team derived stem cells from primordial gonadal tissue obtained from cadaveric fetal tissue (Shamblott et al., 1998). hEG cells, which originate from the primordial reproductive cells of the developing fetus, have properties similar to those of hES cells, although there has been less research into their potential.

The third report, an article in the November 12, 1998, edition of the New York Times, described work funded by Advanced Cell Technology of Worcester, Massachusetts. The report was not published in a scientific journal and therefore did not meet the higher standard of peer review, but the company claimed that its scientists had caused human somatic cells to revert to the primordial state by fusing them with cow eggs. From this fusion product, a small clump of cells resembling ES cells appears to have been isolated (Wade, 1998).

In addition to those research accomplishments, the cloning of Dolly the sheep in 1997 using a technique called somatic cell nuclear transfer or, more simply, nuclear transfer (NT), illustrated another means by which to generate and isolate hES cells. hES cell preparations could potentially be produced by using NT to replace the nucleus of a human oocyte, triggering development, and then isolating hES cells at the blastocyst stage. Such a procedure was recently described by a group of Korean scientists (Hwang et al., 2004). The advantage of using NT to derive hES cells is that the nuclear genomes of the resulting hES cells would be identical with those of the donors of the somatic cells. One obvious benefit is that this would avoid the problem of rejection if cells generated from the hES cells were transplanted into the donor. Whether this approach will be technically or economically feasible is unclear. A more likely benefit of the technology is that it would further facilitate a wide range of experiments to explore the underpinnings of genetic disease and possible forms of amelioration and cure, many of which would not be possible using hES cells derived from blastocysts generated by in vitro fertilization (IVF), whose nuclear genomes are not defined. Although the promise of such research is as yet unrealized, most researchers believe that it will be a critical source of both important knowledge and clinical resources.

It is important to note that stem cells made via NT result from an asexual process that does not involve the generation of a novel combination of genes from two “parents.” In this sense, it may be more acceptable to some than the creation of blastocysts for research purposes by IVF (National Institutes of Health, Human Embryo Research Panel, 1994). Use of NT for biomedical research, as distinct from its use to create a human being, has been considered by several advisory groups to be ethically acceptable under appropriate conditions involving the proper review and conduct of the research (NBAC, 1997, 1999a; NRC, 2002). However, there is near universal agreement that the use of NT to produce a child should not now be permitted. The medical risks are unacceptable, and many people have additional objections concerning the nature of this form of human procreation. In some countries there are statutory bans on the use of NT for reproductive purposes (see Chapter 4).



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