What are stem cells?
Stem cells are cells that are undifferentiated. This means they have not yet committed to becoming a certain cell type, like a brain cell or a muscle cell. There are several designations for stem cells. Unipotent stem cells can only become one cell type. Multipotent stem cells can become multiple cell types. Pluripotent stem cells can become most or all of the over 200 cell types in the human body, and totipotent stem cells can become all cell types in the body, plus other tissue like placenta cells.1
Stem cells have several sources. Embryonic stem cells come from an embryo, 5-7 days after fertilization (the blastocyst stage). These stem cells are considered to be pluripotent. Stem cells are also abundant in umbilical cords, placentas, bone marrow, and several other tissues in the body. These stem cells, although they do not need to come from adults, are referred to as “adult stem cells” to distinguish them from “embryonic stem cells.” Adult stem cells used to be considered only multipotent, but now researchers are finding that they are pluripotent as well, and can form virtually any body tissue.2
Why are stem cells important?
The future possibility of stem cells treating disease is enormous. Because stem cells can become different tissue types, it is thought that they can replace damaged cells or tissue that cause many conditions such as diabetes, Parkinson’s disease, spinal cord injuries, and heart disease. Stem cells take cues from surrounding cells and differentiate accordingly. For example, stem cells in heart tissue will become heart cells, stem cells in bone marrow will become blood cells, etc. In diabetes (Type I), a patient’s cells that produce insulin are damaged, so the diabetic patient needs to inject insulin and monitor blood sugar levels closely. The hope is that stem cells can be introduced to the diabetic’s pancreas, where they would replace the damaged cells and begin to produce insulin.
Is stem cell research ethical?
The answer is not a simple yes or no. Research on stem cells, themselves, is not unethical, they are just cells. Whether stem cell research is ethical depends on how the researchers got the stem cells. Harvesting adult stem cells from umbilical cords or bone marrow does not require that the individual be destroyed. For embryonic stem cells, this is not the case. In order to harvest embryonic stem cells, the embryo must be destroyed. The Catholic Church clearly states that an embryo, from the moment of fertilization, is a human being that deserves respect. To destroy that embryo for its stem cells, no matter how well intentioned the goal, is unethical.
President George Bush understood the distinction between stem cells and how they are derived. In 2001, he announced that the federal government would only fund research on embryonic stem cell lines that were already created, where human embryonic life had already been destroyed. There would be no federal funding for research that required the present or future destruction of human embryos.
This may change. At present, Congress is debating a bill, authored by Senator Bill Frist (R-TN), that would allow federal funding for embryonic stem cell research using “leftover” in vitro fertilization (IVF) embryos. (For more on IVF and biotechnology, see The Slippery Slope topic) There are approximately 400,000 leftover IVF embryos in the United States alone. Four hundred thousand human beings in the deep freeze, and embryonic stem cell researchers want to destroy them for their stem cells. And, when the supply of IVF embryos is exhausted, researchers will insist that therapeutic cloning is the answer. (For more on therapeutic cloning, see the Cloning topic)
Just because the federal government is not currently funding embryonic stem cell research does not mean that embryos are not already being destroyed for their stem cells. Couples are free to donate their leftover IVF embryos to research, because of Roe v. Wade which stated that embryos are not legally considered persons.
Alternatives to using embryos for stem cells
Obviously, pluripotent adult stem cells are the clear alternative to the destruction of embryos for their stem cells. But many researchers still want to explore the possibilities of embryonic stem cells. Is there a way to procure embryonic stem cells without destroying embryos? There is. The President’s Council on Bioethics has prepared a paper called “Alternative Sources of Human Pluripotent Stem Cells.” In it, they suggest four different ways to procure pluripotent stem cells without the destruction of live embryos. The first is to use “early IVF embryos (4-8 cells) that have died spontaneously,” with the stipulation that “only those once-frozen embryos that are thawed and that die spontaneously during efforts to produce a child will be eligible for post-mortem cell extraction.”3
The second approach would be to procure stem cells by biopsying the embryo without harming it. This technique is currently used to diagnose disease in IVF embryos before they are implanted. (For more on genetic testing of IVF embryos, see the Genetics topic.) However, the Council writes, “
Crucial to this approach is finding a stage of early embryonic development at which (a) the removal of one or a few cells by biopsy can be carried out without harming the embryo, while (b) the cell or cells removed from the embryo are usable as a source of pluripotent stem cells.”4
The third proposal would involve a theoretical technique called altered nuclear transfer (ANT), similar to somatic cell nuclear transfer (SCNT), but would not, in theory, result in a cloned human being. (For more on SCNT, see the Cloning
ANT involves “altering the somatic cell nucleus before its transfer to the oocyte, and in such a way that the resulting biological entity, while being a source of pluripotent stem cells, would lack the essential attributes and capacities of a human embryo.”5 Dr. William Hurlbut, the originator of that idea, suggests altering the nucleus of the donor cell by removing certain essential genes so that, when it is introduced into the egg, it could not become a human being.
The final proposal would be to reprogram an adult somatic cell, like a skin cell, back to a pluripotent stem cell state. The Council recognizes that the difficultly here is technical. It may take many, many years to understand the mechanism that causes a cell to differentiate from a stem cell to a somatic cell, let alone find out how to reverse the process.
The first two proposals require embryos that are created by IVF. Catholic teaching maintains that creating a child without the act of sexual intercourse is immoral. So, the first two suggestions by the Council would not be the more ethical of the proposals. There is debate on whether ANT is an ethical alternative to SCNT for deriving ESCs. Several top Catholic ethicists have signed a joint statement endorsing a form of ANT called Oocyte Assisted Reprogramming (OAR). (The statement can be found on the Center for Bioethics and Human Dignity website www.cbhd.org) The Catholic Church has not officially endorsed ANT and OAR. Adrian J.Walker, professor of philosophy at the John Paul II Institute, believes ANT is unethical. He writes, "ANT is technically and morally indistinguishable from human cloning.”6 Walker argues that ANT could not sufficiently alter human DNA so as not to produce a human embryo and remain an effective treatment.
The Council's last proposal does not require embryos at all and, therefore, would kill two birds with one stone. It would not only eliminate the need to destroy embryos for pluripotent stem cells, it would also eliminate the need for cloning for therapeutic purposes. Unfortunately, this technology may be a long way off.
It is crucial to understand the differences between adult stem cells and embryonic stem cells, all the more so because our lawmakers and the media often try to confuse the issue by not making the distinction. While cures from embryonic stem cells are currently not possible, adult stem cells are already curing patients without the moral conundrums. Consequently, the best, most ethical technologies for stem cell treatment come from adult stem cell research.
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1 David A. Prentice, Stem Cells and Cloning, Pearson Education, Inc., San Francisco, 2003, p. 3
3 President’s Council on Bioethics, “Alternative Sources of Human Pluripotent Stem Cells,” May 2005, pp. 3-4