Characterization of MK-4166, a Clinical Agonistic Antibody That Targets Human GITR and Inhibits the Generation and Suppressive Effects of T Regulatory Cells

GITR activation ex vivo impairs CD8 T cell function in people with HIV on antiretroviral therapy

Glucocorticoid-induced tumor necrosis factor related protein (GITR) is a co-stimulatory immune checkpoint molecule constitutively expressed on regulatory T cells (Tregs) and on activated T conventional cells (Tconv). In blood collected from PWH on suppressive ART, GITR expression was reduced in multiple activated CD4 and CD8 T cell subsets but was increased in Tregs. HIV specific CD8 T cells expressed higher levels of GITR and programmed cell death protein 1 (PD-1) compared to total CD8 T cells. Following stimulation with HIV peptides and GITR-ligand (L), we demonstrated a significant decrease in killing by HIV specific CD8 T cells and an increased exhausted profile. T cell receptor co-stimulation with GITR-L abrogated Treg suppression and induced expansion of CD4 Tconv. We conclude that GITR activation is an additional factor contributing to an impaired HIV immune response in PWH on ART and that GITR agonist antibodies should not be pursued for HIV cure strategies.

DNA damage repair profiling of esophageal squamous cell carcinoma uncovers clinically relevant molecular subtypes with distinct prognoses and therapeutic vulnerabilities

BACKGROUND

DNA damage repair (DDR) is a critical process that maintains genomic integrity and plays essential roles at both the cellular and organismic levels. Here, we aimed to characterize the DDR profiling of esophageal squamous cell carcinoma (ESCC), investigate the prognostic value of DDR-related features, and explore their potential for guiding personalized treatment strategies.

METHODS

We analyzed bulk and single-cell transcriptomics data from 377 ESCC cases from our institution and other publicly available cohorts to identify major DDR subtypes. The heterogeneity in cellular and functional properties, tumor microenvironment (TME) characteristics, and prognostic significance of these DDR subtypes were investigated using immunogenomic analysis and in vitro experiments. Additionally, we experimentally validated a combinatorial immunotherapy strategy using syngeneic mouse models of ESCC.

FINDINGS

DDR alteration profiling enabled us to identify two distinct DDR subtypes, DDRactive and DDRsilent, which exhibited independent prognostic values in locoregional ESCC but not in metastatic ESCC. The DDRsilent subtype was characterized by an inflamed but immune-suppressed microenvironment with relatively high immune cell infiltration, abnormal immune checkpoint expression, T-cell exhaustion, and enrichment of cancer-related pathways. Moreover, DDR subtyping indicates that BRCA1 and HFM1 are robust and independent prognostic factors in locoregional ESCC. Finally, we proposed and verified that the concomitant triggering of GITR or blockade of BTLA with PD-1 blockade or cisplatin chemotherapy represents effective combination strategies for high-risk locoregional ESCC tumors.

INTERPRETATION

Our discovery of DDR-based molecular subtypes will enhance our understanding of tumor heterogeneity and have significant clinical implications for the therapeutic and management strategies of locoregional ESCC.

FUNDING

This study was supported by the National Key R&D Program of China (2021YFC2501000, 2022YFC3401003), National Natural Science Foundation of China (82172882), the Beijing Natural Science Foundation (7212085), the CAMS Innovation Fund for Medical Sciences (2021-I2M-1-018, 2021-I2M-1-067), the Fundamental Research Funds for the Central Universities (3332021091), and the Non-profit Central Research Institute Fund of Chinese Academy of Medical Sciences (2019PT310027).

Integrated BATF transcriptional network regulates suppressive intratumoral regulatory T cells

Human regulatory T cells (Tregs) are crucial regulators of tissue repair, autoimmune diseases, and cancer. However, it is challenging to inhibit the suppressive function of Tregs for cancer therapy without affecting immune homeostasis. Identifying pathways that may distinguish tumor-restricted Tregs is important, yet the transcriptional programs that control intratumoral Treg gene expression, and that are distinct from Tregs in healthy tissues, remain largely unknown. We profiled single-cell transcriptomes of CD4+ T cells in tumors and peripheral blood from patients with head and neck squamous cell carcinomas (HNSCC) and those in nontumor tonsil tissues and peripheral blood from healthy donors. We identified a subpopulation of activated Tregs expressing multiple tumor necrosis factor receptor (TNFR) genes (TNFR+ Tregs) that is highly enriched in the tumor microenvironment (TME) compared with nontumor tissue and the periphery. TNFR+ Tregs are associated with worse prognosis in HNSCC and across multiple solid tumor types. Mechanistically, the transcription factor BATF is a central component of a gene regulatory network that governs key aspects of TNFR+ Tregs. CRISPR-Cas9-mediated BATF knockout in human activated Tregs in conjunction with bulk RNA sequencing, immunophenotyping, and in vitro functional assays corroborated the central role of BATF in limiting excessive activation and promoting the survival of human activated Tregs. Last, we identified a suite of surface molecules reflective of the BATF-driven transcriptional network on intratumoral Tregs in patients with HNSCC. These findings uncover a primary transcriptional regulator of highly suppressive intratumoral Tregs, highlighting potential opportunities for therapeutic intervention in cancer without affecting immune homeostasis.

FcγR requirements and costimulatory capacity of Urelumab, Utomilumab, and Varlilumab

Introduction

Targeting costimulatory receptors of the tumor necrosis factor receptor (TNFR) superfamily with agonistic antibodies is a promising approach in cancer immuno therapy. It is known that their efficacy strongly depends on FcγR cross-linking.

Methods

In this study, we made use of a Jurkat-based reporter platform to analyze the influence of individual FcγRs on the costimulatory activity of the 41BB agonists, Urelumab and Utomilumab, and the CD27 agonist, Varlilumab.

Results

We found that Urelumab (IgG4) can activate 41BB-NFκB signaling without FcγR cross-linking, but the presence of the FcγRs (CD32A, CD32B, CD64) augments the agonistic activity of Urelumab. The human IgG2 antibody Utomilumab exerts agonistic function only when crosslinked via CD32A and CD32B. The human IgG1 antibody Varlilumab showed strong agonistic activity with all FcγRs tested. In addition, we analyzed the costimulatory effects of Urelumab, Utomilumab, and Varlilumab in primary human peripheral blood mononuclear cells (PBMCs). Interestingly, we observed a very weak capacity of Varlilumab to enhance cytokine production and proliferation of CD4 and CD8 T cells. In the presence of Varlilumab the percentage of annexin V positive T cells was increased, indicating that this antibody mediated FcγR-dependent cytotoxic effects.

Conclusion

Collectively, our data underscore the importance to perform studies in reductionist systems as well as in primary PBMC samples to get a comprehensive understanding of the activity of costimulation agonists.

