Enhanced prediction of porcine islet yield and posttransplant outcome using a combination of quantitative histomorphometric parameters and flow cytometry

Building Biomimetic Potency Tests for Islet Transplantation

Diabetes is a disease of insulin insufficiency, requiring many to rely on exogenous insulin with constant monitoring to avoid a fatal outcome. Islet transplantation is a recent therapy that can provide insulin independence, but the procedure is still limited by both the availability of human islets and reliable tests to assess their function. While stem cell technologies are poised to fill the shortage of transplantable cells, better methods are still needed for predicting transplantation outcome. To ensure islet quality, we propose that the next generation of islet potency tests should be biomimetic systems that match glucose stimulation dynamics and cell microenvironmental preferences and rapidly assess conditional and continuous insulin secretion with minimal manual handing. Here, we review the current approaches for islet potency testing and outline technologies and methods that can be used to arrive at a more predictive potency test that tracks islet secretory capacity in a relevant context. With the development of potency tests that can report on islet secretion dynamics in a context relevant to their intended function, islet transplantation can expand into a more widely accessible and reliable treatment option for individuals with diabetes.

Vascularization of PLGA-based bio-artificial beds by hypoxia-preconditioned mesenchymal stem cells for subcutaneous xenogeneic islet transplantation

BACKGROUND

Subcutaneous tissue is an attractive extra-hepatic heterotopic site for islet transplantation; however, poor oxygen tension and blood supply during early engraftment of implanted islets have limited the use of this site in clinical applications.

METHODS

This study investigated the vascularization potential of hypoxia-preconditioned mesenchymal stem cells (3% O₂ ; hypo-MSCs) in PLGA-based bio-artificial beds for subsequent subcutaneous islet transplantation. Sheet-typed polymeric PLGA scaffolds coated with hypo-MSCs or normo-MSCs (MSCs cultured under normoxia conditions, 21% O₂ ) were implanted subcutaneously in mice.

RESULTS

Compared to normo-MSCs, hypo-MSCs significantly enhanced vasculogenesis, both on the interior and exterior surfaces of the implanted PLGA devices, which peaked 4 weeks after implantation. Further, infusion of porcine islets inside the prevascularized PLGA bed restored normal glycemic control in 6 of 6 STZ-induced diabetic mice. The mass of the marginal islet was approximately 2000 IEQs, which is comparable to that required for the renal subcapsular space, a highly vascularized site.

CONCLUSIONS

Therefore, PLGA-based bio-artificial devices prevascularized with hypo-MSCs could be a useful modality for successful subcutaneous islet transplantation, which is of high clinical relevance.

Long-term Efficacy and Biocompatibility of Encapsulated Islet Transplantation With Chitosan-Coated Alginate Capsules in Mice and Canine Models of Diabetes

BACKGROUND

Clinical application of encapsulated islet transplantation is hindered by low biocompatibility of capsules leading to pericapsular fibrosis and decreased islet viability. To improve biocompatibility, we designed a novel chitosan-coated alginate capsules and compared them to uncoated alginate capsules.

METHODS

Alginate capsules were formed by crosslinking with BaCl2, then they were suspended in chitosan solution for 10 minutes at pH 4.5. Xenogeneic islet transplantation, using encapsulated porcine islets in 1,3-galactosyltransferase knockout mice, and allogeneic islet transplantation, using encapsulated canine islets in beagles, were performed without immunosuppressants.

RESULTS

The chitosan-alginate capsules showed similar pore size, islet viability, and insulin secretory function compared to alginate capsules, in vitro. Xenogeneic transplantation of chitosan-alginate capsules demonstrated a trend toward superior graft survival (P = 0.07) with significantly less pericapsular fibrosis (cell adhesion score: 3.77 ± 0.41 vs 8.08 ± 0.05; P < 0.001) compared to that of alginate capsules up to 1 year after transplantation. Allogeneic transplantation of chitosan-alginate capsules normalized the blood glucose level up to 1 year with little evidence of pericapsular fibrotic overgrowth on graft explantation.

CONCLUSIONS

The efficacy and biocompatibility of chitosan-alginate capsules were demonstrated in xenogeneic and allogeneic islet transplantations using small and large animal models of diabetes. This capsule might be a potential candidate applicable in the treatment of type 1 diabetes mellitus patients, and further studies in nonhuman primates are required.

Impact of donor age and weaning status on pancreatic exocrine and endocrine tissue maturation in pigs

BACKGROUND

During the process of islet isolation, pancreatic enzymes are activated and released, adversely affecting islet survival and function. We hypothesize that the exocrine component of pancreases harvested from pre-weaned juvenile pigs is immature and hence pancreatic tissue from these donors is protected from injury during isolation and prolonged tissue culture.

