Last month, researchers from the United States and United Kingdom announced they had created the world's first synthetic human embryo models using stem cells — a development that could help advance research into genetic diseases and miscarriages in the future.

The first synthetic human embryo models

Previously, researchers had created model embryo-like structures using stem cells from mice. After about eight days of development, these "embryoids" had the beginnings of a brain, heart, and intestinal tract.

Now, researchers have created the world's first synthetic human embryo model using human stem cells. These model structures were grown from a single embryonic stem cell and are at the earliest stages of human development.

The models have reached the beginning of gastrulation, a developmental milestone in which the embryo goes from being a continuous sheet of cells to forming distinct cell lines and setting the basic body axes. At this stage, the model does not have a brain, heart, or intestines, but there was evidence of primordial cells that are precursors to egg and sperm cells.

Currently, use of these synthetic embryos is limited to test tubes, and it's unclear whether they will be able to mature beyond the earliest stages of development.

"Our human model is the first three-lineage human embryo model that specifies amnion and germ cells, precursor cells of egg and sperm," said Magdalena Zernicka-Goetz, a professor of biology and biological engineering at CalTech and the University of Cambridge.

"I just wish to stress that they are not human embryos," Zernicka-Goetz added. "They are embryo models, but they are very exciting because they are very looking similar to human embryos and very important path towards discovery of why so many pregnancies fail, as the majority of the pregnancies fail around the time of the development at which we build these embryo-like structures."

Commentary

Going forward, the researchers said they hope the model embryos will help reveal more information about the "black box" of human development, or the period 14 days after fertilization, which is the current limit for scientists to grow and study embryos in a lab.

"We know remarkably little about this step in human development, but it is a time where many pregnancies are lost, especially in an IVF setting," said Roger Sturmey, a senior research fellow in maternal and fetal health at the University of Manchester.

"Currently, we can say that these 'synthetic embryos' share a number of features with blastocysts, but it is important to recognise that the way that synthetic embryos are formed is different to what happens when a normal embryo forms a blastocyst," he added. "There is much work to be done to determine the similarities and differences between synthetic embryos and embryos that form from the union of an egg and a sperm."

However, there are several legal and ethical questions surrounding the use of these synthetic embryos, especially since many countries, including the United States, do not currently have any laws about the potential creation and use.

"Unlike human embryos arising from in vitro fertilization (IVF), where there is an established legal framework, there are currently no clear regulations governing stem cell derived models of human embryos," James Briscoe, an associate research director at the Francis Crick Institute. "There is an urgent need for regulations to provide a framework for the creation and use of stem cell derived models of human embryos."

"If the whole intention is that these models are very much like normal embryos, then in a way they should be treated the same," said Robin Lovell-Badge, head of stem cell biology and developmental genetics at the Francis Crick Institute. "Currently in legislation they're not. People are worried about this." (Goodman, CNN, 6/15; Devlin, The Guardian, 6/14)