Source: BioValley

In a new study, researchers from the Weizmann Institute of Science and other institutions in Israel describe how, without the use of sperm, eggs, or fertilization, they coaxed human embryonic stem cells to self-assemble into a model that resembles an early embryo. The advance could help unlock the secrets of instability in early pregnancy, raising hopes for research on miscarriage and birth defects, but also raising new ethical questions. The results were published online in the journal Nature on September 6, 2023, in a paper titled "Complete human day 14 post-implantation embryo models from naive ES cells."

The authors made models of embryos up to 14 days long, the legal limit for laboratory research on human embryos in many countries and the point at which organs such as the brain begin to develop. They say their work is different from the work of other teams because they used chemically modified rather than genetically modified embryonic stem cells, and the models they made are more like real human embryos, with yolk sacs and amniotic chambers.

James Briscoe of the Francis Crick Institute in Britain says these similarities may make the embryo models they build more useful for studying diseases such as miscarriage, birth defects and infertility. Their embryonic model appears to be able to produce all the different types of cells that form tissue early in development.

The authors, as well as scientists not involved in the study, stressed that these embryo models should not be considered human embryos. The structure of these embryonic models is "very similar to what happens in the womb, but [and] not exactly the same." However, the success rate in generating these embryonic models is also low, and the percentage of embryonic stem cells assembled correctly is small.

Image from Nature, 2023, doi:10.1038/s41586-023-06604-5.

Darius Widera, an expert in stem cell biology at the University of Reading in the UK, said, however, that "compared to similar studies published earlier this year, these embryonic-like structures contain most of the cell types of the developing embryo". This study and other recent work suggest that "models of the human embryo are becoming more complex and closer to events that occur during normal development." He added that this highlights "the need for a strong regulatory framework more than ever."

In the UK, the University of Cambridge has begun work on the country's first regulatory framework for stem cell-based models of human embryos. UK law prohibits the cultivation of human embryos in laboratories for more than 14 days, but because similar structures derived from stem cells are artificially formed, existing regulations do not explicitly cover them. Still, most scientists have imposed voluntary restrictions on their work at this stage.

The new study did not develop embryo models older than 14 days, nor did it involve the transfer of these embryo models into the womb of humans or animals.

Reference materials:
1. Bernardo Oldak et al. Complete human day 14 post-implantation embryo models from naïve ES cells. Nature, 2023, doi:10.1038/s41586-023-06604-5.
2. Lab-grown human 'embryos' offer new research hope
https://medicalxpress.com/news/2023-09-lab-grown-human-embryos.html