“If the cell’s behavior is not commensurate with that of an embryo, the cell is not an embryo.”
In December 2004, Dr. William Hurlbut, physician and professor at Stanford University and a member of the President’s Council on Bioethics, presented a proposal to the Council entitled “Altered Nuclear Transfer as a Morally Acceptable Means for the Procure- ment of Human Embryonic Stem Cells.”1 Hurlbut’s premise stated that, using modern cloning technology, it may be scientifically possible to produce embryonic-like (i.e., pluripotent2) stem cells without ever creating and destroying human embryos. Cloning is accom- plished by using somatic cell nuclear transfer (SCNT), in which the nucleus of a somatic (adult body) cell is removed and transferred into an enucleated oocyte (i.e., an egg cell with its nucleus removed). The crucial difference between SCNT for purposes of human cloning and SCNT as proposed by Hurlbut is that in the latter procedure, the genetic material in the somatic cell nucleus is preemptively altered before nuclear transfer in such a way as to create biological conditions incompatible with the coming into existence of embryonic human life, but compatible with the development of pluripotent stem cells. He called his broad conceptual proposal Altered Nuclear Transfer (ANT).
In June 2005, a group of thirty-five scholars (including ethicists, moral theologians, physicians, and scientists), including Dr. Hurlbut, published a joint statement proposing a specific type of ANT called Oocyte Assisted Reprogramming (ANT-OAR).3 ANT-OAR begins from the assumption that the identity and function of each cell in the human body depends on the precise interrelation, communication, and on-off pre-programming of the approximately thirty thousand genes in the cell’s genome. This condition of cell interaction and expression is called the cell’s “epigenetic state” (or “genetic imprinting”). The epigenetic state of the single-celled human embryo (or zygote) is totipotent, that is, it has the develop- mental capacity to differentiate in an orderly and coordinated way into all the tissue types necessary for full organismal development, including into the placenta, umbilical cord, and other extra- embryonic tissues. From the perspective of epigenetics, we might say that totipotency defines a human zygote. It follows that it is reasonable to conclude that where there is a totipotent human cell, there is a human zygote.
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1. Hurlbut published an expanded version of the essay with the same title in Perspectives in Biology and Medicine 48, no. 2 (Spring 2005): 211–228; for a synopsis of the idea, see Hurlbut’s interview with Jennifer Lahl, National Director of the Center for Bioethics and Culture Network, entitled “Altered Nuclear Transfer: Is it the Answer for the Embryonic Stem Cell Research Debate?” available at www.cbc-network.org.
I would like to acknowledge the assistance of Dr. Hurlbut; Dr. Maureen Condic of the Department of Neurobiology and Anatomy at the University of Utah School of Medicine; Thomas Berg, L.C., Executive Director of the Westchester Institute; and Dr. Michael Augros of the Center for Higher Studies of the Legion of Christ for their assistance in preparing this essay.
2. “Pluripotency” is the capacity of a cell to develop into all the various tissue types of the human body. It is important to note that presently no useful embryonic stem cell-based therapies exist. Nonetheless, many scientists believe that embryonic stem cells, because of their pluripotency, promise to provide important tools for the study of disease, and possibly to provide cells and tissues for groundbreaking medical therapies.