Clinical islet transplantation: is the future finally now?

Immunoprotection of cellular transplants for autoimmune type 1 diabetes through local drug delivery

Type 1 diabetes mellitus (T1DM) is an autoimmune condition that results in the destruction of insulin-secreting β cells of the islets of Langerhans. Allogeneic islet transplantation could be a successful treatment for T1DM; however, it is limited by the need for effective, permanent immunosuppression to prevent graft rejection. Upon transplantation, islets are rejected through non-specific, alloantigen specific, and recurring autoimmune pathways. Immunosuppressive agents used for islet transplantation are generally successful in inhibiting alloantigen rejection, but they are suboptimal in hindering non-specific and autoimmune pathways. In this review, we summarize the challenges with cellular immunological rejection and therapeutics used for islet transplantation. We highlight agents that target these three immune rejection pathways and how to package them for controlled, local delivery via biomaterials. Exploring macro-, micro-, and nano-scale immunomodulatory biomaterial platforms, we summarize their advantages, challenges, and future directions. We hypothesize that understanding their key features will help identify effective platforms to prevent islet graft rejection. Outcomes can further be translated to other cellular therapies beyond T1DM.

Adipose-Derived Stromal Cells Preserve Pancreatic Islet Function in a Transplantable 3D Bioprinted Scaffold

Intra-portal islet transplantation is currently the only clinically approved beta cell replacement therapy, but its outcome is hindered by limited cell survival due to a multifactorial reaction against the allogeneic tissue in liver. Adipose-derived stromal cells (ASCs) can potentially improve the islet micro-environment by their immunomodulatory action. The challenge is to combine both islets and ASCs in a relatively easy and consistent long-term manner in a deliverable scaffold. Manufacturing the 3D bioprinted double-layered scaffolds with primary islets and ASCs using a mix of alginate/nanofibrillated cellulose (NFC) bioink is reported. The diffusion properties of the bioink and the supportive effect of human ASCs on islet viability, glucose sensing, insulin secretion, and reducing the secretion of pro-inflammatory cytokines are demonstrated. Diabetic mice transplanted with islet-ASC scaffolds reach normoglycemia seven days post-transplantation with no significant difference between this group and the group received islets under the kidney capsules. In addition, animals transplanted with islet-ASC scaffolds stay normoglycemic and show elevated levels of C-peptide compared to mice transplanted with islet-only scaffolds. The data present a functional 3D bioprinted scaffold for islets and ASCs transplanted to the extrahepatic site and suggest a possible role of ASCs on improving the islet micro-environment.

Human A2-CAR T Cells Reject HLA-A2 + Human Islets Transplanted Into Mice Without Inducing Graft-versus-host Disease

BACKGROUND

Type 1 diabetes is an autoimmune disease characterized by T-cell-mediated destruction of pancreatic beta-cells. Islet transplantation is an effective therapy, but its success is limited by islet quality and availability along with the need for immunosuppression. New approaches include the use of stem cell-derived insulin-producing cells and immunomodulatory therapies, but a limitation is the paucity of reproducible animal models in which interactions between human immune cells and insulin-producing cells can be studied without the complication of xenogeneic graft-versus-host disease (xGVHD).

METHODS

We expressed an HLA-A2-specific chimeric antigen receptor (A2-CAR) in human CD4 + and CD8 + T cells and tested their ability to reject HLA-A2 + islets transplanted under the kidney capsule or anterior chamber of the eye of immunodeficient mice. T-cell engraftment, islet function, and xGVHD were assessed longitudinally.

RESULTS

The speed and consistency of A2-CAR T-cell-mediated islet rejection varied depending on the number of A2-CAR T cells and the absence/presence of coinjected peripheral blood mononuclear cells (PBMCs). When <3 million A2-CAR T cells were injected, coinjection of PBMCs accelerated islet rejection but also induced xGVHD. In the absence of PBMCs, injection of 3 million A2-CAR T cells caused synchronous rejection of A2 + human islets within 1 wk and without xGVHD for 12 wk.

CONCLUSIONS

Injection of A2-CAR T cells can be used to study rejection of human insulin-producing cells without the complication of xGVHD. The rapidity and synchrony of rejection will facilitate in vivo screening of new therapies designed to improve the success of islet-replacement therapies.

Combinatorial islet protective therapeutic approaches in β-cell transplantation: Rationally designed solutions using a target product profile

While progress has been made in the development of islet cell transplantation (ICT) as a viable alternative to the use of exogenous insulin therapy in the treatment of type 1 diabetes, it has not yet achieved its full potential in clinical studies. Ideally, ICT would enable lifelong maintenance of euglycemia without the need for exogenous insulin, blood glucose monitoring or systemic immune suppression. To achieve such an optimal result, therapeutic approaches should simultaneously promote long-term islet viability, functionality, and localized immune protection. In practice, however, these factors are typically tackled individually. Furthermore, while the requirements of optimal ICT are implicitly acknowledged across numerous publications, the literature contains few comprehensive articulations of the target product profile (TPP) for an optimal ICT product, including key characteristics of safety and efficacy. This review aims to provide a novel TPP for ICT and presents promising tried and untried combinatorial approaches that could be used to achieve the target product profile. We also highlight regulatory barriers to the development and adoption of ICT, particularly in the United States, where ICT is only approved for use in academic clinical trials and is not reimbursed by insurance carriers. Overall, this review argues that the clear definition of a TPP in addition to the use of combinatorial approaches could help to overcome the clinical barriers to the widespread adoption of ICT for the treatment of type 1 diabetes.

Localized cytotoxic T cell-associated antigen 4 and antioxidant islet encapsulation alters macrophage signaling and induces regulatory and anergic T cells to enhance allograft survival

The loss of functional β-cell mass is a hallmark of type 1 diabetes. Islet transplantation represents a promising alternative approach, but immune-mediated graft destruction remains a major challenge. We sought to use islet encapsulation technologies to improve graft survival and function without systemic immunosuppression. We hypothesized islet encapsulation with nanothin coatings consisting of tannic acid (TA), an antioxidant; poly(N-vinylpyrrolidone) (PVPON), a biocompatible polymer; and cytotoxic T cell-associated antigen 4 immunoglobulin (CTLA-4-Ig), an inhibitory immune receptor, will elicit localized immunosuppression to prolong islet allograft function and suppress effector T cell responses. In the absence of systemic immunosuppression, we demonstrated (PVPON/TA/CTLA-4-Ig)-encapsulated NOD.Rag islet grafts maintain function significantly longer than control IgG-containing (PVPON/TA/IgG) and nonencapsulated controls after transplantation into diabetic C57BL/6 mice. This protection coincided with diminished proinflammatory macrophage responses mediated by signal transducer and activator of transcription 1 signaling, decreased proinflammatory T cell effector responses, and CTLA-4-Ig-specific concomitant increases in anergic CD4+ T cells and regulatory T cells. Our results provide evidence that conjugation of CTLA-4-Ig to (PVPON/TA) coatings can suppress T cell activation, enhance regulatory T cell populations, prolong islet allograft survival, and induce localized immunosuppression after transplantation.

