Neonatal islets from human PD-L1 transgenic pigs reduce immune cell activation and cellular rejection in humanized nonobese diabetic-scid IL2rγnull mice

Strong xenorejection limits the clinical application of porcine islet transplantation in type 1 diabetes. Targeting T cell-mediated rejection is one of the main approaches to improve long-term graft survival. Here we study engraftment and survival of porcine islet cells expressing human programmed cell death ligand-1 (hPD-L1) in a humanized mouse model. Neonatal islet-like clusters (NPICCs) from transgenic hPD-L1 (hPD-L1-Tg) and wild-type (Wt) pigs were transplanted into nonobese diabetic-scid IL2rγnull mice stably reconstituted with human immune cells (hPD-L1 n = 10; Wt n = 6). Primary endpoint was development of normoglycemia during a 16-week observation period after transplantation. Secondary endpoints were porcine C-peptide levels and immune cell infiltration. Animals transplanted with hPD-L1-Tg neonatal islet-like clusters achieved a superior normoglycemic rate (50% versus 0%) and significantly higher plasma C-peptide levels as compared to the Wt group, indicating long-term beta cell function. Intracytoplasmic fluorescence-activated cell sorting analysis and immunohistochemistry revealed significantly decreased frequencies of interferonγ-expressing splenic hCD8-positive T cells and reduced intragraft-infiltrating immune cells. We here demonstrate that expression of hPD-L1 provides strong islet xenograft protection without administration of immunosuppressive drugs. These findings support the hypothesis that hPD-L1 has the capacity to control cellular rejection and therefore represents a very promising transgene candidate for clinical porcine islet xenotransplantation.

Heterogenous expression of endocrine and progenitor cells within the neonatal porcine pancreatic lobes-Implications for neonatal porcine islet xenotransplantation

Neonatal porcine islets (NPIs) are a source of islets for xenotransplantation. In the pig, the pancreatic lobes remain separate, thus, when optimizing NPI isolation, the pancreatic lobes included in the pancreatic digest should be specified. These lobes are the duodenal (DL), splenic (SL) and connecting (CL) lobe that correspond to the head, body-tail, and uncinate process of the human pancreas. In this study we are the first to evaluate all three neonatal porcine pancreatic lobes and NPIs isolated from these lobes. We report, a significant difference in endocrine and progenitor cell composition between lobes, and observed pancreatic duct glands (PDG) within the mesenchyme surrounding exocrine ducts in the DL and CL. Following in vitro differentiation, NPIs isolated from each lobe differed significantly in the percent increase of endocrine cells and final cell composition. Compared to other recipients, diabetic immunodeficient mice transplanted with NPIs isolated from the SL demonstrated euglycemic control as early as 4 weeks (p < 0.05) and achieved normoglycemia by 6 weeks post-transplant (p < 0.01). For the first time we report significant differences between the neonatal porcine pancreatic lobes and demonstrate that NPIs from these lobes differ in xenograft function.

Bioabsorption of Subcutaneous Nanofibrous Scaffolds Influences the Engraftment and Function of Neonatal Porcine Islets

The subcutaneous space is currently being pursued as an alternative transplant site for ß-cell replacement therapies due to its retrievability, minimally invasive procedure and potential for graft imaging. However, implantation of ß-cells into an unmodified subcutaneous niche fails to reverse diabetes due to a lack of adequate blood supply. Herein, poly (ε-caprolactone) (PCL) and poly (lactic-co-glycolic acid) (PLGA) polymers were used to make scaffolds and were functionalized with peptides (RGD (Arginine-glycine-aspartate), VEGF (Vascular endothelial growth factor), laminin) or gelatin to augment engraftment. PCL, PCL + RGD + VEGF (PCL + R + V), PCL + RGD + Laminin (PCL + R + L), PLGA and PLGA + Gelatin (PLGA + G) scaffolds were implanted into the subcutaneous space of immunodeficient Rag mice. After four weeks, neonatal porcine islets (NPIs) were transplanted within the lumen of the scaffolds or under the kidney capsule (KC). Graft function was evaluated by blood glucose, serum porcine insulin, glucose tolerance tests, graft cellular insulin content and histologically. PLGA and PLGA + G scaffold recipients achieved significantly superior euglycemia rates (86% and 100%, respectively) compared to PCL scaffold recipients (0% euglycemic) (* p < 0.05, ** p < 0.01, respectively). PLGA scaffolds exhibited superior glucose tolerance (* p < 0.05) and serum porcine insulin secretion (* p < 0.05) compared to PCL scaffolds. Functionalized PLGA + G scaffold recipients exhibited higher total cellular insulin contents compared to PLGA-only recipients (* p < 0.05). This study demonstrates that the bioabsorption of PLGA-based fibrous scaffolds is a key factor that facilitates the function of NPIs transplanted subcutaneously in diabetic mice.

