Alternative sources of pluripotent stem cells: altered nuclear transfer.

Altered nuclear transfer (ANT) is one of several methods that have been suggested for obtaining pluripotent stem cells without destroying human embryos. ANT proposes to alter the nucleus of a somatic cell and/or the cytoplasm of an enucleated oocyte such that when the two are combined, they do not produce a zygote, but rather they form a cell capable of producing pluripotent stem cells without being an embryo. The ANT proposal raises the serious question of whether it is possible to know with confidence that this procedure generates a non-embryo, rather than merely an embryo with a deficiency. Here I address the question of how embryos can be distinguished from non-embryos using scientific criteria and apply these criteria to the two forms of ANT proposed thus far: ANT combined with oocyte-assisted reprogramming (ANT-OAR) or with gene deletion (ANT-GD). I propose that the first globally coordinated event in human development, the formation of trophoblast and inner cell mass (ICM) lineages via Cdx2-Oct3/4 mutual cross-repression, is the earliest act of the embryo qua embryo; it is an operation intrinsic to an embryo as such, and entities lacking the power (potentia) for such an act cannot be considered embryos. Thus, I will argue that formation of trophoblast-ICM lineages is a both necessary and sufficient criterion for determining whether ANT produces an embryo or a non-embryonic entity.