Two new studies suggest that at least 25 per cent of the embryonic stem cell (ES cell) lines available for use by federally-funded US researchers have 'little potential even as research tools'. This is because they are too difficult to keep alive and were initially grown using mouse 'feeder' cells, which would cause them to be rejected by patients' immune systems and diminishing their potential as a medical treatment. President Bush has restricted the use of federal funds to ES cell research conducted on cell lines created before 9 August 2001.
One study, being undertaken by researchers at the Salk Institute in La Jolla, California and the University of California San Diego, focuses on the use of mouse cells to cultivate the ES cell lines. Newer cell colonies are not derived in this way and scientists and the Food and Drug Administration (FDA) have already expressed concern that viruses contained in the animal cells could infect the human cells as well as affecting the success of transplantation into patients. While the FDA has said that with rigorous testing, the mouse cell-fed ES cells may one day gain approval for use in humans, it is the other problem causing more concern.
The rejection problem is caused by the fact that mice, like all mammals except humans, have on their surface molecules of N-glycoylneuraminic acid. Human cells have a different molecule, N-acetyl neuraminic acid. The new study shows that human ES cells grown on mouse cells 'consume' the mouse molecules, which appear on the human cell surfaces. Ordinarily, humans have antibodies against these molecules (probably from consumption of mammalian meat). But what this means is that when other human cells - in this case blood serum - were added to the ES cells in the laboratory, antibodies attacked and killed the stem cells. To the immune system, 'these human cells look like animal cells, which leads to death', said Fred Gage, one of the research team leaders. The study has been provisionally accepted for publication in a 'top-tier scientific journal', according to the Washington Post, and full details are embargoed until that time.
The second study, which is as yet unfinished, compares the characteristics of 14 of the 22 colonies approved for use by federally-funded US researchers. Team leader Carol Ware, from the University of Washington, said that at least five of those cell lines 'will never be useful for the clinic' because they are too difficult to grow. In addition, she said, the researchers found that each cell colony had its own 'quirky propensity' to turn into one type of body cell or another, suggesting many more than 22 cell lines will need to be available to investigate the full potential of ES cells.
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At Least 25% of Stem Cell Lines Approved for Federal Funding Have Diminished Potential for Treatment, Studies Say