Multi-layered action mechanisms of CD137 (4-1BB)-targeted immunotherapies

Bispecific and multispecific antibodies in oncology: opportunities and challenges

Research into bispecific antibodies, which are designed to simultaneously bind two antigens or epitopes, has advanced enormously over the past two decades. Owing to advances in protein engineering technologies and considerable preclinical research efforts, bispecific antibodies are constantly being developed and optimized to improve their efficacy and to mitigate toxicity. To date, >200 of these agents, the majority of which are bispecific immune cell engagers, are in either preclinical or clinical evaluation. In this Review, we discuss the role of bispecific antibodies in patients with cancer, including history and development, as well as innovative targeting strategies, clinical applications, and adverse events. We also discuss novel alternative bispecific antibody constructs, such as those targeting two antigens expressed by tumour cells or cells located in the tumour microenvironment. Finally, we consider future research directions in this rapidly evolving field, including innovative antibody engineering strategies, which might enable more effective delivery, overcome resistance, and thus optimize clinical outcomes.

The predictive value of TNF family for pulmonary tuberculosis: a pooled causal effect analysis of multiple datasets

Objective

Despite extensive research on the relationship between pulmonary tuberculosis (PTB) and inflammatory factors, more robust causal evidence has yet to emerge. Therefore, this study aims to screen for inflammatory proteins that may contribute to the susceptibility to PTB in different populations and to explain the diversity of inflammatory and immune mechanisms of PTB in different ethnicity.

Methods

The inverse variance weighted (IVW) model of a two-sample Mendelian Randomization (MR) study was employed to conduct causal analysis on data from a genome-wide association study (GWAS). This cohort consisting PTB GWAS datasets from two European and two East Asian populations, as well as 91 human inflammatory proteins collected from 14,824 participants. Colocalization analysis aimed to determine whether the input inflammatory protein and PTB shared the same causal single nucleotide polymorphisms (SNPs) variation within the fixed region, thereby enhancing the robustness of the MR Analysis. Meta-analyses were utilized to evaluate the combined causal effects among different datasets.

Results

In this study, we observed a significant negative correlation between tumor necrosis factor-beta levels (The alternative we employ is Lymphotoxin-alpha, commonly referred to as LT) (P < 0.05) and tumor necrosis factor receptor superfamily member 9 levels (TNFRSF9) (P < 0.05). These two inflammatory proteins were crucial protective factors against PTB. Additionally, there was a significant positive correlation found between interleukin-20 receptor subunit alpha levels (IL20Ra) (P < 0.05), which may elevate the risk of PTB. Colocalization analysis revealed that there was no overlap in the causal variation between LT and PTB SNPs. A meta-analysis further confirmed the significant combined effect of LT, TNFRSF9, and IL20Ra in East Asian populations (P < 0.05).

Conclusions

Levels of specific inflammatory proteins may play a crucial role in triggering an immune response to PTB. Altered levels of LT and TNFRSF9 have the potential to serve as predictive markers for PTB development, necessitating further clinical validation in real-world settings to ascertain the impact of these inflammatory proteins on PTB.

Treatment advances in high-grade gliomas

High-grade gliomas (HGG) pose significant challenges in modern tumour therapy due to the distinct biological properties and limitations of the blood-brain barrier. This review discusses recent advancements in HGG treatment, particularly in the context of immunotherapy and cellular therapy. Initially, treatment strategies focus on targeting tumour cells guided by the molecular characteristics of various gliomas, encompassing chemotherapy, radiotherapy and targeted therapy for enhanced precision. Additionally, technological enhancements are augmenting traditional treatment modalities. Furthermore, immunotherapy, emphasising comprehensive tumour management, has gained widespread attention. Immune checkpoint inhibitors, vaccines and CAR-T cells exhibit promising efficacy against recurrent HGG. Moreover, emerging therapies such as tumour treating fields (TTFields) offer additional treatment avenues for patients with HGG. The combination of diverse treatments holds promise for improving the prognosis of HGG, particularly in cases of recurrence.

Hypoxia as a potential inducer of immune tolerance, tumor plasticity and a driver of tumor mutational burden: Impact on cancer immunotherapy

In cancer patients, immune cells are often functionally compromised due to the immunosuppressive features of the tumor microenvironment (TME) which contribute to the failures in cancer therapies. Clinical and experimental evidence indicates that developing tumors adapt to the immunological environment and create a local microenvironment that impairs immune function by inducing immune tolerance and invasion. In this context, microenvironmental hypoxia, which is an established hallmark of solid tumors, significantly contributes to tumor aggressiveness and therapy resistance through the induction of tumor plasticity/heterogeneity and, more importantly, through the differentiation and expansion of immune-suppressive stromal cells. We and others have provided evidence indicating that hypoxia also drives genomic instability in cancer cells and interferes with DNA damage response and repair suggesting that hypoxia could be a potential driver of tumor mutational burden. Here, we reviewed the current knowledge on how hypoxic stress in the TME impacts tumor angiogenesis, heterogeneity, plasticity, and immune resistance, with a special interest in tumor immunogenicity and hypoxia targeting. An integrated understanding of the complexity of the effect of hypoxia on the immune and microenvironmental components could lead to the identification of better adapted and more effective combinational strategies in cancer immunotherapy. Clearly, the discovery and validation of therapeutic targets derived from the hypoxic tumor microenvironment is of major importance and the identification of critical hypoxia-associated pathways could generate targets that are undeniably attractive for combined cancer immunotherapy approaches.

Agonism of 4-1BB for immune therapy: a perspective on possibilities and complications

Costimulatory receptors on immune cells represent attractive targets for immunotherapy given that these molecules can increase the frequency of individual protective immune cell populations and their longevity, as well as enhance various effector functions. 4-1BB, a member of the TNF receptor superfamily, also known as CD137 and TNFRSF9, is one such molecule that is inducible on several cell types, including T cells and NK cells. Preclinical studies in animal models have validated the notion that stimulating 4-1BB with agonist reagents or its natural ligand could be useful to augment conventional T cell and NK cell immunity to protect against tumor growth and against viral infection. Additionally, stimulating 4-1BB can enhance regulatory T cell function and might be useful in the right context for suppressing autoimmunity. Two human agonist antibodies to 4-1BB have been produced and tested in clinical trials for cancer, with variable results, leading to the production of a wealth of second-generation antibody constructs, including bi- and multi-specifics, with the hope of optimizing activity and selectivity. Here, we review the progress to date in agonism of 4-1BB, discuss the complications in targeting the immune system appropriately to elicit the desired activity, together with challenges in engineering agonists, and highlight the untapped potential of manipulating this molecule in infectious disease and autoimmunity.

Targeting HER2-positive breast cancer: advances and future directions

The long-sought discovery of HER2 as an actionable and highly sensitive therapeutic target was a major breakthrough for the treatment of highly aggressive HER2-positive breast cancer, leading to approval of the first HER2-targeted drug - the monoclonal antibody trastuzumab - almost 25 years ago. Since then, progress has been swift and the impressive clinical activity across multiple trials with monoclonal antibodies, tyrosine kinase inhibitors and antibody-drug conjugates that target HER2 has spawned extensive efforts to develop newer platforms and more targeted therapies. This Review discusses the current standards of care for HER2-positive breast cancer, mechanisms of resistance to HER2-targeted therapy and new therapeutic approaches and agents, including strategies to harness the immune system.

