Simultaneous Subtotal Pancreatectomy and Streptozotocin Injection for Diabetes Modeling in Cynomolgus Monkeys

Optimal allogeneic islet dose for transplantation in insulin-dependent diabetic Macaca fascicularis monkeys

Many groups are working to improve the results of clinical allogeneic islet transplantation in a primate model. However, few studies have focused on the optimal islet dose for achieving normal glycemia without exogenous insulin after transplantation in primate models or on the relationship between rejection and islet amyloid polypeptide (IAPP) expression. We evaluated the dose (10,000, 20,000, and > 25,000 islet equivalents (IEQ)/kg) needed to achieve normal glycemia without exogenous insulin after transplantation using eleven cynomolgus monkeys, and we analyzed the characteristics exhibited in the islets after transplantation. 10,000 IEQ/kg (N = 2) failed to control blood glucose level, despite injection with the highest dose of exogenous insulin, and 20,000 IEQ/kg group (N = 5) achieved unstable control, with a high insulin requirement. However, 25,000 IEQ/kg (N = 4) achieved normal glycemia without exogenous insulin and maintained it for more than 60 days. Immunohistochemistry results from staining islets found in liver biopsies indicated that as the number of transplanted islets decreased, the amount of IAPP accumulation within the islets increased, which accelerated CD3⁺ T cell infiltration. In conclusion, the optimal transplantation dose for achieving a normal glycemia without exogenous insulin in our cynomolgus monkey model was > 25,000 IEQ/kg, and the accumulation of IAPP early after transplantation, which depends on the transplanted islet dose, can be considered one factor in rejection.

Integrated whole liver histologic analysis of the allogeneic islet distribution and characteristics in a nonhuman primate model

The most obvious method to observe transplanted islets in the liver is direct biopsy, but the distribution and location of the best biopsy site in the recipient's liver are poorly understood. Islets transplanted into the whole liver of five diabetic cynomolgus monkeys that underwent insulin-independent survival for an extended period of time after allo-islet transplantation were analyzed for characteristics and distribution tendency. The liver was divided into segments (S1-S8), and immunohistochemistry analysis was performed to estimate the diameter, beta cell area, and islet location. Islets were more distributed in S2 depending on tissue size; however, the number of islets per tissue size was high in S1 and S8. Statistical analysis revealed that the characteristics of islets in S1 and S8 were relatively similar to other segments despite various transplanted islet dosages and survival times. In conclusion, S1, which exhibited high islet density and reflected the overall characteristics of transplanted islets, can be considered to be a reasonable candidate for a liver biopsy site in this monkey model. The findings obtained from the five monkey livers with similar anatomical features to human liver can be used as a reference for monitoring transplanted islets after clinical islet transplantation.

Multi-layer surface modification of pancreatic islets for magnetic resonance imaging using ferumoxytol

Ferumoxytol is the only clinically available ultrasmall superparamagnetic iron oxide. However, the labeling efficacy of islet magnetic resonance imaging (MRI) using ferumoxytol is not suitable for use in clinical pancreatic islet transplantation (PIT). We evaluated the feasibility of pancreatic islet MRI using ferumoxytol through multi-layer surface modification. A four-layer nanoshield with poly (ethylene) glycol (PEG, 2 layers), ferumoxytol, and heparin was formed on the pancreatic islets. We compared pancreatic islet function, viability, and labeling efficacy of control, ferumoxytol alone-labeled, heparin-PEGylated, and ferumoxytol-heparin-PEGylated islets. With optimization of the ferumoxytol concentration during the ferumoxytol-heparin-PEGylation process, the labeling contrast in ex vivo MRI of ferumoxytol-heparin-PEGylated pancreatic islets was stronger than that of pancreatic islets labeled with ferumoxytol alone, without decreasing ex vivo islet viability or function. In a syngeneic mouse renal subcapsular PIT model, heparin-PEGylation and ferumoxytol-heparin-PEGylation delayed the revascularization of pancreatic islet grafts but did not impair glucose tolerance or revascularization of pancreatic islet grafts four weeks post-transplantation. Pancreatic islet visibility after labeling was also confirmed in a syngeneic mouse intraportal PIT model and in preliminary analysis of a non-human primate intraportal PIT model. In conclusion, multi-layer islet surface modification is a promising option for pancreatic islet MRI in intraportal PIT.

Highly Angiogenic, Nonthrombogenic Bone Marrow Mononuclear Cell-Derived Spheroids in Intraportal Islet Transplantation

Highly angiogenic bone marrow mononuclear cell-derived spheroids (BM-spheroids), formed by selective proliferation of the CD31⁺CD14⁺CD34⁺ monocyte subset via three-dimensional (3D) culture, have had robust angiogenetic capacity in rodent syngeneic renal subcapsular islet transplantation. We wondered whether the efficacy of BM-spheroids could be demonstrated in clinically relevant intraportal islet transplantation models without increasing the risk of portal thrombosis. The thrombogenic potential of intraportally infused BM-spheroids was compared with that of mesenchymal stem cells (MSCs) and MSC-derived spheroids (MSC-spheroids). The angiogenic efficacy and persistence in portal sinusoids of BM-spheroids were examined in rodent syngeneic and primate allogeneic intraportal islet transplantation models. In contrast to MSCs and MSC-spheroids, intraportal infusion of BM-spheroids did not evoke portal thrombosis. BM-spheroids had robust angiogenetic capacity in both the rodent and primate intraportal islet transplantation models and improved posttransplant glycemic outcomes. MRI and intravital microscopy findings revealed the persistence of intraportally infused BM-spheroids in portal sinusoids. Intraportal cotransplantation of allogeneic islets with autologous BM-spheroids in nonhuman primates further confirmed the clinical feasibility of this approach. In conclusion, cotransplantation of BM-spheroids enhances intraportal islet transplantation outcome without portal thrombosis in mice and nonhuman primates. Generating BM-spheroids by 3D culture prevented the rapid migration and disappearance of intraportally infused therapeutic cells.