Long-term survival and function of intrahepatic islet allografts in rhesus monkeys treated with humanized anti-CD154

Cationic nanoparticles-based approaches for immune tolerance induction in vivo

The development of autoimmune diseases and the rejection of transplanted organs are primarily caused by an exaggerated immune response to autoantigens or graft antigens. Achieving immune tolerance is crucial for the effective treatment of these conditions. However, traditional therapies often have limited therapeutic efficacy and can result in systemic toxic effects. The emergence of nanomedicine offers a promising avenue for addressing immune-related diseases. Among the various nanoparticle formulations, cationic nanoparticles have demonstrated significant potential in inducing immune tolerance. In this review, we provide an overview of the underlying mechanism of autoimmune disease and organ transplantation rejection. We then highlight the recent advancements and advantages of utilizing cationic nanoparticles for inducing immune tolerance in the treatment of autoimmune diseases and the prevention of transplant rejection.

The anti-CD40L monoclonal antibody AT-1501 promotes islet and kidney allograft survival and function in nonhuman primates

Prior studies of anti-CD40 ligand (CD40L)-based immunosuppression demonstrated effective prevention of islet and kidney allograft rejection in nonhuman primate models; however, clinical development was halted because of thromboembolic complications. An anti-CD40L-specific monoclonal antibody, AT-1501 (Tegoprubart), was engineered to minimize risk of thromboembolic complications by reducing binding to Fcγ receptors expressed on platelets while preserving binding to CD40L. AT-1501 was tested in both a cynomolgus macaque model of intrahepatic islet allotransplantation and a rhesus macaque model of kidney allotransplantation. AT-1501 monotherapy led to long-term graft survival in both islet and kidney transplant models, confirming its immunosuppressive potential. Furthermore, AT-1501-based regimens after islet transplant resulted in higher C-peptide, greater appetite leading to weight gain, and reduced occurrence of cytomegalovirus reactivation compared with conventional immunosuppression. These data support AT-1501 as a safe and effective agent to promote both islet and kidney allograft survival and function in nonhuman primate models, warranting further testing in clinical trials.

TNX-1500, a crystallizable fragment-modified anti-CD154 antibody, prolongs nonhuman primate cardiac allograft survival

Blockade of the CD40/CD154 T cell costimulation pathway is a promising approach to supplement or replace current clinical immunosuppression in solid organ transplantation. We evaluated the tolerability and activity of a novel humanized anti-CD154 monoclonal antibody, TNX-1500 (TNX), in a nonhuman primate heterotopic cardiac allogeneic (allo) transplant model. TNX-1500 contains a rupluzimab fragment antigen-binding region and an immunoglobin G4 crystallizable fragment region engineered to reduce binding to the crystallizable fragment gamma receptor IIa and associated risks of thrombosis. Recipients were treated for 6 months with standard-dose TNX (sTNX) monotherapy, low-dose TNX monotherapy (loTNX), or loTNX with mycophenolate mofetil (MMF) (loTNX + MMF). Results were compared with historical data using chimeric humanized 5c8 monotherapy dosed as for loTNX but discontinued at 3 months. Median survival time was similar for humanized 5c8 and both loTNX groups, but significantly longer with sTNX (>265 days) than with loTNX (99 days) or loTNX + MMF (88 days) (P < 0.05 for both comparisons against sTNX). Standard-dose TNX prevented antidonor alloantibody elaboration, inhibited chronic rejection, and was associated with a significantly reduced effector T cells/regulatory T cells ratio relative to loTNX with MMF. No thrombotic complications were observed. This study demonstrated that TNX was well tolerated, prolongs allograft survival, and prevents alloantibody production and cardiac allograft vasculopathy in a stringent preclinical nonhuman primate heart allotransplant model.

CD40-CD40L Blockade: Update on Novel Investigational Therapeutics for Transplantation

Effective immune responses require antigen presentation by major histocompatibility complexes with cognate T-cell receptor and antigen-independent costimulatory signaling for T-cell activation, proliferation, and differentiation. Among several costimulatory signals, CD40-CD40L is of special interest to the transplantation community because it plays a vital role in controlling or regulating humoral and cellular immunity. Blockade of this pathway has demonstrated inhibition of donor-reactive T-cell responses and prolonged the survival of transplanted organs. Several anti-CD154 and anti-CD40 antibodies have been used in the transplantation model and demonstrated the potential of extending allograft and xenograft rejection-free survival. The wide use of anti-CD154 antibodies was hampered because of thromboembolic complications in transplant recipients. These antibodies have been modified to overcome the thromboembolic complications by altering the antibody binding fragment (Fab) and Fc (fragment, crystallizable) receptor region for therapeutic purposes. Here, we review recent preclinical advances to target the CD40-CD40L pair in transplantation.

Implantable niche with local immunosuppression for islet allotransplantation achieves type 1 diabetes reversal in rats

Pancreatic islet transplantation efficacy for type 1 diabetes (T1D) management is limited by hypoxia-related graft attrition and need for systemic immunosuppression. To overcome these challenges, we developed the Neovascularized Implantable Cell Homing and Encapsulation (NICHE) device, which integrates direct vascularization for facile mass transfer and localized immunosuppressant delivery for islet rejection prophylaxis. Here, we investigated NICHE efficacy for allogeneic islet transplantation and long-term diabetes reversal in an immunocompetent, male rat model. We demonstrated that allogeneic islets transplanted within pre-vascularized NICHE were engrafted, revascularized, and functional, reverting diabetes in rats for over 150 days. Notably, we confirmed that localized immunosuppression prevented islet rejection without inducing toxicity or systemic immunosuppression. Moreover, for translatability efforts, we showed NICHE biocompatibility and feasibility of deployment as well as short-term allogeneic islet engraftment in an MHC-mismatched nonhuman primate model. In sum, the NICHE holds promise as a viable approach for safe and effective islet transplantation and long-term T1D management.

Linked sensitization by memory CD4+ T cells prevents costimulation blockade–induced transplantation tolerance

Dominant infectious tolerance explains how brief tolerance-inducing therapies result in lifelong tolerance to donor antigens and “linked” third-party antigens, while recipient sensitization and ensuing immunological memory prevent the successful induction of transplant tolerance. In this study, we juxtapose these 2 concepts to test whether mechanisms of dominant infectious tolerance can control a limited repertoire of memory T and B cells. We show that sensitization to a single donor antigen is sufficient to prevent stable transplant tolerance, rendering it unstable. Mechanistic studies revealed that recall antibody responses and memory CD8⁺ T cell expansion were initially controlled, but memory CD4⁺Foxp3^– T cell (Tconv) responses were not. Remarkably, naive donor-specific Tconvs at tolerance induction also acquired a resistance to tolerance, proliferating and acquiring a phenotype similar to memory Tconvs. This phenomenon of “linked sensitization” underscores the challenges of reprogramming a primed immune response toward tolerance and identifies a potential therapeutic checkpoint for synergizing with costimulation blockade to achieve transplant tolerance in the clinic.

