Results from an Integrated Safety Analysis of Urelumab, an Agonist Anti-CD137 Monoclonal Antibody

Approaches of the Innate Immune System to Ameliorate Adaptive Immunotherapy for B-Cell Non-Hodgkin Lymphoma in Their Microenvironment

A dominant paradigm being developed in immunotherapy for hematologic malignancies is of adaptive immunotherapy that involves chimeric antigen receptor (CAR) T cells and bispecific T-cell engagers. CAR T-cell therapy has yielded results that surpass those of the existing salvage immunochemotherapy for patients with relapsed/refractory diffuse large B-cell lymphoma (DLBCL) after first-line immunochemotherapy, while offering a therapeutic option for patients with follicular lymphoma (FL) and mantle cell lymphoma (MCL). However, the role of the innate immune system has been shown to prolong CAR T-cell persistence. Cluster of differentiation (CD) 47-blocking antibodies, which are a promising therapeutic armamentarium for DLBCL, are novel innate immune checkpoint inhibitors that allow macrophages to phagocytose tumor cells. Intratumoral Toll-like receptor 9 agonist CpG oligodeoxynucleotide plays a pivotal role in FL, and vaccination may be required in MCL. Additionally, local stimulator of interferon gene agonists, which induce a systemic anti-lymphoma CD8⁺ T-cell response, and the costimulatory molecule 4-1BB/CD137 or OX40/CD134 agonistic antibodies represent attractive agents for dendritic cell activations, which subsequently, facilitates initiation of productive T-cell priming and NK cells. This review describes the exploitation of approaches that trigger innate immune activation for adaptive immune cells to operate maximally in the tumor microenvironment of these lymphomas.

The foundations of immune checkpoint blockade and the ipilimumab approval decennial

Cancer immunity, and the potential for cancer immunotherapy, have been topics of scientific discussion and experimentation for over a hundred years. Several successful cancer immunotherapies - such as IL-2 and interferon-α (IFNα) - have appeared over the past 30 years. However, it is only in the past decade that immunotherapy has made a broad impact on patient survival in multiple high-incidence cancer indications. The emergence of immunotherapy as a new pillar of cancer treatment (adding to surgery, radiation, chemotherapy and targeted therapies) is due to the success of immune checkpoint blockade (ICB) drugs, the first of which - ipilimumab - was approved in 2011. ICB drugs block receptors and ligands involved in pathways that attenuate T cell activation - such as cytotoxic T lymphocyte antigen 4 (CTLA4), programmed cell death 1 (PD1) and its ligand, PDL1 - and prevent, or reverse, acquired peripheral tolerance to tumour antigens. In this Review we mark the tenth anniversary of the approval of ipilimumab and discuss the foundational scientific history of ICB, together with the history of the discovery, development and elucidation of the mechanism of action of the first generation of drugs targeting the CTLA4 and PD1 pathways.

The immunotoxicity, but not anti-tumor efficacy, of anti-CD40 and anti-CD137 immunotherapies is dependent on the gut microbiota

Immune agonist antibodies (IAAs) are promising immunotherapies that target co-stimulatory receptors to induce potent anti-tumor immune responses, particularly when combined with checkpoint inhibitors. Unfortunately, their clinical translation is hampered by serious dose-limiting, immune-mediated toxicities, including high-grade and sometimes fatal liver damage, cytokine release syndrome (CRS), and colitis. We show that the immunotoxicity, induced by the IAAs anti-CD40 and anti-CD137, is dependent on the gut microbiota. Germ-free or antibiotic-treated mice have significantly reduced colitis, CRS, and liver damage following IAA treatment compared with conventional mice or germ-free mice recolonized via fecal microbiota transplant. MyD88 signaling is required for IAA-induced CRS and for anti-CD137-induced, but not anti-CD40-induced, liver damage. Importantly, antibiotic treatment does not impair IAA anti-tumor efficacy, alone or in combination with anti-PD1. Our results suggest that microbiota-targeted therapies could overcome the toxicity induced by IAAs without impairing their anti-tumor activity.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

CD137 (4-1BB) costimulation of CD8+ T cells is more potent when provided in cis than in trans with respect to CD3-TCR stimulation

CD137 (4-1BB; TNFSR9) is an activation-induced surface receptor that through costimulation effects provide antigen-primed T cells with augmented survival, proliferation and effector functions as well as metabolic advantages. These immunobiological mechanisms are being utilised for cancer immunotherapy with agonist CD137-binding and crosslinking-inducing agents that elicit CD137 intracellular signaling. In this study, side-by-side comparisons show that provision of CD137 costimulation in-cis with regard to the TCR-CD3-ligating cell is superior to that provided in-trans in terms of T cell activation, proliferation, survival, cytokine secretion and mitochondrial fitness in mouse and human. Cis ligation of CD137 relative to the TCR-CD3 complex results in more intense canonical and non-canonical NF-κB signaling and provides a more robust induction of cell cycle and DNA damage repair gene expression programs. Here we report that the superiority of cis versus trans CD137-costimulation is readily observed in vivo and is relevant for understanding the immunotherapeutic effects of CAR T cells and CD137 agonistic therapies currently undergoing clinical trials, which may provide costimulation either in cis or in trans.

Immune Regulatory Processes of the Tumor Microenvironment under Malignant Conditions

The tumor microenvironment (TME) is a critical regulator of tumor growth, progression, and metastasis. Since immune cells represent a large fraction of the TME, they play a key role in mediating pro- and anti-tumor immune responses. Immune escape, which suppresses anti-tumor immunity, enables tumor cells to maintain their proliferation and growth. Numerous mechanisms, which have been intensively studied in recent years, are involved in this process and based on these findings, novel immunotherapies have been successfully developed. Here, we review the composition of the TME and the mechanisms by which immune evasive processes are regulated. In detail, we describe membrane-bound and soluble factors, their regulation, and their impact on immune cell activation in the TME. Furthermore, we give an overview of the tumor/antigen presentation and how it is influenced under malignant conditions. Finally, we summarize novel TME-targeting agents, which are already in clinical trials for different tumor entities.

Immunotherapy of cancer in the era of checkpoint inhibitor

Application of immunotherapy has revolutionized treatment of number of malignancies. We present a review of immunotherapy approaches, early-phase data of number of new immunotherapeutic targets in melanoma, cutaneous squamous cell carcinoma, Merkel cell cancer, and non-small cell lung cancer.

Directing T-Cell Immune Responses for Cancer Vaccination and Immunotherapy

Cancer vaccination and immunotherapy revolutionised the treatment of cancer, a result of decades of research into the immune system in health and disease. However, despite recent breakthroughs in treating otherwise terminal cancer, only a minority of patients respond to cancer immunotherapy and some cancers are largely refractive to immunotherapy treatment. This is due to numerous issues intrinsic to the tumour, its microenvironment, or the immune system. CD4+ and CD8+ αβ T-cells emerged as the primary effector cells of the anti-tumour immune response but their function in cancer patients is often compromised. This review details the mechanisms by which T-cell responses are hindered in the setting of cancer and refractive to immunotherapy, and details many of the approaches under investigation to direct T-cell function and improve the efficacy of cancer vaccination and immunotherapy.

Individualized Treatment Strategy for Cutaneous Melanoma: Where Are We Now and Where Are We Going?

