Inhibition of T cell activation and autoimmune diabetes using a B cell surface-linked CTLA-4 agonist

A better understanding of the role of the CTLA-CD80/86 axis in the treatment of autoimmune diseases

Autoimmune diseases are diseases in which the regulatory mechanisms of the immune response are disturbed. As a result, the body loses self-tolerance. Since one of the main regulatory mechanisms of the immune response is the CTLA4-CD80/86 axis, this hypothesis suggests that autoimmune diseases potentially share a similar molecular basis of pathogenesis. Hence, investigating the CTLA4-CD80/86 axis may be helpful in finding an appropriate treatment strategy. Therefore, this study aims to investigate the molecular basis of the CTLA4-CD80/86 axis in the regulation of the immune response, and then its role in developing some autoimmune diseases, including systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. As well, the main therapeutic strategies affecting the CTLA4-CD80/86 axis have been summarized to highlight the importance of this axis in management of autoimmune diseases.

CD44 is a potential immunotherapeutic target and affects macrophage infiltration leading to poor prognosis

CD44 plays a key role in the communication of CSCs with the microenvironment and the regulation of stem cell properties. UALCAN was used to analyze the expression of CD44 in bladder cancer (BLCA) and normal tissue. The UALCAN was utilized to analyze the prognostic value of CD44 in BLCA. The TIMER database was used to explore the relationship between CD44 and PD-L1; CD44 and tumor-infiltrating immune cells. The regulatory effect of CD44 on PD-L1 was verified by cell experiments in vitro. IHC confirmed the results of the bioinformatics analysis. GeneMania and Metascape were used to analyze protein-protein interaction (PPI) investigations and functional enrichment analysis. We found that BLCA patients with high CD44 expression had worse survival than those with low CD44 expression (P < 0.05). IHC and the TIMER database results showed that CD44 expression was positively correlated with PD-L1 expression (P < 0.05). At the cellular level, the expression of PD-L1 was significantly inhibited after CD44 expression was inhibited by siRNA. Immune infiltration analysis showed that CD44 expression levels in BLCA were significantly correlated with immune infiltration levels of different immune cells. IHC staining results further confirmed that the expression of CD44 in tumor cells was positively associated with the number of CD68⁺ macrophages and CD163⁺ macrophages (P < 0.05). Our results suggest that CD44 is a positive regulator of PD-L1 in BLCA and may be a key regulator of tumor macrophages infiltration and may be involved in M2 macrophage polarization. Our study provided new insights into the prognosis and immunotherapy of BLCA patients through macrophage infiltration and immune checkpoints.

Activation of T cell checkpoint pathways during β-cell antigen presentation by engineered dendritic cells promotes protection from type 1 diabetes

Defective immune regulation has been recognized in type 1 diabetes (T1D). Immune regulatory T cell check-point receptors, which are generally upregulated on activated T cells, have been the molecules of attention as therapeutic targets for enhancing immune response in tumor therapy. Here, we show that pancreatic β-cell antigen (BcAg) presentation by engineered tolerogenic dendritic cells (tDCs) that express CTLA4 selective ligand (B7.1wa) or a combination of CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively; multiligand-DCs) causes an increase in regulatory cytokine and T cell (Treg) responses and suppression of the effector T cell function as compared to engineered control-DCs. Non-obese diabetic (NOD) mice treated with BcAg-pulsed CTLA4-ligand-DCs and multiligand-DCs at pre-diabetic and early-hyperglycemic stages showed significantly lower degree of insulitis, higher frequencies of insulin-positive islets, profound delay in, and reversal of, hyperglycemia for a significant duration. Immune cells from the tDC treated mice not only produced lower amounts of IFNγ and higher amounts of IL10 and TGFβ1 upon BcAg challenge, but also failed to induce hyperglycemia upon adoptive transfer. While both CTLA4-ligand-DCs and multiligand-DCs were effective in inducing tolerance, multiligand-DC treatment produced an overall higher suppressive effect on effector T cell function and disease outcome. These studies show that enhanced engagement of T cell checkpoint receptors during BcAg presentation can modulate T cell function and suppress autoimmunity and progression of the disease in T1D.

The potential for immune checkpoint modulators in cerebrovascular injury and inflammation

Introduction: Neuroinflammation has been linked to poor neurologic and functional outcomes in many cerebrovascular disorders. Immune checkpoints are upregulated in the setting of traumatic brain injury, intracerebral hemorrhage, ischemic stroke, central nervous systems vasculitis, and post-hemorrhagic vasospasm, and are potential mediators of pathologic inflammation. Burgeoning evidence suggests that immune checkpoint modulation is a promising treatment strategy to decrease immune cell recruitment, cytokine secretion, brain edema, and neurodegeneration.Areas covered: This review discusses the role of immune checkpoints in neuroinflammation, and the potential for therapeutic immune checkpoint modulation in inflammatory cerebrovascular disorders. A search of Pubmed and clinicaltrials.gov was performed to find relevant literature published within the last 50 years.Expert opinion: The clinical success of immune-activating checkpoint modulators in human cancers has shown the immense clinical potential of checkpoint-based immunotherapy. Given that checkpoint blockade can also precipitate a pathologic pro-inflammatory or autoimmune response, it is plausible that these pathways may also be targeted to quell aberrant inflammation. A limited but growing number of studies suggest that immune checkpoints play a critical role in regulating the immune response in the central nervous system in a variety of contexts, and that immune-deactivating checkpoint modulators may be a promising treatment strategy for acute and chronic neuroinflammation in cerebrovascular disorders.

Inhibitory receptor agonists: the future of autoimmune disease therapeutics?

