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expert reaction to Guardian reporting news of creation of synthetic embryos using stem cells

The article reports on a plenary address given by Prof Magdalena Żernicka-Goetz on Wednesday at the International Society for Stem Cell Researcher’s annual meeting.


Prof Kathy Niakan, Principal Investigator of the Governance of Stem Cell-Based Embryo Models (G-SCBEM) project, said:

“Stem cell-based embryo models (SCBEMs) can recapitulate aspects of early human development, providing insight into otherwise inaccessible developmental stages, and offering exciting possibilities for our understanding of disease mechanisms and treatments.

“For some time now, our project – Governance of Stem Cell-Based Embryo Models (G-SCBEM) – has been working to address gaps, ambiguities and differences of interpretation in the current regulation of human SCBEMs, particularly within the UK. We believe that greater clarity is required in this area, so that all concerned – including researchers, their funders and institutions, relevant regulators, and the general public – can be confident in their understanding of the types of research that are possible, permissible and legitimate.

“We are currently developing a recommended governance framework for UK research involving SCBEMs. This framework will cover SCBEMs that have been created by researchers to date, and also SCBEMs that could hypothetically be created by researchers in the future.

“Our work brings together key stakeholders including regulators, funders, scientists, bioethicists, legal scholars and patient groups. We have already submitted preliminary recommendations to the UK’s Human Fertilisation and Embryology Authority, in response to its recent consultation on law reform, and our recommended governance framework will be drafted by the end of this year.

“We intend for our framework to:

  • Provide guidance on the responsible conduct of research in vitro into processes of early human development using SCBEMs.
  • Demonstrate responsibility, accountability and transparency on the part of researchers.
  • Help to sustain and build public trust.
  • Help to inform any future legislation or regulation that might apply to human SCBEMs, should this be deemed necessary.”


Prof Alfonso Martinez Arias, ICREA Senior Research Professor, Department of Experimental and Health Sciences, Pompeu Fabra University (UPF), said:

“There was no information available beyond the press reports – no paper or preprint. Therefore, this work is not yet able to be verified. This may be an important scientific step but again, we need to see the full report and data before we can make those claims.”


Dr Ildem Akerman, Associate Professor in Functional Genomics and Diabetes UK RD Lawrence Fellow, University of Birmingham, said:

How much can we glean from this current report? What information on this research is available?

“A human embryonic stem cell has the capacity to become any cell type of the body. In theory, these cells also have the potential to develop into an embryo. This report suggests that there is now proof that human embryonic stem cells can potentially become embryos, confirming their pluripotency. We understand from the report that the scientists generated optimal conditions for the embryo to pass through the first 14 days of development and, in fact, become an embryo. 

“Recently scientists developed methods to keep IVF embryos alive in a dish for 14 days, and these findings confirm that the technology is now available to mimic the first 14 days of development outside the womb.
How significant is this development? What is the scientific importance of work of this kind?  Why are we trying to create synthetic embryos?

“This has significant implications. To begin with, it will provide scientists with a model to investigate the events that occur during the initial 14 days of life. Up until now, we have only been able to observe such processes in animal models like zebrafish and mice. Having this knowledge can be immensely valuable for regenerative medicine, where scientists aim to generate different cell types from stem cells (i.e. pancreatic beta cells for people living with T1 diabetes). It can give us valuable insights into genetic disorders. Additionally, it can contribute to the advancement of in vitro fertilization (IVF) technologies. 

“Finally, it’s important to clarify that although the authors referred to them as “synthetic” embryos, these cell clusters are not truly synthetic in the sense that they are created from scratch. Instead, they are derived from living stem cells that originate from an embryo. Essentially, what scientists do is cultivate a single stem cell and encourage its growth into an organized group of cells that, in theory, possess the potential to develop into an implantable embryo.

What is the regulation around this type of work? Are there any direct implications of this work?

“In the UK, the regulations governing stem cell and embryo research are established by the Warnock Committee, which was formed in response to advancements in the field of in vitro fertilization (IVF). According to these regulations, culturing of human embryos is not permitted beyond a period of 14 days. However, the entities created from stem cells (not coming from IVF) are considered “integrated embryo models” and are advised to be cultures “for a minimum amount of time” without a set time limit. 