Multipotent Mesenchymal Stromal Cells Interact and Support Islet of Langerhans Viability and Function

Type 1 diabetes (T1D) is a widespread disease, affecting approximately 41.5 million people worldwide. It is generally treated with exogenous insulin, maintaining physiological blood glucose levels but also leading to long-term therapeutic complications. Pancreatic islet cell transplantation offers a potential alternative treatment to insulin injections. Shortage of human organ donors has raised the interest for porcine islet xenotransplantation. Neonatal porcine islets are highly available, can proliferate and mature in vitro as well as after transplantation in vivo. Despite promising preclinical results, delayed insulin secretion caused by immaturity and immunogenicity of the neonatal porcine islets remains a challenge for their clinical application. Multipotent mesenchymal stromal cells (MSCs) are known to have pro-angiogenic, anti-inflammatory and immunomodulatory effects. The current state of research emphasizes the great potential of co-culture and co-transplantation of islet cells with MSCs. Studies have shown enhanced islet proliferation and maturation, insulin secretion and graft survival, resulting in an improved graft outcome. This review summarizes the immunomodulatory and anti-inflammatory properties of MSC in the context of islet transplantation.

MRI monitoring of transplanted neonatal porcine islets labeled with polyvinylpyrrolidone-coated superparamagnetic iron oxide nanoparticles in a mouse model

Islet transplantation is a potential treatment option for certain patients with type 1 diabetes; however, it still faces barriers to widespread use, including the lack of tools to monitor islet grafts post-transplantation. This study investigates whether labeling neonatal porcine islets (NPI) with polyvinylpyrrolidone-coated superparamagnetic iron oxide nanoparticles (PVP-SPIO) affects their function, and whether this nanoparticle can be utilized to monitor NPI xenografts with magnetic resonance imaging (MRI) in a mouse model. In vitro, PVP-SPIO-labeled NPI in an agarose gel was visualized clearly by MRI. PVP-SPIO-labeled islets were then transplanted under the kidney capsules of immunodeficient nondiabetic and diabetic mice. All diabetic mice that received transplantation of PVP-SPIO-labeled islets reached normoglycemia. Grafts appeared as hypo-intense areas on MRI and were distinguishable from the surrounding tissues. Following injection of spleen cells from immunocompetent mice, normoglycemic recipient mice became diabetic and islet grafts showed an increase in volume, accompanied by a mixed signal on MRI. Overall, this study demonstrates that PVP-SPIO did not affect the function of NPI that PVP-SPIO-labeled islets were easily seen on MRI, and changes in MRI signals following rejection suggest a potential use of PVP-SPIO-labeled islets to monitor graft viability.

Selection of a novel AAV2/TNFAIP3 vector for local suppression of islet xenograft inflammation

BACKGROUND

Neonatal porcine islets (NPIs) can restore glucose control in mice, pigs, and non-human primates, representing a potential abundant alternative islet supply for clinical beta cell replacement therapy. However, NPIs are vulnerable to inflammatory insults that could be overcome with genetic modifications. Here, we demonstrate in a series of proof-of-concept experiments the potential of the cytoplasmic ubiquitin-editing protein A20, encoded by the TNFAIP3 gene, as an NPI cytoprotective gene.

METHODS

We forced A20 expression in NPI grafts using a recombinant adenovirus 5 (Ad5) vector and looked for impact on TNF-stimulated NF-κB activation and NPI graft function. As adeno-associated vectors (AAV) are clinically preferred vectors but exhibit poor transduction efficacy in NPIs, we next screened a series of AAV serotypes under different transduction protocols for their ability achieve high transduction efficiency and suppress NPI inflammation without impacting NPI maturation.

RESULTS

Forcing the expression of A20 in NPI with Ad5 vector blocked NF-κB activation by inhibiting IκBα phosphorylation and degradation, and reduced the induction of pro-inflammatory genes Cxcl10 and Icam1. A20-expressing NPIs also exhibited superior functional capacity when transplanted into diabetic immunodeficient recipient mice, evidenced by a more rapid return to euglycemia and improved GTT compared to unmodified NPI grafts. We found AAV2 combined with a 14-day culture period maximized NPI transduction efficiency (>70% transduction rate), and suppressed NF-κB-dependent gene expression without adverse impact upon NPI maturation.

