Students of bioethics sometimes imagine that the philosophical, moral and legal status of the human embryo is reducible to the single question: 'Is the human embryo a person?' In English law, a human being is regarded as a 'natural person' from the moment he or she is born alive. Yet, this is hard to justify philosophically.
The problem with framing the status of the embryo as a question of 'personhood' is partly due to the difficulties of establishing an adequate philosophical definition of the 'person'. A preoccupation with this question may also distract us from other questions that are equally necessary for understanding the human embryo. A recent BioNews article by Julian Hitchcock (see BioNews 1089) reminds us that even before asking about the moral or legal status of the embryo, we need to know how to distinguish embryos from non-embryos. Prior to the question of 'personhood' is the question of 'embryohood'.
What, then, is an embryo? It is the early stage of development of a multicellular organism. A mammalian embryo is normally generated by the fusion of male and female gametes in a process termed fertilisation. It might therefore seem reasonable to define the embryo by reference to fertilisation. However, this would be a mistake because, while embryos are generated by successful fertilisation, embryos can also come to be in other ways. For example, somatic cell nuclear transfer, the process that gave us Dolly the sheep (see BioNews 884).
The definition of the embryo is important in patent law, as the European Biotechnology Directive rightly excludes from patentability 'uses of human embryos for industrial or commercial purposes'. This directive was used in a case bought by Greenpeace against Oliver Brüstle, who attempted to patent an embryonic stem cell technique. This case defined a human embryo as an entity that was 'capable of commencing the process of development of a human being'. However, in the subsequent case of the International Stem Cell Corporation, this definition was rejected, or rather, qualified with regards to parthenotes, which are embryo-like entities generated by the 'activation' of an unfertilised oocyte. The opinion of the court was that a parthenote fulfills the definition of an embryo set out by Brüstle, but is not in fact an embryo because, 'in the light of current scientific knowledge, it does not, in itself, have the inherent capacity of developing into a human being'.
The patent decision in the International Stem Cell Corporation case is certainly defensible. The lack of any genetic contribution from a male gamete, and the seeming lack of inherent capacity for development as a human being, distinguish parthenotes from human embryos. If parthenotes are not human embryos then technologies that use parthenotes should not be excluded from patentability on that basis.
Nevertheless, the reasoning in the International Stem Cell Corporation case was flawed. There was no need to reject the definition of the embryo provided by Brüstle. If parthenotes are not human embryos then, ex hypothesi, they are not 'commencing the process of development of a human being'. They are not a stage in the development of a human organism; the processes they undergo have a distinct character and orientation. Furthermore, the alternative test proposed in the International Stem Cell Corporation case is based on a false premise. A human embryo does not have the 'capacity of developing into a human being'. It is a human being in the process of development. As Hitchcock acknowledges: 'a mere zygote is a human being (albeit not a [legal] person)'.
The test proposed in the International Stem Cell Corporation case can be restated as a requirement that a human embryo possesses 'in itself... the inherent capacity of developing as a human being'. Nevertheless, all human beings die and many die before they have reached maturity. How then can we determine the embryohood of entities that seem to commence the process of development of an organism but which subsequently fail to develop?
The birth of Dolly the sheep showed that somatic cell nuclear transfer could generate viable embryos. The fact this was possible provides reason to regard entities generated by somatic cell nuclear transfer that seem to commence development as an organism, but later fail in development, as being or having been embryos. The lack of any such examples in relation to parthenotes suggests that the lack of capacity to develop as an organism in their case may be 'inherent' such that parthenotes are not in fact the embryonic stage of the development of an organism.
A new challenge is how to categorise embryo-like entities generated by assembly of pluripotent stem cells. These structures, variously referred to as blastoids (see BioNews 1020), embryoids, synthetic embryos, SHEEFs or simbryos (see BioNews 1089), have been developed as model systems for the study of early embryogenesis. Currently no embryoid has shown greater capacity for development than a parthenote. For this reason, one might assume that they were not embryos.
However, a key aim of these research programmes is to create and improve platforms that can model the processes of embryonic development. The more such models improve, the more closely they will resemble natural embryos. Thus, researchers working in this area describe this research as, 'pav[ing] the way to creating viable synthetic embryos by using cultured cells.' If this research goal is achieved then it will be a proof in principle that embryos can be generated by self-assembly from stem cells. If sustained research in this area fails to make progress towards this goal then this may indicate the inherent incapacity of such assemblages to behave like embryos. Given the current state of knowledge, neither possibility can be ruled out. Synthetic entities that appear to commence the process of development of a human being but later fail in development should therefore be given the benefit of the doubt and, for the purposes of law and regulation, should be deemed to be human embryos.