Intrahepatic Islet Research Articles

Recreating the Endocrine Niche: Advances in Bioengineering the Pancreas.

Intrahepatic islet transplantation is a promising strategy for β-cell replacement therapy in the treatment of Type 1 Diabetes. However, several obstacles hinder the long-term efficacy of this therapy. A major challenge is the scarcity of donor organs. During the isolation process, islets are disconnected from their extracellular matrix (ECM) and vasculature, leading to significant loss due to anoikis and hypoxia. Additionally, inflammatory and rejection reactions further compromise islet survival and engraftment success. Extensive efforts are being made to improve the efficacy of islet transplantation. These strategies include promoting revascularization and ECM support through bioengineering techniques, exploring alternative sources of insulin-secreting cells, and providing immunomodulation for the graft. Despite these advancements, a significant gap remains in integrating these strategies into a cohesive approach that effectively replicates the native endocrine environment. Specifically, the lack of comprehensive methods to address both the structural and functional aspects of the endocrine niche limits reproducibility and clinical translation. Therefore, bioengineering an endocrine pancreas must aim to recreate the endocrine niche to achieve lifelong efficacy and insulin independence. This review discusses various strategies developed to produce the building blocks for generating a vascularized, immune-protected insulin-secreting construct, emphasizing the importance of the endocrine niche's composition and function.

Liraglutide for the Treatment of Severe Hypoglycemia Following Total Pancreatectomy and Islet Autotransplantation

Abstract Total pancreatectomy and islet autotransplantation (TPIAT) is an effective treatment for chronic and recurrent acute pancreatitis, and it provides a significant potential additional benefit of insulin independence. Spontaneous hypoglycemia in the absence of insulin therapy following TPIAT is a recognized complication, which has been attributed to lack of protective glucagon responses to hypoglycemia, following intrahepatic islet autotransplantation. We describe the use of liraglutide to treat spontaneous hypoglycemia following TPIAT. Continuous glucose monitoring was used to identify timing of hypoglycemia in relation to meals and monitor treatment effect. Liraglutide has been used for management of hypoglycemia following bariatric surgery, but, to our knowledge, this is the first application of its effective use to treat spontaneous severe hypoglycemia following TPIAT.

α- or β-Adrenergic blockade does not affect transplanted islet cell responses to hypoglycemia in type 1 diabetes.

Type 1 diabetes recipients of intrahepatic islet transplantation exhibit glucose-dependent suppression of insulin and activation of glucagon secretion in response to insulin-induced hypoglycemia associated with clinical protection from hypoglycemia. Whether sympathetic activation of adrenergic receptors on transplanted islets is required for these responses in defense against hypoglycemia is not known. To evaluate the adrenergic contribution to posttransplant glucose counterregulation, we performed a randomized, double-blind crossover study of responses during a hyperinsulinemic euglycemic-hypoglycemic clamp under phentolamine (α-adrenergic blockage), propranolol (β-adrenergic blockage), or placebo infusion. Characteristics of participants (5 females/4 males) were as follows: median (range) age 53 (34-63) yr, diabetes duration 29 (18-56) yr, posttransplant 7.0 (1.9-8.4) yr, HbA1c 5.8 (4.5-6.8)%, insulin in-/dependent 5/4, all on tacrolimus-based immunosuppression. During the clamp, blood pressure was lower with phentolamine and heart rate was lower with propranolol versus placebo (P < 0.05). There was no difference in the suppression of endogenous insulin secretion (derived from C-peptide measurements) during the euglycemic or hypoglycemic phases, and although levels of glucagon were similar with phentolamine or propranolol vs. placebo, the increase in glucagon from eu- to hypoglycemia was greater with propranolol vs. placebo (P < 0.05). Pancreatic polypeptide was greater with phentolamine versus placebo during the euglycemic phase (P < 0.05), and free fatty acids were lower and the glucose infusion rate was higher with propranolol versus placebo during the hypoglycemic phase (P < 0.05 for both). These results indicate that neither physiological α- nor β-adrenergic blockade attenuates transplanted islet responses to hypoglycemia, suggesting sympathetic reinnervation of the islet graft is not necessary for posttransplant glucose counterregulation.NEW & NOTEWORTHY Whether adrenergic input to islets is necessary for glucose homeostasis in humans is debated. Here, the adrenergic contribution to intrahepatically transplanted islet cell responses to hypoglycemia in individuals with type 1 diabetes was investigated through α- or β-adrenergic receptor blockade during hyperinsulinemic euglycemic-hypoglycemic clamps. Neither α- nor β-adrenergic blockage affected the suppression of endogenous insulin or activation of glucagon secretion, suggesting that sympathetic reinnervation of islet grafts is not required for posttransplant defense against hypoglycemia.

