Cell Surface Modification by Activated Polyethylene Glycol Prevents Allosensitization after Islet Transplantation

Advances in Encapsulation and Delivery Strategies for Islet Transplantation

Type 1 diabetes mellitus (T1DM) is a chronic metabolic disease caused by the destruction of pancreatic β-cells in response to autoimmune reactions. Shapiro et al. conducted novel islet transplantation with a glucocorticoid-free immunosuppressive agent in 2000 and achieved great success; since then, islet transplantation has been increasingly regarded as a promising strategy for the curative treatment of T1DM. However, many unavoidable challenges, such as a lack of donors, poor revascularization, blood-mediated inflammatory reactions, hypoxia, and side effects caused by immunosuppression have severely hindered the widespread application of islet transplantation in clinics. Biomaterial-based encapsulation and delivery strategies are proposed for overcoming these obstacles, and have demonstrated remarkable improvements in islet transplantation outcomes. Herein, the major problems faced by islet transplantation are summarized and updated biomaterial-based strategies for islet transplantation, including islet encapsulation across different scales, delivery of stem cell-derived beta cells, co-delivery of islets with accessory cells and immunomodulatory molecules are highlighted.

Modulating the foreign body response of implants for diabetes treatment

Diabetes Mellitus is a group of diseases characterized by high blood glucose levels due to patients' inability to produce sufficient insulin. Current interventions often require implants that can detect and correct high blood glucose levels with minimal patient intervention. However, these implantable technologies have not reached their full potential in vivo due to the foreign body response and subsequent development of fibrosis. Therefore, for long-term function of implants, modulating the initial immune response is crucial in preventing the activation and progression of the immune cascade. This review discusses the different molecular mechanisms and cellular interactions involved in the activation and progression of foreign body response (FBR) and fibrosis, specifically for implants used in diabetes. We also highlight the various strategies and techniques that have been used for immunomodulation and prevention of fibrosis. We investigate how these general strategies have been applied to implants used for the treatment of diabetes, offering insights on how these devices can be further modified to circumvent FBR and fibrosis.

Tissue-resident natural killer cells exacerbate tubulointerstitial fibrosis by activating transglutaminase 2 and syndecan-4 in a model of aristolochic acid-induced nephropathy

Despite reports suggesting that tissue-resident natural killer (trNK) cells cause ischemic kidney injury, their contribution to the development of tubulointerstitial fibrosis has not been determined. This study hypothesized that the depletion of trNK cells may ameliorate renal fibrosis by affecting transglutaminase 2/syndecan-4 interactions. Aristolochic acid nephropathy (AAN) was induced in C57BL/6 mice as an experimental model of kidney fibrosis. The mice were treated with anti-asialo GM1 (ASGM1) or anti-NK1.1 antibodies to deplete NK cells. Although both ASGM1 and NK1.1 antibodies suppressed renal NKp46⁺DX5⁺ NK cells, renal NKp46⁺DX5⁻ cells were resistant to suppression by ASGM1 or NK1.1 antibodies during the development of tubulointerstitial fibrosis in the AAN-induced mouse model. Western blot analysis showed that both antibodies increased the expression of fibronectin, transglutaminase 2, and syndecan-4. These findings indicate that trNK cells played an exacerbating role in tubulointerstitial fibrosis by activating transglutaminase 2 and syndecan-4 in the AAN-induced mouse model.

Transplantation of PEGylated islets enhances therapeutic efficacy in a diabetic nonhuman primate model

Islet cell transplantation can lead to insulin independence, reduced hypoglycemia, and amelioration of diabetes complications in patients with type 1 diabetes. The systemic delivery of anti-inflammatory agents, while considered crucial to limit the early loss of islets associated with intrahepatic infusion, increases the burden of immunosuppression. In an effort to decrease the pharmaceutical load to the patient, we modified the pancreatic islet surface with long-chain poly(ethylene glycol) (PEG) to mitigate detrimental host-implant interactions. The effect of PEGylation on islet engraftment and long-term survival was examined in a robust nonhuman primate model via three paired transplants of dosages 4300, 8300, and 10 000 islet equivalents per kg body weight. A reduced immunosuppressive regimen of anti-thymocyte globulin induction plus tacrolimus in the first posttransplant month followed by maintenance with sirolimus monotherapy was employed. To limit transplant variability, two of the three pairs were closely MHC-matched recipients and received MHC-disparate PEGylated or untreated islets isolated from the same donors. Recipients of PEGylated islets exhibited significantly improved early c-peptide levels, reduced exogenous insulin requirements, and superior glycemic control, as compared to recipients of untreated islets. These results indicate that this simple islet modification procedure may improve islet engraftment and survival in the setting of reduced immunosuppression.

