Human/mouse CD137 agonist, JNU-0921, effectively shrinks tumors through enhancing the cytotoxicity of CD8+ T cells in cis and in trans

Agonistic antibodies against CD137 have been demonstrated to completely regress established tumors through activating T cell immunity. Unfortunately, current CD137 antibodies failed to benefit patients with cancer. Moreover, their antitumor mechanisms in vivo remain to be determined. Here, we report the development of a small molecular CD137 agonist, JNU-0921. JNU-0921 effectively activates both human and mouse CD137 through direct binding their extracellular domains to induce oligomerization and signaling and effectively shrinks tumors in vivo. Mechanistically, JNU-0921 enhances effector and memory function of cytotoxic CD8+ T cells (CTLs) and alleviates their exhaustion. JNU-0921 also skews polarization of helper T cells toward T helper 1 type and enhances their activity to boost CTL function. Meanwhile, JNU-0921 attenuates the inhibitory function of regulatory T cells on CTLs. Our current work shows that JNU-0921 shrinks tumors by enhancing the cytotoxicity of CTLs in cis and in trans and sheds light on strategy for developing CD137 small molecular agonists.

IFNγ Production by Functionally Reprogrammed Tregs Promotes Antitumor Efficacy of OX40/CD137 Bispecific Agonist Therapy

Regulatory T cells (Treg) are highly enriched within many tumors and suppress immune responses to cancer. There is intense interest in reprogramming Tregs to contribute to antitumor immunity. OX40 and CD137 are expressed highly on Tregs, activated and memory T cells, and NK cells. In this study, using a novel bispecific antibody targeting mouse OX40 and CD137 (FS120m), we show that OX40/CD137 bispecific agonism induces potent antitumor immunity partially dependent upon IFNγ production by functionally reprogrammed Tregs. Treatment of tumor-bearing animals with OX40/CD137 bispecific agonists reprograms Tregs into both fragile Foxp3+ IFNγ+ Tregs with decreased suppressive function and lineage-instable Foxp3- IFNγ+ ex-Tregs. Treg fragility is partially driven by IFNγ signaling, whereas Treg instability is associated with reduced IL2 responsiveness upon treatment with OX40/CD137 bispecific agonists. Importantly, conditional deletion of Ifng in Foxp3+ Tregs and their progeny partially reverses the antitumor efficacy of OX40/CD137 bispecific agonist therapy, revealing that reprogramming of Tregs into IFNγ-producing cells contributes to the anti-tumor efficacy of OX40/CD137 bispecific agonists. These findings provide insights into mechanisms by which bispecific agonist therapies targeting costimulatory receptors highly expressed by Tregs potentiate antitumor immunity in mouse models.

SIGNIFICANCE

The bispecific antibody FS120, an immunotherapy currently being tested in the clinic, partially functions by inducing anti-tumor activity of Tregs, which results in tumor rejection.

Regulatory T cells and immune escape in HCC: understanding the tumor microenvironment and advancing CAR-T cell therapy

Liver cancer, which most commonly manifests as hepatocellular carcinoma (HCC), is the sixth most common cancer in the world. In HCC, the immune system plays a crucial role in the growth and proliferation of tumor cells. HCC achieve immune escape through the tumor microenvironment, which significantly promotes the development of this cancer. Here, this article introduces and summarizes the functions and effects of regulatory T cells (Tregs) in the tumor microenvironment, highlighting how Tregs inhibit and regulate the functions of immune and tumor cells, cytokines, ligands and receptors, etc, thereby promoting tumor immune escape. In addition, it discusses the mechanism of CAR-T therapy for HCC and elaborate on the relationship between CAR-T and Tregs.

Prognostic Significance of the Microenvironment in Human Papillomavirus Oropharyngeal Carcinoma: A Systematic Review

OBJECTIVE

The immune microenvironment of HPV-associated (HPV+) oropharyngeal squamous cell carcinomas (OPSCCs) (HPV+OPSCCs) differs from that of HPV-independent oropharyngeal cancers (HPV-independent OPSCCs). The literature on the subject is very abundant, demanding an organized synthesis of this wealth of information to evaluate the hypothesis associating the favorable prognosis of HPV+OPSCC patients with a different immune microenvironment. A systematic review of the literature was conducted regarding the microenvironment of HPV+OPSCCs.

