Co-stimulation of antigen-specific CD4 T cells by 4-1BB ligand

Fat-to-blood recirculation of partially dysfunctional PD-1+CD4 Tconv cells is associated with dysglycemia in human obesity

Obesity is characterized by the accumulation of T cells in insulin-sensitive tissues, including the visceral adipose tissue (VAT), that can interfere with the insulin signaling pathway eventually leading to insulin resistance (IR) and type 2 diabetes. Here, we found that PD-1+CD4 conventional T (Tconv) cells, endowed with a transcriptomic and functional profile of partially dysfunctional cells, are diminished in VAT of obese patients with dysglycemia (OB-Dys), without a concomitant increase in apoptosis. These cells showed enhanced capacity to recirculate into the bloodstream and had a non-restricted TCRβ repertoire divergent from that of normoglycemic obese and lean individuals. PD-1+CD4 Tconv were reduced in the circulation of OB-Dys, exhibited an altered migration potential, and were detected in the liver of patients with non-alcoholic steatohepatitis. The findings suggest a potential role for partially dysfunctional PD-1+CD4 Tconv cells as inter-organ mediators of IR in obese patients with dysglycemic.

p40 homodimers bridge ischemic tissue inflammation and heterologous alloimmunity in mice via IL-15 transpresentation

Virus-induced memory T cells often express functional cross-reactivity, or heterologous immunity, to other viruses and to allogeneic MHC molecules that is an important component of pathogenic responses to allogeneic transplants. During immune responses, antigen-reactive naive and central memory T cells proliferate in secondary lymphoid organs to achieve sufficient cell numbers to effectively respond, whereas effector memory T cell proliferation occurs directly within the peripheral inflammatory microenvironment. Mechanisms driving heterologous memory T cell proliferation and effector function expression within peripheral tissues remain poorly understood. Here, we dissected proliferation of heterologous donor-reactive memory CD8+ T cells and their effector functions following infiltration into heart allografts with low or high intensities of ischemic inflammation. Proliferation within both ischemic conditions required p40 homodimer-induced IL-15 transpresentation by graft DCs, but expression of effector functions mediating acute allograft injury occurred only in high-ischemic allografts. Transcriptional responses of heterologous donor-reactive memory CD8+ T cells were distinct from donor antigen-primed memory CD8+ T cells during early activation in allografts and at graft rejection. Overall, the results provide insights into mechanisms driving heterologous effector memory CD8+ T cell proliferation and the separation between proliferation and effector function that is dependent on the intensity of inflammation within the tissue microenvironment.

Potential biomarkers: Identifying powerful tumor specific T cells in adoptive cellular therapy

Tumor-specific T cells (TSTs) are essential components for the success of personalized tumor-infiltrating lymphocyte (TIL)-based adoptive cellular therapy (ACT). Therefore, the selection of a common biomarker for screening TSTs in different tumor types, followed by ex vivo expansion to clinical number levels can generate the greatest therapeutic effect. However, studies on shared biomarkers for TSTs have not been realized yet. The present review summarizes the similarities and differences of a number of biomarkers for TSTs in several tumor types studied in the last 5 years, and the advantages of combining biomarkers. In addition, the review discusses the possible shortcomings of current biomarkers and highlights strategies to identify TSTs accurately using intercellular interactions. Finally, the development of TSTs in personalized TIL-based ACT for broader clinical applications is explored.

Advances in immunotherapy for glioblastoma multiforme

Glioblastoma multiforme (GBM) is the most common and aggressive malignant brain tumor of the central nervous system and has a very poor prognosis. The current standard of care for patients with GBM involves surgical resection, radiotherapy, and chemotherapy. Unfortunately, conventional therapies have not resulted in significant improvements in the survival outcomes of patients with GBM; therefore, the overall mortality rate remains high. Immunotherapy is a type of cancer treatment that helps the immune system to fight cancer and has shown success in different types of aggressive cancers. Recently, healthcare providers have been actively investigating various immunotherapeutic approaches to treat GBM. We reviewed the most promising immunotherapy candidates for glioblastoma that have achieved encouraging results in clinical trials, focusing on immune checkpoint inhibitors, oncolytic viruses, nonreplicating viral vectors, and chimeric antigen receptor (CAR) immunotherapies.

Rapidly Growing Mycobacterium Species: The Long and Winding Road from Tuberculosis Vaccines to Potent Stress-Resilience Agents

Inflammatory diseases and stressor-related psychiatric disorders, for which inflammation is a risk factor, are increasing in modern Western societies. Recent studies suggest that immunoregulatory approaches are a promising tool in reducing the risk of suffering from such disorders. Specifically, the environmental saprophyte Mycobacterium vaccae National Collection of Type Cultures (NCTC) 11659 has recently gained attention for the prevention and treatment of stress-related psychiatric disorders. However, effective use requires a sophisticated understanding of the effects of M. vaccae NCTC 11659 and related rapidly growing mycobacteria (RGMs) on microbiome–gut–immune–brain interactions. This historical narrative review is intended as a first step in exploring these mechanisms and provides an overview of preclinical and clinical studies on M. vaccae NCTC 11659 and related RGMs. The overall objective of this review article is to increase the comprehension of, and interest in, the mechanisms through which M. vaccae NCTC 11659 and related RGMs promote stress resilience, with the intention of fostering novel clinical strategies for the prevention and treatment of stressor-related disorders.

CD137+ T-Cells: Protagonists of the Immunotherapy Revolution

Simple Summary

The CD137 receptor is expressed by activated antigen-specific T-cells. CD137⁺ T-cells were identified inside TILs and PBMCs of different tumor types and have proven to be the naturally occurring antitumor effector cells, capable of expressing a wide variability in terms of TCR specificity against both shared and neoantigenic tumor-derived peptides. The aim of this review is thus summarizing and highlighting their role as drivers of patients’ immune responses in anticancer therapies as well as their potential role in future and current strategies of immunotherapy.

Abstract

The CD137 receptor (4-1BB, TNF RSF9) is an activation induced molecule expressed by antigen-specific T-cells. The engagement with its ligand, CD137L, is capable of increasing T-cell survival, proliferation, and cytokine production. This allowed to identify the CD137⁺ T-cells as the real tumor-specific activated T-cell population. In fact, these cells express various TCRs that are specific for a wide range of tumor-derived peptides, both shared and neoantigenic ones. Moreover, their prevalence in sites close to the tumor and their unicity in killing cancer cells both in vitro and in vivo, raised particular interest in studying their potential role in different strategies of immunotherapy. They indeed showed to be a reliable marker able to predict patient’s outcome to immune-based therapies as well as monitor their response. In addition, the possibility of isolating and expanding this population, turned promising in order to generate effector antitumor T-cells in the context of adoptive T-cell therapies. CD137-targeting monoclonal antibodies have already shown their antitumor efficacy in cancer patients and a number of clinical trials are thus ongoing to test their possible introduction in different combination approaches of immunotherapy. Finally, the intracellular domain of the CD137 receptor was introduced in the anti-CD19 CAR-T cells that were approved by FDA for the treatment of pediatric B-cell leukemia and refractory B-cell lymphoma.

