The author is a science reviewer
Egg plus sperm equals embryo. It’s hard to come up with more fundamental rules in biology. However, we have to reconsider. Last week, at a stem cell conference in Massachusetts, researchers revealed they had created “synthetic” human embryos that used neither eggs nor sperm. These structures, more accurately called embryonic models, are grown from individual living stem cells derived from an actual human embryo. It’s not a one-time achievement: Another team created a model embryo with a heartbeat.
These apparent breakthroughs — yet to be published in a peer-reviewed journal — aim to shed light on infertility, miscarriage and birth defects. But they also raise ethical and legal questions. Science and wider society now need to consider how close these lab-grown artificial embryos—essentially tissue tapestry—close to the real thing. Open discussion—along with updated regulations and careful consideration of how such work can be commercialized—will encourage public support for valuable research that could lead to treatments.
About one in five pregnancies end in miscarriage. However, science knows surprisingly little about why, in part because studying embryos in vivo is difficult. Another approach is to closely examine embryo development in the laboratory, including using leftover embryos donated by IVF patients. The research use of human embryos is governed by strict laws that follow a developmental timetable.
After fertilization, the cells divide for about four days before compacting into a blastocyst. After implantation in the uterus, marking the beginning of pregnancy. By day 14, the embryo begins “gastrulation,” when body morphology begins to form and different cell lines emerge. One hallmark is the “primitive stripe,” a groove that develops as bilateral symmetry develops.
Broadly speaking, human embryos cannot be cultured beyond day 14 in the UK and many other countries. That means the exact scientific details of what happened afterward—including how the embryo self-organized into different tissue types—remain a mystery. Animal embryos that can be cultured for longer periods of time are of limited relevance.
That’s where “stem cell-based embryonic models” come in. A team led by Professor Magdalena Żernicka-Goetz, working at the University of Cambridge, UK, and the Caltech Institute, isolated embryonic stem cells from human embryos and induced the proliferating cells to self-assemble into embryo-like structures after day 14. On the same day, another group led by Jacob Hanna of the Weizmann Institute of Science in Israel published a similar preprint.
Describing unpublished work, a rival team at Cambridge University’s Gurdon Institute says they have developed a synthetic embryo at a stage where a heartbeat can be detected, although it has been deliberately engineered to lack tissues critical for further development.
Why is this important? In many countries, synthetic embryos do not meet the formal definition of an embryo (although the use of embryonic stem cells is still regulated). Instead, they are thought to be more similar to lab-grown human tissue, which is more loosely regulated. But the quest for biological truth sets a catch-22: The more similar an embryonic model is, the more scientifically useful it is—but the more ethically questionable it is.
Synthetic embryos can also be created using reprogrammed adult stem cells, which avoids some limitations. But whatever technology is used, the science is now beyond our ability to regulate it — and it’s not unreasonable to worry about what an unscrupulous scientist might try.
British law prohibits the use of synthetic embryos to create babies, but researchers are already testing the principle on animals. Scientists in China have implanted a model monkey embryo into a female monkey, but it soon aborted spontaneously. Such pregnancies may be doomed; alternatively, technological improvements could make them viable.
If it’s the latter, scientists must remain vigilant — self-regulation didn’t prevent the disaster of gene-edited human babies in China. Cambridge University, at the center of the new research, is undergoing sensible consultations on governance frameworks, but the problem with synthetic embryos is bigger than just one campus. As long as we can avoid the harm, this exciting research on abortion has many scientific benefits and human well-being.