While it has been suggested that deficits in BDNF production play a causal role in the progression of HD [31] and the increasing levels of BDNF may underscore behavioral sparing following MSC transplantation into rodent models of HD, the immune response to these cells also needs to be closely examined, as has been observed in other studies [7,8,27,29]. The gene discussed is BDNF; the disease is Huntington disease.