Update on fetal transplantation: the Swedish experience.

We implanted human embryonic mesencephalic tissue into the striatum of 13 patients with idiopathic Parkinson's disease (PD) and three patients with MPTP-induced parkinsonism. Based on our findings so far, as well as data from other groups, the following conclusions can be drawn: First, grafted dopamine (DA) neurons can survive in the human parkinsonian brain and reinnervate part of the host striatum. Second, long-term graft survival, at least up to 6 years after transplantation, is possible in PD despite a progressive degeneration of the patient's own DA neurons. Third, a majority of patients with surviving grafts show long-term improvement of therapeutic value but the symptomatic relief is, in most cases, incomplete. Presently, the most important research strategy to improve the functional recovery after transplantation is to increase the survival of grafted DA neurons and the density and extent of the dopaminergic reinnervation in the striatum.