Blockade of CD40-mediated signaling is sufficient for inducing islet but not skin transplantation tolerance

Allospecific CD4(+) T cells retain effector function and are actively regulated by Treg cells in the context of transplantation tolerance

Although donor-specific transfusion (DST) plus CD154 blockade represents a robust protocol for inducing transplantation tolerance, the underlying mechanisms are incompletely understood. In a murine T-cell adoptive transfer model, we have visualized alloantigen-specific, TCR-transgenic for H2-A(b) /H2-K(d) 54-68 epitope (TCR75) CD4(+) T cells with indirect allospecificity during the course of tolerance induction. Three main observations were made. First, although the majority of TCR75 CD4(+) T cells were deleted following DST plus CD154 blockade, the surviving TCR75 CD4(+) T cells were capable of making IL-2, upregulating CD44, and undergoing cell division, suggesting that they were functionally active. Indeed, residual TCR75 CD4(+) T cells reisolated from the primary recipients given DST plus CD154 blockade were fully capable of rejecting allografts upon secondary transfer. Second, in tolerant mice, TCR75 CD4(+) T cells were not induced to express Foxp3 in the graft-draining lymph node. TCR75 CD4(+) T cells were also absent in accepted graft tissues in which endogenous Treg cells were enriched. Finally, DST plus CD154 blockade resulted in an abortive expansion of TCR75 CD4(+) T cells, a process that required the presence of endogenous Treg cells. Collectively, surviving TCR75 CD4(+) T cells are immunocompetent but kept in check by an endogenous immunosuppressive network induced by DST plus CD154 blockade.

CD154 blockade alters innate immune cell recruitment and programs alloreactive CD8+ T cells into KLRG-1(high) short-lived effector T cells

CD154/CD40 blockade combined with donor specific transfusion remains one of the most effective therapies in prolonging allograft survival. Despite this, the mechanisms by which these pathways synergize to prevent rejection are not completely understood. Utilizing a BALB/c (H2-K(d)) to B6 (H2-K(b)) fully allogeneic skin transplant model system, we performed a detailed longitudinal analysis of the kinetics and magnitude of CD8(+) T cell expansion and differentiation in the presence of CD154/CD40 pathway blockade. Results demonstrated that treatment with anti-CD154 vs. DST had distinct and opposing effects on activated CD44(high) CD62L(low) CD8(+) T cells in skin graft recipients. Specifically, CD154 blockade delayed alloreactive CD8(+) T cell responses, while DST accelerated them. DST inhibited the differentiation of alloreactive CD8(+) T cells into multi-cytokine producing effectors, while CD40/CD154 blockade led to the diminution of the KLRG-1(low) long-lived memory precursor population compared with either untreated or DST treated animals. Moreover, only CD154 blockade effectively inhibited CXCL1 expression and neutrophil recruitment into the graft. When combined, anti-CD154 and DST acted synergistically to profoundly diminish the absolute number of IFN-γ producing alloreactive CD8(+) T cells, and intra-graft expression of inflammatory chemokines. These findings demonstrate that the previously described ability of anti-CD154 and DST to result in alloreactive T cell deletion involves both delayed kinetics of T cell expansion and differentiation and inhibited development of KLRG-1(low) memory precursor cells.

Human immune system development and rejection of human islet allografts in spontaneously diabetic NOD-Rag1null IL2rgammanull Ins2Akita mice

OBJECTIVE

To create an immunodeficient mouse model that spontaneously develops hyperglycemia to serve as a diabetic host for human islets and stem cell-derived beta-cells in the absence or presence of a functional human immune system.

RESEARCH DESIGN AND METHODS

We backcrossed the Ins2(Akita) mutation onto the NOD-Rag1(null) IL2rgamma(null) strain and determined 1) the spontaneous development of hyperglycemia, 2) the ability of human islets, mouse islets, and dissociated mouse islet cells to restore euglycemia, 3) the generation of a human immune system following engraftment of human hematopoietic stem cells, and 4) the ability of the humanized mice to reject human islet allografts.

RESULTS

We confirmed the defects in innate and adaptive immunity and the spontaneous development of hyperglycemia conferred by the IL2rgamma(null), Rag1(null), and Ins2(Akita) genes in NOD-Rag1(null) IL2rgamma(null) Ins2(Akita) (NRG-Akita) mice. Mouse and human islets restored NRG-Akita mice to normoglycemia. Insulin-positive cells in dissociated mouse islets, required to restore euglycemia in chemically diabetic NOD-scid IL2rgamma(null) and spontaneously diabetic NRG-Akita mice, were quantified following transplantation via the intrapancreatic and subrenal routes. Engraftment of human hematopoietic stem cells in newborn NRG-Akita and NRG mice resulted in equivalent human immune system development in a normoglycemic or chronically hyperglycemic environment, with >50% of engrafted NRG-Akita mice capable of rejecting human islet allografts.