METHODS

Biopsy specimens taken from pancreases harvested from neonatal (5-10 days), pre-weaned juvenile (18-22 days), weaned juvenile (45-60 days), and young adult pigs (>90 days) were fixed and stained with hematoxylin and eosin. Sections were examined under a fluorescent microscope to evaluate exocrine zymogen fluorescence intensity (ZFI) and under an electron microscope to evaluate exocrine zymogen granule density (ZGD).

RESULTS

Exocrine content estimation showed significantly lower ZFI and ZGD in juvenile pig pancreases (1.5 ± 0.04 U/μm(2) , ZFI; 1.03 ± 0.07 × 10(3) /100 μm(2) , ZGD) compared to young adult pigs (2.4 ± 0.05U/μm(2) , ZFI; 1.53 ± 0.08 × 10(3) /100 μm(2) ZGD). Islets in juvenile pig pancreases were on average smaller (105.2 ± 11.2 μm) than islets in young adult pigs (192 ± 7.7 μm), but their insulin content was comparable (80.9 ± 2.2% juvenile; 84.2 ± 0.3% young adult, P > 0.05). All data expressed as mean ± SEM.

CONCLUSION

Porcine islet xenotransplantation continues to make strides toward utilization in clinical trials of type 1 diabetes. Porcine donor age and weaning status influence the extent of exocrine maturation of the pancreas. Juvenile porcine pancreases may represent an alternative donor source for islet xenotransplantation as their exocrine component is relatively immature; this preserves islet viability during extended tissue culture following isolation.

Adult porcine islet isolation using a ductal preservation method and purification with a density gradient composed of histidine-tryptophan-ketoglutarate solution and iodixanol

BACKGROUND

Given the fragility of adult porcine islets, reduction of shearing stress in islet purification using histidine-tryptophan-ketoglutarate (HTK) solution and iodixanol could be an effective strategy. We examined the effect of ductal preservation with HTK solution and an islet purification protocol that utilizes HTK solution and iodixanol in adult porcine islet isolation.

METHODS

Islets were isolated with a modified Ricordi method using adult Prestige World Genetics (PWG) and Yucatan pigs. The discontinuous density gradient was composed of either HTK solution/iodixanol (n = 23, iodixanol group) or Hank's balanced salt solution (HBSS)/Ficoll (n = 17, Ficoll group). In the iodixanol group, ductal injection of HTK solution was performed before purification.

RESULTS

In PWG pigs, significantly higher islet yield after purification (3480 ± 214.2 islet equivalent [IEQ]/g, P = .003) and higher recovery rate (85.45% ± 3.49%, P = .0043) were obtained from the HTK/iodixanol group as compared to the HBSS/Ficoll group (1905 ± 323.2 IEQ/g, and 67.22% ± 4.77%, respectively). Similar results were obtained in Yucatan pigs with greater body weight.

CONCLUSION

Ductal preservation and iodixanol-based islet purification using HTK solution improved the yield of adult porcine islet isolation compared to the conventional method using HBSS and Ficoll. The results of this study support the feasibility of an adult porcine islet isolation protocol using HTK solution and iodixanol, which have the favorable physical properties.

Application of the multiplex cytokine analysis to monitor xenogeneic immune responses to the porcine islet graft in non-human primate

Non-human primate studies must be conducted prior to the clinical trial of xenotransplantation. In order to develop clinically applicable immune-modulatory regimen through non-human primate studies, close monitoring of xenogeneic immune responses is required. We adopted multiplex cytokine analysis in assessment of the immune status during the course of pig-to-non-human primate islet transplantation. This study aimed to assess the feasibility of this multiplex cytokine assay in the development of immune-modulatory regimen. Using this assay, we were able to detect different cytokines with a minimal usage of blood samples, and this allowed us to detect various immunological situations in the recipients. Detection of TNF-α surge (347.8 pg/mL) guided us to block TNF-α in the early phase of transplantation. Supportive information for in vivo efficacy of cytokine neutralizing antibody could be speculated by in vitro neutralization assay (1,250 pg/mL → 0 pg/mL). In addition, periodic monitoring of cytokines in peripheral blood allowed the detection of the infection episode prior to other routine assays. These benefits of multiplex cytokine assay may be generally applied to other pre-clinical research, which is a prerequisite for clinical trials.

