Purpose: Tolerance for pig-to-human islet transplantation could render a feasible and sustainable cure for T1D. We have previously described a triple therapy (TT) approach consisting of (1) ethyl carbodiimide-fixed donor splenocytes (ECDI-SP), (2) anti-CD20, and (3) rapamycin given peritransplantation is highly effective in protecting porcine islet grafts in a pig-to-mouse model. Using a humanized mouse model, the current study investigates the efficacy of TT in porcine islet transplantation to test for its clinical applicability in inducing tolerance against the human immune response to xenotransplantation.

Methods: Streptozocin induced diabetic, NOD-SCID IL2rγ^−/− (NSG) mice with reconstituted human immune systems using human bone marrow-liver-thymus (BLT) tissues were transplanted (day 0) with 3000 adult porcine islet equivalents under the kidney capsule as untreated and TT treated groups. TT was given peritransplantation: ECDI-SP (I.V.) day -7 & +1; anti-CD20 (I.V.) day -9 & 0; rapamycin (I.P.) day -7 to +10. Serum glucose was monitored for graft outcomes. Xenografts were harvested by day 60 (D60) post transplantation.

Results: Using the BLT model, which is known to have the most functional, robust human immune system of all humanized mouse models and highest resistance to GVHD, we verified that 1) All subjects had adequate reconstitution of human T (~40%) and B (~45%) lymphocytes prior to any treatments. 2) Porcine islets restored normoglycemia (glucose <250 mg/dl) in all diabetic subjects within a few days from transplantation. 3) TT treated mice maintained normoglycemia and prolonged graft survival at D60 4) Harvested TT grafts at D60 revealed intact, functioning islets with positive insulin staining on histology. 5) Protected TT grafts at D60 also demonstrated minimal intragraft human lymphocyte infiltration and 6) elevated expression of co-inhibitory molecules (hu-PD1) on ~50% of infiltrating hCD4+ T cells. 7) Inversely, rejected grafts were found to have significant infiltration of human lymphocytes concurrent with sustained hyperglycemia.

Conclusion: TT protected islet xenografts against early rejection in humanized mice for up to 60 days post transplantation. This pig-to-humanized mouse model provides valuable insight by allowing us to test for the clinical applicability of TT in controlling the human immune response to xenotransplantation.

CITATION INFORMATION: Lee F., Dangi A., Burnette M., Zhang X., Hering B., Luo X. An Effective Tolerance Approach for Porcine Islet Xenotransplantation in Humanized Mice Am J Transplant. 2017;17 (suppl 3).

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