Reacción a "Reactions to the two preprints on models of human embryos created from stem cells in the laboratory"

Human embryonic development is largely unknown from implantation and placenta formation, which occurs around day 7.5 post-fertilisation. However, these early days of embryo formation are crucial in explaining fertility problems and failure of apparently healthy embryos to implant. So far, our knowledge has been derived from studies in embryos of other mammals, but not everything is directly extrapolable. Regulations in many countries prohibit the in vitro study of human embryos beyond 14 days when embryo gastrulation and many organ formation processes begin. One way to overcome the lack of knowledge about human embryos is to generate "embryos-like" or embryoids from cultured embryonic cells. In these sets of cells, through genetic manipulation, it is possible to differentiate into different embryonic tissues and to study how this occurs and whether it recapitulates embryonic development. 

Both Jacob Hanna's group (Israel) and Magdalena Zernicka-Goetz's group (UK and USA) have been investigating early embryonic development for some time. They use different methods of aggregating embryonic stem cells with different differentiation profiles (Zernicka-Goetz does this by joining cells transgenic for different differentiation factors, while Hanna uses unmodified pluripotent cells, mixed with others that are genetically modified). The result is human embryoids, or rather, synthetic models of human embryos that recapitulate features of early embryo differentiation.  

Both refer to the generation of the amniotic sac (the extra-embryonic tissues that are biologically derived from the zygote but are not part of the embryo). The results, in preprint format, seem to support that the stem cell-derived embryonic models of Hanna's group are structurally more embryo-like, while those of Zernicka-Goetz's group would be less structured, but gene expression in these embryoids would support that they are differentiating into organ precursors.  

At the moment, they have not gone beyond the stage of a 14-day-old embryo, but they are synthetic embryonic models, created by joining different stem cells, and are not a viable human embryo. There is still a lot of research to be done and the main question at the moment is how these models are categorised, i.e. whether they are considered human embryos or not. At the moment they are not, because they are not viable and do not manifest the full potential of a human embryo. These stem cell-derived embryonic models answer questions about the early stages of embryos, they look very much like embryos, but they are not human embryos. The problem is that they are in legal limbo in many countries, and it is not known which regulations apply to them.  

We have to consider that the day when cellular and genetic manipulation techniques allow it, these models may have potential and viability, so it will be necessary to define - both from a bioethical-legal and scientific point of view - what they are and to determine what rules apply to them, how their generation is controlled and up to what point of development they can be investigated.