Central and peripheral tolerance both contribute to protection against autoimmunity. The pathogenesis of autoimmunity, however, can result from critical deficits or limitations in peripheral and/or central tolerance mechanisms, presenting an opportunity for therapeutic intervention. Recent advances highlight the substantial impact of inhibitory receptors (IRs), which mediate peripheral tolerance, in autoimmunity. Deletion and blockade studies in mice, IR disruption in humans, and correlation with positive disease outcomes all highlight potential clinical benefits of enhancing IR signaling (agonism)-specifically CTLA4, PD1, LAG3, TIM3 and TIGIT-to treat autoimmune disease. Although critical questions remain, IR agonists represent an unappreciated and untapped opportunity for the treatment of autoimmune and inflammatory diseases.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Engineered Dendritic Cell-Directed Concurrent Activation of Multiple T cell Inhibitory Pathways Induces Robust Immune Tolerance

Inhibitory/repressor-receptors are upregulated significantly on activated T cells, and have been the molecules of attention as targets for inducing immune tolerance. Induction of effective antigen specific tolerance depends on concurrent engagement of the TCR and one or more of these inhibitory receptors. Here, we show, for the first time that dendritic cells (DCs) can be efficiently engineered to express multiple T cell inhibitory ligands, and enhanced engagement of T cell inhibitory receptors, upon antigen presentation, by these DCs can induce effective CD4+ T cell tolerance and suppress autoimmunity. Compared to control DCs, antigen presentation by DCs that ectopically express CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively) individually (mono-ligand DCs) or in combination (multi-ligand DCs) causes an inhibition of CD4+ T cell proliferation and pro-inflammatory cytokine response, as well as increase in Foxp3+ Treg frequency and immune regulatory cytokine production. Administration of self-antigen (mouse thyroglobulin; mTg) loaded multi-ligand DCs caused hyporesponsiveness to mTg challenge, suppression of autoantibody production, and amelioration of experimental autoimmune thyroiditis. Overall, this study shows that engineered DC-directed enhanced concurrent activation of multiple T cell coinhibitory pathways is an effective way to induce self-antigen specific T cell tolerance to suppress ongoing autoimmunity.

CTLA-4 polymorphism rs231775: Influence on relapse and survival after allogeneic hematopoietic stem cell transplantation in childhood

OBJECTIVE

Relapse following allogeneic hematopoietic stem cell transplantation (HSCT) is still linked to a poor prognosis. Mainly, donor`s T-cells mediate the graft-versus-leukemia effect. Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is an inhibitory molecule which down-regulates T-cell activation. Single nucleotide polymorphism (SNP) in CTLA-4 may have an effect on immune response.

METHODS

Eighty-eight children with acute leukemia and their donors were genotyped of CTLA-4 gene for rs231775. We searched for an association of CTLA-4 SNP with relapse and survival after allogeneic HSCT.

RESULTS

We identified a significantly reduced relapse rate in children who received a transplant from a donor with the CTLA-4 genotypes AG or GG in comparison with genotype AA of rs231775 (19% vs 40%, P = 0.026). In addition, we observed a significant difference in event-free survival (EFS) depending on the donor´s genotype. The EFS was 70% or 46% if the patient was transplanted from a donor with CTLA-4 genotype AG/GG or AA, respectively (P = 0.025). In multivariate analysis, CTLA-4 genotype was an independent risk factor for relapse rate (P = 0.028).

CONCLUSION

This study suggests that CTLA-4 polymorphism rs231775 is relevant for relapse and survival after allogeneic HSCT in childhood and should be further investigated in clinical trials.

Selective CD28 Inhibition Modulates Alloimmunity and Cardiac Allograft Vasculopathy in Anti-CD154-Treated Monkeys

BACKGROUND

Selective CD28 inhibition is actively pursued as an alternative to B7 blockade using cytotoxic T lymphocyte antigen 4 Ig based on the hypothesis that the checkpoint immune regulators cytotoxic T lymphocyte antigen 4 and programmed death ligand 1 will induce tolerogenic immune signals. We previously showed that blocking CD28 using a monovalent nonactivating reagent (single-chain anti-CD28 Fv fragment linked to alpha-1 antitrypsin [sc28AT]) synergizes with calcineurin inhibitors in nonhuman primate (NHP) kidney and heart transplantation. Here, we explored the efficacy of combining a 3-week "induction" sc28AT treatment with prolonged CD154 blockade.

METHODS

Cynomolgus monkey heterotopic cardiac allograft recipients received sc28AT (10 mg/kg, d0-20, n = 3), hu5C8 (10-30 mg/kg, d0-84, n = 4), or combination (n = 6). Graft survival was monitored by telemetry. Protocol biopsies and graft explants were analyzed for International Society of Heart and Lung Transplantation acute rejection grade and cardiac allograft vasculopathy score. Alloantibody, T-cell phenotype and regulatory T cells were analyzed by flow cytometry. Immunochemistry and gene expression (NanoString) characterized intra-graft cellular infiltration.

RESULTS

Relative to modest prolongation of median graft survival time with sc28AT alone (34 days), hu5C8 (133 days), and sc28AT + hu5C8 (141 days) prolonged survival to a similar extent. CD28 blockade at induction, added to hu5C8, significantly attenuated the severity of acute rejection and cardiac allograft vasculopathy during the first 3 months after transplantation relative to hu5C8 alone. These findings were associated with decreased proportions of circulating CD8 and CD3CD28 T cells, and modulation of inflammatory gene expression within allografts.

CONCLUSIONS

Induction with sc28AT promotes early cardiac allograft protection in hu5C8-treated NHPs. These results support further investigation of prolonged selective CD28 inhibition with CD40/CD154 blockade in NHP transplants.

Immune Checkpoints as Therapeutic Targets in Autoimmunity

Antibodies that block the immune checkpoint receptors PD1 and CTLA4 have revolutionized the treatment of melanoma and several other cancers, but in the process, a new class of drug side effect has emerged—immune related adverse events. The observation that therapeutic blockade of these inhibitory receptors is sufficient to break self-tolerance, highlights their crucial role in the physiological modulation of immune responses. Here, we discuss the rationale for targeting immune checkpoint receptors with agonistic agents in autoimmunity, to restore tolerance when it is lost. We review progress that has been made to date, using Fc-fusion proteins, monoclonal antibodies or other novel constructs to induce immunosuppressive signaling through these pathways. Finally, we explore potential mechanisms by which these receptors trigger and modulate immune cell function, and how understanding these processes might shape the design of more effective therapeutic agents in future.

CTLA-4 polymorphisms: influence on transplant-related mortality and survival in children undergoing allogeneic hematopoietic stem cell transplantation

PURPOSE

Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative approach for a variety of hematological diseases; however, it is still associated with substantial morbidity and mortality. Transplant-related mortality (TRM) after HSCT depends mainly on the toxicity of the conditioning regimen, infections, and graft-versus-host disease. The purpose of this study was to identify the association between CTLA-4 single nucleotide polymorphisms and TRM in children undergoing allogeneic HSCT.