In the past several decades, innovative research in cancer biology and immunology has contributed to novel therapeutics, such as targeted therapy and immunotherapy, which have transformed the management of patients with melanoma. Despite the remarkable therapeutic outcomes of targeted treatments targeting MAPK signaling and immunotherapy that suppresses immune checkpoints, some individuals acquire therapeutic resistance and disease recurrence. This review summarizes the current understanding of melanoma genetic variations and discusses individualized melanoma therapy options, particularly for advanced or metastatic melanoma, as well as potential drug resistance mechanisms. A deeper understanding of individualized treatment will assist in improving clinical outcomes for patients with cutaneous melanoma.

Immunotherapy Approaches in HPV-Associated Head and Neck Cancer

Immunotherapy approaches for head and neck squamous cell carcinoma (HNSCC) are rapidly advancing. Human papillomavirus (HPV) has been identified as a causative agent in a subset of oropharyngeal cancers (OPC). HPV-positive OPC comprises a distinct clinical and pathologic disease entity and has a unique immunophenotype. Immunotherapy with anti-PD1 checkpoint inhibitors has exhibited improved outcomes for patients with advanced HNSCC, irrespective of HPV status. To date, the clinical management of HPV-positive HNSCC and HPV-negative HNSCC has been identical, despite differences in the tumor antigens, immune microenvironment, and immune signatures of these two biologically distinct tumor types. Numerous clinical trials are underway to further refine the application of immunotherapy and develop new immunotherapy approaches. The aim of this review is to highlight the developing role of immunotherapy in HPV-positive HNSCC along with the clinical evidence and preclinical scientific rationale behind emerging therapeutic approaches, with emphasis on promising HPV-specific immune activators that exploit the universal presence of foreign, non-self tumor antigens.

Key Activating and Inhibitory Ligands Involved in the Mobilization of Natural Killer Cells for Cancer Immunotherapies

Natural killer (NK) cells are the most potent arm of the innate immune system and play an important role in immunity, alloimmunity, autoimmunity, and cancer. NK cells recognize “altered-self” cells due to oncogenic transformation or stress due to viral infection and target to kill them. The effector functions of NK cells depend on the interaction of the activating and inhibitory receptors on their surface with their cognate ligand expressed on the target cells. These activating and inhibitory receptors interact with major histocompatibility complex I (MHC I) expressed on the target cells and make decisions to mount an immune response. NK cell immune response includes cytolytic activity and secretion of cytokines to help with the ongoing immune response. The advancement of our knowledge on the expression of inhibitory and activating molecules led us to exploit these molecules in the treatment of cancer. This review discusses the importance of activating and inhibitory receptors on NK cells and their clinical importance in cancer immunotherapy.

Cancer immune therapy with PD-1-dependent CD137 co-stimulation provides localized tumour killing without systemic toxicity

Expression of the cell surface receptor CD137 has been shown to enhance anti-cancer T cell function via engagement with its natural ligand 4-1BBL. CD137 ligation with engineered ligands has emerged as a cancer immunotherapy strategy, yet clinical development of agonists has been hindered by either toxicity or limited efficacy. Here we show that a CD137/PD-1 bispecific antibody, IBI319, is able to overcome these limitations by coupling CD137 activation to PD-1-crosslinking. In CT26 and MC38 syngeneic mouse tumour models, IBI319 restricts T cell co-stimulation to PD-1-rich microenvironments, such as tumours and tumour-draining lymph nodes, hence systemic (liver) toxicity arising from generalised T cell activation is reduced. Besides limiting systemic T cell co-stimulation, the anti-PD-1 arm of IBI319 also exhibits checkpoint blockade functions, with an overall result of T and NK cell infiltration into tumours. Toxicology profiling in non-human primates shows that IBI319 is a well-tolerated molecule with IgG-like pharmacokinetic properties, thus a suitable candidate for further clinical development.

The toxicity arising from generalised stimulation of T cells restricts applicability of CD137 agonists in cancer immune therapy. Here authors show that a bispecific antibody blocking PD-1 while activating CD137 efficiently restricts T cell activation to the tumour microenvironment, resulting in efficient tumour control and reduced liver toxicity.

BT7480, a novel fully synthetic Bicycle tumor-targeted immune cell agonist™ (Bicycle TICA™) induces tumor localized CD137 agonism

Background

CD137 (4-1BB) is an immune costimulatory receptor with high therapeutic potential in cancer. We are creating tumor target-dependent CD137 agonists using a novel chemical approach based on fully synthetic constrained bicyclic peptide (Bicycle®) technology. Nectin-4 is overexpressed in multiple human cancers that may benefit from CD137 agonism. To this end, we have developed BT7480, a novel, first-in-class, Nectin-4/CD137 Bicycle tumor-targeted immune cell agonist™ (Bicycle TICA™).

Methods

Nectin-4 and CD137 co-expression analyses in primary human cancer samples was performed. Chemical conjugation of two CD137 Bicycles to a Nectin-4 Bicycle led to BT7480, which was then evaluated using a suite of in vitro and in vivo assays to characterize its pharmacology and mechanism of action.

Results

Transcriptional profiling revealed that Nectin-4 and CD137 were co-expressed in a variety of human cancers with high unmet need and spatial proteomic imaging found CD137-expressing immune cells were deeply penetrant within the tumor near Nectin-4-expressing cancer cells. BT7480 binds potently, specifically, and simultaneously to Nectin-4 and CD137. In co-cultures of human peripheral blood mononuclear cells and tumor cells, this co-ligation causes robust Nectin-4-dependent CD137 agonism that is more potent than an anti-CD137 antibody agonist. Treatment of immunocompetent mice bearing Nectin-4-expressing tumors with BT7480 elicited a profound reprogramming of the tumor immune microenvironment including an early and rapid myeloid cell activation that precedes T cell infiltration and upregulation of cytotoxicity-related genes. BT7480 induces complete tumor regressions and resistance to tumor re-challenge. Importantly, antitumor activity is not dependent on continuous high drug levels in the plasma since a once weekly dosing cycle provides maximum antitumor activity despite minimal drug remaining in the plasma after day 2. BT7480 appears well tolerated in both rats and non-human primates at doses far greater than those expected to be clinically relevant, including absence of the hepatic toxicity observed with non-targeted CD137 agonists.

Conclusion

BT7480 is a highly potent Nectin-4-dependent CD137 agonist that produces complete regressions and antitumor immunity with only intermittent drug exposure in syngeneic mouse tumor models and is well tolerated in preclinical safety species. This work supports the clinical investigation of BT7480 for the treatment of cancer in humans.

T cells and monocyte-derived myeloid cells mediate immunotherapy-related hepatitis in a mouse model

BACKGROUND & AIMS

Immune checkpoint inhibitors (ICIs) are associated with immune-related adverse events (irAEs) which are more severe when ICIs are used in combination. We aimed to use a mouse model to elucidate the molecular mechanisms of immune-related hepatitis, one of the common irAEs associated with ICIs.

METHODS

Immune phenotyping and molecular profiling were performed on Pdcd1^-/- mice treated with anti-CTLA4 and/or the IDO1 inhibitor epacadostat or a 4-1BB agonistic antibody.

