By KRISTA CONGER

Like their counterparts throughout the country, researchers at Stanford Medical Center have mixed reactions to President George W. Bush's Aug. 9 decision to allow federal funding to support research on existing human embryonic stem cell lines. Scientists who had feared a total ban on the research greeted the news with relief, while others expressed concern that the number and accessibility of the limited pool of cells might slow the pace of medical and scientific research.

Bush's decision prohibits the use of federal funding to derive new stem cells from existing embryos. The president additionally restricted the use of federal funds to those stem cell lines that were created solely for reproductive purposes, and that had been freely given for scientific research by the donors without financial or other inducements.

Proponents believe human embryonic stem cell research holds the key to future therapies for devastating diseases such as Parkinson's and Alzheimer's, as well as for people who have suffered neurological damage from a stroke or spinal cord injury. Opponents argue that human embryos should not be used as material for scientific research. Isolating stem cells from the embryos, created during in vitro fertilization procedures, destroys the embryo.

Embryonic stem cells can become all, or nearly all, cell types in the adult body. Such flexibility makes it possible that scientists could one day coax isolated stem cells to become neurons to replace those damaged in Alzheimer's or Parkinson's diseases, or insulin-secreting cells for diabetics.

Stem cells found in adults, including those in the bone marrow that renew the blood and immune system, can also become other types of cells. Their range of choices seems to be more limited, though, and at least somewhat restricted by the type of tissue from which they were derived. However, recent research by Helen Blau, PhD, professor and chair of molecular pharmacology at Stanford, has shown that the bone marrow cells of adult mice can unexpectedly migrate to the brain and assume characteristics of neurons. Bush devoted $250 million this year to research investigating the therapeutic potential of stem cells isolated from animals, adults, and placenta and umbilical cord blood.

Some scientists and patient advocates have voiced concern about the number and availability of viable cultures, or cell lines, of the stem cells. According to the president, about 60 of these cell lines exist throughout the world, providing ample research opportunities for scientists without requiring the destruction of additional embryos. However, many scientists stress the importance of cataloguing the characteristics of these cell lines -- most of which have not been documented in the scientific literature -- and determining if they are widely available to publicly funded researchers.

Following are comments by Stanford experts regarding the stem cell decision:

Philip A. Pizzo, MD, dean of the School of Medicine and professor of pediatrics and of microbiology and immunology: "While I applaud the care, precision and thoughtfulness of President Bush's deliberations and consideration É I am personally discouraged by the limitations at hand. I fear that this will restrict the progress of important research and that the current oversight of the federal government, which is so important to the quality of research, will be in some ways limited because of the private sector's current control over the research agenda. Nonetheless, progress has been made, and I'm very pleased that President Bush has revised his prior position and is allowing research to continue. It is my hope that over time, the government will reconsider further expansion of embryonic stem cell research."

Paul Berg, PhD, professor emeritus of biochemistry and winner of the 1980 Nobel Prize in chemistry: "Most of the limitations the president has imposed will have to be clarified before we know their true impact. For example, the president's statement that 'more than 60 genetically diverse stem cell lines already exist' caught most scientists by surprise. The scientific literature contains information about approximately 10 human embryonic stem cell lines. It's important to determine if the other 50 or so will be truly available to publicly funded American research scientists without restrictions that may impede research progress. It's also unknown whether the remaining cell lines have been grown and handled in ways that are compatible with high-quality research, and whether each line has maintained the capacity to generate every adult cell type. Nevertheless, my own feeling is that we are far better off now than we were before the president's decision with respect to being able to explore the biology and therapeutic utility of human embryonic stem cells."

Irving Weissman, MD, PhD, professor of pathology and developmental biology: "I think the decision is a huge improvement over where we were on April 1, when it was not clear that we would have any federal funding to do research on human embryonic stem cell lines. Now the question is whether the existing cell lines are adequate for what we want do in the future. For therapeutic purposes, it's very important that the cells have been grown in a way suitable for use in transplantation, which is very unlikely. So they're adequate for many things, but not for all things. There is much more that can and probably should be done in embryonic stem cell research, and we will see how the government and the new bioethics committee responds in the coming months to reasonable requests to create new embryonic stem cell lines to address these issues."

Helen Blau, PhD, professor and chair of molecular pharmacology: "I'm glad the president did not totally ban embryonic stem cell research, which would have been the worst possible outcome. But I hope he will loosen the restrictions so that we can fully explore the potential of this new therapy. This is a nascent field that we know very little about, and we need to do as much research as possible to explore the potentials of both embryonic and adult stem cells. I fear that the current legislation will hinder the development of this technology, which will then be done in other countries and by industry - which may not have the same standards of peer review and quality control as federally funded research, and is not optimal for the American public."

Barbara Koenig, PhD, director of the Stanford Center for Biomedical Ethics and associate professor of medicine (pulmonary and critical care): "I agree with the president that this issue of how we use these cells is of grave moral consequence and I feel a little frustrated with the implication that these cells are a magic tool that will cure diabetes and many other diseases with-in a few weeks. This is far from the truth. It's also important for the public to realize that this incredible scientific moment has happened when the health care system is in a state of collapse. Any new innovations have to be introduced into the health care system and made available to everyone who needs them, which will require funding. Finally, I'm concerned about the fact that these cell are in the hands of the private sector, where the level of research scrutiny is likely to be lower than in federally funded institutions."