METHODS

153 donors and 153 children with acute lymphoblastic leukemia, acute myeloid leukemia or juvenile myelomonocytic leukemia who had undergone allogeneic HSCT were genotyped of CTLA-4 gene for rs3087243 (CT60G>A), rs231775 (+ 49 A>G) and rs4553808 using TaqMan real-time polymerase chain reaction.

RESULTS

We observed a significant association between the donor's CLTA-4 genotype of rs3087243 and TRM in children undergoing allogeneic HSCT. Genotype AG was found in 78 donors (51%), GG in 44 donors (29%) and 31 donors (20%) were homozygous for AA. 30 patients died as a result of transplant-related causes. Interestingly, we observed a significantly reduced TRM in children who were transplanted from a donor with the CTLA-4 genotype GG in comparison to genotype AG or AA (9 versus 19 versus 36%, P = 0.013). In addition, we found significant differences of event-free survival (EFS) depending on the donor's genotype. The EFS was 64, 46 or 32% if the patient was transplanted from a donor with CTLA-4 genotype GG, AG or AA, respectively (P = 0.043). In multivariate analysis, CTLA-4 genotype of rs3087243 was an independent risk factor for TRM (P = 0.011) and EFS (P = 0.035).

CONCLUSION

This study provides first evidence that the CTLA-4 polymorphisms are significant risk factors for TRM and survival in children undergoing allogeneic HSCT and should be evaluated in further trials.

Co-stimulatory and Co-inhibitory Pathways in Autoimmunity

The immune system is guided by a series of checks and balances, a major component of which is a large array of co-stimulatory and co-inhibitory pathways that modulate the host response. Although co-stimulation is essential for boosting and shaping the initial response following signaling through the antigen receptor, inhibitory pathways are also critical for modulating the immune response. Excessive co-stimulation and/or insufficient co-inhibition can lead to a breakdown of self-tolerance and thus to autoimmunity. In this review, we will focus on the role of co-stimulatory and co-inhibitory pathways in two systemic (systemic lupus erythematosus and rheumatoid arthritis) and two organ-specific (multiple sclerosis and type 1 diabetes) emblematic autoimmune diseases. We will also discuss how mechanistic analysis of these pathways has led to the identification of potential therapeutic targets and initiation of clinical trials for autoimmune diseases, as well as outline some of the challenges that lie ahead.

CTLA-4, an Essential Immune-Checkpoint for T-Cell Activation

The response of peripheral T lymphocytes (T cell) is controlled by multiple checkpoints to avoid unwanted activation against self-tissues. Two opposing costimulatory receptors, CD28 and CTLA-4, on T cells bind to the same ligands (CD80 and CD86) on antigen-presenting cells (APCs), and provide positive and negative feedback for T-cell activation, respectively. Early studies suggested that CTLA-4 is induced on activated T cells and binds to CD80/CD86 with much stronger affinity than CD28, providing a competitive inhibition. Subsequent studies by many researchers revealed the more complex mode of T-cell inhibition by CTLA-4. After T-cell activation, CTLA-4 is stored in the intracellular vesicles, and recruited to the immunological synapse formed between T cells and APCs, and inhibits further activation of T cells by blocking signals initiated by T-cell receptors and CD28. CTLA-4-positive cells can also provide cell-extrinsic regulation on other autoreactive T cells, and are considered to provide an essential regulatory mechanism for FoxP3+ regulatory T cells. Genetic deficiency of CTLA-4 leads to CD28-mediated severe autoimmunity in mice and humans, suggesting its function as a fundamental brake that restrains the expansion and activation of self-reactive T cells. In cancer, therapeutic approaches targeting CTLA-4 by humanized blocking antibodies has been demonstrated to be an effective immunotherapy by reversing T-cell tolerance against tumors. This chapter introduces CTLA-4 biology, including its discovery and mechanism of action, and discusses questions related to CTLA-4.

B-1 cells produce insulin and abrogate experimental streptozotocin-induced diabetes

The participation of B-1 cells in a murine model of spontaneous diabetes has been recently reported. Here, we describe the role of B-1 cells in streptozotocin (STZ) induced diabetes in mice. We demonstrated that XID (B-1 cell-deficient) mice are more susceptible to STZ treatment than WT mice, as evidenced by their higher blood glucose level in response to STZ. Unexpectedly, the XID mice that were i.p. transferred with purified B-1 cells, either before or after the STZ treatment, did not develop diabetes. These cell transfers provided long-lasting protection for the XID mice against STZ-induced diabetes, suggesting that B-1 cells play an important role in the experimental diabetes pathobiology. We also showed that B-1 cell culture supernatants were able to regulate the blood glucose level of the diabetic XID mice, and we identified insulin-producing cells when B-1 cells were differentiated in B-1 cell-derived phagocyte in vitro. These findings provide a novel role for B-1 cells in metabolic processes, presenting a new mechanism to explain the pathogenesis of diabetes and a possible therapeutical target.

Targeting dendritic cell function during systemic autoimmunity to restore tolerance

Systemic autoimmune diseases can damage nearly every tissue or cell type of the body. Although a great deal of progress has been made in understanding the pathogenesis of autoimmune diseases, current therapies have not been improved, remain unspecific and are associated with significant side effects. Because dendritic cells (DCs) play a major role in promoting immune tolerance against self-antigens (self-Ags), current efforts are focusing at generating new therapies based on the transfer of tolerogenic DCs (tolDCs) during autoimmunity. However, the feasibility of this approach during systemic autoimmunity has yet to be evaluated. TolDCs may ameliorate autoimmunity mainly by restoring T cell tolerance and, thus, indirectly modulating autoantibody development. In vitro induction of tolDCs loaded with immunodominant self-Ags and subsequent cell transfer to patients would be a specific new therapy that will avoid systemic immunosuppression. Herein, we review recent approaches evaluating the potential of tolDCs for the treatment of systemic autoimmune disorders.

A novel pancreatic β-cell targeting bispecific-antibody (BsAb) can prevent the development of type 1 diabetes in NOD mice

To prepare a novel Bispecific Antibody (BsAb) as a potential targeted therapy for T1D, we produced a "functionally inert" monoclonal antibody (mAb) against Glucose transporter-2 (GLUT-2) expressed on β-cells to serve as an anchoring antibody. The therapeutic arm is an agonistic mAb against Cytotoxic T-Lymphocyte Antigen 4 (CTLA-4), a negative regulator of T-cell activation expressed on activated CD4+ T-cells. A BsAb was prepared by chemically coupling an anti-GLUT2 mAb to an agonistic anti-CTLA-4 mAb. This BsAb was able to bind to GLUT2 and CTLA-4 in vitro, and to pancreatic islets, both in vitro and in vivo. We tested the safety and efficacy of this BsAb by treating Non-Obese Diabetes (NOD) mice and found that it could delay the onset of diabetes with no apparent undesirable side effects. Thus, engagement of CTLA-4 on activated T cells from target tissue can be an effective way to treat type-1 diabetes.