RESULTS

ICI combination-induced hepatitis and 4-1BB agonist-mediated hepatitis share similar features yet maintain distinct immune signatures. Both were characterized by an expansion of periportal infiltrates and pan-zonal inflammation albeit with different morphologic characteristics. In both cases, infiltrates were predominantly CD4+ and CD8+ T cells with upregulated T-cell activation markers, ICOS and CD44. Depletion of CD8+ T cells abolished ICI-mediated hepatitis. Single-cell transcriptomics revealed that the hepatitis induced by combination ICIs is associated with a robust immune activation signature in all subtypes of T cells and T helper 1 skewing. Expression profiling revealed a central role for IFNγ and liver monocyte-derived macrophages in promoting a pro-inflammatory T-cell response to ICI combination and 4-1BB agonism.

CONCLUSION

We developed a novel mouse model which offers significant value in yielding deeper mechanistic insight into immune-mediated liver toxicity associated with various immunotherapies.

LAY SUMMARY

Hepatitis is one of the common immune-related adverse events in cancer patients receiving immune checkpoint inhibitor (ICI) therapy. The mechanisms of ICI-induced hepatitis are not well understood. In this paper, we identify key molecular mechanisms mediating immune intracellular crosstalk between liver T cells and macrophages in response to ICI in a mouse model.

Phase I Study of Stereotactic Body Radiotherapy plus Nivolumab and Urelumab or Cabiralizumab in Advanced Solid Tumors

PURPOSE

CD137 agonism and CSF1R blockade augment stereotactic body radiotherapy (SBRT) and anti-programmed death-1 in preclinical models. We evaluated the safety and efficacy of SBRT with nivolumab+urelumab (CD137 agonist) or nivolumab+cabiralizumab (CSF1R inhibitor).

PATIENTS AND METHODS

This phase I clinical trial enrolled patients with advanced solid tumors that had progressed on standard therapies. SBRT was delivered to 1-4 metastases with nivolumab+urelumab or nivolumab+cabiralizumab given concurrently and following SBRT. Dose-limiting toxicity (DLT) was the primary endpoint with anatomic location-specific SBRT doses deemed safe if ≤33% DLT frequency was observed. Secondary endpoints included RECISTv1.1 response, progression-free survival (PFS), overall survival (OS), and molecular correlative studies.

RESULTS

Sixty patients were enrolled, and median follow-up for living patients is 13.8 months. Of these, 23 (38%) received SBRT+nivolumab+urelumab and 37 (62%) received SBRT+nivolumab+cabiralizumab. Seven patients (12%) experienced a DLT (n = 3 grade 3, n = 4 grade 4) in the following anatomic cohorts: abdominal/pelvic (3/17, 18%), liver (1/13, 8%), central lung (2/14, 14%), and peripheral lung (1/12, 8%). Of 41 patients radiographically evaluable for best overall response including 55 radiated and 23 unirradiated RECIST target lesions, 2 had complete responses (5%), 7 had partial responses (17%), 12 had stable disease (29%), and 20 had progression (49%). Median estimated PFS and OS are 3.0 months [95% confidence interval (CI), 2.9-4.8] and 17.0 months (95% CI, 6.8-undetermined), respectively. No patients with elevated pre-SBRT serum IL8 experienced a response.

CONCLUSIONS

SBRT to ≤4 sites with nivolumab+urelumab or nivolumab+cabiralizumab for treating advanced solid tumors is feasible with acceptable toxicity and modest antitumor activity.See related commentary by Rodriguez-Ruiz et al., p. 5443.

Novel classes of immunotherapy for breast cancer

Immune-checkpoint inhibitors have profoundly changed the treatment landscape for many tumor types. Despite marked improvements in disease control for highly immunogenic cancers, the clinical impact of checkpoint inhibitors in breast cancers to date is limited. Breast cancer is a heterogeneous disease with different levels of PD-L1 expression and variable tumor microenvironment (TME) composition according to molecular subtype. With emerging evidence of the role of different factors involved in immune evasion, there are promising new immunotherapy targets that will reshape early drug development for metastatic breast cancer. This review examines the available evidence for existing and emerging immuno-oncology (IO) approaches including small molecules targeting different regulators of the cancer-immunity cycle.

Peptide-HLA-based immunotherapeutics platforms for direct modulation of antigen-specific T cells

Targeted pharmacologic activation of antigen-specific (AgS) T cells may bypass limitations inherent in current T cell-based cancer therapies. We describe two immunotherapeutics platforms for selective delivery of costimulatory ligands and peptide-HLA (pHLA) to AgS T cells. We engineered and deployed on these platforms an affinity-attenuated variant of interleukin-2, which selectively expands oligoclonal and polyfunctional AgS T cells in vitro and synergizes with CD80 signals for superior proliferation versus peptide stimulation.

Switchable immune modulator for tumor-specific activation of anticancer immunity

Immune stimulatory antibodies and cytokines elicit potent antitumor immunity. However, the dose-limiting systemic toxicity greatly hinders their clinical applications. Here, we demonstrate a chemical approach, termed “switchable” immune modulator (Sw-IM), to limit the systemic exposure and therefore ameliorate their toxicities. Sw-IM is a biomacromolecular therapeutic reversibly masked by biocompatible polymers through chemical linkers that are responsive to tumor-specific stimuli, such as high reducing potential and acidic pH. Sw-IMs stay inert (switch off) in the circulation and healthy tissues but get reactivated (switch on) selectively in tumor via responsive removal of the polymer masks, thus focusing the immune boosting activities in the tumor microenvironment. Sw-IMs applied to anti–4-1BB agonistic antibody and IL-15 cytokine led to equivalent antitumor efficacy to the parental IMs with markedly reduced toxicities. Sw-IM provides a highly modular and generic approach to improve the therapeutic window and clinical applicability of potent IMs in mono- and combinational immunotherapies.

Immunotherapy combinations overcome resistance to bispecific T cell engager treatment in T cell-cold solid tumors

Therapeutic approaches are needed to promote T cell-mediated destruction of poorly immunogenic, "cold" tumors typically associated with minimal response to immune checkpoint blockade (ICB) therapy. Bispecific T cell engager (BiTE) molecules induce redirected lysis of cancer cells by polyclonal T cells and have demonstrated promising clinical activity against solid tumors in some patients. However, little is understood about the key factors that govern clinical responses to these therapies. Using an immunocompetent mouse model expressing a humanized CD3ε chain (huCD3e mice) and BiTE molecules directed against mouse CD19, mouse CLDN18.2, or human EPCAM antigens, we investigated the pharmacokinetic and pharmacodynamic parameters and immune correlates associated with BiTE efficacy across multiple syngeneic solid-tumor models. These studies demonstrated that pretreatment tumor-associated T cell density is a critical determinant of response to BiTE therapy, identified CD8⁺ T cells as important targets and mediators of BiTE activity, and revealed an antagonistic role for CD4⁺ T cells in BiTE efficacy. We also identified therapeutic combinations, including ICB and 4-1BB agonism, that synergized with BiTE treatment in poorly T cell-infiltrated, immunotherapy-refractory tumors. In these models, BiTE efficacy was dependent on local expansion of tumor-associated CD8⁺ T cells, rather than their recruitment from circulation. Our findings highlight the relative contributions of baseline T cell infiltration, local T cell proliferation, and peripheral T cell trafficking for BiTE molecule-mediated efficacy, identify combination strategies capable of overcoming resistance to BiTE therapy, and have clinical relevance for the development of BiTE and other T cell engager therapies.

