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Question: What is the Embryonic Status of Totipotent and Pluripotent Stem Cells?

Does it help us ethically to distinguish scientifically between totipotency and pluripotency? Is it accurate to attribute the status of embryo to totipotent stem cells and deny it to pluripotent stem cells? Even if we are successful at removing pluripotent stem cells from the category of embryos--and, thereby, exempting them from legal restrictions on embryo research--have we really dealt sufficiently with the ethical issues?

Let us review the proposed scientific distinction. Why is it that pluripotent stem cells are one step down the embryonic staircase?The National Bioethics Advisory Commission employs the distinction as introduced by Harold Varmus, then NIH director, at a hearing in January 1999. Totipotent cells have "unlimited capacity. Totipotent... Totipotent stem cells are capable of producing all tissue, including the trophoblast necessary for implantation. Totipotent stem cells have the potential of becoming embryos. Pluripotent stem cells have every capability of the totipotent stem cells minus one, namely, they have no trophoblast. Minus the trophoblast, pluripotent cells cannot for this reason develop into a full human being. In this limited sense, pluripotent cells are not potential embryos.

It may turn out that the difference between totipotency and pluripotency is little more than a verbal distinction. The genetic code remains the same. The potency for making all bodily tissues remains the same. When using the blastocyst as source, the trophechtoderm is removed; and this denies to the internal hES cells access to what is necessary for implantation. What distinguishes the pluripotent stem cells is their loss of the blastocyst environment and the potential for sharing in the benefits of implantation. In sum, it is not nature but rather the laboratory procedure that demotes cells from totipotency to pluripotency.

Relevant here is the question: would a pluripotent stem cell under optimum conditions be able to produce a trophoblast and eventually a placenta for implantation? Why not, if the genetic code is complete and if it has the potential for making any tissue? Already experiments with mice have successfully shown that it is possible to form a fetus from a stem cell.Andràs Nagy, Janet Rossant, Rèka Nagy, Wanda Abramov-Newerly, and John C. Roder, "Derivation of completely cell culture-derived mice from early-passage embryonic stem cells," Proceedings of the... It is the pre-differentiated state of the ES cell that, in principle, makes it capable of producing not only any bodily tissue but also of becoming an embryo.

This forces us to ask: would all ethical concerns previously pertaining to the use of embryos in research now apply to pluirpotent hES cells? It would seem that this is the case. But, there is more. We now need to ask just what is being covered up by the totipotent-pluirpotent distinction and also ask about the implications of possible totipotency in normal somatic cells.

Email link | Printer-friendly | Feedback | Contributed by: Dr. Ted Peters

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