CONCLUSIONS

NRG-Akita mice provide a model system for validation of the function of human islets and human adult stem cell, embryonic stem cell, or induced pluripotent stem cell-derived beta-cells in the absence or presence of an alloreactive human immune system.

Anti-CD40 monoclonal antibody synergizes with CTLA4-Ig in promoting long-term graft survival in murine models of transplantation

Blockade of the CD40/CD154 signaling pathway using anti-CD154 Abs has shown promise in attenuating the alloimmune response and promoting long-term graft survival in murine model systems, although side effects observed in humans have hampered its progression through clinical trials. Appropriately designed anti-CD40 Abs may provide a suitable alternative. We investigated two isoforms of a novel monoclonal rat anti-mouse CD40 Ab (7E1) for characteristics and effects mirroring those of anti-CD154: 7E1-G1 (an IgG1 isotype); and 7E1-G2b (an IgG2b isotype). In vitro proliferation assays to measure the agonist properties of the two anti-CD40 Abs revealed similar responses when plate bound. However, when present as a soluble stimulus, 7E1-G1 but not 7E1-G2b led to proliferation. 7E1-G2b was as effective as anti-CD154 when administered in vivo in concert with CTLA4-Ig in promoting both allogeneic bone marrow chimerism and skin graft survival, whereas 7E1-G1 was not. The protection observed with 7E1-G2b was not due to depletion of CD40-bearing APCs. These data suggest that an appropriately designed anti-CD40 Ab can promote graft survival as well as anti-CD154, making 7E1-G2b an attractive substitute in mouse models of costimulation blockade-based tolerance regimens.

TLR agonists prevent the establishment of allogeneic hematopoietic chimerism in mice treated with costimulation blockade

Activation of TLR4 by administration of LPS shortens the survival of skin allografts in mice treated with costimulation blockade through a CD8 T cell-dependent, MyD88-dependent, and type I IFN receptor-dependent pathway. The effect of TLR activation on the establishment of allogeneic hematopoietic chimerism in mice treated with costimulation blockade is not known. Using a costimulation blockade protocol based on a donor-specific transfusion (DST) and a short course of anti-CD154 mAb, we show that LPS administration at the time of DST matures host alloantigen-presenting dendritic cells, prevents the establishment of mixed allogeneic hematopoietic chimerism, and shortens survival of donor-specific skin allografts. LPS mediates its effects via a mechanism that involves both CD4(+) and CD8(+) T cells and results from signaling through either the MyD88 or the type I IFN receptor pathways. We also document that timing of LPS administration is critical, as injection of LPS 24 h before treatment with DST and anti-CD154 mAb does not prevent hematopoietic engraftment but administration the day after bone marrow transplantation does. We conclude that TLR4 activation prevents the induction of mixed allogeneic hematopoietic chimerism through type I IFN receptor and MyD88-dependent signaling, which leads to the up-regulation of costimulatory molecules on host APCs and the generation of alloreactive T cells. These data suggest that distinct but overlapping cellular and molecular mechanisms control the ability of TLR agonists to block tolerance induction to hematopoietic and skin allografts in mice treated with costimulation blockade.

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.

Islet cell transplantation for the treatment of type 1 diabetes in the USA

Islet cell transplantation (ICTx) is one of the most effective treatments for type 1 diabetes and is less invasive compared to whole organ transplantation. The US has been the leader in the research and clinical applications of ICTx for the last 40 years. ICTx requires complex procedures, including pancreas procurement and preservation; pancreas digestion; islet purification; and transplantation. Even with the dramatic progresses in each of the procedures listed above, there are still challenges to make ICTx the standard therapy. These challenges are: (1) obtaining enough islets from a single donor and (2) preventing graft loss due to allogenic rejection and recurrence of autoimmune islet destruction. A new preservation strategy for pancreata and pancreatic ducts using ET-Kyoto solution as well as a new islet purification method using iodixanol has substantially improved islet yields. Continuous research to improve the efficacy of islet isolation will solve the issue of obtaining enough islets from a single donor. Immunological tolerance is an ideal solution for the issue of rejection and autoimmune recurrence and a regulatory T cell strategy seems promising. Moreover, the SUITO index is a simple and powerful tool to assess engrafted islet mass and is, therefore, useful for evaluating the efficacy of new immunosuppressant strategies. Once ICTx becomes a standard treatment, the donor shortage will become the next challenge. Marginal or living donor islet transplantations could help alleviate this issue; however, bio-artificial islet transplantation with animal islets could be the ultimate solution.

Immunoglobulin-like transcript 3-Fc suppresses T-cell responses to allogeneic human islet transplants in hu-NOD/SCID mice

OBJECTIVE

The aim of our study was to explore the immunomodulatory activity of soluble immunoglobulin (Ig)-like transcript (ILT) 3-Fc in pancreatic islet transplantation and to determine its mechanism of action.

