Opposing effects of anti-activation-inducible lymphocyte-immunomodulatory molecule/inducible costimulator antibody on the development of acute versus chronic graft-versus-host disease

LPSlow-Macrophages Alleviate the Outcome of Graft-Versus-Host Disease Without Aggravating Lymphoma Growth in Mice

Despite significant therapeutic advances, graft-versus-host disease (GvHD) remains the main life-threatening complication following allogeneic hematopoietic stem cell transplantation. The pathogenesis of GvHD is dominated by a dysregulated allogeneic immune response that drives fibrosis and autoimmunity in chronic forms. A multitude of cell therapy approaches, including infusion of myeloid cells, has been proposed to prevent GvHD through tolerance induction but yielded variable results. Myeloid cells like macrophages can be reprogrammed to develop adaptive-like features following antigenic challenge to reinforce or inhibit a subsequent immune response; a phenomenon termed ‘trained immunity’. Here we report that, whereas LPS^low-trained macrophages elicit a suppressor effect on allogeneic T cell proliferation and function in vitro in an IL-10-dependent manner, Bacille Calmette et Guérin (BCG)-trained macrophages exert an opposite effect. In a murine model of sclerodermatous chronic GvHD, LPS^low-trained macrophages attenuate clinical signs of GvHD with significant effects on T cell phenotype and function, autoantibodies production, and tissue fibrosis. Furthermore, infusion of LPS^low-macrophages significantly improves survival in mice with acute GvHD. Importantly, we also provide evidence that LPS^low-macrophages do not accelerate A20-lymphoma tumor growth, which is significantly reduced upon transfer of BCG-macrophages. Collectively, these data indicate that macrophages can be trained to significantly inhibit in vitro and in vivo allo-reactive T cell proliferation without exhibiting pro-tumoral effect, thereby opening the way to promising clinical applications.

Adipose tissue-derived mesenchymal stem cells ameliorate bone marrow aplasia related with graft-versus-host disease in experimental murine models

Graft-versus-host disease (GVHD) constitutes the most frequent complications after the allogeneic hematopoietic stem cell transplantation for a variety of hematological malignancies. In the present study, we explored the prophylactic potential of adipose tissue-derived mesenchymal stem cells (AD-MSCs) in controlling GVHD in murine models with a special focus on bone marrow aplasia related with acute GVHD. The CB6F1 mice were induced GVHD by the injection intravenously of C57BL/6 (B6-Ly-5.1) splenocytes without conditioning irradiation or chemotherapy. AD-MSCs from C3H mice were injected intravenously via tail veins. GVHD was assessed using flowcytometry analysis of peripheral blood cells and histopathologic analysis of target organs. Histopathological analyses revealed that AD-MSCs markedly suppressed the infiltration of lymphocytes into liver as well as the aplasia in bone marrow. This study is the first to clarify the effectiveness of AD-MSCs against bone marrow aplasia in GVHD, supporting a rationale of AD-MSCs for ameliorating bone marrow suppression and infectivity after allo-HSCT in human clinics.

Animal Models for Preclinical Development of Allogeneic Hematopoietic Cell Transplantation

Since its inception in the 1950s, hematopoietic cell transplantation (HCT) has become a highly effective clinical treatment for malignant and nonmalignant hematological disorders. This milestone in cancer therapy was only possible through decades of intensive research using murine and canine animal models that overcame what appeared in the early days to be insurmountable obstacles. Conditioning protocols for tumor ablation and immunosuppression of the recipient using irradiation and chemotherapeutic drugs were developed in mouse and dog models as well as postgrafting immunosuppression methods essential for dependable donor cell engraftment. The random-bred canine was particularly important in defining the role of histocompatibility barriers and the development of the nonmyeloablative transplantation procedure, making HCT available to elderly patients with comorbidities. Two complications limit the success of HCT: disease relapse and graft versus host disease. Studies in both mice and dogs have made significant progress toward reducing and to some degree eliminating patient morbidity and mortality associated with both disease relapse and graft versus host disease. However, more investigation is needed to make HCT more effective, safer, and available as a treatment modality for other non-life-threatening diseases such as autoimmune disorders. Here, we focus our review on the contributions made by both the murine and canine models for the successful past and future development of HCT.

Targeting the Human T-Cell Inducible COStimulator Molecule with a Monoclonal Antibody Prevents Graft-vs-Host Disease and Preserves Graft vs Leukemia in a Xenograft Murine Model

BACKGROUND

Graft-vs-host disease (GVHD) is a major complication of allogenic bone marrow transplantation (BMT). Targeting costimulatory molecules with antagonist antibodies could dampen the excessive immune response that occurs, while preserving the beneficial graft vs leukemia (GVL) of the allogeneic response. Previous studies using a mouse model of GVHD have shown that targeting the T-cell Inducible COStimulator (ICOS, CD278) molecule is beneficial, but it is unclear whether the same applies to human cells.

METHODS

Here, we assessed whether a monoclonal antibody (mAb) to human ICOS was able to antagonize the costimulatory signal delivered in vivo to human T cells. To test this hypothesis, we used a xenogeneic model of GVHD where human peripheral blood mononuclear cells were adoptively transferred in immunocompromised NOD.SCID.gc-null mice (NSG).

RESULTS

In this model, control mice invariably lost weight and died by day 50. In contrast, 65% of the mice receiving a single injection of the anti-hICOS mAb survived beyond 100 days. Moreover, a significant improvement in survival was obtained in a curative xeno-GVHD setting. Mechanistically, administration of the anti-hICOS mAb was associated with a strong reduction in perivascular infiltrates in liver and lungs and reduction in frequencies and numbers of human T cells in the spleen. In addition, the mAb prevented T-cell expansion in the blood during xeno-GVHD. Importantly, GVHD-protected mice retained the ability to control the P815 mastocytoma cell line, mimicking GVL in humans.

CONCLUSION

A mAb-targeting human ICOS alleviated GVHD without impairing GVL in a xenograft murine model. Thus, ICOS represents a promising target in the management of BMT, preventing GVHD while preserving GVL.

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.

Association of the costimulatory molecule gene polymorphisms and active cytomegalovirus infection in hematopoietic stem cell transplant patients

Determinative associations may exist between costimulatory molecule gene polymorphisms with a variety of post hematopoietic stem cell transplantation (HSCT) viral related clinical outcomes especially acute graft versus host disease (aGVHD). Therefore in this study the associations between costimulatory molecule gene polymorphisms including: cytotoxic T-lymphocyte antigen-4 (CTLA4), programmed cell death-1 (PD-1), inducible T cell costimulator (ICOS), and cluster differentiation 28 (CD28) with active cytomegalovirus (CMV) infection were evaluated in HSCT patients. The 72 allogeneic HSCT patients with and without aGVHD were enrolled in this cross sectional study between years: 2004-2011. The single nucleotide polymorphisms in loci of the costimulatory molecules including: CTLA4 gene (-318 C/T, 1722 T/C, 1661 A/G, +49 A/G), PD-1 gene (PD-1.3 A/G, PD-1.9 C/T), ICOS gene (1720 C/T), and CD28 gene (+17 C/T) were analyzed in studied HSCT patients by PCR-RFLP methods. The active CMV infection was evaluated in fresh EDTA-treated blood samples of each allogeneic HSCT patients by CMV antigenemia kit according to manufacturer's instruction. Active CMV infection was found in 11 of 72 (15.27 %) of allogeneic HSCT patients. The T allele and TT genotype of the CD28 +17 C/T were significantly higher frequency in active CMV infected allogeneic HSCT patients experienced aGVHD. The G allele and GG genotype of the CTLA4 -1661 A/G were significantly higher frequent in active CMV infected allogeneic HSCT patients experienced low grade of aGVHD. Finally, finding of significant associations between CD28 +17 C/T and CTLA4 -1661 A/G genotypes with CMV active infection in allogeneic HSCT patients experienced aGVHD emphasize on the importance of the genetic pattern of costimulatory genes in outcomes of active CMV infection in HSCT patients needs completed studies.

