Transplantation into the human brain: present status and future possibilities.

Transplantation of brain tissue into the adult mam- malian CNS is not a new field of research. A century ago, the New York Medical Journal contained an article by W Gilman Thompson' entitled "Successful brain grafting". He exchanged large pieces of neocor- tical tissue between adult cats and dogs and analysed some of the grafts microscopically after survival times ofup to 7 weeks. Despite the positive title ofhis paper, the long-term "grafts" probably consisted only of neuron-free remnants and developing scar tissue. Almost 90 years passed before the first animal experimental data appeared clearly indicating the possible clinical usefulness of the neural grafting technique. In 1979 it was shown23 that intracerebral grafts of rat fetal dopamine (DA) neurons were able to reduce the symptoms of experimental, 6-hydroxydopamine (6-OHDA)-induced Parkinsonism in rats. This was the first example of neurons, being implanted into the adult mammalian brain, which were able to reverse a functional deficit in an animal model of a human neurological disorder. Early on, of course, these findings kindled a hope that it would be possible to develop a transplantation therapy for patients with Parkinson's disease.