Adult oligodendrocyte precursor cells (OPCs) make up approximately 5–8% of the glial cell population in the central nervous system. These cells are derived from the subventricular zone of the lateral ventricles and migrate and mature into myelinating oligodendrocytes in the white matter. Under normal conditions, these cells divide slowly. In response to demyelination, they divide and are thought to differentiate to provide new oligodendrocytes to replace those that have been lost. However, the remyelination process fails in late-stage multiple sclerosis.