DATA SOURCE

MEDLINE/PubMed, Embase, and Cochrane Library databases.

REVIEW METHODS

A literature search was performed following PRISMA guidelines (Moher D. PLoS Med. 2009). The PEO (Population, Exposure, and Outcome) framework is detailed as follows: P: patients with oropharyngeal squamous cell carcinomas, E: human papillomavirus (HPV), and O: histological and immunological composition of the tumoral microenvironment (TME). No meta-analysis was performed.

RESULTS

From 1,202 studies that were screened, 58 studies were included (n = 6,474 patients; n = 3,581 (55%) HPV+OPSCCs and n = 2,861(45%) HPV-independent OPSCCs). The presence of tumor-infiltrating lymphocytes (TIL), CD3+ in 1,733 patients, CD4+ in 520 patients, and CD8+ (cytotoxic T lymphocytes (CTL)) in 3,104 patients, and high levels of PD-L1 expression in 1,222 patients is strongly correlated with an improved clinical outcome in HPV+OPSCCs.

CONCLUSION

This systematic review provides the most comprehensive information on the immune microenvironment of HPV+OPSCCs to date. Tumor-infiltrating lymphocytes and PD-L1 expression are associated with a favorable prognosis. B, CD8+ and resident memory cells densities are higher in HPV+OPSCCs. The importance of myeloid lineages is still a matter of debate and research.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:1507-1516, 2024.

CTLs heterogeneity and plasticity: implications for cancer immunotherapy

Cytotoxic T lymphocytes (CTLs) play critical antitumor roles, encompassing diverse subsets including CD4+, NK, and γδ T cells beyond conventional CD8+ CTLs. However, definitive CTLs biomarkers remain elusive, as cytotoxicity-molecule expression does not necessarily confer cytotoxic capacity. CTLs differentiation involves transcriptional regulation by factors such as T-bet and Blimp-1, although epigenetic regulation of CTLs is less clear. CTLs promote tumor killing through cytotoxic granules and death receptor pathways, but may also stimulate tumorigenesis in some contexts. Given that CTLs cytotoxicity varies across tumors, enhancing this function is critical. This review summarizes current knowledge on CTLs subsets, biomarkers, differentiation mechanisms, cancer-related functions, and strategies for improving cytotoxicity. Key outstanding questions include refining the CTLs definition, characterizing subtype diversity, elucidating differentiation and senescence pathways, delineating CTL-microbe relationships, and enabling multi-omics profiling. A more comprehensive understanding of CTLs biology will facilitate optimization of their immunotherapy applications. Overall, this review synthesizes the heterogeneity, regulation, functional roles, and enhancement strategies of CTLs in antitumor immunity, highlighting gaps in our knowledge of subtype diversity, definitive biomarkers, epigenetic control, microbial interactions, and multi-omics characterization. Addressing these questions will refine our understanding of CTLs immunology to better leverage cytotoxic functions against cancer.

Hypothesis of a CD137/Eomes activating axis for effector T cells in HPV oropharyngeal cancers

Chronic Human Papilloma Virus (HPV) infection is supplanting alcohol and tobacco intoxications as the leading cause of oropharyngeal cancer in developed countries. HPV-related squamous cell carcinomas of the oropharynx (HPV + OSC) present better survival and respond better to radiotherapy and chemotherapy. Regulatory T cells (TREG) are mainly described as immunosuppressive and protumoral in most solid cancers. However, TREG are paradoxically associated with a better prognosis in HPV + OSCs. The transcription factor FoxP3 is the basis for the identification of TREG. Among CD4 + FoxP3 + T cells, some have effector functions. A medical hypothesis is formulated here: the existence of a CD137 (4.1BB)-Eomesodermin (Eomes) activated pathway downstream of TCR-specific activation in a subpopulation of CD4 + FoxP3 + T cells may explain this effector function. Evidence suggest that this axis may exist either in CD4 + FoxP3 + T cells or CD8 + T cells. This pathway could lead T cells to strong antitumor cytotoxic activity in a tumor-specific manner. Furthermore, CD137 is one of the most expected targets for the development of agonist immunotherapies. The identification of CD137 + Eomes + FoxP3+/- T cells could be a key element in the selective activation of the most anti-tumor cells in the HPV + OSC microenvironment.

