Allogeneic Islet Graft Survival Research Articles

Immunomodulation with SA-FasL-Engineered Microgels Achieves Long-Term Survival of Allogeneic Islet Grafts

Introduction and Objective Allogenic islet transplantation has shown efficacy in the clinic for the treatment of type 1 diabetes. However, sustained survival of allogeneic islet grafts requires chronic immunosuppression that has significant adverse effects. T effector (Teff) cells recognizing and responding to allograft antigens are the major culprit of graft rejection. Upon activation, Teff cells upregulate Fas death receptor on their surface and become sensitive to FasL-mediated apoptosis. Fas pathway, therefore, presents an important target for immunomodulation to block alloreactive responses with significant therapeutic potential. Herein, we assessed the efficacy of PEG microgels engineered with a novel form of FasL chimeric with a modified form of core streptavidin, SA-FasL, in achieving sustained survival of allogeneic islet grafts in the absence of chronic immunosuppression. Materials and Methods Microgels presenting biotin on their surface were produced by reacting biotin-PEG-thiol with a maleimide-terminated 4-arm poly(ethylene) glycol macromer, and generating 200 μm diameter microgels crosslinked with dithiothreitol. Biotinylated microgels were engineered with SA-FasL (1 μg/103 microgels) taking the advantage of the high affinity interaction between biotin and streptavidin. The apoptotic activity of SA-FasL-engineered microgels was tested on mouse A20 B cell lymphocytes in vitro. The immunomodulatory function of microgels for the prevention of graft rejection was tested by mixing ~500 BALB/c naïve islets with 1000 SA-FasL-engineered microgels and transplanting under the kidney capsule of streptozotocin-induced diabetic C57BL/6 recipients. A group of recipients were also treated transiently with rapamycin (0.2 mg/kg daily for 15 days starting the day of transplantation). Results and Discussion Biotin-PEG microgels were efficiently coupled with SA-FasL, and showed a dose-dependent apoptotic activity in A20 cells. Co-transplantation of SA-FasL-engineered microgels with naïve islets led to prolonged survival of grafts as compared with the control group (islets + unmodified microgels) with 20% surviving for a 200-day observation period. Transient use of low dose rapamycin, enhanced survival to > 90% of the grafts. In marked contrast, only 20% of islets co-transplanted with PEG microgels, and short-course rapamycin, survived long-term. Importantly, CD4+CD25+FoxP3+ Treg cells were required for graft survival as depletion of this cell population on day 50 post-transplantation resulted in prompt rejection. Conclusion These results provide strong proof-of-efficacy and feasibility for the use of SA-FasL-engineered microgels as an off-the-shelf product for the modulation of alloreactive responses with significant therapeutic potential. Funded in part by NIH (grants R21EB020107, R21AI113348, 185 R56AI121281, and F30AR069472) and the Juvenile Diabetes Research Foundation (2-SRA-186 2014-287-Q-R).

Local immunomodulation Fas ligand-engineered biomaterials achieves allogeneic islet graft acceptance.

Islet transplantation is a promising therapy for type 1 diabetes. However, chronic immunosuppression to control rejection of allogeneic islets induces morbidities and impairs islet function. T-effector cells are responsible for islet allograft rejection and express Fas death receptor following activation, becoming sensitive to Fas-mediated apoptosis. Here, we report that localized immunomodulation using microgels presenting an apoptotic form of Fas ligand (SA-FasL) results in prolonged survival of allogeneic islet grafts in diabetic mice. A short course of rapamycin treatment boosted the immunomodulatory efficacy of SA-FasL-microgels, resulting in acceptance and function of allografts over 200 days. Survivors generated normal systemic responses to donor antigens, implying immune privilege of the graft, and had increased CD4+CD25+FoxP3+ T-regulatory cells in the graft and draining lymph nodes. Deletion of T-regulatory cells resulted in acute rejection of established islet allografts. This localized immunomodulatory biomaterial-enabled approach may provide an alternative to chronic immunosuppression for clinical islet transplantation.