Association of the costimulatory molecule gene polymorphisms and active cytomegalovirus infection in hematopoietic stem cell transplant patients

Determinative associations may exist between costimulatory molecule gene polymorphisms with a variety of post hematopoietic stem cell transplantation (HSCT) viral related clinical outcomes especially acute graft versus host disease (aGVHD). Therefore in this study the associations between costimulatory molecule gene polymorphisms including: cytotoxic T-lymphocyte antigen-4 (CTLA4), programmed cell death-1 (PD-1), inducible T cell costimulator (ICOS), and cluster differentiation 28 (CD28) with active cytomegalovirus (CMV) infection were evaluated in HSCT patients. The 72 allogeneic HSCT patients with and without aGVHD were enrolled in this cross sectional study between years: 2004-2011. The single nucleotide polymorphisms in loci of the costimulatory molecules including: CTLA4 gene (-318 C/T, 1722 T/C, 1661 A/G, +49 A/G), PD-1 gene (PD-1.3 A/G, PD-1.9 C/T), ICOS gene (1720 C/T), and CD28 gene (+17 C/T) were analyzed in studied HSCT patients by PCR-RFLP methods. The active CMV infection was evaluated in fresh EDTA-treated blood samples of each allogeneic HSCT patients by CMV antigenemia kit according to manufacturer's instruction. Active CMV infection was found in 11 of 72 (15.27 %) of allogeneic HSCT patients. The T allele and TT genotype of the CD28 +17 C/T were significantly higher frequency in active CMV infected allogeneic HSCT patients experienced aGVHD. The G allele and GG genotype of the CTLA4 -1661 A/G were significantly higher frequent in active CMV infected allogeneic HSCT patients experienced low grade of aGVHD. Finally, finding of significant associations between CD28 +17 C/T and CTLA4 -1661 A/G genotypes with CMV active infection in allogeneic HSCT patients experienced aGVHD emphasize on the importance of the genetic pattern of costimulatory genes in outcomes of active CMV infection in HSCT patients needs completed studies.

Inducible costimulator (ICOS) up-regulation on activated T cells in chronic graft-versus-host disease after dog leukocyte antigen-nonidentical hematopoietic cell transplantation: a potential therapeutic target

BACKGROUND

Inducible costimulator (ICOS), a member of the CD28 family of costimulatory molecules, is induced on CD4 and CD8 T cells after their activation. ICOS functions as an essential immune regulator and ICOS blockade is a potential approach to immune modulation in allogeneic transplantation. Here, we describe the expression profile of ICOS in dogs and determine whether ICOS expression is up-regulated during chronic graft-versus-host disease (GVHD) and host-versus-graft reactions in the canine hematopoietic cell transplantation model.

METHODS

Monoclonal antibodies (mAbs) against cell surface-expressed ICOS were produced and tested in vitro for suppression of canine mixed leukocyte reactions (MLR). Expression of ICOS on CD3 cells was evaluated by flow cytometry using peripheral blood, lymph nodes, and splenocytes obtained from dogs undergoing graft-versus-host and host-versus-graft reactions.

RESULTS

Canine ICOS was expressed in an inducible pattern on T cells activated by concanavalin A, anti-CD3 mAb in combination with anti-CD28 mAb, and alloantigen stimulation. Immunosuppressive effects of ICOS blockade were observed in MLR using peripheral blood mononuclear cells from dog leukocyte antigen-nonidentical dogs. Immunosuppressive effects of ICOS blockade were observed in MLR when anti-ICOS was combined with suboptimal concentrations of cytotoxic T-lymphocyte antigen 4-Ig or cyclosporine. ICOS expression was significantly up-regulated on T cells in dogs undergoing graft rejection or chronic GVHD after allogeneic hematopoietic cell transplantation.

CONCLUSIONS

These studies suggest that ICOS plays a role in graft rejection and GVHD in an outbred animal model, and ICOS blockade may be an approach to prevention and treatment of chronic GVHD.

Phosphatidylinositol 3-kinase-independent signaling pathways contribute to ICOS-mediated T cell costimulation in acute graft-versus-host disease in mice

We and others have previously shown that ICOS plays an important role in inducing acute graft-versus-host disease (GVHD) in murine models of allogeneic bone marrow transplantation. ICOS potentiates TCR-mediated PI3K activation and intracellular calcium mobilization. However, ICOS signal transduction pathways involved in GVHD remain unknown. In this study, we examined the contribution of ICOS-PI3K signaling in the pathogenic potential of T cells using a knock-in mouse strain, ICOS-YF, which selectively lost the ability to activate PI3K. We found that when total T cells were used as alloreactive T cells, ICOS-YF T cells caused less severe GVHD compared with ICOS wild-type T cells, but they induced much more aggressive disease than ICOS knockout T cells. This intermediate level of pathogenic capacity of ICOS-YF T cells was correlated with similar levels of IFN-γ-producing CD8 T cells that developed in the recipients of ICOS-WT or ICOS-YF T cells. We further evaluated the role of ICOS-PI3K signaling in CD4 versus CD8 T cell compartment using GVHD models that are exclusively driven by CD4 or CD8 T cells. Remarkably, ICOS-YF CD8 T cells caused disease similar to ICOS wild-type CD8 T cells, whereas ICOS-YF CD4 T cells behaved very similarly to their ICOS knockout counterparts. Consistent with their in vivo pathogenic potential, CD8 T cells responded to ICOS ligation in vitro by PI3K-independent calcium flux, T cell activation, and proliferation. Thus, in acute GVHD in mice, CD4 T cells heavily rely on ICOS-PI3K signaling pathways; in contrast, CD8 T cells can use PI3K-independent ICOS signaling pathways, possibly through calcium.

AP-1 is involved in ICOS gene expression downstream of TCR/CD28 and cytokine receptor signaling

It has been proposed that sustained ICOS expression in chronic inflammatory immune conditions, such as autoimmunity and allergy, contributes to symptom exacerbation. Therefore modulation of ICOS gene expression could be a potential therapeutic strategy for such immune diseases. However, the precise molecular mechanisms controlling ICOS gene expression remain poorly understood. In this study, we explored transcription factors involving in ICOS gene expression and examined their roles in a physiological situation. Microarray analysis revealed that one AP-1 molecule, Fos-related antigen-2 (Fra2), was highly correlated with ICOS expression. Ectopic expression of Fra2 and other AP-1 molecules upregulated ICOS expression on T cells. We identified an AP-1-responsive site (AP1-RE) within the ICOS promoter region and demonstrated AP-1 actually binds to AP1-RE upon TCR/CD28 stimulation. Meanwhile, we found several cytokines could upregulate ICOS expression on both naïve and effector T cells in a manner independent of TCR/CD28 stimulation. These cytokine stimuli induced AP-1 binding to AP1-RE. Together, our results indicate AP-1 transcription factors are involved in ICOS gene expression downstream of both TCR/CD28 signaling and cytokine receptor signaling, and suggest AP-1 activation via cytokine receptor signaling may be one of the mechanisms maintaining high level ICOS expression in chronic inflammatory immune responses.

A molecular and computational diagnostic approach identifies FOXP3, ICOS, CD52 and CASP1 as the most informative biomarkers in acute graft-versus-host disease

BACKGROUND

Acute graft-versus-host disease is a severe complication of allogeneic stem cell transplantation in which the functional immune cells of the donor recognize the recipient as foreign and mount an immunological attack. There is an urgent need for better diagnostic instruments for the assessment of acute graft-versus-host disease. In the present study, a novel bioinformatics framework was used to identify gene expression patterns associated with acute graft-versushost disease in patients undergoing allogeneic hematopoietic stem cell transplantation.