“Until this day, an embryo (derived from IVF) and “integrated embryo models”  (derived from stem cells) were two separate things: as the latter didn’t possess the capability of growing further or implanting. The authors potentially broke this separation. Thus it would be up to the individual ethical committee to decide whether the generated entity is an “embryo” or an “embryo model” and whether the entity would be allowed to grow past the 14 day limit. 

“The 14-day limit is intentionally chosen as a specific milestone in embryonic development. On the 15th day, a structure called the “primitive streak” begins to form, marking a critical stage where the fate of the cells within the embryo starts to be determined. After this point, the embryo is no longer capable of splitting to give rise to twins. Additionally, it is clearly ahead of day 22, when the neurons (the brain cells) start to form. 

“Obviously, this research can provide a deeper understanding of how tissues and organs form, potentially leading to advancements in regenerative medicine and the treatment of developmental disorders.  These findings suggest that we would soon develop the technology to grow these cells beyond the 14 day limit, with potentially more insights to gain into human development. Nevertheless, the ability to do something does not justify doing it;  ethical frameworks should be established and maintained in line with the public’s view on the subject. Perhaps it’s time for a new Warnock committee to convene and determine the ethical framework in line with the technology we have and the current public opinion. There are many ethical issues to be discussed.” 


Prof Roger Sturmey, Professor of Reproductive Medicine, Hull York Medical School & Senior Research Fellow – Maternal & Fetal Health, University of Manchester, said:

The work reported in The Guardian builds on a steadily growing foundation of research that demonstrates that stem cells can, under very specialised laboratory conditions, be persuaded to form a structure that resembles the embryonic stage called the blastocyst.  In normal development, the blastocyst is an important structure as it is around this time that the embryo begins the process of implanting into the uterus and establishing pregnancy.  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.  So, models that can enable us to study this period are urgently needed to help to understand infertility and early pregnancy loss.  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.  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.  This work from Zernicka-Goetz hasn’t yet been fully appraised by the scientific community, but it does offer exciting prospects to answer these questions and may provide an important tool to study early development while reducing the reliance on human embryos for such research.  Given the nature of this work, UK lawyers, ethicists and scientists are presently working to establish a set of voluntary guidelines ensure that research on synthetic embryos is done responsibly.” 


Prof James Briscoe FRS FMedSci, Principal Group Leader – Associate Research Director, The Francis Crick Institute, said:

“Without a detailed preprint, or peer reviewed paper to accompany this press report, it is not possible to comment in detail on the scientific significance of this story. More generally, although it is very early days, synthetic models of human embryos based on stem cells have a lot of potential. They could provide fundamental insight into critical stages of human development. These are stages that have been very difficult to study and it’s a time when many pregnancies fail. Fresh insight might lead to a better understanding of the causes of miscarriages and the unique aspects of human development.

“They also raise profound ethical and legal questions. Unlike human embryos arising from in vitro fertilisation (IVF), where there is an established legal framework, there are currently no clear regulations governing stem cell derived models of human embryos. There is an urgent need for regulations to provide a framework for the creation and use of stem cell derived models of human embryos.

“On the one hand, models of human embryos made of stem cells might offer an ethical and more readily available alternative to the use of IVF derived human embryos. On the other hand, the closer stem cell derived models of human embryos mirror human embryos, the more important it is to have clear regulations and guidelines for how they are used. This itself raises challenges. How will comparisons be made given the difficulty of obtaining and studying human embryos at the appropriate stages.

“It is important that research and researchers in this area proceed cautiously, carefully and transparently. The danger is that missteps or unjustified claims will have a chilling effect on the public and policymakers, this would be a major setback for the field.”



Guardian article:



Declared interests

Professor Kathy Niakan: G-SCBEM is led by Cambridge Reproduction – – an interdisciplinary initiative at the University of Cambridge, which brings together researchers from across all disciplines who have a common interest in reproduction.

Kathy Niakan is:

Principal Investigator of the Governance of Stem Cell-Based Embryo Models (G-SCBEM) project

Mary Marshall and Arthur Walton Professor of Reproductive Physiology at the University of Cambridge

Chair of Cambridge Reproduction

Director of the Centre for Trophoblast Research

Dr Ildem Akerman: “I work on regenerative medicine for T1D. I have no competing interests.”

Prof James Briscoe: “No conflicts of interest.”

For all other experts, no reply to our request for DOIs was received.

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