Transplantation of discordant xenogeneic islets using repeated therapy with anti-CD154

BACKGROUND: Costimulatory blockade has been shown to allow long-term survival of xenogeneic islets. The aim of the present study was to analyze the possibility of xenogeneic islet retransplantation using costimulatory blockade. METHODS: Streptozotocin-induced diabetic C57/BL6 mice were transplanted with 1000 human islet equivalents. After 14 days, mice were nephrectomized (graftectomy) and retransplanted with human leukocyte antigen (HLA)-mismatched human islets under contralateral kidney capsule. Four groups were performed: I: all transplants (Tx) without MR1; II: first Tx without MR1, second Tx with MR1; III: first Tx with MR1, second Tx without MR1; and IV: all Tx with MR1. Recipient serums were analyzed by cross-match for serum-mediated cytotoxicity against human lymphocytes and islets. RESULTS: In group I, the second graft rejection was accelerated (graft survival, 5 +/- 3 days) compared with the first graft without MR1 (13 +/- 7 days). In groups II and III, second graft survivals were 16 +/-1 3 and 62 +/- 15 days, respectively. In group IV, second graft function was maintained for >100 days. Pretransplant cross-matches were all negative. Post-second Tx cross-matches were positive in groups I and II and negative in group IV. In group III, post-second Tx cross-matches were negative only for cells with HLA molecules present in the first donor. CONCLUSIONS: MR1 was unable to induce tolerance after sensitization. MR1 given at the first Tx only allowed prolonged survival of the second Tx, but rejection still occurred with development of antibodies against molecules not present on first donor cells, indicating that costimulatory blockade does not induce linked-suppression against species-specific antigens of xenografts but can induce donor-specific unresponsiveness. MR1 given for all sequential transplantation allowed long-term regraft survival and prevented occurrence of antidonor antibodies.