Monitoring β-Cell Survival After Intrahepatic Islet Transplantation Using Dynamic Exendin PET Imaging: A Proof-of-Concept Study in Individuals With Type 1 Diabetes.

This clinical study researched the potential of radiolabeled exendin to follow the fate and survival of intrahepatic islet grafts. Is it feasible to quantitatively detect intrahepatic islet transplants with [68Ga]Ga-NODAGA-exendin-4 (68Ga-exendin) positron emission tomography (PET) imaging? Our study findings indicate that the imaging technique 68Ga-exendin PET can be used to monitor viable islet mass after intrahepatic islet transplantation in humans. Alongside functional measures, 68Ga-exendin PET imaging could significantly aid in the evaluation of strategies designed to improve islet engraftment, survival, and function.

Directed self-assembly of a xenogeneic vascularized endocrine pancreas for type 1 diabetes

Intrahepatic islet transplantation is the standard cell therapy for β cell replacement. However, the shortage of organ donors and an unsatisfactory engraftment limit its application to a selected patients with type 1 diabetes. There is an urgent need to identify alternative strategies based on an unlimited source of insulin producing cells and innovative scaffolds to foster cell interaction and integration to orchestrate physiological endocrine function. We previously proposed the use of decellularized lung as a scaffold for β cell replacement with the final goal of engineering a vascularized endocrine organ. Here, we prototyped this technology with the integration of neonatal porcine islet and healthy subject-derived blood outgrowth endothelial cells to engineer a xenogeneic vascularized endocrine pancreas. We validated ex vivo cell integration and function, its engraftment and performance in a preclinical model of diabetes. Results showed that this technology not only is able to foster neonatal pig islet maturation in vitro, but also to perform in vivo immediately upon transplantation and for over 18 weeks, compared to normal performance within 8 weeks in various state of the art preclinical models. Given the recent progress in donor pig genetic engineering, this technology may enable the assembly of immune-protected functional endocrine organs.

Bioengineering the Vascularized Endocrine Pancreas: A Fine-Tuned Interplay Between Vascularization, Extracellular-Matrix-Based Scaffold Architecture, and Insulin-Producing Cells.

Intrahepatic islet transplantation is a promising β-cell replacement strategy for the treatment of type 1 diabetes. Instant blood-mediated inflammatory reactions, acute inflammatory storm, and graft revascularization delay limit islet engraftment in the peri-transplant phase, hampering the success rate of the procedure. Growing evidence has demonstrated that islet engraftment efficiency may take advantage of several bioengineering approaches aimed to recreate both vascular and endocrine compartments either ex vivo or in vivo. To this end, endocrine pancreas bioengineering is an emerging field in β-cell replacement, which might provide endocrine cells with all the building blocks (vascularization, ECM composition, or micro/macro-architecture) useful for their successful engraftment and function in vivo. Studies on reshaping either the endocrine cellular composition or the islet microenvironment have been largely performed, focusing on a single building block element, without, however, grasping that their synergistic effect is indispensable for correct endocrine function. Herein, the review focuses on the minimum building blocks that an ideal vascularized endocrine scaffold should have to resemble the endocrine niche architecture, composition, and function to foster functional connections between the vascular and endocrine compartments. Additionally, this review highlights the possibility of designing bioengineered scaffolds integrating alternative endocrine sources to overcome donor organ shortages and the possibility of combining novel immune-preserving strategies for long-term graft function.

