Two teams of scientists in the United Kingdom and Israel announced in June 2023 that they had grown late-stage embryo models, which would correspond to a natural embryo 14 days after fertilization.
Barely a month later, other researchers presented in the journal Cell their own embryonic models that replicate human gastrulation [early cell formation] (which occurs between 17 and 21 days after fertilization), thus adding a few days to the scientific limit.
It is a real race to develop these atypical cellular structures, which has been going on for several years. Also, in less than a year, studies have moved from embryonic animal models to human embryonic models.
The International Society for Stem Cell Research (ISSCR) reassured public opinion in a press release dated June 26. These “organized three-dimensional structures” can certainly “replicate aspects of the early-stage development of human embryos,” but they “cannot and will not develop to the equivalent of the postnatal stage humans,” argues the ISSCR.
In its guidelines, the International Society prohibits the transfer of embryonic models into the womb of a human or animal.
These cellular structures are made of human or animal stem cells: embryonic stem cells or somatic cells reprogrammed into stem cells. The result is therefore not the result of a fusion of gametes. Recently, researchers succeeded in cultivating so-called “integrated” embryonic models, i.e. comprising embryonic stem cells and extra-embryonic stem cells.
Published by two researchers from the University of Michigan and the Vienna BioCenter, a summary sheet on embryonic models outlines the biomedical applications that scientists have in mind:
- Infertility treatment
- Improvement of in vitro fertilization
- Development of more effective contraceptives by reducing side effects
- Understanding of the mechanisms behind abnormal developments during the first weeks of pregnancy, such as those caused by the use of alcohol and/or drugs
- Genesis and regeneration of organs in an environment comparable to that of the embryo
These embryonic models, developed in very large numbers from stem cells, avoid having to resort to human embryos that are often not available (and even prohibited in certain countries) at the early stage that interests them. This is one of the advantages put forward by the scientific community. It should be remembered, however, that obtaining the embryonic stem cells used for this research itself involves the destruction of a certain number of “natural” embryos.
Under a principle still well established in most countries – and despite the ISSCR's recommendation to relax the rule – researchers are not allowed to cultivate human embryos in vitro beyond 14 days.
In most countries, embryonic models escape this limit and any legal framework, precisely because they are not human embryos. The researchers hope to be able to learn more about the period between 14 and 28 days after fertilization, which for the moment remains inaccessible to them.
As for the moral point of view, from the moment that this research is based on the murder of embryos, it is totally illegitimate. As for claiming that they are only clusters of cells with no real relationship to the embryonic organization, that is open to discussion. Admittedly, it is not possible to “reconstitute” an embryo, but these cells which are torn from an embryo have very special capacities which it is irresponsible to handle without precautions.
This is the opinion of Robin Lovell-Badge, head of cell biology at the Francis Crick Institute, “If the intention is that these models look a lot like normal embryos, then, in a way, they should be treated the same.”