So what are stem cells and why should you care?

The foundational cells for all life, stem cells can be coaxed into becoming a wide variety of tissues and even organs, scientists believe.

The National Institutes of Health says in its Web-based fact sheet on "stem-cell basics" that two characteristics distinguish stem cells from other types of cells:

--- They are "unspecialized cells that renew themselves for long periods through cell division."

--- Under certain conditions, "they can be induced to become cells with special functions" such as heart muscle or the insulin-producing cells of the pancreas.

Based on successful research on animals, scientists have theorized that stem cells could play a role in preventing or curing a variety of diseases, conditions and disabilities including Parkinson's and Alzheimer's diseases, spinal cord injuries, stroke, heart disease, diabetes, osteoarthritis, rheumatoid arthritis and burns.

But since researchers at the University of Wisconsin discovered in 1998 how to isolate and develop human embryonic stem cells, no human disease or condition has been successfully treated with them.

The only definitive advances in treating humans have come using adult stem cells, such as the blood-forming stem cells in bone marrow, used to treat leukemia, lymphoma and several inherited blood disorders.

In a question-and-answer sheet distributed in 2004, the U.S. bishops' Secretariat for Pro-Life Activities calls the claims about the potential of embryonic stem cells "largely speculation."

"Embryonic stem cells have never treated a human patient, and animal trials suggest that they are too genetically unstable and too likely to form lethal tumors to be used for treatment anytime soon," it said. "This kind of exaggerated 'promise' has misled researchers and patient groups before --- most obviously in the case of fetal tissue from abortions, which a decade ago was said to promise miracle cures and has produced nothing of the kind."

Embryonic stem cells come from living embryos that have been frozen after creation for in vitro fertilization procedures or, less frequently, created by cloning specifically for research. Harvesting stem cells from them always kills the embryos.

Adult stem cells come from three sources --- pregnancy-related tissue such as umbilical cords, placentas and amniotic fluid; adult tissues and organ systems such as bone marrow, liver, skin, intestine, brain and even fat; and, rarely, postmortem human brains up to 20 hours after death.

One of the biggest misconceptions about stem-cell research is that the Catholic Church opposes it, said Father Tadeusz Pacholczyk, who studied neuroscience at Yale University and theology at Gregorian University in Rome. On the contrary, he said, the church supports three of the four ways that stem-cell research currently is being conducted:

--- Adult stem-cell research, involving the growth of stem cells from the patient's own tissue or that of another living donor.

--- Stem cells developed from umbilical cord blood or placentas after a delivery is completed.

--- Cells from fetal tissue derived from miscarriages (also called spontaneous abortions), as long as the parents give informed consent.

Only the use of embryonic stem cells, usually harvested from living embryos five to seven days after their creation in a test tube, is morally unacceptable, because it involves the killing of a human being, he said.

Father Pacholczyk, a priest of the Diocese of Fall River, Mass., who is director of education for the National Catholic Bioethics Center in Philadelphia, spends much of his time on the road, addressing national conferences, college groups, legislators and church-sponsored gatherings on the stem-cell issue.

Introducing the Stem-Cell Research Enhancement Act recently along with Rep. Diana DeGette, D-Colo., Rep. Michael Castle, R-Del., called embryonic stem-cell research "the greatest medical hope of the 21st century."

The legislation would permit federal funding of embryonic stem-cell research using embryos "originally created for fertility treatment purposes" which "will otherwise be discarded." It has 156 co-sponsors in the House, and an identical bill has been introduced in the Senate.

But Father Pacholczyk, director of education for the National Catholic Bioethics Center in Philadelphia, calls embryonic stem-cell research "the worst kind of medicine" and rejected the argument that it is more acceptable to kill embryos that might die anyway.

"Just because someone might throw away frozen embryos doesn't mean it's OK for me to destroy them," he said. "For one wrong to be used to justify another is never good moral reasoning."

---CNS