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Since 1998, when human embryonic stem cells were first isolated, our nation has been locked in a conflict over federal funding of this new field of scientific research. Both sides in the debate are defending important human goods, and both of these goods—opening avenues for advance in medicine and protecting nascent human life—are important to all of us. A purely political solution will leave our country bitterly divided, eroding the social support and sense of noble purpose that is essential for the public funding of biomedical science. While there are currently no federal restrictions on the use of private funds for this research, there is a consensus in the scientific community that without federal support for newly created embryonic stem cell lines, progress in this emerging field of scientific inquiry will be seriously constrained.

In May 2005, acknowledging our national impasse over embryonic stem cell research, the President's Council on Bioethics published a white paper that outlines a series of proposals for obtaining pluripotent stem cells (the functional equivalent of embryonic stem cells) without the creation or destruction of human embryos.1 One of these proposals, "altered nuclear transfer" (ANT) has stirred considerable public interest and affirmation, including several legislative proposals that would provide funding for its further exploration. There is substantial support among leading scientists, moral philosophers, and religious leaders for the view that ANT may offer a scientifically feasible and morally sound way forward on ES cell research.2

At the same time, there has been some confusion about ANT, leading to its mischaracterization in certain reports and published commentaries. In a recent cover story on stem cell research in Time magazine, ANT was described as a project that "would ensure that the embryo lives only long enough to produce stem cells and then dies."3 But the whole idea of ANT is to produce pluripotent stem cells without creating an embryo. Time's description has ANT violating the very moral principle it is intended to uphold.

Acknowledging the complexity of the scientific and ethical issues at the foundation of this proposal, and in the spirit of constructive dialogue, we seek in this essay first to offer a clear and accurate account of ANT, and then to respond to some of the more significant questions and concerns about it. [End Page 42]

Altered Nuclear Transfer: Non-Embryonic Sources of Pluripotent Cells

The President's Council report draws a critical distinction between pluripotency, the capacity of a cell to give rise to many if not all the different cell types of the human body, and totipotency, the capacity of a zygote or other cell to develop as a complete, integrated, living being. A naturally conceived zygote—the single-celled embryo brought into being by fertilization—is totipotent; embryonic stem cells are merely pluripotent.

ANT is a general concept that might take a variety of specific forms. The basic idea is to employ somatic cell nuclear transfer (SCNT), the technique often known simply as "cloning," but to alter it in such a way that pluripotent stem cells are produced without the creation and destruction of human embryos. In standard SCNT, the nucleus of a differentiated body cell is transferred into an egg cell that has had its own nucleus removed.4 The egg cytoplasm then reprograms the transferred nucleus and, if all goes as planned, the newly constituted cell proceeds to divide and develop like a naturally conceived embryo. This is how Dolly the sheep was produced. In ANT, the adult body cell nucleus or the egg cytoplasm (or both) are altered before the nucleus is transferred into the enucleated egg so that the newly constituted cell will, from the outset, lack the integrated unity and developmental potential of an embryo, yet will nevertheless possess the capacity for a certain limited subset of growth sufficient to produce pluripotent stem cells.

This process mirrors certain naturally occurring phenomena. In normal conception, fertilization signals the activation of the organizing principle for the self-development of the human organism towards developmental maturity. But without all of the essential...


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