Baboons undergoing orthotopic concordant cardiac xenotransplantation surviving more than 300 days: effect of immunosuppressive regimen

OBJECTIVE: We reviewed long-term survival among hosts in 3 consecutive series of a rhesus monkey-baboon orthotopic cardiac xenotransplantation model with reference to host immune response, including the effectiveness in preventing rejection and limiting toxicity concerning infection, to evaluate specific immunosuppressive regimens for long-term outcomes. METHODS: Six juvenile baboons surviving more than 300 days after transplantation were reviewed. Regimen A consisted of splenectomy, FK506, methotrexate, and antilymphocyte globulin. Regimen B consisted of pretransplantation and chronic maintenance with cyclosporine A (INN: ciclosporin), methotrexate, and antithymocyte globulin. Regimen C was the same as regimen B plus pretransplantation total lymphoid irradiation and intraoperative donor bone marrow cell infusion. Rejections were detected by means of echocardiography. RESULTS: Long-term survivors in 3 groups were followed for a range of 332 to 515 days (mean, 436 days). Rejection frequency in regimens A, B, and C was 0.35, 0.58, and 0.18 per month, and rescue therapy days were 23 (4.8%), 123 (9.5%), and 20 (2.4%), respectively (P <.0001). Infection frequency was 0.58, 0.56, and 0.19 per month, and therapy days were 192 (38.2%), 164 (12.6%), and 7 (0.9%), respectively (P <.0001). Concerning the host immune response, interleukin 2-activated T cells of all groups during rejection-free periods showed lower numbers compared with those of control animals (P <.0005), and regimen C was the lowest among 3 groups (P <.01). The production of xenoantibody was sufficiently attenuated in all groups. CONCLUSION: Regimen C leads to long-term survival with fewer rejection and infection episodes by means of suppression of the interleukin 2 pathway and xenoantibody production.