Epitope mapping of monoclonal antibodies: a comprehensive comparison of different technologies

Monoclonal antibodies have become an important class of therapeutics in the last 30 years. Because the mechanism of action of therapeutic antibodies is intimately linked to their binding epitopes, identification of the epitope of an antibody to the antigen plays a central role during antibody drug development. The gold standard of epitope mapping, X-ray crystallography, requires a high degree of proficiency with no guarantee of success. Here, we evaluated six widely used alternative methods for epitope identification (peptide array, alanine scan, domain exchange, hydrogen-deuterium exchange, chemical cross-linking, and hydroxyl radical footprinting) in five antibody-antigen combinations (pembrolizumab+PD1, nivolumab+PD1, ipilimumab+CTLA4, tremelimumab+CTLA4, and MK-5890+CD27). The advantages and disadvantages of each technique are demonstrated by our data and practical advice on when and how to apply specific epitope mapping techniques during the drug development process is provided. Our results suggest chemical cross-linking most accurately identifies the epitope as defined by crystallography.

Therapeutic targeting of regulatory T cells in cancer

The success of immunotherapy in oncology underscores the vital role of the immune system in cancer development. Regulatory T cells (Tregs) maintain a fine balance between autoimmunity and immune suppression. They have multiple roles in the tumor microenvironment (TME) but act particularly in suppressing T cell activation. This review focuses on the detrimental and sometimes beneficial roles of Tregs in tumors, our current understanding of recruitment and stabilization of Tregs within the TME, and current Treg-targeted therapeutics. Research identifying subpopulations of Tregs and their respective functions and interactions within the complex networks of the TME will be crucial to develop the next generation of immunotherapies. Through these advances, Treg-targeted immunotherapy could have important implications for the future of oncology.

Preclinical characterization and clinical translation of pharmacodynamic markers for MK-5890: a human CD27 activating antibody for cancer immunotherapy

Background

Immune checkpoint inhibitors (ICI) have radically changed cancer therapy, but most patients with cancer are unresponsive or relapse after treatment. MK-5890 is a CD27 agonist antibody intended to complement ICI therapy. CD27 is a member of the tumor necrosis factor receptor superfamily that plays a critical role in promoting responses of T cells, B cells and NK cells.

Methods

Anti-CD27 antibodies were generated and selected for agonist activity using NF-кB luciferase reporter assays. Antibodies were humanized and characterized for agonism using in vitro T-cell proliferation assays. The epitope recognized on CD27 by MK-5890 was established by X-ray crystallography. Anti-tumor activity was evaluated in a human CD27 knock-in mouse. Preclinical safety was tested in rhesus monkeys. Pharmacodynamic properties were examined in mouse, rhesus monkeys and a phase 1 dose escalation clinical study in patients with cancer.

Results

Humanized anti-CD27 antibody MK-5890 (hIgG1) was shown to bind human CD27 on the cell surface with sub-nanomolar potency and to partially block binding to its ligand, CD70. Crystallization studies revealed that MK-5890 binds to a unique epitope in the cysteine-rich domain 1 (CRD1). MK-5890 activated CD27 expressed on 293T NF-κB luciferase reporter cells and, conditional on CD3 stimulation, in purified CD8+ T cells without the requirement of crosslinking. Functional Fc-receptor interaction was required to activate CD8+ T cells in an ex vivo tumor explant system and to induce antitumor efficacy in syngeneic murine subcutaneous tumor models. MK-5890 had monotherapy efficacy in these models and enhanced efficacy of PD-1 blockade. MK-5890 reduced in an isotype-dependent and dose-dependent manner circulating, but not tumor-infiltrating T-cell numbers in these mouse models. In rhesus monkey and human patients, reduction in circulating T cells was transient and less pronounced than in mouse. MK-5890 induced transient elevation of chemokines MCP-1, MIP-1α, and MIP-1β in the serum of mice, rhesus monkeys and patients with cancer. MK-5890 was well tolerated in rhesus monkeys and systemic exposure to MK-5890 was associated with CD27 occupancy at all doses.

Conclusions

MK-5890 is a novel CD27 agonistic antibody with the potential to complement the activity of PD-1 checkpoint inhibition in cancer immunotherapy and is currently undergoing clinical evaluation.

Combinations of anti-GITR antibody and CD28 superagonist induce permanent allograft acceptance by generating type 1 regulatory T cells

Type 1 regulatory T (Tr1) cells represent a subset of IL-10-producing CD4⁺Foxp3^- T cells and play key roles in promoting transplant tolerance. However, no effective pharmacological approaches have been able to induce Tr1 cells in vivo. We herein report the combined use of a CD28 superagonist (D665) and anti-glucocorticoid-induced tumor necrosis factor receptor-related protein monoclonal antibody (G3c) to induce Tr1 cells in vivo. Large amounts of IL-10/interferon-γ-co-producing CD4⁺Foxp3^- Tr1 cells were generated by D665-G3c sequential treatment in mice. Mechanistic studies suggested that D665-G3c induced Tr1 cells via transcription factors Prdm1 and Maf. G3c contributed to Tr1 cell generation via the activation of mitogen-activated protein kinase-signal transducer and activator of transcription 3 signaling. Tr1 cells suppressed dendritic cell maturation and T cell responses and mediated permanent allograft acceptance in fully major histocompatibility complex-mismatched mice in an IL-10-dependent manner. In vivo Tr1 cell induction is a promising strategy for achieving transplant tolerance.

Implications of regulatory T cells in anti-cancer immunity: from pathogenesis to therapeutics

Regulatory T cells (Tregs) play an essential role in maintaining immune tolerance and suppressing inflammation. However, Tregs present major hurdle in eliciting potent anti-cancer immune responses. Therefore, curbing the activity of Tregs represents a novel and efficient way towards successful immunotherapy of cancer. Moreover, there is an emerging interest in harnessing Treg-based strategies for augmenting anti-cancer immunity in different types of the disease. This review summarises the crucial mechanisms of Tregs’ mediated suppression of anti-cancer immunity and strategies to suppress or to alter such Tregs to improve the immune response against tumors. Highlighting important clinical studies, the review also describes current Treg-based therapeutic interventions in cancer, and discusses Treg-suppression by molecular targeting, which may emerge as an effective cancer immunotherapy and as an alternative to detrimental chemotherapeutic agents.

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Tregs are crucial in maintaining immune tolerance and suppressing inflammation.

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Tregs present a major obstacle to eliciting potent anti-tumor immune responses.

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The review summarizes current Treg-based therapeutic interventions in cancer.

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Treg can be an effective cancer immunotherapy target.

GITR antibodies in cancer: not ready for prime time

GITR agonistic antibodies are expected to increase the antitumor response mainly by reducing the effect of Foxp3+ T regulatory cells. TRX-518 is a novel GITR agonist that has shown good pharmacodynamic activity by depleting T regs in preclinical models, with limited clinical activity demonstrated in patients with advanced solid tumors.

Optimal target saturation of ligand-blocking anti-GITR antibody IBI37G5 dictates FcγR-independent GITR agonism and antitumor activity

Glucocorticoid-induced tumor necrosis factor receptor (GITR) is a co-stimulatory receptor and an important target for cancer immunotherapy. We herein present a potent FcγR-independent GITR agonist IBI37G5 that can effectively activate effector T cells and synergize with anti-programmed death 1 (PD1) antibody to eradicate established tumors. IBI37G5 depends on both antibody bivalency and GITR homo-dimerization for efficient receptor cross-linking. Functional analyses reveal bell-shaped dose responses due to the unique 2:2 antibody-receptor stoichiometry required for GITR activation. Antibody self-competition is observed after concentration exceeded that of 100% receptor occupancy (RO), which leads to antibody monovalent binding and loss of activity. Retrospective pharmacokinetics/pharmacodynamics analysis demonstrates that the maximal efficacy is achieved at medium doses with drug exposure near saturating GITR occupancy during the dosing cycle. Finally, we propose an alternative dose-finding strategy that does not rely on the traditional maximal tolerated dose (MTD)-based paradigm but instead on utilizing the RO-function relations as biomarker to guide the clinical translation of GITR and similar co-stimulatory agonists.

