PRETREATMENT OF ISLETS WITH MITOMYCIN C (MMC) AND BLOCKAGE OF DIRECT ANTIGEN PRESENTATION INDUCE UNRESPONSIVENESS TO ISLET XENOGRAFT

Abstract

124 Introduction: We have previously shown that rat ICAM-1 on APCs can interact with mouse LFA-1 on T cells across species barrier and blockage of this pathway using species specific mAbs produces prolongation of islet xenograft survival. We have also demonstrated that infusion of donor splenocytes pretreated with MMC, induced unresponsiveness to rat cardiac allografts. In this study we try to minimize immunosuppression and induce unresponsiveness to xenograft using blockage of costimulatory pathway with anti-donor ICAM-1 mAb and graft pretreatment with MMC. Materials and Methods: Collagenase-digested WS (RT1k) rat islets, purified by Ficoll density gradient, were incubated for 30 mins with MMC at a dose 10 µg/ml and subsequently cultured for 20 hrs. These crude 300-400 islets were transplanted into the renal subcapsular space of streptozotocin-induced diabetic C57BL/6 (H-2b) mice. Recipients were given anti-recipient (mouse) LFA-1 mAb or/and mouse anti-rat ICAM-1 mAb at a dose of 0.05 mg i.p. on days 0 and 1 after transplantation. Mice bearing xenografts over 100 days were challenged with freshly isolated crude WS islets. Results: Significant prolongation was obtained by transplantation of MMC-treated islets (group 2 vs. 1). When these islets were transplanted into the animals given anti-mouse LFA-1 mAb or combination of anti-mouse LFA-1 and anti-rat ICAM-1 mAbs, graft survival over 100 days was 44% and 75% respectively. Animals given anti-recipient LFA-1 and anti-donor ICAM-1 mAbs were more prone to accept the second graft than animals given anti-recipient LFA-1 mAb alone (group 5 vs. 4; p<0.001). The results were summarized in the table.TableConclusion: Unresponsiveness to crude xenogeneic islets can be induced by graft pretreatment with MMC and blockage of costimulatory pathway using species specific anti-donor ICAM-1 mAb under low-dose immunosupression with anti-recipient LFA-1 mAb.