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May 4, 2005: NCSWA Stem Cell PanelTo save lives, or to protect nascent life, that is the question – at least one of themBy Françoise Chanut SAN FRANCISCO – The promise, limitations, and ethics of stem cell research were the topics of a panel discussion organized on May 4 by the Northern California Science Writers Association. Three stem cell scientists and a bioethicist fielded questions from moderator Bruce Goldman and an audience of 60 reporters and science writers in Genentech Hall, on the Mission Bay campus of the University of California, San Francisco. The event came a few months after California voters passed Proposition 71, which allows the state to sell $3 billion in bonds to fund stem cell research during the next decade. Proposition 71 skirts the 2001 federal ban that forbids researchers to produce new embryonic stem cell lines. All panelists agreed that stem cells hold tremendous promise for treating many grave illnesses and for basic research in human development. But ethical concerns surrounding embryonic stem cells, reproductive cloning, and human-animal chimeras persist. Stem cells are the precursors of all cell types in the human body. By growing them in the lab, scientists hope to uncover the signals that make them proliferate or differentiate into specific tissues. For clinicians, stem cells could provide unlimited access to the graft material they need to cure degenerative diseases or cancer. The prospect of stem cell therapy seems most realistic for diseases that result from the loss of specific cell types, such as insulin-producing cells in type I diabetes, or dopamine-producing cells in Parkinson's disease, said UCSF stem cell researcher Arnold Kriegstein. Alzheimer's disease presents a greater challenge because it affects several brain areas, and because the replacement cells need to connect properly with many other neurons, he said. Researchers have already achieved some therapeutic success with blood-forming stem cells, which can replenish the blood of cancer patients after radiation therapy, said Ann Tsukamoto, one of the discoverers of these cells and now a vice president of StemCells Inc., in Palo Alto. But scientists have not yet found a way to expand blood-forming stem cells into banks that could serve more than one patient. The same is true of stem cells isolated from other differentiated tissues--the so-called "adult stem cells"--except for brain stem cells, Tsukamoto said. Her company is currently testing the capacity of brain stem cells to replace damaged nerves in mice. To illustrate the company's progress, she showed a video of a mouse with a spinal cord injury whose limping was corrected with cells derived from brain stem cells. However, whether scientists can coax brain, blood, or skin stem cells to grow into any cell type--for instance, heart muscle or insulin-producing cells--remains unproven, Kriegstein said. Embryonic stem cells offer greater promise because their natural fate is to produce every cell type in a developing embryo. This should make them more versatile in the dish than adult stem cells. In addition, embryonic stem cells are capable of indefinite self-renewal in culture. UCSF stem cell researcher Susan Fisher has had success growing human embryonic stem cells on a feeder layer of human placental cells, she said. By contrast, earlier embryonic cell lines were contaminated by mouse-derived feeder cells, which makes them unsuitable for future therapeutic applications. Fisher's lab extracts stem cells from three-day old embryos created in an in-vitro fertilization clinic. "We use the discarded embryos that do not look good enough to be implanted in a womb," she said. Her personal feeling is that working with embryonic stem cells has enhanced, rather than diminished, the scientists' respect for embryos, she said. "When we see what these cells can do for humanity, what we feel is awe," she said. Divided public reaction to some of the work conducted by his fellow panelists illustrates that scientists still must reconcile the ethical pros and cons of embryonic stem cell research, said Stanford physician and ethicist William Hurlbut. "Both sides of the debate are defending important human goods that must be taken seriously," Hurlbut said. But he warned against the potential to "coarsen our sense of nascent human life." Hurlbut opposes the current methods of producing embryonic stem cells, which entail the destruction of potentially viable human embryos, because he sees life as a continuum. "A zygote is fully human," he said. As an attempt to satisfy all ethical concerns, Hurlbut presented the idea of Altered Nuclear Transfer to the President's Council on Bioethics last December. The technique would create cell masses with the capacity to yield embryonic stem cells but an intrinsic inability to organize. Scientists already know of genetic conditions that turn embryos into disorganized tissue masses that religious ethicists do not view as human, Hurlbut said. This makes him hopeful that his proposal will gain acceptance from both sides of the issue, he said. Other ethical hurdles await stem cell research. In spite of Goldman's insistent questioning, no one on the panel could guarantee a strict boundary between therapeutic and reproductive cloning. In both cases, the nucleus of an adult cell is inserted into an enucleated egg, a process known as Somatic Cell Nuclear Transfer. But whereas reproductive cloning would re-implant the resulting embryo in a womb to create a cloned human being (the process that gave rise to Dolly the sheep in 1997), the aim of therapeutic cloning is to generate embryonic stem cells for medical purposes, with the advantage of eliminating the problem of graft rejection. "No serious scientist I know… ever thinks of doing reproductive cloning," Fisher said, citing ethical reasons also mentioned by Hurlbut. And most scientists think that, for a host of technical reasons, it could not succeed, she added. Though he agreed with Fisher, Hurlbut mentioned a U.S. poll where "14% of scientists said if there were no medical problems, they would be OK with reproductive cloning." Testing human stem cells in animals is a necessary step to verify the cells' efficiency, Kriegstein said. That raises the specter of animals with partly human brains or reproductive organs. Hurlbut provided a touch of humor on the issue, quoting a student who asked him whether human beings had an "ethical obligation to share our superior neurons with animals." UCSF scientists currently adhere to guidelines similar to those proposed in May by the National Academy of Sciences, Fisher said. Scientists lend enthusiastic support to stem cell research, she noted, because they see human stem cells as a "paradigm shift" for research on development and disease. But that enthusiasm should not overwhelm other ethical concerns, said Hurlbut. He spoke of the profound principles of religious traditions--in particular, Catholicism--and of the diversity of opinions in the President's Council on Bioethics. "It's hard to be a dissenting voice among scientists," he said. He advocated further dialogue to help society reach a difficult, but worthwhile, consensus. In addition to Bruce Goldman, NCSWA board members Natalie DeWitt, Dawn Levy, and Robin Mejia organized the panel discussion. Françoise Chanut is a student in the Science Communication Program at the University of California, Santa Cruz. For more information:
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