4-Octyl itaconate attenuates glycemic deterioration by regulating macrophage polarization in mouse models of type 1 diabetes

BACKGROUND

Pancreatic beta cell dysfunction and activated macrophage infiltration are early features in type 1 diabetes pathogenesis. A tricarboxylic acid cycle metabolite that can strongly activate NF-E2-related factor 2 (Nrf2) in macrophages, itaconate is important in a series of inflammatory-associated diseases via anti-inflammatory and antioxidant properties. However, its role in type 1 diabetes is unclear. We used 4-octyl itaconate (OI), the cell-permeable itaconate derivate, to explore its preventative and therapeutic effects in mouse models of type 1 diabetes and the potential mechanism of macrophage phenotype reprogramming.

METHODS

The mouse models of streptozotocin (STZ)-induced type 1 diabetes and spontaneous autoimmune diabetes were used to evaluate the preventative and therapeutic effects of OI, which were performed by measuring blood glucose, insulin level, pro- and anti-inflammatory cytokine secretion, histopathology examination, flow cytometry, and islet proteomics. The protective effect and mechanism of OI were examined via peritoneal macrophages isolated from STZ-induced diabetic mice and co-cultured MIN6 cells with OI-pre-treated inflammatory macrophages in vitro. Moreover, the inflammatory status of peripheral blood mononuclear cells (PBMCs) from type 1 diabetes patients was evaluated after OI treatment.

RESULTS

OI ameliorated glycemic deterioration, increased systemic insulin level, and improved glucose metabolism in STZ-induced diabetic mice and non-obese diabetic (NOD) mice. OI intervention significantly restored the islet insulitis and beta cell function. OI did not alter the macrophage count but significantly downregulated the proportion of M1 macrophages. Additionally, OI significantly inhibited MAPK activation in macrophages to attenuate the macrophage inflammatory response, eventually improving beta cell dysfunction in vitro. Furthermore, we detected higher IL-1β production upon lipopolysaccharide stimulation in the PBMCs from type 1 diabetes patients, which was attenuated by OI treatment.

CONCLUSIONS

These results provided the first evidence to date that OI can prevent the progression of glycemic deterioration, excessive inflammation, and beta cell dysfunction predominantly mediated by restricting macrophage M1 polarization in mouse models of type 1 diabetes.

Human A2-CAR T cells reject HLA-A2+ human islets transplanted into mice without inducing graft versus host disease

Background

Type 1 diabetes (T1D) is an autoimmune disease characterised by T cell mediated destruction of pancreatic beta-cells. Islet transplantation is an effective therapy, but its success is limited by islet quality and availability along with the need for immunosuppression. New approaches include use of stem cell-derived insulin-producing cells and immunomodulatory therapies, but a limitation is the paucity of reproducible animal models in which interactions between human immune cells and insulin-producing cells can be studied without the complication of xenogeneic graft- versus -host disease (xGVHD).

Methods

We expressed an HLA-A2-specific chimeric antigen receptor (A2-CAR) in human CD4+ and CD8+ T cells and tested their ability to reject HLA-A2+ islets transplanted under the kidney capsule or anterior chamber of the eye of immunodeficient mice. T cell engraftment, islet function and xGVHD were assessed longitudinally.

Results

The speed and consistency of A2-CAR T cells-mediated islet rejection varied depending on the number of A2-CAR T cells and the absence/presence of co-injected peripheral blood mononuclear cells (PBMCs). When <3 million A2-CAR T cells were injected, co-injection of PBMCs accelerated islet rejection but also induced xGVHD. In the absence of PBMCs, injection of 3 million A2-CAR T cells caused synchronous rejection of A2+ human islets within 1 week and without xGVHD for 12 weeks.

Conclusions

Injection of A2-CAR T cells can be used to study rejection of human insulin-producing cells without the complication of xGVHD. The rapidity and synchrony of rejection will facilitate in vivo screening of new therapies designed to improve the success of isletreplacement therapies.

In Vivo Imaging of Naked and Microencapsulated Islet Cell Transplantation

We describe step-by-step methods to label human pancreatic islet cells and murine insulinoma cells and their subsequent transplantation into type I diabetic mouse models with a focus on in vivo imaging using clinically applicable scanners. We also cover islets that are microencapsulated within alginate hydrogels loaded with imaging agents. By following these methods, it is possible to image cell grafts using T1-weighted and T2/T2*-weighted 1H magnetic resonance imaging (MRI), 19F MRI, computed tomography, ultrasound imaging, and bioluminescence imaging in vivo. Considering a myriad of factors that may affect the outcome of proper in vivo detection, we discuss potential issues that may be encountered during and after the process of labeling. The ultimate goal is to use these in vivo imaging approaches to determine and optimize naked and encapsulated islet cell survival, therapeutic function, and engraftment procedures.

Perinatal Stem Cell Therapy to Treat Type 1 Diabetes Mellitus: A Never-Say-Die Story of Differentiation and Immunomodulation

Human term placenta and other postpartum-derived biological tissues are promising sources of perinatal cells with unique stem cell properties. Among the massive current research on stem cells, one medical focus on easily available stem cells is to exploit them in the design of immunotherapy protocols, in particular for the treatment of chronic non-curable human diseases. Type 1 diabetes is characterized by autoimmune destruction of pancreatic beta cells and perinatal cells can be harnessed both to generate insulin-producing cells for beta cell replenishment and to regulate autoimmune mechanisms via immunomodulation capacity. In this study, the strong points of cells derived from amniotic epithelial cells and from umbilical cord matrix are outlined and their potential for supporting cell therapy development. From a basic research and expert stem cell point of view, the aim of this review is to summarize information regarding the regenerative medicine field, as well as describe the state of the art on possible cell therapy approaches for diabetes.