Emerging Targets of Immunotherapy in Gynecologic Cancer

Although programmed cell death protein 1/programmed death-ligand 1 (PD-1/PD-L1) and cytotoxic T lymphocyte antigen-4 (CTLA-4) have been successfully applied in the treatment of tumors, their efficiency is still not high enough. New immune targets need to be identified in order to seek alternative treatment strategies for patients with refractory tumors. Immune targets can be divided into stimulating and inhibiting molecules according to their function after receptor-ligand binding. We herein present a compendious summary of emerging immune targets in gynecologic tumors. These targets included coinhibitory molecules, such as T cell immunoglobulin-3 (TIM-3), T cell immunoglobulin and ITIM domain (TIGIT), lymphocyte activation gene-3 (LAG-3), V-type immunoglobulin domain-containing suppressor of T cell activation (VISTA), and B7-H3 and B7-H4, and co-stimulatory molecules, such as CD27, OX40, 4-1BB, CD40, glucocorticoid-induced tumor necrosis factor receptor (GITR) and inducible co-stimulator (ICOS). In this review, the characteristics and preclinical/clinical progress of gynecological malignancies are briefly discussed. However, the potential mechanisms and interactions of immune targets need to be elucidated in further studies.

The relevance of soluble CD137 in the regulation of immune responses and for immunotherapeutic intervention

CD137 is a potent costimulatory receptor. Several agonistic anti-CD137 antibodies are currently in clinical trials for tumor immunotherapy. Soluble forms of CD137 (sCD137) are generated by differential splicing and antagonize the activities of membrane-bound CD137 (mCD137) and of therapeutic CD137 agonists. sCD137 is found in sera of patients suffering from autoimmune diseases where it is a natural regulator of immune responses, and which has therapeutic potential for immune-mediated diseases. This review summarizes the current knowledge on sCD137, highlights its potential role in immunotherapy against cancer and in autoimmune diseases, and presents important issues to be addressed by future research.

A DNA Vaccine Encoding SA-4-1BBL Fused to HPV-16 E7 Antigen Has Prophylactic and Therapeutic Efficacy in a Cervical Cancer Mouse Model

The SA-4-1BBL, an oligomeric novel form of the natural ligand for the 4-1BB co-stimulatory receptor of the tumor necrosis factor (TNF) superfamily, as a recombinant protein has potent pleiotropic effects on cells of innate, adaptive, and regulatory immunity with demonstrated therapeutic efficacy in several tumor models. However, the production of soluble form of SA-4-1BBL protein and quality control is time and resource intensive and face various issues pertinent to clinical development of biologics. The present study sought to take advantage of the simplicity and translatability of DNA-based vaccines for the production and delivery of SA-4-1BBL for cancer immune prevention and therapy. A chimeric HPV-16 E7 DNA vaccine (SP-SA-E7-4-1BBL) was constructed that contains the signal peptide (SP) of calreticulin (CRT), streptavidin (SA) domain of SA-4-1BBL, HPV-16 E7 double mutant gene, and the extracellular domain of mouse 4-1BBL. Immunization by gene gun with SP-SA-E7-4-1BBL induced greater prophylactic as well as therapeutic effects in C57BL/6 mice against TC-1 tumor model compared with immunization with E7wt, SP-SA-4-1BBL or reference-positive control CRT-E7wt. The therapeutic efficacy of the DNA vaccine was associated with increased frequency of E7-specific T cells producing interferon (IFN)-γ. Overall, our data suggest that this DNA-based vaccine strategy might represent a translational approach because it provides a simpler and versatile alternative to a subunit vaccine based on SA-4-1BBL and E7 proteins.

The Role of Co-Stimulatory Molecules in Chagas Disease

Chagas disease, caused by Trypanosoma cruzi, is a potentially life-threatening tropical disease endemic to Latin American countries that affects approximately 8 million people. In the chronic phase of the disease, individuals are classified as belonging to the indeterminate clinical form or to the cardiac and/or digestive forms when clinical symptoms are apparent. The relationship between monocytes and lymphocytes may be an important point to help clarify the complexity that surrounds the clinical symptoms of the chronic phase of Chagas disease. The co-stimulatory signals are essential to determining the magnitude of T cell response to the antigen. The signals are known to determine the regulation of subsequent adaptive immune response. However, little is known about the expression and function of these molecules in Chagas disease. Therefore, this review aims to discuss the possible role of main pathways of co-stimulatory molecule-receptor interactions in this pathology that could be crucial to understand the disease dynamics.

Stimulating Innate Immunity to Enhance Radiation Therapy-Induced Tumor Control

Novel ligands that target Toll-like receptors and other innate recognition pathways represent a potent strategy for modulating innate immunity to generate antitumor immunity. Although many of the current clinically successful immunotherapies target adaptive T-cell responses, both preclinical and clinical studies suggest that adjuvants have the potential to enhance the scope and efficacy of cancer immunotherapy. Radiation may be a particularly good partner to combine with innate immune therapies, because it is a highly efficient means to kill cancer cells but may fail to send the appropriate inflammatory signals needed to act as an efficient endogenous vaccine. This may explain why although radiation therapy is a highly used cancer treatment, true abscopal effects-regression of disease outside the field without additional systemic therapy-are extremely rare. This review focuses on efforts to combine innate immune stimuli as adjuvants with radiation, creating a distinct and complementary approach from T cell-targeted therapies to enhance antitumor immunity.

The promise of 4-1BB (CD137) mediated immunomodulation and immunotherapy for viral diseases

The T-cell surface receptor, 4-1BB (CD137), has been of increasing interest to immunologists as a co-stimulatory immune checkpoint molecule over the last two decades. Ligation of 4-1BB can activate signals in CD8+ T cells and NK cells, resulting in increased proinflammatory cytokine secretion, cytolytic function and antibody-dependent cell-mediated cytotoxicity. Targeting 4-1BB, using a 4-1BB ligand (4-1BBL) or agonistic monoclonal antibodies, has delivered a new strategy to fight against cancer, autoimmune diseases and viral infections. In this review, different aspects of 4-1BB mediated antiviral responses, the mechanistic basis of such responses and future directions are discussed.

Potential importance of B cells in aging and aging-associated neurodegenerative diseases

Our understanding of B cells as merely antibody producers is slowly changing. Alone or in concert with antibody, they control outcomes of seemingly different diseases such as cancer, rheumatoid arthritis, diabetes, and multiple sclerosis. While their role in activation of effector immune cells is beneficial in cancer but bad in autoimmune diseases, their immunosuppressive and regulatory subsets (Bregs) inhibit autoimmune and anticancer responses. These pathogenic and suppressive functions are not static and appear to be regulated by the nature and strength of inflammation. Although aging increases inflammation and changes the composition and function of B cells, surprisingly, little is known whether the change affects aging-associated neurodegenerative disease, such as Alzheimer's disease (AD). Here, by analyzing B cells in cancer and autoimmune and neuroinflammatory diseases, we elucidate their potential importance in AD and other aging-associated neuroinflammatory diseases.

Aging Converts Innate B1a Cells into Potent CD8+ T Cell Inducers

B cell dysregulation in aging is thought to mostly occur in conventional B2 cells without affecting innate B1 cells. Elderly humans and mice also accumulate 4-1BBL(+)MHC class-I(Hi)CD86(Hi)B cells of unknown origin. In this article, we report that these cells, termed 4BL cells, are activated murine and possibly human B1a cells. The activation is mediated by aging human monocytes and murine peritoneal macrophages. They induce expression and activation of 4-1BBL and IFN-γR1 on B1a cells to subsequently upregulate membrane TNF-α and CD86. As a result, activated B1a/4BL cells induce expression of granzyme B in CD8(+)T cells by targeting TNFR2 via membrane TNF-α and providing costimulation with CD86. Thus, for the first time, to our knowledge, these results indicate that aging affects the function of B1a cells. Upon aging, these cells lose their tumor-supporting activity and become inducers of potentially antitumor and autoimmune CD8(+)T cells.