RESEARCH DESIGN AND METHODS

NOD/SCID mice in which diabetes was induced by streptozotocin injection were transplanted with human pancreatic islet cells. Mice in which the transplant restored euglycemia were humanized with allogeneic peripheral blood mononuclear cells and treated with ILT3-Fc or control human IgG or left untreated. The blood glucose level was monitored twice a week, and rejection was diagnosed after two consecutive readings >350 mg/dl. Tolerated and rejected grafts were studied histologically and by immunostaining for human T-cells and insulin production. CD4 and CD8 T-cells from the spleen were studied for suppressor activity, expression of cytokines, and CD40L.

RESULTS

Although human T-cell engraftment was similar in all groups, ILT3-Fc-treated mice tolerated the islets for the entire period of observation (91 days), whereas control mice rejected the graft within 7 weeks (P < 0.0001). ILT3-Fc treatment suppressed the expression of cytokines and CD40L and induced the differentiation of human CD8(+) T suppressor cells that inhibited Th alloreactivity against graft HLA antigens. T-cells allostimulated in vitro in the presence of ILT3-Fc inhibited CD40L-induced upregulation of CD40 in human pancreatic islet cells. Histochemical studies showed dramatic differences between human pancreatic islets from tolerant, ILT3-Fc-treated mice and control recipients rejecting the grafts.

CONCLUSIONS

The data indicated that ILT3-Fc is a potent immunoregulatory agent that suppressed islet allograft rejection in humanized NOD/SCID mice.

Bioluminescence imaging visualizes activation of nuclear factor-kappaB in mouse cardiac transplantation

BACKGROUND

The purpose of the current study was to evaluate the role of bioluminescence imaging (BLI) in the determination of nuclear factor (NF)-kappaB activation in cardiac allograft rejection and ischemia-reperfusion injury.

METHODS

To visualize NF-kappaB activation, luciferase transgenic mice under the control of a mouse NF-kappaB promoter (NF-kappaB-Luc) were used as donors or recipients of cardiac grafts. Alternatively, NF-kappaB-Luc spleen cells were adoptively transferred into Rag2 -/- mice with or without cardiac allografts. BLI was performed posttransplantation to detect luciferase activity that represents NF-kappaB activation.

RESULTS

The results show that luciferase activity was significantly increased in the cardiac allografts when NF-kappaB-Luc mice were used as recipients as well as donors. Luciferase activity was also elevated in the wild-type cardiac allografts in Rag2 -/- mice that were transferred with NF-kappaB-Luc spleen cells. CD154 monoclonal antibody (mAb) therapy inhibited luciferase activity and induced long-term survival of cardiac allografts. toll-like receptor-9 ligand, CpG DNA, enhanced luciferase activity and abrogated tolerance induction by CD154 mAb. Luciferase activity was also increased in ischemia-reperfusion injury of the cardiac grafts.

CONCLUSION

BLI using Luc-NF-kappaB mice is a noninvasive approach to visualize the activation of NF-kappaB signaling in mouse cardiac allograft rejection and ischemia-reperfusion injury. CD154 mAb can inhibit NF-kappaB activation, which is reversed by toll-like receptor engagement.

N-acetylcysteine derivative inhibits CD40-dependent proinflammatory properties of human pancreatic duct cells

OBJECTIVES

We recently observed that duct cells constitutively express CD40, a membrane molecule whose engagement results in duct cell activation and proinflammatory cytokine secretion. This observation suggests a potential role of this pathway in the pathogenesis of type 1 diabetes, islet graft rejection, or acute pancreatitis. In this article, we investigated whether a salt derivative of N-acetyl-L-cysteine, Nacystelyn, could modulate CD40 expression on duct cells and the response of activated duct cells to CD40 engagement.

METHODS

We assessed the effects of Nacystelyn on CD40 expression and function in human caucasian pancreatic adenocarcinoma, ATCC n degrees THB-80 (CAPAN-2) cells, a human pancreatic duct cell line. CD40 expression was analyzed by flow cytometry. To assess CAPAN-2 cell responses to CD40 engagement, we looked at nuclear factor-kappaB transcription factor activation using enzyme-linked immunosorbent assay and electrophoretic mobility shift assay and cytokine mRNA levels by quantitative real-time reverse transcriptase polymerase chain reaction.

RESULTS

We observed that Nacystelyn dose-dependently inhibited CD40 expression on CAPAN-2 cells as well as CD40-induced nuclear factor kappaB activation and proinflammatory cytokines up-regulation.

CONCLUSIONS

Our data suggest that Nacystelyn could be considered as a useful tool to prevent immune and inflammatory responses in pancreatic disorders by interfering with the CD40 pathway in pancreatic duct cells.