A hydrogel platform for co-delivery of immunomodulatory proteins for pancreatic islet allografts

Type 1 diabetes (T1D), an autoimmune disorder in which the insulin-producing β-cells in the islets of Langerhans in the pancreas are destroyed, afflicts over 1.6 million Americans. Although pancreatic islet transplantation has shown promise in treating T1D, continuous use of required immunosuppression regimens limits clinical islet transplantation as it poses significant adverse effects on graft recipients and does not achieve consistent long-term graft survival with 50%-70% of recipients maintaining insulin independence at 5 years. T cells play a key role in graft rejection, and rebalancing pathogenic T effector and protective T regulatory cells can regulate autoimmune disorders and transplant rejection. The synergy of the interleukin-2 (IL-2) and Fas immunomodulatory pathways presents an avenue for eliminating the need for systemic immune suppression by exploiting IL-2's role in expanding regulatory T cells and leveraging Fas ligand (FasL) activity on antigen-induced cell death of effector T cells. Herein, we developed a hydrogel platform for co-delivering an analog of IL-2, IL-2D, and FasL-presenting microgels to achieve localized immunotolerance to pancreatic islets by targeting the upregulation of regulatory T cells and effector T cells simultaneously. Although this hydrogel provided for sustained, local delivery of active immunomodulatory proteins, indefinite allograft survival was not achieved. Immune profiling analysis revealed upregulation of target regulatory T cells but also increases in Granzyme B-expressing CD8+ T cells at the graft site. We attribute the failed establishment of allograft survival to these Granzyme B-expressing T cells. This study underscores the delicate balance of immunomodulatory components important for allograft survival - whose outcome can be dependent on timing, duration, modality of delivery, and disease model.

Engineering of hybrid spheroids of mesenchymal stem cells and drug depots for immunomodulating effect in islet xenotransplantation

Immunomodulation is an essential consideration for cell replacement procedures. Unfortunately, lifelong exposure to nonspecific systemic immunosuppression results in immunodeficiency and has toxic effects on nonimmune cells. Here, we engineered hybrid spheroids of mesenchymal stem cells (MSCs) with rapamycin-releasing poly(lactic-co-glycolic acid) microparticles (RAP-MPs) to prevent immune rejection of islet xenografts in diabetic C57BL/6 mice. Hybrid spheroids were rapidly formed by incubating cell-particle mixture in methylcellulose solution while maintaining high cell viability. RAP-MPs were uniformly distributed in hybrid spheroids and sustainably released RAP for ~3 weeks. Locoregional transplantation of hybrid spheroids containing low doses of RAP-MPs (200- to 4000-ng RAP per recipient) significantly prolonged islet survival times and promoted the generation of regional regulatory T cells. Enhanced programmed death-ligand 1 expression by MSCs was found to be responsible for the immunomodulatory performance of hybrid spheroids. Our results suggest that these hybrid spheroids offer a promising platform for the efficient use of MSCs in the transplantation field.

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.

Viability and Functionality of Neonatal Porcine Islet-like Cell Clusters Bioprinted in Alginate-Based Bioinks

The transplantation of pancreatic islets can prevent severe long-term complications in diabetes mellitus type 1 patients. With respect to a shortage of donor organs, the transplantation of xenogeneic islets is highly attractive. To avoid rejection, islets can be encapsulated in immuno-protective hydrogel-macrocapsules, whereby 3D bioprinted structures with macropores allow for a high surface-to-volume ratio and reduced diffusion distances. In the present study, we applied 3D bioprinting to encapsulate the potentially clinically applicable neonatal porcine islet-like cell clusters (NICC) in alginate-methylcellulose. The material was additionally supplemented with bovine serum albumin or the human blood plasma derivatives platelet lysate and fresh frozen plasma. NICC were analysed for viability, proliferation, the presence of hormones, and the release of insulin in reaction to glucose stimulation. Bioprinted NICC are homogeneously distributed, remain morphologically intact, and show a comparable viability and proliferation to control NICC. The number of insulin-positive cells is comparable between the groups and over time. The amount of insulin release increases over time and is released in response to glucose stimulation over 4 weeks. In summary, we show the successful bioprinting of NICC and could demonstrate functionality over the long-term in vitro. Supplementation resulted in a trend for higher viability, but no additional benefit on functionality was observed.

3D Printing Mini-Capsule Device for Islet Delivery to Treat Type 1 Diabetes

Transplantation of encapsulated islets has been shown to hold a promising potential treatment for type 1 diabetes (T1D). However, there are several obstacles to overcome, such as immune rejection by the host of the grafts, sustainability of islet function, and retrievability or replacement of the encapsulated system, hinder their clinical applications. In this study, mini-capsule devices containing islets were fabricated by using digital light processing (DLP) 3D printing. To ensure a high survival rate and low immunogenicity of the fabricated islets, 20s was selected as the most suitable printing condition. Meanwhile, the mini-capsule devices with a groove structure were fabricated to prevent islet cells leakage. Subcutaneous transplantations of encapsulated islets in immunocompetent C57BL/6 mice indicated significant improvement in the symptoms of streptozotocin-induced hyperglycemia without any immunosuppression treatment for at least 15 weeks. In vivo intraperitoneal glucose tolerance tests (IPGTT) performed at different time points demonstrated therapeutically relevant glycemic ameliorate of the device. The implants retrieved after 15 weeks still contained viable and adequate numbers of islet cells. The results of this study indicate that the proposed mini-capsule device can deliver sufficient islet cell mass, prevent islet cells leakage, and maintain long-term cell survival while allowing easy retrieval. Furthermore, the proposed encapsulated islets may help with T1D cellular treatment by overcoming the obstacles 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.

Microvessels support engraftment and functionality of human islets and hESC-derived pancreatic progenitors in diabetes models

Islet transplantation is a promising treatment for type 1 diabetes (T1D), yet the low donor pool, poor islet engraftment, and life-long immunosuppression prevent it from becoming the standard of care. Human embryonic stem cell (hESC)-derived pancreatic cells could eliminate donor shortages, but interventions to improve graft survival are needed. Here, we enhanced subcutaneous engraftment by employing a unique vascularization strategy based on ready-made microvessels (MVs) isolated from the adipose tissue. This resulted in improved cell survival and effective glucose response of both human islets and hESC-derived pancreatic cells, which ameliorated preexisting diabetes in three mouse models of T1D.

Update on islet cell transplantation

PURPOSE OF REVIEW

Chronic diabetes-related complications continue to exert a rapidly growing and unsustainable pressure on healthcare systems worldwide. In type 1 diabetes, glycemic control is particularly challenging, as intensive management substantially increase the risk of severe hypoglycemic episodes. Alternative approaches to address this issue are required. Islet cell transplantation offers the best approach to reduce hypoglycemic risks and glycemic lability, while providing optimal glycemic control. Although ongoing efforts have improved clinical outcomes, the constraints in tissue sources and the need for chronic immunosuppression limit the application of islet cell transplantation as a curative therapy for diabetes. This review provides an update on islet cell transplantation, focusing on recent clinical experience, ongoing research, and future challenges.