The PD-L1/4-1BB Bispecific Antibody-Anticalin Fusion Protein PRS-344/S095012 Elicits Strong T-Cell Stimulation in a Tumor-Localized Manner

PURPOSE

While patients responding to checkpoint blockade often achieve remarkable clinical responses, there is still significant unmet need due to resistant or refractory tumors. A combination of checkpoint blockade with further T-cell stimulation mediated by 4-1BB agonism may increase response rates and durability of response. A bispecific molecule that blocks the programmed cell death 1 (PD-1)/programmed cell death 1 ligand 1 (PD-L1) axis and localizes 4-1BB costimulation to a PD-L1-positive (PD-L1+) tumor microenvironment (TME) or tumor draining lymph nodes could maximize antitumor immunity and increase the therapeutic window beyond what has been reported for anti-4-1BB mAbs.

EXPERIMENTAL DESIGN

We generated and characterized the PD-L1/4-1BB bispecific molecule PRS-344/S095012 for target binding and functional activity in multiple relevant in vitro assays. Transgenic mice expressing human 4-1BB were transplanted with human PD-L1-expressing murine MC38 cells to assess in vivo antitumoral activity.

RESULTS

PRS-344/S095012 bound to its targets with high affinity and efficiently blocked the PD-1/PD-L1 pathway, and PRS-344/S095012-mediated 4-1BB costimulation was strictly PD-L1 dependent. We demonstrated a synergistic effect of both pathways on T-cell stimulation with the bispecific PRS-344/S095012 being more potent than the combination of mAbs. PRS-344/S095012 augmented CD4-positive (CD4+) and CD8-positive (CD8+) T-cell effector functions and enhanced antigen-specific T-cell stimulation. Finally, PRS-344/S095012 demonstrated strong antitumoral efficacy in an anti-PD-L1-resistant mouse model in which soluble 4-1BB was detected as an early marker for 4-1BB agonist activity.

CONCLUSIONS

The PD-L1/4-1BB bispecific PRS-344/S095012 efficiently combines checkpoint blockade with a tumor-localized 4-1BB-mediated stimulation burst to antigen-specific T cells, more potent than the combination of mAbs, supporting the advancement of PRS-344/S095012 toward clinical development. See related commentary by Shu et al., p. 3182.

Anticalin®-based therapeutics: Expanding new frontiers in drug development

Anticalin proteins are a novel class of clinical-stage biopharmaceuticals with high potential in various disease areas. Anticalin proteins, derived from extracellular human lipocalins are single-chain proteins, with a highly stable structure that can be engineered to bind with high specificity and potency to targets of therapeutic relevance. The small size and stable structure support their development as inhalable biologics in the field of respiratory diseases as already demonstrated for PRS-060/AZD1402, an Anticalin protein currently undergoing clinical development for the treatment of asthma. Anticalin proteins provide formatting flexibility which allows fusion with the same or other Anticalin proteins, or with other biologics to generate multivalent, multiparatopic or multispecific fusion proteins. The fusion of Anticalin proteins to antibodies allows the generation of potent therapeutic proteins with new modes of action, such as antibody-Anticalin bispecific proteins with tumor-localized activity. Cinrebafusp alfa and PRS-344/S095012 antibody-Anticalin bispecific proteins were designed to reduce potential systemic toxicity by localizing the activity to the tumor, and are currently in clinical development in immuno-oncology. Furthermore, the ease in generating bi- and multispecifics as well as the small and stable structure prompted the investigation of Anticalin proteins for the CAR T space, opening additional potential treatment options based on Anticalin protein therapies.

Machine Learning Identification of Immunotherapy Targets in Low-Grade Glioma using RNA Sequencing Expression Data

PURPOSE

Immunotherapy has revolutionized cancer treatment in the past decade, but significant hurdles remain. Human studies with immune checkpoint inhibitors (ICIs) targeting programmed cell death protein have demonstrated suboptimal efficacy in the setting of low-grade gliomas (LGG). Identification of mechanisms leading to inadequate anti-tumor immunity is paramount. The current study evaluates and validates barriers to immunotherapy using a novel machine learning algorithm.

METHODS

We utilized The Cancer Genome Atlas (TCGA) to generate expression levels of 28 immune genes related to known immunotherapeutic targets or lymphocyte cytolytic activity. We created training and testing groups and three machine learning models to determine the genes most highly correlated to cytolytic activity (CYT). The three models were multiple regression by exhaustive selection, LASSO, and random forest. We validated computational results by comparing expression of pertinent genes in patient-derived glioma samples.

RESULTS

Our models demonstrated linearity, a low mean-squared error, and consistent results with respect to the most important variables. Expression of ICOS, IDO1, and CD40 were the most important variables in all models and demonstrated positive correlation with CYT. Other variables included TIGIT and CD137. Genetic analysis from three IDH-mutants (IDHm) and three IDH-wild type (IDHwt) patient-derived glioma samples validated TCGA data and demonstrated lower levels of CYT in IDHm gliomas compared to IDHwt.

CONCLUSION

This novel methodology has elucidated three potential targets for immunotherapy development in LGG. We also demonstrated a novel method of analyzing data using advanced statistical techniques that can be further employed in developing treatments for other diseases as well.

Soluble CD137 as a dynamic biomarker to monitor agonist CD137 immunotherapies

Background

On the basis of efficacy in mouse tumor models, multiple CD137 (4-1BB) agonist agents are being preclinically and clinically developed. The costimulatory molecule CD137 is inducibly expressed as a transmembrane or as a soluble protein (sCD137). Moreover, the CD137 cytoplasmic signaling domain is a key part in approved chimeric antigen receptors (CARs). Reliable pharmacodynamic biomarkers for CD137 ligation and costimulation of T cells will facilitate clinical development of CD137 agonists in the clinic.

Methods

We used human and mouse CD8 T cells undergoing activation to measure CD137 transcription and protein expression levels determining both the membrane-bound and soluble forms. In tumor-bearing mice plasma sCD137 concentrations were monitored on treatment with agonist anti-CD137 monoclonal antibodies (mAbs). Human CD137 knock-in mice were treated with clinical-grade agonist anti-human CD137 mAb (Urelumab). Sequential plasma samples were collected from the first patients intratumorally treated with Urelumab in the INTRUST clinical trial. Anti-mesothelin CD137-encompassing CAR-transduced T cells were stimulated with mesothelin coated microbeads. sCD137 was measured by sandwich ELISA and Luminex. Flow cytometry was used to monitor CD137 surface expression.

Results

CD137 costimulation upregulates transcription and protein expression of CD137 itself including sCD137 in human and mouse CD8 T cells. Immunotherapy with anti-CD137 agonist mAb resulted in increased plasma sCD137 in mice bearing syngeneic tumors. sCD137 induction is also observed in human CD137 knock-in mice treated with Urelumab and in mice transiently humanized with T cells undergoing CD137 costimulation inside subcutaneously implanted Matrigel plugs. The CD137 signaling domain-containing CAR T cells readily released sCD137 and acquired CD137 surface expression on antigen recognition. Patients treated intratumorally with low dose Urelumab showed increased plasma concentrations of sCD137.

Conclusion

sCD137 in plasma and CD137 surface expression can be used as quantitative parameters dynamically reflecting therapeutic costimulatory activity elicited by agonist CD137-targeted agents.

Targeting ADCC: A different approach to HER2 breast cancer in the immunotherapy era

The clinical outcome of patients with human epidermal growth factor receptor 2 (HER2) amplified breast carcinoma (BC) has improved with the development of anti-HER2 targeted therapies. However, patients can experience disease recurrence after curative intent and disease progression in the metastatic setting. In the current era of evolving immunotherapy agents, the understanding of the immune response against HER2 tumor cells developed by anti-HER2 antibodies (Abs) is rapidly evolving. Trastuzumab therapy promotes Natural Killer (NK) cell activation in patients with BC overexpressing HER2, indicating that the efficacy of short-term trastuzumab monotherapy, albeit direct inhibition of HER, could also be related with antibody-dependent cell-mediated cytotoxicity (ADCC). Currently, dual HER2 blockade using trastuzumab and pertuzumab is the standard of care in early and advanced disease as this combination could confer an additive effect in ADCC. In patients with disease relapse or progression, ADCC may be hampered by several factors such as FcγRIIIa polymorphism and an immunosuppressive environment, among others. Hence, new drug development strategies are being investigated aiming to boost the ADCC response triggered by anti-HER2 therapy. In this review, we summarize these strategies and the rationale, through mAbs engineering and combinatorial strategies, focusing on clinical results and ongoing trials.