Phase IB Study of GITR Agonist Antibody TRX518 Singly and in Combination with Gemcitabine, Pembrolizumab or Nivolumab in Patients with Advanced Solid Tumors

Purpose: TRX518 is a monoclonal antibody engaging the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR). This open-label, phase I study (TRX518-003) evaluated the safety and efficacy of repeated dose TRX518 monotherapy and combination with gemcitabine, pembrolizumab or nivolumab in advanced solid tumors. Experimental Design: TRX518 monotherapy was dose-escalated (Part A) and expanded (Part B) up to 4 mg/kg load, 1 mg/kg Q3W. Parts C-E included dose-escalation (2mg/kg and 4 mg/kg loading followed by 1mg/kg) and dose-expansion (4mg/kg load) phases with gemcitabine (Part C), pembrolizumab (Part D) or nivolumab (Part E). Primary endpoints included incidence of dose-limiting toxicities (DLTs), serious adverse events (SAEs), and pharmacokinetics. Secondary endpoints were efficacy and pharmacodynamics. Results:109 patients received TRX518: 43 (Parts A+B), 30 (Part C), 26 (Part D), and 10 (Part E) respectively. 67% of patients in Parts D+E had received prior anti-PD(L)1 or anti-CTLA-4. No DLTs, treatment-related SAEs and/or G4/5 AEs were observed with TRX518 monotherapy. In Parts C-E, no DLTs were observed, although TRX518-related SAEs were reported in 3.3% (Part C) and 10.0% (Part E) respectively. Objective response rate was 3.2%, 3.8%, 4% and 12.5% in Parts A+B, C, D and E respectively. TRX518 affected peripheral and intratumoral regulatory T cells (Tregs) with different kinetics depending on the combination regimen. Responses with TRX518 monotherapy+anti-PD1 combination were associated with intratumoral Treg reductions and CD8 increases and activation after treatment. Conclusions:TRX518 showed an acceptable safety profile with pharmacodynamic activity. Repeated dose TRX518 monotherapy and in combination resulted in limited clinical responses associated with immune activation.

An anti-PD-1–GITR-L bispecific agonist induces GITR clustering-mediated T cell activation for cancer immunotherapy

Costimulatory receptors such as glucocorticoid-induced tumor necrosis factor receptor–related protein (GITR) play key roles in regulating the effector functions of T cells. In human clinical trials, however, GITR agonist antibodies have shown limited therapeutic effect, which may be due to suboptimal receptor clustering-mediated signaling. To overcome this potential limitation, a rational protein engineering approach is needed to optimize GITR agonist-based immunotherapies. Here we show a bispecific molecule consisting of an anti-PD-1 antibody fused with a multimeric GITR ligand (GITR-L) that induces PD-1-dependent and FcγR-independent GITR clustering, resulting in enhanced activation, proliferation and memory differentiation of primed antigen-specific GITR⁺PD-1⁺ T cells. The anti-PD-1–GITR-L bispecific is a PD-1-directed GITR-L construct that demonstrated dose-dependent, immunologically driven tumor growth inhibition in syngeneic, genetically engineered and xenograft humanized mouse tumor models, with a dose-dependent correlation between target saturation and Ki67 and TIGIT upregulation on memory T cells. Anti-PD-1–GITR-L thus represents a bispecific approach to directing GITR agonism for cancer immunotherapy.

Alvarez and colleagues develop a bispecific anti-PD-1–GITR-L agonist that activates T cells via a mechanism distinct from those found with individual PD-1 and GITR-L agonists and demonstrate its antitumor activity in mice and nonhuman primates.

Emerging Novel Therapeutic Approaches for Treatment of Advanced Cutaneous Melanoma

The prognosis of patients with advanced cutaneous melanoma has radically changed in the past decade. Nevertheless, primary or acquired resistance to systemic treatment occurs in many cases, highlighting the need for novel treatment strategies. This review has the purpose of summarizing the current area of interest for the treatment of metastatic or unresectable advanced cutaneous melanoma, including data from recently completed or ongoing clinical trials. The main fields of investigation include the identification of new immune checkpoint inhibitors (anti-LAG3, GITR agonist and anti-TIGIT), adoptive cell therapy, vaccines, engineered TCR therapy, IL-2 agonists, novel targets for targeted therapy (new MEK or RAF inhibitors, HDAC, IDO, ERK, Axl, ATR and PARP inhibitors), or combination strategies (antiangiogenetic agents plus immune checkpoint inhibitors, intra-tumoral immunotherapy in combination with systemic therapy). In many cases, only preliminary efficacy data from early phase trials are available, which require confirmation in larger patient cohorts. A more in-depth knowledge of the biological effects of the molecules and identifying predictive biomarkers remain crucial for selecting patient populations most likely to benefit from novel emerging treatment strategies.

Enhancing immunotherapy in cancer by targeting emerging immunomodulatory pathways

The discovery and clinical implementation of immune-checkpoint inhibitors (ICIs) targeting CTLA4, PD-1 and PD-L1 has revolutionized the treatment of cancer, as recognized by the 2018 Nobel Prize for Medicine and Physiology. This groundbreaking new approach has improved the outcomes of patients with various forms of advanced-stage cancer; however, the majority of patients receiving these therapies, even in combination, do not derive clinical benefit. Further development of agents targeting additional immune checkpoints, co-stimulatory receptors and/or co-inhibitory receptors that control T cell function is therefore critical. In this Review, we discuss the translational potential and clinical development of agents targeting both co-stimulatory and co-inhibitory T cell receptors. Specifically, we describe their mechanisms of action, and provide an overview of ongoing clinical trials involving novel ICIs including those targeting LAG3, TIM3, TIGIT and BTLA as well as agonists of the co-stimulatory receptors GITR, OX40, 41BB and ICOS. We also discuss several additional approaches, such as harnessing T cell metabolism, in particular via adenosine signalling, inhibition of IDO1, and targeting changes in glucose and fatty acid metabolism. We conclude that further efforts are needed to optimize the timing of combination ICI approaches and, most importantly, to individualize immunotherapy based on both patient-specific and tumour-specific characteristics.

Atypical TNF-TNFR superfamily binding interface in the GITR-GITRL complex for T cell activation

Glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR) is a critical regulatory molecule in modulation of T cell immune responses. Here we report the mouse GITR (mGITR) and mGITR ligand (mGITRL) complex structure and find that the binding interface of mGITR and mGITRL is distinct from the typical tumor necrosis factor superfamily (TNFSF)/TNF receptor superfamily (TNFRSF) members. mGITR binds to its ligand with a single domain, whereas the binding interface on mGITRL is located on the side, which is distal from conserved binding sites of TNFSF molecules. Mutational analysis reveals that the binding interface of GITR/GITRL in humans is conserved with that in the mouse. Substitution of key interacting D93-I94-V95 (DIV) in mGITR with the corresponding K93-F94-S95 (KFS) in human GITR enables cross-recognition with human GITRL and cross-activation of receptor signaling. The findings of this study substantially expand our understanding of the interaction of TNFSF/TNFRSF superfamily molecules and can benefit the future design of biologics by targeting GITR/GITRL.

