A simple definition of a stem cell is a cell that can regenerate itself and also produce a more differentiated cell. This definition suggests the potential for limitless bounty of source material (unlike, say, fetal cell transplants) as well as the potential to create specific neurological cell types that might be better matched to specific patient deficits. As with any new approach to treatment of diseases, however, the transformation of potential into reality is developed through a careful process of controlled clinical trials, with the best refined clinical end points, rigorous development of the product based on the most stringent scientific data, and patience. For example, the very limitless regenerative potential of a stem cell raises concerns regarding possible development of a malignant cell phenotype. For implantation into the central nervous system, even a "benign" slow growth can be deadly. Creating a differentiated cell phenotype with 95% "purity" is not nearly good enough, if the remaining 5 percent are of a different phenotype. We know that stem cells, the state of differentiation notwithstanding, can migrate throughout the body. It would be scant comfort to be able to treat end-stage Parkinson disease if some of those differentiated cells migrated to the A-V node of the heart and caused uncontrolled arrhythmias. The Center for Biologics Evaluation and Research (CBER) has initiated a number of ventures to augment the science needed for clinical trials for stem cells. The CBER and the National Institute of Neurological Disorders and Stroke (NINDS) have signed a memorandum of understanding whereby the Food and Drug Administration (FDA) reviews serve as liaisons to help formulate funding initiatives that will lead to research in areas that concern them; NINDS scientists are attending early FDA meetings with sponsors to learn about the FDA regulatory role in product development. The National Institute on Aging and CBER are collaborating in examining human stem cells with microarrays to determine reproducible markers of differentiation that might be useful for stem cell product characterization.
Noguchi P. Stem Cells: Regulatory Challenges and Initiatives. Arch Neurol. 2003;60(2):296. doi:10.1001/archneur.60.2.296-a