PD-L1-engineered pancreatic islet grafts overcome rejection in allogeneic recipients

Abstract The use of chronic immunosuppression is a major hurdle for clinical islet transplantation as a curative modality for the treatment of type 1 diabetes. T effector cells (Teffs) are a main culprit of allograft rejection, and their pathogenic response is kept in check by CD4+CD25+FoxP3+ T regulatory cells (Tregs). The PD-1/PD-L1 immune checkpoint pathway plays an important role in the Teff/Treg balance with demonstrated clinical efficacy in cancer immunotherapy. This study was designed to assess the immunoregulatory function of PD-L1 in preventing allogeneic islet graft rejection. A chimeric protein (SA-PD-L1) containing the extracellular portion of PD-L1 fused to a modified form of core streptavidin was generated. SA-PD-L1 protein was expressed in insect cells and purified. The protein was functional as it enhanced TGF-beta-induced conversion of Teffs into Tregs and suppressed the proliferation of Teffs in response to alloantigens. Importantly, SA-PD-L1 was transiently displayed on the surface of biotinylated islets, and such engineered islets survived for over 100 days in allogeneic recipients treated with a short course (15 days) of low dose rapamycin. In marked contrast, unmodified islets under the same rapamycin regimen were rejected within 20 days. SA-PD-L1-engineered islets without rapamycin, although showing prolonged survival, were eventually rejected within 40 days. These results provide strong proof-of-efficacy and feasibility for the use of SA-PD-L1 protein as an immunomodulator to promote allogeneic islet graft survival in the absence of continued immunosuppression.

Control of alloreactivity using transient expression of a monoclonal antibody directed chimeric antigen receptor in conventional and regulatory T cells

Abstract The genetic modification of T cells offers many promising cellular therapies, but little known about how the transient targeting of T cell or T cell subsets such as CD4+CD25+FoxP3+ regulatory cells (Treg) could be used to control alloreactivity. We used the expression of a chimeric antigen receptor that recognizes labeled therapeutic monoclonal antibodies, to control T cell activation in vivo. By specifying the location of activation of donor T cells during hematopoietic cell, we modulated graft-versus-host disease and anti-leukemia effects. We also controlled the activation of Treg cells which remain immunoregulatory. When recipient Treg are targeted to activate in response to MHC Class I mismatch, we observed significantly prolonged allogeneic islet graft survival in an antigen-specific manner, as secondary skin grafts were specifically protected against rejection. The transient genetic modification of T and Treg can have lasting effects on the immune system and could be used therapeutically to regulate alloreactivity.

The Use of Monoclonal Antibody Directed Chimeric Antigen Receptors to Facilitate Conventional T Cell and Treg Control of GvHD and Tissue Tolerance in Murine Models