Multiple mechanisms for TRAF3-mediated regulation of the T cell costimulatory receptor GITR

Tumor necrosis factor receptor (TNFR)-associated factor 3 (TRAF3) plays context-specific roles in multiple receptor-mediated signaling pathways in different cell types. Mice lacking TRAF3 in T cells display defective T-cell-mediated immune responses to immunization and infection and demonstrate defective early signaling via the TCR complex. However, the role of TRAF3 in the function of GITR/TNFRSF18, an important costimulatory member of the TNFR superfamily, is unclear. Here we investigated the impact of T cell TRAF3 status on both GITR expression and activation of specific kinases in the GITR signaling pathway in T cells. Our results indicate that TRAF3 negatively regulates GITR functions in several ways. First, expression of GITR protein was elevated in TRAF3-deficient T cells, resulting from both transcriptional and posttranslational regulation that led to greater GITR transcript levels, as well as enhanced GITR protein stability. TRAF3 associated with T cell GITR in a manner dependent upon GITR ligation. TRAF3 also inhibited several events of the GITR mediated early signaling cascade, in a manner independent of recruitment of phosphatases, a mechanism by which TRAF3 inhibits signaling through several other cytokine receptors. These results add new information to our understanding of GITR signaling and function in T cells, which is relevant to the potential use of GITR to enhance immune therapies.

Mechanisms of regulatory T cell infiltration in tumors: implications for innovative immune precision therapies

With the broad application of cancer immunotherapies such as immune checkpoint inhibitors in multiple cancer types, the immunological landscape in the tumor microenvironment (TME) has become enormously important for determining the optimal cancer treatment. Tumors can be immunologically divided into two categories: inflamed and non-inflamed based on the extent of immune cell infiltration and their activation status. In general, immunotherapies are preferable for the inflamed tumors than for non-inflamed tumors. Regulatory T cells (Tregs), an immunosuppressive subset of CD4⁺ T cells, play an essential role in maintaining self-tolerance and immunological homeostasis. In tumor immunity, Tregs compromise immune surveillance against cancer in healthy individuals and impair the antitumor immune response in tumor-bearing hosts. Tregs, therefore, accelerate immune evasion by tumor cells, leading to tumor development and progression in various types of cancer. Therefore, Tregs are considered to be a crucial therapeutic target for cancer immunotherapy. Abundant Tregs are observed in the TME in many types of cancer, both in inflamed and non-inflamed tumors. Diverse mechanisms of Treg accumulation, activation, and survival in the TME have been uncovered for different tumor types, indicating the importance of understanding the mechanism of Treg infiltration in each patient when selecting the optimal Treg-targeted therapy. Here, we review recent advances in the understanding of mechanisms leading to Treg abundance in the TME to optimize Treg-targeted therapy. Furthermore, in addition to the conventional strategies targeting cell surface molecules predominantly expressed by Tregs, reagents targeting molecules and signaling pathways specifically employed by Tregs for infiltration, activation, and survival in each tumor type are illustrated as novel Treg-targeted therapies. The effectiveness of immune precision therapy depends on conditions in the TME of each cancer patient.

Recruitment and Expansion of Tregs Cells in the Tumor Environment-How to Target Them?

Simple Summary

The immune response against cancer is generated by effector T cells, among them cytotoxic CD8⁺ T cells that destroy cancer cells and helper CD4⁺ T cells that mediate and support the immune response. This antitumor function of T cells is tightly regulated by a particular subset of CD4⁺ T cells, named regulatory T cells (Tregs), through different mechanisms. Even if the complete inhibition of Tregs would be extremely harmful due to their tolerogenic role in impeding autoimmune diseases in the periphery, the targeted blockade of their accumulation at tumor sites or their targeted depletion represent a major therapeutic challenge. This review focuses on the mechanisms favoring Treg recruitment, expansion and stabilization in the tumor microenvironment and the therapeutic strategies developed to block these mechanisms.

Abstract

Regulatory T cells (Tregs) are present in a large majority of solid tumors and are mainly associated with a poor prognosis, as their major function is to inhibit the antitumor immune response contributing to immunosuppression. In this review, we will investigate the mechanisms involved in the recruitment, amplification and stability of Tregs in the tumor microenvironment (TME). We will also review the strategies currently developed to inhibit Tregs’ deleterious impact in the TME by either inhibiting their recruitment, blocking their expansion, favoring their plastic transformation into other CD4⁺ T-cell subsets, blocking their suppressive function or depleting them specifically in the TME to avoid severe deleterious effects associated with Treg neutralization/depletion in the periphery and normal tissues.

Structures of mouse and human GITR-GITRL complexes reveal unique TNF superfamily interactions

Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) and GITR ligand (GITRL) are members of the tumor necrosis superfamily that play a role in immune cell signaling, activation, and survival. GITR is a therapeutic target for directly activating effector CD4 and CD8 T cells, or depleting GITR-expressing regulatory T cells (Tregs), thereby promoting anti-tumor immune responses. GITR activation through its native ligand is important for understanding immune signaling, but GITR structure has not been reported. Here we present structures of human and mouse GITR receptors bound to their cognate ligands. Both species share a receptor–ligand interface and receptor–receptor interface; the unique C-terminal receptor–receptor enables higher order structures on the membrane. Human GITR–GITRL has potential to form a hexameric network of membrane complexes, while murine GITR–GITRL complex forms a linear chain due to dimeric interactions. Mutations at the receptor–receptor interface in human GITR reduce cell signaling with in vitro ligand binding assays and minimize higher order membrane structures when bound by fluorescently labeled ligand in cell imaging experiments.

Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) and GITR ligand (GITRL) regulate immune cell activities, including anti-tumor immune responses. Structures and visualization of human and mouse GITR–GITRL complexes offer insight into the architecture of higher-order membrane assemblies, and their signaling.

GITRL on dendritic cells aggravates house dust mite-induced airway inflammation and airway hyperresponsiveness by modulating CD4+ T cell differentiation

Background

Glucocorticoid-induced tumor necrosis factor receptor family-related protein ligand (GITRL) plays an important role in tumors, autoimmunity and inflammation. However, GITRL is not known to modulate the pathogenesis of allergic asthma. In this study, we investigated whether regulating GITRL expressed on dendritic cells (DCs) can prevent asthma and to elucidate its mechanism of action.

Methods

In vivo, the role of GITRL in modulating house dust mite (HDM)-induced asthma was assessed in adeno-associated virus (AAV)-shGITRL mice. In vitro, the role of GITRL expression by DCs was evaluated in LV-shGITRL bone marrow dendritic cells (BMDCs) under HDM stimulation. And the direct effect of GITRL was observed by stimulating splenocytes with GITRL protein. The effect of regulating GITRL on CD4⁺ T cell differentiation was detected. Further, GITRL mRNA in the peripheral blood of asthmatic children was tested.