Chronic activation of 4-1BB signaling induces granuloma development in tumor-draining lymph nodes that is detrimental to subsequent CD8+ T cell responses

The antitumor capabilities of agonistic anti-4-1BB mAbs have made them an attractive target for tumor immunotherapy. However, the adverse side effects associated with agonist antibodies have hindered their clinical development. Here, we aimed to study the immune-related adverse events of repeated doses and long-term use of agonistic anti-4-1BB mAbs. We show that chronic activation of 4-1BB signals induced the accumulation of IFN-γ-producing PD-1+CD8+ T cells in the secondary lymphoid organs of tumor-bearing mice by increasing the number of dividing CD8+ T cells, which was beneficial for suppressing tumor growth in the early phase of anti-4-1BB induction. However, repeated exposure to anti-4-1BB mAbs led to granuloma development in tumor-draining lymph nodes (TDLNs) of mice due to recruitment and accumulation of macrophages via the CD8+ T cell-IFN-γ axis. This was accompanied by excessive lymph node swelling, which impaired the sequential activation of CD8+ T cells. Our data provide insights into the immune-related adverse events of long-term agonist 4-1BB antibody dosing, which should be considered during the clinical development of immunomodulating therapy.

Recent Advances in Engineered Materials for Immunotherapy-Involved Combination Cancer Therapy

Immunotherapy that can activate immunity or enhance the immunogenicity of tumors has emerged as one of the most effective methods for cancer therapy. Nevertheless, single-mode immunotherapy is still confronted with several critical challenges, such as the low immune response, the low tumor infiltration, and the complex immunosuppression tumor microenvironment. Recently, the combination of immunotherapy with other therapeutic modalities has emerged as a powerful strategy to augment the therapeutic outcome in fighting against cancer. In this review, recent research advances of the combination of immunotherapy with chemotherapy, phototherapy, radiotherapy, sonodynamic therapy, metabolic therapy, and microwave thermotherapy are summarized. Critical challenges and future research direction of immunotherapy-based cancer therapeutic strategy are also discussed.

Clinical Research on the Mechanisms Underlying Immune Checkpoints and Tumor Metastasis

This study highlights aspects of the latest clinical research conducted on the relationship between immune checkpoints and tumor metastasis. The overview of each immune checkpoint is divided into the following three sections: 1) structure and expression; 2) immune mechanism related to tumor metastasis; and 3) clinical research related to tumor metastasis. This review expands on the immunological mechanisms of 17 immune checkpoints, including TIM-3, CD47, and OX-40L, that mediate tumor metastasis; evidence shows that most of these immune checkpoints are expressed on the surface of T cells, which mainly exert immunomodulatory effects. Additionally, we have summarized the roles of these immune checkpoints in the diagnosis and treatment of metastatic tumors, as these checkpoints are considered common predictors of metastasis in various cancers such as prostate cancer, non-Hodgkin lymphoma, and melanoma. Moreover, certain immune checkpoints can be used in synergy with PD-1 and CTLA-4, along with the implementation of combination therapies such as LIGHT-VTR and anti-PD-1 antibodies. Presently, most monoclonal antibodies generated against immune checkpoints are under investigation as part of ongoing preclinical or clinical trials conducted to evaluate their efficacy and safety to establish a better combination treatment strategy; however, no significant progress has been made regarding monoclonal antibody targeting of CD28, VISTA, or VTCN1. The application of immune checkpoint inhibitors in early stage tumors to prevent tumor metastasis warrants further evidence; the immune-related adverse events should be considered before combination therapy. This review aims to elucidate the mechanisms of immune checkpoint and the clinical progress on their use in metastatic tumors reported over the last 5 years, which may provide insights into the development of novel therapeutic strategies that will assist with the utilization of various immune checkpoint inhibitors.

A human CD137×PD-L1 bispecific antibody promotes anti-tumor immunity via context-dependent T cell costimulation and checkpoint blockade

Immune checkpoint inhibitors demonstrate clinical activity in many tumor types, however, only a fraction of patients benefit. Combining CD137 agonists with these inhibitors increases anti-tumor activity preclinically, but attempts to translate these observations to the clinic have been hampered by systemic toxicity. Here we describe a human CD137xPD-L1 bispecific antibody, MCLA-145, identified through functional screening of agonist- and immune checkpoint inhibitor arm combinations. MCLA-145 potently activates T cells at sub-nanomolar concentrations, even under suppressive conditions, and enhances T cell priming, differentiation and memory recall responses. In vivo, MCLA-145 anti-tumor activity is superior to immune checkpoint inhibitor comparators and linked to recruitment and intra-tumor expansion of CD8 + T cells. No graft-versus-host-disease is observed in contrast to other antibodies inhibiting the PD-1 and PD-L1 pathway. Non-human primates treated with 100 mg/kg/week of MCLA-145 show no adverse effects. The conditional activation of CD137 signaling by MCLA-145, triggered by neighboring cells expressing >5000 copies of PD-L1, may provide both safety and potency advantages.

New emerging targets in cancer immunotherapy: CD137/4-1BB costimulatory axis

CD137 (4-1BB) is a surface glycoprotein that belongs to the tumour necrosis factor receptor family (TNFRSF9). Its expression is induced on activation on a number of leucocyte types. Interestingly, for cancer immunotherapy, CD137 becomes expressed on primed T and natural killer (NK) cells, which on ligation provides powerful costimulatory signals. Perturbation of CD137 by CD137L or agonist monoclonal antibodies on activated CD8 T cells protects such antigen-specific cytotoxic T lymphocytes from apoptosis, enhances effector functionalities and favours persistence and memory differentiation. As a consequence, agonist antibodies exert potent antitumour effects in mouse models and the CD137 signalling domain is critical in chimeric antigen receptors (CAR) of CAR T cells approved to be used in the clinic. New formats of CD137 agonist moieties are being clinically developed, seeking potent costimulation targeted to the tumour microenvironment to avoid liver inflammation side effects, that have thus far limited and delayed clinical development.

Anti-tumor effects of RTX-240: an engineered red blood cell expressing 4-1BB ligand and interleukin-15

Recombinant agonists that activate co-stimulatory and cytokine receptors have shown limited clinical anticancer utility, potentially due to narrow therapeutic windows, the need for coordinated activation of co-stimulatory and cytokine pathways and the failure of agonistic antibodies to recapitulate signaling by endogenous ligands. RTX-240 is a genetically engineered red blood cell expressing 4-1BBL and IL-15/IL-15Rα fusion (IL-15TP). RTX-240 is designed to potently and simultaneously stimulate the 4-1BB and IL-15 pathways, thereby activating and expanding T cells and NK cells, while potentially offering an improved safety profile through restricted biodistribution. We assessed the ability of RTX-240 to expand and activate T cells and NK cells and evaluated the in vivo efficacy, pharmacodynamics and tolerability using murine models. Treatment of PBMCs with RTX-240 induced T cell and NK cell activation and proliferation. In vivo studies using mRBC-240, a mouse surrogate for RTX-240, revealed biodistribution predominantly to the red pulp of the spleen, leading to CD8 + T cell and NK cell expansion. mRBC-240 was efficacious in a B16-F10 melanoma model and led to increased NK cell infiltration into the lungs. mRBC-240 significantly inhibited CT26 tumor growth, in association with an increase in tumor-infiltrating proliferating and cytotoxic CD8 + T cells. mRBC-240 was tolerated and showed no evidence of hepatic injury at the highest feasible dose, compared with a 4-1BB agonistic antibody. RTX-240 promotes T cell and NK cell activity in preclinical models and shows efficacy and an improved safety profile. Based on these data, RTX-240 is now being evaluated in a clinical trial.

