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Function of microencapsulated adult porcine islet xenografts in streptozotocin-diabetic non-human primates

Susan A. Safley¹, Norma S. Kenyon², Dora M. Berman², Antonello Pileggi², Norman Kenyon², Hong Cui¹, Idelberto Badell¹, Allan D. Kirk¹, Robert W. Holdcraft³, Lawrence Gazda³, Camillo Ricordi², Collin J. Weber¹

¹Surgery, Emory University, Atlanta, GA; ²Surgery, University of Miami, Miami, FL; ³Xenia Division, The Rogosin Institute, Xenia, OH; United States

We assessed the function of microencapsulated adult porcine islets (APIs) in immunosuppressed, streptozotocin (SZN) diabetic non-human primates (NHPs). NHPs (n=6) were transplanted i.p. with APIs (48,000 – 91,000 IEQ/kg) in barium-gelled 3.3% LVM alginate microcapsules and treated with CTLA4-Ig plus either LFA3-Ig and anti-LFA-1mAb (n=2), anti-CD40 mAb (n=1) or anti-CD154 mAb (n=3). In 5 NHPs, fasting blood glucose was normal on POD 1 without exogenous insulin and remained in the normal BG range for 2, 5, 8, 28, and 38 days, with lower HbA1c levels and insulin requirements 25-50% lower than pre-transplant. In 4 NHPs, porcine C-peptide values were 1.3-1.6 ng/ml on POD 3-11 but declined thereafter. All NHPs had post-prandial hyperglycemia with delayed clearance of glucose (and delayed porcine C-peptide release) compared to normal NHPs. At graft failure in 4-of-5 NHPs, we found clean free-floating capsules and relatively low levels of peritoneal cytokines and chemokines. Pre-existing anti-porcine and anti-Gal antibody levels did not rise post-transplant, but APIs in retrieved capsules stained positively for primate IgG. Explanted capsules from 2 NHPs corrected diabetes in STZ-diabetic nude mice, suggesting that some islets were still functional.

In one NHP given sub-optimal doses of CTLA4-Ig, porcine C-peptide values were 0.47 ng/ml on POD 14 and declined thereafter. At sacrifice, capsules were aggregated and surrounded by CD4⁺ and CD8⁺ T cells, CD19⁺ B cells, and CD68⁺ macrophages. Increased peritoneal cytokine and chemokine levels, plus elevated serum IgM and IgG, suggested a host cellular and humoral response. One NHP died on POD 1 with symptoms consistent with heavy metal toxicity.

We conclude that microencapsulation with adequate costimulatory blockade can inhibit host cellular responses to API xenografts in SZN-diabetic NHPs, but host humoral responses may contribute to graft failure. We predict that optimized capsules that exclude host IgG will promote longer-term graft survival.