307.3: Bioengineering of an iPSC Derived Vascularized Endocrine Pancreas (iVEP) for T1D

Introduction: Intrahepatic islet transplantation in patients with type 1 diabetes is limited by donor availability and lack of engraftment. To overcome these limitations, new sources of β cells and alternative sites are needed. Organ decellularization is an emerging strategy in organ regeneration. Based on our experience with decellularized rat lung as scaffold for the generation of Vascularized Islet Organ (lung scaffold repopulated by murine islets and HUVEC cells), we used the same platform to engineer an iPSC-based version named iVEP (iPSC-derived Vascularized Endocrine Pancreas). Methods: iPSC-derived β (iβ) and endothelial (iEC) cells were characterized in flow cytometry. Rat lung was decellularized by vascular perfusion with 1% SDS and 0.1% Triton and seeded with commercially available iβ and iEC. The recellularized scaffold matured in vitro for 7 days in a customized perfusion bioreactor specifically designed to allow cell/compartment integration. The iβ death was estimated during ex vivo organ maturation compared to 7 days of iβ in vitro culture evaluating miR-375 expression by droplet digital PCR. At day 7, fluorangiography assay was performed to evaluate the vascular compartment structure and function while for the endocrine compartment, insulin production was measured by dynamic glucose perifusion and insulin quantification (ELISA/IF). Matured iVEPs were then transplanted subcutaneously into NSG diabetic mice followed for 30 days, compared to the deviceless (DL) implantation site and explanted iVEPs were assessed for IF evaluation. Results: iEC/iβ maintained for 7 days in vitro their phenotype expressing endothelial (>95% CD31+/CD105+/CD73+/CD90- cells) and β-cell (>60% PDX1+/insulin+ cells) markers respectively. Matured iVEPs showed a regenerated vascular network (CD31+) able to sustain the direct distribution of a perfusate with iβ cells (insulin+) integrated. In mature iVEP, iβ preserved insulin expression. miR-375, a marker of β cell death, was expressed in iβ but not in iECs. iVEP was able to significantly reduce β cell death: the amount of lost iβ was ≤18% during organ maturation, while >70% during in vitro culture (p<0.05). In iVEPs, lung ECM was able to sustain iβ engraftment and insulin secretion during the maturation process (AUC first phase iVEPs: 3.9465±1.23 Vs 1.44±0.83 p<0.05). Preliminary preclinical results demonstrated the ability of iVEP to engraft and restore normoglycemia in diabetic recipient mice compared to the iβ implanted in the DL site. Conclusion: To our knowledge, we assembled the first human entirely iPSC-derived Vascularized Endocrine Organ able to provide both in vitro and in vivo insulin production and regenerated vascular network.

P.168: Biofabrication of a Functional Vascularized Endocrine Pancreas (VEP) for Type 1 Diabetes