Emerging local immunomodulatory strategies to circumvent systemic immunosuppression in cell transplantation

INTRODUCTION

Cell transplantation is a promising curative therapeutic strategy whereby impaired organ functions can be restored without the need for whole organ transplantation. A key challenge in allotransplantation is the requirement for life-long systemic immunosuppression to prevent rejection, which is associated with serious adverse effects such as increased risk of opportunistic infections and the development of neoplasms. This challenge underscores the urgent need for novel strategies to prevent graft rejection while abrogating toxicity-associated adverse events.

AREAS COVERED

We review recent advances in immunoengineering strategies for localized immunomodulation that aim to support allograft function and provide immune tolerance in a safe and effective manner.

EXPERT OPINION

Immunoengineering strategies are tailored approaches for achieving immunomodulation of the transplant microenvironment. Biomaterials can be adapted for localized and controlled release of immunomodulatory agents, decreasing the effective dose threshold and frequency of administration. The future of transplant rejection management lies in the shift from systemic to local immunomodulation with suppression of effector and activation of regulatory T cells, to promote immune tolerance.

Extended survival versus accelerated rejection of nonhuman primate islet allografts: Effect of mesenchymal stem cell source and timing

Mesenchymal stem cells (MSC) have been shown to be immunomodulatory, tissue regenerative, and graft promoting; however, several questions remain with regard to ideal MSC source and timing of administration. In this study, we utilized a rigorous preclinical model of allogeneic islet cell transplantation, incorporating reduced immune suppression and near to complete mismatch of major histocompatibility antigens between the diabetic cynomolgus monkey recipient and the islet donor, to evaluate both the graft promoting impact of MSC source, that is, derived from the islet recipient, the islet donor or an unrelated third party as well as the impact of timing. Co-transplant of MSC and islets on post-operative day 0, followed by additional IV MSC infusions in the first posttransplant month, resulted in prolongation of rejection free and overall islet survival and superior metabolic control for animals treated with recipient as compared to donor or third-party MSC. Immunological analyses demonstrated that infusion of MSC from either source did not prevent alloantibody formation to the islet or MSC donor; however, treatment with recipient MSC resulted in significant downregulation of memory T cells, decreased anti-donor T cell proliferation, and a trend toward increased Tregulatory:Tconventional ratios.

Endogenous memory T cells with donor-reactivity: early post-transplant mediators of acute graft injury in unsensitized recipients

The pretransplant presence of endogenous donor-reactive memory T cells is an established risk factor for acute rejection and poorer transplant outcomes. A major source of these memory T cells in unsensitized recipients is heterologously generated memory T cells expressing reactivity to donor allogeneic MHC molecules. Multiple clinical studies have shown that the pretransplant presence of high numbers of circulating endogenous donor-reactive memory T cells correlates with higher incidence of acute rejection and decreased graft function during the first-year post-transplant. These findings have spurred investigation in preclinical models to better understand mechanisms underlying endogenous donor-reactive memory T-cell-mediated allograft injury in unsensitized graft recipients. These studies have led to the identification of unique mechanisms underlying the activation of these memory T cells within allografts at early times after transplant. In particular, optimal activation to mediate acute allograft injury is dependent on the intensity of ischaemia-reperfusion injury. Therapeutic strategies directed at the recruitment and activation of endogenous donor-reactive memory T cells are effective in attenuating acute injury in allografts experiencing increased ischaemia-reperfusion injury in preclinical models and should be translatable to clinical transplantation.

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.

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.

Macrophages affect immune inflammation and proliferation in benign prostatic hyperplasia via androgen receptor and CD40/CD40L signaling pathway

OBJECTIVE

Considering the association of macrophage migration inhibitory factor with development of prostate diseases, this study aims to explore the effect and mechanism of macrophages (MAs) in inflammation and proliferation of benign prostate hyperplasia (BPH) cells.

METHODS

Totally 85 prostate tissues (75 from BPH patients and 10 from brain death patients) were collected for determination of biomarkers of T lymphocyte (CD4 and CD8), B lymphocyte (CD20) and MAs (CD68), as well as androgen receptor (AR) and CD40/CD40L. MAs stimulated by phorbol myristate acetate (PMA) were cultured with BPH cells (BPH-1), followed by AR inhibitor or anti-CD40 L antibody treatment. Proliferation and cell apoptosis were observed by MTT assay, colony formation assay and flow cytometer. Expressions of apoptotic related proteins and MAPK signaling pathway-related proteins were determined by qRT-PCR and Western blot.

RESULTS

BPH tissues had increased expressions of AR, CD40 and CD40 L, as well as elevated expressions of inflammation biomarkers (CD4, CD8, CD20 and CD68) in comparison to normal prostate tissues. MAs could increase the expressions of lymphocytes and inflammation biomarkers, in addition to promoting cell proliferation and inhibiting cell apoptosis. Cell proliferation and inflammation reaction could be attenuated by anti-CD40 L antibody and AR inhibitor in a concentration dependent manner through inhibiting the phosphorylation of JNK, ERK1/2 and p38.

CONCLUSION

MAs regulate AR and CD40/CD40L expression to promote the inflammation and proliferation as well as inhibiting apoptosis of BPH-1 cells through activation of the MAPK signaling pathway. This conclusion may provide a therapeutic strategy for BPH patients.

Long-term tolerance of islet allografts in nonhuman primates induced by apoptotic donor leukocytes

Immune tolerance to allografts has been pursued for decades as an important goal in transplantation. Administration of apoptotic donor splenocytes effectively induces antigen-specific tolerance to allografts in murine studies. Here we show that two peritransplant infusions of apoptotic donor leukocytes under short-term immunotherapy with antagonistic anti-CD40 antibody 2C10R4, rapamycin, soluble tumor necrosis factor receptor and anti-interleukin 6 receptor antibody induce long-term (≥1 year) tolerance to islet allografts in 5 of 5 nonsensitized, MHC class I-disparate, and one MHC class II DRB allele-matched rhesus macaques. Tolerance in our preclinical model is associated with a regulatory network, involving antigen-specific Tr1 cells exhibiting a distinct transcriptome and indirect specificity for matched MHC class II and mismatched class I peptides. Apoptotic donor leukocyte infusions warrant continued investigation as a cellular, nonchimeric and translatable method for inducing antigen-specific tolerance in transplantation.

Injection of donor apoptotic cells induces graft tolerance in mice. Here the authors combine this approach with short immunosuppressive therapy to achieve long-term tolerance to allogeneic islets and restoration of normoglycemia in diabetic nonhuman primates, and delineate cellular and molecular correlates of tolerance induction.

Transplant research in nonhuman primates to evaluate clinically relevant immune strategies in organ transplantation

Research in transplant immunology using non-human primate (NHP) species to evaluate immunologic strategies to prevent rejection and prolong allograft survival has yielded results that have translated successfully into human organ transplant patient management. Other therapies have not proceeded to human translation due to failure in NHP testing, arguably sparing humans the futility and risk of such testing. The NHP transplant models are ethically necessary for drug development in this field and provide the closest analogue to human transplant patients available. The refinement of this resource with respect to colony MHC typing, reagent and assay development, and availability to the research community has greatly enhanced knowledge about transplant immunology and drug development.