Type 1 IFN mediates cross-talk between innate and adaptive immunity that abrogates transplantation tolerance

TLR activation of innate immunity prevents the induction of transplantation tolerance and shortens skin allograft survival in mice treated with costimulation blockade. The mechanism by which TLR signaling mediates this effect has not been clear. We now report that administration of the TLR agonists LPS (TLR4) or polyinosinic:polycytidylic acid (TLR3) to mice treated with costimulation blockade prevents alloreactive CD8(+) T cell deletion, primes alloreactive CTLs, and shortens allograft survival. The TLR4- and MyD88-dependent pathways are required for LPS to shorten allograft survival, whereas polyinosinic:polycytidylic acid mediates its effects through a TLR3-independent pathway. These effects are all mediated by signaling through the type 1 IFN (IFN-alphabeta) receptor. Administration of IFN-beta recapitulates the detrimental effects of TLR agonists on transplantation tolerance. We conclude that the type 1 IFN generated as part of an innate immune response to TLR activation can in turn activate adaptive immune responses that abrogate transplantation tolerance. Blocking of type 1 IFN-dependent pathways in patients may improve allograft survival in the presence of exogenous TLR ligands.

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-beta 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-beta 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-beta engagement.

Different mechanisms control peripheral and central tolerance in hematopoietic chimeric mice

Regulatory T cells (Treg) are important in peripheral tolerance, but their role in establishing and maintaining hematopoietic mixed chimerism and generating central tolerance is unclear. We now show that costimulation blockade using a donor-specific transfusion and anti-CD154 antibody applied to mice given bone marrow and simultaneously transplanted with skin allografts leads to hematopoietic chimerism and permanent skin allograft survival. Chimeric mice bearing intact skin allografts fail to generate effector/memory T cells against allogeneic targets as shown by the absence of IFNgamma-producing CD44(high)CD8+ T cells and in vivo cytotoxicity. Depletion of Tregs by injection of anti-CD4 or anti-CD25 antibody prior to costimulation blockade prevents chimerism, shortens skin allograft survival and leads to generation of effector/memory cytotoxic T cells. Depletion of Tregs by injection of anti-CD4 or anti-CD25 antibody two months after transplantation leads to loss of skin allografts even though mice remain chimeric and exhibit little in vivo cytotoxicity. In contrast, chimerism is lost, but skin allografts survive following naïve T-cell injection. We conclude that hematopoietic chimerism and peripheral tolerance may be maintained by different mechanisms in mixed hematopoietic chimeras.

Diabetes induces rapid suppression of adaptive immunity followed by homeostatic T-cell proliferation

Surprisingly, the effect of acute diabetes on immunity has not been examined in detail. We, herein, show for the first time that untreated acute diabetes causes rapid lymphopenia followed by homeostatic T-cell proliferation. The diabetes-induced lymphopenia was associated with an immunosuppressed state that could be sufficiently strong to allow engraftment of fully allogeneic beta-cells or block rejection of islet transplants. In contrast, homeostatic proliferation and recovery of T-cell numbers were associated with islet rejection. Thus, the timing of islet transplant challenge in relation to diabetes induction was critical in determining whether islets were accepted or rejected. In addition, we tested whether diabetes-related immunosuppression could result in an overestimation of the efficacy of a tolerance-inducing protocol. Consistent with this possibility, a protocol targeting CD40L and ICOS that we have shown induces tolerance in diabetic recipients was unable to induce tolerance in non-diabetic recipients. The data uncover a previously unrecognized suppressive effect of diabetes on adaptive immunity. Furthermore, they suggest that the standard methods of testing new tolerance-inducing protocols in islet transplantation require modification and that diabetes itself can contribute to homeostatic proliferation, a process associated with autoimmunity and a resistance to tolerance induction.

Costimulatory Blockade Induces Hyporesponsiveness in T Cells that Recognize Alloantigen via Indirect Antigen Presentation

BACKGROUND

Blockade of T cell costimulation by treatment with donor-specific transfusion (DST) and anti-CD154 monoclonal antibody (mAb) induces prolonged allograft survival in mice. This effect is due in part to deletion of host CD8 and CD4 T cells that recognize alloantigen by direct presentation. The fate of host CD4 T cells that recognize alloantigen by indirect presentation, however, is unclear.

METHODS

We studied Tg361 TCR transgenic CD4 T cells that recognize alloantigen by indirect presentation. Carboxyfluorescein diacetate, succinimidyl ester-labeled Tg361 cells were adoptively transferred into syngeneic nontransgenic recipients and their fate in the peripheral blood, spleen, and lymph nodes following treatment with DST and anti-CD154 was analyzed.