Novel anti-4-1BB×PD-L1 bispecific antibody augments anti-tumor immunity through tumor-directed T-cell activation and checkpoint blockade

Background

Stimulation of 4-1BB with agonistic antibodies is a promising strategy for improving the therapeutic efficacy of immune checkpoint inhibitors (ICIs) or for overcoming resistance to ICIs. However, dose-dependent hepatotoxicity was observed in clinical trials with monoclonal anti-4-1BB agonistic antibodies due to the activation of 4-1BB signaling in liver resident Kupffer cells.

Methods

To avoid this on-target liver toxicity, we developed a novel bispecific antibody (4-1BB×PD-L1 bispecific antibody, termed “ABL503”) uniquely designed to activate 4-1BB signaling only in the context of PD-L1, while also blocking PD-1/PD-L1 signaling.

Results

Functional evaluation using effector cells expressing both 4-1BB and PD-1 revealed superior biological activity of ABL503 compared with the combination of each monoclonal antibody. ABL503 also augmented T-cell activation in in vitro assays and further enhanced the anti-PD-L1-mediated reinvigoration of tumor-infiltrating CD8⁺ T cells from patients with cancer. Furthermore, in humanized PD-L1/4-1BB transgenic mice challenged with huPD-L1-expressing tumor cells, ABL503 induced superior anti-tumor activity and maintained an anti-tumor response against tumor rechallenge. ABL503 was well tolerated, with normal liver function in monkeys.

Conclusion

The novel anti-4-1BB×PD-L1 bispecific antibody may exert a strong anti-tumor therapeutic efficacy with a low risk of liver toxicity through the restriction of 4-1BB stimulation in tumors.

PD-1 and beyond to Activate T Cells in Cutaneous Squamous Cell Cancers: The Case for 4-1BB and VISTA Antibodies in Combination Therapy

Non-melanoma skin cancers (NMSC) have a higher incidence than all other cancers combined with cutaneous squamous cell carcinoma (cSCC), capable of metastasis, representing approximately 20% of NMSCs. Given the accessibility of the skin, surgery is frequently employed to treat localized disease, although certain localities, the delineation of clear margins, frequency and recurrence of tumors can make these cancers inoperable in a subset of patients. Other treatment modalities, including cryotherapy, are commonly used for individual lesions, with varying success. Immunotherapy, particularly with checkpoint antibodies, is increasingly a promising therapeutic approach in many cancers, offering the potential advantage of immune memory for protection against lesion recurrence. This review addresses a role for PD-1, 4-1BB and VISTA checkpoint antibodies as monotherapies, or in combination as a therapeutic treatment for both early and late-stage cSCC.

Antitumor efficacy and reduced toxicity using an anti-CD137 Probody therapeutic

Costimulation via CD137 (4-1BB) enhances antitumor immunity mediated by cytotoxic T lymphocytes. Anti-CD137 agonist antibodies elicit mild liver inflammation in mice, and the maximum tolerated dose of Urelumab, an anti-human CD137 agonist monoclonal antibody, in the clinic was defined by liver inflammation-related side effects. A protease-activated prodrug form of the anti-mouse CD137 agonist antibody 1D8 (1D8 Probody therapeutic, Pb-Tx) was constructed and found to be selectively activated in the tumor microenvironment. This construct, which encompasses a protease-cleavable linker holding in place a peptide that masks the antigen binding site, exerted antitumor effects comparable to the unmodified antibody but did not result in liver inflammation. Moreover, it efficaciously synergized with both PD-1 blockade and adoptive T-cell therapy. Surprisingly, minimal active Pb-Tx reached tumor-draining lymph nodes, and regional lymphadenectomy did not abrogate antitumor efficacy. By contrast, S1P receptor-dependent recirculation of T cells was absolutely required for efficacy. The preferential cleavage of the anti-CD137 Pb-Tx by tumor proteases offers multiple therapeutic opportunities, including neoadjuvant therapy, as shown by experiments in which the Pb-Tx is given prior to surgery to avoid spontaneous metastases.

Generation of a safe and efficacious llama single-domain antibody fragment (vHH) targeting the membrane-proximal region of 4-1BB for engineering therapeutic bispecific antibodies for cancer

Background

The discovery of checkpoint inhibitors towards cytotoxic T-lymphocyte protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1) has been revolutionary for the treatment of cancers. These therapies have only offered an average of 20%–30% response rates across the tumor spectrum and the combination of agonists towards the tumor-necrosis superfamily members, such as 4-1BB and CD40, has shown potent efficacy in preclinical studies; however, these agonists have exhibited high degrees of toxicity with limited efficacy in human trials. In this study, we have generated a single-domain antibody towards a unique epitope of 4-1BB that limits its potential on-target toxicity while maintaining sufficient potency. This 4-1BB binder is ideal for use in the engineering of multispecific antibodies to localize 4-1BB activation within the tumor microenvironment, as shown here by a anti-PD-L1/4-1BB bispecific candidate (PM1003).

Methods

To determine the functional activity of the 4-1BB- and PD-L1-binding elements of PM1003, in vitro luciferase reporter and primary cell assays were used to test the potency of programmed cell death 1 ligand 1 (PD-L1) blockade and PD-L1-mediated 4-1BB activation via cross-bridging. X-ray crystallography was conducted to resolve the binding epitopes of the respective binding arms, and accurate binding kinetics were determined using standard affinity measurement techniques. Human 4-1BB and/or PD-L1 knock-in mice were used in cancer models for testing the in vivo antitumor efficacy of PM1003, and safety was evaluated further.

Results

PM1003 shows potent activation of 4-1BB and blockade of PD-L1 in cell-based assays. 4-1BB activation was exerted through the bridging of PD-L1 on target cells and 4-1BB on effector cells. No PD-L1-independent activation of 4-1BB was observed. Through X-ray crystallography, a unique binding epitope in the cysteine-rich domain 4 (CRD4) region was resolved that provides high potency and potentially low on-target toxicity as determined by primary immune cell assays and toxicity evaluation in vivo.

Conclusions

A unique single-domain antibody was discovered that binds to the CRD4 domain of 4-1BB. When incorporated into a 4-1BB/PD-L1 bispecific (PM1003), we have shown the potent inhibition of PD-L1 activity with 4-1BB agonism upon cross-bridging with PD-L1 in vitro. Antitumor activity with minimal toxicity was found in vivo. Thus, PM1003 is a uniquely differentiating and next generation therapeutic agent for cancer therapy.

Tumor-targeted CD28 bispecific antibodies enhance the antitumor efficacy of PD-1 immunotherapy

Monoclonal antibodies that block the programmed cell death 1 (PD-1) checkpoint have revolutionized cancer immunotherapy. However, many major tumor types remain unresponsive to anti-PD-1 therapy, and even among responsive tumor types, most of the patients do not develop durable antitumor immunity. It has been shown that bispecific antibodies activate T cells by cross-linking the TCR/CD3 complex with a tumor-specific antigen (TSA). The class of TSAxCD3 bispecific antibodies have generated exciting results in early clinical trials. We have recently described another class of "costimulatory bispecifics" that cross-link a TSA to CD28 (TSAxCD28) and cooperate with TSAxCD3 bispecifics. Here, we demonstrate that these TSAxCD28 bispecifics (one specific for prostate cancer and the other for epithelial tumors) can also synergize with the broader anti-PD-1 approach and endow responsiveness-as well as long-term immune memory-against tumors that otherwise do not respond to anti-PD-1 alone. Unlike CD28 superagonists, which broadly activate T cells and induce cytokine storm, TSAxCD28 bispecifics display little or no toxicity when used alone or in combination with a PD-1 blocker in genetically humanized immunocompetent mouse models or in primates and thus may provide a well-tolerated and "off the shelf" combination approach with PD-1 immunotherapy that can markedly enhance antitumor efficacy.

