(St. Louis Post-Dispatch) -- While politicians, ethicists and religious leaders argue over the social and moral implications of funding research on stem cells taken from human embryos, researchers say the scientific debate on the topic is far from over. Stem cells are primordial cells capable of generating many different types of body parts. The question confronting scientists involved in stem cell research is whether stem cells taken from adults are as flexible as stem cells derived from embryos.
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For years, scientists thought that only embryonic stem cells were able to produce all of the cells in the human body. Stem cells taken from adult tissues such as brain, bone marrow or fat were thought to be less capable and only able to make a subset of body tissues. New research is challenging that view and leading many scientists to call for federal support for both types of research. Adult tissues may actually be more promising sources than embryos of stem cells used for transplants, said David Prentice, a cell biologist at Indiana State University in Terre Haute. Prentice is one of the founding members of Do No Harm, a group of scientists and others who challenge embryonic stem cell research on ethical grounds. Prentice says that work with adult stem cells has shown progress in treating lupus, Parkinson's disease and damaged corneas and hearts, while embryonic stem cells have failed to live up to their potential. He admits that his is a minority opinion. Many other scientists and professional societies contend that embryonic stem cells may hold greater promise in treating a wide range of human diseases and disorders including heart disease, diabetes, brain-degenerating diseases such as Alzheimer's disease and Huntington's disease, arthritis and paralysis.
They say 20 years of research on embryonic stem cells from mice has shown that embryo cells have the potential to become any of the more than 200 types of cells that make up the human body. But no one is yet sure how many tissues adult stem cells can make. That's good enough reason to fund both types of research, these scientists say.Embryonic stem cells are harvested from a mass of cells inside the early embryo. Scientists say that those cells are pluripotent - that is, they are able to divide and replicate almost indefinitely, and they are capable of making many different types of cells. Adult stem cells stop dividing after about 50 generations. As development progresses, the cells are led into one of three developmental pathways. Adult stem cells are already committed to follow one of those pathways. Scientists used to think that adult cells were incapable of reversing or changing their programming to go down a different developmental path. But recent work with mouse cells indicates that adult stem cells may be more flexible than previously thought. In mice, blood-forming stem cells have been shown to make liver cells; separately, liver stem cells can form heart cells. Those cells seemed to have crossed developmental boundaries - something scientists didn't belie ve was possible before. The results are still preliminary and need to be replicated before scientists will completely accept them, said Ida Chow, executive officer for the Society for Developmental Biology, headquartered in Bethesda, Md. No one knows how the cells are able to accomplish the identity switch, and the experiments have not been duplicated outside an animal. Scientists say conducting the experiments in a petri dish is necessary to fully understand and control the cells. Embryonic stem cells can be coaxed into making heart cells that beat in a petri dish, or nerve cells that behave like nerve cells, Chow said. It is still much too early to say whether adult stem cells or embryonic stem cells are better for developing practical treatments for diseases, said James Huettner, a cell biologist at Washington University School of Medicine. The fact that new research reports on the capabilities of each type of stem cell are published nearly every week is evidence that scientists still have too little information to answer the question, Huettner said.