DESIGN AND METHODS

Peripheral blood cells were collected prospectively from patients who did develop acute graftversus-host disease (YES) and from those who did not (NO). Gene expression profiling was performed using a panel of 47 candidate genes potentially involved in alloreactive responses. The entire population of YES/NO acute graft-versus-host disease patients formed the experimental validation set. Personalized modeling based on a gene selection technique was applied to identify the most significant mRNA transcripts, which were then used to profile individual data samples for training and testing the classification/prediction framework.

RESULTS

A leave-one-out cross-validation procedure was performed to investigate the robustness of the classification framework producing the following results: 100% on the training dataset and 97% on the testing dataset. According to our integrated methodology, transcripts for FOXP3, ICOS, CD52 and CASP1, genes involved in immune alloreactive responses and participating in immune cell interactions, were identified as the most informative biomarkers in allogeneic stem cell transplant recipients experiencing acute graft-versus-host disease.

CONCLUSIONS

This study demonstrates that the integrated methodology proposed is useful for the selection of valid gene targets for the diagnosis of acute graft-versus-host disease, producing satisfactory accuracy over independent clinical features of the allogeneic transplanted population.

Roles of CD28, CTLA4, and inducible costimulator in acute graft-versus-host disease in mice

T cells deficient for CD28 have reduced ability to expand and survive, but still cause graft-versus-host disease (GVHD). Inducible costimulator (ICOS), a member of the CD28 family, is expressed on antigen-activated T cells and plays unique roles in T cell activation and effector function. We hypothesized that ICOS contributes to the development of GVHD in the absence of B7:CD28/CTLA4 costimulation. In this study, we evaluated the roles of CD28, CTLA4, and ICOS in the pathogenesis of acute GVHD after myeloablative allogeneic bone marrow transplantation. Unexpectedly, we found that blocking CD28 and CTLA4 signals using the clinically relevant reagent CTLA4-Ig increases the severity of GVHD mediated by CD4(+) T cells, and that such treatment does not add any benefit to the blockade of ICOS. In contrast, selectively blocking CD28 and ICOS, but not CTLA4, prevents GVHD more effectively than blocking either CD28 or ICOS alone. Taken together, these results indicate that CD28 and ICOS are synergistic in promoting GVHD, whereas the CTLA4 signal is required for T cell tolerance regardless of ICOS signaling. Thus, blocking CD28 and ICOS while sparing CTLA4 represents a promising approach for abrogating pathogenic T cell responses after allogeneic bone marrow transplantation.

Intervention with costimulatory pathways as a therapeutic approach for graft-versus-host disease

Graft-versus-host disease (GVHD) is mediated by mature donor T cells contained in the hematopoietic stem cell graft. During the development of GVHD, signaling through a variety of costimulatory receptors plays an important role in allogeneic T cell responses. Even though delivery of costimulatory signals is a prerequisite for full activation of donor T cells in the phase of their interactions with host APCs, their involvement with GVHD might occur over multiple stages. Like many other aspects of GVHD, promise of therapeutic interventions with costimulatory pathways has been gleaned from preclinical models. In this review, I summarize some of the advances in roles of costimulatory molecules in GVHD pathophysiology and discuss preclinical approaches that warrant further exploration in the clinic, focusing on novel strategies to delete pathogenic T cells.

T-cell costimulatory molecules in acute-graft-versus host disease: therapeutic implications

Acute Graft-versus-host disease (GVHD) is a major complication after allogeneic hematopoietic stem cell transplantation. Although this process is thought to consist of several phases, T-cell activation plays a critical role in the pathogenesis of acute GVHD. To become efficient effectors, T-cells require additional costimulation after T-cell receptor signaling. A number of molecules are involved in costimulation of T-cells such as CD28, CD40L, CD30, OX40, 4-1BB, ICOS, and LIGHT. The system is regulated by inhibitory molecules, CTLA-4, and PD-1. There is experimental evidence that those molecules are implicated in the pathogenesis of GHVD. We describe how these molecules are involved in acute GVHD and how the blockade of costimulatory molecules may have potential implications for the treatment of patients with acute GVHD.

The inducible T-cell co-stimulator molecule is expressed on subsets of T cells and is a new marker of lymphomas of T follicular helper cell-derivation

BACKGROUND

T follicular helper (T(FH)) cells reside in the light zone of germinal centers and are considered the cell of origin of angioimmunoblastic T-cell lymphoma. Recently, CXCL13, PD-1 and SAP were described as useful markers for T(FH) cells and angioimmunoblastic T-cell lymphoma but also reported in some peripheral T-cell lymphomas, not otherwise specified.

DESIGN AND METHODS

In the present study the expression pattern of ICOS protein was investigated by immunohistochemistry-based techniques in routine sections of normal lymphoid tissues and 633 human lymphomas.

RESULTS

Cells strongly positive for ICOS were restricted to the light zone of germinal centers and co-expressed T(FH)-associated molecules. In addition, weak to moderate ICOS expression was observed in a small proportion of FOXP3-positive cells. In lymphomas, ICOS expression was confined to angioimmunoblastic T-cell lymphoma (85/86), peripheral T-cell lymphomas of follicular variant (18/18) and a proportion of peripheral T-cell lymphomas, not otherwise specified (24/56) that also expressed other T(FH)-associated molecules.

CONCLUSIONS

ICOS is a useful molecule for identifying T(FH) cells and its restricted expression to angioimmunoblastic T-cell lymphoma and a proportion of peripheral T-cell lymphomas, not otherwise specified (showing a T(FH)-like profile) suggests its inclusion in the antibody panel for diagnosing T(FH)-derived lymphomas. Our findings provide further evidence that the histological spectrum of T(FH)-derived lymphomas is broader than previously assumed.

Contribution of B7RP-1/ICOS co-stimulation to lethal acute GVHD

Co-stimulatory molecules expressed on T cells critically regulate donor T-cell activation and are implicated in acute GVHD after allogeneic BMT. We here investigated the role of interaction between B7-related protein-1 (B7RP-1) and ICOS in murine acute GVHD model that received T cell-depleted BM cells and splenocytes. Administration of blocking anti-B7RP-1 mAb significantly reduced the lethality and symptoms in acute GVHD. A significant hypo-responsiveness of splenocytes to host alloantigen was observed in the recipient mice treated with anti-B7RP-1 mAb. Moreover, acute GVHD was significantly reduced in the recipients of T cells composed of ICOS-deficient CD8 T cells and WT CD4 T cells compared with that in the recipients of T cells composed of WT CD8 T cells and ICOS-deficient CD4 T cells. These results suggested that B7RP-1/ICOS co-stimulatory signal plays a role in the activation of alloantigen-reactive donor T cells, particularly in CD8 T cells, in murine acute GVHD model, and that the blockade of B7RP-1/ICOS interaction may be useful for selectively manipulating allo-reactive T cells in the recipients with acute GVHD.

Suppression of Con A-induced hepatitis induction in ICOS-deficient mice

Although there is growing evidence that NKT cells play an important role in various immune responses through the invariant T cell receptor, other cell surface molecules responsible for their function are not fully understood. Here we study the role of ICOS, the third member of the CD28 family of costimulatory receptors, in in vivo and in vitro NKT cell responses. To establish its in vivo role in systems dependent on NKT cells, we examined the development of Con A-induced hepatitis in ICOS knockout (ICOS(-/-)) mice. We demonstrated that hepatic injury in ICOS(-/-) mice was greatly suppressed as evidenced by the reduced elevation of serum transaminases, reduced apoptosis of hepatocytes and mild histopathological changes. In investigating the cause of this defect, we first found that the NKT cell population is significantly reduced in the liver and spleen of ICOS(-/-) mice. We made and analyzed mixed bone marrow chimera mice with bone marrow cells from ICOS(+/+) and ICOS(-/-) mice, and demonstrated that the defect in ICOS-mediated costimulation results in a significant defect in the development of NKT cells, especially of Valpha14i NKT cells, in the thymus. When we examined the function of residual NKT cells in ICOS(-/-) mice, we found that their cytokine production following stimulation with alpha-galactosylceramide (alpha-GalCer) was strongly impaired. Based on these findings, we propose that ICOS-mediated costimulation may play a critical role in both the development and the optimal function of NKT cells, and that defective ICOS-mediated costimulation may result in impaired Con A-induced hepatitis in ICOS(-/-) mice.

