In a groundbreaking development, scientists have reported the creation of the first synthetic human embryos that eliminate the need for sperm and eggs. These embryo-like structures are made entirely from human stem cells and can develop to a stage equivalent to that of natural embryos about 14 days after fertilization. This is the first time that such advanced human embryo models have been achieved without using eggs or sperm.
The synthetic embryos could offer unprecedented opportunities to study human embryonic development and understand the causes of genetic diseases or miscarriages. They could also help researchers test new drugs or therapies for various conditions. However, they also raise ethical and legal questions about the status and regulation of these artificial entities that resemble human life.
The research was presented at the annual meeting of the International Society for Stem Cell Research in Boston, Massachusetts, on 14 June 2023 by two teams led by developmental biologist Magdalena Zernicka-Goetz at the University of Cambridge, UK, and by stem-cell biologist Jacob Hanna at the Weizmann Institute of Science in Rehovot, Israel. Both groups had previously created similar embryo models from mouse cells that developed to the stage when organs such as the heart and brain begin to form.
The synthetic human embryos were created by coaxing human embryonic stem cells to self-assemble into three distinct tissue layers: the cells that form the embryo itself, the cells that form the placenta, and the cells that form the yolk sac outside the embryo. The researchers say that these embryo models show structures and gene expression patterns found in human embryos between 6 to 14 days after fertilization — during and after the stage called gastrulation, when the cells that will form the embryo become organized into a layer between the amniotic cavity and the yolk sac.
One of the remarkable features of these synthetic embryos is that they contain germ cells that would go on to develop into egg and sperm in natural embryos. This could open up new possibilities for studying human reproduction and fertility. However, it also raises ethical concerns about whether these embryo models could potentially develop into viable human beings if implanted into a womb.
Zernicka-Goetz stressed that these are not human embryos, but embryo models that are very similar to human embryos. She said that they are very important for discovering why so many pregnancies fail, as most of them fail around the time of development at which they build these embryo-like structures. She also said that they follow strict ethical guidelines and do not allow their synthetic embryos to develop beyond 14 days, which is the legal limit for natural human embryos in many countries.
However, some bioethics experts have argued that these synthetic embryos should be subject to more regulation and oversight, as they push ever closer to the edge of life. They have also questioned whether the 14-day rule is still adequate for these artificial entities that can mimic human development beyond that point. They have called for more public debate and engagement on this emerging field of research.