CONCLUSION

We report a new protocol that allows for high-efficiency genetic modification of NPIs, which can be utilized to introduce candidate genes without the need for germline engineering. This approach would be suitable for preclinical and clinical testing of beneficial molecules. We also report for the first time that A20 is cytoprotective for NPI, such that A20 gene therapy could aid the clinical development of NPIs for beta cell replacement.

Cost and Scalability Analysis of Porcine Islet Isolation for Islet Transplantation: Comparison of Juvenile, Neonatal and Adult Pigs

The limited availability of human islets has led to the examination of porcine islets as a source of clinically suitable tissue for transplantation in patients with diabetes mellitus. Islets from porcine donors are commonly used in both in vitro and in vivo experiments studying diabetes mellitus. However, there are significant differences in quality and quantity of islet yield depending on donor pig age, as well as substantial differences in the costs of pancreas procurement in adult versus neonatal and juvenile pigs. In this study, we compared the total cost per islet of juvenile pig pancreata with that of neonatal and adult pigs. Although adult porcine pancreata yield, on average, more than five times the amount of islets than do juvenile and neonatal pancreata, we found that the high price of adult pigs led to the cost per islet being more than twice that of juvenile and neonatal islets (US $0.09 vs $0.04 and $0.02, respectively). In addition, neonatal and juvenile islets are advantageous in their scalability and retention of viability after culture. Our findings indicate that isolating neonatal and juvenile porcine islets is more cost-effective and scalable than isolating adult porcine islets.

Protective effect of cyanidin-3-O-glucoside on neonatal porcine islets

Oxidative stress is a major cause of islet injury and dysfunction during isolation and transplantation procedures. Cyanidin-3-O-glucoside (C3G), which is present in various fruits and vegetables especially in Chinese bayberry, shows a potent antioxidant property. In this study, we determined whether C3G could protect neonatal porcine islets (NPI) from reactive oxygen species (H₂O₂)-induced injury in vitro and promote the function of NPI in diabetic mice. We found that C3G had no deleterious effect on NPI and that C3G protected NPI from damage induced by H₂O₂ Significantly higher hemeoxygenase-1 (HO1) gene expression was detected in C3G-treated NPI compared to untreated islets before and after transplantation (P < 0.05). Western blot analysis showed a significant increase in the levels of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3K/Akt) proteins in C3G-treated NPI compared to untreated islets. C3G induced the nuclear translocation of nuclear erythroid 2-related factor 2 (NRF2) and the significant elevation of HO1 protein. Recipients of C3G-treated NPI with or without C3G-supplemented drinking water achieved normoglycemia earlier compared to recipients of untreated islets. Mice that received C3G-treated islets with or without C3G-supplemented water displayed significantly lower blood glucose levels at 5-10 weeks post-transplantation compared to mice that received untreated islets. Mice that received C3G-treated NPI and C3G-supplemented drinking water had significantly (P < 0.05) lower blood glucose levels at 7 and 8 weeks post-transplantation compared to mice that received C3G-treated islets. These findings suggest that C3G has a beneficial effect on NPI through the activation of ERK1/2- and PI3K/AKT-induced NRF2-mediated HO1 signaling pathway.

Engraftment and reversal of diabetes after intramuscular transplantation of neonatal porcine islet-like clusters

BACKGROUND

Intraportal infusion is currently the method of choice for clinical islet cell transplantation but suffers from poor efficacy. As the liver may not represent an optimal transplantation site for Langerhans islets, we examined the potential of neonatal porcine islet-like clusters (NPICCs) to engraft in skeletal muscle as an alternative transplantation site.

METHODS

Neonatal porcine islet-like clusters were isolated from 2- to 5-day-old piglets and either transplanted under the kidney capsule (s.k.) or injected into the lower hindlimb muscle (i.m.) of streptozotocin-diabetic NOD-SCID IL2rγ(-/-) (NSG) mice. Survival, vascularization, maturation, and functional activity were analyzed by intraperitoneal glucose tolerance testing and immunohistochemical analyses.

RESULTS

Intramuscular transplantation of NPICCs resulted in development of normoglycemia and restored glucose homeostasis. Time to reversal of diabetes and glucose tolerance (AUC glucose and AUC insulin) did not significantly differ as compared to s.k. transplantation. Intramuscular grafts exhibited rapid neovascularization and graft composition with cytokeratin-positive ductal cells and beta cells at post-transplant weeks 2 and 8 and after establishment of normoglycemia was comparable in both groups.

CONCLUSIONS

Intramuscular injection represents a minimally invasive but efficient alternative for transplantation of NPICCs and, thus, offers an attractive alternative site for xenotransplantation approaches. These findings may have important implications for improving the outcome and the monitoring of pig islet xenotransplantation.