INDUCING DONOR-SPECIFIC TOLERANCE TO ISLET ALLOGRAFTS IN DIABETIC NOD MICE BY POSTTRANSPLANT DONOR LYMPHOCYTE INFUSION

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P939 Aims: A substantial level of donor lymphocyte chimerism is required to protect donor-specific islet allografts in the mouse model with autoimmune diabetes. Donor islet allografts can be rejected in diabetic NOD mice with a low level of donor lymphocyte chimerism. In this study, we investigated whether posttransplant donor lymphocyte infusion increases donor chimerism and induces donor-specific tolerance to islet allografts in diabetic NOD mice. Methods: Donor BALB/c (H-2d) splenocytes were injected into prediabetic NOD/Lt mice (H-2g7) and diabetic NOD mice at day -3, followed by one dose of cyclophosphamide at day -1. BALB/c bone marrow cells (4x 107) were infused at day 0. Anti-CD40L mAb and rapamycin were given from day 0 to day 14. Donor islets were transplanted under left kidney capsule simultaneously with bone marrow transplantation in diabetic NOD mice. Donor lymphocyte infusion (1x107) was given in prediabetic NOD mice at 2 and 4 weeks post-bone marrow transplantation. In diabetic NOD mice, donor lymphocyte infusion (2x 107 or 3x 107) was given at 2, 4, and 6 weeks post-bone marrow transplantation. Mixed chimerism was measured by flow cytometric analysis. Islet graft function was monitored by measuring blood glucose. Left nephrectomy was performed in diabetic NOD mice with islet graft function at 100 days posttransplant. To test donor-specific tolerance, second donor-specific or third-party islets were transplanted under right kidney capsule of these NOD mice 1 week after left nephrectomy. Results: Donor lymphocyte chimerism was achieved in all prediabetic and diabetic NOD mice without or with posttransplant donor lymphocyte infusion. At 8 weeks post-bone marrow transplantation, the percentage of donor lymphocyte chimerism was 20.7±4.3% in prediabetic NOD mice without posttransplant donor lymphocyte infusion (N=11). Donor lymphocyte chimerism was significantly increased to 39.0±24.9% in prediabetic NOD mice with posttransplant donor lymphocyte infusion (N=9, P<0.05). The percentage of donor lymphocyte chimerism was 10.8±4.7% in diabetic NOD mice without posttransplant donor lymphocyte infusion (N=13). While posttransplant donor lymphocyte infusion was given, donor lymphocyte chimerism was significantly increased to 32.5±22.1% in diabetic NOD mice (N=9, P<0.05). Without posttransplant donor lymphocyte infusion, donor islet grafts survival was 30.8% in diabetic NOD mice at 100 days posttransplant (N=13). With posttransplant donor lymphocyte infusion, donor islet graft survival was 89% in diabetic NOD mice at 100 days posttransplant (N=9, P<0.01). The return of hyperglycemia in these NOD mice after nephrectomy confirmed islet graft function. Furthermore, long-term second donor-specific islet graft survival was achieved. Graft-versus-host disease was not observed in these NOD mice without or with posttransplant donor lymphocyte infusion. Conclusions: Our data demonstrate that adoptive immunotherapy with posttransplant donor lymphocyte infusion enhances donor chimerism and induces donor-specific tolerance to islet allografts in the setting of autoimmune diabetes.