IDEC-131 (anti-CD154), sirolimus and donor-specific transfusion facilitate operational tolerance in non-human primates.

CD154-specific antibody therapy prevents allograft rejection in many experimental transplant models. However, initial clinical transplant trials with anti-CD154 have been disappointing suggesting the need for as of yet undetermined adjuvant therapy. In rodents, donor antigen (e.g., a donor blood transfusion), or mTOR inhibition (e.g., sirolimus), enhances anti-CD154's efficacy. We performed renal transplants in major histocompatibility complex-(MHC) mismatched rhesus monkeys and treated recipients with combinations of the CD154-specific antibody IDEC-131, and/or sirolimus, and/or a pre-transplant donor-specific transfusion (DST). Therapy was withdrawn after 3 months. Triple therapy prevented rejection during therapy in all animals and led to operational tolerance in three of five animals including donor-specific skin graft acceptance in the two animals tested. IDEC-131, sirolimus and DST are highly effective in preventing renal allograft rejection in primates. This apparently clinically applicable regimen is promising for human renal transplant trials.

Human renal allograft rejection despite the absence of allogeneic passenger leukocytes.

Passenger leukocytes have been suggested to be both pro-tolerant and immunogenic. The opportunity to evaluate the role of allogeneic passenger leukocytes in humans was presented by a 47-year-old man who donated bone marrow to his HLA-identical leukemic sister. Eleven years later he developed renal failure. The sister's marrow was noted to be 100% XY karyotype and free of malignancy. She donated a kidney to her brother. Immunosuppression was tapered following transplantation. After 6 months, the recipient was on monotherapy sirolimus, 1 mg every third day. A surveillance biopsy was normal and sirolimus was stopped. Eight weeks later, he presented with severe rejection that reversed with Thymoglobulin. Renal function returned to baseline and has been stable on conventional immunosuppression.

Rabbit antithymocyte globulin induction and sirolimus monotherapy supports prolonged islet allograft function in a nonhuman primate islet transplantation model.

BACKGROUND: We reported that rabbit anti-thymocyte globulin (RATG) induction followed by maintenance immunosuppression with sirolimus supports human kidney allograft survival and asked if this combination would promote islet allograft survival in our primate model. METHODS: Using intra-arterial streptozotocin infusion, we rendered four cynomolgus primates diabetic with undetectable C-peptide levels. Animals were maintained on insulin therapy for at least 1 month, and then islets from mixed lymphocyte reaction mismatched primates were infused into the portal vein. Immediately before the islet allotransplant and for 6 additional days, primates were infused with RATG (20 mg/kg) and given a sirolimus dose to achieve a 24-hr trough level of 8 to 14 ng/mL. RESULTS: The regimen resulted in profound peripheral and lymph node lymphocyte depletion for up to 1 month. Repopulation was gradual thereafter. One primate remained insulin-independent for 169 days and rejected after a sirolimus-dose reduction. Two primates died on day 23 while insulin independent because of wound dehiscence, and a third died on day 30 with high sirolimus levels. Liver sections revealed well-vascularized islets with no signs of inflammation. CONCLUSION: Using a nonhuman primate islet transplant model, RATG plus sirolimus supports islet survival as long as proper sirolimus levels are maintained, but the therapy is limited by sirolimus toxicity. Our findings suggest that RATG is not toxic for islets and thus may be considered in future clinical trails while recognizing that sirolimus monotherapy, with its difficult-to-achieve therapeutic dosing, may not be sufficient to maintain long-term islet allograft function in an autoimmune environment.

Studies investigating pretransplant donor-specific blood transfusion, rapamycin, and the CD154-specific antibody IDEC-131 in a nonhuman primate model of skin allotransplantation.

Anti-CD154 variably prolongs allograft survival in nonhuman primates. Rodent studies suggest that adding pretransplant donor-specific transfusion (DST) and/or rapamycin to anti-CD154 improves survival. The CD154-specific Ab IDEC-131 was tested alone and in combination with rapamycin for its ability to inhibit rhesus MLRs. The ability of the Ab to block endothelial activation was also assessed. IDEC-131 was then tested alone and in combination with DST and/or rapamycin for its ability to prevent rejection of full-thickness, MHC-mismatched rhesus skin allografts. Animals were monitored for donor-specific hyporesponsiveness by MLR and alloantibody determination. IDEC-131 modestly inhibited rhesus MLRs and inhibited CD154-dependent endothelial cell activation. Rapamycin combined with IDEC-131 additively inhibited MLRs. IDEC-131 modestly prolonged allograft survival when compared with no treatment, rapamycin alone, or DST plus rapamycin. Adding DST to IDEC-131 did not prolong survival beyond IDEC-131 alone. IDEC-131 plus rapamycin was effective in prolonging graft survival, although animals had episodes of acute rejection before graft demise. Therapy with IDEC-131, rapamycin, and DST induced long-term allograft survival without intermittent acute rejection. However, no evidence for MLR inhibition was seen, and most animals eventually developed alloantibody. All animals ultimately rejected their grafts after drug withdrawal. IDEC-131 modestly prolongs rhesus skin allograft survival. Rapamycin and rapamycin plus DST improves the efficacy of IDEC-131 in prolonging allograft survival. IDEC-131, rapamycin, and DST are a promising combination for clinical evaluation in allotransplantation.