Analysis of the immunomodulatory properties of two heat-killed mycobacterial preparations in a human whole blood model

The significant role played by mycobacteria in modulating immune responses through enhancing the crosstalk between innate and adaptive immunity has been highlighted in several studies. Owing to their unique antigenic profile, heat killed (HK) preparations of rapid-growing mycobacteria, currently undergoing clinical development, have been assessed as adjuvant therapy in various diseases. The purpose of this study is to investigate the regulation of leukocyte surface receptors, in whole blood from healthy donors, following in vitro stimulation with HK Mycobacterium vaccae (M. vaccae) or M. obuense. We have demonstrated the ability of both mycobacterial preparations to target monocytes and neutrophils and to regulate the surface expression of selected adhesion receptors, antigen-presenting and costimulatory receptors, pattern recognition receptors, complement and Fc receptors, as well as cytokine/chemokine receptors. Toll-like receptors (TLRs) 1 and 2 were also shown to be involved in mediating the M. obuense-induced upregulation of selected surface receptors on monocytes. Whole blood stimulation with M. vaccae or M. obuense resulted in a significant increase in the secretion of a specific set of cytokines and chemokines. Both mycobacterial preparations induced strong antigen-specific proliferative responses in peripheral blood mononuclear cells. Collectively, our data shows that M. vaccae and M. obuense have the potential to act as potent immunomodulators. Future research based on these findings may reveal novel immune pathways induced by these preparations with potential implication for their use in diverse immunotherapeutic approaches.

CD137 stimulation and p38 MAPK inhibition improve reactivity in an in vitro model of glioblastoma immunotherapy

Dendritic cell vaccination has become an interesting option for cancer immunotherapy. Tumor-lysate-pulsed dendritic cells (DC) can prime naïve T cells and induce the regression of established tumors including gliomas as shown in various animal models. Despite hopeful results even in clinical studies, the outcome for many patients is still unsatisfying. In the present study, we tested the combination of tumor-lysate-pulsed dendritic cells (TPDC) with a monoclonal antibody against CD137, a monoclonal antibody against CD25 (daclizumab) and a specific p38 mitogen-activated protein kinase (p38 MAPK) inhibitor (SB203580) for improving immunostimulation in an in vitro model of immunotherapy for human gliomas. We observed a higher secretion of interferon gamma by TPDC-primed peripheral blood mononuclear cells (PBMC) that were incubated with an antibody against CD137 or the p38 MAPK inhibitor. In addition, we observed higher specific lysis of tumor cells after incubation of PBMC with the p38 MAPK inhibitor or the anti-CD137 antibody. In contrast, incubation of TPDC-primed PBMC with the anti-CD25 antibody did enhance neither interferon gamma secretion nor cellular cytotoxicity. Cell depletion experiments demonstrated that the immune reaction induced by TPDC is strongly dependent on CD4-positive and CD8-positive cells. Incubation of DC during maturation and antigen loading with the anti-CD137 antibody did not enhance cytotoxicity and interferon gamma secretion in comparison with application of the anti-CD137 antibody during priming. In conclusion, our data suggest that p38 MAPK inhibition and anti-CD137 antibodies can enhance the immune response against glioblastoma cells.

Targeting of the tumor necrosis factor receptor superfamily for cancer immunotherapy

The tumor necrosis factor (TNF) ligand and cognate TNF receptor superfamilies constitute an important regulatory axis that is pivotal for immune homeostasis and correct execution of immune responses. TNF ligands and receptors are involved in diverse biological processes ranging from the selective induction of cell death in potentially dangerous and superfluous cells to providing costimulatory signals that help mount an effective immune response. This diverse and important regulatory role in immunity has sparked great interest in the development of TNFL/TNFR-targeted cancer immunotherapeutics. In this review, I will discuss the biology of the most prominent proapoptotic and co-stimulatory TNF ligands and review their current status in cancer immunotherapy.

Using monoclonal antibodies to stimulate antitumor cellular immunity

Monoclonal antibodies (mAbs) have an established role in current cancer therapy with seven approved for the treatment of a wide variety of tumors. The approved mAbs directly target tumor cells; however, it is becoming increasingly clear that as well as their direct effects, these mAbs can present antigens to the immune system. This stimulates long-lasting T-cell immunity, which may correlate with long-term survival. A more direct approach is to use mAbs to target antigens directly to antigen-presenting cells. One approach, ImmunoBody, which has just entered the clinic, stimulates antitumor immunity using mAbs genetically engineered to express tumor-specific T-cell epitopes. T cells not only respond via their T-cell receptors recognizing T-cell epitopes presented on MHC but are also influenced by stimulation of a wide variety of costimulatory molecules. mAbs targeting these molecules can also influence antitumor immunity. The main protagonist in this class of mAbs is ipilimumab, which has recently been shown to improve survival at 2 years in 23% of advanced melanoma patients. Combinations of mAbs targeting tumor antigens to activated antigen-presenting cells and mAbs targeting costimulatory receptors may provide effective therapy for a broad range of tumors.

Co-signals in organ transplantation

PURPOSE OF REVIEW

The nonimmune effects of currently used immunosuppressive drugs result in a high incidence of late graft loss due to nephrotoxicity and death. As an immune-specific alternative to conventional immunosuppressants, new biotechnology tools can be used to block the costimulation signal of T-cell activation.

RECENT FINDINGS

Many experimental studies, particularly preclinical studies in nonhuman primates, have focused on blocking 'classical' B7/CD28 and CD40/CD40L pathways, which are critical in primary T-cell activation, but also on new B7/CD28 and TNF/TNF-R pathways families of costimulatory molecules that can deliver positive or negative costimulation signals to regulate the alloimmune response.

SUMMARY

Belatacept is a new fusion protein derived from CTLA4-Ig that can be used to prevent acute rejection in renal transplantation instead of calcineurin inhibitors. Belatacept can also prevent acute rejection efficiently in humans and, more interestingly, can improve renal function and cardiovascular risk factors in this population.

4-1BB as a therapeutic target for human disease

4-1BB (CD137) is being thought of as an attractive target for immunotherapy of many human immune diseases based on encouraging results with 4-1BB agonistic antibody treatment in mouse models of cancer, autoimmune disease, asthma and additionally as a means to improve vaccination. In this review, we will summarize the results of basic research on 4-1BB and 4-1BB immunotherapy of disease and provide some potential mechanistic insights into the many stimulatory and regulatory functions of 4-1BB.

Radiotherapy enhances antitumor effect of anti-CD137 therapy in a mouse Glioma model

Previously, we reported that peripheral vaccination of mice with modified autologous tumor cells secreting granulocyte-macrophage colony-stimulating factor (GM-CSF) combined with ionizing radiation to the whole brain cured 50% of mice using a syngeneic, intracranial model of murine high-grade glioma. Here, we tested the combination of radiotherapy (4 Gy x 2) with an immunotherapeutic approach using an anti-CD137 antibody directed to the co-stimulatory molecule CD137. The CD137 antibody has shown promise in generating effective antitumor responses in several animal models and has demonstrated a favorable toxicity profile in the clinic. The combination of radiation and anti-CD137 therapy resulted in complete tumor eradication and prolonged survival in six of nine (67%) mice with established brain tumors (P = 0.0009). Five of six (83%) long-term survivors in the combination group demonstrated antitumor immunity by rejecting challenge tumors. Antitumor immunity was associated with an increased number of tumor-infiltrating lymphocytes (TILs) in brain tumors and increased tumor-specific production of gammaIFN. In view of the finding that radiation enhanced the antitumor effect of anti-CD137 therapy, this approach should be studied further for clinical translation.

