T-cell Costimulatory Pathways Research Articles

T-Cells Expressing a Highly Potent PRAME-Specific T-Cell Receptor in Combination with a Chimeric PD1-41BB Co-Stimulatory Receptor Show a Favorable Preclinical Safety Profile and Strong Anti-Tumor Reactivity.

Simple SummaryThe development of effective adoptive T-cell therapies (ATCs) to treat solid tumors has several challenges: the choice of a suitable target antigen, the generation of a specific T-cell receptor (TCR) directed against this target, and the hostile tumor microenvironment (TME). The cancer/testis antigen Preferentially Expressed Antigen in Melanoma (PRAME) is a promising target for ATCs since it is highly expressed in several solid tumor indications, while its expression in normal tissues is mainly restricted to the testis. Using our well-established high throughput TCR generation and characterization process, we identified a highly potent PRAME-specific TCR. To convert the inhibitory PD-1 signal in T-cells to an activating signal, we designed a chimeric receptor consisting of the extracellular domain of PD-1 and the signaling domain of 4-1BB. Combining this PD1-41BB receptor with our lead PRAME-TCR generated a very promising T-cell product with a favorable preclinical in vitro safety profile and enhanced in vitro and in vivo anti-tumor efficacy.The hostile tumor microenvironment (TME) is a major challenge for the treatment of solid tumors with T-cell receptor (TCR)-modified T-cells (TCR-Ts), as it negatively influences T-cell efficacy, fitness, and persistence. These negative influences are caused, among others, by the inhibitory checkpoint PD-1/PD-L1 axis. The Preferentially Expressed Antigen in Melanoma (PRAME) is a highly relevant cancer/testis antigen for TCR-T immunotherapy due to broad expression in multiple solid cancer indications. A TCR with high specificity and sensitivity for PRAME was isolated from non-tolerized T-cell repertoires and introduced into T-cells alongside a chimeric PD1-41BB receptor, consisting of the natural extracellular domain of PD-1 and the intracellular signaling domain of 4-1BB, turning an inhibitory pathway into a T-cell co-stimulatory pathway. The addition of PD1-41BB to CD8+ T-cells expressing the transgenic PRAME-TCR enhanced IFN-γ secretion, improved cytotoxic capacity, and prevented exhaustion upon repetitive re-challenge with tumor cells in vitro without altering the in vitro safety profile. Furthermore, a single dose of TCR-Ts co-expressing PD1-41BB was sufficient to clear a hard-to-treat melanoma xenograft in a mouse model, whereas TCR-Ts without PD1-41BB could not eradicate the PD-L1-positive tumors. This cutting-edge strategy supports development efforts to provide more effective TCR-T immunotherapies for the treatment of solid tumors.

GVHD Prophylaxis 2020.

Graft-vs. host disease (GVHD), both acute and chronic are among the chief non-relapse complications of allogeneic transplantation which still cause substantial morbidity and mortality despite significant advances in supportive care over the last few decades. The prevention of GVHD therefore remains critical to the success of allogeneic transplantation. In this review we briefly discuss the pathophysiology and immunobiology of GVHD and the current standards in the field which remain centered around calcineurin inhibitors. We then discuss important translational advances in GVHD prophylaxis, approaching these various platforms from a mechanistic standpoint based on the pathophysiology of GVHD including in-vivo and ex-vivo T-cell depletion alongwith methods of selective T-cell depletion, modulation of T-cell co-stimulatory pathways (checkpoints), enhancing regulatory T-cells (Tregs), targeting T-cell trafficking as well as cytokine pathways. Finally we highlight exciting novel pre-clinical research that has the potential to translate to the clinic successfully. We approach these methods from a pathophysiology based perspective as well and touch upon strategies targeting the interaction between tissue damage induced antigens and T-cells, regimen related endothelial toxicity, T-cell co-stimulatory pathways and other T-cell modulatory approaches, T-cell trafficking, and cytokine pathways. We end this review with a critical discussion of existing data and novel therapies that may be transformative in the field in the near future as a comprehensive picture of GVHD prophylaxis in 2020. While calcineurin inhibitors remain the standard, post-transplant eparinsphamide originally developed to facilitate haploidentical transplantation is becoming an attractive alternative to traditional calcinuerin inhibitor based prophylaxis due to its ability to reduce severe forms of acute and chronic GVHD without compromising other outcomes, even in the HLA-matched setting. In addition T-cell modulation, particularly targeting some important T-cell co-stimulatory pathways have resulted in promising outcomes and may be a part of GVHD prophylaxis in the future. Novel approaches including targeting early events in GVHD pathogenesis such as interactions bvetween tissue damage associated antigens and T-cells, endothelial toxicity, and T-cell trafficking are also promising and discussed in this review. GVHD prophylaxis in 2020 continues to evolve with novel exicitng therapies on the horizon based on a more sophisticated understanding of the immunobiology of GVHD.