Background: Intrahepatic islet transplantation in patients with type 1 diabetes is limited by donor availability and lack of engraftment. To overcome these limitations, based on our experience with decellularized rat lung as scaffold for the generation of Vascularized Islet Organ (VIO, lung scaffold repopulated by murine islets and HUVEC cells), we prototyped our platform to engineer an upgrade based on human blood-derived endothelial cells (BOECs - Blood Outgrowing Endothelial Cells) and immature neonatal porcine islet clusters (NPIs). Material and Methods: NPIs and BOECs phenotype profile was assessed by flow cytometry, insulin secretion test and tubule formation assay. Rat lung was decellularized by vascular perfusion with 1% SDS and 0.1% Triton and seeded with NPIs and BOECs, generating a Vascularized Endocrine Pancreas (VEP). For ex vivo maturation VEP was cultured for 7 days in a customized bioreactor specifically designed to allow cell integration. The NPIs β cell death in mature VEPs was estimated during ex vivo organ maturation evaluating miR-375 expression by droplet digital PCR compared to batch matched NPIs in standard condition. Matured VEPs and control NPIs function were measured by dynamic glucose perifusion and insulin quantification (by ELISA/IF). Once validated in vitro, VEPs were subcutaneously transplanted in diabetic immunodeficient NSG recipients and compared for in vivo function with matched NPIs transplanted in different implantation sites: kidney capsule (KC-NPIs), deviceless (DL-NPIs) and liver (LV-NPIs). Results: Matured VEPs showed regenerated vascular network (CD31+) with NPIs (insulin+) integrated. miR-375, a marker of β cell death, was expressed in NPIs but not in BOECs, as expected. VEP was able to significantly reduce β cell death: the amount of lost NPIs were ≤ 5% during VEPs maturation, while >71% during in vitro culture (p<0.05). Matured VEPs were able to sustain NPIs engraftment, survival and significantly improve insulin secretion during the maturation process compared to batch matched NPIs cultured in standard conditions (AUC VEPs first phase: 3.765±0.90; NPIs 1.60±0.25 p<0.01). In long-term transplants in diabetic mice, VEPs demonstrated a significant NPIs engraftment with a prompt VEPs function after implantation and the reversal of the glycemia within 2 days until 60 days after implantation. Additionally, VEPs showed a significant superior function compared to all the internal controls (KC-NPIs, DL-and LV-NPIs). Conclusion: We conclude that ex vivo bio-fabrication of VEPs enables NPIs engraftment, maturation and vascularization before transplantation. VEP is the first organ to our knowledge assembled with relevant source of endocrine and endothelial cells suitable for future clinical translation. Given recent progress in gene editing, this technology may enable assembly of functional personalized endocrine organs to escape immunoreaction against the graft. This study was supported by a grant from Juvenile Diabetes Research Foundation (JDRF 1-SRA-2019-771-S-B).

Intraperitoneal administration of human "Neo-Islets", 3-D organoids of mesenchymal stromal and pancreatic islet cells, normalizes blood glucose levels in streptozotocin-diabetic NOD/SCID mice: Significance for clinical trials.

Globally, individuals with autoimmune Type 1 diabetes mellitus (T1DM) continue to depend for survival on insulin injections. While pancreas and intrahepatic pancreatic islet transplants can produce insulin-independence and ameliorate serious complications, both therapies depend on potentially toxic anti-rejection drugs. Furthermore, the scarcity of pancreas donors and islet transplant failures limit the general availability of such interventions. Recently, fetal and induced Pluripotent Stem Cells have been successfully differentiated to generate insulin producing β-like cells that generate euglycemia in diabetic mice. However, their clinical use still depends on anti-rejection drugs or immune-isolating encapsulation systems. We reported recently that allogeneic “Neo-Islets” (NI), 3-D organoids of Mesenchymal Stromal and Islet Cells are immune protected and permanently correct autoimmune diabetes in NOD mice by omental engraftment and endocrine cell redifferentiation. This new “endocrine pancreas” delivers islet hormones physiologically into the hepatic portal vein. Furthermore, treatment of insulin-dependent dogs with allogeneic canine NIs (ongoing FDA-approved Pilot Study) consistently improved glycemic control without the need for antirejection drugs. As there remains a critical need for curative therapies of T1DM, we engineered human NIs and tested their ability, after i.p. administration, to reestablish euglycemia in streptozotocin (STZ)-diabetic NOD/SCID mice. This diabetes model reproduces, in part, the clinical situation in which recipients of allogeneic biotherapies must take potent anti-rejection drugs that similarly create a life-long immune-compromised status. The present study demonstrates that human NI therapy (2x10e5/kg bw NIs/mouse) of STZ-diabetic NOD/SCID mice (n = 6), compared to controls (n = 6) significantly improved glycemic control, and most importantly, that a second dose given to the initial group normalized blood glucose levels long-term. Conclusion: Despite the limitations of the utilized diabetic NOD/SCID mouse model, the obtained data show that human NIs are curative, an observation that has high translational relevance and significantly supports the planned conduct of clinical trials with human NIs.

Minimizing Post-Infusion Portal Vein Bleeding during Intrahepatic Islet Transplantation in Mice.

