably take on responsibility for synthetic embryos. However, it is currently illegal to transfer synthetic embryos into a uterus, and animal research by a Chinese team suggests that in the current state of the field, it would not lead to pregnancy.
Understanding more about early embryonic development may shed light on what goes wrong when early pregnancies miscarry and could help us understand how embryonic organs form and grow, which one day could lead to doctors being able to grow organs in the lab for transplants.