Immuno-comparative screening of adult-derived human liver stem/progenitor cells for immune-inflammatory-associated molecules.

One of the main challenges in liver cell therapy is the replacement of damaged cells and the induction of a tolerogenic microenvironment to promote graft acceptance by the recipient. Adult-derived human liver stem/progenitor cells (ADHLSCs) are currently evaluated at the clinical levels as a promising pro-regenerative and immune-modulatory tool. The expression profile of several immunological molecules may influence the local immune-inflammatory response and, therefore, modulate the tissue healing process. To increase the quality and safety of ADHLSCs before transplantation requires an appropriate analysis and characterization of their pattern expression of immune-inflammatory-associated molecules. The expression of 27 molecules belonging to T-cell co-stimulatory pathway, CD47 partners, Ikaros family, CD300 family and TNF family were analyzed using flow cytometry. We compared their expression profiles to PBMCs, hepatocytes and ADHLSCs in both expansion and after hepatogenic differentiation culture conditions. This original immuno-comparative screening revealed that liver cell populations do not constitutively present significant immunological pattern compared to PBMCs. Moreover, our findings highlight that neither the expansion nor the hepatogenic differentiation induces the expression of immune-inflammatory molecules. The detailed expression characteristics (percentage of positive cells and median fluorescence intensity) of each molecule were analyzed and presented. By analyzing 27 relevant molecules, our immuno-comparative screening demonstrates that ADHLSCs keep a non-immunogenic profile independent of their expansion or hepatogenic differentiation state. Accordingly, the immunological profile of ADHLSCs seems to support their safe and efficient use in liver tissue therapeutic repair strategy.

Unique expansion of IL-21+ Tfh and Tph cells under control of ICOS identifies Sjögren’s syndrome with ectopic germinal centres and MALT lymphoma

ObjectivesTo explore the relevance of T-follicular-helper (Tfh) and pathogenic peripheral-helper T-cells (Tph) in promoting ectopic lymphoid structures (ELS) and B-cell mucosa-associated lymphoid tissue (MALT) lymphomas (MALT-L) in Sjögren’s syndrome (SS)...

CD137/OX40 Bispecific Antibody Induces Potent Antitumor Activity that Is Dependent on Target Coengagement.

Following the success of immune checkpoint blockade therapy against cancer, agonistic antibodies targeting T-cell costimulatory pathways are in clinical trials. The TNF superfamily of receptors (TNFRSF) members CD137 and OX40 are costimulatory receptors that stimulate T-cell proliferation and activation upon interaction with their cognate ligands. Activating CD137 and OX40 with agonistic mAbs stimulates the immune system due to their broad expression on CD4+ and CD8+ T cells and natural killer cells and has antitumor effects in preclinical models. Most TNFRSF agonist antibodies require crosslinking via Fcγ receptors (FcγR), which can limit their clinical activity. FS120 mAb2, a dual agonist bispecific antibody targeting CD137 and OX40, activated both CD4+ and CD8+ T cells in an FcγR-independent mechanism, dependent on concurrent binding. A mouse surrogate version of the bispecific antibody displayed antitumor activity in syngeneic tumor models, independent of T regulatory cell depletion and of FcγR interaction, but associated with peripheral T-cell activation and proliferation. When compared with a crosslink-independent CD137 agonist mAb, the FS120 surrogate induced lower liver T-cell infiltration. These data support initiation of clinical development of FS120, a first-in-class dual agonist bispecific antibody for the treatment of human cancer.

