Researchers at USC's Keck Medicine are testing an experimental stem cell therapy aimed at restoring the brain's ability to produce dopamine, the chemical whose deficiency causes Parkinson's disease. In an early stage clinical trial, lab-grown dopamine-producing cells are implanted directly into a key area of the brain that controls movement. The aim of this therapy is to slow down the progression of the disease and improve the patients' motor function. Dopaminergic neurons, which are destroyed in Parkinson's disease, are cultured in the laboratory and then transplanted into the brain[6]. Scientists have successfully developed neural transplants that are invisible to the immune system, reducing the need for anti-rejection drugs[6]. Stem cells can be turned into any type of cell, and researchers have effectively made them invisible to the immune system[6].