Differential requirements for CD4+ T cells in the efficacy of the anti-PD-1+LAG-3 and anti-PD-1+CTLA-4 combinations in melanoma flank and brain metastasis models

BACKGROUND

Although the anti-PD-1+LAG-3 and the anti-PD-1+CTLA-4 combinations are effective in advanced melanoma, it remains unclear whether their mechanisms of action overlap.

METHODS

We used single cell (sc) RNA-seq, flow cytometry and IHC analysis of responding SM1, D4M-UV2 and B16 melanoma flank tumors and SM1 brain metastases to explore the mechanism of action of the anti-PD-1+LAG-3 and the anti-PD-1+CTLA-4 combination. CD4+ and CD8+ T cell depletion, tetramer binding assays and ELISPOT assays were used to demonstrate the unique role of CD4+T cell help in the antitumor effects of the anti-PD-1+LAG-3 combination.

RESULTS

The anti-PD-1+CTLA-4 combination was associated with the infiltration of FOXP3+regulatory CD4+ cells (Tregs), fewer activated CD4+T cells and the accumulation of a subset of IFNγ secreting cytotoxic CD8+T cells, whereas the anti-PD-1+LAG-3 combination led to the accumulation of CD4+T helper cells that expressed CXCR4, TNFSF8, IL21R and a subset of CD8+T cells with reduced expression of cytotoxic markers. T cell depletion studies showed a requirement for CD4+T cells for the anti-PD-1+LAG-3 combination, but not the PD-1-CTLA-4 combination at both flank and brain tumor sites. In anti-PD-1+LAG-3 treated tumors, CD4+T cell depletion was associated with fewer activated (CD69+) CD8+T cells and impaired IFNγ release but, conversely, increased numbers of activated CD8+T cells and IFNγ release in anti-PD-1+CTLA-4 treated tumors.

CONCLUSIONS

Together these studies suggest that these two clinically relevant immune checkpoint inhibitor (ICI) combinations have differential effects on CD4+T cell polarization, which in turn, impacted cytotoxic CD8+T cell function. Further insights into the mechanisms of action/resistance of these clinically-relevant ICI combinations will allow therapy to be further personalized.

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

Cytotoxic CD4+ T cells in chronic viral infections and cancer

CD4+ T cells play an important role in immune responses against pathogens and cancer cells. Although their main task is to provide help to other effector immune cells, a growing number of infections and cancer entities have been described in which CD4+ T cells exhibit direct effector functions against infected or transformed cells. The most important cell type in this context are cytotoxic CD4+ T cells (CD4+ CTL). In infectious diseases anti-viral CD4+ CTL are mainly found in chronic viral infections. Here, they often compensate for incomplete or exhausted CD8+ CTL responses. The induction of CD4+ CTL is counter-regulated by Tregs, most likely because they can be dangerous inducers of immunopathology. In viral infections, CD4+ CTL often kill via the Fas/FasL pathway, but they can also facilitate the exocytosis pathway of killing. Thus, they are very important effectors to keep persistent virus in check and guarantee host survival. In contrast to viral infections CD4+ CTL attracted attention as direct anti-tumor effectors in solid cancers only recently. Anti-tumor CD4+ CTL are defined by the expression of cytolytic markers and have been detected within the lymphocyte infiltrates of different human cancers. They kill tumor cells in an antigen-specific MHC class II-restricted manner not only by cytolysis but also by release of IFNγ. Thus, CD4+ CTL are interesting tools for cure approaches in chronic viral infections and cancer, but their potential to induce immunopathology has to be carefully taken into consideration.

