Few advances in science have proven as controversial as embryonic stem cell research. The relevant facts are straightforward. Human embryonic stem cells retain the potential to become any tissue in the body, and thus have enormous promise for treating a wide range of diseases. In mice lacking immune defenses, researchers have used embryonic stem cells to cure type 1 diabetes, Parkinsons, damaged heart muscle such as produced in heart attacks, and injured nerve tissue.
Human embryonic stem cells are very difficult to isolate and establish in culture, but perhaps a dozen lines have been successfully obtained from the inner cell mass of six-day blastocysts. It is important to isolate the cells at this early stage, before development begins the process of restricting what sorts of tissues the stem cells can become.
The blastocysts are obtained from reproductive clinics, which routinely produce excess embryos in the process of helping infertile couples have children by in vitro fertilization. This month the RAND Group reported that more than 400,000 frozen embryos have accumulated in the freezers of American fertility clinics.
However, obtaining embryonic stem cells destroys the early embryo in the process; for this reason, stem cell research raises profound ethical issues. The timeless question of when human life begins cannot be avoided when human embryos are being deliberately destroyed. What is the moral standing of a six-day human embryo? In resolving the tension between scientific knowledge and moral sensibilities, religious, philosophical, and cultural issues all come into play. The accompanying table illustrates the range of issues being discussed.
It will come as no surprise that government, which funds much of modern biomedical research, has become embroiled in the controversy. In Britain, reproductive cloning is banned, but stem cell research and cloning to obtain clinically useful stem cells are both permitted. Because the research is funded by the government, there is careful ethical supervision of all research by a variety of governmental oversight committees. Britains Human Fertilization and Embryology Authority (HFEA), for example, is a panel of scientists and ethicists accountable to parliament, which oversees government-funded stem cell research. Similar arrangements are being established in Japan and France. Germany, by contrast, discourages all stem cell research.
In the United States, the situation is ambivalent. American stem cell research is chiefly carried out in private research labs using no government funds and thus are subject to no ethical oversight. This leaves American scientists pretty much free to do what they want, so long as they use private money. Federal funds were made available in the summer of 2001 for research on a small number of existing human embryonic stem cell lines. In what has become a very political contest between those favoring increased stem cell research and those opposing all such research on ethical grounds, it seems certain that federal government policies with regard to stem cell research will fluctuate for some time to come.
Researchers are chomping at the bit. Two years ago, researchers at the Rockefeller University reported a way to use stem cells to replace damaged tissues without immune rejection — that is, a way to avoid having a patients immune system attack injected stem cells as foreign.
Their solution to the immune rejection problem? They first isolated skin cells from a patient mouse. Then, using the same procedure that created Dolly the cloned sheep, they create a 120-cell early embryo, called a blastocyst. The blastocyst is then destroyed, its embryonic stem cells harvested for transfer to injured tissues. Since the embryonic stem cells are cloned from the bodys own tissues, they pass the immune systems self identity check, and the body readily accepts them.
Using this procedure, called therapeutic cloning or, more accurately, somatic cell nuclear transfer, the researchers succeeded in making cells from the tail of an immunologically normal mouse convert into the dopamine-producing cells of the brain that are lost in Parkinsons disease.
Viewed through a cloud of ethical and political controversy, the key question must be: Will somatic cell nuclear transplant therapy work as well in humans as in mice? The relevant experiments have not yet been reported, but most researchers are guardedly optimistic. If yes is the answer, then a host of ethical and political issues, no longer hypothetical, will have to be addressed. How we do so will have an enormous impact on the human condition.
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