TNF receptor agonists induce distinct receptor clusters to mediate differential agonistic activity

Monoclonal antibodies (mAb) and natural ligands targeting costimulatory tumor necrosis factor receptors (TNFR) exhibit a wide range of agonistic activities and antitumor responses. The mechanisms underlying these differential agonistic activities remain poorly understood. Here, we employ a panel of experimental and clinically-relevant molecules targeting human CD40, 4-1BB and OX40 to examine this issue. Confocal and STORM microscopy reveal that strongly agonistic reagents induce clusters characterized by small area and high receptor density. Using antibody pairs differing only in isotype we show that hIgG2 confers significantly more receptor clustering than hIgG1 across all three receptors, explaining its greater agonistic activity, with receptor clustering shielding the receptor-agonist complex from further molecular access. Nevertheless, discrete receptor clustering patterns are observed with different hIgG2 mAb, with a unique rod-shaped assembly observed with the most agonistic mAb. These findings dispel the notion that larger receptor clusters elicit greater agonism, and instead point to receptor density and subsequent super-structure as key determinants.

Nanotechnology synergized immunoengineering for cancer

Novel strategies modulating the immune system yielded enhanced anticancer responses and improved cancer survival. Nevertheless, the success rate of immunotherapy in cancer treatment has been below expectation(s) due to unpredictable efficacy and off-target effects from systemic dosing of immunotherapeutic(s). As a result, there is an unmet clinical need for improving conventional immunotherapy. Nanotechnology offers several new strategies, multimodality, and multiplex biological targeting advantage to overcome many of these challenges. These efforts enable programming the pharmacodynamics, pharmacokinetics, and delivery of immunomodulatory agents/co-delivery of compounds to prime at the tumor sites for improved therapeutic benefits. This review provides an overview of the design and clinical principles of biomaterials driven nanotechnology and their potential use in personalized nanomedicines, vaccines, localized tumor modulation, and delivery strategies for cancer immunotherapy. In this review, we also summarize the latest highlights and recent advances in combinatorial therapies availed in the treatment of cold and complicated tumors. It also presents key steps and parameters implemented for clinical success. Finally, we analyse, discuss, and provide clinical perspectives on the integrated opportunities of nanotechnology and immunology to achieve synergistic and durable responses in cancer treatment.

Targeting Solid Tumors Using CD3 Bispecific Antibodies

Immunotherapies to treat cancer have made tremendous progress over the past decade. In particular, T cell-directed therapies have gained considerable attention with CD3 bispecific antibodies and CAR T cells showing potent responses against hematologic tumors. At present, the ability to adapt these therapeutics to treat solid tumors is less established. Herein, we discuss recent advances in T cell-engaging CD3 bispecific antibodies targeting solid tumors, potential mechanisms of resistance, and future prospects. A better understanding of the mechanisms of immune evasion in solid tumors will enable the development of strategies to overcome this resistance and inform choices of therapeutic combinations.

Engineered red blood cells as an off-the-shelf allogeneic anti-tumor therapeutic

Checkpoint inhibitors and T-cell therapies have highlighted the critical role of T cells in anti-cancer immunity. However, limitations associated with these treatments drive the need for alternative approaches. Here, we engineer red blood cells into artificial antigen-presenting cells (aAPCs) presenting a peptide bound to the major histocompatibility complex I, the costimulatory ligand 4-1BBL, and interleukin (IL)-12. This leads to robust, antigen-specific T-cell expansion, memory formation, additional immune activation, tumor control, and antigen spreading in tumor models in vivo. The presence of 4-1BBL and IL-12 induces minimal toxicities due to restriction to the vasculature and spleen. The allogeneic aAPC, RTX-321, comprised of human leukocyte antigen-A*02:01 presenting the human papilloma virus (HPV) peptide HPV16 E7_11-19, 4-1BBL, and IL-12 on the surface, activates HPV-specific T cells and promotes effector function in vitro. Thus, RTX-321 is a potential 'off-the-shelf' in vivo cellular immunotherapy for treating HPV + cancers, including cervical and head/neck cancers.

CD137 as an Attractive T Cell Co-Stimulatory Target in the TNFRSF for Immuno-Oncology Drug Development

Immune checkpoint inhibitors have altered the treatment landscape significantly in several cancers, yet not enough for many cancer patients. T cell costimulatory receptors have been pursued as targets for the next generation of cancer immunotherapies, however, sufficient clinical efficacy has not yet been achieved. CD137 (TNFRSF9, 4-1BB) provides co-stimulatory signals and activates cytotoxic effects of CD8+ T cells and helps to form memory T cells. In addition, CD137 signalling can activate NK cells and dendritic cells which further supports cytotoxic T cell activation. An agonistic monoclonal antibody to CD137, urelumab, provided promising clinical efficacy signals but the responses were achieved above the maximum tolerated dose. Utomilumab is another CD137 monoclonal antibody to CD137 but is not as potent as urelumab. Recent advances in antibody engineering technologies have enabled mitigation of the hepato-toxicity that hampered clinical application of urelumab and have enabled to maintain similar potency to urelumab. Next generation CD137 targeting molecules currently in clinical trials support T cell and NK cell expansion in patient samples. CD137 targeting molecules in combination with checkpoint inhibitors or ADCC-enhancing monoclonal antibodies have been sought to improve both clinical safety and efficacy. Further investigation on patient samples will be required to provide insights to understand compensating pathways for future combination strategies involving CD137 targeting agents to optimize and maintain the T cell activation status in tumors.

Looking into a Better Future: Novel Therapies for Metastatic Melanoma

Even though melanoma represents a small percentage of all cutaneous cancers, it is responsible for most deaths from skin neoplasms. In early stages it can be successfully treated with surgery, but as the disease expands the survival rate drops significantly. For many years the mainstay of treatment for metastatic melanoma was chemotherapeutic agents, even though they failed to prove survival prolongation. After the advent of ipilimumab, a survival benefit and better overall response rate could be offered to the patients. Other new therapies, such as immunotherapies, targeted therapies, vaccines, and small molecules, are currently being studied. Also, combination regimens have demonstrated superiority to some monotherapies. Nowadays, ipilimumab should no longer be considered the first-line therapy given its severe toxicity and lower efficacy, while nivolumab remains efficacious and has a good safety profile. T-VEC as monotherapy has been shown to be an elegant alternative even for the elderly or cases of head and neck melanomas. If the BRAF mutation status is positive, the combination of dabrafenib and trametinib could be an option to consider. Despite the success of the novel treatments, their effectiveness is still limited. New studies have opened up new avenues for future research in melanoma treatment, which is expected to lead to better therapeutic outcomes for our patients. The objective of this review is to discuss the novel therapies for metastatic melanoma that have been tested in humans during the last 3 years to obtain a sharper perspective of the available treatment options for specific patient characteristics.

