New York, Sep 25 : US scientists have in a significant experiment transplanted stem cells into mice and found reduction of brain abnormalities typical of Alzheimer's disease. The team from Stanford University transplanted blood stem and progenitor cells into mice, effectively leading to the replacement of a type of neural cell, called microglia, that's defective in mice with the disease. 'This cell therapy approach is unique in the field because most researchers are working to find pills or injectables to treat Alzheimer's disease,' said Marius Wernig, Professor of pathology and a researcher at the Stanford Institute for Stem Cell Biology and Regenerative Medicine. Microglia cells protect other brain cells against invaders and function as a cleanup crew, taking out the metabolic trash that can accumulate in the brain. Scientists have observed that some genetic variations in microglia show a strong correlation with an increased risk of Alzheimer's disease. One such correlation involves a gene called TREM2, which plays an essential role in how microglia detect and address neurodegeneration. 'Certain genetic variants of TREM2 are among the strongest genetic risk factors for Alzheimer's disease,' Wernig said, in the paper published in the journal Cell Stem Cell. 'The data are convincing that microglial dysfunction can cause neurodegeneration in the brain, so it makes sense that restoring defective microglial function might be a way to fight neurodegeneration in Alzheimer's disease,' he added. In the study, mice with a defective TREM2 gene received hematopoietic stem and progenitor cell transplants from mice with normal TREM2 function. The researchers found that the transplanted cells reconstituted the blood system and that some of them efficiently incorporated into the recipients' brains and became cells that looked and behaved like microglia. 'We showed that most of the brain's original microglia were replaced by healthy cells, which led to a restoration of normal TREM2 activity,' Wernig said. Next, they found that in the transplanted mice there was a clear reduction in the deposits of amyloid plaques normally seen in TREM2-deficient mice, Wernig said. The scientists were also able to show a restoration of microglial function and reduction of other disease markers, indicating that functional restoration of this one gene had widespread positive effects. Wernig and colleagues said they could transplant cells engineered to have supercharged TREM2 activity that may have an even greater effect. /IANS