Remodeling the tumor microenvironment to overcome treatment resistance in HPV-negative head and neck cancer

Despite intensive efforts and refined techniques, overall survival in HPV-negative head and neck cancer remains poor. Robust immune priming is required to elicit a strong and durable antitumor immune response in immunologically cold and excluded tumors like HPV-negative head and neck cancer. This review highlights how the tumor microenvironment could be affected by different immune and stromal cell types, weighs the need to integrate metabolic regulation of the tumor microenvironment into cancer treatment strategies and summarizes the emerging clinical applicability of personalized immunotherapeutic strategies in HPV-negative head and neck cancer.

CD4+ cytotoxic T cells: an emerging effector arm of anti-tumor immunity

While CD8+ cytotoxic T cells have long been considered the primary effector in controlling tumors, the involvement of CD4+ "helper" T cells in anti-tumor immunity has been underappreciated. The investigations of intra-tumoral T cells, fueled by the recent advances in genomic technologies, have led to a rethinking of the indirect role of CD4+ T cells that have traditionally been described as a "helper". Accumulating evidence from preclinical and clinical studies indicates that CD4+ T cells can acquire intrinsic cytotoxic properties and directly kill various types of tumor cells in a major histocompatibility complex class II (MHC-II)-dependent manner, as opposed to the indirect "helper" function, thus underscoring a potentially critical contribution of CD4+ cytotoxic T cells to immune responses against a wide range of tumor types. Here, we discuss the biological properties of anti-tumor CD4+ T cells with cytotoxic capability and highlight the emerging observations suggesting their more significant role in anti-tumor immunity than previously appreciated. [BMB Reports 2023; 56(3): 140-144].

In or out of control: Modulating regulatory T cell homeostasis and function with immune checkpoint pathways

Regulatory T cells (Tregs) are the master regulators of immunity and they have been implicated in different disease states such as infection, autoimmunity and cancer. Since their discovery, many studies have focused on understanding Treg development, differentiation, and function. While there are many players in the generation and function of truly suppressive Tregs, the role of checkpoint pathways in these processes have been studied extensively. In this paper, we systematically review the role of different checkpoint pathways in Treg homeostasis and function. We describe how co-stimulatory and co-inhibitory pathways modulate Treg homeostasis and function and highlight data from mouse and human studies. Multiple checkpoint pathways are being targeted in cancer and autoimmunity; therefore, we share insights from the clinic and discuss the effect of experimental and approved therapeutics on Treg biology.

Regulation of CD4 T Cell Responses by the Transcription Factor Eomesodermin

Central to the impacts of CD4 T cells, both positive in settings of infectious disease and cancer and negative in the settings of autoimmunity and allergy, is their ability to differentiate into distinct effector subsets with specialized functions. The programming required to support such responses is largely dictated by lineage-specifying transcription factors, often called ‘master regulators’. However, it is increasingly clear that many aspects of CD4 T cell immunobiology that can determine the outcomes of disease states involve a broader transcriptional network. Eomesodermin (Eomes) is emerging as an important member of this class of transcription factors. While best studied in CD8 T cells and NK cells, an increasing body of work has focused on impacts of Eomes expression in CD4 T cell responses in an array of different settings. Here, we focus on the varied impacts reported in these studies that, together, indicate the potential of targeting Eomes expression in CD4 T cells as a strategy to improve a variety of clinical outcomes.

CD4 + Cytotoxic T Lymphocytes in Cancer Immunity and Immunotherapy

CD4⁺ T cells have the ability to differentiate into relatively specialized effector subsets after exposure to innate immune signals. The remarkable plasticity of CD4⁺ T cells is required to achieve immune responses in different tissues and against various pathogens. Numerous studies have shown that CD4⁺ T cells can play direct and indispensable roles in protective immunity by killing infected or transformed cells. Although the lineage decision of commitment to the CD4⁺ or CD8⁺ cell lineage is once thought to be inflexible, the identification of antigen-experienced CD4⁺ T cells with cytotoxic activity suggests the existence of unexpected plasticity for these cells. The recognition of CD4⁺ cytotoxic T lymphocytes (CTLs) and the mechanisms driving the differentiation of this particular cell subset create opportunities to explore the roles of these effector cells in protective immunity and immune-related pathology. CD4⁺ CTLs are proven to play a protective role in antiviral immunity. Here, the latest investigations on the phenotypic and functional features of CD4⁺ CTLs and their roles in antitumor immunity and immunotherapy are briefly reviewed.

