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Stem Cell Research

Stem cells are found in plants and animals, but most moral issues involve human stem cells. Such cells have two significant properties: (1) they can divide to form other types of cells and (2) they can divide indefinitely—that is, they are potentially “immortal.” There are three major types of stem cells. A totipotent stem cell can divide to form any kind of bodily cell, as well as an entire organism; an example is a fertilized egg (zygote). A pluripotent stem cell can divide to form many different kinds of bodily cells, such as neurons or heart cells. A multipotent stem cell can divide to form cells of a specific kind: Blood stem cells can form the various types of blood cells, such as red and white blood cells, but cannot divide to form liver or pancreatic cells.

Stem cells can be harvested from the adult (such as from bone marrow or brain tissue), from umbilical cord blood, from the placenta, and from embryos. Human embryonic stem cells (hES) are harvested from the inner cell mass of the embryo at the blastocyst stage, about 1 week after conception. The sources of embryos include aborted fetuses, but more often, spare embryos donated from fertility clinics. Stem cells can also be harvested from embryos made through cloning adult body cells.

Stem cell research is promising because stem cells could be used to grow replacements for damaged body cells, such as neurons to treat victims of spinal cord injury, Parkinson's disease, or Alzheimer's disease. Other possible diseases that could be treated include heart disease and diabetes. One day, entire organs may be grown.

There has been virtually no opposition on moral grounds to research on adult, umbilical cord blood, and placental stem cells (the placenta, which like the umbilical cord is part of the afterbirth, is a nutrientcarrying organ joining the umbilical cord to the wall of the uterus). Stem cells from cord blood and the placenta are usually classified as adult stem cells. But many scientists believe that because embryonic stem cells, unlike adult stem cells, are naturally pluripotent, they could be used more effectively to grow many types of cells. In contrast to adult stem cell research, embryonic stem cell research has stirred a storm of controversy, with the lines of debate paralleling the abortion issue.

The Moral Status of the Embryo

Since embryos are destroyed in harvesting hES, a key issue is the moral status of the embryo. Is it a human person, with full human rights? Is it a group of cells with no more rights than an isolated group of liver cells? Or does its status lie somewhere in between? Those who believe in the embryo's personhood hold that harvesting hES is immoral, equivalent to manslaughter. They argue that any line drawn after conception limiting human personhood is arbitrary. They further argue that adult stem cells (including cord blood and placental stem cells) can be used just as effectively to develop treatments for disease.

Those who deny any special moral status to the embryo support harvesting hES. They argue that the embryo lacks personhood due to the early embryo's absence of sentience and a developed nervous system. Some argue that because such embryos, either discarded from fertility clinics or cloned for the purpose of harvesting stem cells, will not develop in the womb (because they will not be implanted), they lack any special status above other body tissues.

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