T-cell co-stimulation in combination with targeting FAK drives enhanced anti-tumor immunity.

Focal Adhesion Kinase (FAK) inhibitors are currently undergoing clinical testing in combination with anti-PD-1 immune checkpoint inhibitors. However, which patients are most likely to benefit from FAK inhibitors, and what the optimal FAK/immunotherapy combinations are, is currently unknown. We identify that cancer cell expression of the T-cell co-stimulatory ligand CD80 sensitizes murine tumors to a FAK inhibitor and show that CD80 is expressed by human cancer cells originating from both solid epithelial cancers and some hematological malignancies in which FAK inhibitors have not been tested clinically. In the absence of CD80, we identify that targeting alternative T-cell co-stimulatory receptors, in particular OX-40 and 4-1BB in combination with FAK, can drive enhanced anti-tumor immunity and even complete regression of murine tumors. Our findings provide rationale supporting the clinical development of FAK inhibitors in combination with patient selection based on cancer cell CD80 expression, and alternatively with therapies targeting T-cell co-stimulatory pathways.

Signaling pathways involved in the T-cell-mediated immunity against Epstein-Barr virus: Lessons from genetic diseases.

Primary immunodeficiencies (PIDs) provide researchers with unique models to understand in vivo immune responses in general and immunity to infections in particular. In humans, impaired immune control of Epstein-Barr virus (EBV) infection is associated with the occurrence of several different immunopathologic conditions; these include non-malignant and malignant B-cell lymphoproliferative disorders, hemophagocytic lymphohistiocytosis (HLH), a severe inflammatory condition, and a chronic acute EBV infection of T cells. Studies of PIDs associated with a predisposition to develop severe, chronic EBV infections have led to the identification of key components of immunity to EBV - notably the central role of T-cell expansion and its regulation in the pathophysiology of EBV-associated diseases. On one hand, the defective expansion of EBV-specific CD8 T cells results from mutations in genes involved in T-cell activation (such as RASGRP1, MAGT1, and ITK), DNA metabolism (CTPS1) or co-stimulatory pathways (CD70, CD27, and TNFSFR9 (also known as CD137/4-1BB)) leads to impaired elimination of proliferating EBV-infected B cells and the occurrence of lymphoma. On the other hand, protracted T-cell expansion and activation after the defective killing of EBV-infected B cells is caused by genetic defects in the components of the lytic granule exocytosis pathway or in the small adapter protein SH2D1A (also known as SAP), a key activator of T- and NK cell-cytotoxicity. In this setting, the persistence of EBV-infected cells results in HLH, a condition characterized by unleashed T-cell and macrophage activation. Moreover, genetic defects causing selective vulnerability to EBV infection have highlighted the role of co-receptor molecules (CD27, CD137, and SLAM-R) selectively involved in immune responses against infected B cellsvia specific T-B cell interactions.

Abstract 563: A biparatopic agonist antibody for OX40 that exhibits superior activity without secondary crosslinking

Abstract The development of agonistic antibodies that activate T-cell co-stimulatory pathways represents a therapeutic strategy with significant clinical potential. However, challenges remain for the translation from in vitro efficacy to clinical success. OX40 and other tumor necrosis factor receptor (TNFR) superfamily members are notorious for requiring high-order receptor clustering in order to achieve full activity. For monoclonal antibodies, this high-order clustering is generally achieved through secondary cross-linking strategies. In vivo, this secondary cross-linking is often supplied through internal immune effector cells via Fc engagement. Bispecific and biparatopic antibodies represent an emerging class of drug molecules that enable unique mechanisms of action relative to their monoclonal counterparts. Here, we describe the use of our bispecific platform for the generation of large panels of biparatopic antibodies which enabled high-throughput screening for the discovery of an array of OX40 agonistic molecules. We have optimized these multivalent antibodies that exceed the potency of the OX40 ligand in NFkB activation without the need for secondary cross-linking. These agonist antibodies have additionally been characterized using primary T cell assays to monitor the kinetics of growth proliferation and cytokine secretion, outperforming cross-linked antibodies currently being tested in clinical trials. In co-culture systems, these agonist antibodies were effective in inhibiting immuno-suppressive properties of Tregs. Our lead OX40 agonist antibody has been optimized for activity and developability and has entered stable cell line development to further support pre-clinical activities. Citation Format: Bonnie Hammer, Mandar Bawadekar, Matthew Bissen, John Painter, Lauren Lehmann, Francis Qufei Li, Lucas Bailey, Bryan Glaser, Roland Green. A biparatopic agonist antibody for OX40 that exhibits superior activity without secondary crosslinking [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 563.

