Stem Cells

Stem Cells

BIBLIOGRAPHY

A stem cell has two special qualities: the ability to produce offspring of itself indefinitely, and the ability to differentiate into different types of specialized cells. “Adult” stem cells are found in various organs of fully formed organisms. For example, umbilical cord blood and bone marrow contain stem cells capable of producing the various cells found in the blood, such as red blood cells, white cells, and platelets.

Public debate about ethical, social, religious, and legal issues involving stem cells has centered on a different kind of stem cell, so-called embryonic stem cells, usually obtained from excess embryos created by in vitro fertilization (IVF), but sometimes created specifically for research or therapeutic purposes. These human embryonic stem cells (hESCs) have the capacity to form any tissue in the body; that is, they are totipotential.

HESCs are of scientific and medical interest for three reasons: (1) they provide an opportunity to do laboratory research on normal and abnormal differentiation; (2) they provide an opportunity to test experimental therapies, including drugs and genes, at a cellular level, without exposing living animals or humans to risk; (3) they present an opportunity to develop and transplant cell lines that can replace vital molecules such as insulin (for patients with diabetes mellitus) or dopamine (for patients with Parkinson’s disease), or to replace damaged tissue in the heart, nervous system, or elsewhere.

HESCs from residual IVF embryos are unlikely to be sufficient for all research and therapeutic interests. If, for example, stem cells are to be useful in treating diabetes, it will be important to create a cell line that is genetically identical to the recipient, so that it will not be rejected after transplantation. This can be accomplished by removing the nucleus of an egg, replacing it with the nucleus from a cell obtained from the potential recipient, and allowing the egg to grow to a stage when stem cells can be removed. This is called “somatic cell nuclear transfer” (SCNT).

SCNT is also of interest for laboratory research on genetic disorders such as cystic fibrosis or Tay Sachs disease. An embryo is created using the nucleus from a somatic cell of a patient with the disorder being studied, and then stem cells with the abnormal gene are obtained from the early embryo. This is sometimes called “research cloning.” SCNT for the purpose of creating a cell line that would be used for treatment is sometimes called “therapeutic cloning.”

Objections to research involving hESCs involve several concerns. First, some believe that an embryo has the same moral status as a fully formed human and is entitled to the same protections. Destruction of an embryo, in this view, is morally equivalent to murder. Proponents of hESC research point out that residual embryos are used only when the parents intend to destroy them anyway, and are not destroyed because of the interest in stem cell research. They also point out that tens of thousands of residual IVF embryos are destroyed annually without similar objection.

Second, opponents also argue that there are alternative approaches to obtaining totipotential stem cells, such as using adult stem cells. Most experts believe adult stem cells are not totipotential and therefore should not divert research funds from the more promising embryonic stem cells.

Third, opponents object to SCNT combined with hESC research because of concerns that it is a critical technical step for reproductive cloning, the creation of genetically identical replicas of existing persons. Advocates of hESC research argue that reproductive cloning is nearly universally opposed at the present time, largely because of concerns about biologic safety, and that “slippery slope” arguments are insufficient to prohibit research that can help alleviate suffering, disability, and death from diseases affecting large numbers of existing persons.

Fourth, concerns have been raised that the transfer of human cells into the developing brain of laboratory animals could result in an animal capable of human experience and therefore with moral status comparable to a human. Although most neuroscientists consider this to be unlikely, some groups have proposed prohibiting full gestation of nonhuman primates if human stem cells have been implanted in their central nervous systems early in embryonic development.

Governmental policies reflect a range of approaches in different countries and states, and policies within any jurisdiction are often in flux, subject to the success of politicians with various views. Some prohibit human embryonic stem cell research; some permit it but have restrictions on use of public funds; some permit research using existing embryos but prohibit creation of embryos for research; and some restrict somatic nuclear cell transfer because of concerns that it may accelerate human reproductive cloning.

SEE ALSO Ethics in Experimentation; Medicine; Neuroscience; Public Policy; Reproductive Politics

BIBLIOGRAPHY

McHugh, Paul R. 2004. Zygote and Clonote—The Ethical Use of Embryonic Stem Cells. New England Journal of Medicine 351 (3): 209–211.

National Academy of Sciences. 2006. Understanding Stem Cells: An Overview of the Science and Issues from the National Academies. http://dels.nas.edu/bls/stemcells/booklet.shtml.

Sandel, Michael J. 2004. Embryo Ethics: The Moral Logic of Stem-Cell Research. New England Journal of Medicine 351 (3): 207–209.

Walters, LeRoy. 2002. Human Embryonic Stem Cell Research: An Intercultural Perspective. Kennedy Institute of Ethics Journal 14 (1): 3–38.

Norman Fost