Results

GITRL was significantly increased in HDM-challenged mice. In GITRL knockdown mice, allergen-induced airway inflammation, serum total IgE levels and airway hyperresponsiveness (AHR) were reduced. In vitro, GITRL expression on BMDCs was increased after HDM stimulation. Further, knocking down GITRL on DCs partially restored the balance of Th1/Th2 and Th17/Treg cells. Moreover, GITRL stimulation in vitro inhibited Treg cell differentiation and promoted Th2 and Th17 cell differentiation. Similarly, GITRL mRNA expression was increased in the peripheral blood from asthmatic children.

Conclusions

This study identified a novel role for GITRL expressed by DCs as a positive regulator of CD4⁺ T cells responses in asthma, which implicates that GITRL inhibitors may be a potential immunotherapy for asthma.

Phase I Study of MK-4166, an Anti-human Glucocorticoid-Induced TNF Receptor Antibody, Alone or with Pembrolizumab in Advanced Solid Tumors

PURPOSE

In this first-in-human phase I study (NCT02132754), we explored MK-4166 [humanized IgG1 agonist mAb targeting glucocorticoid-induced TNF receptor (GITR)] with and without pembrolizumab in advanced solid tumors.

PATIENTS AND METHODS

MK-4166 was tested alone (0.0015-900 mg i.v. every 3 weeks for four doses) or with pembrolizumab (200 mg i.v. every 3 weeks for ≤35 doses) in patients with metastatic solid tumors (dose escalation/confirmation) and advanced melanoma (expansion). Primary objectives were to evaluate the safety and tolerability and establish the MTD of MK-4166. Exploratory endpoints were objective response rate (ORR) and T cell-inflamed gene expression profile (GEP) analysis using RNA from baseline tumor samples.

RESULTS

A total of 113 patients were enrolled [monotherapy, n = 48; combination therapy, n = 65 (20 in the expansion)]. Forty-six patients (40.7%) had grade ≥3 adverse events, 9 (8.0%) of which were treatment related. No treatment-related deaths were observed. One dose-limiting toxicity event with monotherapy (bladder perforation in patient with neobladder) was considered related to study drug. MTD was not reached. MK-4166 pharmacodynamics showed decreased GITR availability on circulating T cells with increasing doses. One objective response (ORR, 2.2%) was achieved with combination therapy in the dose escalation/confirmation (n = 45). In the expansion, 8 of 13 patients with immune checkpoint inhibitor (ICI)-naïve melanoma achieved a response (ORR, 62%; 95% confidence interval, 32-86; 5 complete responses and 3 partial responses). None of the ICI-pretreated patients (n = 7) responded. High response rates were observed in ICI-naïve patients irrespective of GEP status.

CONCLUSIONS

MK-4166 900 mg i.v. every 3 weeks as monotherapy and with pembrolizumab was tolerable. Responses were observed with combination therapy, mostly in patients with ICI-naïve melanoma.

Experimental Medicine Study to Measure Immune Checkpoint Receptors PD-1 and GITR Turnover Rates In Vivo in Humans

Development of monoclonal antibodies (mAbs) targeting immune-checkpoint receptors (IMRs) for the treatment of cancer is one of the most active areas of investment in the biopharmaceutical industry. A key decision in the clinical development of anti-IMR mAbs is dose selection. Dose selection can be challenging because the traditional oncology paradigm of administering the maximum tolerated dose is not applicable to anti-IMR mAbs. Instead, dose selection should be informed by the pharmacology of immune signaling. Engaging an IMR is a key initial step to triggering pharmacologic effects, and turnover (i.e., the rate of protein synthesis) of the IMR is a key property to determining the dose level needed to engage the IMR. Here, we applied the stable isotope labeling mass spectrometry technique using ¹³ C₆ -leucine to measure the in vivo turnover rates of IMRs in humans. The ¹³ C₆ -leucine was administered to 10 study participants over 15 hours to measure ¹³ C₆ -leucine enrichment kinetics in 2 IMR targets that have been clinically pursued in oncology: GITR and PD-1. We report the first measurements of GITR and PD-1 median half-lives associated with turnover to be 55.6 and ≥ 49.5 hours, respectively. The approach outlined here can be applied to other IMRs and, more generally, to protein targets.

Safety and Clinical Activity of MEDI1873, a Novel GITR Agonist, in Advanced Solid Tumors

PURPOSE

The safety and preliminary efficacy of MEDI1873, an agonistic IgG1 fusion protein targeting glucocorticoid-induced TNF receptor-related protein (GITR), were evaluated in an open-label, first-in-human, phase I, dose escalation study in previously treated patients with advanced solid tumors.

PATIENTS AND METHODS

Two single-patient cohorts at 1.5 and 3 mg i.v. were followed by 3+3 dose escalation in six cohorts at 7.5, 25, 75, 250, 500, and 750 mg, all every 2 weeks, for up to 52 weeks. Primary endpoints were safety and tolerability, dose-limiting toxicities (DLT), and MTD. Secondary endpoints included antitumor activity, pharmacokinetics, immunogenicity, and pharmacodynamics.

RESULTS

Forty patients received MEDI1873. Three experienced DLTs: grade 3 worsening tumor pain (250 mg); grade 3 nausea, vomiting, and headache (500 mg); and grade 3 non-ST segment elevation myocardial infarction (750 mg). An MTD was not reached and treatment was well tolerated up to 500 mg. Most common treatment-related adverse events were headache (25%), infusion-related reaction (17.5%), and decreased appetite (17.5%). MEDI1873 exposure was dose proportional. Antidrug-antibody incidence was low. MEDI1873 increased peripheral CD4⁺ effector memory T-cell proliferation as well as cytokines associated with effector T-cell activation at dose levels ≥75 mg. The best response was stable disease (SD) in 17 patients (42.5%), including 1 unconfirmed partial response. Eight patients (20.0%) had SD ≥24 weeks.

CONCLUSIONS

MEDI1873 showed acceptable safety up to 500 mg i.v. every 2 weeks with pharmacodynamics activity, and prolonged SD in some patients. However, further development is not planned because of lack of demonstrated tumor response.

First-in-human phase 1 study of MK-1248, an anti-glucocorticoid-induced tumor necrosis factor receptor agonist monoclonal antibody, as monotherapy or with pembrolizumab in patients with advanced solid tumors

BACKGROUND

Ligation of glucocorticoid-induced tumor necrosis factor receptor (GITR) decreases regulatory T cell-mediated suppression and enhances T-cell proliferation, effector function, and survival. MK-1248 is a humanized immunoglobulin G4 anti-GITR monoclonal antibody agonist.

METHODS

In patients with advanced solid tumors, MK-1248 (starting dose, 0.12 mg) was tested alone and with pembrolizumab (200 mg) according to a 3 + 3 dose escalation design (ClinicalTrials.gov identifier NCT02553499); both treatments were administered intravenously every 3 weeks for ≤4 and ≤35 cycles, respectively. The safety and tolerability, maximum tolerated dose, and pharmacokinetics/pharmacodynamics were explored.