In situ application of hydrogel-type fibrin-islet composite optimized for rapid glycemic control by subcutaneous xenogeneic porcine islet transplantation

Maximum engraftment of transplanted islets is essential for the clinical application of a subcutaneous site. Significant barriers to the current approaches are associated with their low effectiveness, complexity and unproven biosafety. Here, we evaluated and optimized a fibrin-islet composite for effective glycemic control in a subcutaneous site whose environment is highly hypoxic due to low vascularization potential. In the setting of xenogeneic porcine islet transplantation into the subcutaneous space of a diabetic mouse, the in vivo islet functions were greatly affected by the concentrations of fibrinogen and thrombin. The optimized hydrogel-type fibrin remarkably reduced the marginal islet mass to approximately one tenth that of islets without fibrin. This marginal islet mass was comparable to that in the setting of the subcapsular space of the kidney, which is a highly vascularized organ. Highly vascularized structures were generated inside and on the outer surface of the grafts. A hydrogel-type fibrin-islet composite established early diabetic control within an average of 3.4days after the transplantation. In the mechanistic studies, fibrin promoted local angiogenesis, enhanced islet viability and prevented fragmentation of islets into single cells. In conclusion, in situ application of hydrogel-type fibrin-islet composite may be a promising modality in the clinical success of subcutaneous islet transplantation.

The combined expression of Pdx1 and MafA with either Ngn3 or NeuroD improves the differentiation efficiency of mouse embryonic stem cells into insulin-producing cells

The use of pancreatic β-cells differentiated from embryonic stem (ES) cells or induced pluripotent stem (iPS) cells is a promising strategy in cell therapy. Pancreatic β-cell development is regulated by the sequential expression of a molecular network of transcription factors. In this experiment, we adopted a three-step differentiation protocol to differentiate mES (mouse ES) cells into insulin-secreting cells and overexpressed transcription factors by adenoviral vectors at various combinations at different time of differentiation. We found that the coexpression of Pdx1 and MafA with either Ngn3 or NeuroD, especially at the final stage of the three-step differentiation, significantly increased the differentiation efficiency. It also increased the glucose-stimulated insulin and C-peptide secretion in insulin-secreting cells derived from mES cells compared to the control green fluorescent protein (GFP) vector-transduced group. For the first time, we have demonstrated that the coexpression of Pdx1 and MafA during a specific time window of development can act synergistically with either Ngn3 or NeuroD to promote the differentiation of mES cells into insulin-secreting cells.

Islet isolation from adult designated pathogen-free pigs: use of the newer bovine nervous tissue-free enzymes and a revised donor selection strategy would improve the islet graft function

BACKGROUND

In clinical trials using adult porcine islet products, islets should be isolated from the designated pathogen-free (DPF) pigs under the current good manufacturing practice (GMP) regulations. Our previous studies suggested that male DPF pigs are better donors than retired breeder pigs and histomorphometrical parameters of donor pancreas predict the porcine islet quality. We aimed to investigate whether the use of the newer bovine nervous tissue-free enzymes and a revised donor selection strategy could improve the islet graft function in the context of islet isolation with DPF pigs.

METHODS

Using 30 DPF pigs within a closed herd, we compared the islet yield of porcine islets isolated with Liberase PI (n = 11, as a historical control group), Liberase MTF C/T, which is a GMP-grade enzyme (n = 12), and CIzyme collagenase MA/BP protease (n = 7). We analyzed the relationship between the diabetes reversal rate of recipient NOD/SCID mice (n = 75) and histomorphometric parameters of each donor pancreas as well as donor characteristics.

RESULTS

Proportion of islets larger than 200 μm from the biopsied donor pancreas (P = 0.006) better predicted islet yield than age (P = 0.760) or body weight (P = 0.371) of donor. The proportion of islets larger than 200 μm from the biopsied donor pancreas was not related to the sex of the donor miniature pig (P = 0.358). The islet yield obtained with the three enzymes did not differ, even after stratification of the donor with the histomorphometric parameters of the biopsied donor pancreas and the sex of donor. The use of the newer bovine nervous tissue-free enzymes (P < 0.001), a higher proportion of large islets in donor pancreas (P = 0.006), and a male sex of the donor (P = 0.025) were independent predictors of earlier diabetes reversal.

CONCLUSIONS

Use of the newer bovine nervous tissue-free enzymes including a GMP-grade enzyme resulted in better islet quality than that of islet isolated using Liberase PI. To obtain high-quality islet from DPF pigs, the donor should be male pig and histomorphometrical parameters from donor pancreas should be considered.

In situ induction of dendritic cell-based T cell tolerance in humanized mice and nonhuman primates

Administration of an ICAM-1–specific antibody arrests dendritic cells in a semi-immature state and facilitates antigen-specific T cell tolerance to islet allografts in humanized mice and Rhesus monkeys.

