Early barriers to neonatal porcine islet engraftment in a dual transplant model

Abstract

Porcine islet xenografts have the potential to provide an inexhaustible source of islets for β cell replacement. Proof-of-concept has been established in nonhuman primates. However, significant barriers to xenoislet transplantation remain, including the poorly understood instant blood-mediated inflammatory reaction and a thorough understanding of early xeno-specific immune responses. A paucity of data exist comparing xeno-specific immune responses with alloislet (AI) responses in primates. We recently developed a dual islet transplant model, which enables direct histologic comparison of early engraftment immunobiology. In this study, we investigate early immune responses to neonatal porcine islet (NPI) xenografts compared with rhesus islet allografts at 1 hour, 24 hours, and 7 days. Within the first 24 hours after intraportal infusion, we identified greater apoptosis (caspase 3 activity and TUNEL [terminal deoxynucleotidyl transferase dUTP nick end labeling])-positive cells) of NPIs compared with AIs. Macrophage infiltration was significantly greater at 24 hours compared with 1 hour in both NPI (wild-type) and AIs. At 7 days, IgM and macrophages were highly specific for NPIs (α1,3-galactosyltransferase knockout) compared with AIs. These findings demonstrate an augmented macrophage and antibody response toward xenografts compared with allografts. These data may inform future immune or genetic manipulations required to improve xenoislet engraftment.

The role of human CD46 in early xenoislet engraftment in a dual transplant model

“…Like the two early studies in this dual transplant series, we observed a nonspecific milieu of antibody, complement, and coagulation immediately following intraportal infusion of NPIs . At 1‐hour, human CD46 expression on NPIs did not provide any perceived advantage at this stage.…”

“…That the effects seen in this series of experiments relate more to cellular accumulation, it suggests that a reduction in the chemotactic effects of non‐bound complement breakdown products may be the most relevant in this setting. Interestingly, we have previously reported on increased staining of C4d in allogeneic islets compared to NPIs 7 days post‐infusion . Although C3d and C4d are widely used as marker for complement activation, they have not been verified in the setting of IBMIR .…”

“…We had difficulty in achieving sufficient technical successes in the extended dual islet transplant group. Unlike our last report in this series, where we used an experimental drug regimen including anti‐CD154 and anti‐LFA1 in the extended dual transplant arm, only clinically available immunosuppressive drugs were used in these studies. To date, there is no regimen that is limited to clinically available agents that consistently achieves xenoislet engraftment.…”

“…Individual islet infusions were prepared using 20 mL CMRL 1066 without phenol red (Corning), 100 units of heparin sodium, and 1.5 mg/kg of etanercept (Enbrel Immunex Corp). Islet transplantation was performed as previously described . In brief, two islet preparations were made for each transplant recipient, one for each islet phenotype, and delivered to hemilivers via left or right portal vein.…”

“…26 All procedures were performed in accordance with the "Guide for transplantation was performed as previously described. 24,25 In brief, two islet preparations were made for each transplant recipient, one for each islet phenotype, and delivered to hemilivers via left or right portal vein. The side of the infusion was randomized to control for any potential differences segregating with lateralization.…”