RESULTS

Twenty patients received MK-1248 monotherapy; 17 received combination therapy. The most frequent tumor types were colorectal cancer (n = 8), melanoma (n = 6), and renal cell carcinoma (n = 4). MK-1248 was generally well tolerated at the maximum tested doses of 170 (monotherapy) and 60 mg (combination). No dose-limiting toxicities (DLTs) or treatment-related deaths occurred. Adverse events (AEs) occurred in 36 of the 37 patients (97%); the most common were vomiting (n = 13 [35%]), anemia (n = 10 [27%]), and decreased appetite (n = 10 [27%]). Grade 3 to 5 AEs occurred in 19 of the 37 patients (51%). Treatment-related AEs occurred in 18 of the 37 patients (49%): 9 of the 20 patients (45%) on monotherapy and 9 of the 17 patients (53%) on combination therapy. Among the 17 patients receiving combination therapy, 1 achieved a complete response and 2 achieved a partial response, for an objective response rate of 18%; no patients achieved an objective response with monotherapy. The disease control rate (stable disease or better) was 15% with monotherapy and 41% with combination therapy.

CONCLUSIONS

MK-1248 was generally well tolerated at doses up to 170 (monotherapy) and 60 mg (combination), with no DLTs or treatment-related deaths. Combination therapy provided limited antitumor responses.

Discovery of New Immune Checkpoints: Family Grows Up

The first generation of immune checkpoint inhibitors (ICIs) including anti-CTLA-4 and anti-PD-1/anti-PD-L1 has achieved profound and great success. Till 2019 Q1, there are nine ICIs landing the oncology market: Ipilimumab (anti-CTLA-4, Bristol-Myers Squibb), Nivolumab (anti-PD-1, Bristol-Myers Squibb), Pembrolizumab (anti-PD-1, Merck), Atezolizumab (anti-PD-L1, Roche/Genentech), Durvalumab (anti-PD-L1, Astra Zeneca), Tremelimumab (anti-CTLA-4, Astra Zeneca), Cemiplimab (anti-PD-1, Sanofi/Regeneron), Toripalimab (anti-PD-1, Junshi), and Sintilimab (anti-PD-1, Innovent), which have covered the majority of hematologic and solid malignancies' indication. Beyond the considerable benefits for the patients, frustrated boundary still exists: limited response rate in monotherapy in late-stage population, poor effectiveness in neoplasms with immune desert and immune excluded types, and immune-related toxicities, some are life-threatened and with higher incidence in I-O combination regiment. Moreover, clinicians observed some cases switching to progression after achieving partial or complete response, indicating treatment failure or drug resistance. So people begin looking for the next generation of immune checkpoint members.

GITR Agonism Triggers Antitumor Immune Responses through IL21-Expressing Follicular Helper T Cells

Although treatment with the glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) agonistic antibody (DTA-1) has shown antitumor activity in various tumor models, the underlying mechanism is not fully understood. Here, we demonstrate that interleukin (IL)-21-producing follicular helper T (Tfh) cells play a crucial role in DTA-1-induced tumor inhibition. The administration of DTA-1 increased IL21 expression by Tfh cells in an antigen-specific manner, and this activation led to enhanced antitumor cytotoxic T lymphocyte (CTL) activity. Mice treated with an antibody that neutralizes the IL21 receptor exhibited decreased antitumor activity when treated with DTA-1. Tumor growth inhibition by DTA-1 was abrogated in Bcl6 ^fl/fl Cd4 ^Cre mice, which are genetically deficient in Tfh cells. IL4 was required for optimal induction of IL21-expressing Tfh cells by GITR costimulation, and c-Maf mediated this pathway. Thus, our findings identify GITR costimulation as an inducer of IL21-expressing Tfh cells and provide a mechanism for the antitumor activity of GITR agonism.

Synergistic combination of oncolytic virotherapy with CAR T-cell therapy

For patients with advanced hematological malignancies the therapeutic landscape has been transformed by the emergence of adoptive cell transfer utilizing autologous chimeric antigen receptor (CAR)-redirected T-cells. However, solid tumors have proved far more resistant to this approach. Here, we summarize the numerous challenges faced by CAR T-cells designed to target solid tumors, highlighting, in particular, issues related to impaired trafficking, expansion, and persistence. In parallel, we draw attention to exciting developments in the burgeoning field of oncolytic virotherapy and posit strategies for the synergistic combination of oncolytic viruses with CAR T-cells to improve outcomes for patients with advanced solid tumors.

Expression of costimulatory and inhibitory receptors in FoxP3+ regulatory T cells within the tumor microenvironment: Implications for combination immunotherapy approaches

The unprecedented success of immune checkpoint inhibitors has given rise to a rapidly growing number of immuno-oncology agents undergoing preclinical and clinical development and an exponential increase in possible combinations. Defining a clear rationale for combinations by identifying synergies between immunomodulatory pathways has therefore become a high priority. Immunosuppressive regulatory T cells (Tregs) within the tumor microenvironment (TME) represent a major roadblock to endogenous and therapeutic tumor immunity. However, Tregs are also essential for the maintenance of immunological self-tolerance, and share many molecular pathways with conventional T cells including cytotoxic T cells, the primary mediators of tumor immunity. Hence the inability to specifically target and neutralize Tregs within the TME of cancer patients without globally compromising self-tolerance poses a significant challenge. Here we review recent advances in the characterization of tumor-infiltrating Tregs with a focus on costimulatory and inhibitory receptors. We discuss receptor expression patterns, their functional role in Treg biology and mechanistic insights gained from targeting these receptors in preclinical models to evaluate their potential as clinical targets. We further outline a framework of parameters that could be used to refine the assessment of Tregs in cancer patients and increase their value as predictive biomarkers. Finally, we propose modalities to integrate our increasing knowledge on Treg phenotype and function for the rational design of checkpoint inhibitor-based combination therapies. Such combinations have great potential for synergy, as they could concomitantly enhance cytotoxic T cells and inhibit Tregs within the TME, thereby increasing the efficacy of current cancer immunotherapies.

Rational design of anti-GITR-based combination immunotherapy

Modulating T cell homeostatic mechanisms with checkpoint blockade can efficiently promote endogenous anti-tumor T cell responses1-11. However, many patients still do not benefit from checkpoint blockade12, highlighting the need for targeting of alternative immune pathways13. Glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) is an attractive target for immunotherapy, owing to its capacity to promote effector T cell (Teff) functions14,15 and hamper regulatory T cell (Treg) suppression16-20. On the basis of the potent preclinical anti-tumor activity of agonist anti-GITR antibodies, reported by us and others16,21,22, we initiated the first in-human phase 1 trial of GITR agonism with the anti-GITR antibody TRX518 ( NCT01239134 ). Here, we report the safety profile and immune effects of TRX518 monotherapy in patients with advanced cancer and provide mechanistic preclinical evidence to rationally combine GITR agonism with checkpoint blockade in future clinical trials. We demonstrate that TRX518 reduces circulating and intratumoral Treg cells to similar extents, providing an easily assessable biomarker of anti-GITR activity. Despite Treg reductions and increased Teff:Treg ratios, substantial clinical responses were not seen. Similarly, in mice with advanced tumors, GITR agonism was not sufficient to activate cytolytic T cells due to persistent exhaustion. We demonstrate that T cell reinvigoration with PD-1 blockade can overcome resistance of advanced tumors to anti-GITR monotherapy. These findings led us to start investigating TRX518 with PD-1 pathway blockade in patients with advanced refractory tumors ( NCT02628574 ).