Targeting 4-1BB for tumor immunotherapy from bench to bedside

Immune dysfunction has been proposed as a factor that may contribute to disease progression. Emerging evidence suggests that immunotherapy aims to abolish cancer progression by modulating the balance of the tumor microenvironment. 4-1BB (also known as CD137 and TNFRS9), a member of tumor necrosis factor receptor superfamily, has been validated as an extremely attractive and promising target for immunotherapy due to the upregulated expression in the tumor environment and its involvement in tumor progression. More importantly, 4-1BB-based immunotherapy approaches have manifested powerful antitumor effects in clinical trials targeting 4-1BB alone or in combination with other immune checkpoints. In this review, we will summarize the structure and expression of 4-1BB and its ligand, discuss the role of 4-1BB in the microenvironment and tumor progression, and update the development of drugs targeting 4-1BB. The purpose of the review is to furnish a comprehensive overview of the potential of 4-1BB as an immunotherapeutic target and to discuss recent advances and prospects for 4-1BB in cancer therapy.

Murine CAR19 Tregs suppress acute graft-versus-host disease and maintain graft-versus-tumor responses

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) efficacy is complicated by graft-versus-host disease (GVHD), a leading cause of morbidity and mortality. Regulatory T cells (Tregs) have shown efficacy in preventing GVHD. However, high Treg doses are often required, necessitating substantial ex vivo or in vivo expansion that may diminish suppressor function. To enhance in vivo suppressor function, murine Tregs were transduced to express an anti-human CD19 chimeric antigen receptor (hCAR19) and infused into lethally irradiated, hCD19-transgenic recipients for allo-HSCT. Compared with recipients receiving control transduced Tregs, those receiving hCAR19 Tregs had a marked decrease in acute GVHD lethality. Recipient hCD19 B cells and murine hCD19 TBL12-luciferase (TBL12luc) lymphoma cells were both cleared by allogeneic hCAR19 Tregs, which was indicative of graft-versus-tumor (GVT) maintenance and potentiation. Mechanistically, hCAR19 Tregs killed syngeneic hCD19+ but not hCD19- murine TBL12luc cells in vitro in a perforin-dependent, granzyme B-independent manner. Importantly, cyclophosphamide-treated, hCD19-transgenic mice given hCAR19 cytotoxic T lymphocytes without allo-HSCT experienced rapid lethality due to systemic toxicity that has been associated with proinflammatory cytokine release; in contrast, hCAR19 Treg suppressor function enabled avoidance of this severe complication. In conclusion, hCAR19 Tregs are a potentially novel and effective strategy to suppress GVHD without loss of GVT responses.

Effective generation of tumor-infiltrating lymphocyte products from metastatic non-small-cell lung cancer (NSCLC) lesions irrespective of location and previous treatments

Background

Non-small-cell lung cancer (NSCLC) is the leading cause of cancer-related mortality worldwide. Because current treatment regimens show limited success rates, alternative therapeutic approaches are needed. We recently showed that treatment-naïve, stage I/II primary NSCLC tumors contain a high percentage of tumor-reactive T cells, and that these tumor-reactive T cells can be effectively expanded and used for the generation of autologous tumor-infiltrating T cell (TIL) therapy. Whether these promising findings also hold true for metastatic lesions is unknown yet critical for translation into the clinic.

Materials and methods

We studied the lymphocyte composition using flow cytometry from 27 metastatic NSCLC lesions obtained from different locations and from patients with different histories of treatment regimens. We determined the expansion capacity of TILs with the clinically approved protocol, and measured their capacity to produce the key pro-inflammatory cytokines interferon-γ, tumor necrosis factor and interleukin 2 and to express CD137 upon co-culture of expanded TILs with the autologous tumor digest.

Results

The overall number and composition of lymphocyte infiltrates from the various metastatic lesions was by and large comparable to that of early-stage primary NSCLC tumors. We effectively expanded TILs from all metastatic NSCLC lesions to numbers that were compatible with TIL transfusion, irrespective of the location of the metastasis and of the previous treatment. Importantly, 16 of 21 (76%) tested TIL products displayed antitumoral activity, and several contained polyfunctional T cells.

