The positive potential of stem cell research is accompanied by ethical quandaries, which have been the driving force behind the U.S. policy debate.

The ethical questions surrounding the issue are focused on embryonic stem cells. Adult stem cell research is, in general, "not morally difficult," said Hilary Bok, a bioethicist at Johns Hopkins University.

In a January 2004 report, the President's Council on Bioethics says a challenge to the ethical debate about embryonic stem cell research is that so much is unknown. No human therapies have been developed, even though scientists are excited about the potential of the research to save human lives.

Because of the unknowns -- and the politics and emotions involved -- it's difficult to find the full truth behind the potential of stem cell research, the report says.

Some of the major ethical questions involved with embryonic stem cell research are explored here.

1. Is it acceptable to destroy a human embryo for research if it will someday result in lifesaving therapies?

Most critics of embryonic stem cell research argue that the research is unethical because extracting stem cells destroys a human embryo. Thus, the debate centers on the status of human embryos. Are they clusters of cells or human individuals? Most people tend to gravitate to a position between these two extremes, but the discussion is unresolved in policy and legal debates.

Bok acknowledged that embryos are living and they are human -- but does that make them living humans? Do they deserve moral status? She pointed out that cancer cells are also living and human, yet those qualities certainly don't make them worth protecting.

Bok said that although she is "not particularly troubled" by the embryonic destruction that's involved with stem cell research, she said embryos demand some respect.

But Alfonso Gómez-Lobo, a member of the President's Council on Bioethics and a professor of metaphysics and moral philosophy at Georgetown University, has another view on the status of embryos. In March 2003 testimony before the Maryland House Health and Government Operations Committees, Gómez-Lobo said embryos are human beings at an early stage of their lives.

"If implanted under proper conditions, they would grow to become adults like you and me," he said.

In a November 2005 presentation to educators and the media, Gómez-Lobo said "exploiting" embryos "is equivalent to exploiting living human beings of any other age or condition."

To sidestep the ethical dilemma of destroying embryos, current U.S. policy allows federal funding only for embryonic stem cell research that is conducted on stem cell lines that were created before Aug. 9, 2001. Such research uses replicated cells from stem cells that have already been extracted from an embryo. But critics argue that even using existing lines is unethical because, at one point, an embryo was destroyed.

However, proponents of the research argue that excess embryos at in-vitro fertilization clinics would eventually be discarded and destroyed -- and if that's morally acceptable, destroying embryos for research that may someday produce lifesaving human therapies is ethically sound.

They also argue that it would be unethical not to conduct research to treat life-threatening diseases such as Parkinson's disease and diabetes.

Research proponents also point out that in the natural reproductive process, human embryos are often fertilized but don't implant in the uterus. Thus, they say a fertilized egg can't be considered a human being at least until it has been implanted in a woman's uterus. Indeed, even prominent “pro-life” Sen. Orrin Hatch, R-Utah, supports federal funding of human embryonic stem cell research, saying in May 2005 that he believes “life does not begin in a Petri dish.”

2. Under what circumstances can embryos be ethically donated for research?

Embryos used for stem cell research come from fertility clinics. Excess embryos are created during in-vitro fertilization because harvested eggs can't be frozen for later use -- but embryos can. Thus, women get their eggs harvested once, and several embryos are made in case the couple decides to undergo further reproductive treatments in the future. The couple then has the option of having the embryos stored for their future use (and if left unused, they are discarded) or donating their embryos to research.

According to most polls, many in the general public believe that excess embryos from in-vitro fertilization procedures can ethically be used for embryonic stem-cell research, since they are going to be discarded anyway.

In the fall of 2005, an embryonic stem cell researcher from South Korea -- Hwang Woo Suk -- stepped down as head of a global stem cell hub and issued an apology for ethical breaches in how he obtained embryos for research. (Later, Hwang's cloning breakthrough was found to have been fabricated.)

Two junior members of Hwang's team donated egg cells for research, and several other women had been paid for their eggs. Such practices raise ethical questions in international scientific circles because of the possibility of coercion and exploitation.

When the U.S. policy for federal funding of stem cell research was implemented in 2001, existing stem cell lines were identified as "acceptable" for research funding if they had been derived:

• with the informed consent of the donors;
• from excess embryos created solely for reproductive purposes; and
• without any financial inducements to the donors.

These ethical stipulations are internationally accepted when it comes to sources of embryos for research purposes.

3. Is it right to use somatic cell nuclear transfer, or SCNT, to produce embryos for research?

Embryonic stem cells created through SCNT, often called therapeutic cloning, raise ethical issues surrounding cloning. Poll after poll in the past several years has shown the vast majority of the American public opposes cloning for reproductive purposes. Although support varies widely for therapeutic cloning -- depending on the organizations that conducted the polls -- the bulk show that the majority of Americans support SCNT after they read a description of it.

But the idea of SCNT raises the issue of creating embryos solely for research purposes, which some see as devaluing human life, while others worry about the potential for exploitation and abuse.

Bok said the issue of therapeutic cloning is more morally difficult than using excess embryos from in-vitro fertilization techniques, since cloning involves creating embryos only to destroy them.

4. How does the language used sway public opinion?

No matter what side of the fence you're on, chances are your opinions were influenced, in part, from the very terminology used in this debate.

William Neaves, the president and CEO of the Stowers Institute for Medical Research in Kansas City, Mo., argues even the name "embryonic" stem cell research is inaccurate.

Neaves said an embryo isn't really created until it is implanted along a woman's uterine wall -- so a blastocyst is never an embryo in a laboratory setting. Thus, he said the use of the word "embryo" for research purposes is misleading.

The President's Council on Bioethics report analyzes some of the other terms used to describe the process. They suggest that referring to the excess embryos from in-vitro fertilization procedures as "spare" suggests that embryos are interchangeable and nothing much is lost should the "spare" ones disappear.

Referring to such embryos as "left over" has the same connotations.

"The term 'leftover' embryos always makes me think about meatloaf left over in the refrigerator," said Dr. Dan Kaufman, a researcher at the University of Minnesota's Stem Cell Institute. He said researchers generally avoid the term as not to show disrespect to embryos.

The influence of media coverage goes beyond language choices. Matthew Nisbet, an assistant professor in the School of Communication at The Ohio State University, conducted a review of media coverage of stem cell research from 1975 to 2002. He found that although research on adult stem cells derived from bone marrow and other sources has been ongoing since the 1960s, there was very limited coverage of stem cell research until the turn of the century.

But once embryonic stem cell research entered the political debate, coverage of the issue spiked, Nisbet found.

This suggests that the media is more likely to report on stem cell research when it's in the political and moral arena -- rather than in the scientific realm, where the coverage would include complex technical explanations.

Conclusion

The ethical debate surrounding embryonic stem cell research is filled with tough questions that will continue to divide policymakers until more scientific evidence arises to answer some of the questions involved.

Or perhaps the social climate will shift with changes in policymakers and other leaders throughout the world, which would result in changes in ethical norms.

However, if embryonic stem cell research is halted altogether, it would be impossible to find conclusive answers to any of the ethical questions surrounding the issue.