Functional polymorphism of CTLA-4 and ICOS genes in allogeneic hematopoietic stem cell transplantation

BACKGROUND

T cells play a critical role in alloimmune recognition and thus contribute to graft-versus-host disease (GVHD) and relapse prevention in hematopoietic stem cell transplantation (HSCT). Cytotoxic T lymphocyte antigen-4 (CTLA-4) and inducible costimulator (ICOS) are costimulatory molecules of T cell activation and their genetic variations can affect the capacity of T cells to become activated or inactivated.

METHODS

We examined CTLA-4 (-318 C/T and +49 A/G) and ICOS (c.602 A/C and c.1624 C/T) genotypes in 123 patients with HSCT and their HLA-matched sibling donors, and then evaluated the impacts of the genetic polymorphisms on GVHD, disease relapse, and survival.

RESULTS

By multivariate analysis, the donor CTLA-4 -318 TT genotype increased the risk of disease relapse (Hazard ratio [HR]: 5.91, 95% confidence interval [CI]: 1.17-29.79, P=0.0313). Recipients who received a graft from a donor with ICOS c.602 CC genotype had worse disease-free survival (HR: 5.97, 95% CI: 1.49-23.87, P=0.0115). Additionally, recipients with ICOS c.1624 TT genotype had worse overall survival (HR: 12.98, 95% CI: 2.58-65.35, P=0.0019). Nevertheless, CTLA-4 and ICOS genotypes were not associated with acute and chronic GVHD.

CONCLUSIONS

Both donor and recipient CTLA-4 and ICOS gene polymorphisms might be of importance for the outcome of allogeneic HSCT.

Characterization of YM-58483/BTP2, a novel store-operated Ca2+ entry blocker, on T cell-mediated immune responses in vivo

YM-58483/BTP2 is a blocker of store-operated Ca2+ entry (SOCE), which regulates the activation of non-excitable cells such as lymphocytes. YM-58483 has been reported to inhibit cytokine production and proliferation in T cells, and to be useful as a probable medicinal candidate for treatment of bronchial asthma. The present study investigated the pharmacological profile and therapeutic potential of YM-58483 in relation to cell-mediated immune responses. In the mouse graft-versus-host disease (GVHD) model, YM-58483 (1-30 mg/kg, p.o.) and cyclosporine A (1-30 mg/kg, p.o.) inhibited donor anti-host cytotoxic T lymphocyte (CTL) activity and IFN-gamma production, and also reduced the number of donor T cells, especially donor CD8+ T cells, in the spleen. YM-58483 and cyclosporine A inhibited T cell proliferation in a one-way mixed lymphocyte reaction (MLR) with IC50 values of 330 and 12.7 nM, respectively. Additionally, YM-58483 (1-10 mg/kg, p.o.) and cyclosporine A (2, 10 mg/kg, p.o.) inhibited the sheep red blood cell (SRBC)-induced delayed type hypersensitivity (DTH) response. These results suggest that the inhibition of SOCE leads to the prevention of antigen-induced T cell responses, which participate in autoimmune diseases such as autoimmune hepatitis and rheumatoid arthritis.

Down-regulation of ICOS ligand by interaction with ICOS functions as a regulatory mechanism for immune responses

Although it is well-known that the ICOS-ICOS ligand (ICOSL) costimulatory pathway is important for many immune responses, recent accumulated evidence suggests that dysregulation of this pathway may lead to and/or exaggerate autoimmune responses. ICOS is induced on the cell surface after T cell activation. Similarly, ICOSL is up-regulated on APCs by several mitogenic stimuli. However, the mechanism regulating expression of the ICOS-ICOSL pair, and the significance of controlling their expression for an appropriate immune response, is largely unknown. To gain a better understanding of the importance of fine control of the ICOS-ICOSL costimulatory pathway, we generated ICOS-transgenic (Tg) mice that have high constitutive expression of ICOS in all T cells. Using ICOS-Tg mice, we studied whether in vivo immune responses were affected. Unexpectedly, we first found that ICOS-Tg mice exhibited a phenotype resembling ICOS-deficient mice in their Ag-specific Ab response, such as a defect in class switch recombination. Further examination revealed that ICOSL expression of APCs was significantly suppressed in ICOS-Tg mice. Interestingly, suppression of ICOSL was induced by interaction of ICOSL with ICOS, and it seemed to be regulated at the posttranscriptional level. The suppressive effect of the ICOS-ICOSL interaction overcame the positive effect of CD40 or B cell activation factor of the TNF family (BAFF) stimulation on ICOSL expression. Together, our studies demonstrate a novel mechanism for the regulation of ICOSL expression in vivo and suggest that the ICOS costimulatory pathway is subject to negative feedback regulation by ICOSL down-regulation in response to ICOS expression.

Critical role of activation-inducible lymphocyte immunomediatory molecule/inducible costimulator in the effector function of human T cells: a comparative in vitro study of effects of its blockade and CD28 blockade in human beings and monkeys

Activation-inducible lymphocyte immunomediatory molecule (AILIM; also referred to as inducible costimulator, ICOS) is the third homolog of the "professional" costimulatory molecule, CD28. To date, the characteristics and role of AILIM/ICOS, especially in effector function of T cells, have been determined through numerous studies in vitro and in vivo using mice. Considering potential differences among species, whether the AILIM/ICOS blockade acts as an efficacious immunomodulator for human diseases remains to be elucidated. In the present study, ability of AILIM/ICOS blockade to modulate immune responses of human and monkey cells was investigated using a fully human antibody (JTA-009), comparing the effect of CD28 blockade. JTA-009 blocked the response of human and monkey T cells co-stimulated with anti-CD3 and AILIM/ICOS ligand, B7h. AILIM/ICOS and CD28 blockade both inhibited human mixed lymphocyte reaction in different fashions, as well as cytokine production in T helper (Th) 1-/Th2-type recall responses. In monkeys however, CD28 blockade by CTLA4-Ig effectively prevented mixed lymphocyte reaction to a greater extent than AILIM/ICOS blockade. These results suggest that AILIM/ICOS blockade is valuable for suppressing both primary allogenic response and recall responses of T cell in human beings, and that there are differences between human and monkey use preferences for costimulatory molecules.

Unexpected role of B and T lymphocyte attenuator in sustaining cell survival during chronic allostimulation

B and T lymphocyte attenuator (BTLA; CD272) can deliver inhibitory signals to B and T cells upon binding its ligand herpesvirus entry mediator. Because CD28, CTLA-4, programmed death-1, and ICOS regulate the development of acute graft-vs-host disease (GVHD), we wished to assess if BTLA also played a role in this T cell-mediated response. In the nonirradiated parental-into-F1 model of acute GVHD, BTLA+/+ and BTLA-/- donor lymphocytes showed equivalent engraftment and expansion during the first week of the alloresponse. Unexpectedly, BTLA-/- donor T cells failed to sustain GVHD, showing a decline in surviving donor cell numbers beginning at day 9 and greatly reduced by day 11. Similarly, inhibition of BTLA-herpesvirus entry mediator engagement by in vivo administration of a blocking anti-BTLA Ab also caused reduced survival of donor cells. Microarray analysis revealed several genes that were differentially expressed by BTLA-/- and BTLA+/+ donor CD4+ T cells preceding the decline in BTLA-/- donor T cells. Several genes influencing Th cell polarization were differentially expressed by BTLA+/+ and BTLA-/- donor cells. Additionally, the re-expression of the IL-7Ralpha subunit that occurs in BTLA+/+ donor cells after 1 wk of in vivo allostimulation was not observed in BTLA-/- donor CD4+ cells. The striking loss of BTLA-/- T cells in this model indicates a role for BTLA activity in sustaining CD4+ T cell survival under the conditions of chronic stimulation in the nonirradiated parental-into-F1 GVHD.