Co-stimulatory agonists: An insight into the immunotherapy of cancer

Immune checkpoint pathways consist of stimulatory pathways, which can function like a strong impulse to promote T helper cells or killer CD8⁺ cells activation and proliferation. On the other hand, inhibitory pathways keep self-tolerance of the immune response. Increasing immunological activity by stimulating and blocking these signaling pathways are recognized as immune checkpoint therapies. Providing the best responses of CD8⁺ T cell needs the activation of T cell receptor along with the co-stimulation that is generated via stimulatory checkpoint pathways ligation including Inducible Co-Stimulator (ICOS), CD40, 4-1BB, GITR, and OX40. In cancer, programmed cell death receptor-1 (PD-1), Programmed cell death ligand-1(PD-L1) and Cytotoxic T Lymphocyte-Associated molecule-4 (CTLA-4) are the most known inhibitory checkpoint pathways, which can hinder the immune responses which have specifically anti-tumor characteristics and attenuate T cell activation and also cytokine production. The use of antagonistic monoclonal antibodies (mAbs) that block CTLA-4 or PD-1 activation is used in a variety of malignancies. It has been reported that they can lead to an increase in T cells and thereby strengthen anti-tumor immunity. Agonists of stimulatory checkpoint pathways can induce strong immunologic responses in metastatic patients; however, for achieving long-lasting benefits for the wide range of patients, efficient combinatorial therapies are required. In the present review, we focus on the preclinical and basic research on the molecular and cellular mechanisms by which immune checkpoint inhibitor blockade or other approaches with co-stimulatory agonists work together to improve T-cell antitumor immunity.

Revving the CAR - Combination strategies to enhance CAR T cell effectiveness

Chimeric antigen receptor (CAR) T cell therapy is currently approved for treatment of refractory B-cell malignancies. Response rates in these diseases are impressive by historical standards, but most patients do not have a durable response and there remains room for improvement. To date, CAR T cell activity has been even more limited in solid malignancies. These limitations are thought to be due to several pathways of resistance to CAR T cells, including cell-intrinsic mechanisms and the immunosuppressive tumor microenvironment. In this review, we discuss current experimental strategies that combine small molecules and monoclonal antibodies with CAR T cells to overcome these resistance mechanisms. We describe the biological rationale, pre-clinical data and clinical trials in progress that test the efficacy and safety of these combinations.

Exploratory Pilot Study of Circulating Biomarkers in Metastatic Renal Cell Carcinoma

Simple Summary

The identification of biomarkers in response to therapeutic treatment is one of the main objectives of personalized oncology. Predictive biomarkers are particularly relevant for oncologists challenged by the busy scenario of possible therapeutic options in mRCC patients, including immunotherapy and TKIs. In fact the activation of the immune system can determine the outcome and success of the different therapeutic strategies. In this study we evaluated changes in the immune system of TKI mRCC-treated patients defining immunological profiles related to response characterized by specific biomarkers. The validation of the proposed immune portrait to an extended number of patients could allow characterization and selection of responsive and non-responsive patients from the beginning of the therapeutic process.

Abstract

With the introduction of immune checkpoint inhibitors (ICIs) and next-generation vascular endothelial growth factor receptor–tyrosine kinase inhibitors (VEGFR–TKIs), the survival of patients with advanced renal cell carcinoma (RCC) has improved remarkably. However, not all patients have benefited from treatments, and to date, there are still no validated biomarkers that can be included in the therapeutic algorithm. Thus, the identification of predictive biomarkers is necessary to increase the number of responsive patients and to understand the underlying immunity. The clinical outcome of RCC patients is, in fact, associated with immune response. In this exploratory pilot study, we assessed the immune effect of TKI therapy in order to evaluate the immune status of metastatic renal cell carcinoma (mRCC) patients so that we could define a combination of immunological biomarkers relevant to improving patient outcomes. We profiled the circulating levels in 20 mRCC patients of exhausted/activated/regulatory T cell subsets through flow cytometry and of 14 immune checkpoint-related proteins and 20 inflammation cytokines/chemokines using multiplex Luminex assay, both at baseline and during TKI therapy. We identified the CD3⁺CD8⁺CD137⁺ and CD3⁺CD137⁺PD1⁺ T cell populations, as well as seven soluble immune molecules (i.e., IFNγ, sPDL2, sHVEM, sPD1, sGITR, sPDL1, and sCTLA4) associated with the clinical responses of mRCC patients, either modulated by TKI therapy or not. These results suggest an immunological profile of mRCC patients, which will help to improve clinical decision-making for RCC patients in terms of the best combination of strategies, as well as the optimal timing and therapeutic sequence.

Mechanisms utilized by feline adipose-derived mesenchymal stem cells to inhibit T lymphocyte proliferation

BACKGROUND

Feline adipose-derived mesenchymal stem cells (ASCs) have been successfully used in clinical trials for the treatment of immune-mediated diseases with T cell dysregulation. However, the immunomodulatory pathways utilized by feline ASCs to suppress T cell activation have not been fully determined. We investigated the mechanisms used by feline ASCs to inhibit T cell proliferation, including the soluble factors and the cell-cell contact ligands responsible for ASC-T cell interaction.

METHODS

The immunomodulatory activity of feline ASCs was evaluated via cell cycle analysis and in vitro mixed leukocyte reaction using specific immunomodulatory inhibitors. Cell-cell interactions were assessed with static adhesion assays, also with inhibitors.

RESULTS

Feline ASCs decrease T cell proliferation by causing cell cycle arrest in G0-G1. Blocking prostaglandin (PGE₂), but not IDO, partially restored lymphocyte proliferation. Although PDL-1 and CD137L are both expressed on activated feline ASCs, only the interaction of intercellular adhesion molecule 1 (ICAM-1, CD54) with its ligand, lymphocyte function-associated antigen 1 (LFA-1, CD11a/CD18), was responsible for ASC-T cell adhesion. Blocking this interaction reduced cell-cell adhesion and mediator (IFN-γ) secretion and signaling.

CONCLUSIONS

Feline ASCs utilize PGE₂ and ICAM-1/LFA-1 ligand interaction to inhibit T cell proliferation with a resultant cell cycle arrest in G0-G1. These data further elucidate the mechanisms by which feline ASCs interact with T cells, help define appropriate T cell-mediated disease targets in cats that may be amenable to ASC therapy, and may also inform potential translational models for human diseases.

Co-stimulatory and co-inhibitory pathways in cancer immunotherapy

Cancer remains the leading cause of death worldwide. Traditional treatments such as surgery, radiation, and chemotherapy have had limited efficacy, especially with late stage cancers. Cancer immunotherapy and targeted therapy have revolutionized how cancer is treated, especially in patients with late stage disease. In 2013 cancer immunotherapy was named the breakthrough of the year, partially due to the established efficacy of blockade of CTLA-4 and PD-1, both T cell co-inhibitory molecules involved in tumor-induced immunosuppression. Though early trials promised success, toxicity and tolerance to immunotherapy have hindered long-term successes. Optimizing the use of co-stimulatory and co-inhibitory pathways has the potential to increase the effectiveness of T cell-mediated antitumor immune response, leading to increased efficacy of cancer immunotherapy. This review will address major T cell co-stimulatory and co-inhibitory pathways and the role they play in regulating immune responses during cancer development and treatment.