Beyond Antibodies: The DARPin® Drug Platform

The DARPin^® drug platform was established with a vision to expand the medical use of biologics beyond what was possible with monoclonal antibodies. It is based on naturally occurring ankyrin repeat domains that are typically building blocks of multifunctional human proteins. The platform allows for the generation of diverse, well-behaved, multifunctional drug candidates. Recent clinical data illustrate the favorable safety profile of the first DARPin^® molecules tested in patients. With the positive phase III results of the most advanced DARPin^® drug candidate, abicipar, the DARPin^® drug platform is potentially about to achieve its first marketing approval. This review highlights some of the key milestones and decisions encountered when transforming the DARPin^® platform from an academic concept to a biotech drug pipeline engine.

Characterization of 7A5: A Human CD137 (4-1BB) Receptor Binding Monoclonal Antibody with Differential Agonist Properties That Promotes Antitumor Immunity

The CD137 receptor plays a key role in mediating immune response by promoting T cell proliferation, survival, and memory. Effective agonism of CD137 has the potential to reinvigorate potent antitumor immunity either alone or in combination with other immune-checkpoint therapies. In this study, we describe the discovery and characterization of a unique CD137 agonist, 7A5, a fully human IgG1 Fc effector-null monoclonal antibody. The biological properties of 7A5 were investigated through in vitro and in vivo studies. 7A5 binds CD137, and the binding epitope overlaps with the CD137L binding site based on structure. 7A5 engages CD137 receptor and activates NF-κB cell signaling independent of cross-linking or Fc effector function. In addition, T cell activation measured by cytokine IFNγ production is induced by 7A5 in peripheral blood mononuclear cell costimulation assay. Human tumor xenograft mouse models reconstituted with human immune cells were used to determine antitumor activity in vivo. Monotherapy with 7A5 inhibits tumor growth, and this activity is enhanced in combination with a PD-L1 antagonist antibody. Furthermore, the intratumoral immune gene expression signature in response to 7A5 is highly suggestive of enhanced T cell infiltration and activation. Taken together, these results demonstrate 7A5 is a differentiated CD137 agonist antibody with biological properties that warrant its further development as a cancer immunotherapy. GRAPHICAL ABSTRACT: http://mct.aacrjournals.org/content/molcanther/19/4/988/F1.large.jpg.

Development of Immunotherapy Combination Strategies in Cancer

Harnessing the immune system to treat cancer through inhibitors of CTLA4 and PD-L1 has revolutionized the landscape of cancer. Rational combination strategies aim to enhance the antitumor effects of immunotherapies, but require a deep understanding of the mechanistic underpinnings of the immune system and robust preclinical and clinical drug development strategies. We review the current approved immunotherapy combinations, before discussing promising combinatorial approaches in clinical trials and detailing innovative preclinical model systems being used to develop rational combinations. We also discuss the promise of high-order immunotherapy combinations, as well as novel biomarker and combinatorial trial strategies. SIGNIFICANCE: Although immune-checkpoint inhibitors are approved as dual checkpoint strategies, and in combination with cytotoxic chemotherapy and angiogenesis inhibitors for multiple cancers, patient benefit remains limited. Innovative approaches are required to guide the development of novel immunotherapy combinations, ranging from improvements in preclinical tumor model systems to biomarker-driven trial strategies.

An Fc-free EGFR-specific 4-1BB-agonistic Trimerbody Displays Broad Antitumor Activity in Humanized Murine Cancer Models without Toxicity

PURPOSE

The induction of 4-1BB signaling by agonistic antibodies can drive the activation and proliferation of effector T cells and thereby enhance a T-cell-mediated antitumor response. Systemic administration of anti-4-1BB-agonistic IgGs, although effective preclinically, has not advanced in clinical development due to their severe hepatotoxicity.

EXPERIMENTAL DESIGN

Here, we generated a humanized EGFR-specific 4-1BB-agonistic trimerbody, which replaces the IgG Fc region with a human collagen homotrimerization domain. It was characterized by structural analysis and in vitro functional studies. We also assessed pharmacokinetics, antitumor efficacy, and toxicity in vivo.

RESULTS

In the presence of a T-cell receptor signal, the trimerbody provided potent T-cell costimulation that was strictly dependent on 4-1BB hyperclustering at the point of contact with a tumor antigen-displaying cell surface. It exhibits significant antitumor activity in vivo, without hepatotoxicity, in a wide range of human tumors including colorectal and breast cancer cell-derived xenografts, and non-small cell lung cancer patient-derived xenografts associated with increased tumor-infiltrating CD8⁺ T cells. The combination of the trimerbody with a PD-L1 blocker led to increased IFNγ secretion in vitro and resulted in tumor regression in humanized mice bearing aggressive triple-negative breast cancer.

CONCLUSIONS

These results demonstrate the nontoxic broad antitumor activity of humanized Fc-free tumor-specific 4-1BB-agonistic trimerbodies and their synergy with checkpoint blockers, which may provide a way to elicit responses in most patients with cancer while avoiding Fc-mediated adverse reactions.

Engaging the Innate and Adaptive Antitumor Immune Response in Lymphoma

Immunotherapy has emerged as a powerful therapeutic strategy for many malignancies, including lymphoma. As in solid tumors, early clinical trials have revealed that immunotherapy is not equally efficacious across all lymphoma subtypes. For example, immune checkpoint inhibition has a higher overall response rate and leads to more durable outcomes in Hodgkin lymphomas compared to non-Hodgkin lymphomas. These observations, combined with a growing understanding of tumor biology, have implicated the tumor microenvironment as a major determinant of treatment response and prognosis. Interactions between lymphoma cells and their microenvironment facilitate several mechanisms that impair the antitumor immune response, including loss of major histocompatibility complexes, expression of immunosuppressive ligands, secretion of immunosuppressive cytokines, and the recruitment, expansion, and skewing of suppressive cell populations. Accordingly, treatments to overcome these barriers are being rapidly developed and translated into clinical trials. This review will discuss the mechanisms of immune evasion, current avenues for optimizing the antitumor immune response, clinical successes and failures of lymphoma immunotherapy, and outstanding hurdles that remain to be addressed.

Intratumoral virotherapy with 4-1BBL armed modified vaccinia Ankara eradicates solid tumors and promotes protective immune memory

Background Human cancers are extraordinarily heterogeneous in terms of tumor antigen expression, immune infiltration and composition. A common feature, however, is the host′s inability to mount potent immune responses that prevent tumor growth effectively. Often, naturally primed CD8⁺ T cells against solid tumors lack adequate stimulation and efficient tumor tissue penetration due to an immune hostile tumor microenvironment.

Methods To address these shortcomings, we cloned tumor-associated antigens (TAA) and the immune-stimulatory ligand 4-1BBL into the genome of modified vaccinia Ankara (MVA) for intratumoral virotherapy.

Results Local treatment with MVA-TAA-4-1BBL resulted in control of established tumors. Intratumoral injection of MVA localized mainly to the tumor with minimal leakage to the tumor-draining lymph node. In situ infection by MVA-TAA-4-1BBL triggered profound changes in the tumor microenvironment, including the induction of multiple proinflammatory molecules and immunogenic cell death. These changes led to the reactivation and expansion of antigen-experienced, tumor-specific cytotoxic CD8⁺ T cells that were essential for the therapeutic antitumor effect. Strikingly, we report the induction of a systemic antitumor immune response including tumor antigen spread by local MVA-TAA-4-1BBL treatment which controlled tumor growth at distant, untreated lesions and protected against local and systemic tumor rechallenge. In all cases, 4-1BBL adjuvanted MVA was superior to MVA.