INTRODUCTIONRegulatory T cells (Treg) modulate allograft immune responses and Treg-based cellular therapies can be used for prevention of graft-versus-host disease (GvHD) following hematopoietic cell transplantation and for prevention of allograft rejection following tissue or organ transplantation. Treg adoptive transfer has limitations including that Treg do not necessarily home to sites where they are needed and can become inactivated in inflammatory milieus.METHODSWe used new technologies of T cell engineering to force the expression of a chimeric antigen receptor on T cells and Treg that recognizes labeled therapeutic monoclonal antibodies (mabCAR), allowing for precise control of their localization in vivo. The mabCAR recognizes fluorescein isothiocyanate (FITC) through a FITC-specific single-chain variable fragment fused to a CD28 and TCRζ costimulatory domain. Any monoclonal antibody (mab) coupled to FITC within its Fc domain can be recognized. We tested this approach with T cells and Treg to ameliorate GvHD and induce tolerance to pancreatic islet grafts.RESULTSWe first tested our mabCAR construct in conventional T cells (Tcon) which when transfected and stimulated with a FITC-mab become activated and expressed higher levels of CD44 (p=0.0003), CD25 (p=0.009) and produced more IFNγ (p=0.04). To test if mabCAR transient transfection alters Tcon homing after adoptive transfer, we injected luc+ mabCAR Tcon directed against MAdCAM1 (a gut and lymph node endothelial integrin) or SDF1 (a chemokine mainly expressed in the bone marrow) into allogeneic hosts. MAdCAM1-directed Tcon mainly homed to the gut and lymph nodes, while SDF1-directed Tcon homed to bones and spleen. SDF1-directed Tcon induced a milder GvHD (p<0.001), demonstrating that cell homing impacts GvHD severity.We then tested mabCAR Treg ability to maintain their suppressive activity in vitro and in vivo. We found that mabCAR transiently transfected into Treg have increased ability to proliferate in response to anti-CD3/CD28 stimulatory beads (p<0.01) and highly suppress Tcon proliferation when co-cultured with allogeneic irradiated splenocytes. We injected MAdCAM1 directed Treg in an allogeneic GvHD model and these mabCAR Treg prolonged survival (p=0.03), improved GvHD score (p<0.001) and mouse weight profile (p<0.001), thus demonstrating that mabCAR Treg retain regulatory functions.Finally, we tested if mabCAR Treg could induce tolerance to allogeneic pancreatic islet grafts in sublethally irradiated hosts. Luc+gfp+ mabCAR Treg homed and expanded over time (p<0.05) to the site of the allogeneic islet grafts (right kidney capsule) when FITC-anti-allogeneic MHC-I mab directed the Treg as compared to isotype mab controls (see figure). Allo-MHC-I directed mabCAR-Treg prolonged allogeneic islet graft survival in comparison to isotype-mabCAR Treg (p=0.002) allowing for production of higher insulin levels. To assess if allo-MHC-I Treg promoted antigen-specific tolerance, we performed secondary skin graft transplantation. We found that mice which received MHC-I Treg showed a significant delay in the rejection of skin grafts from mice with the same MHC mismatch as the previous islet-allografts in comparison to third-party skin grafts (p=0.02) offering strong evidence that CAR-Treg could be used to enhance antigen-specific graft protection.CONCLUSIONMabCAR expression can be used to control immune cell homing after transfer in different models according to localizing mab availability. We believe that the mabCAR approach may represent a new tool for optimizing cellular therapies to modulate GvHD and for inducing tolerance in islet and organ transplantation. [Display omitted] DisclosuresPierini:Stanford University: Patents & Royalties. Iliopoulou:Stanford University: Patents & Royalties. Negrin:Stanford University: Patents & Royalties. Kim:Stanford University: Patents & Royalties. Meyer:Stanford University: Patents & Royalties.

COMP-Ang1 promotes long-term survival of allogeneic islet grafts in a bioinert perforated chamber by inhibiting inflammation via inhibition of the TLR4 signaling pathway.

To evaluate the effects of cartilage oligomeric matrix protein (COMP)- angiopoietin-1 (Ang1) on allogeneic islet graft survival in a bioinert perforated chamber. COMP-Ang1 treatment significantly decreased lipopolysaccharide-induced cell apoptosis and islet-related lymph node cell proliferation (both P<0.01). Tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 levels in the chamber exudate were significantly lower in the COMP-Ang1+chamber group than in the chamber group (all P<0.05), as were the protein expression levels. COMP-Ang1 significantly inhibited the expression of Toll-like receptor 4 (TLR4) in cultured islets. Finally, full COMP-Ang1 treatment resulted in the longest survival time among the treatment groups. Combined use of the bioinert perforated chamber with COMP-Ang1 is an effective strategy for improving islet allograft survival.

Pilot Study Evaluating Regulatory T Cell–Promoting Immunosuppression and Nonimmunogenic Donor Antigen Delivery in a Nonhuman Primate Islet Allotransplantation Model

The full potential of islet transplantation will only be realized through the development of tolerogenic regimens that obviate the need for maintenance immunosuppression. Here, we report an immunotherapy regimen that combines 1-ethyl-3-(3'-dimethylaminopropyl)-carbodiimide (ECDI)-treated donor lymphoid cell infusion (ECDI-DLI) with thymoglobulin, anti-interleukin-6 receptor antibody and rapamycin to achieve prolonged allogeneic islet graft survival in a nonhuman primate (NHP) model. Prolonged graft survival is associated with Treg expansion, donor-specific T cell hyporesponsiveness and a transient absence of donor-specific alloantibody production during the period of graft survival. This regimen shows promise for clinical translation.