Chronic retroviral infection of mice promotes tumor development, but CD137 agonist therapy restores effective tumor immune surveillance

T cell responses are crucial for anti-tumor immunity. In chronic viral infections, anti-tumor T cell responses can be compromised due to various immunological mechanisms, including T cell exhaustion. To study mechanisms of anti-tumor immunity during a chronic viral infection, we made use of the well-established Friend virus (FV) mouse model. Chronically FV-infected mice are impaired in their ability to reject FBL-3 cells-a virus-induced tumor cell line of C57BL/6 origin. Here we aimed to explore therapeutic strategies to overcome the influence of T cell exhaustion during chronic viral infection, and reactivate effector CD8+ and CD4+ T cells to eliminate tumor cells. For T cell stimulation, agonistic antibodies against the tumor necrosis factor receptor (TNFR) superfamily members CD137 and CD134 were used, because they were reported to augment the cytotoxic program of T cells. αCD137 agonistic therapy, but not αCD134 agonistic therapy, resulted in FBL-3 tumor elimination in chronically FV-infected mice. CD137 stimulation significantly enhanced the cytotoxic activity of both CD4+ and CD8+ T cells, which were both required for efficient tumor control. Our study suggests that agonistic antibodies to CD137 can efficiently enhance anti-tumor immunity even in the setting of chronic viral infection, which might have promising therapeutic applications.

On the Other Side: Manipulating the Immune Checkpoint Landscape of Dendritic Cells to Enhance Cancer Immunotherapy

Monoclonal antibodies targeting co-inhibitory immune checkpoint molecules have been successful in clinical trials of both solid and hematological malignancies as acknowledged by the 2018 Nobel Prize in Medicine, however improving clinical response rates is now key to expanding their efficacy in areas of unmet medical need. Antibodies to checkpoint inhibitors target molecules on either T cells or tumor cells to stimulate T cells or remove tumor mediated immunosuppression, respectively. However, many of the well-characterized T cell immune checkpoint receptors have their ligands on antigen presenting cells or exert direct effects on those cells. Dendritic cells are the most powerful antigen presenting cells; they possess the ability to elicit antigen-specific responses and have important roles in regulation of immune tolerance. Despite their theoretical benefits in cancer immunotherapy, the translation of DC therapies into the clinic is yet to be fully realized and combining DC-based immunotherapy with immune checkpoint inhibitors is an attractive strategy. This combination takes advantage of the antigen presenting capability of DC to maximize specific immune responses to tumor antigens whilst removing tumor-associated immune inhibitory mechanisms with immune checkpoint inhibition. Here we review the expression and functional effects of immune checkpoint molecules on DC and identify rational combinations for DC vaccination to enhance antigen-specific T cell responses, cytokine production, and promotion of long-lasting immunological memory.

Stimulating T Cells Against Cancer With Agonist Immunostimulatory Monoclonal Antibodies

Elimination of cancer cells through antitumor immunity has been a long-sought after goal since Sir F. Macfarlane Burnet postulated the theory of immune surveillance against tumors in the 1950s. Finally, the use of immunotherapeutics against established cancer is becoming a reality in the past 5years. Most notable are the monoclonal antibodies (mAbs) directed against inhibitory T-cell receptors cytotoxic T lymphocyte antigen-4 and programmed death-1. The next generation of mAbs targeting T cells is designed to stimulate costimulatory receptors on T cells. Here we review the recent progress on these immunostimulatory agonist antibodies against the costimulatory receptors CD137, GITR, OX40, and CD27.

Next generation immune-checkpoints for cancer therapy

The discovery and clinical application of immune-checkpoint inhibitors has dramatically improved the treatments, outcomes and therapeutic concepts in multiple tumor settings. This breakthrough was mainly based on monoclonal antibodies blocking the inhibitory molecule CTLA-4 and or the PD-1/PD-L1 axis, with the aim of counteracting major tumor immune evasion mechanisms. Even acknowledging these important successes, not all the patients benefit from these treatments. Translational and clinical research efforts are ongoing to explore the potentialities of a new generation of immune-modulatory molecules to extend current clinical applications and contrast the unsolved issues of resistance and disease relapse that still affects a considerable rate of patients. New immune-checkpoints, with either stimulatory or inhibitory functions are emerging with key roles in regulating T cell response but also affecting other crucial effectors belonging to the innate immune response (e.g., natural killer). Their therapeutic exploitation, either alone or in strategical combinations, is providing important preclinical results, holding promises currently explored in initial clinical trials. The first results point toward favorable safety profiles with selective hints of activity in challenging settings. Important issues regarding the dose, schedule and rational combinations remain open and data from the clinical studies are needed. Here we provide an overview of the main emerging stimulatory or inhibitory immune-checkpoints exploitable in cancer treatment, briefly reporting their biological function, preclinical activity and preliminary clinical data.

Selection of single chain antibody fragments binding to the extracellular domain of 4-1BB receptor by phage display technology

The 4-1BB is a surface glycoprotein that pertains to the tumor necrosis factor-receptor family. There is compelling evidence suggesting important roles for 4-1BB in the immune response, including cell activation and proliferation and also cytokine induction. Because of encouraging results of different agonistic monoclonal antibodies against 4-1BB in the treatment of cancer, infectious, and autoimmune diseases, 4-1BB has been suggested as an attractive target for immunotherapy. In this study, single chain variable fragment phage display libraries, Tomlinson I+J, were screened against specific synthetic oligopeptides (peptides I and II) designed from 4-1BB extracellular domain. Five rounds of panning led to selection of four 4-1BB specific single chain variable fragments (PI.12, PI.42, PII.16, and PII.29) which showed specific reaction to relevant peptides in phage enzyme-linked immunosorbent assay. The selected clones were successfully expressed in Escherichia coli Rosetta-gami 2, and their expression was confirmed by western blot analysis. Enzyme-linked immunosorbent assay experiments indicated that these antibodies were able to specifically recognize 4-1BB without any cross-reactivity with other antigens. Flow cytometry analysis demonstrated an acceptable specific binding of the single chain variable fragments to 4-1BB expressed on CCRF-CEM cells, while no binding was observed with an irrelevant antibody. Anti-4-1BB single chain variable fragments enhanced surface CD69 expression and interleukin-2 production in stimulated CCRF-CEM cells which confirmed the agonistic effect of the selected single chain variable fragments. The data from this study have provided a rationale for further experiments involving the biological functions of anti-4-1BB single chain variable fragments in future studies.

Second- and third-generation drugs for immuno-oncology treatment-The more the better?