Adjuvantive effects of anti-4-1BB agonist Ab and 4-1BBL DNA for a HIV-1 Gag DNA vaccine: different effects on cellular and humoral immunity

Plasmid DNA immunizations induce low levels but a broad spectrum of cellular and humoral immune responses. Here, we investigate the potential of co-stimulation through 4-1BB as an adjuvant for a HIV-1 DNA vaccine in mice. We designed plasmid DNAs expressing either the membrane bound or soluble form of 4-1BBL, and compared with the agonistic anti-4-1BB Ab for their ability to adjuvant the Gag DNA vaccine. Both, anti-4-1BB agonistic Ab as well as 4-1BBL DNA enhanced the Gag-specific cellular immune responses. However, in complete contrast to the agonistic Ab that suppressed humoral immunity to Gag, 4-1BBL DNA adjuvanted vaccines enhanced Gag-specific IgG responses. Importantly, the expression of Gag and 4-1BBL from the same plasmid was critical for the adjuvant activity. Collectively, our data suggest that for a HIV-1 vaccine where both antigen-specific cellular and humoral immunity are desirable, 4-1BBL expressed by a DNA vaccine is a superior adjuvant than anti-4-1BB agonistic Ab.

Anti-leukemia activity of MS-275 histone deacetylase inhibitor implicates 4-1BBL/4-1BB immunomodulatory functions

Histone deacetylase inhibitors (HDACi) have demonstrated promising therapeutic potential in clinical trials for hematological malignancies. HDACi, such as SAHA/Vorinostat, Trichostatin A, and MS-275 were found to induce apoptosis of leukemic blasts through activation of the death receptor pathway and transcriptional induction of the Tumor Necrosis Factor (TNF)-related pro-apoptotic family members, TRAIL and FasL. The impact of HDACi on TNF-related costimulatory molecules such as 4-1BB ligand (4-1BBL/TNFSF9) is however not known. Following exposure to SAHA/Vorinostat, Trichostatin A, and MS-275, transcript levels were determined by real time PCR in Jurkat, Raji and U937 cells. Treatment with HDACi up-regulated TNFSF9 gene expression in the three leukemia cell lines, yet to different extend and with distinct kinetics, which did not require de novo protein synthesis and was not associated with DNAse I hypersensitive chromatin remodeling. Transcriptional activity of TNFSF9 promoter-luciferase constructs was induced up to 12 fold by HDACi, and implication of Sp1/Sp3 transcription factors binding to functional GC-box elements was evidenced by reporter gene assays, site-directed mutagenesis, and electrophoretic mobility shift assays. Functionality of modulated target genes was assessed in allogeneic mixed leukocyte reaction experiments. MS-275- and to a lesser extent Trichostatin A- and SAHA-treated Raji cells significantly up regulated T lymphocytes proliferation which was reduced by about 50% by a 4-1BB blocking recombinant protein, while MS-275- but neither Trichostatin A- nor SAHA-treated cells up-regulated IFNγ secretion by T lymphocytes. Our results identify 4-1BBL/4-1BB as a downstream target of HDACi, especially of MS-275 anti-leukemia action in vitro. Thus, HDACi such as MS-275 displaying dual TNF-dependent proapoptotic and costimulatory activities might be favored for inclusion in HDACi-based anti-cancer therapeutic strategies.

Costimulatory and coinhibitory receptors in anti-tumor immunity

SUMMARY

Despite the expression of antigens by tumor cells, spontaneous immune-mediated rejection of cancer seems to be a rare event. T-cell receptor engagement by peptide/major histocompatibility complexes constitutes the main signal for the activation of naive T cells but is not sufficient to initiate a productive generation and maintenance of effector cells. Full activation of T cells requires additional signals driven by costimulatory molecules present on activated antigen-presenting cells but rarely on tumors. Following the discovery of B7-1 (CD80), several other costimulatory molecules have been shown to contribute to T-cell activation and have relevance for improving anti-tumor immunity. Moreover, increasing the understanding of coinhibitory receptors has highlighted key additional pathways that can dominantly inhibit anti-tumor T-cell function. Improving positive costimulation, and interfering with negative regulation, continues to represent an attractive immunotherapeutic approach for the treatment of cancer. This review focuses upon those pathways with the highest potential for clinical application in human cancer patients.

Cytokine, chemokine, and co-stimulatory fusion proteins for the immunotherapy of solid tumors

This chapter describes the generation of novel reagents for the treatment of cancer using fusion proteins constructed with natural ligands of the immune system. Immunotherapy is a powerful therapeutic modality that has not been fully harnessed for the treatment of cancer. We and others have hypothesized that if the proper immunoregulatory ligands can be targeted to the tumor, an effective immune response can be mounted to treat both established primary tumors and distant metastatic lesions. Though it is generally believed that immunotherapy has the potential to treat only residual disease, we offer evidence that this approach can, by itself, destroy large tumor masses and produce lasting remissions of experimental solid tumors. From these studies, three major classes of immune activators, namely, cytokines, chemokines, and costimulatory molecules, have been shown to generate antitumor responses in animal models. In addition, the reversal of immune tolerance by the deletion of T regulatory (Treg) cells has been shown to be equally important for effective immunotherapy. In an attempt to identify reagents that can provide an enhanced immune stimulation and treatment of cancer, our laboratory has developed a novel monoclonal antibody targeting approach, designated Tumor Necrosis Therapy (TNT), which utilizes stable intracellular antigens present in all cell types but which are only accessible in dead and/or dying cells. Since tumors contain necrotic and degenerating regions that account for 30-80% of the tumor mass, this targeting approach can be used to deliver therapeutic reagents to the core of tumors, a site abundant in tumor antigens. In our first set of reagents, a panel of cytokine fusion proteins was genetically engineered using monoclonal antibody chimeric TNT-3 (chTNT-3) directed against necrotic regions of tumors (single-stranded DNA) fused with IL-2, or GM-CSF, or TNFalphaa, or IFNgamma. Tested against different solid tumors, these reagents were found to mount an effective although transient immune response to tumor especially when used in combination. To improve upon these results, additional chTNT-3 fusion proteins using the liver-expression chemokine (LEC) and the costimulatory molecule B7.1 were constructed. Both of these reagents were found to work significantly better than the above cytokine fusion proteins due to their ability to stimulate multiple arms of the immune system deemed useful for cancer immunotherapy. Finally, the Tumor Necrosis Factor Superfamily (TNFSF) gene DC137L was used to generate chTNT-3 antibody (targeted) and soluble Fc (untargeted) fusion proteins. When used alone, both forms of costimulatory fusion proteins were found to produce in a s dose-dependent manner, complete regression of murine solid tumors. Evidence is presented to show that Treg cells play an important role in suppressing antitumor immunity since the deletion of these cells, when used in combination with LEC or costimulatory fusion proteins, produced profound and effective treatment with sustained memory. It is hoped that these data will further the preclinical development of soluble Fc and antibody based fusion proteins fro the immunotherapy of cancer.

