Two independent scientific teams have created cultures of human cells that develop into embryos in the laboratory. Embryoids, as they are called, acquire the different types of cells from which a fetus could develop, but they do not have the cells necessary to form the placenta, so they could not give rise to a pregnancy.

The objective of both projects is to study the initial stages of human embryonic development, affirm the authors of the investigations, which today present their results in the journal Nature. Whether the pregnancy is viable depends on what happens in these stages and, if it is, the health of the person for life.

However, the study of this critical period of development has been limited until now by the restrictions on research with human embryos. It is “the black box of human embryonic development”, declared yesterday at a press conference Magdalena Zernicka-Goetz, from the University of Cambridge (United Kingdom), who has directed one of the investigations.

“We would want to study events leading up to around day 14 [of embryonic development]. It could help us to better understand important biomedical issues, such as pregnancy terminations or developmental disorders,” explains Berna Sozen, from Yale University in New Haven (USA), who led the other research, by email.

60% of pregnancies are interrupted in the first 14 days after fertilization, before the woman knows she is pregnant, according to data provided by Zernicka-Goetz, from the University of Cambridge. Of those who pass the 14-day milestone, one in four discontinues involuntarily. The researcher hopes that embryoid studies will help reduce unwanted pregnancy terminations.

But the creation of embryoids from stem cells opens an ethical and legal debate on how to define and regulate them, since they are not exactly the same as embryos but could give rise to viable pregnancies in the future. “A consistent regulatory framework is urgently needed,” says Darius Widera, a stem cell specialist at the University of Reading who was not involved in the research, speaking to the UK’s Science Media Centre.

The Yale University research has been conducted using human pluripotent stem cells, which have the potential to become any type of cell in the body. They have been cultivated in a suitable medium so that they became embryonic cells.

According to the results presented in Nature, in 72 hours they had acquired a spheroidal shape like that of a human embryo. They had differentiated the cells of the epiblast (from which the fetus is formed) and those of the hypoblast (from which the yolk sac is formed, which provides nutrients and oxygen to the embryo). But they did not have the trophoblast cells (from which the placenta develops).

The researchers let the embryoids develop until the phase in which the body begins to take shape, which in a human embryo occurs 14 days after fertilization.

Research led by the University of Cambridge has developed human embryo models also from stem cells but using a different method. Also in this case the embryoids formed three-dimensional structures and were allowed to grow until the equivalent of about 14 days of development.

They had differentiated the tissues from which the fetus is formed, as well as those that give rise to the structures that surround the fetus. But, as in the other research, they were missing the cells from which the placenta is formed.

At least two other research teams, one in Israel and one in China, have developed similar human embryo models, The New York Times has reported. The teams from the universities of Cambridge and Yale are the first to present their results in a scientific journal.

“Our system offers a reproducible, manageable, and scalable experimental platform for understanding the basic cellular and molecular mechanisms that underpin human development,” the Yale team concludes in Nature.

Along the same lines, Bailey Weatherbee, first author of the Cambridge research, stressed at the press conference that “the objective is to create a research platform” to study a crucial period in the development of the human body.