RECENT FINDINGS

Current evidence demonstrates advances in terms of long-term glycemic control, improved insulin independence rates, and novel approaches to eliminate chronic immunosuppression requirements after islet cell transplantation. Advances in stem cell-based therapies provide a promising path towards truly personalized regenerative therapies, solving both tissue supply shortage and the need for lifelong immunosuppression, enabling widespread use of this potentially curative treatment. However, as these therapies enter the clinical realm, regional access variability and ethical questions regarding commercialization are becoming increasingly important and require a collaborative solution.

SUMMARY

In this state-of-the-art review, we discuss current clinical evidence and discuss key aspects on the present and future of islet cell transplantation.

Strategies for durable β cell replacement in type 1 diabetes

Technological advancements in blood glucose monitoring and therapeutic insulin administration have improved the quality of life for people with type 1 diabetes. However, these efforts fall short of replicating the exquisite metabolic control provided by native islets. We examine the integrated advancements in islet cell replacement and immunomodulatory therapies that are coalescing to enable the restoration of endogenous glucose regulation. We highlight advances in stem cell biology and graft site design, which offer innovative sources of cellular material and improved engraftment. We also cover cutting-edge approaches for preventing allograft rejection and recurrent autoimmunity. These insights reflect a growing understanding of type 1 diabetes etiology, β cell biology, and biomaterial design, together highlighting therapeutic opportunities to durably replace the β cells destroyed in type 1 diabetes.

Xenotransplantation of tannic acid-encapsulated neonatal porcine islets decreases proinflammatory innate immune responses

BACKGROUND

Islet transplantation with neonatal porcine islets (NPIs) is a promising treatment for type 1 diabetes (T1D), but immune rejection poses a major hurdle for clinical use. Innate immune-derived reactive oxygen species (ROS) synthesis can facilitate islet xenograft destruction and enhance adaptive immune responses.

METHODS

To suppress ROS-mediated xenograft destruction, we utilized nanothin encapsulation materials composed of multilayers of tannic acid (TA), an antioxidant, and a neutral polymer, poly(N-vinylpyrrolidone) (PVPON). We hypothesized that (PVPON/TA)-encapsulated NPIs will maintain euglycemia and dampen proinflammatory innate immune responses following xenotransplantation.

RESULTS

(PVPON/TA)-encapsulated NPIs were viable and glucose-responsive similar to non-encapsulated NPIs. Transplantation of (PVPON/TA)-encapsulated NPIs into hyperglycemic C57BL/6.Rag or NOD.Rag mice restored euglycemia, exhibited glucose tolerance, and maintained islet-specific transcription factor levels similar to non-encapsulated NPIs. Gene expression analysis of (PVPON/TA)-encapsulated grafts post-transplantation displayed reduced proinflammatory Ccl5, Cxcl10, Tnf, and Stat1 while enhancing alternatively activated macrophage Retnla, Arg1, and Stat6 mRNA accumulation compared with controls. Flow cytometry analysis demonstrated significantly reduced innate immune infiltration, MHC-II, co-stimulatory molecule, and TNF expression with concomitant increases in arginase-1⁺ macrophages and dendritic cells. Similar alterations in immune responses were observed following xenotransplantation into immunocompetent NOD mice.

CONCLUSION

Our data suggest that (PVPON/TA) encapsulation of NPIs is an effective strategy to decrease inflammatory innate immune signals involved in NPI xenograft responses through STAT1/6 modulation without compromising islet function.

The impact of locally-delivered tacrolimus-releasing microspheres and polyethylene glycol-based islet surface modification on xenogeneic islet survival

Pancreatic islet replacement therapy is an advanced choice for severe cases of type I diabetes. Nevertheless, extensive host immune response toward islet grafts remains a huge challenge for long-term graft function, and a lack of islet donors further increases the difficulties associated with upscaling this therapy. Mounting evidence suggests local delivery of immunosuppressive agents provides a feasible means of enhancing graft-protection. Among many immunosuppressants, tacrolimus (FK506) is one of the most potent interleukin-2 (IL-2)-mediated T-cell proliferation blockers. Here, we reported the effect of locally-delivered FK506-releasing PLGA microspheres (FK506-M) combined with polyethylene glycol (PEG)-based islet surface modification on xenogeneic islet survival in C57BL/6 mouse model. FK506-M was prepared using an emulsion method to a particle size of 10-40 μm and released FK506 over 40 days in vitro. Around 80% of the initial dose of FK506-M stably localized near transplanted islets, as observed under a bioimaging instrument and by immunofluorescence staining of islet grafts. Interestingly, FK506-M at very low-doses (equivalent to 150 to 2400 ng FK506 per recipient) was found to inhibit the infiltration of immune cells into grafts and reduce serum IL-1β levels, thereby improving graft survival times dose-dependently. The PEGylation of islets alone was not enough to protect islets from early rejection. However, combined treatment with FK506-M additively prolonged xenograft survival. In conclusion, this study describes a safe, effective approach for translating a systemic exposure-free local drug delivery into clinical trials of islet transplantation.

Impact of ischemia time on islet isolation success and posttransplantation outcomes: A retrospective study of 452 pancreas isolations

Many variables impact islet isolation, including pancreas ischemia time. The ischemia time upper limit that should be respected to avoid a negative impact on the isolation outcome is not well defined. We have performed a retrospective analysis of all islet isolations in our center between 2008 and 2018. Total ischemia time, cold ischemia time, and organ removal time were analyzed. Isolation success was defined as an islet yield ≥200 000 IEQ. Of the 452 pancreases included, 288 (64%) were successfully isolated. Probability of isolation success showed a significant decrease after 8 hours of total ischemia time, 7 hours of cold ischemia time, and 80 minutes of organ removal time. Although we observed an impact of ischemia time on islet yield, a probability of isolation success of 50% was still present even when total ischemia time exceeds 12 hours. Posttransplantation clinical outcomes were assessed in 32 recipients and no significant difference was found regardless of ischemia time. These data indicate that although shorter ischemia times are associated with better islet isolation outcomes, total ischemia time >12 hours can provide excellent results in appropriately selected donors.