Although the liver is currently accepted as the primary transplantation site for human islets in clinical settings, islets are transplanted under the kidney capsule in most rodent preclinical islet transplantation studies. This model is commonly used because murine intrahepatic islet transplantation is technically challenging, and a high percentage of mice could die from surgical complications, especially bleeding from the injection site post-transplantation. In this study, two procedures that can minimize the incidence of post-infusion portal vein bleeding are demonstrated. The first method applies an absorbable hemostatic gelatin sponge to the injection site, and the second method involves penetrating the islet injection needle through the fat tissue first and then into the portal vein by using the fat tissue as a physical barrier to stop bleeding. Both methods could effectively prevent bleeding-induced mouse death. The whole liver section showing islet distribution and evidence of islet thrombosis post-transplantation, a typical feature for intrahepatic islet transplantation, were presented. These improved protocols refine the intrahepatic islet transplantation procedures and may help laboratories set up the procedure to study islet survival and function in pre-clinical settings.

Minimizing Post-Infusion Portal Vein Bleeding during Intrahepatic Islet Transplantation in Mice

Minimizing Post-Infusion Portal Vein Bleeding during Intrahepatic Islet Transplantation in Mice

Alpha-1 antitrypsin suppresses macrophage activation and promotes islet graft survival after intrahepatic islet transplantation.

Alpha-1 antitrypsin (AAT) has protective functions in animal islet transplantation models. While the therapeutic effect of AAT therapy is currently being tested in clinical trials, we investigated the mechanism of AAT protection in a clinically relevant marginal intrahepatic human islet transplantation model. In recipients receiving islets and AAT, 68.9% (20/29) reached normoglycemia, compared to 35.7% (10/28) in those receiving islets only, at 60days posttransplant (PT). AAT-treated mice had lower serum levels of inflammatory cytokines immediately PT. Reduced M1 macrophages were observed in livers of AAT-treated recipients compared to controls as evidenced by flow cytometry and RNA-seq transcriptional profiling analysis. In vitro AAT suppressed IFN-γ-induced M1 macrophage activation/polarization via suppression of STAT1 phosphorylation and iNOS production. AAT inhibits macrophage activation induced by cytokines or dying islets, and consequently leads to islet cell survival. In a macrophage depletion mouse model, the presence of M1 macrophages in the liver contributed to graft death. AAT, through suppressing macrophage activation, protected transplanted islets from death and dysfunction in the human islet and NOD-SCID mouse model. The protective effect of AAT was confirmed in a major mismatch allogeneic islet transplantation model. Taken together, AAT suppresses liver macrophage activation that contributes to graft survival after transplantation.

Early-Phase Luciferase Signals of Islet Grafts Predicts Successful Subcutaneous Site Transplantation in Rats.

The transplantation of pancreatic islets is a promising cell replacement therapy for type 1 diabetes. Subcutaneous islet transplantation is currently under investigation as a means to circumvent problems associated with standard intra-hepatic islet transplantation. As modifications are being developed to improve the efficacy of subcutaneous islet transplantation, it is important to have robust methods to assess engraftment. Experimentally, ATP-dependent bioluminescence imaging using luciferase reporter genes has been effective for non-invasively tracking engraftment. However, it was heretofore unknown if the bioluminescence of subcutaneously transplanted luciferase-expressing islet grafts correlates with diabetes reversal, a primary outcome of transplantation. A retrospective analysis was conducted using data obtained from subcutaneous islet transplantations in Lewis rats. The analysis included transplantations from our laboratory in which islet donors were transgenic rats ubiquitously expressing luciferase and recipients were wild type, streptozotocin-induced diabetic rats. Data from 79 bioluminescence scans were obtained from 27 islet transplantations during the post-transplant observation period (up to 6 weeks). The bioluminescence intensity of the subcutaneously transplanted grafts, captured after the intravenous administration of luciferin, was correlated with diabetes reversal. After subcutaneous transplantation, islet bioluminescence decreased over time, dropping > 50 % from 1 to 3 weeks post-transplant. Bioluminescence intensity in the early post-transplant phase (1-2 weeks) correlated with the subsequent reversal of diabetes; based on optimized bioluminescence cutoff values, the bioluminescence intensity of islets at 1 and 2 weeks predicted successful transplantations. However, intensity in the late post-transplant phase (≥ 4 weeks) did not reflect transplantation outcomes. Early-phase bioluminescence imaging of luciferase-expressing islets could serve as a useful tool to predict the success of subcutaneous islet transplantations by preceding changes in glucose homeostasis.

