A significant proportion of intraportally infused islets are destroyed by an instant blood mediated inflammatory reaction (IBMIR) that includes preformed antibody, complement, platelets, neutrophils, and macrophages. Genetic modifications are being designed to attenuate IBMIR-mediated destruction and enhance islet survival. We have developed a dual transplant model that rigorously compares two genetically modified islet preparations transplanted into isolated hemi-livers of a single non-human primate recipient. We first compared wild-type and galactose-Α1,3-galactose (gal) deficient xenoislets.

Anesthetized Rhesus macaques underwent liver hilum dissection, including right and left portal venous branch isolation. Approximately 25,000 IEQ/kg of wild-type or gal-deficient neonatal porcine islets were infused into each hemiliver through the corresponding portal venous inflow branch. Animals were sacrificed at 1 (n=5) or 24 hour (n=5) time points for detailed immunohistochemical analysis. An additional two animals were transplanted with inert polyethylene microspheres and served as embolic controls. Slides derived from predetermined anatomical locations within each hemi-liver were quantitatively analyzed with Aperio Imagescope software.

Wild-type and gal-deficient islet preparations were confined within their respective hemiliver based upon gal expression analysis (p=0.02). At 1 hour, gal-deficient islets exhibited less macrophage infiltration (p=0.02) and a trend towards decreased C4d deposition (p=0.15). Temporal evaluation of both islet preparations considered together demonstrated a decrease in IgM/IgG binding (p=0.01, p=0.02) and increased macrophage infiltration (p=0.01) between 1 and 24 hours. This was accompanied by a trend towards decreased insulin expression (p=0.08) and reduced neutrophil infiltration (p=0.18). The magnitude of platelet aggregation was statistically equivalent to that seen in microsphere embolic controls.

Gal-deficient islets attract fewer macrophages and less complement deposition 1 hour post-intraportal infusion. As the inflammatory response evolves over the next 24 hours macrophage infiltration increases and antibody binding, neutrophil infiltration, and insulin expression decrease within islet clusters. We are currently extending this model to the evaluation of multi-transgene islets expressing CD55/CD59/CD39/Thrombomodulin on a gal-deficient background.

« Back to 2013 American Transplant Congress