> Human eggs are not exactly available in unlimited quantities.
I'm glad you raised this issue. If a demand rises for donated eggs,
we will have to ensure that potential donors are treated ethically.
> But assuming that the nuclear transfers were successful and the
> manipulated "semi-embryos" began to grow in culture, then what are you
> going to do? Are you going to transfer them to the uterus of a
> hormonally prepared "mother" to serve as a host for what you hope will
> be a new organ?
When I raised the possibility, I had assumed that in vitro techniques
would be sufficient for growing "cloned" tissue. Even so, there are
some disturbing elements about such a procedure.
> Another strategy might be to isolate a human embryonic stem cell line
> which could be genetically manipulated in culture and/or subjected to
> various treatments (different growth factors, hormones, extracellular
> matrices, etc.) that would push it down specific developmental pathways
> in culture. Mouse embryonic stem cell lines, for example, will form
> cardiac muscle tissue under certain culture conditions and it actually
> contracts rhythmically in the culture dish! Current research is aimed
> at inducing these cell lines to develop into a number of different
> tissues "upon command." Performing such procedures with a human
> embryonic stem cell line does raise some serious ethical issues,
> however, because the development of such a cell line would involve the
> sacrifice of at least one cleavage-stage human embryo. Once
> established, however, the embryonic stem cell line would provide a
> virtually unlimited supply of undifferentiated human cells that,
> theoretically, could develop into any organ or tissue of the human
> body. Personally I don't favor the development of a human embryonic
> stem cell line for the reason mentioned above and because the potential
> for abuse of this resource is just too great.
Good points, all.