Grb2 and Gads exhibit different interactions with CD28 and play distinct roles in CD28-mediated costimulation

Although both CD28 and ICOS bind PI3K and provide stimulatory signal for T cell activation, unlike CD28, ICOS does not costimulate IL-2 secretion. CD28 binds both PI3K and Grb2, whereas ICOS binds only PI3K. We have generated an ICOS mutant, which can bind Grb2 by replacement of its PI3K binding motif YMFM with the CD28 YMNM motif, and shown that it induces significant activation of the IL-2 promoter. However, this mutant ICOS was insufficient to activate the NF-kappaB pathway. In this study, we show that Gads, but not Grb2, is essential for CD28-mediated NF-kappaB activation, and its binding to CD28 requires the whole CD28 cytoplasmic domain in addition to the YMNM motif. Mutagenesis experiments have indicated that mutations in the N-terminal and/or C-terminal PXXP motif(s) of CD28 significantly reduce their association with Gads, whereas their associations with Grb2 are maintained. They induced strong activity of the NFAT/AP-1 reporter comparable with the CD28 wild type, but weak activity of the NF-kappaB reporter. Grb2- and Gads-dominant-negative mutants had a strong effect on NFAT/AP-1 reporter, but only Gads-dominant-negative significantly inhibited NF-kappaB reporter. Our data suggest that, in addition to the PI3K binding motif, the PXXP motif in the CD28 cytoplasmic domain may also define a functional difference between the CD28- and ICOS-mediated costimulatory signals by binding to Gads.

Opposing effects of ICOS on graft-versus-host disease mediated by CD4 and CD8 T cells

ICOS, a CD28 family member expressed on activated CD4(+) and CD8(+) T cells, plays important roles in T cell activation and effector function. Here we studied the role of ICOS in graft-vs-host disease (GVHD) mediated by CD4(+) or CD8(+) T cells in allogeneic bone marrow transplantation. In comparison of wild-type and ICOS-deficient T cells, we found that recipients of ICOS(-/-) CD4(+) T cells exhibited significantly less GVHD morbidity and delayed mortality. ICOS(-/-) CD4(+) T cells had no defect in expansion, but expressed significantly less Fas ligand and produced significantly lower levels of IFN-gamma and TNF-alpha. Thus, ICOS(-/-) CD4(+) T cells were impaired in effector functions that lead to GVHD. In contrast, recipients of ICOS(-/-) CD8(+) T cells exhibited significantly enhanced GVHD morbidity and accelerated mortality. In the absence of ICOS signaling, either using ICOS-deficient donors or ICOS ligand-deficient recipients, the levels of expansion and Tc1 cytokine production of CD8(+) T cells were significantly increased. The level of expansion was inversely correlated with the level of apoptosis, suggesting that increased ability of ICOS(-/-) CD8(+) T cells to induce GVHD resulted from the enhanced survival and expansion of those cells. Our findings indicate that ICOS has paradoxical effects on the regulation of alloreactive CD4(+) and CD8(+) T cells in GVHD.

Expression level of costimulatory receptor ICOS is critical for determining the polarization of helper T cell function

We found that inducible costimulator (ICOS)-deficient spleen cells have a defect in the ability to induce Th2-mediated chronic graft-versus-host disease (GVHD), whereas they were fully capable of inducing Th1-mediated acute GVHD. In contrast, CD28-deficient spleen cells induced neither acute nor chronic GVHD. To define the mechanisms of how these two CD28 family molecules manifest distinct functions in GVHD, the kinetics of their surface expression by donor T cells in two types of GVHD were investigated. It was found that expression of ICOS by donor T cells dramatically up-regulated after adoptive transfer in both acute and chronic GVHD, but in acute GVHD this up-regulation was transient and quickly down-regulated. In contrast, donor T cells in chronic GVHD maintained high levels of ICOS expression throughout the experiment. These results suggested that ICOS-mediated costimulatory signals are predominantly active in Th2-dominant responses. Changing patterns of CD28 expression by donor T cell were identical in both GVHD as they exhibited slight but sustained up-regulation after transfer, suggesting that CD28 provides a costimulatory signal necessary for the initial T cell activation, regardless of whether in Th1 or Th2 responses. These results lead us to propose that the expression levels of costimulatory receptors are critical for determining the polarization of helper T cell function.

CD28-dependent differentiation into the effector/memory phenotype is essential for induction of arthritis in interleukin-1 receptor antagonist-deficient mice

OBJECTIVE

Interleukin-1 receptor antagonist (IL-1Ra)-deficient mice on a BALB/c background spontaneously develop a chronic inflammatory polyarthropathy closely resembling that of rheumatoid arthritis in humans. To elucidate the role of CD28 costimulatory signals in the development of this disease, we studied IL-1Ra/CD28-double-deficient mice.

METHODS

We crossed IL-1Ra-deficient mice with CD28-deficient mice and observed the incidence and severity of arthritis. To investigate functions of IL-1Ra/CD28-double-deficient T cells, cells were stimulated with CD3 monoclonal antibody or allogeneic antigen-presenting cells (APCs) and their proliferative responses and levels of cytokine production were measured.

RESULTS

Disease severity was lower in IL-1Ra/CD28-double-deficient mice than in mice that were deficient only in IL-1Ra, although incidence of arthritis was not affected by the presence or absence of CD28. When pathogenic IL-1Ra-KO T cells were transferred into nude mice, severe arthritis developed. Even though T cells from double-deficient mice showed the same diminished proliferative capacity as was seen in T cells from CD28-single-deficient animals, nude mice into which double-deficient T cells were transferred never developed arthritis.

CONCLUSION

These findings indicate that IL-1Ra/CD28-double-deficient T cells can be activated by IL-1Ra-deficient activated APCs, resulting in induction of arthritis; however, these T cells did not induce the disease under normal conditions, because they did not differentiate into effector/memory phenotype.

Inducible co-stimulatory molecule ligand is protective during the induction and effector phases of crescentic glomerulonephritis

The inducible co-stimulatory molecule (ICOS)/ICOS ligand (ICOSL) co-stimulatory pathway is critical in T cell activation, differentiation, and effector function. Its role was investigated in a model of Th1-driven crescentic glomerulonephritis (GN). GN was induced by sensitizing mice to sheep globulin (day 0) and challenging them with sheep anti-mouse glomerular basement membrane antibody (Ab; day 10). Disease and immune responses were assessed on day 20. For testing the role of ICOSL in the induction of GN, control or anti-ICOSL mAb were administered from days 0 to 8. For examining the role of ICOSL in the effector phase of GN, treatment lasted from days 10 to 18. Blockade of ICOSL during the induction of GN increased glomerular accumulation of CD4+ T cells and macrophages and augmented renal injury. These results correlated with attenuated splenocyte production of protective Th2 cytokines IL-4 and IL-10 and decreased apoptosis of splenic CD4+ T cells. ICOSL was upregulated within glomeruli of mice with GN. Inhibition of ICOSL during the effector phase of GN enhanced glomerular T cell and macrophage accumulation and augmented disease, without affecting the systemic immune response (cytokine production, T cell apoptosis/proliferation, Ab levels). Increased presence of leukocytes in glomeruli of mice that received anti-ICOSL mAb was associated with enhanced cellular proliferation and upregulation of P-selectin and intercellular adhesion molecule-1 within glomeruli. These studies demonstrate that ICOSL is protective during the induction of GN by augmenting Th2 responses and CD4+ T cell apoptosis. They also show that ICOSL is upregulated in nephritic glomeruli, where it locally reduces accumulation of T cells and macrophages and attenuates renal injury.

