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New stem cell results: what's the real news? By John Timmer | Published: March 12, 2007 - 05:05AM CT A stem cell study should be appearing shortly at the Nature Medicine site that will probably hit most of the papers tomorrow; Reuters already has coverage. Is this a big breakthrough or more hype? The paper is informative in a variety of ways, but perhaps not in the ways that might seem obvious based on the results alone. The study modeled Sandhoff disease in mice. In humans, this genetic disease results in early mental retardation and death during infancy due to the lack of a gene that helps nerve cells clear out sugars from their surface and environment. Mice lacking the gene become symptomatic at 90 days, and die within a few weeks of the appearance of symptoms (normal mouse life span is two to three years). The researchers then injected a number of different types of stem cells in newborn mutant mice (more on the types later), and showed that the mice lived an extra 30 days, and had the onset of symptoms pushed back two-and-a-half weeks. Neurons derived from stem cells were present widely in the brain, and behaved like normal neurons, showing electrical activity. Although it was clearly not a permanent cure, the results showed that stem cells could clearly improve the progression of this diseases. The types of stem cells added another layer of interest to the data. Mouse neural stem cells worked well, but human stem cells seemed to work just as well, if not better. These human cells worked either when they were neural stem cells or embryonic stem cells directed down a neural path. None of these cells, including the human ones, set off an immune response in the host mouse. So, are stem cell therapies the real deal? It's hard to tell from this report. The disease itself is caused by the lack of a protein that's normally shipped outside of the cells. Stem cells had a normal copy, and so could ship the protein outside in a way that might have been sufficient to compensate for its absence in neighboring cells. As such, it wasn't even clear if their ability to make this protein or nerve cells was more important; it's possible that any cell type that produced the protein would work. How about the ethical mine field surrounding stem cells? The similar behavior of embryonic and neural stem cells in this test probably isn't that significant-I don't think there was much doubt that neural stem cells would work in repairing neural damage. Embryonic stem cells are generally viewed as needed for the repair of tissues that we don't have a supply of stem cells for. Neural stem cells come with their own problems. Current techniques for making neural stem cells involve isolating them from embryos after the brain has formed, which is more likely to be morally objectionable than dissociating a small mass of cells, which is how embryonic stem cells are created. So, the fact that nonembryonic stem cells work well in these experiments doesn't get us out of the ethical problems people have with these cells. But that isn't the end of the trouble. The experiments created mice with a complement of human cells (called a chimera). A number of proposed legal restrictions on stem cells would specifically ban the creation of chimeras, and have presented them as horrifying human/animal hybrids. This isn't to say that these results are a reason for pessimism. They are significant, but primarily because they show that stem cells can not only cross boundaries between individuals, but between entire species without setting off an immune response. This suggests that we may have a great deal of flexibility if and when we attempt to create a stem cell population intended for therapeutic uses. Filed under: brain, nerves, stem cells, disease ---------------------------------------------------------------------- To sign-off Parkinsn send a message to: mailto:[log in to unmask] In the body of the message put: signoff parkinsn