Enhancement of islet engraftment and achievement of long-term islet allograft survival by Toll-like receptor 4 blockade.

Toll-like receptors are key players in sterile inflammation phenomena and can link the innate and adaptive immune systems by enhancing graft immunogenicity. They are also considered mediators of types 1 and 2 diabetes development. The aim of the present study was to assess the role of Toll-like receptor-4 (TLR4) in mediating the inflammatory and immune responses to pancreatic islets, thereby promoting inflammatory destruction and immune rejection of islet grafts. Experiments were conducted in murine and human in vitro systems and in vivo murine islet transplant models, using species-specific anti-TLR4 monoclonal antibodies. In vitro, mixed lymphocyte-islet reaction experiments were performed to assess T-cell activation and proliferation. In vivo, both a syngeneic (B6-to-B6) marginal mass islet transplant model to assess the impact of TLR4 blockade on islet engraftment and an allogeneic (DBA1-to-B6) model were used. In vitro TLR4 blockade decreased lipopolysaccharide-mediated β-cell apoptosis and T-cell activation and proliferation against allogeneic islets. In vivo, TLR4 blockade resulted in significantly better syngeneic marginal mass islet engraftment and in indefinite allogeneic islet graft survival. Tolerance was not observed because donor-specific skin graft rechallenge in nonrejecting animals resulted in rejection of both skin and islets, but without accelerated rejection as compared to naive animals. Taken together, our data indicate that TLR4 blockade leads to a significant improvement of syngeneic islet engraftment and of allogeneic islet graft survival. A mechanism of graft accommodation with concurrent inhibition of donor-specific immune memory is likely to be involved.

Long-Term Allogeneic Islet Graft Survival in Prevascularized Subcutaneous Sites Without Immunosuppressive Treatment

Establishment of noninvasive and efficient islet transplantation site together with the avoidance of immunosuppressive drugs for islet engraftment is currently the two major tasks for islet transplantation approach to treat patients with type 1 diabetes. Here, we proposed a method to achieve long-term allogeneic islet graft function without immunosuppression after transplantation in subcutaneous sites. Two agarose rods with basic fibroblast growth factor and heparin were implanted for 1 week in dorsal subcutaneous sites in diabetic rats. After rod removal, 1500 islets were transplanted into the prevascularized pockets. Islets transplanted in prevascularized but not nontreated subcutaneous sites rapidly reverted hyperglycemia in all streptozotocin-induced diabetic rats. In contrast to transient normalization of blood glucose when allogeneic islets were transplanted into liver, allogeneic islets transplanted into this prevascularized subcutaneous site demonstrated long-term graft survival and function in all three rat strain combinations (Fisher 344 to ACI, Lewis to ACI and Fisher 344 to Wistar), evidenced by nonfasting blood glucose level, plasma insulin concentration, intraperitoneal glucose tolerance test and immunohistochemistry. These results indicated that a subcutaneous site prevascularized by this method is potentially a suitable site for successful allogeneic islet transplantation without immunosuppression.

Short-Term Treatment of VCAM-1-Targeting Antibody Induces Immunological Tolerance Against Allogeneic Islet Grafts

Background: Blocking adhesion domain of VCAM-1 prevents trafficking of immune cells into the inflammatory sites, and thereby prolongs longterm survival of allogeneic islet grafts in mice. In this study, we developed novel antibody targeting the sixth non-adhesive immunoglobulin-like domain of VCAM-1 and evaluated its efficacy with allogeneic-islet transplantation model. Methods: Chimeric rabbit/human VCAM-1 antibody (anti-VCAM-1-D6) targeting Ig-like domain six of VCAM-1 was generated using phage display technology. Balb/c islets were transplanted underneath of the kidney capsule of diabetic C57BL/6 mouse with the transient anti-VCAM-1-D6 (100ug/day on day -1, 0,1,2,3,4,5,6,7 after transplantation) treatment. Antigen-specific tolerance induction was confirmed by second-party transplantation of Balb/c islets or tail skin. Results: Short-term treatment of anti-VCAM-1-D6 antibody led to the long-term survival of islet allografts in 5 out of 5 mice. Donor-specific-IL-2, IFN-r, Granzyme B- secreting cell population significantly decreased in VACM-1-D6 treated-mouse in ELISPOT analysis. In the grafts, peri-islet infiltrates of leukocytes were observed with intact insulin-positive beta cells in long-term survived mice. Importantly, secondary-islet allograft, but not secondary-skin graft, was survived without evident graft rejection for more than 80 days, meaning tissue-specific tolerance was induced by the short-term treatment of anti-VCAM-1 antibody. Conclusion: Developing VCAM-1 targeting antibody may be a promising therapeutic modality in inducing antigen-specific tolerance in allogeneic islet transplantation.