Effects of a novel low volume resuscitation solutions on coagulation and platelet function

Background

Novel crystalloid solutions containing polyethylene glycol polymers (PEG-20k) produce dramatic resuscitation effects but dose-dependently produce a hypocoagulative state. The objective of this study was to examine possible mechanisms of this effect. Based on previous thromboelastography data, we hypothesize the effect is largely due to platelet interactions with the polymers.

Methods

Whole citrated blood from healthy volunteers was diluted ex-vivo 10% with crystalloids and tested for coagulation and platelet function. The specific tests included prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen and von Willebrand factor (vWf) activity, thrombin generation, thromboelastography with and without platelet mapping, platelet flow cytometry, and erythrocyte sedimentation rate.

Findings

Fibrinogen and vWF activities, PT, and aPTT were not affected by PEG-20k dilutions. Thrombin activity was mildly suppressed with PEG-20k (TTP- 20%). Platelet mapping demonstrated significantly greater % inhibition of both ADP and arachidonic acid-induced platelet aggregation with PEG-20k, but direct ADP-activated gpIIa/IIIb (PAC1) and P-selectin (CD62P) binding site expression was not altered. Mild dose-dependent suppression of TEG-MA was seen with PEG-20k using platelet poor plasma. Erythrocyte Sedimentation Rates (ESR) were dramatically accelerated after dilution with 10% PEG-20k, which was competitively blocked by smaller PEG polymers, suggesting nonspecific PEG-20k cell binding effects.

Conclusions

PEG-20k creates a mild hypocoagulative state in whole blood at concentrations ≥10%, which may be due to platelet-PEG interactions at the IIb/IIIa interface with lesser effects on fibrin polymerization. This interaction may cause a functional thrombasthenia induced by nonspecific platelet surface passivation by the PEG polymer.

Biomaterials for Stem Cell Therapy for Cardiac Disease

Myocardial Infarction (MI) in cardiac disease is the result of heart muscle losses due to a wide range of factors. Cardiac muscle failure is a crucial condition that provokes life-threatening outcomes. Heretofore, regeneration therapies in MI have used stem-cell-based therapy instantly after a myocardial injury to prevent the disease process and tissue malfunction. Despite the therapeutic utility of stem-cell-based regenerative therapy, barriers to successful treatment have been addressed. In this chapter, we illustrate a variety of emerging biomaterial strategies for enhancing the function of therapeutic stem cells, such as cell surface modification to synthetically endowing stem cells with new characteristics and hydrogels with its biological and mechanical properties. These investments offer a potential accompaniment to traditional stem-cell-based therapies for enhancing the efficacy of stem cell therapy to design properly activating cardiac tissues.

Molecularly Engineered Islet Cell Clusters for Diabetes Mellitus Treatment

Pancreatic islet transplantation is a promising method for curing diabetes mellitus. We proposed in this study a molecularly engineered islet cell clusters (ICCs) that could overcome problems posed by islet transplantation circumstances and host's immune reactions. A gene containing highly releasable exendin-4, an insulinotropic protein, was delivered into single islet cells to enhance glucose sensitivity; thereafter, the cells were reaggregated into small size ICCs. Then the surface of ICCs was modified with biocompatible poly(ethylene glycol)-lipid (PEG) (C18) for preventing immune reactions. The regimen of ICCs with low doses of anti-CD154 mAb and tacrolimus could effectively maintain the normal glucose level in diabetic mice. This molecularly engineered PEG-Sp-Ex-4 ICC regimen prevented cell death in transplantation site, partly through improving the regulation of glucose metabolism and by preventing hypoxia- and immune response-induced apoptosis. Application of this remedy is also potentially far-reaching; one would be to help overcome islet supply shortage due to the limited availability of pancreas donors and reduce the immunosuppressant regimens to eliminate their adverse effects.

Concentration and chain length of polyethylene glycol in islet isolation solution: evaluation in a pancreatic islet transplantation model

To improve graft preservation and consequently reduce conservation injuries, the composition of preservation solution is of outmost importance. It was demonstrated that the colloid polyethylene glycol (PEG), used in SCOT solution, has protective effects on cell membranes and immunocamouflage properties. The aim of this study was to optimize the concentration and chain length of PEG to improve pancreatic islet preservation and outcome. In a model of murine islet allotransplantation, islets were isolated with SCOT containing various concentrations of PEG 20 kDa or 35 kDa. Better islet yield (IEQ) was obtained with SCO +PEG at 15-30 g/L versus other PEG concentrations and control CMRL-1066 + 1% BSA solution (p < 0.05). Allograft survival was better prolonged (up to 20 days) in the groups SCOT + PEG 20 kDa 10-30 g/L compared to PEG 35 kDa (less than 17.8 days) and to control solutions (less than 17.5 days). In terms of graft function recovery, the use of PEG 20 kDa 15-30 g/L induced no primary nonfunction and delayed graft function contrary to CMRL-1066 and other PEG solutions. The use of the extracellular-type solution SCOT containing PEG 20 kDa 15 g/L as colloid could be a new way to optimize graft integrity preservation and allograft outcome.