Inducible Pluripotent Stem Cells as a Potential Cure for Diabetes

Over the last century, diabetes has been treated with subcutaneous insulin, a discovery that enabled patients to forego death from hyperglycemia. Despite novel insulin formulations, patients with diabetes continue to suffer morbidity and mortality with unsustainable costs to the health care system. Continuous glucose monitoring, wearable insulin pumps, and closed-loop artificial pancreas systems represent an advance, but still fail to recreate physiologic euglycemia and are not universally available. Islet cell transplantation has evolved into a successful modality for treating a subset of patients with ‘brittle’ diabetes but is limited by organ donor supply and immunosuppression requirements. A novel approach involves generating autologous or immune-protected islet cells for transplant from inducible pluripotent stem cells to eliminate detrimental immune responses and organ supply limitations. In this review, we briefly discuss novel mechanisms for subcutaneous insulin delivery and define their shortfalls. We describe embryological development and physiology of islets to better understand their role in glycemic control and, finally, discuss cell-based therapies for diabetes and barriers to widespread use. In response to these barriers, we present the promise of stem cell therapy, and review the current gaps requiring solutions to enable widespread use of stem cells as a potential cure for diabetes.

Tregs and Mixed Chimerism as Approaches for Tolerance Induction in Islet Transplantation

Pancreatic islet transplantation is a promising method for the treatment of type 1 and type 3 diabetes whereby replacement of islets may be curative. However, long-term treatment with immunosuppressive drugs (ISDs) remains essential for islet graft survival. Current ISD regimens carry significant side-effects for transplant recipients, and are also toxic to the transplanted islets. Pre-clinical efforts to induce immune tolerance to islet allografts identify ways in which the recipient immune system may be reeducated to induce a sustained transplant tolerance and even overcome autoimmune islet destruction. The goal of these efforts is to induce tolerance to transplanted islets with minimal to no long-term immunosuppression. Two most promising cell-based therapeutic strategies for inducing immune tolerance include T regulatory cells (Tregs) and donor and recipient hematopoietic mixed chimerism. Here, we review preclinical studies which utilize Tregs for tolerance induction in islet transplantation. We also review myeloablative and non-myeloablative hematopoietic stem cell transplantation (HSCT) strategies in preclinical and clinical studies to induce sustained mixed chimerism and allograft tolerance, in particular in islet transplantation. Since Tregs play a critical role in the establishment of mixed chimerism, it follows that the combination of Treg and HSCT may be synergistic. Since the success of the Edmonton protocol, the feasibility of clinical islet transplantation has been established and nascent clinical trials testing immune tolerance strategies using Tregs and/or hematopoietic mixed chimerism are underway or being formulated.

The effect of liver donors' age, gender and metabolic state on pancreatic lineage activation

Autologous cells replacement therapy by liver to pancreas transdifferentiation (TD) allows diabetic patients to be also the donors of their own therapeutic tissue. Aim: To analyze whether the efficiency of the process is affected by liver donors' heterogeneity with regard to age, gender and the metabolic state. Materials & methods: TD of liver cells derived from nondiabetic and diabetic donors at different ages was characterized at molecular and cellular levels, in vitro. Results: Neither liver cells proliferation nor the propagated cells TD efficiency directly correlate with the age (3-60 years), gender or the metabolic state of the donors. Conclusion: Human liver cells derived from a wide array of ages and metabolic states can be used for autologous cells therapies for diabetics.

Particulate-Based Single-Dose Local Immunosuppressive Regimen for Inducing Tolerogenic Dendritic Cells in Xenogeneic Islet Transplantation

Recent studies emphasize on developing immune tolerance by an interim administration of various immunosuppressive drugs. In this study, a robust protocol is reported for local immunomodulation using a single-dose of FK506 microspheres and clodronate liposomes (mFK+CLO) in a xenogeneic model of islet transplantation. Surprisingly, the single-dose treatment with mFK+CLO induce tolerance to the islet xenograft. The recipient mice display tolerogenic dendritic cells (tDCs) with decreased antigen presenting ability and T cell activation capacity. Furthermore, a reduced percentage of CD4⁺ and CD8⁺ T cells and an impaired differentiation of naïve CD4⁺ T cells into interferon-γ producing Th1 and interleukin-17 producing Th17 cells are observed. In addition, the immunosuppressive protocol leads to the generation of Foxp3⁺ regulatory T cells (Tregs) which are required for the long-term graft survival. The enhanced generation of tDCs and Tregs by the single treatment of mFK+CLO cause xenograft tolerance, suggesting a possible clinical strategy which may pave the way towards improving therapeutic outcomes of clinical islet transplantation.

In Vivo Imaging of Pancreatic Islet Grafts in Diabetes Treatment

Transplantation of pancreatic islets has potential to offer life-long blood glucose management in type I diabetes and severe type II diabetes without the need of exogenous insulin administration. However, islet cell therapy suffers from autoimmune and allogeneic rejection as well as non-immune related factors. Non-invasive techniques to monitor and evaluate the fate of cell implants in vivo are essential to understand the underlying causes of graft failure, and hence to improve the precision and efficacy of islet therapy. This review describes how imaging technology has been employed to interrogate the distribution, number or volume, viability, and function of islet implants in vivo. To date, fluorescence imaging, PET, SPECT, BLI, MRI, MPI, and ultrasonography are the many imaging modalities being developed to fulfill this endeavor. We outline here the advantages, limitations, and clinical utility of each particular imaging approach.

Transplant strategies for type 1 diabetes: whole pancreas, islet and porcine beta cell therapies

Whole-organ pancreas and islet transplantations are performed in a highly selected group of patients with diabetes mellitus, primarily those with type 1 diabetes mellitus, complicated by recurrent severe hypoglycaemia or renal failure requiring kidney transplantation. Clinical accessibility to pancreases or islets, and patient characteristics and therapeutic goals, may dictate choice of procedure. Pancreas transplantation is most often performed simultaneous with a kidney transplant, but patients with particularly labile type 1 diabetes may be considered for a pancreas transplant alone. While highly successful at restoring insulin independence, pancreas transplants carry the significant risks of major surgery and immunosuppression. Islet transplantation is a relatively minor procedure, usually performed for labile type 1 diabetes with severe hypoglycaemia. It is highly successful at resolving hypoglycaemia, but more than one pancreas donor may be required for insulin independence. Both pancreas and islet transplantation are limited in applicability by a paucity of deceased donors. Pigs provide one promising replenishable source of islets. Porcine islets can successfully reverse diabetes mellitus in non-human primates under the appropriate immunosuppressive conditions, with promise for eventually translating this success to a larger population of patients with diabetes mellitus in the future. Graphical abstract.