Immune suppression or enhancement by CD137 T cell costimulation during acute viral infection is time dependent

CD137 is expressed on activated T cells and ligands to this costimulatory molecule have clinical potential for amplifying CD8 T cell immunity to tumors and viruses, while suppressing CD4 autoimmune T cell responses. To understand the basis for this dichotomy in T cell function, CD4 and CD8 antiviral immunity was measured in lymphocytic choriomeningitis virus (LCMV) Armstrong- or A/PR8/34 influenza-infected mice injected with anti-CD137 mAbs. We found that the timing of administration of anti-CD137 mAbs profoundly altered the nature of the antiviral immune response during acute infection. Antiviral immunity progressed normally for the first 72 hours when the mAb was administered early in infection before undergoing complete collapse by day 8 postinfection. Anti-CD137-injected LCMV-infected mice became tolerant to, and persistently infected with, LCMV Armstrong. Elevated levels of IL-10 early in the response was key to the loss of CD4(+) T cells, whereas CD8(+) T cell deletion was dependent on a prolonged TNF-alpha response, IL-10, and upregulation of Fas. Blocking IL-10 function rescued CD4 antiviral immunity but not CD8(+) T cell deletion. Anti-CD137 treatment given beyond 72 hours after infection significantly enhanced antiviral immunity. Mice treated with anti-CD137 mAb 1 day before infection with A/PR8/34 virus experienced 80% mortality compared with 40% mortality of controls. When treatment was delayed until day 1 postinfection, 100% of the infected mice survived. These data show that anti-CD137 mAbs can induce T cell activation-induced cell death or enhance antiviral immunity depending on the timing of treatment, which may be important for vaccine development.

Enhancement of the anti-leukemic activity of cytokine induced killer cells with an anti-CD19 chimeric receptor delivering a 4-1BB-ζ activating signal

OBJECTIVE

There is growing interest in the use of cytokine-induced killer (CIK) cells in cancer therapy. In this study, we sought to maximize the antileukemic activity of anti-CD19 receptor-modified CIK cells against B-lineage acute lymphoblastic leukemia (ALL).

MATERIALS AND METHODS

CIK cells were transduced with retroviral vectors carrying different types of anti-CD19 chimeric receptors: anti-CD19-zeta, anti-CD19-DAP10, anti-CD19-4-1BB-zeta, and anti-CD19-CD28-zeta. A truncated form of the receptor was used as a control. Transduced CIK cells were then analyzed for their cytotoxic activity against ALL cells and for their capability to proliferate and to release cytokines after ALL encounter.

RESULTS

CIK cells were efficiently transduced with all the anti-CD19 retroviral vectors. Anti-CD19 receptor expression conferred powerful killing activity against ALL cells. However, there were clear advantages when receptors containing the co-stimulatory molecules 4-1BB or CD28 were transduced. Such cells had significantly more potent cytotoxicity than cells expressing the anti-CD19-zeta or anti-CD19-DAP10. Moreover, the presence of 4-1BB or CD28 in the receptor increased the production of interleukin (IL)-2, tumor necrosis factor (TNF)-alpha, TNF-beta, IL-5, IL-6, and IL-8 elicited by coculture with ALL cells. Notably, anti-CD19-4-1BB-zeta CIK cells secreted particularly low levels of interleukin-10 and proliferated strongly after contact with ALL cells.

CONCLUSIONS

Anti-CD19 chimeric receptors delivering primary and costimulatory signals render CIK cells powerfully cytotoxic against ALL cells and induce secretion of immunostimulatory cytokines and proliferation. These results support the testing of genetically modified CIK cells in clinical trials.

CD134 Costimulation Couples the CD137 Pathway to Induce Production of Supereffector CD8 T Cells That Become IL-7 Dependent

The TNFR superfamily members 4-1BB (CD137) and OX40 (CD134) are costimulatory molecules that potently boost CD8 and CD4 T cell responses. Concomitant therapeutic administration of agonist anti-CD137 and -CD134 mAbs mediates rejection of established tumors and fosters powerful CD8 T cell responses. To reveal the mechanism, the role of CD137 expression by specific CD8 T cells was determined to be essential for optimal clonal expansion and accumulation of effector cells. Nonetheless, dual costimulation induced production of supereffector CD8 T cells when either the specific T cells or the host alone bore CD137. Perhaps surprisingly, the total absence of CD137 prevented anti-CD134 augmentation of supereffector differentiation demonstrating an unappreciated link between these related pathways. Ultimately, it was reasoned that these powerful dual costimulatory responses involved common gamma family members, and we show substantial increases of CD25 and IL-7Ralpha-chain expression by the specific CD8 T cells. To investigate this further, it was shown that IL-7 mediated T cell accumulation, but importantly, a gradual and preferential effect of survival was directed toward supereffector CD8 T cells. In fact, a clear enhancement of effector differentiation was demonstrated to be proportional to the increasing amount of IL-7Ralpha expression by the specific CD8 T cells. Therefore, dual costimulation through CD137 and CD134 drives production and survival of supereffector CD8 T cells through a distinct IL-7-dependent pathway.

CD8+ T cell dysfunction and increase in murine gammaherpesvirus latent viral burden in the absence of 4-1BB ligand

Studies of costimulatory receptors belonging to the TNFR family have revealed their diverse roles in affecting different stages of the T cell response. The 4-1BB ligand (4-1BBL)/4-1BB pathway has emerged as a receptor-ligand pair that impacts not the initial priming, but later phases of the T cell response, such as sustaining clonal expansion and survival, maintaining memory CD8(+) T cells, and supporting secondary expansion upon Ag challenge. Although the role of this costimulatory pathway in CD8(+) T cell responses to acute viral infections has been well-studied, its role in controlling chronic viral infections in vivo is not known to date. Using the murine gammaherpesvirus-68 (MHV-68) model, we show that 4-1BBL-deficient mice lack control of MHV-68 during latency and show significantly increased latent viral loads. In contrast to acute influenza infection, the numbers of MHV-68-specific memory CD8(+) T cells were maintained during latency. However, the virus-specific CD8(+) T cells showed defects in function, including decreased cytolytic function and impaired secondary expansion. Thus, 4-1BBL deficiency significantly affects the function, but not the number, of virus-specific CD8(+) T cells during gammaherpesvirus latency, and its absence results in an increased viral burden. Our study suggests that the 4-1BB costimulatory pathway plays an important role in controlling chronic viral infections.

Targeted and untargeted CD137L fusion proteins for the immunotherapy of experimental solid tumors

INTRODUCTION

CD137L is a member of the tumor necrosis factor superfamily that provides a costimulatory signal to T cells. In this study, two novel CD137L fusion proteins were produced and compared with the CD137 agonist antibody 2A.

MATERIALS AND METHODS

Murine CD137L was linked to the COOH terminus of either the Fc fragment of immunoglobulin (untargeted version) or TNT-3 (targeted version), an antibody that binds to necrotic regions of tumors. Groups of mice bearing established Colon 26 tumors were then treated daily x 5 with each fusion protein or 2A to determine their immunotherapeutic potential.

RESULTS

Both fusion proteins retained CD137L activity in vitro and TNT-3/CD137L showed tumor-binding activity by biodistribution analysis in tumor-bearing mice. The fusion proteins also produced similar responses in vivo at the 1 nmol per dose range and showed a 60% (TNT-3/CD137L) or 40% (Fc/CD137L) survival of treated mice at 150 days after tumor implantation, similar to the effects of 2A. Morphologic and immunohistochemical analyses showed massive central necrosis and infiltration of granzyme B-positive cells in necrotic areas and viable peripheral regions of treated tumors. Finally, cell depletion studies showed that CD137L-mediated tumor regression was CD8(+) T cell dependent.