Influence of Tacrolimus on Depressive-Like Behavior in Diabetic Rats Through Brain-Derived Neurotrophic Factor Regulation in the Hippocampus

The neurotoxicity of immunosuppressive agents and diabetes mellitus are known risk factors of neurological complications in kidney transplant recipients. The aim of the present study was to investigate the influence of tacrolimus on brain-derived neurotrophic factor (BDNF), the critical protein for maintenance of neuronal functions, in the hippocampus in a diabetic condition. A diabetic rat model was established by a single streptozotocin injection (60 mg/kg). Control and diabetic rats then received daily tacrolimus (1.5 mg/kg per day) injections for 6 weeks. BDNF expression in the hippocampus was examined in the dentate gyrus (DG) and CA3 region using immunohistochemistry. There was a significant decrease of BDNF expression in the DG and CA3 region in tacrolimus-treated and diabetic rats compared with that of the control group injected with vehicle only. However, there was no difference in BDNF expression between the two experimental groups. Tacrolimus treatment in diabetic rats further decreased the BDNF expression level in the DG and CA3 region. Interestingly, mossy fiber sprouting, demonstrated by prominent punctate immunolabeling of BDNF with synaptoporin, was observed in the diabetic group treated with tacrolimus, which localized at the stratum oriens of the CA3 region. These data suggest that tacrolimus treatment or a diabetic condition decreases BDNF expression in the hippocampus, and that tacrolimus treatment in the diabetic condition further injures the CA3 region of the hippocampus. In addition to BDNF expression, decreased locomotor activity and evident depressive behavior were observed in tacrolimus-treated diabetic rats. Moreover, there were significant decreases of the mRNA levels of γ-aminobutyric acid and serotonin receptors in the diabetic hippocampus with tacrolimus treatment. This finding suggests that tacrolimus treatment may cause further psychiatric and neurological complications for patients with diabetes, and should thus be used with caution.

JAK3 inhibitor-based immunosuppression in allogeneic islet transplantation in cynomolgus monkeys

Islet transplantation is efficacious to prevent severe hypoglycemia and glycemic liability of selected patients of type 1 diabetes. However, since calcineurin inhibitor (CNI) causes β-cell and nephrotoxicity, alternative drug(s) with similar potency and safety profile to CNI will be highly desirable. Here we tested whether JAK3 inhibitor, tofacitinib could be used instead of tacrolimus in CIT07 immunosuppression regimen in cynomolgus nonhuman primate (NHP) model. Five independent streptozotocin (STZ)-induced diabetic monkeys were transplanted with MHC-mismatched allogeneic islets and three animals were further re-transplanted upon insufficient glycemic control or early islet graft rejection. After islet transplantation, blood glucose levels were quickly stabilized and maximal islet graft survival as measured by serum C-peptide concentration was >330, 98, >134, 31, or 22 days, respectively, after transplantation (median survival day; 98 days). Cellular and humoral immune responses were efficiently suppressed by JAK3 inhibitor-based immunosuppression during the follow-up periods. Although intermittent increases of the genome copy number of cynomolgus cytomegalovirus (CMV) were detected by quantitative real-time PCR analyses, serious infections or posttransplant lymphoproliferative disease (PTLD) was not found in all animals. Taken together, we have shown that JAK3 inhibitor could be used in replacement of tacrolimus in a highly translatable NHP islet transplantation model and these results suggest that JAK3 inhibitor will be potentially incorporated in human allogeneic islet transplantation.

Contemporary Strategies and Barriers to Transplantation Tolerance

The purpose of this review is to discuss immunologic tolerance as it applies to solid organ transplantation and to identify barriers that hinder the achievement of this long-term goal. First, the definition of tolerance and an introduction of mechanisms by which tolerance exists or can be achieved will be discussed. Next, a review of contemporary attempts at achieving transplant tolerance will be described. Finally, a discussion of the humoral barriers to transplantation tolerance and potential ways to overcome these barriers will be presented.

Microporous Polymer Scaffolds for the Transplantation of Embryonic Stem Cell Derived Pancreatic Progenitors to a Clinically Translatable Site for the Treatment of Type I Diabetes

Type I diabetes mellitus, which affects an estimated 1.5 million Americans, is caused by autoimmune destruction of the pancreatic beta cells that results in the need for life-long insulin therapy. Allogeneic islet transplantation for the treatment of type I diabetes is a therapy in which donor islets are infused intrahepatically, which has led to the transient reversal of diabetes. However, therapeutic limitations of allogeneic transplantation, which include a shortage of donor islets, long-term immunosuppression, and high risk of tissue rejection, have led to the investigation of embryonic or induced pluripotent stem cells as an unlimited source of functional beta-cells. Herein, we investigate the use of microporous scaffolds for their ability to promote the engraftment of stem cell derived pancreatic progenitors and their maturation toward mono-hormonal insulin producing β-cells at a clinically translatable, extrahepatic site. Initial studies demonstrated that microporous scaffolds supported cell engraftment, and their maturation to become insulin positive; however, the number of insulin positive cells and the levels of C-peptide secretion were substantially lower than what was observed with progenitor cell transplantation into the kidney capsule. The scaffolds were subsequently modified to provide a sustained release of exendin-4, which has previously been employed to promote maturation of pancreatic progenitors in vitro and has been employed to promote engraftment of transplanted islets in the peritoneal fat. Transplantation of stem cell derived pancreatic progenitors on scaffolds releasing exendin-4 led to significantly increased C-peptide production compared to scaffolds without exendin-4, with C-peptide and blood glucose levels comparable to the kidney capsule transplantation cohort. Image analysis of insulin and glucagon producing cells indicated that monohormonal insulin producing cells were significantly greater compared to glucagon producing and polyhormonal cells in scaffolds releasing exendin-4, whereas a significantly decreased percentage of insulin-producing cells were present among hormone producing cells in scaffolds without exendin-4. Collectively, a microporous scaffold, capable of localized and sustained delivery of exendin-4, enhanced the maturation and function of pluripotent stem cell derived pancreatic progenitors that were transplanted to a clinically translatable site.

Design, Synthesis, and Evaluation of Novel Immunomodulatory Small Molecules Targeting the CD40⁻CD154 Costimulatory Protein-Protein Interaction

We report the design, synthesis, and testing of novel small-molecule compounds targeting the CD40⁻CD154 (CD40L) costimulatory interaction for immunomodulatory purposes. This protein-protein interaction (PPI) is a TNF-superfamily (TNFSF) costimulatory interaction that is an important therapeutic target since it plays crucial roles in the activation of T cell responses, and there is resurgent interest in its modulation with several biologics in development. However, this interaction, just as all other PPIs, is difficult to target by small molecules. Following up on our previous work, we have now identified novel compounds such as DRI-C21091 or DRI-C21095 that show activity (IC50) in the high nanomolar to low micromolar range in the binding inhibition assay and more than thirty-fold selectivity versus other TNFSF PPIs including OX40⁻OX40L, BAFFR-BAFF, and TNF-R1-TNFα. Protein thermal shift (differential scanning fluorimetry) assays indicate CD154 and not CD40 as the binding partner. Activity has also been confirmed in cell assays and in a mouse model (alloantigen-induced T cell expansion in a draining lymph node). Our results expand the chemical space of identified small-molecule CD40⁻CD154 costimulatory inhibitors and provide lead structures that have the potential to be developed as orally bioavailable immunomodulatory therapeutics that are safer and less immunogenic than corresponding biologics.