Interleukin-21 Is Critically Required in Autoimmune and Allogeneic Responses to Islet Tissue in Murine Models

OBJECTIVEType 1 diabetes is an incurable chronic autoimmune disease. Although transplantation of pancreatic islets may serve as a surrogate source of insulin, recipients are subjected to a life of immunosuppression. Interleukin (IL)-21 is necessary for type 1 diabetes in NOD mice. We examined the efficacy of an IL-21–targeted therapy on prevention of diabetes in NOD mice, in combination with syngeneic islet transplantation. In addition, we assessed the role of IL-21 responsiveness in islet allograft rejection in mouse animal models.RESEARCH DESIGN AND METHODSNOD mice were treated with IL-21R/Fc, an IL-21–neutralizing chimeric protein. This procedure was combined with syngeneic islet transplantation to treat diabetic NOD mice. Survival of allogeneic islet grafts in IL-21R–deficient mice was also assessed.RESULTSEvidence is provided that IL-21 is continually required by the autoimmune infiltrate, such that insulitis was reduced and reversed and diabetes inhibited by neutralization of IL-21 at a late preclinical stage. Recovery from autoimmune diabetes was achieved by combining neutralization of IL-21 with islet transplantation. Furthermore, IL-21–responsiveness by CD8+ T-cells was sufficient to mediate islet allograft rejection.CONCLUSIONSNeutralization of IL-21 in NOD mice can inhibit diabetes, and when paired with islet transplantation, this therapeutic approach restored normoglycemia. The influence of IL-21 on a graft-mounted immune response was robust, since the absence of IL-21 signaling prevented islet allograft rejection. These findings suggest that therapeutic manipulation of IL-21 may serve as a suitable treatment for patients with type 1 diabetes.

Rapamycin-Conditioned Donor Dendritic Cells Differentiate CD4+CD25+Foxp3+ T Cells In Vitro with TGF-β1 for Islet Transplantation

Dendritic cells (DCs) conditioned with the mammalian target of rapamycin (mTOR) inhibitor rapamycin have been previously shown to expand naturally existing regulatory T cells (nTregs). This work addresses whether rapamycin-conditioned donor DCs could effectively induce CD4(+)CD25(+)Foxp3(+) Tregs (iTregs) in cell cultures with alloantigen specificities, and whether such in vitro-differentiated CD4(+)CD25(+)Foxp3(+) iTregs could effectively control acute rejection in allogeneic islet transplantation. We found that donor BALB/c bone marrow-derived DCs (BMDCs) pharmacologically modified by the mTOR inhibitor rapamycin had significantly enhanced ability to induce CD4(+)CD25(+)Foxp3(+) iTregs of recipient origin (C57BL/6 (B6)) in vitro under Treg driving conditions compared to unmodified BMDCs. These in vitro-induced CD4(+)CD25(+)Foxp3(+) iTregs exerted donor-specific suppression in vitro, and prolonged allogeneic islet graft survival in vivo in RAG(-/-) hosts upon coadoptive transfer with T-effector cells. The CD4(+)CD25(+)Foxp3(+) iTregs expanded and preferentially maintained Foxp3 expression in the graft draining lymph nodes. Finally, the CD4(+)CD25(+)Foxp3(+) iTregs were further able to induce endogenous naïve T cells to convert to CD4(+)CD25(+)Foxp3(+) T cells. We conclude that rapamycin-conditioned donor BMDCs can be exploited for efficient in vitro differentiation of donor antigen-specific CD4(+)CD25(+)Foxp3(+) iTregs. Such in vitro-generated donor-specific CD4(+)CD25(+)Foxp3(+) iTregs are able to effectively control allogeneic islet graft rejection.