RESULTS

Treatment of mice with DST plus anti-CD154 mAb does not delete Tg361 CD4 T cells, but instead renders them hyporesponsive to rechallenge with alloantigen. Mice circulating hyporesponsive CD4 T cells also fail to reject skin allografts. The hyporesponsive state of the T cells is not reversed by the addition of interleukin-2, anti-CD28 mAb, or an agonistic anti-CD134 mAb in the presence of antigen. These T cells are capable of activation, however, as evidenced by in vitro proliferation in response to anti-CD3 mAb.

CONCLUSIONS

These results demonstrate that costimulation blockade can induce hyporesponsiveness of host CD4 T cells recognizing alloantigens by indirect presentation, thus prolonging graft survival by a mechanism that does not involve deletion of alloreactive T cells.

IL-12p40 is not required for islet allograft rejection

AIM

To investigate whether IL-12p40 plays a crucial role in regulating islet allograft rejection in a streptozotocin (STZ)-induced diabetes mouse model.

METHODS

C57BL/6 and IL-12p40 gene knockout mice were selected as recipient mice, to which the diabetes was induced with a treatment of STZ (150-200 mg/kg) by a single ip injection. BALB/c mice were selected as donor mice and islet cells were isolated from the mice. The 500 islets were transplanted into recipient mice beneath the capsule of the left kidney. Following the islet transplantation the glucose from the mice sera was monitored and the rejection rate of islets was analyzed.

RESULTS

STZ could induce diabetes in the recipient mice within 1 week. After transplantation of allograft islets, the increased glucose in wild-type (WT) mice returned to normal level and was maintained for 10 d. Unexpectedly, the rejection rate of islet allograft between IL-12p40-deficient mice and WT mice was similar.

CONCLUSION

The results suggested that, although islet allograft rejection is believed to be Th1-cell predominant, the Th1 response inducer, IL-12 and IL-23 are not essential to induce islet allograft rejection.

Anti-mouse CD154 antibody treatment facilitates generation of mixed xenogeneic rat hematopoietic chimerism, prevents wasting disease and prolongs xenograft survival in mice

BACKGROUND

The induction of xenogeneic hematopoietic chimerism is an attractive approach for overcoming the host response to xenografts, but establishing xenogeneic chimerism requires severe myeloablative conditioning of the recipient. The goal of this study was to determine if co-stimulation blockade would facilitate chimerism and xenograft tolerance in irradiation-conditioned concordant recipients.

METHODS

Wistar Furth rat bone marrow (BM) cells were injected into irradiation-conditioned C57BL/6 mice with or without co-administration of anti-mouse CD154 monoclonal antibody (mAb). Chimerism was quantified by flow cytometry, and mice were transplanted with WF rat skin and islet xenografts.

RESULTS

Blockade of CD40-CD154 interaction facilitated establishment of xenogeneic chimerism in mice conditioned with 600 cGy irradiation. Anti-CD154 mAb was not required for establishment of chimerism in mice treated with 700 cGy. However, mice irradiated with 700 cGy but not treated with anti-CD154 mAb developed a "graft-versus-host disease (GVHD)-like" wasting syndrome and died, irrespective of their development of chimerism. Xenogeneic chimeras established with irradiation and anti-CD154 mAb treatment exhibited prolonged skin and, in many cases, permanent islet xenograft survival. Chimerism was unstable and eventually lost in most recipients. Skin xenografts were rejected even in mice that remained chimeric, whereas most islet xenografts survived to the end of the observation period.

CONCLUSIONS

Blockade of host CD40-CD154 interaction facilitates the establishment of xenogeneic chimerism and prevents wasting disease and death. Chimerism permits prolonged xenograft survival, but chimerism generated in this way is unstable over time. Skin xenografts are eventually rejected, whereas most islet xenografts survive long term and perhaps permanently.

Targeting LFA-1 and cd154 suppresses the in vivo activation and development of cytolytic (cd4-Independent) CD8+ T cells

Short-term immunotherapy targeting both LFA-1 and CD40/CD154 costimulation produces synergistic effects such that long-term allograft survival is achieved in the majority of recipients. This immunotherapeutic strategy has been reported to induce the development of CD4+ regulatory T cells. In the current study, the mechanisms by which this immunotherapeutic strategy prevents CD8+ T cell-dependent hepatocyte rejection in CD4 knockout mice were examined. Combined blockade of LFA-1 and CD40/CD154 costimulation did not influence the overall number or composition of inflammatory cells infiltrating the liver where transplanted hepatocytes engraft. Expression of T cell activation markers CD43, CD69, and adhesion molecule CD103 by liver-infiltrating cells was suppressed in treated mice with long-term hepatocellular allograft survival compared to liver-infiltrating cells of untreated rejector mice. Short-term immunotherapy with anti-LFA-1 and anti-CD154 mAb also abrogated the in vivo development of alloreactive CD8+ cytotoxic T cell effectors. Treated mice with long-term hepatocyte allograft survival did not reject hepatocellular allografts despite adoptive transfer of naive CD8+ T cells. Unexpectedly, treated mice with long-term hepatocellular allograft survival demonstrated prominent donor-reactive delayed-type hypersensitivity responses, which were increased in comparison to untreated hepatocyte rejectors. Collectively, these findings support the conclusion that short-term immunotherapy with anti-LFA-1 and anti-CD154 mAbs induces long-term survival of hepatocellular allografts by interfering with CD8+ T cell activation and development of CTL effector function. In addition, these recipients with long-term hepatocellular allograft acceptance show evidence of immunoregulation which is not due to immune deletion or ignorance and is associated with early development of a novel CD8+CD25high cell population in the liver.