Alternative splice forms of CTLA-4 induced by antisense mediated splice-switching influences autoimmune diabetes susceptibility in NOD mice

Activated and regulatory T cells express the negative co-stimulatory molecule cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) that binds B7 on antigen-presenting cells to mediate cellular responses. Single nucleotide polymorphisms in the CTLA-4 gene have been found to affect alternative splicing and are linked to autoimmune disease susceptibility or resistance. Increased expression of a soluble splice form (sCTLA-4), lacking the transmembrane domain encoded by exon 3, has been shown to accelerate autoimmune pathology. In contrast, an exon 2-deficient form lacking the B7 ligand binding domain (liCTLA-4), expressed by diabetes resistant mouse strains has been shown to be protective when expressed as a transgene in diabetes susceptible non-obese diabetic (NOD) mice. We sought to employ an antisense-targeted splice-switching approach to independently produce these CTLA-4 splice forms in NOD mouse T cells and observe their relative impact on spontaneous autoimmune diabetes susceptibility. In vitro antisense targeting of the splice acceptor site for exon 2 produced liCTLA-4 while targeting exon 3 produced the sCTLA-4 form in NOD T cells. The liCTLA-4 expressing T cells exhibited reduced activation, proliferation and increased adhesion to intercellular adhesion molecule-1 (ICAM-1) similar to treatment with agonist α-CTLA-4. Mice treated to produce liCTLA-4 at the time of elevated blood glucose levels exhibited a significant reduction in the incidence of insulitis and diabetes, whereas a marked increase in the incidence of both was observed in animals treated to produce sCTLA-4. These findings provide further support that alternative splice forms of CTLA-4 affects diabetes susceptibility in NOD mice and demonstrates the therapeutic utility of antisense mediated splice-switching for modulating immune responses.

Breakdown in peripheral tolerance in type 1 diabetes in mice and humans

Type 1 Diabetes (T1D), also called juvenile diabetes because of its classically early onset, is considered an autoimmune disease targeting the insulin-producing β cells in the pancreatic islets of Langerhans. T1D reflects a loss of tolerance to tissue self-antigens caused by defects in both central tolerance, which aims at eliminating potentially autoreactive lymphocytes developing in the thymus, and peripheral tolerance, which normally controls autoreactive T cells that escaped the thymus. Like in other autoimmune diseases, the mechanisms leading to T1D are multifactorial and depend on a complex combination of genetic, epigenetic, molecular, and cellular elements that result in the breakdown of peripheral tolerance. In this article, we discuss the contribution of these factors in the development of the autoimmune response targeting pancreatic islets in T1D and the therapeutic strategies currently being explored to correct these defects.

A bispecific protein capable of engaging CTLA-4 and MHCII protects non-obese diabetic mice from autoimmune diabetes

Crosslinking ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) with a bispecific fusion protein (BsB) comprised of a mutant mouse CD80 and lymphocyte activation antigen-3 (LAG-3) has been shown to attenuate TCR signaling and to direct T-cell differentiation toward Foxp3⁺ regulatory T cells (Tregs) in an allogenic mixed lymphocyte reaction (MLR). Here, we show that antigen-specific Tregs can also be induced in an antigen-specific setting in vitro. Treatment of non-obese diabetic (NOD) female mice between 9–12 weeks of age with a short course of BsB elicited a transient increase of Tregs in the blood and moderately delayed the onset of autoimmune type 1 diabetes (T1D). However, a longer course of treatment (10 weeks) of 4–13 weeks-old female NOD animals with BsB significantly delayed the onset of disease or protected animals from developing diabetes, with only 13% of treated animals developing diabetes by 35 weeks of age compared to 80% of the animals in the control group. Histopathological analysis of the pancreata of the BsB-treated mice that remained non-diabetic revealed the preservation of insulin-producing β-cells despite the presence of different degrees of insulitis. Thus, a bifunctional protein capable of engaging CTLA-4 and MHCII and indirectly co-ligating CTLA-4 to the TCR protected NOD mice from developing T1D.

Mechanistic basis of immunotherapies for type 1 diabetes mellitus

Type 1 diabetes (T1D) is an autoimmune disease for which there is no cure. The pancreatic beta cells are the source of insulin that keeps blood glucose normal. When susceptible individuals develop T1D, their beta cells are destroyed by autoimmune T lymphocytes and no longer produce insulin. T1D patients therefore depend on daily insulin injections for survival. Gene therapy in T1D aims at the induction of new islets to replace those that have been destroyed by autoimmunity. A major goal of T1D research is to restore functional beta cell mass while eliminating diabetogenic T cells in the hope of achieving insulin independence. Multiple therapeutic strategies for the generation of new beta cells have been under intense investigations. However, newly formed beta cells would be immediately destroyed by diabetogenic T cells. Therefore, successful islet induction therapy must be supported by potent immunotherapy that will protect the newly formed beta cells. Herein, we will summarize the current information on immunotherapies that aim at modifying T cell response to beta cells. We will first outline the immune mechanisms that underlie T1D development and progression and review the scientific background and rationale for specific modes of immunotherapy. Numerous clinical trials using antigen-specific strategies and immune-modifying drugs have been published, though most have proved too toxic or have failed to provide long-term beta cell protection. To develop an effective immunotherapy, there must be a continued effort on defining the molecular basis that underlies T cell response to pancreatic islet antigens in T1D.

