For scientists, the great attraction of the cells is twofold: their ability to make almost limitless copies of themselves in laboratory dishes and, wh
The cells on the outside of that sphere go on to become the placenta, the bridge of tissue connecting the embryo to the mother's womb. The cluster of cells inside the sphere, called the inner cell mass, goes on to form all the tissues of the developing embryo itself. Embryonic stem cells are extracted from this inner mass.
For scientists, the great attraction of the cells is twofold: their ability to make almost limitless copies of themselves in laboratory dishes and, when tweaked by specific chemical signals, their potential to become almost any cell or tissue in the body. That includes the brain cells lost in Parkinson's disease, the heart muscle cells that die after a heart attack or the pancreatic cells that go awry in diabetes.
This is what distinguishes embryonic stem cells from so-called adult stem cells found in bone marrow, the brain and other organs, each of which has the capacity to become certain kinds of cells -- but not every kind.
Scientists hope someday to be able to transplant brain cells, heart cells or other kinds of cells grown from embryonic stem cells into patients. Scientists also see embryonic stem cells as powerful tools for studying diseases on the cellular level.
Thomson and his colleagues isolated cells from human embryos donated by fertility clinic patients. Other scientists and doctors immediately sought to replicate his discovery, but that raised profound questions about the ethics of using human embryos as sources of research material.
Religious conservatives, in particular, believe that even human embryos the earliest stages of life are beings with moral standing.
Proponents of the research, in contrast, allow that human embryos deserve respect but have argued that it is wrong to grant them the same moral standing as a fetus, which has reached a more complex stage of development, or a newborn. In general, proponents have argued for the right to do research on embryos until they reach 14 days of development -- when it is possible to discern the beginnings of a spinal cord and nervous system.
After Thomson's announcement, the National Institutes of Health created a panel of experts to consider the issue. Two years later, as the Clinton administration was coming to an end, the panel recommended policies that would have allowed scientists to use federal money to study colonies of embryonic stem cells as long as certain ethics rules were followed. Central were the requirements that the embryos must have been created for fertility treatment, were no longer needed by the couple that made them and were donated by the couple for research.
Before that policy went into effect, however, President Bush came into power and took the matter under consideration. He announced his decision in his first televised address to the nation -- an address dedicated solely to the topic of stem cells. The date was Aug. 9, 2001.
Bush declared that federal money could be used to study embryonic stem cell colonies made only from embryos that had been destroyed by that date. He said that, based on information provided by the NIH, there were more than 60 such colonies, a number that later grew into the low 70s.
Over the following months, however, it turned out that cells from only a handful of colonies were available for distribution and study. That number has never exceeded 24. Moreover, it became clear that virtually all those colonies had been maintained in culture dishes with blood products from rodents, calling into question their usefulness as medical products because of the risk of animal viruses and other contaminants.
Over time, it also became clear that some of the colonies, including those developed by Thomson, were not aging well, and were accumulating mutations and other defects.
A few U.S. labs have produced additional cell colonies using private money, but they have complained that the process requires them to waste resources to ensure that those colonies be kept separate from those under study using federal money.
For scientists, the great attraction of the cells is twofold: their ability to make almost limitless copies of themselves in laboratory dishes and, when tweaked by specific chemical signals, their potential to become almost any cell or tissue in the body. That includes the brain cells lost in Parkinson's disease, the heart muscle cells that die after a heart attack or the pancreatic cells that go awry in diabetes.
This is what distinguishes embryonic stem cells from so-called adult stem cells found in bone marrow, the brain and other organs, each of which has the capacity to become certain kinds of cells -- but not every kind.
Scientists hope someday to be able to transplant brain cells, heart cells or other kinds of cells grown from embryonic stem cells into patients. Scientists also see embryonic stem cells as powerful tools for studying diseases on the cellular level.
Thomson and his colleagues isolated cells from human embryos donated by fertility clinic patients. Other scientists and doctors immediately sought to replicate his discovery, but that raised profound questions about the ethics of using human embryos as sources of research material.
Religious conservatives, in particular, believe that even human embryos the earliest stages of life are beings with moral standing.
Proponents of the research, in contrast, allow that human embryos deserve respect but have argued that it is wrong to grant them the same moral standing as a fetus, which has reached a more complex stage of development, or a newborn. In general, proponents have argued for the right to do research on embryos until they reach 14 days of development -- when it is possible to discern the beginnings of a spinal cord and nervous system.
After Thomson's announcement, the National Institutes of Health created a panel of experts to consider the issue. Two years later, as the Clinton administration was coming to an end, the panel recommended policies that would have allowed scientists to use federal money to study colonies of embryonic stem cells as long as certain ethics rules were followed. Central were the requirements that the embryos must have been created for fertility treatment, were no longer needed by the couple that made them and were donated by the couple for research.
Before that policy went into effect, however, President Bush came into power and took the matter under consideration. He announced his decision in his first televised address to the nation -- an address dedicated solely to the topic of stem cells. The date was Aug. 9, 2001.
Bush declared that federal money could be used to study embryonic stem cell colonies made only from embryos that had been destroyed by that date. He said that, based on information provided by the NIH, there were more than 60 such colonies, a number that later grew into the low 70s.
Over the following months, however, it turned out that cells from only a handful of colonies were available for distribution and study. That number has never exceeded 24. Moreover, it became clear that virtually all those colonies had been maintained in culture dishes with blood products from rodents, calling into question their usefulness as medical products because of the risk of animal viruses and other contaminants.
Over time, it also became clear that some of the colonies, including those developed by Thomson, were not aging well, and were accumulating mutations and other defects.
A few U.S. labs have produced additional cell colonies using private money, but they have complained that the process requires them to waste resources to ensure that those colonies be kept separate from those under study using federal money.
posted by wonderwan at 11:45 AM
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