Expression and Regulation of Human CD275 on Endothelial Cells in Healthy and Inflamed Mucosal Tissues

The CD275-CD278 costimulatory pathway is a new pathway for CD28-B7 family molecules involved in the effector phase of T-cell-mediated immune responses. Expression of CD275 in oral mucosa at healthy and disease states has not been examined. We generated monoclonal antibodies against human CD275 and investigated its expression and regulation in cultured tissue cell lines and oral mucosal tissues. CD275 on monocytes was efficiently upregulated by interleukin-4, while interferon-gamma abrogated this effect. CD275 on cultured endothelial cells (EC) was rapidly enhanced by tumour necrosis factor-alpha. In healthy oral mucosa, CD275 was not detected on keratinocytes, Langerhans cells or intraepithelial lymphocytes within the epithelium or on interstitial dendritic cells or lymphocytes in the sub-epithelium. Constitutive expression of CD275 on EC in the connective tissues was observed in healthy mucosa, but CD275 expression on EC in oral lichen planus was either upregulated or down regulated. Approximately 20% of the T cells found within infiltrating mononuclear cells in the sub-epithelium expressed high levels of the CD278 receptor. CD275 on lymphoid and nonlymphoid cells is positively or negatively regulated by various cytokines. Our results suggest that CD275 on EC is involved in the recruitment or extravasation of receptor-positive effector T cells into inflamed tissues.

Expression of Functional B7-H2 and B7.2 Costimulatory Molecules and Their Prognostic Implications in De novo Acute Myeloid Leukemia

PURPOSE

The B7 family molecules have been shown to regulate immune responses in both positive and negative fashions. Their roles in the progression of human cancers, however, are not well established. The aim of this study was to examine whether leukemic cells of acute myeloid leukemia express functional B7 family molecules and, if so, whether such expression has any clinical significance.

EXPERIMENTAL DESIGN

The expression of four B7 family molecules, B7.1, B7.2, B7-H1, and B7-H2, on leukemic cells from acute myeloid leukemia patients was analyzed by flow cytometry. The function of the expressed molecules was examined by the allogeneic mixed lymphocyte-leukemic cell reaction, and their relationship to the clinical data and survival was analyzed.

RESULTS

Although B7.1 and B7-H1 expressions were rare, the cells from a substantial number of acute myeloid leukemia cases expressed B7.2 and B7-H2 molecules [mean percentages of B7.2- and B7-H2-positive cells were 28.9% (n = 58) and 15.3% (n = 59), respectively]. Patients in whom >25% of leukemic cells expressed B7-H2 had significantly shorter survival, and this B7-H2 positivity had the strongest prognostic value when B7-H2 and other prognostic factors were analyzed together by multivariate analysis (P = 0.0108). Furthermore, B7.2 expression was associated with hyperleukocytosis (P = 0.026). Consistent with this finding, acute myeloid leukemia cells expressing B7.2 and B7-H2 induced allogeneic CD4+ T cells to proliferate and secrete interleukin-4 and interleukin-10 in vitro, effects that were partially blocked by antibodies against B7.2 and B7-H2.

CONCLUSIONS

Our results indicate the expression of functional B7.2 and B7-H2 molecules, and these molecules may facilitate progression of acute myeloid leukemia.

Absence of inducible costimulator on alloreactive T cells reduces graft versus host disease and induces Th2 deviation

Inducible costimulator (ICOS) is expressed on activated and memory T cells and is involved in the regulation of cytokine production. We studied the role of ICOS on alloreactive T cells in graft versus host disease (GVHD) and determined that ICOS expression was up-regulated on alloreactive T cells in recipients of an allogeneic hematopoietic stem cell transplantation (allo-HSCT) with GVHD. We compared ICOS-/- T cells with wild-type (WT) T cells in 2 GVHD models. In both models, recipients of ICOS-/- T cells demonstrated significantly less GVHD morbidity and mortality, which was associated with less intestinal and hepatic GVHD but increased cutaneous GVHD. In addition, recipients of ICOS-/- donor T cells displayed a slight decrease in graft versus leukemia (GVL) activity. Further analysis of alloreactive ICOS-/- T cells showed no defect in activation, proliferation, cytotoxicity, and target organ infiltration. Recipients of ICOS-/- T cells had decreased serum levels of interferon-gamma (IFN-gamma), while interleukin-4 (IL-4) and IL-10 levels were increased, suggesting that alloreactive ICOS-/- T cells are skewed toward T helper-2 (Th2) differentiation. These data suggest a novel role for ICOS in the regulation of Th1/Th2 development of activated T cells. In conclusion, alloreactive ICOS-/- donor T cells induce less GVHD due to a Th2 immune deviation while GVL activity is slightly diminished.

Role of the ICOS-B7h Costimulatory Pathway in the Pathophysiology of Chronic Allograft Rejection

BACKGROUND

Inducible costimulator (ICOS) is the third member of the CD28 superfamily and has a unique role in T cell activation and function. Recent studies indicated that the ICOS-B7h pathway plays an important role in alloimmune responses. We further investigated the role of the ICOS pathway in the pathologic process of chronic rejection in vivo.

METHODS

An established major histocompatibility complex class II disparate cardiac transplantation model was used. We treated mice with a blocking anti-B7h monoclonal antibody (mAb) either in the initiation phase (early blockade) or in the progression phase (delayed blockade) of disease. In addition, some mice received mAb in the entire period (whole blockade). At 6 weeks after transplantation, cardiac grafts were evaluated by histopathologic analysis in terms of vasculopathy, fibrosis, and cellular infiltration. The intragraft expressions of cytokines and chemokines were also examined by quantitative real-time polymerase chain reaction analysis.

RESULTS

Early blockade of the ICOS-B7h pathway did not show any protective effect on chronic allograft rejection compared with untreated controls. In contrast, delayed blockade significantly inhibited the development of vasculopathy, fibrosis, and cellular infiltration (P=0.043, P=0.004, and P=0.03 vs. untreated control, respectively). Interestingly, whole blockade did not prevent the chronic rejection process. Furthermore, the inhibitory effect of delayed ICOS blockade on chronic rejection was associated with down-regulation of local intragraft expression of several cytokines and chemokines.

CONCLUSIONS

These data suggest that the ICOS-B7h pathway is critical in the activation of effector/memory T cells that are necessary for the progression of chronic rejection and provide the rationale to develop novel and specific therapies to prevent this process.

The Pathophysiology of Acute Graft-Versus-Host Disease

Despite improvements in allogeneic stem cell transplantation, acute graft-versus-host disease (GVHD) remains a significant problem after transplantation, and it is still a major cause of post-transplant mortality. Disease progression is characterized by the differentiation of alloreactive T cells to effector cells leading to tissue damage, recruitment of additional inflammatory cell populations and further cytokine dysregulation. To make the complex process of acute GVHD more explicit, the pathophysiology of acute GVHD is often divided into three different phases. This review summarizes the mechanisms involved in the three phases of acute GVHD.

Two waves of memory B-cell generation in the primary immune response

Memory B cells can be generated independently of germinal center (GC) formation and affinity maturation in Bcl-6-deficient mice, but the contribution of the GC-independent pathway for memory B-cell generation in normal mice remains unknown. To examine this, we administrated anti-inducible co-stimulator (ICOS) mAbs into mice at the onset of GC formation in the primary response. This manipulation affected the generation of GC B cells in the spleen, but neither IgG1 memory B cell nor production of IgG1 long-term antibody was affected. In ICOS-manipulated mice, GC B cells accumulated somatic mutations in the IgV(H) genes and underwent affinity maturation; however, memory B cells scarcely accumulated mutations and reconstituted the secondary response by low affinity, supporting the notion that low-affinity memory B cells are generated in a GC-independent manner. Thus, it appears that memory B cells are established by two different pathways, associated with or without GC reaction and affinity maturation. The generation and long-term persistence of low-affinity IgG1 memory B cells and antibodies in ICOS-manipulated mice support the idea that low-affinity memory B cells may give rise to long-term antibody-forming cells.

