Last reviewed and revised on March 1, 2012
By Anthony L. Komaroff, M.D.
Brigham and Women's Hospital
Embryonic stem cells appear to be much more capable of turning into virtually any type of specialized cell. That's what gives them a theoretical advantage in cell therapy over adult stem cells. When embryonic stem cells come from human embryos, however, they are the subject of a huge ethical controversy.
The Moral Arguments
Much of the research so far on embryonic stem cells has involved human embryos that are the result of an abortion or have been created through in vitro fertilization and are not being used. But some people oppose methods for making human embryonic stem cells, such as nuclear transfer, because it still involves destroying an early-stage embryo (blastocyst).
Everyone agrees that it is immoral to destroy a human life. The ethical questions about human embryonic stem cell research involve the question of when life begins.
Arguments Opposing the Research | Arguments Favoring the Research | An embryo that had the potential to implant in a woman's uterus and develop into a baby has the moral status of a person and should not be destroyed, no matter how great the human benefit. | It is moral to use embryos that come from abortions or in vitro fertilization because those embryos would have otherwise been thrown away. | Even if scientists are able to re-create human embryonic stem cells by nuclear transfer, it still involves the destruction of a human blastocyst, similar to using embryos from abortions. | A human being can grow only from an embryo that has been placed into a woman's uterus: Since that does not occur with nuclear transfer, no potential human life has been destroyed. | Human embryos never should be created experimentally and then implanted in a woman's uterus with the goal of creating a "cloned" human being. | It is immoral to prohibit the research using tissue from a legal abortion, in vitro fertilization or nuclear-transfer experiment, if slowing down research is likely to delay the day when embryonic stem cells can save human lives. | | In mice, it is possible to create blastocysts by nuclear transfer that produce embryonic stem cells but are unable to implant in a woman's uterus and therefore unable to develop into a baby. If that could be achieved in humans, then research involving such blastocysts would be ethical. | |
One issue on which virtually all scientists and the general public agree is that creating a human clone and then trying to let that embryo grow into a human baby is unethical. Such "reproductive cloning" has been performed successfully in animals, the most famous example being the sheep named Dolly.
In 2007, cells very much like embryonic stem cells were created in both mice and humans by reprogramming specialized cells, and without creating an embryo! Since the ethical questions around human embryonic stem cells involve destroying an embryo from which embryonic stem cells have been taken, successful reprogramming in humans would be unlikely to raise ethical concerns.
The Legal Realities
There are two legal realities in the United States that affect the argument over the morality of using embryonic stem cells. The first is that abortion has been legalized by the U.S. Supreme Court — under certain conditions.
The second legal reality is that in August 2001, President George W. Bush allowed federal funds to be spent only on a few lines of human stem cells already in existence. The result is an inadequate supply of stem cells. No use of embryonic stem cells to treat human disease is possible without a lot more research. Many scientists have argued that the human stem cell lines available before August 2001 are too few and too fraught with risks to be very useful for serious research.
Shortly after his inauguration, President Barack Obama signed an order allowing federal funding for expanded research on embryonic stem cells.
Can Scientific Research Change the Ethical Argument?
There are three possibilities that could make the ethical conflict irrelevant.
- Reprogramming – This involves tricking specialized cells from humans to turn back into the embryonic stem cells. This would eliminate the need to collect embryonic stem cells from embryos.
- Giving adult stem cells the same ability as embryonic stem cells to turn into virtually any tissue. – This means there would be no need for embryonic stem cells. Recently, some adult stem cells called "multipotent adult progenitor cells" have been discovered that may have greater potential than most adult stem cells. However, it is too early to know if this potential will be so great that it avoids the need for embryonic stem cells.
- Coaxing specialized cells to reproduce themselves – Recently, Harvard researchers found that, in mice, the insulin-producing cells of the pancreas can do just this. If other specialized cells could be similarly coaxed, and if this could occur in humans as well as in mice, it could also eliminate the need for stem cell therapies.
- Transforming one specialized cell into another type of specialized cell, without first creating a stem cell – Recently, Harvard researchers accomplished this feat in living mice. One kind of pancreas cell was transformed into a beta cell — the kind of cell in the pancreas that makes insulin. If this feat could be achieved in humans, it could have important implications for treating diabetes. If this feat could be achieved with other types of specialized cells in other organs — for example, transforming one type of heart cell into heart muscle cells, to replace cells killed during a heart attack — it could have implications for many other diseases, as well.
Back to Stem Cells Home Anthony L. Komaroff, M.D., is professor of medicine and editor-in-chief of Harvard Health Publications at Harvard Medical School. Dr. Komaroff also is senior physician and was formerly director of the Division of General Medicine at Brigham and Women's Hospital. Dr. Komaroff has served on various advisory committees to the federal government, and is an elected Fellow of the American Association for the Advancement of Science.
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