Lack of T-cell-mediated IL-2 and TNFα production is linked to decreased CD58 expression in intestinal tissue during acute simian immunodeficiency virus infection.

For an effective T-cell activation and response, co-stimulation is required in addition to the antigen-specific signal from their antigen receptors. The CD2/CD58 interaction is considered as one of the most important T-cell co-stimulatory pathways for T-cell activation and proliferation, and its role in regulating intestinal T-cell function in acute and chronic SIV -infected macaques is poorly documented. Here, we demonstrated a significant reduction of CD58 expression in both T- and B-cell populations during acute SIV infection along with high plasma viral load and a loss of intestinal CD4+ T cells compared to SIV-uninfected control macaques. The reduction of CD58 expression in T cells was correlated with the reduced expression of T-cell-mediated IL-2 and TNFα production. Together, these results indicate that reduction in the CD2/CD58 interaction pathway in mucosal lymphocytes might play a crucial role in mucosal T-cell dysfunction during acute SIV/HIV infection.

Lack of T-cell mediated IL2 and TNFa production is linked with the decreased CD58 expression in intestinal tissue during acute simian immunodeficiency virus infection

Abstract Human immunodeficiency virus type 1 (HIV-1)/simian immunodeficiency virus (SIV) infection causes a progressive impairment of the immune system characterized by massive CD4+ T-cell loss, CD8+ T-cell expansion and sustained immune activation and inflammation. Our data also suggest that pathogenic SIVMAC251 infection in rhesus macaques (RMs) leads to decreased production of several T-helper 1 (TH1) and TH2 cytokines and increased production of IL-17, IFNg, CCL4 and GM-CSF by intestinal CD8+ T-cells 21 days after infection. For an effective T-cell activation and response, costimulation is required in addition to the antigen-specific signal from their antigen receptors. The CD2/CD58 interaction is considered as one of the important T-cell costimulatory pathway for T-cell activation and proliferation. Intestinal lamina propria T cells were reported to be highly responsive to a stimulus delivered by CD2 pathway compared to the conventional CD3/TCR pathway. The role of CD2/CD58 in regulating intestinal T-cell function of acute and chronic SIV infected RMs is poorly documented. Here, we demonstrated a significant reduction of CD58 expression in both T- and B-cell population during acute SIV infection along with the loss of intestinal CD4+ T-cells and high plasma viral load compared to SIV-uninfected normal RMs. The reduction of CD58 expression in T-cells was positively correlated with the reduced expression of T-cell mediated IL2 and TNFa production. Together, these results indicate that the reduction in CD2/CD58 interaction pathway in mucosal lymphocytes might play a crucial role in mucosal T-cell dysfunction during acute SIV/HIV infection.

The immune molecular landscape of the B7 and TNFR immunoregulatory ligand–receptor families in head and neck cancer: A comprehensive overview and the immunotherapeutic implications