Localized Immunosuppression With Tannic Acid Encapsulation Delays Islet Allograft and Autoimmune-Mediated Rejection

Type 1 diabetes (T1D) is an autoimmune disease of insulin-producing β-cells. Islet transplantation is a promising treatment for T1D, but long-term graft viability and function remain challenging. Oxidative stress plays a key role in the activation of alloreactive and autoreactive immunity toward the engrafted islets. Therefore, targeting these pathways by encapsulating islets with an antioxidant may delay immune-mediated rejection. Utilizing a layer-by-layer approach, we generated nanothin encapsulation materials containing tannic acid (TA), a polyphenolic compound with redox scavenging and anti-inflammatory effects, and poly(N-vinylpyrrolidone) (PVPON), a biocompatible polymer. We hypothesize that transplantation of PVPON/TA-encapsulated allogeneic C57BL/6 islets into diabetic NOD mice will prolong graft function and elicit localized immunosuppression. In the absence of systemic immunosuppression, diabetic recipients containing PVPON/TA-encapsulated islets maintained euglycemia and delayed graft rejection significantly longer than those receiving nonencapsulated islets. Transplantation of PVPON/TA-encapsulated islets was immunomodulatory because gene expression and flow cytometric analysis revealed significantly decreased immune cell infiltration, synthesis of reactive oxygen species, inflammatory chemokines, cytokines, CD8 T-cell effector responses, and concomitant increases in alternatively activated M2 macrophage and dendritic cell phenotypes. Our results provide evidence that reducing oxidative stress following allotransplantation of PVPON/TA-encapsulated islets can elicit localized immunosuppression and potentially delay graft destruction in future human islet transplantation studies.

Functionalization of Alginate with Extracellular Matrix Peptides Enhances Viability and Function of Encapsulated Porcine Islets

Translation of transplanted alginate-encapsulated pancreatic islets to treat type 1 diabetes has been hindered by inconsistent long-term efficacy. This loss of graft function can be partially attributed to islet dysfunction associated with the destruction of extracellular matrix (ECM) interactions during the islet isolation process as well as immunosuppression-associated side effects. This study aims at recapitulating islet-ECM interactions by the direct functionalization of alginate with the ECM-derived peptides RGD, LRE, YIGSR, PDGEA, and PDSGR. Peptide functionalization is controlled in a concentration-dependent manner and its presentation is found to be homogeneous across the microcapsule environment. Preweaned porcine islets are encapsulated in peptide-functionalized alginate microcapsules, and those encapsulated in RGD-functionalized alginate displays enhanced viability and glucose-stimulated insulin release. Effects are RGD-specific and not observed with its scrambled control RDG nor with LRE, YIGSR, PDGEA, and PDSGR. This study supports the sustained presentation of ECM-derived peptides in helping to maintain health of encapsulated pancreatic islets and may aid in prolonging longevity of encapsulated islet grafts.

NLRP3 Inflammasome is Activated in Rat Pancreatic Islets by Transplantation and Hypoxia

Hypoxia, IL-1β production and oxidative stress are involved in islet graft dysfunction and destruction. However, the link between these events has not yet been determined in transplanted islets. The goal of this study was to determine whether NLRP3 inflammasome is responsible for IL-1β production and if it is activated by hypoxia-induced oxidative stress in transplanted islets. Rat islets were transplanted under the kidney capsule of immunodeficient mice. At different times post-transplantation, blood samples were collected and islet grafts harvested. Rat islets were also incubated in vitro either under normoxia or hypoxia for 24 h, in the absence or presence of inhibitors of NLRP3 inflammasome (CASP1 inhibitor) or oxidative stress (NAC). NLRP3, CASP1, IL1B, BBC3 pro-apoptotic and BCL2 anti-apoptotic genes in transplanted and in vitro incubated islets were then studied using real time PCR. IL-1β released in the blood and in the supernatant was quantified by ELISA. Cell death was analysed by propidium iodide and Annexin-V staining. NLRP3, CASP1 and BBC3 in transplanted rat islets and IL-1β in blood transiently increased during the first days after transplantation. In islets incubated under hypoxia, NRLP3, IL1B and CASP1 and IL-1β released in supernatant increased compared to islets incubated under normoxia. These effects were prevented by the inhibition of NLRP3 inflammasome by CASP1 or oxidative stress by NAC. However, these inhibitors did not prevent hypoxia-induced rat islet death. These data show that NLRP3 inflammasome in rat islets is transiently activated after their transplantation and induced through oxidative stress in vitro. However, NRLP3 inflammasome inhibition does not protect islet cells against hypoxia.

Cell therapy for type 1 diabetes

INTRODUCTION

Type 1 diabetes (T1D) is a lifelong condition resulting from autoimmune destruction of insulin-producing β-cells. Islet or whole-pancreas transplantation is limited by the shortage of donors and need for chronic immune suppression. Novel strategies are needed to prevent β-cell loss and to rescue production of endogenous insulin.

AREAS COVERED

This review covers the latest advances in cell-based therapies for the treatment and prevention of T1D. Topics include adoptive transfer of cells with increased immunoregulatory potential for β-cell protection, and β-cell replacement strategies such as generation of insulin-producing β-like cells from unlimited sources.

EXPERT OPINION

Cell therapy provides an opportunity to prevent or reverse T1D. Adoptive transfer of autologous cells having enhanced immunomodulatory properties can suppress autoimmunity and preserve β-cells. Such therapies have been made possible by a combination of genome-editing techniques and transplantation of tolerogenic cells. In-vitro modified autologous hematopoietic stem cells and tolerogenic dendritic cells may protect endogenous and newly generated β-cells from a patient's autoimmune response without hampering immune surveillance for infectious agents and malignant cellular transformations. However, methods to generate cells that meet quality and safety standards for clinical applications require further refinement.

Targeting CXCR1/2 Does Not Improve Insulin Secretion After Pancreatic Islet Transplantation: A Phase 3, Double-Blind, Randomized, Placebo-Controlled Trial in Type 1 Diabetes

OBJECTIVE

Reparixin is an inhibitor of CXCR1/2 chemokine receptor shown to be an effective anti-inflammatory adjuvant in a pilot clinical trial in allotransplant recipients.

RESEARCH DESIGN AND METHODS

A phase 3, multicenter, randomized, double-blind, parallel-assignment study (NCT01817959) was conducted in recipients of islet allotransplants randomized (2:1) to reparixin or placebo in addition to immunosuppression. Primary outcome was the area under the curve (AUC) for C-peptide during the mixed-meal tolerance test at day 75 ± 5 after the first and day 365 ± 14 after the last transplant. Secondary end points included insulin independence and standard measures of glycemic control.

