Despite the promise of stem cells, research using human stem cells has stirred considerable controversy in the United States and in some other parts of the world. The controversy mainly surrounds the use of stem cells that come from human embryos, in particular embryos left over from infertility treatments. During a treatment known as in vitro fertilization, eggs that have been surgically removed from a female ovary are placed in a laboratory dish with male sperm. In some cases more than one egg becomes fertilized, creating extra embryos. Embryonic stem cells come from embryos at a very early stage, about the time the embryo would have attached to the wall of a uterus.
The use of human embryonic stem cells in medical research raises a fundamental question: Do these cells come from human tissue or from humans? Some people oppose the use of anything, including stem cells, from an embryo that is viable (able to grow). For people who take this philosophical position, stem cell research involves the destruction of a human life. An opposing viewpoint states that these embryos would never develop into humans, because they would be either discarded or kept frozen in laboratories for future research. Consequently, some people argue that this material should be used in any way that could possibly improve human life.
Some people who oppose the use of embryonic stem cells point out that scientific investigators could rely on other sources. A variety of body tissues—including bone marrow and blood from an umbilical cord—can provide adult stem cells. However, adult stem cells are not equal to embryonic cells in their versatility and thus in their potential for treating human disease.
Ethical uncertainty hangs over a related area of research on human embryonic stem cells. Human embryos contain stem cells that have the ability to develop into almost any type of cell. Scientists hope to direct stem cells to produce certain types of human tissue. It is possible that someday these cells might be used for transplants or for growing new tissue that can be grafted into the human body. For example, scientists hope that stem cells might one day be used to replace nerve cells destroyed by spinal injury, or heart muscle cells damaged during a heart attack. Interest in this field was heightened considerably when scientists announced in 1998 that they had learned how to grow human embryonic stem cells in the laboratory.
At present the U.S. government has banned federal funding for human-embryo research, although private biotechnology companies are exempt from this ban and have been vigorously pursuing research on embryonic cells. In 2000 the federally funded National Institutes of Health (NIH) ruled that this ban was not necessary for studies using cells derived from human embryos, since these cells are not embryos. The NIH established guidelines enabling federal funds to be used in cases where cells were derived from frozen embryos that were created for the purposes of fertility treatment but were not going to be used and were therefore slated for destruction. Other nations currently differ widely in their policies: France, for example, has forbidden human-embryo research. No laws in Canada regulate human-embryo research, although scientists or institutions receiving federal funding must follow strict guidelines governing research on human embryos. The United Kingdom has laws permitting some forms of human-embryo research, going so far as to create guidelines allowing scientists to apply cloning technology to human embryonic cells to create genetically identical cells for a potential patient.
But the ethical questions remain: Is it morally acceptable to use tissue taken from human embryos? One recent development might change the nature of this argument. Scientists discovered in 1999 that stem cells taken from adult mice, and not human embryos, also display an ability to change their function. Some stem-cell research continued with the use of adult mouse cells. In 2007 government medical authorities in the United Kingdom approved the creation of embryos that combine human and animal cells for use in medical research. British researchers claimed the hybrid embryos were vital in the fight against disease.