ABSTRACTThe B7 family and tumor necrosis factor receptor (TNFR) superfamily play a vital role in the T-cell co-stimulatory and co-inhibitory pathways, regulating T-cell activation, tolerance, and exhaustion; therapeutic modulation of these pathways is translated into effective new cancer treatments. Better understanding of the immune molecular landscapes of the B7 and TNFR families would guide head and neck immuno-oncology clinical research. We performed comprehensive molecular profiling of 10 B7 and 6 TNFR family members in head and neck cancer. Over 20% of patients had B7 and TNFR gene alterations. B7 gene amplifications were relatively more common (3–11%) than TNFR gene amplifications (0–5%). Analysis of 496 sequenced samples revealed that all genes were upregulated: B7 and TNFR mRNA were upregulated in 158 cases (> 30%) and 83 cases (∼15%), respectively. B7-H1 (PD-L1) mRNA upregulation was the most common (∼10%). Promoter methylation analysis indicated an epigenetic basis for B7 and TNFR gene regulation (especially B7-H1, which was relatively strongly correlated with promoter methylation). B7-H1 expression was significantly associated with worse overall survival, and its expression was increased in cases with gene amplifications. Human papillomavirus (HPV) status correlated significantly with B7-H1 alterations at genetic level. Almost half (47.1%) of HPV-negative patients had deep or shallow B7-H1 deletion; >90% of HPV-positive patients had diploid, copy number gain, or amplification of B7-H1. This is the first study elucidating the immune molecular landscapes of the B7 and TNFR families in head and neck cancer, providing a potential novel rationale for clinical investigations.

The immunomodulatory properties of human bone marrow-derived mesenchymal stromal cells are defined according to multiple immunobiological criteria.

Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are well known to modulate T cells. However, the molecular mechanisms that mark hBM-MSCs immunomodulation of T cells are not fully resolved. hBM-MSCs harvested from sternum or iliac crest of five healthy donors and characterized in accordance with the International Society of Cellular Therapy (ISCT) guidelines are co-cultured with T cells. Additionally, modulatory effects of MSCs on T-cell viability, proliferation, cytokine profile, co-stimulatory pathway, activation and immunomodulation are also determined. hBM-MSCs significantly reduced the expression of T-cell activation marker CD38 as well as co-stimulatory markers CD134 and CD154, whilst that of CD27 remained unchanged. BrdU, CFSE and Ki67 proliferation assays showed that hBM-MSCs reduced T-cell proliferation. Moreover, viability of T cells remained unchanged when co-cultured with hBM-MSCs. Finally, T cells when co-cultured with hBM-MSCs showed increased secretion of IL-10 and IL-11. Collectively, hBM-MSCs are able to modulate the main steps involved in T-cell response toward a tolerogenic state. Thus, establishing immunobiological criteria defining the immunosuppressive effect of hBM-MSCs is of importance to reach efficient immunotherapeutic intervention.

Identifying Molecular Mechanisms of the Late-Phase Asthmatic Response by Integrating Cellular, Gene, and Metabolite Levels in Blood.

Individuals with allergic asthma respond differently, but reproducibly, to allergen inhalation challenge. Some individuals develop an isolated early response (early responders) (ERs), whereas others go on to develop a late response (dual responders) (DRs). It is not understood why late responses do not develop in all sensitized individuals. The aim of this study was to identify blood biomarkers that can discriminate ERs and DRs using cellular frequencies and gene and metabolite expression from whole blood. Thirty-two individuals participated in the allergen inhalation challenge as part of the AllerGen Clinical Investigator Collaborative. Fifteen participants were classified as ERs and 17 as DRs. Blood samples were collected before (pre) and 2 hours after (post) the allergen challenge. Cell counts were obtained using a hematolyzer, gene transcript relative levels using RNA sequencing, and metabolite concentrations using tandem mass spectrometry. An integrative ensemble algorithm that was based on canonical correlation analysis was used to classify ERs and DRs using all three data sets, adjusting for age and sex. The objective of this algorithm was to identify a correlated subset of molecules from each data set that best discriminated ERs from DRs. Gene set enrichment analysis was performed using Enrichr (Chen et al., BMC Bioinformatics 2013;128). The pre-challenge multisignature classifier (error = 30%) outperformed the post-challenge multisignature classifier (error = 50%) in separating ERs from DRs. The cells selected in the prechallenge multisignature panel included eosinophils, lymphocytes, and neutrophils. The selected metabolites were enriched for glycerophospholipids. The subset of gene transcripts in the multisignature panel was enriched for the T-cell receptor and costimulatory signaling pathway (P = 3.4 × 10(-6)) (Wikipathways) and positive regulation of antigen receptor-mediated signaling pathway (P = 5.7 × 10(-4)) (GO Ontology). This study provides a systems perspective on the deregulated molecular processes between early and dual responses in whole blood. The integrative biomarker analysis suggests that a molecular signature that is predictive of the late-phase response can be identified. The variability in the onset of the late response may explain the poor predictive performance of the postchallenge multiomic biomarker signature. Replication of the prechallenge biomarker signature in additional independent samples is required to validate this panel.