CONCLUSIONS

From these studies, it was determined that both targeted and untargeted CD137L fusion proteins showed effective antitumor activity, but that the targeted version was more potent. Therefore, the use of the natural CD137 ligand is a promising approach to the treatment of solid tumors by virtue of its ability to produce physiologic costimulation within the tumor, limiting side effects often seen with agonist antibody therapies.

4-1BB triggers IL-13 production from T cells to limit the polarized, Th1-mediated inflammation

4-1BB (CD137) triggering typically induces Th1 response by increasing IFN-gamma from T cells upon TCR ligation. We found recently that 4-1BB costimulation increased the expression of IL-13 from CD4(+) T cells, as well as CD8(+) T cells. The enhanced IL-13 expression by agonistic anti-4-1BB treatment was mediated via MAPK1/2, PI-3K, JNK, mammalian target of rapamycin, NF-AT, and NF-kappaB signaling pathways. The signaling for IL-13 induction was similar to that of IFN-gamma production by anti-4-1BB treatment in T cells. When the anti-4-1BB-mediated IL-13 expression was tested in an in vivo viral infection model such as HSV-1 and vesicular stomatitis virus, 4-1BB stimulation enhanced IL-13 expression of CD4(+) T, rather than CD8(+) T cells. Although IL-13 was enhanced by anti-4-1BB treatment, the increased IL-13 did not significantly alter the anti-4-1BB-induced Th1 polarization of T cells--increase of T-bet and decrease of GATA-3. Nevertheless, anti-4-1BB treatment polarized T cells excessively in the absence of IL-13 and even became detrimental to the mice by causing liver inflammation. Therefore, we concluded that IL-13 was coinduced following 4-1BB triggering to maintain the Th1/2 balance of immune response.

Exploiting 4-1BB Costimulation for Enhancing Antiviral Vaccination

4-1BB, a member of the tumor necrosis factor receptor (TNFR) superfamily, is emerging as an important costimulatory molecule, particularly in the regulation of CD8(+) T cell responses. Costimulation through 4-1BB, such as by utilizing agonistic anti-4-1BB monoclonal antibodies, has been well studied in various tumor models. However, 4-1BB is also an important regulator of antiviral CD8(+) T cell responses. This review summarizes these findings and describes how 4-1BB is beginning to be exploited in terms of boosting antiviral vaccine responses.

4-1BBL coexpression enhances HIV-specific CD8 T cell memory in a poxvirus prime-boost vaccine

We have constructed a recombinant fowlpox virus expressing HIV antigens and the costimulatory molecule 4-1BBL. When included in the boost, but not the prime of a poxvirus prime-boost strategy, 4-1BBL significantly enhanced the anti-HIV T cell response generated to this vaccination in BALB/c mice, as detected by ex vivo IFNgamma ELISPOT responses, intracellular cytokine staining to HIV Gag antigens, and enumeration of Gag-reactive CD8 T cells. 4-1BBL however, is not capable of modulating the CD4 T cell response, nor the antibody response to this vaccination strategy. Enhancement of the T cell response by 4-1BBL continues into the memory phase, as detected 2 months post vaccination. This data is the first to show modulation of the immune response to a viral vaccine by coexpression of 4-1BBL and supports this strategy as an exciting approach for enhancement of T cell memory in prime-boost vaccines.

Approaches to studying costimulation of human antiviral T cell responses: prospects for immunotherapeutic vaccines

The generation of strong and specific CD8 T cell responses is important in the control of viral infections. Costimulatory molecules provide signals necessary for the development or maintenance of these responses. A major focus of our laboratory is to investigate the role of costimulatory molecules of the TNFR and CD28 families in antiviral responses. Our aim is to translate information obtained using murine models to the study of these molecules using human cells. We have devised an in vitro system using recombinant replication- deficient adenovirus to deliver costimulatory molecules to antigen-presenting cells that are then used to stimulate autologous T cells from both healthy and HIV-infected individuals. Here we describe our findings and discuss the implications of incorporating costimulatory molecules into viral vector vaccine strategies.

Impaired maturation and altered regulatory function of plasmacytoid dendritic cells in multiple sclerosis

Plasmacytoid dendritic cells (pDCs) represent a DC subtype that exerts divergent functions in innate and adoptive immunity including the immediate reaction to microbial factors and the induction of immunoregulatory responses. It is thought that different DC subtypes may be critically involved in the pathogenesis of multiple sclerosis (MS). In our study we assessed the phenotype, maturation and functional properties of peripheral blood pDCs from 35 clinically stable, untreated multiple sclerosis patients, 30 healthy controls and 9 patients with pneumonia, which was used as a non-specific inflammatory condition (NIC). Ex vivo expression of CD86 and 4-1BBL was significantly lower on pDCs from multiple sclerosis patients than from controls and patients with NIC (22 versus 47 versus 41% and 12 versus 35 versus 32%, respectively). When stimulated with IL-3 and CD40L, pDCs of multiple sclerosis patients showed inefficient maturation as demonstrated by significantly lower or delayed upregulation of CD86, 4-1BBL, CD40 and CD83. Additionally, in multiple sclerosis, stimulation of pDCs by unmethylated cytosine-phosphate-guanosine oligodeoxynucleotides (CpG ODN) resulted in a significantly lower interferon (IFN) alpha secretion than in controls. In multiple sclerosis, but not in controls, pDCs failed to upregulate proliferative responses and IFN-gamma secretion of autologous peripheral blood mononuclear cells (PBMC) in a co-culture system. Moreover, depletion of pDCs in multiple sclerosis patients, but not in controls, had no effect on generation of CD4+Foxp3+ regulatory T cells. We also provide data showing that glatiramer acetate (GA) treatment partially restores phenotype and function of pDCs in multiple sclerosis patients. These findings suggest functional abnormalities of pDCs in these patients, which might be of importance in the understanding of the development of immune dysregulation in this disease.

Cooperation between 4-1BB and ICOS in the immune response to influenza virus revealed by studies of CD28/ICOS-deficient mice

CD28, ICOS, and 4-1BB each play distinct roles in the CD8 T cell response to influenza virus. CD28-/- mice are severely impaired in primary CD8 T cell expansion and fail to mount a secondary response to influenza. Influenza-specific CD8 T cells expand normally in ICOS-/- mice, with only a small and transient defect late in the primary response and an unimpaired secondary response. Conversely, 4-1BB/4-1BBL interaction is dispensable for the primary CD8 T cell response to influenza, but maintains CD8 T cell survival and controls the size of the secondary response. Previous results showed that a single dose of agonistic anti-4-1BB Ab at priming allowed partial restoration of primary CD8 T cell expansion and full recovery of the secondary CD8 T cell responses to influenza in CD28-/- mice. In this study we show that anti-4-1BB fails to correct the CD8 T cell defect in CD28-/-ICOS-/- mice, suggesting that ICOS partially compensates for CD28 in this model. In support of this hypothesis, we found that anti-4-1BB enhances ICOS expression on both T cell subsets and that anti-4-1BB and anti-ICOS can synergistically activate CD4 and CD8 T cells. Furthermore, ICOS and 4-1BB can cooperate to directly stimulate isolated CD28-/- CD8 T cells. These results reveal a novel interaction between the ICOS and 4-1BB costimulatory pathways as well as unexpected redundancy between CD28 and ICOS in primary CD8 T cell expansion. These findings have implications for costimulation of human T cell responses in diseases such as AIDS or rheumatoid arthritis, in which CD28- T cells accumulate.