RESULTS

The intention-to-treat analysis did not show a significant difference in C-peptide AUC at both day 75 (27 on reparixin vs. 18 on placebo, P = 0.99) and day 365 (24 on reparixin vs. 15 on placebo, P = 0.71). There was no statistically significant difference between treatment groups at any time point for any secondary variable. Analysis of patient subsets showed a trend for a higher percentage of subjects retaining insulin independence for 1 year after a single islet infusion in patients receiving reparixin as compared with patients receiving placebo (26.7% vs. 0%, P = 0.09) when antithymocyte globulin was used as induction immunosuppression.

CONCLUSIONS

In this first double-blind randomized trial, islet transplantation data obtained with reparixin do not support a role of CXCR1/2 inhibition in preventing islet inflammation-mediated damage.

Local release of NECA (5'-(N-ethylcarboxamido)adenosine) from implantable polymeric sheets for enhanced islet revascularization in extrahepatic transplantation site

Clinical intraportal pancreatic islet infusion is popular for treating type I diabetes. However, multiple doses of islets and anti-rejection protocols are needed to compensate for early large cell losses post-infusion due to the harsh hepatic environment. Thus, extrahepatic sites are utilized to enable efficient islet engraftment and reduce islet mass. Here, we reported an effective islet revascularization protocol that was based on the co-implantation of islet/fibrin gel construct with poly(lactic-co-glycolic) acid sheet releasing NECA (5'-(N-ethylcarboxamido) adenosine; a potent agonist of adenosine) into mouse epididymal fat pad. Thin, flexible sheets (d = 4 mm) prepared by simple casting exhibited sustained NECA release for up to 21 days, which effectively improved early islet engraftment with a median diabetic reversal time of 18.5 days. Western blotting revealed the facilitative effect of NECA on VEGF expression from islets in vitro and from grafts in vivo. In addition, NECA directly promoted the angiogenic activities of islet-derived endothelial cells by enhancing their proliferation and vessel-like tube formation. As a result, neovasculatures were effectively formed in the engrafted islet vicinity, as evidenced by vasculature imaging and immunofluorescence. Taken together, we suggest NECA-releasing PLGA sheets offer a safe and effective drug delivery system that enhances islet engraftment while reducing islet mass at extrahepatic sites for clinical relevance.

Shaping Pancreatic β-Cell Differentiation and Functioning: The Influence of Mechanotransduction

Embryonic and pluripotent stem cells hold great promise in generating β-cells for both replacing medicine and novel therapeutic discoveries in diabetes mellitus. However, their differentiation in vitro is still inefficient, and functional studies reveal that most of these β-like cells still fail to fully mirror the adult β-cell physiology. For their proper growth and functioning, β-cells require a very specific environment, the islet niche, which provides a myriad of chemical and physical signals. While the nature and effects of chemical stimuli have been widely characterized, less is known about the mechanical signals. We here review the current status of knowledge of biophysical cues provided by the niche where β-cells normally live and differentiate, and we underline the possible machinery designated for mechanotransduction in β-cells. Although the regulatory mechanisms remain poorly understood, the analysis reveals that β-cells are equipped with all mechanosensors and signaling proteins actively involved in mechanotransduction in other cell types, and they respond to mechanical cues by changing their behavior. By engineering microenvironments mirroring the biophysical niche properties it is possible to elucidate the β-cell mechanotransductive-regulatory mechanisms and to harness them for the promotion of β-cell differentiation capacity in vitro.

Smoothed Particle Hydrodynamics multiphase modelling of an experimental microfluidic device for conformal coating of pancreatic islets

The paper discusses a Smoothed Particle Hydrodynamics (SPH) model for the analysis of the multiphase flow occurring in an experimental microfluidic device for conformal coating of pancreatic islets with a biocompatible and permeable polymer. The proposed numerical model, based on a weakly-compressible SPH approach, accurately mimics the encapsulation process while assuring phase conservation, thus overcoming potential limitations of grid-based models. The proposed SPH model is a triphasic multi-phase model that allows one: (i) to reproduce the physics of islet conformal coating, including the effects of surface tension at the interface of the involved fluids and of the islet diameter; and (ii) to evaluate how modulation of process parameters influences the fluid dynamics within the microfluidic device and the resulting coating characteristics. This model can represent a valuable, time- and cost-effective tool for the definition of optimized encapsulation conditions through in silico screening of novel combinations of conformal coating parameters, including polymeric coating blends, size range of insulin-secreting cell clusters, utilized chemical reagents, device geometry and scale.

Glycaemic control in diabetic rats treated with islet transplantation using plasma combined with hydroxypropylmethyl cellulose hydrogel

Islet transplantation is one of the most efficient cell therapies used in clinics and could treat a large proportion of patients with diabetes. However, it is limited by the high requirement of pancreas necessary to provide the sufficient surviving islet mass in the hepatic tissue and restore normoglycaemia. Reduction in organ procurement requirements could be achieved by extrahepatic transplantation using a biomaterial that enhances islet survival and function. We report a plasma-supplemented hydroxypropyl methylcellulose (HPMC) hydrogel, engineered specifically using a newly developed technique for intra-omental islet infusion, known as hOMING (h-Omental Matrix Islet filliNG). The HPMC hydrogel delivered islets with better performance than that of the classical intrahepatic infusion. After the validation of the HPMC suitability for islets in vivo and in vitro, plasma supplementation modified the rheological properties of HPMC without affecting its applicability with hOMING. The biomaterial association was proven to be more efficient both in vitro and in vivo, with better islet viability and function than that of the current clinical intrahepatic delivery technique. Indeed, when the islet mass was decreased by 25% or 35%, glycaemia control was observed in the group of plasma-supplemented hydrogels, whereas no regulation was observed in the hepatic group. Plasma gelation, observed immediately post infusion, decreased anoïkis and promoted vascularisation. To conclude, the threshold mass for islet transplantation could be decreased using HPMC-Plasma combined with the hOMING technique. The simplicity of the hOMING technique and the already validated use of its components could facilitate its transfer to clinics. STATEMENT OF SIGNIFICANCE: One of the major limitations for the broad deployment of current cell therapy for brittle type 1 diabetes is the islets' destruction during the transplantation process. Retrieved from their natural environment, the islets are grafted into a foreign tissue, which triggers massive cell loss. It is mandatory to provide the islets with an 3D environment specifically designed for promoting isletimplantation to improve cell therapy outcomes. For this aim, we combined HPMC and plasma. HPMC provides suitable rheological properties to the plasma to be injectable and be maintained in the omentum. Afterwards, the plasma polymerises around the graft in vivo, thereby allowing their optimal integration into their transplantation site. As a result, the islet mass required to obtain glycaemic control was reduced by 35%.