Requirements for induction and maintenance of peripheral tolerance in stringent allograft models

Peripheral tolerance can be achieved in many but not all murine allograft models. The requirements for controlling more aggressive immune responsiveness and generating peripheral tolerance in stringent allograft models are unknown. Understanding these requirements will provide insight toward ultimately achieving tolerance in humans, which are also resistant. We now demonstrate that the combination of donor-specific transfusion, anti-CD45RB, and anti-CD154 uniformly achieves >90-d survival of BALB/c skin allografts on C57BL/6 recipients. Recipients exhibit marked hyporesponsiveness to alloantigen in vitro. In distinct contrast to less rigorous models, engraftment remains absolutely dependent on cytotoxic T lymphocyte antigen 4 signaling, even after grafts are healed, suggesting that prolonged engraftment cannot simply be attributed to more effective depletion of alloreactive T cells but is actively maintained by regulation. Concordantly, we show that both CD4 and CD8 regulatory cells are required and can transfer donor-specific tolerance to naïve recipients. Nonetheless, most recipients ultimately develop gradual graft loss (median survival time = 140 d), suggesting that alloreactive cells emerging from the thymus eventually overwhelm regulatory capacity. In agreement, adding thymectomy to the regimen results in permanent engraftment (>250 d) and donor-specific tolerance not observed previously in this model. These results highlight the potency of both CD4 and CD8 regulatory cells but also suggest that in stringent settings, regulatory T cell longevity and capacity for infectious tolerance compete with prolonged graft immunogenicity and thymic output. These results provide insight into the mechanisms of tolerance in stringent models and provide a rational basis for innovative tolerogenic strategies in humans.

A functional CD40 receptor is expressed in pancreatic beta cells

AIMS/HYPOTHESIS

Despite differences in function and embryonic origin, pancreatic islet cells and neurons express proteins belonging to the tumour necrosis factor receptor superfamily. While neurons express the CD40 receptor, it is unknown whether islet cells also express it. We investigated CD40 expression in human and mouse pancreatic islets as well as in NIT-1 insulinoma cells.

METHODS

CD40 expression was studied by reverse transcriptase polymerase chain reaction, flow cytometry, immunohistochemistry and western blot. Responses mediated by CD40 were assessed by a luciferase gene reporter assay following stimulation with a CD40 agonist antibody.

RESULTS

We found that CD40 is expressed in mouse and human pancreatic islet cells. CD40 is expressed by beta cells, and its expression is upregulated by proinflammatory cytokines (IL-1beta, IFN-gamma and TNF-alpha). CD40 signalling in NIT-1 insulinoma cells activates nuclear factor kappa-B, demonstrating that CD40 is functional.

CONCLUSIONS/INTERPRETATION

We present evidence that, in addition to immune cell types, mouse and human pancreatic beta cells express CD40. Its expression is upregulated by proinflammatory stimuli, and signalling through this receptor activates NF-kappaB. We suggest that the effects of inflammatory stimuli that affect beta cell function and survival may be also mediated by signalling through the CD40 receptor. Thus, CD40 may have a role in processes associated with islet autoimmunity and transplantation.

Autoimmune diabetes and resistance to xenograft transplantation tolerance in NOD mice

Costimulation blockade induces prolonged rat islet and skin xenograft survival in C57BL/6 mice. Nonobese diabetic (NOD) mice, which are used to model human autoimmune diabetes, are resistant to costimulation blockade-induced allograft tolerance. We tested the hypothesis that NOD mice would also be resistant to costimulation blockade-induced rat xenograft tolerance. We report that rat islet xenograft survival is short in spontaneously diabetic NOD mice treated with a tolerizing regimen of donor-specific transfusion and anti-CD154 antibody. Rat islet xenograft survival is only marginally longer in chemically diabetic NOD mice treated with costimulation blockade but is prolonged further in NOD Idd congenic mice bearing C57-derived chromosome 3 loci. Reciprocally, the presence of NOD-derived chromosome 3 loci shortens islet xenograft survival in tolerized C57BL/6 mice. Islet xenograft survival is longer in tolerized NOD.CD4a(-/-) and (NOD x C57BL/6)F1 mice than in NOD mice but still much shorter than in C57BL/6 mice. Skin xenograft survival in (NOD x C57BL/6)F1 mice treated with costimulation blockade is short, suggesting a strong genetic resistance to skin xenograft tolerance induction. We conclude that the resistance of NOD mice to xenograft tolerance induction involves some mechanisms that also participate in the expression of autoimmunity and other mechanisms that are distinct.