Recent success in cancer immunotherapy (anti-CTLA-4, anti-PD1/PD-L1) has confirmed the hypothesis that the immune system can control many cancers across various histologies, in some cases producing durable responses in a way not seen with many small-molecule drugs. However, only less than 25% of all patients do respond to immuno-oncology drugs and several resistance mechanisms have been identified (e.g. T-cell exhaustion, overexpression of caspase-8 and β-catenin, PD-1/PD-L1 gene amplification, MHC-I/II mutations). To improve response rates and to overcome resistance, novel second- and third-generation immuno-oncology drugs are currently evaluated in ongoing phase I/II trials (either alone or in combination) including novel inhibitory compounds (e.g. TIM-3, VISTA, LAG-3, IDO, KIR) and newly developed co-stimulatory antibodies (e.g. CD40, GITR, OX40, CD137, ICOS). It is important to note that co-stimulatory agents strikingly differ in their proposed mechanism of action compared with monoclonal antibodies that accomplish immune activation by blocking negative checkpoint molecules such as CTLA-4 or PD-1/PD-1 or others. Indeed, the prospect of combining agonistic with antagonistic agents is enticing and represents a real immunologic opportunity to 'step on the gas' while 'cutting the brakes', although this strategy as a novel cancer therapy has not been universally endorsed so far. Concerns include the prospect of triggering cytokine-release syndromes, autoimmune reactions and hyper immune stimulation leading to activation-induced cell death or tolerance, however, toxicity has not been a major issue in the clinical trials reported so far. Although initial phase I/II clinical trials of agonistic and novel antagonistic drugs have shown highly promising results in the absence of disabling toxicity, both in single-agent studies and in combination with chemotherapy or other immune system targeting drugs; however, numerous questions remain about dose, schedule, route of administration and formulation as well as identifying the appropriate patient populations. In our view, with such a wealth of potential mechanisms of action and with the ability to fine-tune monoclonal antibody structure and function to suit particular requirements, the second and third wave of immuno-oncology drugs are likely to provide rapid advances with new combinations of novel immunotherapy (especially co-stimulatory antibodies). Here, we will review the mechanisms of action and the clinical data of these new antibodies and discuss the major issues facing this rapidly evolving field.

[Expression of CD137 in tumor cells of Hodgkin lymphoma from Northern China and its application in pathological differential diagnosis]

目的

明确CD137在北方地区经典型霍奇金淋巴瘤（cHL）中的表达，探讨其作为cHL辅助病理鉴别诊断新指标的可能应用价值。

方法

收集54例cHL患者资料，以55例伴有“HRS样细胞”的非cHL患者为对照。在病理组织标本中选取“HRS细胞”或“HRS样细胞”丰富的区域制作组织芯片；以“HRS细胞”或“HRS样细胞”为观察对象，cHL组应用CD30、CD15、CD20、PAX5、CD3免疫组织化学染色；同时对两组患者标本进行CD137（BBK-2）抗体免疫组织化学染色及采用EBV编码的小RNA（EBER）原位杂交法检测EBV感染状态。

结果

54例cHL患者均为淋巴结内原发，中位年龄45.5（22.0~68.0）岁；男女比例1.7∶1；对照组患者结内54例，结外（皮肤）1例，中位年龄50.0（12.0~81.0）岁；男女比例1.9∶1。54例cHL患者均表达CD30，HRS细胞主要诊断相关免疫标志物CD30、CD15、CD20、CD3阳性表达率依次为100.0%、70.4%、18.5％和0，可见PAX5弱至中等强度表达，阳性率70.4%；EBV感染阳性率25.9%（对照组阳性率21.8%）。cHL组CD137阳性率57.4%，对照组阳性率14.5%，差异有统计学意义（P<0.001）。将cHL组及对照组按照患者年龄（≥60/<60岁）、性别、有无EBV感染、组织学亚型以及主要诊断相关标志物的表达与否进行分组，CD137阳性率差异均无统计学意义（P值均> 0.05）。以2013年为界进行分组，2013年前后两组cHL患者的CD137阳性率差异有统计学意义（39.4%对85.7%，P=0.001），对照组差异无统计学意义（12.5％对16.1%，P=0.705）；2013以后存档的标本中cHL组与对照组患者CD137阳性率差异有统计学意义（85.7％对16.1%，P<0.001）。

结论

通过研究初步证实北方地区大多数cHL患者的HRS细胞表达CD137，而对照组患者“HRS样细胞”CD137阳性率较低。保存期3年以内较保存期3年以上的cHL患者标本CD137阳性率高，更适于进行CD137免疫组织化学染色检测。CD137有望作为辅助cHL病理鉴别诊断的新指标。

Perspectives in immunotherapy: meeting report from the “Immunotherapy Bridge”, Napoli, December 5th 2015

Harnessing the immune system and preventing immune escape, the immunotherapy of cancer provides great potential for clinical application, in broad patient populations, achieving both conventional and unconventional clinical responses. After the substantial advances in melanoma, the focus of cancer immunotherapy has expanded to include many other cancers. Targeting immune checkpoints and further mechanisms used by tumors to avoid anticancer immunity, different approaches are under evaluation, including combination therapies.

The first Immunotherapy Bridge meeting focused on various cancer types including melanoma, non-small cell lung cancer, renal cell, breast and ovarian carcinoma, and discussed mechanisms of action of single agents and combination strategies, and the prediction of clinical responses.

Optimising Cancer Immunotherapy: Challenges and Opportunities

Cancer immunotherapy has moved to the forefront in the treatment of patients with cancer, providing a unique opportunity to achieve dramatic and lasting anti-tumour responses in a variety of tumour types. When it comes to patient selection and development of novel immunotherapeutic agents and combinations, so far we have merely scratched the surface of this therapeutic approach. Leading experts in the field of cancer immunotherapy gathered in Amsterdam, Netherlands, on 21st May 2016 for a Scientific Exchange to discuss the current status of immunotherapy within the field of oncology and explore the future of this evolving therapeutic strategy. Current challenges and limitations regarding the use of immunotherapy were addressed for tumour types such as melanoma, lung cancer, bladder cancer, and renal cell carcinoma (RCC). Recent advances and future directions in the areas of immunotherapy biomarkers and mechanisms of resistance were also examined. Current evidence for combination strategies with immunotherapy was highlighted, including combinations with other immunotherapies or with radiotherapy. Below is a summary of the key points discussed during this scientific exchange.

Assessing Immune-Related Adverse Events of Efficacious Combination Immunotherapies in Preclinical Models of Cancer

New combination immunotherapies are displaying both efficacy and immune-related adverse events (irAE) in humans. However, grade 3/4 irAEs occur in a high proportion, which can lead to discontinuation of treatment and can result in fatalities if not promptly treated. Prolonged T regulatory cell (Treg) depletion in tumor-bearing Foxp3-DTR mice using diphtheria toxin (DT) mirrored the spectrum of antitumor responses and severity of irAEs that can occur in ipilimumab/nivolumab-treated patients. In contrast, transient Treg depletion or anti-CTLA-4/PD-1 therapy had equivalent effects in mice, lowering the immune tolerance threshold and allowing irAEs to be more easily induced following treatment with additional immunomodulatory antibodies. Transient Treg depletion of DT in combination with anti-PD-1 or anti-TIM-3 monoclonal antibodies had a high therapeutic window compared with DT plus anti-CD137. In contrast, DT plus anti-CD137-treated mice developed severe irAEs similar to grade 3/4 clinical symptoms. These irAEs appeared because of an infiltration of activated proliferating effector T cells in the tissues producing IFNγ and TNF; however, TNF blockade decreased irAEs severity without impacting on tumor growth. Cancer Res; 76(18); 5288-301. ©2016 AACR.

Deciphering CD137 (4-1BB) signaling in T-cell costimulation for translation into successful cancer immunotherapy

CD137 (4-1BB, TNF-receptor superfamily 9) is a surface glycoprotein of the TNFR family which can be induced on a variety of leukocyte subsets. On T and NK cells, CD137 is expressed following activation and, if ligated by its natural ligand (CD137L), conveys polyubiquitination-mediated signals via TNF receptor associated factor 2 that inhibit apoptosis, while enhancing proliferation and effector functions. CD137 thus behaves as a bona fide inducible costimulatory molecule. These functional properties of CD137 can be exploited in cancer immunotherapy by systemic administration of agonist monoclonal antibodies, which increase anticancer CTLs and enhance NK-cell-mediated antibody-dependent cell-mediated cytotoxicity. Reportedly, anti-CD137 mAb and adoptive T-cell therapy strongly synergize, since (i) CD137 expression can be used to select the T cells endowed with the best activities against the tumor, (ii) costimulation of the lymphocyte cultures to be used in adoptive T-cell therapy can be done with CD137 agonist antibodies or CD137L, and (iii) synergistic effects upon coadministration of T cells and antibodies are readily observed in mouse models. Furthermore, the signaling cytoplasmic tail of CD137 is a key component of anti-CD19 chimeric antigen receptors that are used to redirect T cells against leukemia and lymphoma in the clinic. Ongoing phase II clinical trials with agonist antibodies and the presence of CD137 sequence in these successful chimeric antigen receptors highlight the importance of CD137 in oncoimmunology.