Engineering immunomodulatory biomaterials for type 1 diabetes

A cure for type 1 diabetes (T1D) would help millions of people worldwide, but remains elusive thus far. Tolerogenic vaccines and beta cell replacement therapy are complementary therapies that seek to address aberrant T1D autoimmune attack and subsequent beta cell loss. However, both approaches require some form of systematic immunosuppression, imparting risks to the patient. Biomaterials-based tools enable localized and targeted immunomodulation, and biomaterial properties can be designed and combined with immunomodulatory agents to locally instruct specific immune responses. In this Review, we discuss immunomodulatory biomaterial platforms for the development of T1D tolerogenic vaccines and beta cell replacement devices. We investigate nano- and microparticles for the delivery of tolerogenic agents and autoantigens, and as artificial antigen presenting cells, and highlight how bulk biomaterials can be used to provide immune tolerance. We examine biomaterials for drug delivery and as immunoisolation devices for cell therapy and islet transplantation, and explore synergies with other fields for the development of new T1D treatment strategies.

An elastin-based vasculogenic scaffold promotes marginal islet mass engraftment and function at an extrahepatic site

In islet transplantation, one of the major obstacles to optimal engraftment is the loss of islet natural vascularization and islet-specific extracellular matrix (ECM) during the islet isolation process. Thus, transplanted islets must re-establish nutritional and physical support through formation of new blood vessels and new ECM. To promote this critical process, we developed an elastin-based vasculogenic and ECM-promoting scaffold engineered for extrahepatic islet transplantation. The scaffold by design consisted of type I collagen (Coll) blended with 20wt% of elastin (E) shown to promote angiogenesis as well as de novo ECM deposition. The resulting "CollE" scaffolds h ad interconnected pores with a size distribution tailored to accommodate seeding of islets as well as growth of new blood vessels. In vitro, CollE scaffolds enabled prolonged culture of murine islets for up to one week while preserving their integrity, viability and function. In vivo, after only four weeks post-transplant of a marginal islet mass, CollE scaffolds demonstrated enhanced vascularization of the transplanted islets in the epididymal fat pad and promoted a prompt reversal of hyperglycemia in previously diabetic recipients. This outcome was comparable to that of kidney capsular (KC) islet transplantation, and superior to that of islets transplanted on the control collagen-only scaffolds (Coll). Crucial genes associated with angiogenesis (VEGFA, PDGFB, FGF1, and COL3A1) as well as de novo islet-specific matrix deposition (COL6A1, COL4A1, LAMA2 and FN1) were all significantly upregulated in islets on CollE scaffolds in comparison to those on Coll scaffolds. Finally, CollE scaffolds were also able to support human islet culture in vitro. In conclusion, CollE scaffolds have the potential to improve the clinical outcome of marginal islet transplantation at extrahepatic sites by promoting angiogenesis and islet-specific ECM deposition.

Stem cells in the treatment of diabetes mellitus - Focus on mesenchymal stem cells

Diabetes mellitus type 1 and type 2 have become a global epidemic with dramatically increasing incidences. Poorly controlled diabetes is associated with severe life-threatening complications. Beside traditional treatment with insulin and oral anti-diabetic drugs, clinicians try to improve patient's care by cell therapies using embryonic stem cells (ESC), induced pluripotent stem cells (iPSC) and adult mesenchymal stem cells (MSC). ESC display a virtually unlimited plasticity, including the differentiation into insulin producing β-cells, but they raise ethical concerns and bear, like iPSC, the risk of tumours. IPSC may further inherit somatic mutations and remaining somatic transcriptional memory upon incomplete re-programming, but allow the generation of patient/disease-specific cell lines. MSC avoid such issues but have not been successfully differentiated into β-cells. Instead, MSC and their pericyte phenotypes outside the bone marrow have been recognized to secrete numerous immunomodulatory and tissue regenerative factors. On this account, the term 'medicinal signaling cells' has been proposed to define the new conception of a 'drug store' for injured tissues and to stay with the MSC nomenclature. This review presents the biological background and the resulting clinical potential and limitations of ESC, iPSC and MSC, and summarizes the current status quo of cell therapeutic concepts and trials.

Generation of Human Stem Cell-Derived Pancreatic Organoids (POs) for Regenerative Medicine

Insulin-dependent diabetes mellitus or type 1 diabetes mellitus (T1DM) is an auto-immune condition characterized by the loss of pancreatic β-cells. The curative approach for highly selected patients is the pancreas or the pancreatic islet transplantation. Nevertheless, these options are limited by a growing shortage of donor organs and by the requirement of immunosuppression.Xenotransplantation of porcine islets has been extensively investigated. Nevertheless, the strong xenoimmunity and the risk of transmission of porcine endogenous retroviruses, have limited their application in clinic. Generation of β-like cells from stem cells is one of the most promising strategies in regenerative medicine. Embryonic, and more recently, adult stem cells are currently the most promising cell sources exploited to generate functional β-cells in vitro. A number of studies demonstrated that stem cells could generate functional pancreatic organoids (POs), able to restore normoglycemia when implanted in different preclinical diabetic models. Nevertheless, a gradual loss of function and cell dead are commonly detected when POs are transplanted in immunocompetent animals. So far, the main issue to be solved is the post-transplanted islet loss, due to the host immune attack. To avoid this hurdle, nanotechnology has provided a number of polymers currently under investigation for islet micro and macro-encapsulation. These new approaches, besides conferring PO immune protection, are able to supply oxygen and nutrients and to preserve PO morphology and long-term viability.Herein, we summarize the current knowledge on bioengineered POs and the stem cell differentiation platforms. We also discuss the in vitro strategies used to generate functional POs, and the protocols currently used to confer immune-protection against the host immune attack (micro- and macro-encapsulation). In addition, the most relevant ongoing clinical trials, and the most relevant hurdles met to move towards clinical application are revised.

Biomarkers in Islet Cell Transplantation for Type 1 Diabetes

PURPOSE OF REVIEW

Islet transplantation, an important approach to achieve insulin independence for individuals with type 1 diabetes, is limited by the lack of accurate biomarkers to track beta-cell death post islet infusion. In this review, we will discuss existing and recently described biomarkers.

RECENT FINDINGS

As beta cells are killed by the immune system, fragments of beta cell-specific cell-free DNA and proteins are released into the periphery. Several different strategies to identify these fragments have been described. Some circulating, non-coding microRNAs, particularly miRNA-375 are also showing potential to reflect the rate of beta cell loss post-clinical islet transplantation. Recent advances in identifying accurate beta cell-specific biomarkers such as differentially methylated insulin cell-free DNA and circulating miRNA-375 may help predict clinical outcomes. More studies are required to examine the robustness of these biomarkers to detect chronic beta-cell loss in islet transplantation recipients.