Advances in CTLA-4-Ig-mediated modulation of inflammatory cell and immune response activation in rheumatoid arthritis

Rheumatoid arthritis (RA) is a multifactorial and polygenic immune-mediated disease, the pathogenesis of which involves different cell types. T and B lymphocytes, macrophages, endothelial cells, fibroblasts and osteoclasts have all been implicated in mediating the production of autoantibodies, proinflammatory cytokines and ultimately bone erosions. Cytotoxic T lymphocyte-associated antigen 4 immunoglobulin fusion protein (CTLA-4-Ig, abatacept) is a unique biologic agent targeting the co-stimulatory molecules CD80/CD86, and is indicated for the treatment of moderate-to-severe RA in patients who have had an inadequate response to one or more disease-modifying anti-rheumatic drugs, including methotrexate or anti-tumor necrosis factor agents. There is a growing body of evidence that, through selective modulation of the CD80/CD86 co-stimulatory molecules expressed by a variety of activated cell types, CTLA-4-Ig may inhibit the pathogenic RA process at several levels, both directly and indirectly. Here, we provide an overview of recent mechanistic studies of the action of CTLA-4-Ig on different cell types involved in mediating inflammation and joint damage in RA.

Cutting edge: chronic inflammatory liver disease in mice expressing a CD28-specific ligand

Inflammation of the normally tolerant liver microenvironment precedes the development of chronic liver disease. Study of the pathogenesis of autoimmune liver diseases, such as autoimmune hepatitis (AIH), has been hampered by a lack of autochthonous chronic animal models. Through our studies of T cell costimulation, we generated transgenic mice expressing a ligand specific for the CD28 receptor, which normally shares ligands with the related inhibitory receptor CTLA-4. The mice spontaneously develop chronic inflammatory liver disease with several pathologies found in AIH, including elevated serum aminotransferases in the context of normal alkaline phosphatase and bilirubin levels, lymphocytic inflammation, focal necrosis, oval cell hyperplasia, and fibrosis. The prevalence of IFN-γ-producing CD8(+) T cells in the livers of transgenic mice suggests a role for autoimmune cytotoxicity in the chronic disease state. The CD28 ligand-specific transgenic mice will facilitate evaluation of CD8(+) T cell function in liver disease pathologies found in AIH.

Preclinical efficacy and immunological safety of FR104, an antagonist anti-CD28 monovalent Fab' antibody

Antagonist anti-CD28 antibodies prevent T cell costimulation and differentiate from CTLA4Ig since they cannot block CTLA-4 and PDL-1 coinhibitory signals. They demonstrated efficacy in suppressing effector T cells while enhancing regulatory T cells function and immune tolerance. However, anti-CD28 antibodies devoid of immunotoxicity and with a good pharmacokinetic profile have not yet been developed. Here, we describe FR104, a novel humanized pegylated anti-CD28 Fab' antibody fragment presenting a long elimination half-life in monkeys. In vitro, FR104 failed to induce human T cell proliferation and cytokines secretion, even in the presence of anti-CD3 antibodies or when cross-linked with secondary antibodies. Furthermore, in humanized NOD/SCID mice adoptively transferred with human PBMC, whereas superagonist and divalent antibodies elicited rapid cytokines secretion and human T cell activation, FR104 did not. These humanized mice developed a florid graft-versus-host disease, which was prevented by administration of FR104 in a CTLA4-dependent manner. Interestingly, administration of high doses of CTLA4-Ig was ineffective to prevent GVHD, whereas administration of low doses was partially effective. In conclusion, we demonstrated that FR104 is devoid of agonist activity on human T cells and thus compatible with a clinical development that might lead to higher therapeutic indexes, by sparing CTLA-4, as compared to CD80/CD86 antagonists.

Ligation of cytotoxic T lymphocyte antigen-4 to T cell receptor inhibits T cell activation and directs differentiation into Foxp3+ regulatory T cells

Cross-linking of ligand-engaged cytotoxic T lymphocyte antigen-4 (CTLA-4) to the T cell receptor (TCR) during the early phase of T cell activation attenuates TCR signaling, leading to T cell inhibition. To promote this event, a bispecific fusion protein comprising a mutant mouse CD80 (CD80w88a) and lymphocyte activation antigen-3 was engineered to concurrently engage CTLA-4 and cross-link it to the TCR. Cross-linking is expected to be attained via ligation of CTLA-4 first to MHCII and then indirectly to the TCR, generating a CTLA-4-MHCII-TCR trimolecular complex that forms between T cells and antigen-presenting cells during T cell activation. Treating T cells with this bispecific fusion protein inhibited T cell activation. In addition, it induced the production of IL-10 and TGF-β and attenuated AKT and mTOR signaling. Intriguingly, treatment with the bispecific fusion protein also directed early T cell differentiation into Foxp3-positive regulatory T cells (Tregs). This process was dependent on the endogenous production of TGF-β. Thus, bispecific fusion proteins that engage CTLA-4 and co-ligate it to the TCR during the early phase of T cell activation can negatively regulate the T cell response. Bispecific biologics with such dual functions may therefore represent a novel class of therapeutics for immune modulation. These findings presented here also reveal a potential new role for CTLA-4 in Treg differentiation.

Profiling of differentially expressed genes in haemophilia A with inhibitor

Inhibitor development is the most significant complication in the therapy of haemophilia A (HA) patients. In spite of many studies, not much is known regarding the mechanism underlying inhibitor development. To understand the mechanism, we analysed profiles of differentially expressed genes (DEGs) between inhibitor and non-inhibitor HA via a microarray technique. Twenty unrelated Korean HAs were studied: 11 were non-inhibitor and nine were HA with inhibitor (≥5 BU mL(-1)). Microarray analysis was conducted using a Human Ref-8 expression Beadchip system (Illumina) and the data were analysed using Beadstudio software. We identified 545 DEGs in inhibitor HA as compared with the non-inhibitor patients; 384 genes were up-regulated and 161 genes were down-regulated. Among them, 75 genes whose expressions were altered by at least two-fold (>+2 or <-2) were selected and classified via the PANTHER classification method. The expressions of signal transduction and immunity-related genes differed significantly in the two groups. For validation of the DEGs, semi-quantitative RT-PCR (semi-qRT-PCR) was conducted with the six selected DEGs. The results corresponded to the microarray data, with the exception of one gene. We also examined the expression of the genes associated with the antigen presentation process via real-time PCR. The average levels of IL10, CTLA4 and TNFα slightly reduced, whereas that of IFNγ increased in the inhibitor HA group. We are currently unable to explain whether this phenomenon is a function of the inhibitor-inducing factor or is an epiphenomenon of antibody production. Nevertheless, our results provide a possible explanation for inhibitor development.