Boosting Cancer Immunotherapy with Anti-CD137 Antibody Therapy

In the past 5 years, immunomodulatory antibodies have revolutionized cancer immunotherapy. CD137, a member of the tumor necrosis factor receptor superfamily, represents a promising target for enhancing antitumor immune responses. CD137 helps regulate the activation of many immune cells, including CD4(+) T cells, CD8(+) T cells, dendritic cells, and natural killer cells. Recent studies indicate that the antitumor efficacy of therapeutic tumor-targeting antibodies can be augmented by the addition of agonistic antibodies targeting CD137. As ligation of CD137 provides a costimulatory signal in multiple immune cell subsets, combination therapy of CD137 antibody with therapeutic antibodies and/or vaccination has the potential to improve cancer treatment. Recently, clinical trials of combination therapies with agonistic anti-CD137 mAbs have been launched. In this review, we discuss the recent advances and clinical promise of agonistic anti-CD137 monoclonal antibody therapy.

Hypoxia-induced soluble CD137 in malignant cells blocks CD137L-costimulation as an immune escape mechanism

Hypoxia is a common feature in solid tumors that has been implicated in immune evasion. Previous studies from our group have shown that hypoxia upregulates the co-stimulatory receptor CD137 on activated T lymphocytes and on vascular endothelial cells. In this study, we show that exposure of mouse and human tumor cell lines to hypoxic conditions (1% O₂) promotes CD137 transcription. However, the resulting mRNA is predominantly an alternatively spliced form that encodes for a soluble variant, lacking the transmembrane domain. Accordingly, soluble CD137 (sCD137) is detectable by ELISA in the supernatant of hypoxia-exposed cell lines and in the serum of tumor-bearing mice. sCD137, as secreted by tumor cells, is able to bind to CD137-Ligand (CD137L). Our studies on primed T lymphocytes in co-culture with stable transfectants for CD137L demonstrate that tumor-secreted sCD137 prevents co-stimulation of T lymphocytes. Such an effect results from preventing the interaction of CD137L with the transmembrane forms of CD137 expressed on T lymphocytes undergoing activation. Indeed, silencing CD137 with shRNA renders more immunogenic tumor-cell variants upon inoculation to immunocompetent mice but which readily grafted on immunodeficient or CD8⁺ T-cell-depleted mice. These mechanisms are interpreted as a molecular strategy deployed by tumors to repress lymphocyte co-stimulation via CD137/CD137L.

Multimodal imaging analysis of an orthotopic head and neck cancer mouse model and application of anti-CD137 tumor immune therapy

BACKGROUND

Recent technical progress makes sophisticated noninvasive imaging methods available for murine models. For the first time, in this study, we applied fluorodeoxyglucose (FDG)-positron emission tomography (PET)-CT and FDG-PET-MRI to a murine orthotopic model of head and neck cancer immunotherapy.

METHODS

Tumor growth of floor of the mouth tumors was evaluated by multimodal small-animal imaging using FDG-PET-CT and FDG-PET-MRI. The immunotherapeutic effects of anti-CD137 antibody therapy were examined on body weight, tumor growth, and tumor-infiltrating immune cells in longitudinal imaging studies and immunohistochemical analyses.

RESULTS

Imaging revealed aggressive, fast-growing tumors without evidence of local or distant metastases. CD137 immunotherapy decreased tumor take and growth and stabilized body weight over time. A clear case of tumor regression was demonstrated by longitudinal PET-CT.

CONCLUSION

The murine model mimics the characteristics of head and neck cancer in humans and offers excellent opportunities to investigate immunomodulatory anticancer drugs. The CD137 antibody showed antitumor effects in some therapy-responsive mice.

Agonists of Co-stimulation in Cancer Immunotherapy Directed Against CD137, OX40, GITR, CD27, CD28, and ICOS

T and natural killer (NK) lymphocytes are considered the main effector players in the immune response against tumors. Full activation of T and NK lymphocytes requires the coordinated participation of several surface receptors that meet their cognate ligands through structured transient cell-to-cell interactions known as immune synapses. In the case of T cells, the main route of stimulation is driven by antigens as recognized in the form of short polypeptides associated with major histocompatibility complex (MHC) antigen-presenting molecules. However, the functional outcome of T-cell stimulation towards clonal expansion and effector function acquisition is contingent on the contact of additional surface receptor-ligand pairs and on the actions of cytokines in the milieu. While some of those interactions are inhibitory, others are activating and are collectively termed co-stimulatory receptors. The best studied belong to either the immunoglobulin superfamily or the tumor necrosis factor-receptor (TNFR) family. Co-stimulatory receptors include surface moieties that are constitutively expressed on resting lymphocytes such as CD28 or CD27 and others whose expression is induced upon recent previous antigen priming, ie, CD137, GITR, OX40, and ICOS. Ligation of these glycoproteins with agonist antibodies actively conveys activating signals to the lymphocyte. Those signals, acting through a potentiation of the cellular immune response, give rise to anti-tumor effects in mouse models. Anti-CD137 antibodies are undergoing clinical trials with evidence of clinical activity and anti-OX40 monoclonal antibodies (mAbs) induce interesting immunomodulation effects in humans. Antibodies anti-CD27 and GITR have recently entered clinical trials. The inherent dangers of these immunomodulation strategies are the precipitation of excessive systemic inflammation or/and invigorating silent autoimmunity. Agonist antibodies, recombinant forms of the natural ligands, and polynucleotide-based aptamers constitute the pharmacologic tools to manipulate such receptors. Preclinical data suggest that the greatest potential of these agents is achieved in combined treatment strategies.

Depletion of Alloreactive T-Cells by Anti-CD137-Saporin Immunotoxin

Depletion of alloreactive T-lymphocytes from allogeneic bone marrow tansplants may prevent graft-versus-host disease (GVHD) without impairing donor cell engraftment, immunity, and the graft-versus-leukemia (GVL) effect. Alloreactive T-cells may be identified by their expression, upon activation, of CD137, a costimulatory receptor and putative surrogate marker for antigen-specific effector T-cells. In this context, we tested the use of anti-CD137-saporin immunotoxin to selectively deplete mouse and human alloreactive T-cells. Anti-CD137 antibodies were internalized by cells within 4 h of binding to the cell surface CD137, and anti-CD137-saporin immunotoxin effectively killed polyclonally activated T-cells or antigen-stimulated T-cells. Transfer of donor T-cells after allodepletion with anti-CD137-saporin immunotoxin failed to induce any evident expression of GVHD; however, a significant GVL effect was observed. Targeting of CD137 with an immunotoxin was also effective in killing polyclonally activated or alloreactive human T-cells. Our results indicate that anti-CD137-saporin immunotoxin may be used to deplete alloreactive T-cells prior to bone marrow transplantation and thereby prevent GVHD and the relapse of leukemia.