Effect of inflammation on costimulation blockade-resistant allograft rejection

Previously, we reported that allogeneic skin grafts were rapidly rejected by CD28 and CD40 ligand double deficient mice mediated by CD8+ T cells. These results indicated that some elements in addition to CD28- and CD40-mediated costimulation provide stimulatory signals for the activation of donor-specific CD8+ T cells. In this report, we investigated the role of inflammation associated with transplantation on costimulation-independent priming of CD8+ T cell during graft rejection. B6 RAG1 KO mice were transplanted with BALB/c-skin and adoptively transferred with syngeneic CD8+ T cells the same day or 50 days after transplantation. When blockade of CD28- and CD40-mediated costimulation failed to prevent acute rejection of freshly transplanted skin grafts, it efficiently delayed rejection of well-healed skin grafts. These results showed that factors associated with transplantation have essential roles in inducing costimulation blockade-resistant allograft rejection. Costimulation blockade failed to prevent acute graft-infiltration of NK cells and increasing expression of intragraft IL-12 and IL-15. These factors may trigger the graft-infiltration and priming of CD8+ T cells to induce costimulation blockade-resistant allograft rejection.

ICOS-mediated costimulation on Th2 differentiation is achieved by the enhancement of IL-4 receptor-mediated signaling

ICOS is the third member of the CD28 family molecules and plays a critical role in many T cell-dependent immune responses. Although accumulated data suggest that ICOS costimulatory signals play an important role in Th2-mediated immune responses, the molecular basis for this selective differentiation mechanism is largely unknown. To clarify this mechanism, we used DO11.10 TCR transgenic ICOS-/- mice and evaluated the nature of ICOS costimulatory signals during the process of Ag-specific activation and differentiation of naive CD4+ T cells. Results obtained from these experiments demonstrated that Ag stimulation of naive CD4+ T cells in the absence of an ICOS signal resulted in impaired Th2 development. Unlike previous reports, we found that primary IL-4 production by these T cells was intact and that IL-4R sensitivity of these T cells was reduced as evidenced by a profound defect in IL-4-induced Stat6 phosphorylation and the early induction of GATA-3. The fact that ICOS ligation of wild-type T cells significantly enhanced IL-4-induced Stat6 phosphorylation and primary GATA-3 induction, but not IL-4 transcription, of naive CD4+ T cells was consistent with the results obtained from ICOS-/- T cell experiments. These observations led us to propose that the predominant effect of ICOS-mediated costimulation on Th2 differentiation is achieved by the enhancement of IL-4R-mediated signaling.

[Regulation of immune response by T cell co-signaling. ]

The activation of naive T cells requires two signals from the antigen presenting cells (APC). Firstly, an antigen specific signal which is triggered by the binding of the T cell receptor (TCR) to the peptide-MHC complex, and secondly, antigen nonspecific signals initiated through a set of co-signalling receptors. Co-signalling molecules are cell-surface glycoproteins that play essential roles for the communication of a T cell with virtually all other host cells by modulating and fine-tuning TCR signals. On the basis of their functional outcome, co-signalling molecules can be divided into co-stimulators and co-inhibitors, which promote or suppress T-cell activation, respectively. By expression at the appropriate time and location, co-signalling molecules positively and negatively control the priming, growth, differentiation and functional maturation of a T-cell response. In this article, I overview property of co-signaling molecules in the CD28- and TNFR family and discuss their potential functional relationships with each other. In addition, role of these co-signalling molecules in various diseases, such as autoimmune diseases, graft rejection, allergy, inflammatory bowel disease, and cancer, and the therapeutic potential of targeting these molecules to enhance or curtail an ongoing immune response in these diseases are discussed.

The balance of immune responses: costimulation verse coinhibition

Many of the B7 superfamily members (e.g., B7-1, B7-2, ICOS-L, B7-H1, B7-DC) were initially characterized as T cell costimulatory molecules. However, more recently it has become clear they can also coinhibit T cell responses. We review many of the B7 family members, with a particular focus on B7-H1, and examine their role in autoimmunity, transplant rejection, and cancer pathogenesis. It is crucial to understand that many B7 family members have opposing effects on an immune response. This cautions against using clinical immunotherapeutic reagents targeted against these molecules until we gain a better understanding of the circumstances that regulate the outcomes of the T cell response.

Effects of double blockade of CD28 and inducible-costimulator signaling on anti–glomerular basement membrane glomerulonephritis

Inducible costimulator (ICOS) is the third member of the CD28 superfamily, expressed on antigen-primed T-cells, enhancing Th2 differentiation. Anti-glomerular basement membrane (anti-GBM) glomerulonephritis results from multiple effects generated by both Th1 and Th2 cells. To evaluate the contribution of these T-cells to the progression of anti-GBM glomerulonephritis, we investigated the effect of double blockade of CD28 and ICOS signaling. Anti-GBM glomerulonephritis was induced in C57BL/6 mice, a Th1-prone strain. CD28 signaling was inhibited with the use of fusion proteins of cytolytic T-lymphocyte-associated antigen-4 (CTLA4 immunoglobulin) and ICOS signaling by the monoclonal antibody (mAb) for ICOS. Blood and urine samples were collected 5 and 14 days after induction of anti-GBM glomerulonephritis. Mice were killed to facilitate histopathologic analyses at the same time. Anti-GBM glomerulonephritis was prevented from functionally deteriorating (eg, proteinuria or increasing serum creatinine) by CTLA4 immunoglobulin or anti-activation-inducible lymphocyte immunomodulatory molecule (AILIM) mAb as an anti-ICOS mAb. Nevertheless, double or single blockade of ICOS signaling showed a weaker inhibitory effect than single blockade of CD28 signaling in terms of the serum immunoglobulin level and histopathologic change. There is no synergistic effect between CTLA4 immunoglobulin and anti-AILIM mAb when simultaneously administered in experimental anti-GBM glomerulonephritis. Double blockade of both CD28 signaling and ICOS signaling is effective for preventing functional deterioration in this model. However, CD28 single blockade is more effective than double blockade both serologically and histopathologically.

Involvement of ICOS-B7RP-1 costimulatory pathway in the regulation of immune responses to Leishmania major and Nippostrongylus brasiliensis infections

The ICOS-B7RP-1-mediated T cell costimulatory pathway has been implicated crucial for T cell activation and differentiation. In this study, we investigated the role of this costimulation in the regulation of immune responses to parasitic infections by using blocking antibody against B7RP-1 as well as ICOS-deficient mice. The administration of anti-B7RP-1 monoclonal antibody (mAb) significantly suppressed the footpad swelling in susceptible BALB/c mice upon Leishmania major infection. The observation was consistent not only with the significant suppression of IL-4, IL-5 and IL-10 secretion from lymph node cells, which were derived from L. major-infected mice, but also with the significant reduction of total serum IgE and IgG(1) in anti-B7RP-1 mAb-treated BALB/c mice. Infection of ICOS-deficient mice with L. major also suggested the impaired Th2 immune responses in the absence of this costimulation. The immunological function of ICOS-B7RP-1 costimulatory pathway in infection was further confirmed by infecting anti-B7RP-1 mAb-treated wild type or ICOS-deficient mice with Nippostrongylus brasiliensis. The characteristic elevation of total serum IgE and eosinophilia upon N. brasiliensis infection was suppressed by blocking this costimulation. Moreover, the protection to N. brasiliensis adult worms was suppressed in anti-B7RP-1 mAb-treated wild type or ICOS-deficient mice. These results suggest the crucial role of this costimulatory pathway in the regulation of Th2-biased T cell differentiation and in host immune responses against L. major and N. brasiliensis infections.