Common gamma chain cytokines promote rapid in vitro expansion of allo-specific human CD8+ suppressor T cells

Human CD8⁺ regulatory T cells, particularly the CD8⁺CD28⁻ T suppressor cells, have emerged as an important modulator of alloimmunity. Understanding the conditions under which these cells are induced and/or expanded would greatly facilitate their application in future clinical trials. In the current study, we develop a novel strategy that combines common gamma chain (γc) cytokines IL-2, IL-7 and IL-15 and donor antigen presenting cells (APCs) to stimulate full HLA-mismatched allogeneic human CD8⁺ T cells which results in significant expansions of donor-specific CD8⁺CD28⁻ T suppressor cells in vitro. The expanded CD8⁺CD28⁻ T cells exhibit increased expressions of CTLA-4, FoxP3, and CD25, while down-regulate expressions of CD56, CD57, CD127, and perforin. Furthermore, these cells suppress proliferation of CD4⁺ T cells in a contact-dependent and cytokine-independent manner. Interestingly, the specificity of suppression is restricted by the donor HLA class I antigens but promiscuous to HLA class II antigens, providing a potential mechanism for linked suppression. Taken together, our results demonstrate a novel role for common γc cytokines in combination with donor APCs in the expansion of donor-specific CD8⁺CD28⁻ T suppressor cells, and represent a robust strategy for in vitro generation of such cells for adoptive cellular immunotherapy in transplantation.

Selective CD28 blockade attenuates acute and chronic rejection of murine cardiac allografts in a CTLA-4-dependent manner

Selective blockade of CD28 is a promising therapy to inhibit pathogenic alloimmunity. However, evaluation of this approach in transplantation has been very limited. Using a novel nonactivating single-chain Fv-based reagent (α28scFv), we have investigated the role of CD28 and cytotoxic T lymphocyte antigen 4 (CTLA-4) in a murine cardiac transplant model. Blockade of CD28 for 2 weeks after engraftment promoted allograft survival, and significantly attenuated chronic rejection when combined with transient CD154-blockade or calcineurin inhibition. Graft acceptance was associated with decreased alloantibody production, increased proportion of early graft infiltration by regulatory T cells and increased expression of regulatory dendritic cell genes. Blockade of CTLA-4 during α28scFv-based treatments led to prompt rejection in all animals and inhibited expression of forkhead box P3 (Foxp3), programmed death (PD)-1 and 2,3-indoleamine dioxygenase (IDO) in the graft. These results show that CD28 signaling during the first weeks after transplant is a pivotal mediator of pathogenic alloimmunity, and that selective CD28 blockade prolongs graft acceptance by at least two immunomodulatory mechanisms. Selective CD28 inhibition while sparing CTLA-4 is thus a promising approach to inhibit pathogenic alloimmunity.

Intrinsic and extrinsic control of peripheral T-cell tolerance by costimulatory molecules of the CD28/ B7 family

Positive and negative costimulation by members of the CD28 family is critical for the development of productive immune responses against foreign pathogens and their proper termination to prevent inflammation-induced tissue damage. In addition, costimulatory signals are critical for the establishment and maintenance of peripheral tolerance. This paradigm has been established in many animal models and has led to the development of immunotherapies targeting costimulation pathways for the treatment of cancer, autoimmune disease, and allograft rejection. During the last decade, the complexity of the biology of costimulatory pathways has greatly increased due to the realization that costimulation does not affect only effector T cells but also influences regulatory T cells and antigen-presenting cells. Thus, costimulation controls T-cell tolerance through both intrinsic and extrinsic pathways. In this review, we discuss the influence of costimulation on intrinsic and extrinsic pathways of peripheral tolerance, with emphasis on members of the CD28 family, CD28, cytotoxic T-lymphocyte antigen-4 (CTLA-4), and programmed death-1 (PD-1), as well as the downstream cytokine interleukin-1 (IL-2).

OX40 engagement stabilizes Mxd4 and Mnt protein levels in antigen-stimulated T cells leading to an increase in cell survival

OX40 engagement on activated T cells leads to increased proliferation, expansion and survival of Ag-specific T cells. Direct ex vivo examination of Ag-stimulated murine T cells show that the Myc antagonists, Mxd4 and Mnt, are transiently upregulated and translocated to the nucleus following OX40 engagement and may be involved in suppressing cell death. Both Mxd4 and Mnt are upregulated following OX40 stimulation through increased protein stability and we identify a critical phosphorylation site in Mxd4 that controls Mxd4 stability. The upregulation of Mxd4 and Mnt contributes to OX40-mediated T-cell survival because siRNA knockdown of Mxd4 and Mnt led to increased cell death. We hypothesize the upregulation of c-Myc following OX40 engagement drives T-cell proliferation and that upregulation of Mxd4 and Mnt suppresses Myc-dependent cell death. Thus, Mxd4 and Mnt upregulation following OX40 engagement most likely increases T-cell survival.

Recent insights into the mechanism of action of glatiramer acetate

Glatiramer acetate (GA, Copaxone®, co-polymer 1) is an immunomodulatory therapy approved in 1996 by the United States Food and Drug Administration for treatment of relapsing-remitting multiple sclerosis. GA has a good safety profile, moderate efficacy, and a unique mode of action. Recent evidence in an animal model of MS, experimental autoimmune encephalomyelitis (EAE), suggests that GA effects on NK cells and B cells may contribute to therapeutic efficacy. We review the mechanism of action of GA, with particular focus on recent data suggesting a role for regulatory B cells.

Determinants of thyroid autoantibody production in Hashimoto's thyroiditis

Hashimoto's thyroiditis (HT) is the most prevalent thyroid autoimmune disorder, characterized by the presence of specific thyroid autoantibodies (TAb). The development of autoimmunity, including TAb production and clinical presentation of HT, is determined by a complex interplay of genetic susceptibility and several endogenous and environmental factors, which are discussed in this article. During the progression of the disease, TAb production precedes clinical manifestations, although the correlation between TAb concentrations and thyroid function is weak. We do not treat euthyroid HT patients despite elevated TAb; while in hypothyroidism, replacement therapy with l-thyroxine is required. Until now, an effective approach to prevent TAb production and the development of clinical disease has not yet been established. However, further identification of risk factors and their interaction may help in the prevention of thyroid autoimmunity.