Evaluation of donor-specific transfusion sources: unique failure of bone marrow cells to induce prolonged skin allograft survival with anti-CD154 monoclonal antibody

BACKGROUND

Treatment with anti-CD154 monoclonal antibody (mAb) plus a donor-specific transfusion (DST) of spleen cells prolongs skin allograft survival in mice through a mechanism involving deletion of host alloreactive CD8(+) T cells. It is unknown if other lymphohematopoietic cell populations can be used as a DST.

METHODS

Murine recipients of allogeneic skin grafts on day 0 were either untreated or given a DST on day -7 plus 4 doses of anti-CD154 mAb on days -7, -4, 0, and +4. Deletion of CD8(+) alloreactive cells was measured using "synchimeric" CBA recipients, which circulate trace populations of TCR transgenic alloreactive CD8(+) T cells.

RESULTS

Transfusion of splenocytes, thymocytes, lymph node cells, or buffy coat cells led to prolonged skin allograft survival in recipients treated with anti-CD154 mAb. In contrast, bone marrow DST failed to delete host alloreactive CD8(+) T cells and was associated with brief skin allograft survival. Transfusions consisting of bone marrow-derived dendritic cells or a mixture of splenocytes and bone marrow cells were also ineffective.

CONCLUSIONS

Donor-specific transfusions of splenocytes, thymocytes, lymph node cells, or buffy coat cells can prolong skin allograft survival in recipients treated with costimulation blockade. Bone marrow cells fail to serve this function, in part by failing to delete host alloreactive CD8(+) T cells, and they may actively interfere with the function of a spleen cell DST. The data suggest that transplantation tolerance induction protocols that incorporate bone marrow cells to serve as a DST may not be effective.

Regulation of skin and islet allograft survival in mice treated with costimulation blockade is mediated by different CD4+ cell subsets and different mechanisms

BACKGROUND

Donor-specific transfusion (DST) and a brief course of anti-CD154 monoclonal antibody (mAb) induces permanent islet and prolonged skin allograft survival in mice. Induction of skin allograft survival requires the presence of CD4 cells and deletion of alloreactive CD8 cells. The specific roles of CD4 and CD4CD25 cells and the mechanism(s) by which they act are not fully understood.

METHODS

We used skin and islet allografts, a CD8 T cell receptor (TCR) transgenic model system, and in vivo depleting antibodies to analyze the role of CD4 cell subsets in regulating allograft survival in mice treated with DST and anti-CD154 mAb.

RESULTS

Deletion of CD4 or CD25 cells during costimulation blockade induced rapid rejection of skin but only minimally shortened islet allograft survival. Deletion of CD4 or CD25 cells had no effect upon survival of healed-in islet allografts, and CD25 cell deletion had no effect upon healed-in skin allograft survival. In the TCR transgenic model, DST plus anti-CD154 mAb treatment deleted alloreactive CD8 T cells, and anti-CD4 mAb treatment prevented that deletion. In contrast, injection of anti-CD25 mAb did not prevent alloreactive CD8 T cell deletion.

CONCLUSIONS

These data document that (1) both CD4CD25 and CD4CD25 cells are required for induction of skin allograft survival, (2) CD4CD25 T cells are not required for alloreactive CD8 T cell deletion, and (3) CD4CD25 regulatory cells are not critical for islet allograft tolerance. It appears that skin and islet transplantation tolerance are mediated by different CD4 cell subsets and different mechanisms.

The Development of Functional CD8 T Cell Memory afterListeria monocytogenesInfection Is Not Dependent on CD40

The immunologic requirements for generating long-lived protective CD8 T cell memory remain unclear. Memory CD8 populations generated in the absence of CD4 Th cells reportedly have functional defects, and at least a subset of CD8 T cells transiently express CD40 after activation, suggesting that direct CD4-CD8 T cell interactions through CD40 may influence the magnitude and functional quality of memory CD8 populations. To ascertain the role of CD40 in such direct T cell interactions, we investigated CD8 T cell responses in CD40-/- mice after infection with Listeria monocytogenes, an intracellular bacterium that induces APC activation and thus priming of CD8 T cells independently of CD4 Th cell help through CD40. In this study we show that memory CD8 T cells generated in CD40-deficient mice show in vivo cytotoxicity and cytokine production equivalent to CD8 memory T cells from wild-type mice. Upon secondary Listeria infection, CD40-/- memory CD8 T cells expand to greater numbers than seen in wild-type mice. These results indicate that CD40 ligation on CD8 T cells, although reportedly a part of CD8 T cell memory development in an H-Y-directed response, is not needed for the development of functional memory CD8 T cell populations after Listeria infection.

