Research Casts Doubt On Circulating Stem Cells

Adult stem cells taken from bone marrow are the "shooting stars" of their field. Many research scientists have been speculating that the cells might be able to pass through the blood into diseased organs and replace defective tissue. Such cells are seen as the potential key to the treatment of certain muscle diseases. However, a study currently being conducted at Bonn's University Clinic has produced some sobering findings: although the cells are able to migrate into the muscle fibres, they do not generally take on any tissue-specific functions. This, according to the Bonn medical scientists, means the cells would not serve as a substitute for defective muscle cells. The study is reported on 1st August in the online section of the science journal PNAS (www.pnas.org , PNAS Early Edition). Bone marrow constantly produces stem cells from which, among other things, the white and red blood corpuscles are formed. The dream of many scientists is to breed other types of tissue from bone marrow-derived cells. In recent years a great deal of hype has been generated around the idea of a "cellular jack of all trades" – not least because some studies gave grounds for hope. Using irradiation techniques, researchers managed to destroy the bone marrow in mice and replace it with cells which became green-fluorescent thanks to a genetic addition. A short time later they then discovered green-fluorescent nerve cells in the mice's brains. This appeared to them to be evidence that the stem cells circulating in the blood could actually transform themselves into nerve tissue. It looked like the discovery of a completely new mechanism: the repairing of tissue using stem cells from the blood stream.