A novel combination of chemotherapy and immunotherapy controls tumor growth in mice with a human immune system

Mice reconstituted with a human immune system and bearing human tumors represent a promising model for developing novel cancer immunotherapies. Here, we used mass cytometry and multi-parametric flow cytometry to characterize human leukocytes infiltrating a human breast cancer tumor model in immunocompromised NOD.SCID.γc-null mice reconstituted with a human immune system and compared it to samples of breast cancer patients. We observed highly activated human CD4⁺ and CD8⁺ T cells in the tumor, as well as minor subsets of innate immune cells in both settings. We also report that ICOS⁺ CD4⁺ regulatory T cells (Treg) were enriched in the tumor relative to the periphery in humanized mice and patients, providing a target to affect Treg and tumor growth. Indeed, administration of a neutralizing mAb to human ICOS reduced Treg proportions and numbers and improved CD4 + T cell proliferation in humanized mice. Moreover, a combination of the anti-ICOS mAb with cyclophosphamide reduced tumor growth, and that was associated with an improved CD8 to Treg ratio. Depletion of human CD8⁺ T cells or of murine myeloid cells marginally affected the effect of the combination therapy. Altogether, our results indicate that a combination of anti-ICOS mAb and chemotherapy controls tumor growth in humanized mice, opening new perspectives for the treatment of breast cancer. One sentence summary: Targeting ICOS in combination with chemotherapy is a promising strategy to improve tumor immunity in humans.

Prevalence and Cellular Distribution of Novel Immune Checkpoint Targets Across Longitudinal Specimens in Treatment-naïve Melanoma Patients: Implications for Clinical Trials

PURPOSE

Immunotherapies targeting costimulating and coinhibitory checkpoint receptors beyond PD-1 and CTLA-4 have entered clinical trials. Little is known about the relative abundance, coexpression, and immune cells enriched for each specific drug target, limiting understanding of the biological basis of potential treatment outcomes and development of predictive biomarkers for personalized immunotherapy. We sought to assess the abundance of checkpoint receptors during melanoma disease progression and identify immune cells enriched for them.Experimental Design: Multiplex immunofluorescence staining for immune checkpoint receptors (ICOS, GITR, OX40, PD-1, TIM-3, VISTA) was performed on 96 melanoma biopsies from 41 treatment-naïve patients, including patient-matched primary tumors, nodal metastases, and distant metastases. Mass cytometry was conducted on tumor dissociates from 18 treatment-naïve melanoma metastases to explore immune subsets enriched for checkpoint receptors.

RESULTS

A small subset of tumor-infiltrating leukocytes expressed checkpoint receptors at any stage of melanoma disease. GITR and OX40 were the least abundant checkpoint receptors, with <1% of intratumoral T cells expressing either marker. ICOS, PD-1, TIM-3, and VISTA were most abundant, with TIM-3 and VISTA mostly expressed on non-T cells, and TIM-3 enriched on dendritic cells. Tumor-resident T cells (CD69⁺/CD103⁺/CD8⁺) were enriched for TIGIT (>70%) and other coinhibitory but not costimulatory receptors. The proportion of GITR⁺ T cells decreased from primary melanoma (>5%) to lymph node (<1%, P = 0.04) and distant metastases (<1%, P = 0.0005).

CONCLUSIONS

This study provides the first comprehensive assessment of immune checkpoint receptor expression in any cancer and provides important data for rational selection of targets for trials and predictive biomarker development.

Immune checkpoint blockade and its combination therapy with small-molecule inhibitors for cancer treatment

Initially understood for its physiological maintenance of self-tolerance, the immune checkpoint molecule has recently been recognized as a promising anti-cancer target. There has been considerable interest in the biology and the action mechanism of the immune checkpoint therapy, and their incorporation with other therapeutic regimens. Recently the small-molecule inhibitor (SMI) has been identified as an attractive combination partner for immune checkpoint inhibitors (ICIs) and is becoming a novel direction for the field of combination drug design. In this review, we provide a systematic discussion of the biology and function of major immune checkpoint molecules, and their interactions with corresponding targeting agents. With both preclinical studies and clinical trials, we especially highlight the ICI + SMI combination, with its recent advances as well as its application challenges.

Dose escalation results from a first-in-human, phase 1 study of glucocorticoid-induced TNF receptor-related protein agonist AMG 228 in patients with advanced solid tumors

Background

This open-label, first-in-human, phase 1 study evaluated the safety, pharmacokinetics, pharmacodynamics, and maximum tolerated dose (MTD) of AMG 228, an agonistic human IgG1 monoclonal antibody targeting glucocorticoid-induced tumor necrosis factor receptor−related protein (GITR), in patients with refractory advanced solid tumors.

Methods

AMG 228 was administered intravenously every 3 weeks (Q3W). Dose escalation was in two stages: single-patient cohorts (3, 9, 30, and 90 mg), followed by “rolling six” design (n = 2–6; 180, 360, 600, 900, and 1200 mg). Primary endpoints included incidence of dose-limiting toxicities (DLTs), AEs, and pharmacokinetics. Additional endpoints were objective response and pharmacodynamic response.

Results

Thirty patients received AMG 228, which was well tolerated up to the maximum planned dose (1200 mg). No DLTs occurred; the MTD was not reached. The most common treatment-related AEs were fatigue (13%), infusion-related reaction (7%), pyrexia (7%), decreased appetite (7%), and hypophosphatemia (7%). Two patients had binding anti−AMG 228 antibodies (one at baseline); no neutralizing antibodies were detected. AMG 228 exhibited target-mediated drug disposition, and serum exposure was approximately dose proportional at 180–1200 mg and greater than dose proportional at 3–1200 mg. Doses > 360 mg Q3W achieved serum trough coverage for 95% in vitro GITR occupancy. Despite GITR coverage in peripheral blood and tumor biopsies, there was no evidence of T-cell activation or anti-tumor activity.

Conclusions

In patients with advanced solid tumors, AMG 228 Q3W was tolerable up to the highest tested dose (1200 mg), exhibited favorable pharmacokinetics, and provided target coverage indicating a pharmacokinetic profile appropriate for longer intervals. However, there was no evidence of T-cell activation or anti-tumor activity with AMG 228 monotherapy.

Trial registration

ClinicalTrials.gov, NCT02437916.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0407-x) contains supplementary material, which is available to authorized users.

Anti-glucocorticoid-induced Tumor Necrosis Factor-Related Protein (GITR) Therapy Overcomes Radiation-Induced Treg Immunosuppression and Drives Abscopal Effects

Despite the potential to cure metastatic disease, immunotherapy on its own often fails outright or early on due to tumor immune evasion. To address this obstacle, we investigated combinations of anti-GITR, anti-PD1 and radiation therapy (XRT) in our previously developed anti-PD1 resistant 344SQ non-small cell lung adenocarcinoma preclinical tumor model. We hypothesized that targeting multiple mechanisms of immune evasion with this triple therapy would lead to an enhanced tumor-specific immune response and improve survival more so than any mono- or dual therapy. In a two tumor 344SQR murine model, treatment with anti-GITR, anti-PD1, and XRT led to significantly improved survival and an abscopal response, with half of the mice becoming tumor free. These mice showed durable response and increased CD4+ and CD8+ effector memory on tumor rechallenge. Regulatory T cells (Tregs) expressed the highest level of GITR at the tumor site and anti-GITR therapy drastically diminished Tregs at the tumor site. Anti-tumor effects were largely dependent on CD4+ T cells and partially dependent on CD8+ T cells. Anti-GITR IgG2a demonstrated superior efficacy to anti-GITR IgG1 in driving antitumor effects. Collectively, these results suggest that combinatorial strategies targeting multiple points of tumor immune evasion may lead to a robust and lasting antitumor response.