Organ-on-Chip Recapitulates Thrombosis Induced by an anti-CD154 Monoclonal Antibody: Translational Potential of Advanced Microengineered Systems

Clinical development of Hu5c8, a monoclonal antibody against CD40L intended for treatment of autoimmune disorders, was terminated due to unexpected thrombotic complications. These life-threatening side effects were not discovered during preclinical testing due to the lack of predictive models. In the present study, we describe the development of a microengineered system lined by human endothelium perfused with human whole blood, a "Vessel-Chip." The Vessel-Chip allowed us to evaluate key parameters in thrombosis, such as endothelial activation, platelet adhesion, platelet aggregation, fibrin clot formation, and thrombin anti-thrombin complexes in the Chip-effluent in response to Hu5c8 in the presence of soluble CD40L. Importantly, the observed prothrombotic effects were not observed with Hu5c8-IgG2σ designed with an Fc domain that does not bind the FcγRIIa receptor, suggesting that this approach may have a low potential risk for thrombosis. Our results demonstrate the translational potential of Organs-on-Chips, as advanced microengineered systems to better predict human response.

Paracrine Interactions within the Pancreatic Islet Determine the Glycemic Set Point

Every animal species has a signature blood glucose level or glycemic set point. These set points are different, and the normal glycemic levels (normoglycemia) of one species would be life threatening for other species. Mouse normoglycemia can be considered diabetic for humans. The biological determinants of the glycemic set point remain unclear. Here we show that the pancreatic islet imposes its glycemic set point on the organism, making it the bona fide glucostat in the body. Moreover, and in contrast to rodent islets, glucagon input from the alpha cell to the insulin-secreting beta cell is necessary to fine-tune the distinctive human set point. These findings affect transplantation and regenerative approaches to treat diabetes because restoring normoglycemia may require more than replacing only the beta cells. Furthermore, therapeutic strategies using glucagon receptor antagonists as hypoglycemic agents need to be reassessed, as they may reset the overall glucostat in the organism.

Small-Molecule Inhibitors of the CD40-CD40L Costimulatory Protein-Protein Interaction

Costimulatory interactions are required for T cell activation and development of an effective immune response; hence, they are valuable therapeutic targets for immunomodulation. However, they, as all other protein-protein interactions, are difficult to target by small molecules. Here, we report the identification of novel small-molecule inhibitors of the CD40-CD40L interaction designed starting from the chemical space of organic dyes. For the most promising compounds such as DRI-C21045, activity (IC50) in the low micromolar range has been confirmed in cell assays including inhibition of CD40L-induced activation in NF-κB sensor cells, THP-1 myeloid cells, and primary human B cells as well as in murine allogeneic skin transplant and alloantigen-induced T cell expansion in draining lymph node experiments. Specificity versus other TNF-superfamily interactions (TNF-R1-TNF-α) and lack of cytotoxicity have also been confirmed at these concentrations. These novel compounds provide proof-of-principle evidence for the possibility of small-molecule inhibition of costimulatory protein-protein interactions, establish the structural requirements needed for efficient CD40-CD40L inhibition, and serve to guide the search for such immune therapeutics.

Comparative Evaluation of αCD40 (2C10R4) and αCD154 (5C8H1 and IDEC-131) in a Nonhuman Primate Cardiac Allotransplant Model

BACKGROUND

Specific blockade of T cell costimulation pathway is a promising immunomodulatory approach being developed to replace our current clinical immunosuppression therapies. The goal of this study is to compare results associated with 3 monoclonal antibodies directed against the CD40/CD154 T cell costimulation pathway.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients were treated with either IDEC-131 (humanized αCD154, n = 9), 5C8H1 (mouse-human chimeric αCD154, n = 5), or 2C10R4 (mouse-rhesus chimeric αCD40, n = 6) monotherapy using a consistent, comparable dosing regimen for 3 months after transplant.

RESULTS

Relative to the previously reported IDEC-131-treated allografts, median survival time (35 ± 31 days) was significantly prolonged in both 5C8H1-treated (142 ± 26, P < 0.002) and 2C10R4-treated (124 ± 37, P < 0.020) allografts. IDEC-131-treated grafts had higher cardiac allograft vasculopathy severity scores during treatment relative to either 5C8H1 (P = 0.008) or 2C10R4 (P = 0.0002). Both 5C8H1 (5 of 5 animals, P = 0.02) and 2C10R4 (6/6, P = 0.007), but not IDEC-131 (2/9), completely attenuated IgM antidonor alloantibody (alloAb) production during treatment; 5C8H1 (5/5) more consistently attenuated IgG alloAb production compared to 2C10R4 (4/6) and IDEC-131 (0/9). All evaluable explanted grafts experienced antibody-mediated rejection. Only 2C10R4-treated animals exhibited a modest, transient drop in CD20 lymphocytes from baseline at day 14 after transplant (-457 ± 152 cells/μL) compared with 5C8H1-treated animals (16 ± 25, P = 0.037), and the resurgent B cells were primarily of a naive phenotype.

CONCLUSIONS

In this model, CD154/CD40 axis blockade using IDEC-131 is an inferior immunomodulatory treatment than 5C8H1 or 2C10R4, which have similar efficacy to prolong graft survival and to delay cardiac allograft vasculopathy development and antidonor alloAb production during treatment.

Automated, High-Throughput Assays for Evaluation of Human Pancreatic Islet Function

An important challenge in pancreatic islet transplantation in association with type 1 diabetes is to define automatic high-throughput assays for evaluation of human islet function. The physiological techniques presently used are amenable to small-scale experimental samples and produce descriptive results. The postgenomic era provides an opportunity to analyze biological processes on a larger scale, but the transition to high-throughput technologies is still a challenge. As a first step to implement high-throughput assays for the study of human islet function, we have developed two methodologies: multiple automated perifusion to determine islet hormone secretion and high-throughput kinetic imaging to examine islet cellular responses. Both technologies use fully automated devices that allow performing simultaneous experiments on multiple islet preparations. Our results illustrate that these technologies can be applied to study the functional status and explore the pharmacological profiles of islet cells. These methodologies will enable functional characterization of human islet preparations before transplantation and thereby provide the basis for the establishment of predictive tests for β-cell potency.