Induction of antigen-specific T cell tolerance would aid treatment of diverse immunological disorders and help prevent allograft rejection and graft versus host disease. In this study, we establish a method of inducing antigen-specific T cell tolerance in situ in diabetic humanized mice and Rhesus monkeys receiving porcine islet xenografts. Antigen-specific T cell tolerance is induced by administration of an antibody ligating a particular epitope on ICAM-1 (intercellular adhesion molecule 1). Antibody-mediated ligation of ICAM-1 on dendritic cells (DCs) led to the arrest of DCs in a semimature stage in vitro and in vivo. Ablation of DCs from mice completely abrogated anti–ICAM-1–induced antigen-specific T cell tolerance. T cell responses to unrelated antigens remained unaffected. In situ induction of DC-mediated T cell tolerance using this method may represent a potent therapeutic tool for preventing graft rejection.

Endothelial colony-forming cell coating of pig islets prevents xenogeneic instant blood-mediated inflammatory reaction

Instant blood-mediated inflammatory reaction (IBMIR) causes rapid islet loss in islet transplantation. Endothelial colony-forming cells (ECFCs) display unique abilities to promote angiogenesis and repair vascular injury compared to those of endothelial cells (ECs), which inhibits the allogeneic and xenogeneic IBMIR. We investigated the coating of pig islets with ex vivo-expanded ECFCs as a strategy to overcome xenogeneic IBMIR. Porcine islets were cocultured with human ECFCs in a specially modified culture medium for 2 days to obtain 70-90% coverage. The coating of pig islets with human ECFCs did not affect the glucose-stimulated insulin secretion capacity or diabetes reversal rate after the transplantation of a marginal islet mass under the kidney capsules of diabetic nude mice compared to that of untreated islets. Uncoated islets, PBS control without islets, and the ECFC-coated islets were examined with an in vitro tubing loop assay using human blood. After 60 min of incubation in human blood, the ECFC-coated islets showed platelet consumption inhibition and low C3a and TAT assay results compared to those of the uncoated islets. Furthermore, there was very little macroscopic or microscopic clotting in the human ECFC-coated pig islets. The protective effect was more prominent compared to that of human EC coating of pig islets in our previous study. We investigated the changes in human-specific MCP-1, IL-8, and tissue factor (TF) levels after the coating of pig islets with human ECFCs or human ECs. The IL-8 levels after coating pig islets with ECFCs were significantly lower than those after coating pig islets with ECs, but there were no significant differences in the MCP-1 or TF levels between the ECFCs and ECs. In conclusion, the coating of pig islets with ECFCs completely prevented all components of xenogeneic IBMIR. ECFCs may be a better source of protection against xenogeneic IBMIR than are mature ECs.

The sequential combination of a JNK inhibitor and simvastatin protects porcine islets from peritransplant apoptosis and inflammation

Intraductal administration of a c-Jun NH(2)-terminal kinase (JNK) inhibitor enhances islet viability. However, its role in reducing the inflammatory response in islets is unknown. It is also unknown whether a JNK inhibitor could act in synergy with statins. We examined if the sequential combination of a JNK inhibitor and simvastatin would reduce islet inflammation and improve islet viability. We performed porcine islet isolation with or without intraductal administration of SP600125, a JNK inhibitor. This was followed by culture medium supplementation with either nicotinamide alone or nicotinamide plus simvastatin. We assessed the viability of islets by flow cytometry, islet loss during overnight culture, graft function in NOD/SCID mice, and expression of inflammation-related genes in islets. The sequential combination of a JNK inhibitor and simvastatin increased the β-cell viability index of porcine islets cultured overnight (p = 0.015) as well as islet viability as assessed by a DNA binding dye staining (p = 0.011). The combination of a JNK inhibitor and simvastatin significantly increased the islet survival rate (p = 0.027) when the histomorphometry of donor pancreas indicated a large islet proportion of greater than 50.55%. When we transplanted the same islet mass per recipient for each group, there was no difference in overall islet graft function. Intraductal administration of JNK inhibitor significantly suppressed mRNA expression levels of interleukin-1β (IL-1β), interferon-γ, tumor necrosis factor-α, IL-6, IL-8, and macrophage chemoattractant protein-1. It also decreased the concentration of IL-1β (p = 0.040) and IL-8 (p = 0.023) in the culture supernatant. In conclusion, the sequential combination of a JNK inhibitor and simvastatin protected porcine islets from peritransplant apoptosis. Inhibition of JNK reduced the inflammatory response and could be considered an alternative target for suppression of porcine islet inflammation.