Human stem-cell-based embryo models: ethical and legal challenges

The rapid development of biotechnology, particularly in the field of stem cell research, has introduced ethical and legal dilemmas that society is only beginning to address. One of the most pressing issues is the regulation of human stem-cell-based embryo models (SCBEMs). Created from stem cells, SCBEMs mimic the early stages of human development. These structures, while holding great promise for advancing scientific research, raise important ethical questions about their potential, their status and how they should be treated under the law.

The Nuffield Council on Bioethics published a report on SCBEMs in November 2024 (see BioNews 1267a and 1267b). The report examines both scientific and ethical considerations, offering recommendations for regulatory reform. This process should start by incorporating the recently developed Code of Practice for the Generation and Use of Human Stem-Cell-Based Embryo Models (the SCBEM Code of Practice), published jointly by PET and Cambridge Reproduction in July 2024 (see BioNews 1246a and 1246b), while also establishing the groundwork for clearer prohibitions and formal regulation.

I chaired the working group that produced the Nuffield Council's report, and I have recently developed one aspect of the report in an open access article published in the Journal of Law and the Biosciences.

The article distinguishes between three entities:

• 'Embryos' are the early stages of human development following fertilisation of an egg with a sperm, in vivo (in the body) or in vitro (in a laboratory).
• 'Stem-cell-based embryo models' (SCBEMs) is an umbrella term that incorporates a range of model types that emulate aspects of embryonic development.
• 'Embryo-like structures' (ELSs) encompass SCBEMs, and also a subset of entities that might come about if, in future, they lose their status as 'models' because they are considered by a state to be such good copies of embryos that they achieve equivalence to them.

At the heart of the regulatory challenge is the distinction between traditional human embryos and ELSs. Most people agree that SCBEMs are currently so different to embryos that they should be regulated separately. This is true both of models of distinct aspects of the embryo, such as tissue or cell types, and of more complete models that seek to emulate the whole of the embryo. Accordingly, at present, regulations applying to human embryos – such as the rule that they cannot be cultured for longer than 14 days from fertilisation (see BioNews 1268, 1213, 1152 and 885) – do not apply to SCBEMs.

But what if the copies become better in future? What if the copy is so good that it can't be considered a model anymore, and becomes instead a stem-cell-based replica of the embryo? This possibility is some years off, and may never come to pass. But because the development of this science is not linear, and the science is developing at pace, it is a regulatory consideration that all states engaging in this research should consider.

My article builds on the Nuffield Council report's recommendation that, even if some structures become so similar to the embryo that they are no longer considered to be 'models', separate regulation is preferable to regulating that subset as embryos.

Human embryos, formed through fertilisation, carry with them the potential to develop into a human being and have long been associated with significant ethical, moral and legal considerations. The regulation of human embryos typically focuses on the protection of human life at its earliest stages, acknowledging the possibility that embryos could develop into persons.

In contrast, ELSs mimic the early developmental stages of human embryos, but differ in term of their origin and can develop at a different pace to embryos (see BioNews 1282, 1259, 1234, 1229, 1221 and 1124). There is international agreement that ELSs should not be used for reproductive purposes.

As ELSs improve in their ability to emulate embryos, the two entities are likely to share some morally relevant features. These features should be treated consistently in law. But ELSs are not identical to embryos, and consistency in the response to morally relevant features does not require that they are considered as a single entity in law.

To illustrate the point, consider this example. A synthetic diamond and a natural diamond, sharing the same chemical properties, are indistinguishable to most people and even to some experts. It is only when the synthetic diamond is split open that the absence of the natural layering formed during the compression of a natural diamond becomes evident. The regulations governing these two types of diamonds, despite their similarities, reflect not only their differing monetary values but also the distinct processes involved in their creation.

I propose that regulatory frameworks that treat embryos and ELSs under the same umbrella, are inadequate for addressing the distinct ethical and scientific concerns each category raises. Applying the same regulations could fail to account for the complexities of these new technologies.

Building on the Nuffield Council's report, my article emphasises the need for distinct regulatory approaches that reflect the differences between embryos and ELSs. While human embryos have long been the subject of ethical and legal protections, ELSs represent a new frontier in biotechnology and their regulation should be flexible, informed by scientific progress and sensitive to ethical concerns.

By adopting more nuanced regulatory frameworks, society can better balance the potential for scientific innovation with the need to respect deeply held moral convictions. As biotechnology continues to advance, it is essential to ensure that the regulation of these technologies reflects the complexities of both science and ethics, allowing for the responsible development of life-like structures without overstepping moral boundaries.