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AIMS: This study aimed to investigate the therapeutic potential of a homogenous clonal population of mesenchymal stem cells (cMSC) and their extracellular vesicles (cMSC-EV) subpopulations on isolated rat islets in vitro and in inflammatory-mediated type 1 diabetes (T1D) non-human primate models. MAIN METHODS: EV subpopulations were isolated from human bone marrow-derived cMSC supernatant by low- and high-speed ultracentrifuge (EV-20K and EV-U110K) and sucrose density gradient (EV-S110K). The EVs were characterized generally and for the level of albumin, acetylcholinesterase (AChE) activity, co-isolate apoptotic markers, and expression of CD63+/annexin V+. Rat islet-derived single cells (iSCs) proliferation was measured using a Ki-67 proliferation assay. Diabetes was induced by multiple low-dose administrations of streptozotocin in rhesus monkeys. The diabetic monkeys were divided into three groups: the cMSC group, received two injections of 1.5 × 106 cMSC/kg body weight; the EV group received two injections of EVs isolated from 1.5 × 106 cMSC/kg, and the vehicle group received phosphate-buffered saline. KEY FINDINGS: EV-S110K showed higher AChE activity, lower expression of CD63+/annexin V+, and lower apoptotic co-isolates. EV-S110K induced ß-cell proliferation in vitro in a dose-dependent manner. The administration of EV-S110K and/or cMSC in diabetic monkeys demonstrated no significant changes in general diabetic indices and ß-cell mass in the pancreas of the monkeys. Both treatments demonstrated a lowering trend in blood glucose levels and reduced pro-inflammatory cytokines. In contrast, regulatory T cells and anti-inflammatory cytokines were increased. SIGNIFICANCE: cMSC and cMSC-EV provided initial evidence to attenuate clinical symptoms in inflammatory-mediated T1D non-human primates through immunomodulation.

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OBJECTIVE: Isolated pancreatic islets are valuable resources for a wide range of research, including cell replacement studies and cell-based platforms for diabetes drug discovery and disease modeling. Islet isolation is a complex and stepwise procedure aiming to obtain pure, viable, and functional islets for in vitro and in vivo studies. It should be noted that differences in rodent strains, gender, weight, and density gradients may affect the isolated islet's properties. We evaluated the variables affecting the rat islet isolation procedure to reach the maximum islet yield and functionality, which would be critical for further studies on islet regenerative biology. MATERIALS AND METHODS: The present experimental study compared the yield and purity of isolated islets from nondiabetic rats of two different strains. Next, islet particle number (IPN) and islet equivalent (IEQ) were compared between males and females, and the weight range that yields the highest number of islets was investigated. Moreover, the influence of three different density gradients, namely Histopaque, Pancoll, and Lymphodex, on final isolated islets purity and yield were assessed. Finally, the viability and functionality of isolated islets were measured. RESULTS: The IEQ, IPN, and purity of isolated islets in 15 Lister hooded rats (LHRs) were significantly (P≤0.05) higher than those of the other strains. Male LHRs resulted in significantly higher IEQ compared to females (P≤0.05). Moreover, IPN and IEQ did not significantly vary among different weight groups. Also, the utilization of Histopaque and Pancoll leads to higher yield and purity. In vivo assessments of the isolated islets presented significantly reduced blood glucose percentage in the transplanted group on days 2-5 following transplantation. CONCLUSION: Based on these results, an optimal protocol for isolating high-quality rat islets with a constant yield, purity, and function has been established as an essential platform for developing diabetes research.

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Type 1 diabetes (T1D) is caused by low insulin production and chronic hyperglycemia due to destruction of pancreatic ß-cells. Cell transplantation is an attractive alternative approach compared to insulin injection. However, cell therapy has been limited by major challenges, including life-long requirement for immunosuppressive drugs to prevent host immune responses. Encapsulation of the transplanted cells can solve the problem of immune rejection, by providing a physical barrier between the transplanted cells and the recipient's immune cells. Despite current disputes in cell encapsulation approaches, thanks to recent advances in the fields of biomaterials and transplantation immunology, extensive effort has been dedicated to immunoengineering strategies, in combination with encapsulation technologies, to overcome the problem of host's immune responses. This review summarizes the most commonly used encapsulation and immunoengineering strategies combined with cell therapy, which have been applied as a novel approach to improve cell replacement therapies for management of T1D. Recent advances in the fields of biomaterial design, nanotechnology, as well as deeper knowledge about immune modulation had significantly improved cell encapsulation strategies. However, further progress requires combined application of novel immunoengineering approaches and islet/ß-cell transplantation. Impact statement Cell encapsulation shows promising potential in preventing host's immune responses and rejection of islets or ß-cells by providing a selectively permeable barrier between the host and the transplanted cells. Innovative materials, conformal nanocoatings, and immunomodulation have provided promising approaches in the field of encapsulation technology. Novel nanocarriers have been synthesized to release and deliver immunosuppressive agents to islets/ß-cells within the capsules in a controlled manner. The immunoengineering approach (immunosuppressive and immunomodulatory agents) could overcome the challenges of cell replacement therapy in type 1 diabetes.

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Although transplantation of pancreatic islets is a promising approach for treatment of type 1 diabetes mellitus, the engraftment efficiency of these islets is limited by host immune responses. Extensive efforts have been made to immunoisolate these islets by introducing barriers on the islet surface. To date, these barriers have not successfully protected islets from attack by the immune system. In addition, the inevitable permeability of an islet capsule cannot prevent filtration by proinflammatory cytokines and islet self-antigens. Thus, we have developed a surface engineering approach for localized immonumodulation of the islet microenvironment. Jagged-1 (JAG-1), as a potent immunomodulatory factor, was immobilized on the islet surface by mediation of a double-layer of heterobifunctional poly (ethylene glycol) (PEG). Immobilization and functionality of JAG-1 on PEGylated islet surfaces were established. When co-cultured with splenocytes, the JAG-1 conjugated islets induced a significant increase in regulatory T cells and regulated the cytokine levels produced by immune cells. The results demonstrated that JAG-1 immobilization could improve immunoprotection of pancreatic islets by localized modulation of the immune milieu from an inflammatory to an anti-inflammatory state. We also evaluated the effects of surface modification of these islets by JAG-1 in a xenotransplantation model. The transplanted JAG-1/PEG/islets group showed a significantly reduced blood glucose levels compared with the control group of diabetic mice during the acute phase of the immune response to the transplanted islets. Our results demonstrated that surface modification has the potential to shift the immune system from an inflammatory to anti-inflammatory milieu and may offer a new prospective for immunoprotection of pancreatic islets.

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