Conclusion Intratumoral 4-1BBL-armed MVA immunotherapy induced a profound reactivation and expansion of potent tumor-specific CD8⁺ T cells as well as favorable proinflammatory changes in the tumor microenvironment, leading to elimination of tumors and protective immunological memory.

Update of early phase clinical trials in cancer immunotherapy

Immunotherapy has revolutionized the landscape of cancer treatment and become a standard pillar of the treatment. The two main drivers, immune checkpoint inhibitors and chimeric antigen receptor T cells, contributed to this unprecedented success. However, despite the striking clinical improvements, most patients still suffer from disease progression because of the evolution of primary or acquired resistance. This mini-review summa-rizes new treatment options including novel targets and interesting combinational approaches to increase our understanding of the mechanisms of the action of and resistance to immunotherapy, to expand our knowledge of advances in biomarker and therapeutics development, and to help to find the most appropriate option or a way of overcoming the resistance for cancer patients.

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.

Anticancer immunity induced by a synthetic tumor-targeted CD137 agonist

Background

In contrast to immune checkpoint inhibitors, the use of antibodies as agonists of immune costimulatory receptors as cancer therapeutics has largely failed. We sought to address this problem using a new class of modular synthetic drugs, termed tumor-targeted immune cell agonists (TICAs), based on constrained bicyclic peptides (Bicycles).

Methods

Phage libraries displaying Bicycles were panned for binders against tumor necrosis factor (TNF) superfamily receptors CD137 and OX40, and tumor antigens EphA2, Nectin-4 and programmed death ligand 1. The CD137 and OX40 Bicycles were chemically conjugated to tumor antigen Bicycles with different linkers and stoichiometric ratios of binders to obtain a library of low molecular weight TICAs (MW <8 kDa). The TICAs were evaluated in a suite of in vitro and in vivo assays to characterize their pharmacology and mechanism of action.

Results

Linking Bicycles against costimulatory receptors (e.g., CD137) to Bicycles against tumor antigens (e.g., EphA2) created potent agonists that activated the receptors selectively in the presence of tumor cells expressing these antigens. An EphA2/CD137 TICA (BCY12491) efficiently costimulated human peripheral blood mononuclear cells in vitro in the presence of EphA2 expressing tumor cell lines as measured by the increased secretion of interferon γ and interleukin-2. Treatment of C57/Bl6 mice transgenic for the human CD137 extracellular domain (huCD137) bearing EphA2-expressing MC38 tumors with BCY12491 resulted in the infiltration of CD8+ T cells, elimination of tumors and generation of immunological memory. BCY12491 was cleared quickly from the circulation (plasma t_1/2 in mice of 1–2 hr), yet intermittent dosing proved effective.

Conclusion

Tumor target-dependent CD137 agonism using a novel chemical approach (TICAs) afforded elimination of tumors with only intermittent dosing suggesting potential for a wide therapeutic index in humans. This work unlocks a new path to effective cancer immunotherapy via agonism of TNF superfamily receptors.

Case Report: An EGFR-Targeted 4-1BB-agonistic Trimerbody Does Not Induce Hepatotoxicity in Transgenic Mice With Liver Expression of Human EGFR

Agonistic monoclonal antibodies (mAbs) targeting the co-stimulatory receptor 4-1BB are among the most effective immunotherapeutic agents across pre-clinical cancer models. However, clinical development of full-length 4-1BB agonistic mAbs, has been hampered by dose-limiting liver toxicity. We have previously developed an EGFR-targeted 4-1BB-agonistic trimerbody (1D8^N/CEGa1) that induces potent anti-tumor immunity without systemic toxicity, in immunocompetent mice bearing murine colorectal carcinoma cells expressing human EGFR. Here, we study the impact of human EGFR expression on mouse liver in the toxicity profile of 1D8^N/CEGa1. Systemic administration of IgG-based anti-4-1BB agonist resulted in nonspecific immune stimulation and hepatotoxicity in a liver-specific human EGFR-transgenic immunocompetent mouse, whereas in 1D8^N/CEGa1-treated mice no such immune-related adverse effects were observed. Collectively, these data support the role of FcγR interactions in the major off-tumor toxicities associated with IgG-based 4-1BB agonists and further validate the safety profile of EGFR-targeted Fc-less 4-1BB-agonistic trimerbodies in systemic cancer immunotherapy protocols.

B7-H3×4-1BB bispecific antibody augments antitumor immunity by enhancing terminally differentiated CD8+ tumor-infiltrating lymphocytes

Cancer immunotherapy with 4-1BB agonists has limited further clinical development because of dose-limiting toxicity. Here, we developed a bispecific antibody (bsAb; B7-H3×4-1BB), targeting human B7-H3 (hB7-H3) and mouse or human 4-1BB, to restrict the 4-1BB stimulation in tumors. B7-H3×m4-1BB elicited a 4-1BB-dependent antitumor response in hB7-H3-overexpressing tumor models without systemic toxicity. BsAb primarily targets CD8 T cells in the tumor and increases their proliferation and cytokine production. Among the CD8 T cell population in the tumor, 4-1BB is solely expressed on PD-1⁺Tim-3⁺ "terminally differentiated" subset, and bsAb potentiates these cells for eliminating the tumor. Furthermore, the combination of bsAb and PD-1 blockade synergistically inhibits tumor growth accompanied by further increasing terminally differentiated CD8 T cells. B7-H3×h4-1BB also shows antitumor activity in h4-1BB-expressing mice. Our data suggest that B7-H3×4-1BB is an effective and safe therapeutic agent against B7-H3-positive cancers as monotherapy and combination therapy with PD-1 blockade.

Antibody to CD137 Activated by Extracellular Adenosine Triphosphate Is Tumor Selective and Broadly Effective In Vivo without Systemic Immune Activation

Agonistic antibodies targeting CD137 have been clinically unsuccessful due to systemic toxicity. Because conferring tumor selectivity through tumor-associated antigen limits its clinical use to cancers that highly express such antigens, we exploited extracellular adenosine triphosphate (exATP), which is a hallmark of the tumor microenvironment and highly elevated in solid tumors, as a broadly tumor-selective switch. We generated a novel anti-CD137 switch antibody, STA551, which exerts agonistic activity only in the presence of exATP. STA551 demonstrated potent and broad antitumor efficacy against all mouse and human tumors tested and a wide therapeutic window without systemic immune activation in mice. STA551 was well tolerated even at 150 mg/kg/week in cynomolgus monkeys. These results provide a strong rationale for the clinical testing of STA551 against a broad variety of cancers regardless of antigen expression, and for the further application of this novel platform to other targets in cancer therapy. SIGNIFICANCE: Reported CD137 agonists suffer from either systemic toxicity or limited efficacy against antigen-specific cancers. STA551, an antibody designed to agonize CD137 only in the presence of extracellular ATP, inhibited tumor growth in a broad variety of cancer models without any systemic toxicity or dependence on antigen expression.See related commentary by Keenan and Fong, p. 20.This article is highlighted in the In This Issue feature, p. 1.