Akt is a neutral amplifier for Th cell differentiation

Both CD28 and its relative, inducible costimulator (ICOS), have a binding motif for phosphatidylinositol 3-kinase (PI3K) in their cytoplasmic tail, and the binding of PI3K leads to activation of a serine/threonine kinase, Akt. The role of Akt in cytokine production and helper T (Th) cell differentiation remains obscure. In this study, we found that enforced expression of the constitutively active form (E40K) of Akt rendered CD4(+) T cells activated. Wild-type of Akt and E40K promoted Th1 cell differentiation in C57BL/6-derived and Th1-polarized BALB/c-derived CD4(+) T cells, while both promoted Th2 cell differentiation in BALB/c-derived and Th2-polarized C57BL/6 CD4(+) T cells. E40K also facilitated Th1 differentiation in CD4(+) T cells from IL-4-deficient mice with the BALB/c background. E40K up-regulated expression of NF-AT and c-Myb, which may be related to the augmentation of cytokine production by E40K. These findings indicate that the mechanism by which Akt augments cytokine production via CD28 and ICOS is Th cell type-specific and reflects the intracellular status affected by the cytokine milieu. We conclude that Akt is a neutral amplifier of T cell activation and Th differentiation.

New B7 family members with positive and negative costimulatory function

The B7 family of T-cell costimulatory molecules has expanded considerably in recent years. Among the new costimulatory molecules discovered are inhibitory and activating pathways. Both ligands and receptors often have multiple binding partners, adding to the complexity of T-cell regulation. Some B7 molecules also exhibit reverse signaling, affecting activation of both antigen-presenting cells and T cells. An increased understanding of these pathways of T-cell regulation results in promising new therapeutics because T-cell interference can be better targeted to specific states of activation or location. This will decrease side-effects such as systemic immunosuppression and increase efficiency. Targeting B7 molecular pathways for either inhibiting or increasing cell-mediated immunity has so far shown promising results in models of autoimmunity, transplant rejection and tumor immunotherapy.

Involvement of inducible costimulator-B7 homologous protein costimulatory pathway in murine lupus nephritis

Inducible costimulator (ICOS)-B7 homologous protein (B7h) is a new member of the CD28-B7 family of costimulatory molecules that regulates T cell-dependent humoral immune responses. In this study, we examined the involvement of this costimulatory pathway in the development and progression of lupus in NZB/W F(1) mice. Expression of ICOS on T cells was enhanced with disease progression, whereas B7h expression on B cells was down-regulated. Administration of anti-B7h mAb before the onset of renal disease significantly delayed the onset of proteinuria and prolonged survival. Blockade of B7h effectively inhibited all subclasses of IgG autoantibody production and accumulation of both Th1 and Th2 cells. Hypercellularity and deposition of IgG and C3 in glomeruli were significantly reduced. B7h blockade after the onset of proteinuria prevented the disease progression and improved the renal pathology. Our results demonstrated the involvement of the ICOS-B7h costimulatory pathway in the pathogenesis of lupus nephritis, and the blockade of this pathway may be beneficial for the treatment of human systemic lupus erythematosus.

The role of the ICOS-B7h T cell costimulatory pathway in transplantation immunity

Inducible costimulatory molecule (ICOS) plays a pivotal role in T cell activation and Th1/Th2 differentiation. ICOS blockade has disparate effects on immune responses depending on the timing of blockade. Its role in transplantation immunity, however, remains incompletely defined. We used a vascularized mouse cardiac allograft model to explore the role of ICOS signaling at different time points after transplantation, targeting immune initiation (early blockade) or the immune effector phase (delayed blockade). In major histocompatibility-mismatched recipients, ICOS blockade prolonged allograft survival using both protocols but did so more effectively in the delayed-treatment group. By contrast, in minor histocompatibility-mismatched recipients, early blockade accelerated rejection and delayed blockade prolonged graft survival. Alloreactive CD4+ T cell expansion and alloantibody production were suppressed in both treatment groups, whereas only delayed blockade resulted in suppression of effector CD8+ T cell generation. After delayed ICOS blockade, there was a diminished frequency of allospecific IL-10-producing cells and an increased frequency of both IFN-gamma- and IL-4-producing cells. The beneficial effects of ICOS blockade in regulating allograft rejection were seen in the absence of CD28 costimulation but required CD8+ cells, cytotoxic T lymphocyte antigen-4, and an intact signal transducer and activator of transcription-6 pathway. These data define the complex functions of the ICOS-B7h pathway in regulating alloimmune responses in vivo.

Pathogenesis and treatment of graft-versus-host disease after bone marrow transplant

Stem cell transplantation is being used to treat a number of hematologic malignancies as well as hematologic and immune deficiency states. The ages of patients being offered this therapy and the donor marrow sources have been expanded. One persistent problem has been graft-versus-host disease (GVHD). This article reviews the basic biology of GVHD, clinical manifestations of acute and chronic GVHD, prophylaxis and treatment of acute GVHD, and treatment of chronic GVHD.

Evaluation of inducible costimulator/B7-related protein-1 as a therapeutic target in a murine model of allergic airway inflammation

Given its primary role in the execution of T cell, and especially Th2, effector activity, the inducible costimulator (ICOS)/B7-related protein (RP)-1 costimulatory pathway is currently being heralded as a promising therapeutic target for immune-inflammatory disorders such as asthma. This study investigates the merits of ICOS blockade in a murine model of experimental asthma in which mice are sensitized to ovalbumin (OVA) through the respiratory mucosa. Intraperitoneal treatment of mice with anti-ICOS neutralizing antibody during sensitization resulted in a marked reduction in airway eosinophilia and IL-5 in bronchoalveolar lavage, but had no effect on interleukin (IL)-4, IL-13, and eotaxin content in bronchoalveolar lavage or the production of OVA-specific immunoglobulin E in serum. Cultured splenocytes from mice sensitized to OVA in the context of ICOS ablation produced enhanced levels of IL-4 and IL-5 upon stimulation with OVA, and this correlated with elevated inflammation and immunoglobulin E secretion upon long-term in vivo OVA recall; the deleterious effects ICOS blockade, however, were not associated with reduced IL-10 production by splenocytes. Peculiarly, anti-ICOS intervention during OVA rechallenge had no effect on airway inflammation or immunoglobulin production, despite high levels of ICOS expression on infiltrating CD4+ T cells. This study provides in vivo evidence of an exacerbated long-term immune-inflammatory response following acute ICOS blockade, and suggests that ICOS costimulation is functionally redundant in established allergic disease.

Acceptance of islet allografts in the liver of mice by blockade of an inducible costimulator

BACKGROUND

An inducible costimulator (ICOS) has been found to be a novel costimulator for T-cell activation, although its precise role in transplant immunobiology remains unclear. This study determined whether ICOS plays an essential role in rejection of intrahepatic islet allografts in streptozotocin-induced diabetic mice.

METHODS

Mononuclear cells in the liver of mice were isolated and examined by flow cytometry with respect to expression of ICOS in association with rejection, and the effects of in vivo treatment with an anti-ICOS antibody on survival of intrahepatic islet allografts were determined. RESULTSFlow cytometric analysis of mononuclear cells in the liver of normal untreated mice revealed that ICOS is expressed on CD4+CD3int natural killer T cells. The expression of ICOS was up-regulated on CD4+CD3bright T cells and expanded CD8 T cells in the liver in association with rejection. Posttransplant short-term administration of anti-ICOS antibody alone produced a significant prolongation of islet allograft survival. Administration of the antibody in conjunction with a subtherapeutic regimen of FK506 prevented rejection, leading to the acceptance of islet allografts.

CONCLUSION

ICOS has an essential role in rejection of intrahepatic islet allografts and the blockade of ICOS interaction might be a novel approach for preventing islet allograft rejection.