A phase I study of MEDI6383, an OX40 agonist, in adult patients with select advanced solid tumors.

TPS3093 Background: Enhancing T-cell function in cancer patients (pts) through T-cell co-stimulatory pathways such as OX40 has the potential to overcome cancer-induced immune suppression. MEDI6469,...

Driving CAR-Based T-Cell Therapy to Success

T cells that have been genetically modified, activated, and propagated ex vivo can be infused to control tumor progression in patients who are refractory to conventional treatments. Early-phase clinical trials demonstrate that the tumor-associated antigen (TAA) CD19 can be therapeutically engaged through the enforced expression of a chimeric antigen receptor (CAR) on clinical-grade T cells. Advances in vector design, the architecture of the CAR molecule especially as associated with T-cell co-stimulatory pathways, and understanding of the tumor microenvironment, play significant roles in the successful treatment of medically fragile patients. However, some recipients of CAR(+) T cells demonstrate incomplete responses. Understanding the potential for treatment failure provides a pathway to improve the potency of adoptive transfer of CAR(+) T cells. High throughput single-cell analyses to understand the complexity of the inoculum coupled with animal models may provide insight into the therapeutic potential of genetically modified T cells. This review focuses on recent advances regarding the human application of CD19-specific CAR(+) T cells and explores how their success for hematologic cancers can provide a framework for investigational treatment of solid tumor malignancies.

Targeting co-stimulatory pathways: transplantation and autoimmunity.

The myriad of co-stimulatory signals expressed, or induced, upon T-cell activation suggests that these signalling pathways shape the character and magnitude of the resulting autoreactive or alloreactive T-cell responses during autoimmunity or transplantation, respectively. Reducing pathological T-cell responses by targeting T-cell co-stimulatory pathways has met with therapeutic success in many instances, but challenges remain. In this Review, we discuss the T-cell co-stimulatory molecules that are known to have critical roles during T-cell activation, expansion, and differentiation. We also outline the functional importance of T-cell co-stimulatory molecules in transplantation, tolerance and autoimmunity, and we describe how therapeutic blockade of these pathways might be harnessed to manipulate the immune response to prevent or attenuate pathological immune responses. Ultimately, understanding the interplay between individual co-stimulatory and co-inhibitory pathways engaged during T-cell activation and differentiation will lead to rational and targeted therapeutic interventions to manipulate T-cell responses and improve clinical outcomes.

Association of CTLA4, CD28 and ICOS gene polymorphisms with clinicopathologic characteristics of childhood IgA nephropathy in Korean population

Primary IgA nephropathy (IgAN) is the most common glomerular disease in children and adolescents who undergo renal biopsy because of isolated microscopic haematuria or haematuria associated with proteinuria (Coppo 2008). Some evidence suggests the importance of the abnormal T-cell response in the pathogenesis of IgAN, and co-stimulatory molecules such as cytotoxic T-lymphocyte antigen 4 (CTLA4), CD28 molecule and inducible costimulator (ICOS) have been found to be vital for naive T-cells to initiate and terminate immune responses (Carreno and Collins 2002; Carreno et al. 2005). In this study, we tested single nucleotide polymorphisms (SNPs) of CTLA4/CD28/ICOS genes, and they were found to be associated with pathophisipology of paediatric IgAN in Korean population. The best-characterized T-cell co-stimulatory pathway involves receptors such as the CD28 and CTLA4 (also known as CD152). In addition, the ICOS has been also defined recently as a new pathway (Keir and Sharpe 2005). The CD28/CTLA4/ICOS genes lie within the 300-kb region on human chromosome 2q33 and their expressions are differentially regulated; although CD28 is constitutively present on naive T-cells, whereas CTLA4 and ICOS are present only after activation (Collins et al. 2005). Moreover, all of these molecules were found to be expressed by regulatory T-cells for the development and maintenance (Keir and Sharpe 2005).

