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Stem Cell Options

5/23/2005 - 6:00 AM PST

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Bioethics Council Ponders 4 Proposals

WASHINGTON, D.C., MAY 23, 2005 (Zenit) - On May 10 the President's Council on Bioethics presented a report looking on alternative sources of stem cells. Entitled "Alternative Sources of Human Pluripotent Stem Cells," the report explains that human embryonic stem cells are of great interest because of their pluripotency, that is, their capacity to give rise to the various specialized cells of the body. Nevertheless, many people reject the use of such cells, given that they cannot be obtained without destroying embryos.

The council, established by President George Bush in 2001 to advise him on bioethical issues, looked at other ways of obtaining stem cells and proposed four possibilities: stem cells from dead embryos; from living embryos, by non-destructive biopsy; from bioengineered embryolike artifacts; and from reprogrammed adult somatic cells.

The report stipulates that it is only a preliminary study, noting that more research is needed regarding the scientific viability of the alternatives. In addition, "more discussion is surely required on some of the ethical issues we have identified."

Really dead?

The first proposal makes an analogy with the use of human cadavers for biomedical research or as sources of organs. Similarly, stem cells from early in-vitro fertilization embryos that have spontaneously died could be used for the benefit of others. The concept of death for the early-stage human embryo would be the irreversible loss of the capacity for continued cellular division and growth.

In most cases this cessation of development is associated with chromosomal abnormalities in the developing embryos. But some of them have cells that appear normal, and that may turn out to be a source of embryonic stem cells. The proposal contemplates using already-frozen IVF embryos, which would be thawed and examined for viability, so as to avoid putting other embryos at risk.

In general, this looks ethically acceptable, the Council on Bioethics states, insofar as it is based on the use of cells from embryos that die naturally. However, the report adds, "the final ethical assessment of this proposal will depend very much on exactly how it is implemented."

The report does, however, raise some doubts. Concerning the definition of death, the problem is that, as the harvested cells are to serve as a source of stem cells, it is not feasible to wait for the death of each and every cell before declaring the embryo dead and, hence, eligible for use in research. Therefore, the question arises as to whether the embryo is really dead. Identifying the criteria for death of an organism at such an early stage of life as this is not easy, the council warns.

Extraction from the living

In the second proposal, stem cells are to be derived by means of a biopsy of an early human embryo. Already, the study notes, extractions are made from living IVF embryos to conduct pre-implantation genetic diagnosis.

Here, the council observes, the major ethical issue concerns the question of possible harm to the still-living embryo whose cells are removed. Moreover, since the extraction is not being performed for the good of the embryo, it might be hard to justify the procedure.

Another objection arises from the possibility that some may want to use this method, not only on embryos to be transferred to a woman, but also on "spare" embryos not selected for implantation. Because of the still-unknown risk of harm due to a biopsy, the bioethics council notes that some have suggested that the procedure can be ethically done only on an embryo that is not going to become a child. This in turn leads to objections from those who consider such a utilitarian treatment of embryos to be morally unacceptable, the report notes.

Biological artifacts

The third approach involves several proposals that contemplate engineering "biological artifacts." So far, these projects are untested, even on animals. One of these proposals, presented to the bioethics council last December, involves a variation on techniques used in cloning.

In cloning, a somatic cell nucleus is introduced into an oocyte (egg cell) whose own nucleus has been removed. The proposal involves modifying the somatic cell nucleus before its transfer, in such a way that the result, while being a source of pluripotent stem cells, would lack the essential attributes and capacities of a human embryo.

In favor of this proposal is the argument that no embryo creation or destruction is involved. But, the council comments, critics of the idea are worried that "the proposed biological artifact has, from the beginning, a built-in genetic defect that prevents it from developing normally." So rather than being the production of a non-human entity, it may involve ...

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