Transplanted tissues or organs from a donor other than the recipient; also called nonself transplant. Allografts sometimes used as treatment for Parkinson’s disease include neural grafts and stem cell implants. Most such procedures are still considered experimental and are not consistently successful. Donor tissues and organs are carefully screened for pathogens and other contaminants before use. A slight risk of infection or other problems remains, however. As well, there is the possibility that the recipient’s body will reject the transplanted tissue, negating the effects of the transplant and potentially causing additional health problems.