359-OR: a- or ß-Adrenergic Blockade Does Not Affect Transplanted Islet Responses to Hypoglycemia in Type 1 Diabetes (T1D)

Recipients of intrahepatic islet transplantation for T1D exhibit appropriate suppression of endogenous insulin and activation of glucagon secretion in response to insulin-induced hypoglycemia with restored glucose counterregulation and protection against clinically significant hypoglycemia. Whether sympathetic activation of adrenergic receptors on transplanted islets is required for these responses is not known. To evaluate the adrenergic contribution to post-transplant glucose counterregulation, we performed a randomized, double-blind crossover study of responses during a hyperinsulinemic (1 mU·kg-1·min-1) euglycemic (EU, ∼90 mg/dL)-hypoglycemic (HYPO, ∼50 mg/dL) clamp conducted under phentolamine (0.95 µg·kg-1·min-1; α-adrenergic blockage), propranolol (0.48 µg·kg-1·min-1; β-adrenergic blockage), or placebo infusion. Subjects were 5F/4M with median (range) age 53 (34 - 63) years, T1D duration 29 (18 - 56) years, post-transplant 7 (2 - 8) years, HbA1c 5.8 (4.5 - 6.8) %, insulin in-/dependent 5/4, on tacrolimus-based immunosuppression, and spent 97 (76 - 99) % time in range 70 - 180 mg/dL and 1 (0 - 3) % time with hypoglycemia &amp;lt; 70 mg/dL by CGM. During the EU-HYPO clamp, blood pressure was lower with phentolamine and heart rate lower with propranolol vs. placebo (P &amp;lt; 0.05). There was no difference in suppression of C-peptide or activation of glucagon with phentolamine or propranolol vs. placebo. Pancreatic polypeptide was greater with phentolamine vs. placebo during EU (P &amp;lt; 0.05), and free fatty acids were lower and the glucose infusion rate higher with propranolol vs. placebo during HYPO (P &amp;lt; 0.05) with no differences seen for endogenous glucose production. These results indicate physiologic α- and β-adrenergic blockage had no effect on transplanted islet responses to hypoglycemia. Sympathetic re-innervation, as occurs with re-vascularization of intrahepatic islets, may not be necessary for post-transplant recovery of glucose counterregulation in T1D. Disclosure M.R. Rickels: Consultant; Self; Semma Therapeutics, Inc. Research Support; Self; Xeris Pharmaceuticals, Inc. M. Bellin: Research Support; Self; Dexcom, Inc., Viacyte, Inc. Other Relationship; Self; Insulet Corporation. D. Stefanovski: None. A.J. Peleckis: None. C.V. Dalton-Bakes: None. E. Markmann: None. H.T. Nguyen: None. A. Naji: None. Funding National Institutes of Health (R01DK091331, UL1TR001878, P30DK19525)

Donor-Specific Regulatory T Cell-Mediated Immune Tolerance in an Intrahepatic Murine Allogeneic Islet Transplantation Model with Short-Term Anti-CD154 mAb Single Treatment

Anti-CD154 blockade-based regimens remain unequaled in prolonging graft survival in various organ transplantation models. Several studies have focused on transplantation tolerance with the anti-CD154 blockade, but none of these studies has investigated the mechanisms associated with its use as the sole treatment in animal models, delaying our understanding of anti-CD154 blockade-mediated immune tolerance. The purpose of this study was to investigate the mechanism underlying the anti-CD154 monoclonal antibody (mAb) blockade in inducing immune tolerance using an intrahepatic murine allogeneic islet transplantation model. Allogeneic BALB/c AnHsd (BALB/c) islets were infused into the liver of diabetic C57BL/6 (B6) mice via the cecal vein. Anti-CD154 mAb (MR1) was administered on −1, 0, 1, 3, 5, and 7 d posttransplantation at 0.5 mg per mouse. We showed that short-term MR1 monotherapy could prolong the allogeneic islet grafts to more than 250 d in the murine intrahepatic islet transplantation model. The second islet grafts transplanted under the kidney capsule of the recipients were protected from rejection. We also found that rejection of same-donor skin grafts transplanted to the tolerant mice was modestly delayed. Using a DEREG mouse model, FoxP3+ regulatory T (Treg) cells were shown to play important roles in transplantation tolerance. In mixed lymphocyte reactions, Treg cells from the tolerant mice showed more potency in suppressing BALB/c splenocyte-stimulated Teff cell proliferation than those from naïve mice. In this study, we demonstrated for the first time that a short-term anti-CD154 mAb single treatment could induce FoxP3+ Treg cell-mediated immune tolerance in the intrahepatic murine allogeneic islet transplantation model.