Dendritic cell-directed CTLA-4 engagement during pancreatic beta cell antigen presentation delays type 1 diabetes

The levels of expression of alternatively spliced variants of CTLA-4 and insufficient CTLA-4 signaling have been implicated in type 1 diabetes. Hence, we hypothesized that increasing CTLA-4-specific ligand strength on autoantigen-presenting dendritic cells (DCs) can enhance ligation of CTLA-4 on T cells and lead to modulation of autoreactive T cell response. In this study, we show that DC-directed enhanced CTLA-4 engagement upon pancreatic beta cell Ag presentation results in the suppression of autoreactive T cell response in NOD mice. The T cells from prediabetic NOD mice treated with an agonistic anti-CTLA-4 Ab-coated DC (anti-CTLA-4-Ab DC) showed significantly less proliferative response and enhanced IL-10 and TGF-beta1 production upon exposure to beta cell Ags. Furthermore, these mice showed increased frequency of Foxp3+ and IL-10+ T cells, less severe insulitis, and a significant delay in the onset of hyperglycemia compared with mice treated with control Ab-coated DCs. Further analyses showed that diabetogenic T cell function was modulated primarily through the induction of Foxp3 and IL-10 expression upon Ag presentation by anti-CTLA-4-Ab DCs. The induction of Foxp3 and IL-10 expression appeared to be a consequence of increased TGF-beta1 production by T cells activated using anti-CTLA-4-Ab DCs, and this effect could be enhanced by the addition of exogenous IL-2 or TGF-beta1. Collectively, this study demonstrates the potential of a DC-directed CTLA-4 engagement approach not only in treating autoimmunity in type 1 diabetes, but also in altering diabetogenic T cell function ex vivo for therapy.

Mechanisms maintaining peripheral tolerance

The presentation of self-peptide-MHC complexes in the periphery to potentially autoreactive T cells that have escaped negative selection in the thymus poses an important problem to the immune system. In this review, I discuss data that reveal barriers preventing peripheral T cell recognition of self-peptide-MHC complexes, as well as the physiological mechanisms that ensure the elimination or functional inactivation (anergy) of T cells that do come to recognize self-peptide-MHC and threaten the health of the individual.

B cells from glatiramer acetate-treated mice suppress experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) thought to be primarily mediated by T cells. However, emerging evidence supports an important role for B cells in the pathogenesis and inhibition of MS. Glatiramer acetate (GA), a Food and Drug Administration-approved drug for the treatment of MS, has a good safety profile. But GA's mechanism of action in MS is still elusive. In this study, we showed that B cells from GA-treated mice increased production of IL-10 and reduced expression of co-stimulatory molecules viz.: CD80 and CD86. B cells from GA-treated mice also diminished proliferation of myelin oligodendrocyte glycoprotein (MOG(35-55)) specific T cells. Purified B cells transferred from GA-treated mice suppressed experimental autoimmune encephalomyelitis (EAE) in recipient mice compared with B cells transferred from mice treated with PBS or ovalbumin. The treatment effect of GA in EAE was abrogated in B cell-deficient mice. Transfer of B cells from GA-treated mice inhibited the proliferation of autoreactive T cells as well as the development of Th1 and Th17 cells but promoted IL-10 production in recipient mice. The number of peripheral CD11b(+) macrophages in recipient mice also decreased after transfer of B cells from GA-treated mice; however, the number of dendritic cells and regulatory T cells remained unaltered. These results suggest that B cells are important to the protective effects of GA in EAE.

Transgenic expression of single-chain anti-CTLA-4 Fv on beta cells protects nonobese diabetic mice from autoimmune diabetes

T cell-mediated immunodestruction of pancreatic beta cells is the key process responsible for both the development of autoimmune diabetes and the induction of rejection during islet transplantation. In this study, we investigate the hypothesis that transgenic expression of an agonistic, membrane-bound single-chain anti-CTLA-4 Fv (anti-CTLA-4 scFv) on pancreatic beta cells can inhibit autoimmune processes by selectively targeting CTLA-4 on pathogenic T cells. Strikingly, transgenic expression of anti-CTLA-4 scFv on pancreatic beta cells significantly protected NOD mice from spontaneous autoimmune diabetes. Interestingly, local expression of this CTLA-4 agonist did not alter the diabetogenic properties of systemic lymphocytes, because splenocytes from transgenic mice or their nontransgenic littermates equally transferred diabetes in NOD/SCID recipients. By analyzing the T cell development in anti-CTLA-4 scFv/Th1/Th2 triple transgenic mice, we found that beta cell-specific expression of CTLA-4 agonist did not affect the development of Th1/Th2 or CD4(+)CD25(+) regulatory T cells. Most strikingly, islets from transgenic mice inhibited T cell response to immobilized anti-CD3 in a T cell-islet coculture system, suggesting a trans-mediated inhibition provided by transgenic islets. Finally, transgenic islets implanted in diabetic recipients survived much longer than did wild-type islets, indicating a therapeutic potential of this genetically modified islet graft in autoimmune diabetes.

CTLA-4 on alloreactive CD4 T cells interacts with recipient CD80/86 to promote tolerance

Although the inhibitory receptor CTLA-4 (CD152) has been implicated in peripheral CD4 T-cell tolerance, its mechanism of action remains poorly defined. We analyzed mechanisms of CD4 cell tolerance in a model of tolerance induction involving establishment of mixed hematopoietic chimerism in recipients of fully MHC-mismatched allogeneic bone marrow cells with anti-CD154 mAb. Animals lacking CD80 and CD86 failed to achieve chimerism. We detected no T cell-intrinsic requirement for CD28 for chimerism induction. However, a CD4 T cell-intrinsic signal through CTLA-4 was shown to be essential within the first 48 hours of exposure to alloantigen for the establishment of tolerance and mixed chimerism. This signal must be provided by a recipient CD80/86(+) non-T-cell population. Donor CD80/86 expression was insufficient to achieve tolerance. Together, our findings demonstrate a surprising role for interactions of CTLA-4 expressed by alloreactive peripheral CD4 T cells with CD80/86 on recipient antigen-presenting cells (APCs) in the induction of early tolerance, suggesting a 3-cell tolerance model involving directly alloreactive CD4 cells, donor antigen-expressing bone marrow cells, and recipient antigen-presenting cells. This tolerance is independent of regulatory T cells and culminates in the deletion of directly alloreactive CD4 T cells.

