Most Americans know someone afflicted with an incurable medical condition. The possibility of stem cell "cures" has given hope to many who face such suffering and loss. Unfortunately, there is a tremendous amount of misinformation about stem-cell therapies. To make sound decisions about this rapidly advancing field of research, it is important to understand what stem cells are and what promise they actually offer patients and their families.

How might stem cells help human patients? Stem cells may be medically useful for replacing tissue damaged by injury or disease. Following a heart attack, for example, many cells of the heart die and are not replaced, leaving the heart weakened and less able to pump blood. If replacement heart muscle cells could be produced from stem cells, these muscle cells could be used to repair the heart and restore normal heart function.

Stem cells are present in human tissues, including many adult tissues, at all stages of life. Yet stem cells from different sources have different properties, and in some cases, involve grave ethical problems.

The earliest stem cells are found in the human embryo during the first few days of life. These embryonic stem cells (or ESCs) can reproduce themselves indefinitely and are very flexible: they normally give rise to all of the tissues of the mature body. To obtain such embryonic stem cells for research and for possible future therapies, however, the embryo must be destroyed. This raises the critical ethical question of whether the life of one human being (albeit at a very early stage) can be sacrificed in order to advance scientific research or benefit the health of an older human being.

In contrast to ESCs, there are many sources of stem cells that do not raise ethical problems. Stem cells can be obtained from a patient's own bone marrow or other tissues, as well as from a variety of birth-associated tissues, including placenta, amniotic fluid, umbilical cord and umbilical cord blood. All of these non-embryonic sources of stem cells are commonly (and somewhat confusingly) referred to as "adult" stem cells, to distinguish them from stem cells obtained by destroying human embryos.

Thirdly, recent work has shown that stem cells can be produced easily and without controversy by introducing a small number of factors into ordinary adult skin cells.

In formulating a sound opinion about stem cell research, it is important to consider what kinds of stem cells are most likely to be useful for medical treatments and what kind of ethical boundaries we are willing to cross for the promise of medical cures.

Many people, including many scientists, claim that because ESCs can reproduce themselves indefinitely and, Non-embryonic stem cells offer best hope for patients because they naturally generate all the cells of the mature body, stem cells from embryos will be the most useful for medical treatments. Are ESCs really the best option for human therapies?

Quite apart from the grave ethical problem of destroying human embryos for research, there are significant, long-standing scientific problems with ESCs that must be overcome before they could be considered safe for use in human patients, which include tumor development, immune rejection and the fact the cells are unstable.

Stem cells can be derived from many of a patient's own tissues, including bone marrow, muscle tissue, nasal mucosa and even fat. While embryonic stem cells have been studied intensively for a quarter of a century, most types of stem cells from mature tissue have been discovered only recently. Consequently, we are just beginning to understand the properties of adult stem cells and to explore their current and future medical applications.

Many people, including many scientists, claim that adult stem cells will not be as useful for human medical therapies because these cells do not divide readily in the laboratory and they produce only a limited number of mature cell types. These claims have been discredited, however, by new data from the rapidly advancing area of adult stem cell research.

Stem cells from more mature tissues present significant advantages for use in medical therapies. First, stem cells from more mature tissues do not make tumors and are not genetically unstable. Because adult stem cells and their derivatives can be safely transplanted to patients, more than 1,500 clinical studies are currently underway, testing the medical usefulness of adult stem cells for diverse medical conditions, including (among others) diabetes, heart disease, amyotrophic lateral sclerosis (Lou Gehrig's disease), multiple sclerosis (MS), arthritis, sickle cell disorder and many types of cancer. In contrast, in the quarter century since their discovery, not a single clinical study has been approved for ESCs, due to the serious safety concerns discussed above.

Also in contrast to embryonic stem cells, stem cells from more mature tissues can be immune-matched to patients relatively easily. Stem cells taken from a patient's own tissues are a perfect match. When it is not possible to obtain stem cells from the patient directly, donor registries, similar to the bone marrow registry, could provide a wide range of immune matches. Finally, with over four million births in the United States every year, stem cells from birth-associated tissues could provide immune matches for the great majority of American patients.

Lastly, while stem cells from mature tissue may be more limited in the kinds of mature cells they can produce, the flip-side of this "limitation" is that the cells produced are much more likely to be fully mature and therefore clinically safe and clinically useful.

Second practical conclusion: While "adult" stem cells have only recently been discovered, they have already proven themselves to be safe and clinically promising for a wide range of medical conditions. As citizens and as Christians who truly care about patients and their families, we need to ask ourselves: Why should money be diverted from stem cell research that is currently helping patients in favor of ethically and scientifically problematic embryonic stem cell research?

Serious hurdles must be overcome before embryonic stem cells can be used for medical treatments, and surmounting these hurdles is likely to take many decades and huge sums of money. Out of compassion for patients, we are obligated to focus our research spending on approaches that are most likely to result in relief of human suffering. On purely practical grounds, embryonic stem cell research is not the most effective use of research money, and does not offer the greatest hope to patients.

On a more fundamental level, we must not be so blinded by our concern for patients and their families that we ignore the moral cost of scientific research. Science and medicine, like all human endeavors, cannot be justified by the "good outcomes" they might produce, independent of the means by which those outcomes are obtained. Medical stem cell research must operate within the constraints of ethical principles, with the first principle being "do no harm." Research on human embryonic stem cells involves the intentional destruction of human life at its earliest and most vulnerable stage. Regardless of any potential benefit this research may offer, as citizens and as Christians, we must ask ourselves: Can medical cures justify the price of destroying human life? As former embryos, we should all stand in solidarity with our brothers and sisters who are not yet capable of speaking for themselves on this question of vital importance to their future and our own.