A Simple and Cost-Effective Method for the Isolation of Islets from Nonhuman Primates

Recent advances in islet cell transplantation have led to insulin independence in a majority of islet transplant recipients. However, there exists a need to overcome the shortage of donor tissue and the necessity for lifelong immunosuppression. Preclinical studies in large animal models are necessary to evaluate the safety and efficacy of alternative approaches for clinical islet transplantation. The nonhuman primate serves as an appropriate animal model for such investigations; however, a major impediment in performing such preclinical research has been the difficulty in isolating islets of sufficient quantity and quality. The current study describes a simple and cost-effective method to isolate nonhuman primate islets to support preclinical islet transplantation research. The results of islet isolations from 54 cynomolgus monkeys and 4 baboons are reported. The pancreas was infused with Liberase HI and subjected to static digestion. The digested tissue was shaken, filtered through a mesh screen, applied to a discontinuous gradient, and centrifuged in much the same manner as with conventional rodent islet isolations. Islets were collected from the two interfaces, washed, and transplanted. Following purification, cynomolgus monkey islet isolation yields were 50,100 ± 3120 IE total or 8760 ± 420 IE/g pancreas with the percent purity and viability of 90.8 ± 0.9 and 90.7 ± 0.7, respectively. Total insulin content of the isolated islets was 405 ± 53 μg insulin with DNA content being and 976 ± 117 μg DNA, corresponding to a ratio of 0.57 μg insulin/μg DNA. STZ-induced diabetes was reversed in both mouse and nonhuman primate recipients, which possessed significant levels of c-peptide following transplantation and well-granulated islet grafts. The technique yields sufficient numbers of pure and viable islets to support preclinical research to develop improved strategies to prevent the immune destruction of the transplanted islet graft.

Adenovirus-Mediated CTLA4Ig or CD40Ig Gene Transfer Delays Pancreatic Islet Rejection in a Rat-to-Mouse Xenotransplantation Model after Systemic but Not Local Expression

Transient costimulation signal blockade of either CD28/CD80–86 interactions and/or CD40/CD154 interactions can prevent islet rejection in some models of both allo- and xenotransplantation. We have used adenoviruses coding for CTLA4Ig or CD40Ig and compared the efficacy of genetic modification of islets to systemic production through either intramuscular (IM) or intravenous (IV) injection of these vectors in a rat-to-mouse islet transplantation model. When gene transfer was performed into islets, a high level of primary nonfunction was induced. Furthermore, transduced functional grafts were rejected with the same kinetics as nontransduced islets. In contrast, IM AdCTLA4Ig and IV AdCD40Ig significantly delayed rejection (mean survival time of 54 ± 26.9 and 67.6 ± 44.9 days, respectively, vs. 24.3 ± 9.7 days for unmodified islets, p < 0.05). Combination of ex vivo AdCTLA4Ig islet transduction and IV AdCD40Ig did not improve graft survival further. In conclusion, islet graft transduction with adenoviruses coding for costimulation inhibitors resulted in local expression with low serum concentrations of CTLA4Ig or CD40Ig and was unable to protect islet xenografts from rejection. In contrast, IM or IV gene transfer resulted in high serum concentrations of these molecules and was highly efficient in prolonging xenograft survival. These results contrast with the efficacy of AdCTLA4Ig we observed in a rat islet allotransplantation model and suggest that islet xenograft rejection might be more difficult to control.

Islet Cell Transplantation: In Vivo and in Vitro Functional Assessment of Nonhuman Primate Pancreatic Islets

Transplantation of pancreatic islets of Langerhans as a therapeutic approach for treatment of type I diabetes offers an alternative to subcutaneous insulin injections. Normalization of blood glucose levels by transplanted islets may prevent the development of diabetes-related complications. Problems related to rejection, recurrence of autoimmunity, and local inflammation upon transplantation of islets into the liver need to be solved before the implementation of islet cell transplantation can be viewed as a justifiable procedure in a large cohort of patients. Islet cell isolation has been quite successful in small animals, but the translation of this approach to nonhuman primates has been less rewarding. One of the main problems encountered in nonhuman primate models is the difficulty of isolating an adequate number of functional islets for transplantation. The aim of the present study was to develop a method for isolating a sufficient number of viable islets from nonhuman primates to allow for reversal of diabetes. By implementing minor modifications in the automated method for human islet isolation we were able to obtain viable, functional islets that responded normally to glucose stimulation in vitro. These islets were also able to reverse diabetes in immunocompromised nude mice, rendered diabetic by streptozotocin. This method of islet cell isolation has enabled us to proceed with protocols of allogeneic islet cell transplantation in preclinical, nonhuman primate models.

Isolated Pancreatic Islets in Three-Dimensional Matrices are Responsive to Stimulators and Inhibitors of Angiogenesis

The formation of a new microvasculature is essential for the long-term survival and function of the islet graft. In this study we examined endothelium of isolated pancreatic islets by stimulation with growth factors, different culture conditions, and genetic modification. We also inspected the effect of immunosuppressives used in human transplantation on angiogenesis. Isolated islets were embedded in a three-dimensional fibrin or Matrigel matrix. The effect of hyperglycemia, hypoxia, and the addition of VEGF and bFGF was investigated. We exposed islets from transgenic mice expressing the VEGF gene (RIP1VEGF-A) to high glucose (16.7 mmol/L) medium and tested the immunosuppressive agents rapamycin (100 ng/ml) and FK506 (100 ng/ml). To quantify angiogenesis the percentage of sprouting islets was determined. New endothelial capillary-like structures protruded from isolated pancreatic islets. Addition of VEGF to the islets and transgenic RIP-VEGF islets showed a two- to threefold increase of sprouting islets compared to control. Hypoxic culture conditions stimulated angiogenesis, resulting in a twofold increase of capillary sprouting. Rapamycin and FK506 proved to be potent inhibitors of angiogenesis in this system, because a decrease of sprouting islets of more than 20% by both agents was observed. Isolated pancreatic islets are capable of forming new capillary structures and are susceptible to pro- and antiangiogenic stimuli.

Mitigating hypoxic stress on pancreatic islets via in situ oxygen generating biomaterial

A major obstacle in the survival and efficacy of tissue engineered transplants is inadequate oxygenation, whereby unsupportive oxygen tensions result in significant cellular dysfunction and death within the implant. In a previous report, we developed an innovative oxygen generating biomaterial, termed OxySite, to provide supportive in situ oxygenation to cells and prevent hypoxia-induced damage. Herein, we explored the capacity of this biomaterial to mitigate hypoxic stress in both rat and nonhuman primate pancreatic islets by decreasing cell death, supporting metabolic activity, sustaining aerobic metabolism, preserving glucose responsiveness, and decreasing the generation of inflammatory cytokines. Further, the impact of supplemental oxygenation on in vivo cell function was explored by the transplantation of islets previously co-cultured with OxySite into a diabetic rat model. Transplant outcomes revealed significant improvement in graft efficacy for OxySite-treated islets, when transplanted within an extrahepatic site. These results demonstrate the potency of the OxySite material to mitigate activation of detrimental hypoxia-induced pathways in islets during culture and highlights the importance of in situ oxygenation on resulting islet transplant outcomes.