Rejection of human islets and human HLA-A2.1 transgenic mouse islets by alloreactive human lymphocytes in immunodeficient NOD-scid and NOD-Rag1nullPrf1null mice

Immunodeficient NOD mice engrafted with human peripheral blood mononuclear cells (PBMCs) were used in two models of human islet allograft rejection. Model one: human PBMCs were engrafted into chemically diabetic NOD-scid mice bearing established subrenal human islet allografts. Inflammation and often complete islet allograft rejection were observed. Model 2 incorporated three key advances. First, we developed a new immunodeficient recipient, NOD-RagI(null)Prf1(null) mice. Second, graft-lymphocyte interactions were optimized by intrasplenic co-transplantation of islets and human PBMC. Third, NOD-scid islets expressing human HLA-A2.1 were used as allograft targets. Diabetic NOD-RagI(null)Prf1(null) recipients of HLA-A2.1 transgenic mouse islets, alone or co-engrafted with HLA-A2-positive human PBMC, exhibited durable graft survival and euglycemia. Contrastingly, co-transplantation with HLA-A2-negative human PBMC led to islet graft rejection without evidence of graft-vs.-host disease (GVHD). We propose that diabetic NOD-RagI(null)Prf1(null) mice co-engrafted with HLA-A2 mouse transgenic islets and allogeneic human PBMC provide an effective in vivo model of human islet allograft rejection.

Islet allograft survival induced by costimulation blockade in NOD mice is controlled by allelic variants of Idd3

NOD mice develop type 1 autoimmune diabetes and exhibit genetically dominant resistance to transplantation tolerance induction. These two phenotypes are genetically separable. Costimulation blockade fails to prolong skin allograft survival in (NOD x C57BL/6)F1 mice and in NOD-related strains made diabetes-resistant by congenic introduction of protective major histocompatibility complex (MHC) or non-MHC Idd region genes. Here, we tested the hypothesis that the genetic basis for the resistance of NOD mice to skin allograft tolerance also applies to islet allografts. Surprisingly, costimulation blockade induced permanent islet allograft survival in (NOD x C57BL/6)F1 mice but not in NOD mice. After costimulation blockade, islet allograft survival was prolonged in diabetes-resistant NOD.B6 Idd3 mice and shortened in diabetes-free C57BL/6 mice congenic for the NOD Idd3 variant. Islet allograft tolerance could not be induced in diabetes-resistant NOD.B10 Idd5 and NOD.B10 Idd9 mice. The data demonstrate that 1) NOD mice resist islet allograft tolerance induction; 2) unlike skin allografts, resistance to islet allograft tolerance is a genetically recessive trait; 3) an Idd3 region gene(s) is an important determinant of islet allograft tolerance induction; and 4) there may be overlap in the mechanism by which the Idd3 resistance locus improves self-tolerance and the induction of allotolerance.

CD40 expression on human pancreatic duct cells: role in nuclear factor-kappa B activation and production of pro-inflammatory cytokines

AIMS/HYPOTHESIS

Human pancreatic duct cells are closely associated with islet beta cells, and contaminate islet suspensions transplanted in Type 1 diabetes mellitus patients. Activated duct cells produce cytotoxic mediators and possibly contribute to the pathogenesis of Type 1 diabetes mellitus or islet graft rejection. As CD40 transduces activation signals involved in inflammatory and immune disorders, we investigated CD40 expression on duct cells and their response to CD40 engagement.

METHODS

CD40 expression on human pancreatic duct cells was analysed by flow cytometry and immunohistochemical analyses. To assess the function of CD40 expression on duct cells, activation of the transcription factor nuclear factor-kappa B was determined using electrophoretic mobility shift assay and ELISA. Cytokine mRNA levels were quantified by real-time RT-PCR, and protein levels by Luminex technology.

RESULTS

Isolated human pancreatic duct cells and Capan-2 cell lines were found to express constitutively CD40. The expression of CD40 on duct cells was confirmed in vivo on human normal and pathological pancreatic specimens. CD40 ligation on Capan-2 cells induced rapid nuclear factor-kappa B activation, and supershift assays demonstrated that p50/p65 heterodimers and p50/p50 homodimers were present in the activated complexes in the nucleus. This activation was accompanied by tumour necrosis factor-a and interleukin-1beta mRNA accumulation. Tumour necrosis factor-alpha protein secretion was confirmed in CD40-activated Capan-2 cells and in isolated human pancreatic duct cells.

CONCLUSIONS/INTERPRETATION

Interaction between activated T lymphocytes expressing CD40 ligand and duct cells expressing CD40 may contribute to the immune responses involved in Type 1 diabetes mellitus and islet graft rejection. Interfering with CD40-mediated duct cell activation could alleviate beta cell damage of immune origin.