Immunomodulation by blockade of the TRANCE co-stimulatory pathway in murine allogeneic islet transplantation

We explore herein the effect of TNF-related activation-induced cytokine (TRANCE) co-stimulatory pathway blockade on islet survival after allograft transplantation. Expression of TRANCE on murine C57Bl/6 (B6) CD4+ T cells after allogeneic activation was analyzed by fluorescence-activated cell sorter (FACS). The effect of a TRANCE receptor fusion protein (TR-Fc) and anti-CD154 antibody (MR1) on B6 spleen cell proliferation after allogeneic activation was assessed by mixed lymphocyte reaction (MLR). Three groups of B6 mice were transplanted with allogeneic islets (DBA2): Control; short-term TR-Fc-treatment (days 0-4); and prolonged TR-Fc-treatment (days -1 to 13). Donor-specific transfusion (DST) was performed at the time of islet transplantation in one independent experiment. Transplantectomy samples were analyzed by immunohistochemistry. TRANCE expression was upregulated in stimulated CD4+ T cells in vitro. In MLR experiments, TR-Fc and MR1 both reduced spleen cell proliferation, but less than the combination of both molecules. Short-course TR-Fc treatment did not prolong islet graft survival when compared with controls (10.6 +/- 1.9 vs. 10.7 +/- 1.5 days) in contrast to prolonged treatment (20.7 +/- 3.2 days; P < 0.05). After DST, primary non function (PNF) was observed in half of control mice, but never in TR-Fc-treated mice. Immunofluorescence staining for Mac-1 showed a clear decrease in macrophage recruitment in the treated groups. TRANCE-targeting may be an effective strategy for the prolongation of allogeneic islet graft survival, thanks to its inhibitory effects on co-stimulatory signals and macrophage recruitment.

ECDI-fixed allogeneic splenocytes induce donor-specific tolerance for long-term survival of islet transplants via two distinct mechanisms

A major challenge for human allogeneic islet transplantation is the development of effective methods to induce donor-specific tolerance to obviate the need for life-long immunosuppression that is toxic to the insulin-producing beta cells and detrimental to the host. We developed an efficient donor-specific tolerance therapy that utilizes infusions of ethylene carbodiimide (ECDI)-treated donor splenic antigen-presenting cells that results in indefinite survival of allogeneic islet grafts in the absence of immunosuppression. Furthermore, we show that induction of tolerance is critically dependent on synergistic effects between an intact programmed death 1 receptor-programmed death ligand 1 signaling pathway and CD4(+)CD25(+)Foxp3(+) regulatory T cells. This highly efficient antigen-specific therapy with a complete avoidance of immunosuppression has significant therapeutic potential in human islet cell transplantation.

Prolonged Islet Allograft Survival by Alpha-1 Antitrypsin: The Role of Humoral Immunity

Immunomodulatory properties have been recognized for human alpha-1 antitrypsin (hAAT). However, production of anti-hAAT antibodies in mice may inactivate the protein. In this study, we evaluated the effects of chronic hAAT administration on allogeneic islet graft survival. Chemically diabetic mice lacking an efficient humoral response due to the targeted disruption of the Ig mu-chain (muMT mice) or wild-type (WT) C57BL/6 mice received DBA/2 mouse islets under the kidney capsule. hAAT (Prolastin or Aralast) was given intraperitoneally on day 0 and every 3 days thereafter. Control animals received no treatment. hAAT administration in WT mice resulted in prolongation of islet allograft survival in a dose-dependent fashion in both hAAT-treated groups. Lack of Ig response (muMT mice) per se conferred a beneficial effect on graft survival that worsened in the Prolastin-treated groups but improved in the Aralast-treated group. Our data indicate that systemic administration of hAAT results in prolongation of islet allograft survival. Absence of mature B cells and Ig mu-chain resulted in improved graft survival, pointing to a role for B cells in the rejection process in this model. Treatment with Prolastin worsened graft survival in muMT mice, whereas Aralast did improve it, suggesting a different efficacy and possible actions of the two drug formulations.

