EOSINOPHIL INFILTRATION AND ELEVATED IL-5 LEVELS CORRELATE WITH REJECTION OF ENCAPSULATED PORCINE ISLET XENOGRAFTS IN DIABETIC NOD MICE, BUT DEPLETION OF EOSINOPHILS WITH ANTI-IL-5 MAB DOES NOT PROLONG GRAFT SURVIVAL.

Abstract

P1082 Aims: Islet cell transplantation is a promising strategy for a cure for Type 1 diabetes, but a major limitation is the small number of donated human pancreases. The purpose of this study was to test the efficacy of poly-lysine alginate encapsulated porcine islet xenografts transplanted intraperitoneally (i.p.) in spontaneously diabetic NOD mice. Methods: Mice were transplanted i.p. with 9,000 islet equivalents (IEQ) of encapsulated porcine islets or 6,000 IEQ non-encapsulated islets under the renal capsule. Graft survival was monitored by random blood glucose (RBG) levels. Technically successful grafts reduced RBG to <150 mg/dl for 3 days in the first week post-transplantation. Graft rejection was defined as the first of two consecutive days with RBG >250 mg/dl after successful engraftment. Normal mice and mice implanted with empty capsules served as controls. To identify the host cells mediating xenograft destruction in this model, peritoneal cells (PEC) were analyzed by FACS. Peritoneal lavage was performed and fluids were analyzed for IL-5 levels by ELISA. Some mice were treated with anti-IL-5 monoclonal antibody (mAb) (28 μg, days 0,6, 10, and weekly thereafter) to inhibit eosinophilia. Results: Microencapsulated adult porcine islets survived longer (13±1 days) in NOD recipients than non-encapsulated islets (4.5 ± 0.5 days). The numbers of CD19+ B cells, CD4+ T cells, CD8+ T cells, macrophages, neutrophils, and eosinophils were equivalent in control mice implanted with empty capsules and normal NOD mice, implying that capsules do not elicit immune or foreign-body responses. The numbers of CD4+ T cells and neutrophils were significantly higher in transplanted mice than in normal NODs (p<0.01). At graft rejection, the numbers of CD8+ T cells, macrophages, and eosinophils were significantly greater than in normal NODs (p<0.01). Eosinophils were significantly higher in mice with rejected grafts compared to normal NODs and NODs with functioning grafts, in absolute numbers and percentages. Histological analysis of PEC stained with Giemsa confirmed these results. Kinetic studies showed that peritoneal levels of IL-5 increased dramatically between days 11 to 20 in transplanted NODs, correlating with the influx of eosinophils at the time of graft rejection. To determine whether eosinophils had a role in graft destruction, mice transplanted with encapsulated porcine islets were treated with anti-IL-5 mAb. Eosinophils were depleted by anti-IL-5 mAb, but graft survival was not significantly different than in untreated mice (11.4 ± 1 days). Conclusions: These results suggest that eosinophils are not required for xenograft rejection in our model, but our findings do not rule out the possibility that eosinophils and/or their products may play a role in xenograft destruction.