Focusing and sustaining the antitumor CTL effector killer response by agonist anti-CD137 mAb

Cancer immunotherapy is undergoing significant progress due to recent clinical successes by refined adoptive T-cell transfer and immunostimulatory monoclonal Ab (mAbs). B16F10-derived OVA-expressing mouse melanomas resist curative immunotherapy with either adoptive transfer of activated anti-OVA OT1 CTLs or agonist anti-CD137 (4-1BB) mAb. However, when acting in synergistic combination, these treatments consistently achieve tumor eradication. Tumor-infiltrating lymphocytes that accomplish tumor rejection exhibit enhanced effector functions in both transferred OT-1 and endogenous cytotoxic T lymphocytes (CTLs). This is consistent with higher levels of expression of eomesodermin in transferred and endogenous CTLs and with intravital live-cell two-photon microscopy evidence for more efficacious CTL-mediated tumor cell killing. Anti-CD137 mAb treatment resulted in prolonged intratumor persistence of the OT1 CTL-effector cells and improved function with focused and confined interaction kinetics of OT-1 CTL with target cells and increased apoptosis induction lasting up to six days postadoptive transfer. The synergy of adoptive T-cell therapy and agonist anti-CD137 mAb thus results from in vivo enhancement and sustainment of effector functions.

Functional expression of CD137 (4-1BB) on T helper follicular cells

CD137 (4-1BB) is a surface protein initially discovered to mark activated T lymphocytes. However, its broader expression pattern also encompasses activated NK cells, B cells and myeloid cells, including mature dendritic cells. In this study, we have immunostained for CD137 on paraffin-embedded lymphoid tissues including tonsils, lymph nodes, ectopic tertiary lymphoid tissue in Hashimoto thyroiditis and cancer. Surprisingly, immunostaining mainly decorated intrafollicular lymphocytes in the tissues analyzed, with only scattered staining in interfollicular areas. Moreover, pathologic lymphoid follicles in follicular lymphoma and tertiary lymphoid tissue associated with non-small cell lung cancer showed a similar pattern of immunostaining. Multispectral fluorescence cytometry demonstrated that CD137 expression was restricted to CD4⁺ CXCR5⁺ follicular T helper lymphocytes (T_FH cells) in tonsils and lymph nodes. Short-term culture of lymph node cell suspensions in the presence of either an agonistic anti-CD137 monoclonal antibody (mAb) or CD137-ligand stimulated the functional upregulation of T_FH cells in 3 out of 6 cases, as indicated by CD40L surface expression and cytokine production. As a consequence, immunostimulatory monoclonal antibodies targeting CD137 (such as urelumab and PF-05082566) should be expected to primarily act on this lymphocyte subset, thus modifying ongoing humoral immune responses in patients with autoimmune disease and cancer.

NKT cell-targeted vaccination plus anti-4-1BB antibody generates persistent CD8 T cell immunity against B cell lymphoma

Harnessing the immune adjuvant properties of natural killer T (NKT) cells is an effective strategy to generate anticancer immunity. The objective of this study was to increase the potency and durability of vaccine-induced immunity against B cell lymphoma by combining α-galactosylceramide (α-GalCer)-loaded tumor cell vaccination with an agonistic antibody targeting the immune checkpoint molecule 4–1BB (CD137). We observed potent synergy when combining vaccination and anti-4–1BB antibody treatment resulting in significantly enhanced survival of mice harboring Eμ-myc tumors, including complete eradication of lymphoma in over 50% of mice. Tumor-free survival required interferon γ (IFNγ)-dependent expansion of CD8⁺ T cells and was associated with 4–1BB-mediated differentiation of KLRG1⁺ effector CD8⁺ T cells. 'Cured' mice were also resistant to lymphoma re-challenge 80 days later indicating successful generation of immunological memory. Overall, our results demonstrate that therapeutic anticancer vaccination against B cell lymphoma using an NKT cell ligand can be boosted by subsequent co-stimulation through 4–1BB leading to a sustainable immune response that may enhance outcomes to conventional treatment.

SA-4-1BBL as a novel adjuvant for the development of therapeutic cancer vaccines

Tumor associated antigen (TAA)-based therapeutic vaccines have great potential as a safe, practical, and cost-efficient alternative to standard treatments for cancer. Clinical efficacy of TAA-based vaccines, however, has yet to be realized and will require adjuvants with pleiotropic functions on immune cells. Such adjuvants need not only to generate/boost T cell responses, but also reverse intrinsic/extrinsic tumor immune evasion mechanisms for therapeutic efficacy. This review focuses on a novel agonistic ligand, SA-4-1BBL, for 4-1BB costimulatory receptor as an adjuvant of choice because of its ability to: i) serve as a vehicle to deliver TAAs to dendritic cells (DCs) for antigen uptake and cross-presentation to CD8(+) T cells; ii) augment adaptive Th1 and innate immune responses; and iii) overcome various immune evasion mechanisms, cumulatively translating into therapeutic efficacy in preclinical tumor models.

Combination of 4-1BB agonist and PD-1 antagonist promotes antitumor effector/memory CD8 T cells in a poorly immunogenic tumor model

Immunotherapies targeting the programmed death 1 (PD-1) coinhibitory receptor have shown great promise for a subset of patients with cancer. However, robust and safe combination therapies are still needed to bring the benefit of cancer immunotherapy to broader patient populations. To search for an optimal strategy of combinatorial immunotherapy, we have compared the antitumor activity of the anti-4-1BB/anti-PD-1 combination with that of the anti-PD-1/anti-LAG-3 combination in the poorly immunogenic B16F10 melanoma model. Pronounced tumor inhibition occurred only in animals receiving anti-PD-1 and anti-4-1BB concomitantly, while combining anti-PD-1 with anti-LAG-3 led to a modest degree of tumor suppression. The activity of the anti-4-1BB/anti-PD-1 combination was dependent on IFNγ and CD8(+) T cells. Both 4-1BB and PD-1 proteins were elevated on the surface of CD8(+) T cells by anti-4-1BB/anti-PD-1 cotreatment. In the tumor microenvironment, an effective antitumor immune response was induced as indicated by the increased CD8(+)/Treg ratio and the enrichment of genes such as Cd3e, Cd8a, Ifng, and Eomes. In the spleen, the combination treatment shaped the immune system to an effector/memory phenotype and increased the overall activity of tumor-specific CD8(+) CTLs, reflecting a long-lasting systemic antitumor response. Furthermore, combination treatment in C57BL/6 mice showed no additional safety signals, and only minimally increased severity of the known toxicity relative to 4-1BB agonist alone. Therefore, in the absence of any cancer vaccine, anti-4-1BB/anti-PD-1 combination therapy is sufficient to elicit a robust antitumor effector/memory T-cell response in an aggressive tumor model and is therefore a candidate for combination trials in patients.

Boosting antibody-dependant cellular cytotoxicity against tumor cells with a CD137 stimulatory antibody

Monoclonal antibodies (mAb) induce tumor regression through antibody-dependant cellular cytotoxicity (ADCC). We recently showed that an agonistic anti-CD137 mAb stimulates natural killer (NK) cells which have been activated by a tumor-specific mAb, resulting in increased ADCC against cancer cells.

Immunomodulatory antibody therapy of cancer: the closer, the better

Immune checkpoint blockade therapies have demonstrated promising therapeutic effects; however, clinical outcomes are variable, with only a subgroup of cancer patients achieving durable complete responses. New therapeutic strategies, including local administration of immunomodulatory antibodies, have been considered as better routes for improving the overall efficacy of antibody-based therapy.