The Role of T-Cell Costimulatory Pathways in Regulation of Autoimmune Diabetes

Many factors contribute to the pathogenesis of autoimmune diabetes. Targets for treating this debilitating disease will become more apparent by understanding the nature of immune activation. This review examines the possibility of targeting costimulation and discusses the molecules found on the T cell and the antigen-presenting cell (APC) that participate in T-cell activation. The B7-1/B7-2:CD28/cytotoxic T lymphocyte antigen-4 (CTLA-4) pathway has been shown to be crucial in regulating T-cell activation and tolerance. Novel members of the B7-CD28 superfamily have recently been discovered, and they appear to be particularly important for regulating the responses of previously activated T cells. Superimposition of inhibitory signals, such as those delivered by CTLA-4 and the programmed death (PD)-1-PD-1 ligand (PD-L1) pathway, leads to a complex network of positive and negative costimulatory signals, the integration of which modulates immune responses. Furthermore, expression of the B7 homolog B7-H4 on cells in peripheral tissues indicates new mechanisms for regulating T-cell responses. This review focuses on our current understanding of the members of the B7:CD28 superfamily and discusses their therapeutic potential in autoimmune diabetes.

Differential Requirement of CD27 Costimulatory Signaling for Naïve Versus Alloantig(en‐Primed Effector/Memory CD8+ T Cells

CD8(+) memory T cells endanger allograft survival by causing acute and chronic rejection and prevent tolerance induction. We explored the role of CD27:CD70 T-cell costimulatory pathway in alloreactive CD8(+)/CD4(+) T-cell activation. CD27-deficient (CD27(-/-)) and wild-type (WT) B6 mice rejected BALB/c cardiac allografts at similar tempo, with or without depletion of CD4(+) or CD8(+) T cells, suggesting that CD27 is not essential during primary T-cell alloimmune responses. To dissect the role of CD27 in primed effector and memory alloreactive T cells, CD27(-/-) or WT mice were challenged with BALB/c hearts either 10 or 40 days after sensitization with donor-type skin grafts. Compared to WT controls, allograft survival was prolonged in day 40- but not day 10-sensitized CD27(-/-) recipients. Improved allograft survival was accompanied by diminished secondary responsiveness of memory CD8(+) T cells, which resulted from deficiency in memory formation rather than their lack of secondary expansion. Chronic allograft vasculopathy and fibrosis were diminished in CD27(-/-) recipients of class I- but not class II-mismatched hearts as compared to WT controls. These data establish a novel role for CD27 as an important costimulatory molecule for alloreactive CD8(+) memory T cells in acute and chronic allograft rejection.

Suppression of Activation and Costimulatory Signaling in Splenic CD4 + T Cells after Trauma-Hemorrhage Reduces T-Cell Function : A Mechanism of Post-Traumatic Immune Suppression

Reduced immune function is frequently a consequence of serious injury such as trauma-hemorrhage (T-H). Injury may lead to reduced T-cell activation, resulting in decreased engagement of costimulatory molecules after antigen recognition and in subsequent immunological compromise and anergy. We hypothesized that inhibition of CD28 expression is one possible mechanism by which immune functions are suppressed after T-H. Male C3H/HeN mice (with or without ovalbumin immunization) were subjected to sham operation or T-H and sacrificed after 24 hours. Splenic T cells were then stimulated with concanavalin A or ovalbumin in vivo or in vitro, and CD28, cytotoxic T-lymphocyte antigen 4 (CTLA-4), CD69, and phospho-Akt expression was determined. T-cell proliferation/cytokine production was measured in vitro. Stimulation-induced CD69, CD28, and phospho-Akt up-regulation were significantly impaired after T-H compared with sham-operated animals; however, CTLA-4 expression was significantly higher in the T-H group. Over a 3-day span, stimulated T cells from sham-operated animals showed significantly higher proliferation compared with the T-H group. IL-2 and IFN-gamma were elevated in sham-operated animals, whereas IL-4 and IL-5 rose in the T-H group, revealing a shift from T(H)1 to T(H)2 type cytokine production after T-H. Dysregulation of the T-cell costimulatory pathway is therefore likely to be a significant contributor to post-traumatic immune suppression.