Combined CD137 (4-1BB) and adjuvant therapy generates a developing pool of peptide-specific CD8 memory T cells

In practice, vaccines should induce lasting and efficacious T cell immunity without promoting deleterious pathological consequences. To accomplish this goal we immunized mice with ovalbumin peptide, polyinosinic-polycytidylic and anti-CD137. Vaccinated mice retained a massive functional CD8 T cell memory pool in lymphoid and non-lymphoid tissues for >1 year. The memory T cells clonally expanded, produced substantial amounts of IFNgamma, and responded vigorously to vesicular stomatitis virus infection. To understand how the vaccine might function, we showed that the antigen-specific T cells must bear CD137 in order for optimal priming to occur. Thus, anti-CD137 agonist mAb directly stimulated peptide-specific CD8 T cells and conditioned them to survive. In contrast, CD137-deficient CD8 T cells did not survive despite CD137 expression by antigen presenting cells. Taken together, the data indicate that CD137 and adjuvant combined therapy is an efficacious vaccine strategy for immunization with non-replicating inert antigen.

Production of Recombinant Human Trimeric CD137L (4-1BBL)

The interaction between 4-1BB ligand (CD137L), a member of the tumor necrosis factor superfamily, and its receptor 4-1BB provides a co-stimulatory signal for T lymphocyte proliferation and survival. However, the structure of 4-1BBL has not been thoroughly investigated, and none of the human recombinant 4-1BBL molecules available have been described as capable of co-stimulating T cells. The present work provides a model of the three-dimensional structure of the tumor necrosis factor homology domain of 4-1BBL and describes the production of a recombinant human soluble 4-1BBL whose originality lies in that it contains the whole extracellular tail preceding the tumor necrosis factor homology domain and an AviTag peptide (AviTag-4-1BBL) allowing enzymatic biotinylation and multimerization via streptavidin. We provide evidence that this chimeric protein exists as a homotrimer, whereas commercial FLAG-tagged 4-1BBL does not. This resulted in a much higher affinity for 4-1BB (1.2 nM) as compared with FLAG-4-1BBL (55.2 nM). We demonstrate that the single extracellular cysteine residue in the tail (Cys-51) could form a disulfide bond, both in our recombinant protein and in physiologically expressed 4-1BBL. The mutation of this cysteine residue exerted no effect on trimerization but increased the dissociation rate of AviTag-4-1BBL from 4-1BB. In its soluble form, AviTag-4-1BBL did not stimulate purified T cells but dramatically inhibited proliferation of peripheral blood mononuclear cells stimulated with anti-CD3 mAb. In contrast, a very significant co-stimulatory effect was observed on purified T cells once AviTag-4-1BBL was immobilized onto streptavidin beads. In addition, we show that the cross-linking of two trimeric AviTag-4-1BBL molecules was the minimum step required to elicit significant costimulatory activity.

Peptide-specific CD8 T regulatory cells use IFN-gamma to elaborate TGF-beta-based suppression

We identified a murine peptide-specific CD8 T regulatory cell population able to suppress responding CD4 T cells. Immunization with OVA, poly(I:C), and anti-4-1BB generated a population of SIINFEKL-specific CD8 T regulatory cells that profoundly inhibited peptide-responding CD4 T cells from cellular division. The mechanism of suppression required IFN-gamma, but IFN-gamma alone was not sufficient to suppress the responding CD4 T cells. The data show that CD8 T regulatory cells were unable to suppress unless they engaged IFN-gamma. Furthermore, even in the absence of recall with peptide, the CD8 T regulatory cells suppressed CD4 responses as long as IFN-gamma was present. To examine the effector mechanism of suppression, we showed that neutralizing TGF-beta inhibited suppression because inclusion of anti-TGF-beta rescued the proliferative capacity of the responding cells. TGF-beta-based suppression was dependent completely upon the CD8 T regulatory cells being capable of binding IFN-gamma. This was the case, although peptide recall of primed IFN-gamma (-/-) or IFN-gammaR(-/-) CD8 T cells up-regulated pro-TGF-beta protein as measured by surface latency-associated peptide expression but yet were unable to suppress. Finally, we asked whether the CD8 T regulatory cells were exposed to active TGF-beta in vivo and showed that only wild-type CD8 T regulatory cells expressed the TGF-beta-dependent biomarker CD103, suggesting that latency-associated peptide expression is not always congruent with elaboration of active TGF-beta. These data define a novel mechanism whereby IFN-gamma directly stimulates CD8 T regulatory cells to elaborate TGF-beta-based suppression. Ultimately, this mechanism may permit regulation of pathogenic Th1 responses by CD8 T regulatory cells.

Enhanced CD4 T Cell Responsiveness in the Absence of 4-1BB

The 4-1BB (CD137) is a member of the TNFR superfamily, and is expressed on several cell types, including activated T cells. Although 4-1BB ligation by agonistic Ab or 4-1BB ligand-expressing APCs can costimulate T cells, the physiological significance of 4-1BB expression in vivo during T cell responses is still being elucidated. In this study, we have addressed the impact on CD4 T cell priming when 4-1BB is absent after gene targeting. Surprisingly, 4-1BB(-/-) mice generated more enhanced effector CD4 T cell responses to OVA protein in adjuvant, even though Ab responses in 4-1BB(-/-) mice were normal. Using an adoptive transfer system with OT-II TCR transgenic CD4 T cells, we found that 4-1BB(-/-) CD4 cells responding in a 4-1BB-sufficient environment had enhanced cell division compared with wild-type cells and displayed augmented clonal expansion during the primary response. This was not due to a developmental defect as 4-1BB-deficient CD4 cells could respond normally to Ag in vitro. These results demonstrate that the absence of 4-1BB can make CD4 T cells hyperresponsive to protein Ag in vivo, suggesting a new unappreciated negative regulatory role of 4-1BB when expressed on a T cell.

Enhancement of CD4 and CD8 immunity by anti-CD137 (4-1BB) monoclonal antibodies during hepatitis C vaccination with recombinant adenovirus

The induction of protective or therapeutic cellular immunity against hepatitis C virus (HCV) is a difficult goal. In a previous work we showed that immunization with a recombinant adenovirus encoding HCV-NS3 (RAdNS3) could partially protect mice from challenge with a vaccinia virus encoding HCV antigens. We sought to investigate whether systemic administration of an immunostimulatory monoclonal antibody directed against the lymphocyte surface molecule CD137 could enhance the immunity elicited by RAdNS3. It was found that treatment with anti-CD137 mAb after the administration of a suboptimal dose of RAdNS3 enhanced cytotoxic and T helper cell responses against HCV NS3. Importantly, the ability of RAdNS3 to induce protective immunity against challenge with a recombinant vaccinia virus expressing HCV proteins was markedly augmented. Thus, combination of immunostimulatory anti-CD137 mAb with recombinant adenoviruses expressing HCV proteins might be useful in strategies of immunization against HCV.

Role of T cell costimulation in anti-viral immunity

Members of both the CD28 and TNFR families can have costimulatory roles in T cell activation. Gene targeted mice as well as in vivo blocking experiments have established distinct roles for CD28/B7; ICOS/ICOSL; CD27/CD70; 4-1BB/4-1BBL and OX40/OX40L during viral infection. Many issues remain to be addressed, including the timing and location of the interactions, the possibility of partial redundancy between related family members and the molecular basis for the specific phenotypes observed in the different gene targeted mice.