The Role of Vitamin D and Omega-3 PUFAs in Islet Transplantation.

Recurrence of autoimmunity and allograft rejection represent major challenges that impact the success of islet transplantation. Despite the remarkable improvements achieved in immunosuppression strategies after the publication of the Edmonton protocol, long-term data of intra-hepatic islet transplantation show a gradual decline in beta-cell function. Therefore, there is a growing interest in the investigation of novel, safe and effective anti-inflammatory and immunomodulatory strategies able to promote long-term islet graft survival and notable improvements in clinical outcomes of islet transplant recipients. Vitamin D has been shown to exert anti-inflammatory and immunomodulatory effects. Pre-clinical studies investigating the use of vitamin D and its analogs (alone or in combination with immunosuppressive agents and/or other anti-inflammatory agents, such as omega-3 polyunsaturated fatty acids) showed beneficial results in terms of islet graft survival and prevention of recurrence of autoimmunity/allograft rejection in animal models of syngeneic and allogeneic islet transplantation. Moreover, epidemiologic studies demonstrated that vitamin D deficiency is highly prevalent after solid organ transplantation (e.g., heart, liver or kidney transplantation). However, studies that critically assess the prevalence of vitamin D deficiency among islet transplant recipients have yet to be conducted. In addition, prospective studies aimed to address the safety and efficacy of vitamin D supplementation as an adjuvant immunomodulatory strategy in islet transplant recipients are lacking and are therefore awaited in the future.

CCL2/MCP-1 and CXCL12/SDF-1 blockade by L-aptamers improve pancreatic islet engraftment and survival in mouse.

The blockade of pro-inflammatory mediators is a successful approach to improve the engraftment after islet transplantation. L-aptamers are chemically synthesized, nonimmunogenic bio-stable oligonucleotides that bind and inhibit target molecules conceptually similar to antibodies. We aimed to evaluate if blockade-aptamer-based inhibitors of C-C Motif Chemokine Ligand 2/monocyte chemoattractant protein-1 (CCL2/MCP-1) and C-X-C Motif Chemokine Ligand 12/stromal cell-derived factor-1 (CXCL12/SDF-1) are able to favor islet survival in mouse models for islet transplantation and for type 1 diabetes. We evaluated the efficacy of the CCL2-specific mNOX-E36 and the CXCL12-specific NOX-A12 on islet survival in a syngeneic mouse model of intraportal islet transplantation and in a multiple low doses of streptozotocin (MLD-STZ) diabetes induction model. Moreover, we characterized intrahepatic infiltrated leukocytes by flow cytometry before and 3 days after islet infusion in presence or absence of these inhibitors. The administration for 14days of mNOX-E36 and NOX-A12 significantly improved islet engraftment, either compound alone or in combination. Intrahepatic islet transplantation recruited CD45+ leucocytes and more specifically CD45+/CD11b+ mono/macrophages; mNOX-E36 and NOX-A12 treatments significantly decreased the recruitment of inflammatory monocytes, CD11b+ /Ly6Chigh /CCR2+ and CD11b+ /Ly6Chigh /CXCR4+ cells, respectively. Additionally, both L-aptamers significantly attenuated diabetes progression in the MLD-STZ model. In conclusion, CCL2/MCP-1 and CXCL12/SDF-1 blockade by L-aptamers is an efficient strategy to improve islet engraftment and survival.

