Restoration of Function with Human Islets in Humanized Diabetic Mice with Subsequent Rejection of Islet Allografts by Allogeneic Engrafted Human T Cells: 967

Background: Islet transplantation is a curative therapy for type 1 diabetes. However, its success is limited by graft loss which, in part, appears to be cellular mediated rejection. In this study, we used a humanized mouse model for in vivo studies of human islet transplantation. Our aim was to assess the capacity of engrafted human cells to reject allogeneic human islets. Methods: NOD/LtSz-scidL2Rgnull mice with streptozotocin-induced diabetes were transplanted with 2000 human islets. BSL< 10mmol/L demonstrated successful islet function. Transplanted and control mice were reconstituted with 5-10 × 106 human peripheral blood mononuclear cells (hPBMC)/human spleen mononuclear cells (hSPMC). In vivo reconstitution was assessed using flow cytometry weekly. Results: Both hPBMC and hSPMC engrafted in NOD/LtSz-scidL2Rgnull mice (n=6 by hPBMC and n=10 by hSPMC) by week 3 as assessed by presence of hCD45+ cells. Although both dose and time after reconstitution were important. In mice reconstituted with hPBMC, almost all cells were hCD3+/hCD45+ T cells (at week 5-6) (99.2%±0.3 double positive in peripheral blood (PB) and 99.1%±0.8 double positive in spleen). In mice reconstituted with hSPMC CD19+ B cells (8.9%±5.1 in mouse spleen, n=3) and CD56+ NK cells (6.8%±7.2 in PB, and 3.7%±2.5 in spleen) were detected by week 5-6 although the majority of engrafted cells were CD3+ T cells (93.7%±9.2 in PB,90.6%±4.5 in spleen). CD3+ T cells included CD4+ and CD8+ subsets as well as NKT and gamma delta T cells. However, the proportion of Tregs (hCD4+Foxp3+) present in reconstituted mice was reduced in both the PB (2.3%±2) and spleen (4.5%±1.5) when compared to the proportion present in hPBMC (8.7%). Moreover, the proportion of CD4+Foxp3+ T cells decreased further by week 9 after reconstitution when GVHD had occurred (0.4%±0.4)(p< 0.05). Functional islet allografts were rejected with a median survival time of 25 days in both the hPBMC mice and hSPMC mice in the absence of GVHD at the time of rejection. Both CD4+ and CD8+ T cell were found in rejecting islet grafts. Conclusions: Stable and high-level hematopoetic cell engraftment (CD3) was achieved with hPBMC and hSPMC in NOD/LtSz-scidIL2Rγnull. CD3 T cells are capable of rejecting human islet allografts in this humanised mouse model.