Targeted deletion of Traf2 allows immunosuppression-free islet allograft survival in mice

AIMS/HYPOTHESIS

Administration of anti-CD40 ligand (CD40L) antibodies has been reported to allow long-term islet allograft survival in non-human primates without the need for exogenous immunosuppression. However, the use of anti-CD40L antibodies was associated with thromboembolic complications. Targeting downstream intracellular components shared between CD40 and other TNF family co-stimulatory molecules could bypass these complications. TNF receptor associated factor 2 (TRAF2) integrates multiple TNF receptor family signalling pathways that are critical for T cell activation and may be a central node of alloimmune responses.

METHODS

T cell-specific Traf2-deficient mice (Traf2TKO) were generated to define the role of TRAF2 in CD4⁺ T cell effector responses that mediate islet allograft rejection in vivo. In vitro allograft responses were tested using mixed lymphocyte reactions and analysis of IFN-γ and granzyme B effector molecule expression. T cell function was assessed using anti-CD3/CD28-mediated proliferation and T cell polarisation studies.

RESULTS

Traf2TKO mice exhibited permanent survival of full MHC-mismatched pancreatic islet allografts without exogenous immunosuppression. Traf2TKO CD4⁺ T cells exhibited reduced proliferation, activation and acquisition of effector function following T cell receptor stimulation; however, both Traf2TKO CD4⁺ and CD8⁺ T cells exhibited impaired alloantigen-mediated proliferation and acquisition of effector function. In polarisation studies, Traf2TKO CD4⁺ T cells preferentially converted to a T helper (Th)2 phenotype, but exhibited impaired Th17 differentiation. Without TRAF2, thymocytes exhibited dysregulated TNF-mediated induction of c-Jun N-terminal kinase (JNK) and canonical NFκB pathways. Critically, targeting TRAF2 in T cells did not impair the acute phase of CD8-dependent viral immunity. These data highlight a specific requirement for a TRAF2-NFκB and TRAF2-JNK signalling cascade in T cell activation and effector function in rejecting islet allografts.

CONCLUSION/INTERPRETATION

Targeting TRAF2 may be useful as a therapeutic approach for immunosuppression-free islet allograft survival that avoids the thromboembolic complications associated with the use of anti-CD40L antibodies.

Advances in targeting co-inhibitory and co-stimulatory pathways in transplantation settings: the Yin to the Yang of cancer immunotherapy

In the past decade, the power of harnessing T-cell co-signaling pathways has become increasingly understood to have significant clinical importance. In cancer immunotherapy, the field has concentrated on two related modalities: First, targeting cancer antigens through highly activated chimeric antigen T cells (CAR-Ts) and second, re-animating endogenous quiescent T cells through checkpoint blockade. In each of these strategies, the therapeutic goal is to re-ignite T-cell immunity, in order to eradicate tumors. In transplantation, there is also great interest in targeting T-cell co-signaling, but with the opposite goal: in this field, we seek the Yin to cancer immunotherapy's Yang, and focus on manipulating T-cell co-signaling to induce tolerance rather than activation. In this review, we discuss the major T-cell signaling pathways that are being investigated for tolerance induction, detailing preclinical studies and the path to the clinic for many of these molecules. These include blockade of co-stimulation pathways and agonism of coinhibitory pathways, in order to achieve the delicate state of balance that is transplant tolerance: a state which guarantees lifelong transplant acceptance without ongoing immunosuppression, and with preservation of protective immune responses. In the context of the clinical translation of immune tolerance strategies, we discuss the significant challenge that is embodied by the fact that targeted pathway modulators may have opposing effects on tolerance based on their impact on effector vs regulatory T-cell biology. Achieving this delicate balance holds the key to the major challenge of transplantation: lifelong control of alloreactivity while maintaining an otherwise intact immune system.

Overlooked Mechanisms in Type 1 Diabetes Etiology: How Unique Costimulatory Molecules Contribute to Diabetogenesis

Type 1 Diabetes (T1D) develops when immune cells invade the pancreatic islets resulting in loss of insulin production in beta cells. T cells have been proven to be central players in that process. What is surprising, however, is that classic mechanisms of tolerance cannot explain diabetogenesis; alternate mechanisms must now be considered. T cell receptor (TCR) revision is the process whereby T cells in the periphery alter TCR expression, outside the safety-net of thymic selection pressures. This process results in an expanded T cell repertoire, capable of responding to a universe of pathogens, but limitations are that increased risk for autoimmune disease development occurs. Classic T cell costimulators including the CD28 family have long been thought to be the major drivers for full T cell activation. In actuality, CD28 and its family member counterparts, ICOS and CTLA-4, all drive regulatory responses. Inflammation is driven by CD40, not CD28. CD40 as a costimulus has been largely overlooked. When naïve T cells interact with antigen presenting cell CD154, the major ligand for CD40, is induced. This creates a milieu for T cell (CD40)-T cell (CD154) interaction, leading to inflammation. Finally, defined pathogenic effector cells including TH40 (CD4⁺CD40⁺) cells can express FOXP3 but are not Tregs. The cells loose FOXP3 to become pathogenic effector cells. Each of these mechanisms creates novel options to better understand diabetogenesis and create new therapeutic targets for T1D.

Safe use of anti-CD154 monoclonal antibody in pig islet xenotransplantation in monkeys

Anti-CD154mAb is a powerful co-stimulation blockade agent that is efficacious in preventing rejection, even in xenogeneic settings. It has been used in the majority of successful long-term pig-to-non-human primate islet transplantation models. However, its clinical use was halted as a result of thromboembolic complications that were also observed in preclinical and clinical organ transplantation models. An anti-CD154mAb was administered to 14 streptozotocin-induced diabetic cynomolgus monkey recipients of porcine islets, some of which received the agent for many months. Monkeys were monitored for complications, and blood monitoring was carried out frequently. After euthanasia, multiple biopsies of all organs were examined for histological features of thromboembolism. Anti-CD154mAb prevented rejection of genetically engineered pig islets in all monkeys. No significant complications were attributable specifically to anti-CD154mAb. There was no evidence of thromboembolism in multiple histological sections from all major organs, including the brain. Our data suggest that in diabetic monkeys with pig islet grafts, anti-CD154mAb would appear to be an effective and safe therapy, and is not associated with thromboembolic complications.

Nonhuman primate models of transplant tolerance: closer to the holy grail

PURPOSE OF REVIEW

Transplantation tolerance, successful acceptance of an organ without the perils of immunosuppression, has been a central goal of transplant research. Many strategies to achieve this tolerance have been examined over the past three decades, culminating in several human trials of transplant tolerance. This progression from the 'benchtop to the clinic' has depended on the successful implementation of these tolerance strategies in nonhuman primates. This review will examine the described methods of transplant tolerance induction in nonhuman primates.

RECENT FINDINGS

Although costimulatory blockade and mixed chimerism have an established record of achieving transplant tolerance in nonhuman primates, some of the most innovative recent techniques of tolerance induction have relied on cellular transfer. This review will fully examine the role of regulatory T-cell transfer and the use of mesenchymal stem/stromal cells to promote tolerance of organ allografts in nonhuman primates.