Operational immune tolerance towards transplanted allogeneic pancreatic islets in mice and a non-human primate.

Patients with autoimmune type 1 diabetes transplanted with pancreatic islets to their liver experience significant improvement in quality of life through better control of blood sugar and enhanced awareness of hypoglycaemia. However, long-term survival and efficacy of the intrahepatic islet transplant are limited owing to liver-specific complications, such as immediate blood-mediated immune reaction, hypoxia, a highly enzymatic and inflammatory environment and locally elevated levels of drugs including immunosuppressive agents, all of which are injurious to islets. This has spurred a search for new islet transplant sites and for innovative ways to achieve long-term graft survival and efficacy without life-long systemic immunosuppression and its complications. We used our previously established approach of islet transplant in the anterior chamber of the eye in allogeneic recipient mouse models and a baboon model of diabetes, which were treated transiently with anti-CD154/CD40L blocking antibody in the peri-transplant period. Survival of the intraocular islet allografts was assessed by direct visualisation in the eye and metabolic variables (blood glucose and C-peptide measurements). We evaluated longitudinally the cytokine profile in the local microenvironment of the intraocular islet allografts, represented in aqueous humour, under conditions of immune rejection vs tolerance. We also evaluated the recall response in the periphery of the baboon recipient using delayed-type hypersensitivity (DTH) assay, and in mice after repeat transplant in the kidney following initial transplant with allogeneic islets in the eye or kidney. Results in mice showed >300days immunosuppression-free survival of allogeneic islets transplanted in the eye or kidney. Notably, >70% of tolerant mice, initially transplanted in the eye, exhibited >400days of graft survival after re-transplant in the kidney without immunosuppression compared with ~30% in mice that were initially transplanted in the kidney. Cytokine and DTH data provided evidence of T helper 2-driven local and peripheral immune regulatory mechanisms in support of operational immune tolerance towards the islet allografts in both models. We are currently evaluating the safety and efficacy of intraocular islet transplantation in a phase 1 clinical trial. In this study, we demonstrate immunosuppression-free long-term survival of intraocular islet allografts in mice and in a baboon using transient peri-transplant immune intervention. These results highlight the potential for inducing islet transplant immune tolerance through the intraocular route. Therefore, the current findings are conceptually significant and may impact markedly on clinical islet transplantation in the treatment of diabetes.

Unsurpassed Intrahepatic Islet Engraftment - the Quest for New Sites for Beta Cell Replacement.

The liver is currently the site of choice for clinical islet transplantation, even though many alternative implantation sites have lately been proposed as more ideal for graft survival. The suggested sites, for example intramuscular space, omentum, bone marrow, and spleen, are sometimes difficult to compare due to differences in animal model, islet isolation procedure, and islet quality. In addition, the variation in transplanted islet mass is vast. The aim of this commentary is to review alternative implantation sites tested experimentally as well as in clinical islet transplantation. Although many sites have been investigated, none have convincingly proved better suited for clinical islet transplantation than intraportal injection to the liver, regardless of whether it is autologous or allogeneic transplantation. However, in order to fully evaluate upcoming bioengineering techniques, such as scaffolds containing insulin-producing cells derived from stem cells, the need of an alternative site has arisen to enable cellular monitoring, which currently cannot be achieved within the liver.

The Fate of Allogeneic Pancreatic Islets following Intraportal Transplantation: Challenges and Solutions.

Pancreatic islet transplantation as a therapeutic option for type 1 diabetes mellitus is gaining widespread attention because this approach can restore physiological insulin secretion, minimize the risk of hypoglycemic unawareness, and reduce the risk of death due to severe hypoglycemia. However, there are many obstacles contributing to the early mass loss of the islets and progressive islet loss in the late stages of clinical islet transplantation, including hypoxia injury, instant blood-mediated inflammatory reactions, inflammatory cytokines, immune rejection, metabolic exhaustion, and immunosuppression-related toxicity that is detrimental to the islet allograft. Here, we discuss the fate of intrahepatic islets infused through the portal vein and propose potential interventions to promote islet allograft survival and improve long-term graft function.