Introduction: Islet transplantation (Tx) is a promising strategy to cure type 1 diabetes. However, a broad clinical application is currently limited by a shortage of islet donors. A promising alternative islet source are pig islets. Development and validation of novel beta-cell replacement therapies are mainly examined in small animal models or in non-human primates (NHP), both associated with several limitations in translating findings to human patients. Therefore, a non-NHP large animal model for islet transplantation using diabetic INS^C94Y transgenic pigs was established and used to evaluate the efficacy of intraportal neonatal porcine islet (NPI) transplantation.

Methods: Minimal invasive percutaneous intraportal islet transplantation (PIPIT) was performed to transplant wild-type NPIs (3,300 – 9,700 IEQ/kg body weight) in diabetic INS^C94Y transgenic pigs (n = 4) (1). Immunosuppressive regime was adapted from the Edmonton protocol. It consisted of tacrolimus (0.25 mg/kg BW) and mycophenolate mofetil (500 mg) every 12 hours orally, starting one day before transplantation. In addition, the pigs obtained a daily dose of acetylsalicylic acid (100 mg) as anti-platelet treatment. In the observation period, post transplantation fasting blood glucose values were examined on a regular basis. For animal welfare reasons exogenous insulin replacement therapy was performed according to the measured blood glucose values. After a post-transplantation monitoring period between 71 to 103 days, the liver was systematically processed for detailed histological analysis of graft clusters.

Results: Three of four pigs which had received NPI grafts reached normoglycemia (<130 mg/dl glucose) after 2 months, thereof two without need of exogenous insulin therapy. These animals accepted oral immunosuppressive drug intake constantly and had a continuous decrease of blood glucose concentration, paralleled with reduced need of exogenous insulin therapy (Fig. 1). The fourth animal lowered blood glucose level constantly below 200 mg/dl after NPI transplantation. Histological analysis of graft-bearing livers revealed graft clusters of heterogenous size (19 µm x 44 µm – 250 µm x 453µm) mainly consisting of beta cells (Fig. 2), with a broad distribution over the transplanted liver lobe. In total, 72 paraffin-embedded liver slices per animal were analyzed with immunohistochemistry. On average, 41% of the examined slices contained islet cell clusters, of which Ø 69% were insulin positive.

Conclusion: NPI grafts were able to restore normoglycemia in diabetic recipient pigs. Furthermore, islet Tx lowered or eliminated the need of exogenous insulin treatment. Therefore, this animal model is a novel tool in regenerative medicine to investigate islet cell transplantation settings with a high comparability to human islet cell transplantation.