Neural tissue xenotransplantation: What is needed prior to clinical trialsin Parkinson's disease?

Embryonic allografted human tissue in patients with Parkinson's disease has been shown to survive and ameliorate many of the symptoms of this disease. Despite this success, the practical problems of using this tissue coupled to the ethical restrictions of using aborted human fetal tissue have lead t o an exploration for alternative sources of suitable material for grafting, including xenogeneic embryonic dopaminergic-rich neural tissue. Neverthele ss, xenografted neural tissue itself generates a number of practical, ethic al, safety, and immunological issues that have to be addressed prior to any clinical xenotransplant program. In this article we review these critical issues and set out the criteria that we consider need to be met in the deve lopment of our clinical xenotransplantation research programs. We advocate that these, or similar, criteria should he adopted and made explicit by oth er centers contemplating similar clinical trials.