Initial evidence that blockade of the CD40/CD154 costimulation pathway alone is sufficient as maintenance therapy in xenotransplantation.

The Editor, Wewish to report an observation that we believe may be important to the future development of clinical pig organ xenotransplantation. There has been considerable discussion on the strength of the primate immune response to a pig organ, even if the graft comes from a pig genetically engineered to protect the organ from the human innate immune response.1 It has frequently been suggested that the primate adaptive immune response to apig xenograft is stronger than to anallograft, and that the intensity of immunosuppressive therapywill need to be greater than in allotransplantation.We determined to test whether this was the case.