SUMMARY

Use of translational nonhuman primate transplant models is a vital intermediate step to advance new approaches of transplant tolerance induction from the lab to the clinic. This review will explore numerous techniques of tolerance induction that have been piloted in primates, including depletional techniques, induction of mixed hematopoietic chimerism, costimulation blockade, and adoptive transfer of tolerogenic cell populations.

Isolation of Pancreatic Islets from Nonhuman Primates

Nonhuman primates (NHP) constitute a highly relevant pre-clinical animal model to develop strategies for beta cell replacement. The close phylogenetic and immunologic relationship between NHP and humans results in cross-reactivity of various biological agents with NHP cells, as well as a very similar cytoarchitecture between islets from human and NHP that is strikingly different from that observed in rodent islets. The composition and location of endocrine cells in human or NHP islets, randomly distributed and associated with blood vessels, have functional consequences and a predisposition for paracrine interactions. Furthermore, translation of approaches that proved successful in rodent models to the clinic has been limited. Consequently, data collected from NHP studies can form the basis for an IND submission to the FDA. This chapter describes in detail the key aspects for isolation of islets from NHP, from organ procurement up to assessment of islet function, comparing and emphasizing the similarities between isolation procedures for human and NHP islets.

Update on CD40 and CD154 blockade in transplant models

Generation of an effective immune response against foreign antigens requires two distinct molecular signals: a primary signal provided by the binding of antigen-specific T-cell receptor to peptide-MHC on antigen-presenting cells and a secondary signal delivered via the engagement of costimulatory molecules. Among various costimulatory signaling pathways, the interactions between CD40 and its ligand CD154 have been extensively investigated given their essential roles in the modulation of adaptive immunity. Here, we review current understanding of the role CD40/CD154 costimulation pathway has in alloimmunity, and summarize recent mechanistic and preclinical advances in the evaluation of candidate therapeutic approaches to target this receptor-ligand pair in transplantation.

Differential sensitivity of regulatory and effector T cells to cell death: a prerequisite for transplant tolerance

Despite significant progress achieved in transplantation, immunosuppressive therapies currently used to prevent graft rejection are still endowed with severe side effects impairing their efficiency over the long term. Thus, the development of graft-specific, non-toxic innovative therapeutic strategies has become a major challenge, the goal being to selectively target alloreactive effector T cells while sparing CD4⁺Foxp3⁺ regulatory T cells (Tregs) to promote operational tolerance. Various approaches, notably the one based on monoclonal antibodies or fusion proteins directed against the TCR/CD3 complex, TCR coreceptors, or costimulatory molecules, have been proposed to reduce the alloreactive T cell pool, which is an essential prerequisite to create a therapeutic window allowing Tregs to induce and maintain allograft tolerance. In this mini review, we focus on the differential sensitivity of Tregs and effector T cells to the depleting and inhibitory effect of these immunotherapies, with a particular emphasis on CD3-specific antibodies that beyond their immunosuppressive effect, also express potent tolerogenic capacities.

Pig-to-baboon heterotopic heart transplantation--exploratory preliminary experience with pigs transgenic for human thrombomodulin and comparison of three costimulation blockade-based regimens

BACKGROUND

Three costimulation blockade-based regimens have been explored after transplantation of hearts from pigs of varying genetic backgrounds to determine whether CTLA4-Ig (abatacept) or anti-CD40mAb+CTLA4-Ig (belatacept) can successfully replace anti-CD154mAb.

METHODS

All pigs were on an α1,3-galactosyltransferase gene-knockout/CD46 transgenic (GTKO.CD46) background. Hearts transplanted into Group A baboons (n=4) expressed additional CD55, and those into Group B (n=3) expressed human thrombomodulin (TBM). Immunosuppression included anti-thymocyte globulin with anti-CD154mAb (Regimen 1: n=2) or abatacept (Regimen 2: n=2) or anti-CD40mAb+belatacept (Regimen 3: n=2). Regimens 1 and 2 included induction anti-CD20mAb and continuous heparin. One further baboon in Group B (B16311) received a modified Regimen 1. Baboons were followed by clinical/laboratory monitoring of immune/coagulation parameters. At biopsy, graft failure, or euthanasia, the graft was examined by microscopy.

RESULTS

Group A baboons survived 15 to 33 days, whereas Group B survived 52, 99, and 130 days, respectively. Thrombocytopenia and reduction in fibrinogen occurred within 21 days in Group A, suggesting thrombotic microangiopathy (TM), confirmed by histopathology. In Group B, with follow-up for >4 m, areas of myofiber degeneration and scarring were seen in two hearts at necropsy. A T-cell response was documented only in baboons receiving Regimen 2.

CONCLUSIONS

The combination of anti-CD40mAb+belatacept proved effective in preventing a T-cell response. The expression of TBM prevented thrombocytopenia and may possibly delay the development of TM and/or consumptive coagulopathy.

Targeting the adaptive immune system: new strategies in the treatment of atherosclerosis

Atherosclerosis is a lipid-driven chronic inflammatory disease of the arterial wall. Current treatment of atherosclerosis is focused on limiting its risk factors, such as hyperlipidemia or hypertension. However, treatments that target the inflammatory nature of atherosclerosis are still under development. Discovery of novel targets involved in the inflammation of the arterial wall creates opportunities to design new therapeutics that successfully modulate atherosclerosis. Here, we review drug targets that have proven to play pivotal roles in the adaptive immune system in atherosclerosis, and we discuss their potential as novel therapeutics.

Initial in vivo experience of pig artery patch transplantation in baboons using mutant MHC (CIITA-DN) pigs

BACKGROUND

In the pig-to-nonimmunosuppressed baboon artery patch model, a graft from an α1,3-galactosyltransferase gene-knockout pig transgenic for human CD46 (GTKO/CD46) induces a significant adaptive immune response (elicited anti-pig antibody response, increase in T cell proliferation on MLR, cellular infiltration of the graft), which is effectively prevented by anti-CD154mAb-based therapy.

METHODS

As anti-CD154mAb is currently not clinically applicable, we evaluated whether it could be replaced by CD28/B7 pathway blockade or by blockade of both pathways (using belatacept + anti-CD40mAb [2C10R4]). We further investigated whether a patch from a GTKO/CD46 pig with a mutant human MHC class II transactivator (CIITA-DN) gene would allow reduction in the immunosuppressive therapy administered.

RESULTS

When grafts from GTKO/CD46 pigs were transplanted with blockade of both pathways, a minimal or insignificant adaptive response was documented. When a GTKO/CD46/CIITA-DN graft was transplanted, but no immunosuppressive therapy was administered, a marked adaptive response was documented. In the presence of CD28/B7 pathway blockade (abatacept or belatacept), there was a weak adaptive response that was diminished when compared with that to a GTKO/CD46 graft. Blockade of both pathways prevented an adaptive response.

CONCLUSION

Although expression of the mutant MHC CIITA-DN gene was associated with a reduced adaptive immune response when immunosuppressive therapy was inadequate, when blockade of both the CD40/CD154 and CD28/B7 pathways was present, the response even to a GTKO/CD46 graft was suppressed. This was confirmed after GTKO/CD46 heart transplantation in baboons.