Interleukin (IL)-10 induced by CD11b(+) cells and IL-10-activated regulatory T cells play a role in immune modulation of mesenchymal stem cells in rat islet allografts

Mesenchymal stem cells (MSCs) are suggested to be immune modulators because of their therapeutic potential in transplantation. In the present study, we evaluated the therapeutic potential of autologous MSCs for preventing graft rejection after allogeneic rat islet transplantation. We assessed the ability of MSCs to elicit an antiproliferative response in alloreactive lymphocytes and tested the immunosuppressive effect of MSCs in allogeneic islet transplantation. In islet allotransplantation, injection of autologous MSCs or a subtherapeutic dose of cyclosporine A (CsA; 5 mg/kg) alone did not prolong allograft survival. However, graft survival was attained for >100 d in 33% of autologous MSC-plus-CsA-treated recipients, indicating that graft acceptance was achieved in a subgroup of allograft recipients. Splenocytes from autologous MSC-plus-CsA-treated rats exhibited a reduced mixed lymphocyte reaction (MLR)-proliferative response to donor stimulators and increased interleukin (IL)-10 release. Interestingly, after excluding host CD11b(+) cells, splenic T cells from autologous MSC-plus-CsA-treated rats did not produce IL-10 or did not inhibit proliferative responses under the same conditions. The use of autologous MSC-plus-CsA downregulated immune responses, inducing donor-specific T-cell hyporesponsiveness by reducing the production of proinflammatory cytokines and inducing antiinflammatory cytokine production, especially that of IL-10, during the early posttransplantation period. T-regulatory cells made a contribution at a later phase. In conclusion, the combined use of autologous MSCs and low-dose CsA exerted a synergistic immunosuppressive effect in an islet allograft model, suggesting a role for autologous MSCs as an immune modulator.

The synergistic effect of Tautomycetin on Cyclosporine A-mediated immunosuppression in a rodent islet allograft model

Most immunosuppressive drugs that support successful allograft survival act by inhibiting or depleting T lymphocytes. Tautomycetin (TMC) is a specific inhibitor of protein phosphatase 1, which has a role in cell-cycle control and T-cell activation and promotes T-cell-specific apoptosis. In this study, we investigated the effect on rat islet transplantation of TMC alone and in combination with cyclosporine A (CsA). TMC treatment inhibited splenocyte proliferation in mixed lymphocyte reactions (MLR) without affecting cell viability. When used alone in islet allograft recipients, TMC did not significantly increase the survival of grafted islets. However, cotreatment of TMC and subtherapeutic doses of CsA significantly prolonged islet graft survival from 5.1 d to more than 100 d (P<0.05). At 100 d, there was no evidence of specific organ toxicity, and histological analyses of grafted liver tissue revealed the presence of viable islets. CD4+ and CD8+ T-cell infiltration and interleukin (IL)-2 mRNA levels were decreased in TMC/CsA-cotreated rats, whereas IL-10 levels were increased. In addition, the number of FoxP3-expressing cells and FoxP3 mRNA levels were also increased. We suggest that CsA and TMC act synergistically to reduce the function of T-effector cells and enhance regulatory cell function in this islet allotransplantation model.

Immune tolerance induction by integrating innate and adaptive immune regulators

A diversity of immune tolerance mechanisms have evolved to protect normal tissues from immune damage. Immune regulatory cells are critical contributors to peripheral tolerance. These regulatory cells, exemplified by the CD4(+)Foxp3(+) regulatory T (Treg) cells and a recently identified population named myeloid-derived suppressor cells (MDSCs), regulate immune responses and limiting immune-mediated pathology. In a chronic inflammatory setting, such as allograft-directed immunity, there may be a dynamic "cross-talk" between the innate and adaptive immunomodulatory mechanisms for an integrated control of immune damage. CTLA4-B7-based interaction between the two branches may function as a molecular "bridge" to facilitate such "cross-talk." Understanding the interplays among Treg cells, innate suppressors, and pathogenic effector T (Teff) cells will be critical in the future to assist in the development of therapeutic strategies to enhance and synergize physiological immunosuppressive elements in the innate and adaptive immune system. Successful development of localized strategies of regulatory cell therapies could circumvent the requirement for very high number of cells and decrease the risks associated with systemic immunosuppression. To realize the potential of innate and adaptive immune regulators for the still elusive goal of immune tolerance induction, adoptive cell therapies may also need to be coupled with agents enhancing endogenous tolerance mechanisms.