Role of NKT cells in allogeneic islet graft survival

Although NKT cells expressing CD1d-reactive TCR exerted protective role in autoimmune diseases, the regulatory function of CD1d-dependent NKT cells in alloimmune responses has not been investigated thoroughly. Here, we demonstrated the regulatory effects of NKT cells using a pancreas islet transplantation model. CD40/CD154 blocking induced long-term graft survival in most B6 recipients, but B6.CD1d −/− recipients showed co-stimulation blockade-resistant rejection. Adoptive transfer of NKT cells into B6.CD1d −/− restored tolerizing capacity of co-stimulatory blockade. Activation of NKT cells was effective for the prolongation of graft survival and up-regulated membrane-bound TGF-β expression transiently on their cell surface. The activated CD1d-dependent NKT cells inhibited alloantigen-driven cell proliferation through cell contacts and the beneficial effect of CD154 blocking for allograft survival was related to TGF-β pathway. Thus, we can conclude that NKT cells are essential for the stable allograft survival and the regulatory function is dependent on, at least in part, TGF-β engagement.

Systemic Overexpression of Interleukin-10 Fails to Protect Allogeneic Islet Transplants in Nonobese Diabetic Mice

Interleukin (IL)-10 has proven effective in various allogeneic transplantation models and for preventing recurrent autoimmune rejection of syngeneic islets in NOD mice. Therefore, we evaluated systemic IL-10 overexpression on allogeneic islet graft survival. Diabetic NOD mice received a single injection of recombinant adeno-associated virus (rAAV) serotype 2 encoding murine IL-10 (rAAV-IL-10) four weeks prior to renal subcasular islet transplantation. In a model having both autoimmune and allogeneic responses, IL-10 failed to protect C57BL/6 islets in spontaneously diabetic NOD mice. In an allograft model (C57BL/6 islets into young male streptozotocin-induced diabetic NOD mice), long-term (i.e., >169 days) islet survival was only seen in 2 of 14 rAAV-IL-10 treated mice. These failures occurred despite in vivo IL-10 production at transplant previously associated with protection of syngeneic islet grafts in NOD mice. Thus, IL-10 appears insufficient in protecting transplanted islet cells from allogeneic rejection and suggests important mechanistic variances between alloreactivity and autoimmunity in terms islet graft loss.

Prolonged Allogeneic Islet Graft Survival by Protoporphyrins.

Transplantation of islets of Langerhans in patients with type 1 diabetes allows for improved metabolic control and insulin independence. The need for chronic immunosuppression limits this procedure to selected patients with brittle diabetes. Definition of therapeutic strategies allowing permanent engraftment without the need for chronic immunosuppression could overcome such limitations. We tested the effect of the use of protoporphyrins (CoPP and FePP), powerful inducers of the cytoprotective protein hemeoxygenase 1 (HO-1), on allogeneic islet graft survival. Chemically induced diabetic C57BL/6 mice received DBA/2 islets. Treatment consisted in peritransplant administration of CoPP or saline. Islets were either cultured in the presence of FePP or vehicle before implant. Short-course administration of CoPP led to long-term islet allograft survival in a sizable proportion of recipients. Long-term graft-bearing animals rejected third-party islets while accepting a second set donor-specific graft permanently, without additional treatment. Preconditioning of islets with FePP by itself led to improved graft survival in untreated recipients, and provided additional advantage in CoPP-treated recipients, resulting in an increased proportion of long-term surviving grafts. Preconditioning of the graft with protoporphyrins prior to implant resulted in reduction of class II expression. Administration of protoporphyrins to the recipients of allogeneic islets also resulted in transient powerful immunosuppression with reduced lymphocyte proliferative responses, increased proportion of regulatory cells (CD4+CD25+), decreased mononuclear cell infiltrating the graft, paralleled by a systemic upregulation of HO-1 expression. All these mechanisms may have contributed to the induction of donor-specific hyporesponsiveness in a proportion of the protoporphyrintreated animals.

