Neural Transplantation in the Nonhuman Primate Model of Parkinson’s Disease

Neural transplantation research for Parkinson’s disease has followed a circuitous and, at times, an unpredictable path. Based primarily on successful rodent studies, clinical trials using adrenal medullary tissue or fetal mesencephalic tissue were initiated throughout the world, but highly variable results in both transplant paradigms sent researchers back to the animal models for further study. Based on a then, newly available neurotoxin, MPTP was used in nonhuman primates to better model the neuropathology and behavior of Parkinson’s disease. Using the MPTP, dopamine-depleted primate model, researchers have been able to address questions that were unanswered before advancing to clinical trials and which rodent models could not or did not answer. New investigations pursued questions regarding immunorejection, sources of dopamine-producing cells, transplant location, and even characteristics of the host. While this may give the impression that neural transplantation research had taken a step backward, the nonhuman primate model has helped to lay a foundation from which other transplant approaches could be compared before moving into clinical trials. Polymer encapsulated cells and neural progenitor cell lines are two such approaches that will be examined in the nonhuman primate model before being attempted in the Parkinson’s patient population. While feasibility has been proven in the primate model, clinical applicability is still dependent on the creation of a stable source of donor cells.