4-1BB and OX40 Act Independently to Facilitate Robust CD8 and CD4 Recall Responses

Mice deficient in OX40 or 4-1BB costimulatory pathways show defects in T cell recall responses, with predominant effects on CD4 vs CD8 T cells, respectively. However, OX40L can also stimulate CD8 T cells and 4-1BBL can influence CD4 T cells, raising the possibility of redundancy between the two TNFR family costimulators. To test this possibility, we generated mice deficient in both 4-1BBL and OX40L. In an adoptive transfer model, CD4 T cells expressed 4-1BB and OX40 sequentially in response to immunization, with little or no overlap in the timing of their expression. Under the same conditions, CD8 T cells expressed 4-1BB, but no detectable OX40. Thus, in vivo expression of 4-1BB and OX40 can be temporally and spatially segregated. In the absence of OX40L, there were decreased CD4 T cells late in the primary response and no detectable secondary expansion of adoptively transferred CD4 T cells under conditions in which primary expansion was unaffected. The 4-1BBL had a minor effect on the primary response of CD4 T cells in this model, but showed larger effects on the secondary response, although 4-1BBL(-/-) mice show less impairment in CD4 secondary responses than OX40L(-/-) mice. The 4-1BBL(-/-) and double knockout mice were similarly impaired in the CD8 T cell response, whereas OX40L(-/-) and double knockout mice were similarly impaired in the CD4 T cell response to both protein Ag and influenza virus. Thus, 4-1BB and OX40 act independently and nonredundantly to facilitate robust CD4 and CD8 recall responses.

Modulation of antitumor responses by dendritic cells

The discovery that dendritic cells (DC) play a key role in regulating antitumor immunity has prompted considerable efforts in developing DC-based cancer vaccines for use in clinical oncology. Early translational trials using antigen-loaded DC have established clear evidence of vaccine safety, and demonstrated bioactivity by stimulating immunological and even clinical responses in selected subjects. Despite these encouraging results, the vaccine-induced immune responses achieved to date are not yet sufficient to attain a robust and durable therapeutic effect in the cancer patient. Therefore, further improvements are required to enhance vaccine potency and optimize the potential for clinical success. This article presents a set of emerging concepts that, together, form a framework for a multi-pronged approach that will further enhance the efficacy of DC-based vaccination by either directly improving DC-mediated T cell activation or by inhibiting mechanisms that suppress the induction of an effective antitumor response. The clinical translation of these concepts will result in new opportunities to successfully modulate immune responses in clinical settings.

New immunosuppressants with potential implication in multiple sclerosis

New immunosuppressants are consistently developed to treat autoimmune diseases and some of them might have implications in multiple sclerosis (MS). A new antiproliferative agent, pixantrone, an analogue of mitoxantrone (MX), has a much lower cardiotoxicity and exerts the same potent immunosuppressive effects in experimental allergic encephalomyelitis (EAE). A phase I trial in MS patients is planned in the next future. New monoclonal antibodies (mAb) and other biological constructs containing foreign proteins are developed but their potential immunogenicity is a considerable drawback to their long-term administration. In addition, their beneficial effects in MS are not evident so far. Small molecules targeting the voltage-gated Kv1.3K+ channel regulating CA2+ signaling in T lymphocytes, specifically target activated, pathogenic T cells. Already found effective in EAE, those agents would be easier to handle than T-cell vaccination. Two new immunosuppressants with a unique mechanism of action (FTY720 and Epomycine M) selectively impair autoreactive T-cell homing, without affecting the other components of the immune response. The potent protective effect of TRY720 has been demonstrated in EAE and a phase I trial in MS appears warranted. Finally, a new concept about immunosuppressive treatments in organ transplantation, "tolerogenic immunosuppression", may have potential in MS.

Expression and function of 4-1BB during CD4 versus CD8 T cell responsesin vivo

4-1BBL(-/-) mice have a defect in recall CD8+ T cell responses to viruses, whereas CD4+ T cell responses to virus are unimpaired in these mice. In contrast, both CD4+ and CD8+ T cells respond to 4-1BB ligand (4-1BBL) in vitro. To clarify the role of 4-1BB/4-1BBL in CD4+ versus CD8+ T cell responses in vivo, we compared CD4 (OT-II) and CD8 (OT-I) TCR transgenic T cells responding to the same antigen in an in vivo adoptive transfer model in 4-1BBL(+/+) versus 4-1BBL(-/-) mice. During primary and secondary responses, expression of 4-1BB on in vivo-activated TCR transgenic T cells was earlier and more transient than previously observed in vitro, correlating with expression of the early activation antigen CD69 and preceding the transition to the CD44hi state. Although 4-1BB is expressed early in the primary response, there was no effect of 4-1BBL deficiency on initial CD8 T cell expansion and only a minor effect on initial CD4 T cell expansion. The major effect of 4-1BB/4-1BBL interaction is on the T cell recall response. This is due to effects of 4-1BBL on maintenance of T cell numbers at the end of the primary response with additional effects of 4-1BBL on secondary expansion of T cells.

Costimulatory ligand 4-1BBL (CD137L) as an efficient adjuvant for human antiviral cytotoxic T cell responses

Effective adjuvants capable of inducing strong cytotoxic T cell responses in humans are lacking. In this study, we tested 4-1BBL as an adjuvant for activation of human memory antiviral CD8 T cell responses ex vivo. A recombinant replication-defective 4-1BBL adenovirus was used to convert autologous monocytes into efficient antigen-presenting cells after overnight incubation, bypassing the need to generate dendritic cells. Together with viral peptides, 4-1BBL led to robust memory responses of human Epstein-Barr virus- and influenza virus-specific cytotoxic T cells, with expansion of peptide-specific CD8 effector cells; up-regulation of Bcl-x(L), granzyme A, and perforin; enhanced cytotoxic activity; and increased cytokine production. The response was significant even at a 100-fold lower peptide dose, compared with responses obtained with control adenovirus. Adenovirus-delivered B7.1 also expanded and activated virus-specific CD8 T cells, but 4-1BBL was more effective in driving the T cells toward a more fully differentiated CD27(-) effector state. Thus, 4-1BBL is a promising adjuvant for human memory CD8 T cells and will likely be most effective in the boost phase of a prime-boost strategy.

Role of costimulatory pathways in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

Multiple sclerosis is an immune-mediated disorder of the central nervous system. T lymphocytes are thought to play a central role in the initiation and potentially in the propagation of this disease. Two signals are required for T-cell activation. The first signal consists of the interaction of the T-cell receptor with antigen presented by the MHC molecule on antigen-presenting cells. The second signal requires engagement of costimulatory receptors on T cells with their ligands on antigen-presenting cells. Several costimulatory pathways have been shown to play an important role in T-lymphocyte activation. Here we will review the current literature on the contribution of the B7-1/2-CD28/CTLA-4, inducible costimulatory molecule-B7h, programmed death pathway 1-programmed death pathway ligand 1/ligand 2, CD40-CD154, OX40-OX40 ligand, and CD137-CD137 ligand pathways to the pathogenesis of multiple sclerosis and their potential roles as therapeutic targets.

4-1BB cross-linking enhances the survival and cell cycle progression of CD4 T lymphocytes

4-1BB, a T cell co-stimulatory receptor, prolongs the survival and multiplication of CD4 T cells. Cross-linking 4-1BB stimulated expression of the anti-apoptotic genes bcl-XL and bcl-2, as well as of cyclins D2 and E, and inhibited expression of the cyclin-dependent kinase (cdk) inhibitor p27kip1. Ova-activated CD4 T cells of 4-1BB-deficient/DO11.10 TCR transgenic mice survived less well and underwent less expansion than cells of wild type DO11.10 TCR transgenic mice. These findings demonstrate that 4-1BB is a co-stimulatory molecule for CD4 T cell survival and expansion in vivo.