Stem-Cell Gamble

Stem-Cell Gamble - Technology Review: If anything, embryonic stem cells are too powerful. Early on, scientists hoped they would be magic bullets for a variety of diseases. Just inject them—and watch them race to injury sites and fill in for dying cells. In one early study, embryonic stem cells placed in the brains of rats suffering from symptoms of Parkinson's disease did precisely that. Not only did the cells become new neurons, but they began to squirt out dopamine, the chemical lost in Parkinson's. The problem was that they often ran amok, multiplying into frightening tumors called teratomas—disorganized mixtures of tissues, such as teeth, hair, and jawbone. Rats that developed such tumors died.