The effect of simultaneous CD154 and LFA-1 blockade on the survival of allogeneic islet grafts in nonobese diabetic mice.

The rate of success in clinical transplantation of islets of Langerhans has dramatically improved with perspectives of wide-scale applicability for patients with type 1 diabetes. One drawback is the need for lifelong immunosuppression, which is associated with significant side effects. Immunomodulatory strategies devoid of side effects and with tolerogenic potential, such as co-stimulatory blockade, would be a great improvement if successful. In this study, the authors have explored the effect of simultaneous blockade of CD40/CD154 and intercellular adhesion molecule (ICAM)/lymphocyte function-associated antigen (LFA)-1 interactions. Spontaneously diabetic nonobese diabetic (NOD) mice underwent transplantation with allogeneic (C57BL/6) islets and were treated with anti-CD154 monoclonal antibody (mAb) (500 microg, three doses), anti-LFA-1 mAb (100 microg, three doses), or a combination of both in the early peritransplant period. In another set of experiments, LFA-1 engagement was impaired by transplanting islets isolated from ICAM-1-knockout (KO) mice. Untreated animals rejected their grafts within 10 days. LFA-1 blockade alone did not result in improved islet graft survival, whereas CD154 blockade alone increased graft survival to 18 days. Simultaneous blockade of both pathways led to significantly improved islet graft survival to 30 days (ICAM-1-KO islets plus anti-CD154), 35 days (anti-LFA-1 plus anti-CD154), and 44 days (ICAM-1-KO islets plus anti-LFA-1 plus anti-CD154). These data suggest that a synergistic effect for prolonged graft survival can be obtained by simultaneously targeting CD154 and LFA-1 in the challenging model of islet allotransplantation in NOD mice. The observation of similar results with anti-LFA-1 mAb and with ICAM-1-KO grafts suggests a key role of direct antigen presentation for the activation of LFA-1-driven signaling.

Immunotherapy with nondepleting anti-CD4 monoclonal antibodies but not CD28 antagonists protects islet graft in spontaneously diabetic nod mice from autoimmune destruction and allogeneic and xenogeneic graft rejection.

T-cell activation and the subsequent induction of effector functions require not only the recognition of antigen peptides bound to MHC molecules by T-cell receptor (TCR) for antigen but also a costimulatory signal provided by antigen presenting cells. CD4 T-cell activation and function require the CD4 molecule as a coreceptor of TCR. The CD28/B7 pathway is a major costimulatory signal for T-cell activation and differentiation. The effect of targeting CD4 by nondepleting anti-CD4 monoclonal antibodies (mAbs) versus blocking CD28/B7 by CTLA4Ig, anti-CD80 mAbs, and anti-CD86 mAbs on the prevention of recurrence of autoimmune diabetes after MHC-matched nonobese diabetes-resistant (NOR) islet transplantation in nonobese diabetic (NOD) mice were compared. Whether nondepleting anti-CD4 mAbs prolong allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice were studied. Furthermore, the effect of nondepleting anti-CD4 mAbs combined with CTLA4Ig on allogeneic islet graft survival in NOD mice was investigated. Recurrence of autoimmune diabetes can be prevented by nondepleting anti-CD4 mAbs. Blocking the CD28/B7 costimulatory pathway by CTLA4Ig or by anti-CD80 mAbs and anti-CD86 mAbs cannot prevent recurrence of autoimmune diabetes after islet transplantation. Short-term treatment with nondepleting anti-CD4 mAbs significantly prolongs allogeneic islet graft survival and xenogeneic pig islet graft survival in diabetic NOD mice. But nondepleting anti-CD4 mAbs combined with CTLA4Ig decreased allogeneic islet graft survival. Nondepleting anti-CD4 mAbs but not CD28 antagonists protect islet grafts in diabetic NOD mice from autoimmune destruction and allogeneic and xenogeneic graft rejection. The efficacy of nondepleting anti-CD4 mAbs is compromised when it combines with CTLA4Ig.