Membrane-tethered proteins for basic research, imaging, and therapy

Secreted and intracellular proteins including antibodies, cytokines, major histocompatibility complex molecules, antigens, and enzymes can be redirected to and anchored on the surface of mammalian cells to reveal novel functions and properties such as reducing systemic toxicity, altering the in vivo distribution of drugs and extending the range of useful drugs, creating novel, specific signaling receptors and reshaping protein immunogenicity. The present review highlights progress in designing vectors to target and retain chimeric proteins on the surface of mammalian cells. Comparison of chimeric proteins indicates that selection of the proper cytoplasmic domain and introduction of oligiosaccharides near the cell surface can dramatically enhance surface expression, especially for single-chain antibodies. We also describe progress and limitations of employing surface-tethered proteins for preferential activation of prodrugs at cancer cells, imaging gene expression in living animals, performing high-throughput screening, selectively activating immune cells in tumors, producing new adhesion molecules, creating local immune privileged sites, limiting the distribution of soluble factors such as cytokines, and enhancing polypeptide immunogenicity. Surface-anchored chimeric proteins represent a rich source for developing new techniques and creating novel therapeutics.

CD28/CD154 blockade prevents autoimmune diabetes by inducing nondeletional tolerance after effector t-cell inhibition and regulatory T-cell expansion

OBJECTIVE

Blocking T-cell signaling is an effective means to prevent autoimmunity and allograft rejection in many animal models, yet the clinical translation of many of these approaches has not resulted in the success witnessed in experimental systems. Improved understanding of these approaches may assist in developing safe and effective means to treat disorders such as autoimmune diabetes.

RESEARCH DESIGN AND METHODS

We studied the effect of anti-CD154 and CTLA4-Ig on diabetes development, and the requirements to induce tolerance in nod.scid mice after transfer of transgenic beta-cell reactive BDC2.5.NOD T-cells.

RESULTS

Nod.scid recipients of diabetogenic BDC2.5.NOD cells were protected indefinitely from diabetes by a short course of combined costimulation blockade, despite the continued diabetogenic potential of their T-cells. The presence of pathogenic T-cells in the absence of disease indicates peripheral immune tolerance. T-cell maturation occurred in protected recipients, yet costimulation blockade temporarily blunted early T-cell proliferation in draining pancreatic nodes. Tolerance required preexisting regulatory T-cells (Tregs), and protected recipients had greater numbers of Tregs than diabetic recipients. Diabetes protection was successful in the presence of homeostatic expansion and high T-cell precursor frequency, both obstacles to tolerance induction in other models of antigen-specific immunity.

CONCLUSIONS

Immunotherapies that selectively suppress effector T-cells while permitting the development of natural regulatory mechanisms may have a unique role in establishing targeted long-standing immune protection and peripheral tolerance. Understanding the mechanism of these approaches may assist in the design and use of therapies for human conditions, such as type 1 diabetes.

Enhanced engagement of CTLA-4 induces antigen-specific CD4+CD25+Foxp3+ and CD4+CD25- TGF-beta 1+ adaptive regulatory T cells

CTLA-4 is a critical negative regulator of T cell response and is instrumental in maintaining immunological tolerance. In this article, we report that enhanced selective engagement of CTLA-4 on T cells by Ag-presenting dendritic cells resulted in the induction of Ag-specific CD4(+)CD25(+)Foxp3(+) and CD4(+)CD25(-)TGF-beta1(+) adaptive Tregs. These cells were CD62L(low) and hyporesponsive to stimulation with cognate Ag but demonstrated a superior ability to suppress Ag-specific effector T cell response compared with their CD62L(high) counterparts. Importantly, treatment of mice with autoimmune thyroiditis using mouse thyroglobulin (mTg)-pulsed anti-CTLA-4 agonistic Ab-coated DCs, which results in a dominant engagement of CTLA-4 upon self-Ag presentation, not only suppressed thyroiditis but also prevented reemergence of the disease upon rechallenge with mTg. Further, the disease suppression was associated with significantly reduced mTg-specific T cell and Ab responses. Collectively, our results showed an important role for selective CTLA-4 signaling in the induction of adaptive Tregs and suggested that approaches that allow dominant CTLA-4 engagement concomitant with Ag-specific TCR ligation can be used for targeted therapy.

Programmed cell death 1 (PD-1) and its ligand PD-L1 are required for allograft tolerance

Programmed cell death-1 (PD-1, CD279) and its widely expressed, inducible ligand, PD-L1 (CD274), together dampen T cell activation, but whether they are essential for allograft tolerance is unknown. We show, using gene-deficient mice and blocking mAbs in wild-type mice, that costimulation blockade is ineffectual in PD-1(-/-) or PD-L1(-/-) allograft recipients, or in wild-type allograft recipients treated with anti-PD-1 or anti-PD-L1 mAb. Alloreactive PD-1(-/-) CD4 and CD8 T cells had enhanced proliferation and cytokine production compared to wild-type controls, and anergy could not be induced in PD-1-deficient CD4 T cells. We conclude that without inhibitory signals from PD-1 ligation, alloantigen-induced T cell proliferation and expansion cannot be regulated by costimulation blockade, and peripheral tolerance induction cannot occur.

Tertiary lymphoid structures in the pancreas promote selection of B lymphocytes in autoimmune diabetes

Autoimmune diabetes occurs when invading lymphocytes destroy insulin-producing beta cells in pancreatic islets. The role of lymphocytic aggregates at this inflammatory site is not understood. We find that B and T lymphocytes attacking islets in NOD mice organize into lymphoid structures with germinal centers. Analysis of BCR L chain genes was used to investigate selection of B lymphocytes in these tertiary lymphoid structures and in draining pancreatic lymph nodes. The pancreatic repertoire as a whole was found to be highly diverse, with the profile of L chain genes isolated from whole pancreas differing from that observed in regional lymph nodes. A Vkappa14 L chain predominated within the complex pancreatic repertoire of NOD mice. Skewing toward Vkappa4 genes was observed in the pancreas when the repertoire of NOD mice was restricted using a fixed Ig H chain transgene. Nucleotide sequencing of expressed Vkappas identified shared mutations in some sequences consistent with Ag-driven selection and clonal expansion at the site of inflammation. Isolated islets contained oligoclonal B lymphocytes enriched for the germinal center marker GL7 and for sequences containing multiple mutations within CDRs, suggesting local T-B interactions. Together, these findings identify a process that selects B lymphocyte specificities within the pancreas, with further evolution of the selected repertoire at the inflamed site. This interpretation is reinforced by Ag-binding studies showing a large population of insulin-binding B lymphocytes in the pancreas compared with draining lymph nodes.