Mechanisms of hypoxia-mediated immune escape in cancer

An important aspect of malignant progression is the acquired ability of tumor cells to avoid recognition and destruction by the immune system (immune escape). Clinical cancer progression is also associated with the development of tumor hypoxia, which is mechanistically linked to the acquisition of malignant phenotypes in cancer cells. Despite the well-established role of hypoxia in tumor cell invasion and metastasis, and resistance to therapy, relatively few studies have examined the contribution of hypoxia to cancer immune escape. Accumulating evidence reveals that hypoxia can impair anticancer immunity by altering the function of innate and adaptive immune cells and/or by increasing the intrinsic resistance of tumor cells to the cytolytic activity of immune effectors. Here, we discuss certain aspects of the contribution of hypoxia to tumor immune escape and provide evidence for a novel role of cyclic guanosine monophosphate (cGMP) signaling in the regulation of hypoxia-induced immune escape. Thus, we propose that activation of cGMP signaling in cancer cells may have important immunotherapeutic applications.

SA-4-1BBL and monophosphoryl lipid A constitute an efficacious combination adjuvant for cancer vaccines

Vaccines based on tumor-associated antigens (TAA) have limited therapeutic efficacy due to their weak immunogenic nature and the various immune evasion mechanisms active in advanced tumors. In an effort to overcome these limitations, we evaluated a combination of the T-cell costimulatory molecule SA-4-1BBL with the TLR4 agonist monophosphoryl lipid A (MPL) as a novel vaccine adjuvant system. In the TC-1 mouse allograft model of human papilloma virus (HPV)-induced cancer, a single administration of this combination adjuvant with HPV E7 protein caused tumor rejection in all tumor-bearing mice. On its own, SA-4-1BBL outperformed MPL in this setting. Against established tumors, two vaccinations were sufficient to elicit rejection in the majority of mice. In the metastatic model of Lewis lung carcinoma, vaccination of the TAA survivin with SA-4-1BBL/MPL yielded superior efficacy against pulmonary metastases. Therapeutic efficacy of SA-4-1BBL/MPL was achieved in the absence of detectable toxicity, correlating with enhanced dendritic cell activation, CD8(+) T-cell function, and an increased intratumoral ratio of CD8(+) T effector cells to CD4(+)FoxP3(+) T regulatory cells. Unexpectedly, use of MPL on its own was associated with unfavorable intratumoral ratios of these T-cell populations, resulting in suboptimal efficacy. The efficacy of MPL monotherapy was restored by depletion of T regulatory cells, whereas eliminating CD8(+) T cells abolished the efficacy of its combination with SA-4-1BBL. Mechanistic investigations showed that IFNγ played a critical role in supporting the therapeutic effect of SA-4-1BBL/MPL. Taken together, our results offer a preclinical proof of concept for the use of a powerful new adjuvant system for TAA-based cancer vaccines.

Design of vaccine adjuvants incorporating TNF superfamily ligands and TNF superfamily molecular mimics

TNF superfamily ligands play a critical role in the regulation of adaptive immune responses, including the costimulation of dendritic cells, T cells, and B cells. This costimulation could potentially be exploited for the development of prophylactic vaccines and immunotherapy. Despite this, there have been only a limited number of reports on the use of this family of molecules as gene-based adjuvants to enhance DNA and/or viral vector vaccines. In addition, the molecule latent membrane protein 1 (LMP1), a viral mimic of the TNF superfamily receptor CD40, provides an alternative approach for the design of novel molecular adjuvants. Here, we discuss advances in the development of recombinant TNF superfamily ligands as adjuvants for HIV vaccines and as cancer immunotherapy, including the use of LMP1 and LMP1-CD40 chimeric fusion proteins to mimic constitutive CD40 signaling.

Agonistic anti-CD137 antibody treatment leads to antitumor response in mice with liver cancer

Immunotherapy is a promising strategy against hepatocellular carcinoma (HCC). We assessed the therapeutic effects of stimulating CD137, a member of the TNF receptor family, with agonistic monoclonal antibodies (mAb). Agonistic anti-CD137 mAb treatment was tested on two in situ models of HCC in immunocompetent mice. We also studied the mediators involved at different time points. In an orthotopic HCC the treatment consistently leads to complete tumor regression in 40-60% of animals. The protection is long lasting in the animals responding to the treatment, which can reject a second tumor challenge more than 3 months after treatment and eradication of the first malignancy. The main mediators of the effect are T lymphocytes and NK cells, demonstrated through depletion experiments. In addition, adoptive transfer of splenocytes prepared from anti-CD137 mAb-treated and -cured mice to naive mice allowed them to, in turn, reject the tumor. The efficacy of anti-CD137 mAb treatment is associated with early, sustained recruitment of iNOS-positive macrophages within tumor nodules. Moreover, in the absence of treatment, tumor development is accompanied by infiltration by myeloid derived suppressor cells (MDSC) and regulatory T lymphocytes. In mice responding to the anti-CD137 mAb treatment, this infiltration is very limited, and a combination treatment with a depletion of MDSC leads to the recovery of 80% of the mice. These results demonstrate that agonistic anti-CD137 mAb is a promising therapeutic strategy for anti-tumor immunity stimulation against HCC.

Human and mouse CD137 have predominantly different binding CRDs to their respective ligands

Monoclonal antibodies (mAbs) to CD137 (a.k.a. 4-1BB) have anti-tumor efficacy in several animal models and have entered clinical trials in patients with advanced cancer. Importantly, anti-CD137 mAbs can also ameliorate autoimmunity in preclinical models. As an approach to better understand the action of agonistic and antagonistic anti-CD137 mAbs we have mapped the binding region of the CD137 ligand (CD137L) to human and mouse CD137. By investigating the binding of CD137L to cysteine rich domain II (CRDII )and CRDIII of CD137, we found that the binding interface was limited and differed between the two species in that mouse CD137L mainly combined with CRDII and human CD137L mainly combined with CRDIII.

Combined immunostimulatory monoclonal antibodies extend survival in an aggressive transgenic hepatocellular carcinoma mouse model

PURPOSE

Immunostimulatory monoclonal antibodies (ISmAb) that unleash antitumor immune responses are showing efficacy in cancer clinical trials. Anti-B7-H1 (PD-L1) monoclonal antibodies (mAb) block a critical inhibitory pathway in T cells, whereas anti-CD137 and OX40 mAbs provide T-cell costimulation. A combination of these ISmAbs (anti-CD137 + anti-OX40 + anti-B7-H1) was tested using a transgenic mouse model of multifocal and rapidly progressing hepatocellular carcinoma, in which c-myc drives transformation and cytosolic ovalbumin (OVA) is expressed in tumor cells as a model antigen.

EXPERIMENTAL DESIGN

Flow-cytometry and immunohistochemistry were used to quantify tumor-infiltrating lymphocytes (TIL) elicited by treatment and assess their activation status and cytolytic potential. Tolerance induction and its prevention/reversal by treatment with the combination of ISmAbs were revealed by in vivo killing assays.

RESULTS

The triple combination of ISmAbs extended survival of mice bearing hepatocellular carcinomas in a CD8-dependent fashion and synergized with adoptive T-cell therapy using activated OVA-specific TCR-transgenic OT-1 and OT-2 lymphocytes. Mice undergoing therapy showed clear increases in tumor infiltration by activated and blastic CD8(+) and CD4(+) T lymphocytes containing perforin/granzyme B and expressing the ISmAb-targeted receptors on their surface. The triple combination of ISmAbs did not result in enhanced OVA-specific cytotoxic T lymphocyte (CTL) activity but other antigens expressed by cell lines derived from such hepatocellular carcinomas were recognized by endogenous TILs. Adoptively transferred OVA-specific OT-1 lymphocytes into tumor-bearing mice were rendered tolerant, unless given the triple mAb therapy.

CONCLUSION

Extension of survival and dense T-cell infiltrates emphasize the translational potential of combinational immunotherapy strategies for hepatocellular carcinoma. Clin Cancer Res; 19(22); 6151-62. ©2013 AACR.