Esculetin Ameliorates Psoriasis-Like Skin Disease in Mice by Inducing CD4+Foxp3+ Regulatory T Cells

Psoriasis is an autoimmune and inflammatory skin disease affecting around 2-3% of the world's population. Patients with psoriasis need extensive treatments with global immunosuppressive agents that may cause severe side effects. Esculetin, a type of coumarins, is an active ingredient extracted mainly from the bark of Fraxinus rhynchophylla, which has been used to treat inflammatory and autoimmune diseases in China. However, the antipsoriatic effects of esculetin have not been reported. In this study, we aimed to investigate the effects of esculetin on psoriatic skin inflammation in a mouse model and explored the potential molecular mechanisms underlying its action. We found that esculetin ameliorated the skin lesion and reduced PASI scores as well as weight loss in imiquimod-induced psoriasis-like mice, accompanied with weakened proliferation and differentiation of keratinocytes and T cell infiltration in esculetin-treated psoriatic mice. In addition, esculetin reduced the frequency of CD8⁺CD44^highCD62L^low effector T cells in psoriatic mice. In contrast, it increased the frequency of CD4⁺Foxp3⁺ Tregs in both lymph nodes and spleens of the psoriatic mice while promoting the differentiation of CD4⁺CD25^- T cells into CD4⁺Foxp3⁺ Tregs in vitro. Interestingly, depleting CD4⁺Foxp3⁺ Tregs largely reversed esculetin-mediated reduction in PASI scores, indicating that esculetin attenuates murine psoriasis mainly by inducing CD4⁺Foxp3⁺ Tregs. Furthermore, the mRNA levels of proinflammatory cytokines in the psoriatic mouse skin, including IL-6, IL-17A, IL-22, IL-23, TNF-α, and IFN-γ, were dramatically decreased by the treatment with esculetin. Finally, we found that esculetin inhibited the phosphorylation of IKKα and P65 in the psoriatic skin, suggesting that it inhibits the activation of NF-κB signaling. Thus, we have demonstrated that esculetin attenuates psoriasis-like skin lesion in mice and may be a potential therapeutic candidate for the treatment of psoriasis in clinic.

The promise and challenges of immune agonist antibody development in cancer

Immune cell functions are regulated by co-inhibitory and co-stimulatory receptors. The first two generations of cancer immunotherapy agents consist primarily of antagonist antibodies that block negative immune checkpoints, such as programmed cell death protein 1 (PD1) and cytotoxic T lymphocyte protein 4 (CTLA4). Looking ahead, there is substantial promise in targeting co-stimulatory receptors with agonist antibodies, and a growing number of these agents are making their way through various stages of development. This Review discusses the key considerations and potential pitfalls of immune agonist antibody design and development, their differentiating features from antagonist antibodies and the landscape of agonist antibodies in clinical development for cancer treatment.

Cancer Immunotherapy: A Focus on the Regulation of Immune Checkpoints

In recent years, the role of cancer immunotherapy has become increasingly important compared to traditional cancer treatments, including surgery, chemotherapy and radiotherapy. Of note, the clinical successes of immune checkpoint blockade, such as PD-1 and CTLA-4, represent a landmark event in cancer immunotherapy development. Therefore, further exploration of how immune checkpoints are regulated in the tumor microenvironment will provide key insights into checkpoint blockade therapy. In this review, we discuss in details about the regulation of immune checkpoints mediated by immune cells, oncolytic viruses, epigenetics, and gut microbiota and mutual regulation by co-expressed checkpoints. Finally, predictions are made for future personalized cancer immunotherapy based on different checkpoint modulations.

Herbal Components of a Novel Formula PSORI-CM02 Interdependently Suppress Allograft Rejection and Induce CD8+CD122+PD-1+ Regulatory T Cells

A recipient usually rejects a transplanted organ and thus needs immunosuppressive treatments to prevent rejection. Achieving long-term allograft survival without continuous global immunosuppression is highly desirable in transplantation as long-term immunosuppression causes various side effects. Therefore, it is necessary to search for medicine with potentially less side effects. Traditional Chinese medicine PSORI-CM01 (Yin Xie Ling), a formula with seven natural herbs, has been used to treat patients with psoriasis. Here, we investigated a “sharpened” formula, PSORI-CM02 consisting of only five herbs from PSORI-CM01: Curcumae rhizoma, Radix paeoniae rubra, Rhizoma smilacis glabrae, Mume fructus, and Sarcandrae herba. We examined whether or not PSORI-CM02 would suppress alloimmunity and found that PSORI-CM02 significantly inhibited murine skin allograft rejection and reduced graft-infiltration of CD3+ T cells. Interestingly, omitting any single herbal component rendered the whole formula ineffective in suppression, indicating that these herbal components exert their effects cooperatively as a whole. Moreover, PSORI-CM02 increased CD8+CD122+PD-1+ Treg frequency with CD4+FoxP3+ Tregs remaining unchanged in recipient mice, whereas CsA reduced CD4+FoxP3+ Treg frequency. PSORI-CM02 also hindered CD11c+ DC maturation posttransplantation. Importantly, PSORI-CM02-induced CD8+CD122+PD-1+ Tregs were more potent in suppression of allograft rejection in Rag-/- mice than control Tregs. On the other hand, PSORI-CM02 suppressed T cell proliferation in vitro and reduced their phosphorylation of P70S6K and P50/P65, suggesting that it inhibits both mTOR and NFκB signaling pathways. It also increased IL-10 production while reducing IFNγ level in the supernatant of activated T cells co-cultured with CD8+CD122+PD-1+ Tregs. Furthermore, HPLC fingerprinting ruled out that PSORI-CM02 contained CsA or rapamycin. PSORI-CM02 also did not cause any illness and toxic injury in recipient mice. Thus, we demonstrate that PSORI-CM02 formula suppresses allograft rejection without toxicity.

The tumor microenvironment: Thousand obstacles for effector T cells

The immune system is endowed with the capability to recognize and destroy transformed cells, but even in the presence of an immune infiltrate many tumors do progress. In the last decades new discoveries have shed light into (some of) the underlying mechanisms. Immune effector cells are not only under the influence of immune suppressive cell subsets, but also intrinsically regulated by immune check point molecules that under physiological condition avoid attach of healthy tissue. Moreover, tumor cells are modifying the surrounding microenvironment through secretion of immune modulators as well as via their own metabolism, thus further impairing the development of immune effector functions. Different approaches are currently being evaluated in the clinic to overcome those regulatory mechanisms and to unleash effector T cells.