In a scientific first, scientists have successfully created synthetic models of 14-day-old human embryos derived entirely from stem cells grown in a lab. Their work, published in the journal Nature, provides an unprecedented glimpse into the mysterious earliest stages of human development and could open up new avenues of research into infertility, congenital disabilities, and organ growth.
Scientists reprogrammed skin cells to become stem cells that can differentiate into the many cell types that make up an embryo. They then combined the stem cells in different combinations and used chemicals to induce them to become more like specific tissue types typically found in early pregnancy. After about 8.5 days of culture, the resulting model structures looked similar to natural embryos. They had a beating heart, blood vessels, a head region with folds, the beginnings of a gut tube, and more. They also had a cell activity level indicating the cells were alive.
The clumps of cells, which were created in the laboratory of Prof. Jacob Hanna at Israel’s Weizmann Institute of Science, reached a stage of development corresponding to day 14 of normal human embryonic development when the embryo acquires internal structures but is not yet starting to lay down the foundations for body organs. This is around when most countries consider it ethical to stop growing embryos in the lab after 14 days, following advice from the U.S. Department of Health and the U.K. Warnock Committee years earlier.
These models did not have a placenta, as is typical in a human embryo, which could explain why they failed to implant and grow, although Hanna says this may be something his team can address in the future. However, the embryo mimics do contain precursors to sperm and eggs and have the structure of an amnion, the membrane that surrounds an actual embryo in a womb.
The researchers continue refining their technique, hoping to get the models to more closely resemble an embryo at day 21 of development and improve their success rate in creating them. This is a challenge, as the success rate of this type of artificial embryo creation has been low, with the cells organizing correctly only about 50 percent of the time.
While creating these model embryos is a significant scientific breakthrough, many scientists not involved in the research are cautioning that it is essential to separate what are essentially stem cell-based “models” from actual human embryos. Magdalena Zernicka-Goetz, a professor of developmental biology at Cambridge University, notes that it will be “some time” before we can reach the stage where the embryo models produce actual human fetuses. But she adds that, just as it is inappropriate to stop nuclear physics simply because a few bad actors have used the technology for evil, we should not stop researching and refining techniques that may ultimately be useful. Several other laboratories have already achieved similar results this year, including two others that also created model embryos without sperm or eggs.