Taming inflammation by targeting cytokine signaling: new perspectives in the induction of transplantation tolerance

Transplantation tolerance remains an elusive goal, partly due to limitations in our understanding of the interplay between inflammatory mediators and their role in the activation and regulation of T lymphocytes. Although multiple mechanisms acting both centrally and peripherally are responsible for tolerance induction, the signaling pathways leading to activation or regulation of adaptive immunity are often complex, branched, redundant and modulated by the microenvironment's inflammatory milieu. Accumulating evidence clearly indicates that inflammatory cytokines limit the tolerogenic potential of immunomodulatory protocols by supporting priming of the immune system and counteracting regulatory mechanisms, ultimately promoting rejection. In this review, we summarize recent progress in the development of novel therapeutics to manipulate this inflammatory environment and achievements in targeted inhibition of inflammatory cytokine signaling. Ultimately, robust transplant tolerance induction will probably require a multifaceted, holistic approach that integrates the various mechanisms of tolerance induction, incorporates the dynamic alterations in costimulatory requirements of alloreactive T cells, while maintaining endogenous mechanisms of immune regulation.

Implementation of a simplified method of islet isolation for allogeneic islet transplantation in cynomolgus monkeys

OBJECTIVES

The present study describes a simple and cost-effective islet isolation procedure. Using this method, allogeneic islets reverse diabetes in cynomolgus monkeys.

METHODS

Pancreatic tissue from 11 cynomolgus monkeys were digested, collected, and purified using a simplified method. Islet quantification, purity, viability, and glucose static incubation were conducted immediately after isolation. Five streptozotocin-induced monkeys with diabetes were transplanted intrahepatically, and liver biopsies from 3 of these monkeys were taken at different time points for histologic study.

RESULTS

The mean (SD) of viability, purity, and static glucose incubation stimulation index were 94.4% (2.3%), 91.8% (3.4%), and 2.6 (1.7), respectively. Monkeys who received a mean (SD) dose of 19,968 (2273) islet equivalent per kilogram (n = 4) from 2 to 3 donors who achieved prolonged normoglycemia (57-232 days), whereas the single monkey who received an islet dose of 8000 islet equivalent per kilogram did not experience diabetes reversal. Immunohistochemical assessment of the liver biopsies taken from the monkeys with normoglycemia revealed an insulin- and glucagon-positive islet graft for up to 6 months with minimal peri-islet inflammatory infiltration.

CONCLUSIONS

This study demonstrates that cynomolgus monkey islets can be successfully and efficiently harvested using a simple isolation method, and these islets can restore normoglycemia in monkeys with diabetes.

Tolerance--is it worth it?

We are entering an exciting time in the study of immunologic tolerance. Several cellular and molecular strategies have been developed that show promise in nonhuman transplant models and these approaches are just now appearing in clinical trials. Tolerance strategies that prevent immune rejection and obviate the need for immunosuppressive medications (with inherent risk of cancer, infection, and organ toxicity) would improve both graft and patient survival. Each tolerance protocol brings its own set of associated risks. As the results of these trials become available, we must continue to evaluate their successes and failures. The balance of these outcomes will help us answer the question: "Tolerance-Is it worth it?"

Practical and critical instruction for nonhuman primate diabetic models

Diabetes mellitus, a disease of metabolic dysregulation, is characterized by inappropriate hyperglycemia resulting from progressive loss of insulin secretion or action. The potential of nonhuman primate (NHP) models in diabetes research has been well understood. NHPs have long been regarded as the "gold standard" for preclinical studies. However, there are persistent, severe obstacles to the development and application of these models. At present, a consensus for standardized strategies of diabetic induction has not been achieved. The different modeling methods of diabetes has led to various characterizations of the pathology of the disease; however, there are deficiencies of systemic evaluation programs for nonhuman primate diabetes models. In this scenario, experimental systemic programs provide the highly required guidelines for NHP diabetic models. Moreover, given the expensive and relatively small population of primates and the fatal diabetic complications, it is imperative to carefully manage the care and use of these animals in biomedical research studies. This article briefly reviews the technical and managerial aspects of NHP diabetes models providing practical and critical instruction on housing and care, routine management, development strategy, modeling diagnosis, evaluation, and disease control, as well as guidelines for model selection for various purposes. The present article sought to provide guidelines for NHP models of diabetes in their development and application. It is not intended to outline mandatory requirements for clinical accreditation.

Nonhuman primate models of type 1 diabetes mellitus for islet transplantation

Islet transplantation is an attractive treatment of type 1 diabetes mellitus (T1DM). Animal models of diabetes mellitus (DM) contribute a lot to the experimental studies of islet transplantation and to evaluations of isolated islet grafts for future clinical applications. Diabetic nonhuman primates (NHPs) represent the suitable models of DMs to better evaluate the effectiveness of islet transplantation, to assess new strategies for controlling blood glucose (BG), relieving immune rejection, or prolonging islet survival, and eventually to translate the preclinical data into tangible clinical practice. This review introduces some NHP models of DM, clarifies why and how the models should be used, and elucidates the usefulness and limitations of the models in islet transplantation.

Long-term functions of encapsulated islets grafted in nonhuman primates without immunosuppression

BACKGROUND

Long-term survival and functions of encapsulated islet grafts need to be evaluated in the absence of immunosuppression. The present study aimed to assess the viability and functions of macroencapsulated islets grafted in nonhuman primates without immunosuppression for 1 year.

METHODS

Islet transplantations were performed in partially pancreatectomized rhesus monkeys (two autologous and four allogenic) without immunosuppression using immunoisolatory devices. Macroencapsulated islets were implanted subcutaneously (5000-8000 IEQ/device) at two sites (left thigh and interscapular region) and were explanted at 2, 6, and 12 months after implantation. Staining for viability and apoptosis, in vivo and in vitro glucose-stimulated insulin release, expression of insulin and glucagon genes, and histopathologic examination of the device were used to assess engraftment potential, viability, and functions of islets. Animals were regularly monitored for dietary intake, body weight, and fasting blood glucose levels after islet transplantation.

RESULTS

Devices explanted showed vascularization at the end of 2, 6, and 12 months with occasional lymphocytes and minimal fibrosis outside the device. Flow cytometric analysis revealed 97.9%±1.5% and 94.3%±5.71% viable β cells in interscapular site and thigh in autologous recipients and 85.6%±4.01% (interscapular site) and 74.1%±12.05% (thigh) viable β cells in allogenic islet recipients. In vivo glucose challenge test revealed significantly increased glucose-stimulated insulin release (P=0.028) in the left thigh with implant (17.58±3.13 mU/L) compared with the thigh without implant (9.86±1.063 mU/L). Insulin and glucagon gene expression was evident in islets recovered from explanted device.

CONCLUSIONS

These results indicate that subcutaneous implantation of macroencapsulated islets is minimally invasive and has potential for transplantation without immunosuppression.