Conclusions

Metastatic NSCLC lesions constitute a viable source for the generation of tumor-reactive TIL products for therapeutic purposes irrespective of their location and the pre-treatment regimens.

•

T cells can be efficiently isolated and expanded from late-stage NSCLC lesions.

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TIL products from metastatic NSCLC lesions are polyfunctional.

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Metastatic location or pre-treatment regimen does not affect T cells.

•

Adoptive TIL therapy is a therapeutic option for late-stage NSCLC patients.

Regulatory CAR-T cells in autoimmune diseases: Progress and current challenges

CAR (Chimeric Antigen Receptor) T-cell therapy has revolutionized the field of oncology in recent years. This innovative shift in cancer treatment also provides the opportunity to improve therapies for many patients suffering from various autoimmune diseases. Recent studies have confirmed the therapeutic suppressive potential of regulatory T cells (Tregs) to modulate immune response in autoimmune diseases. However, the polyclonal character of regulatory T cells and their unknown TCR specificity impaired their therapeutic potency in clinical implementation. Genetical engineering of these immune modulating cells to express antigen-specific receptors and using them therapeutically is a logical step on the way to overcome present limitations of the Treg strategy for the treatment of autoimmune diseases. Encouraging preclinical studies successfully demonstrated immune modulating properties of CAR Tregs in various mouse models. Still, there are many concerns about targeted Treg therapies relating to CAR target selectivity, suppressive functions, phenotype stability and safety aspects. Here, we summarize recent developments in CAR design, Treg biology and future strategies and perspectives in CAR Treg immunotherapy aiming at clinical translation.

The Road Less Taken: Less Appreciated Pathways for Manipulating CD8+ T Cell Exhaustion

Exhausted CD8+ T (Tex) cells are a distinct cell population that arise during persistent antigen exposure in the context of chronic infections and cancers. Although characterized by progressive loss of effector functions, high and sustained inhibitory receptor expression and distinct transcriptional and epigenetic programs, Tex cells are heterogeneous. Among these, a self-renewing TCF-1+ Tex population, having unique characteristics and the ability to respond to immune-checkpoint blockade, gives rise to TCF-1- terminally Tex cells. These TCF-1+ cells have stem cell-like properties similar to memory T cell populations, but the signals that regulate the developmental pathways and relationships among exhausted cell populations are still unclear. Here, we review our current understanding of Tex cell biology, and discuss some less appreciated molecules and pathways affecting T cell exhaustion. We highlight two co-stimulatory receptors, CD226 and CD137, and their role in inducing or restraining T cell exhaustion, as well as signaling pathways that may be amenable to pharmacological inhibition with a focus on Phosphoinositide-3 Kinase and IL-2 partial agonists. Finally, we discuss novel methods that may increase TCF-1+ populations and therefore improve immunotherapy responsiveness. Understanding features of and pathways to exhaustion has important implications for the success of immunotherapy, including checkpoint blockade and adoptive T-cell transfer therapies.

Hyperprogression, a challenge of PD-1/PD-L1 inhibitors treatments: potential mechanisms and coping strategies

Immunotherapy is now a mainstay in cancer treatments. Programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) immune checkpoint inhibitor (ICI) therapies have opened up a new venue of advanced cancer immunotherapy. However, hyperprogressive disease (HPD) induced by PD-1/PD-L1 inhibitors caused a significant decrease in the overall survival (OS) of the patients, which compromise the efficacy of PD-1/PD-L1 inhibitors. Therefore, HPD has become an urgent issue to be addressed in the clinical uses of PD-1/PD-L1 inhibitors. The mechanisms of HPD remain unclear, and possible predictive factors of HPD are not well understood. In this review, we summarized the potential mechanisms of HPD and coping strategies that can effectively reduce the occurrence and development of HPD.

The Era of Cytotoxic CD4 T Cells

In 1986, Mosmann and Coffman identified 2 functionally distinct subsets of activated CD4 T cells, Th1 and Th2 cells, being key in distinct T cell mediated responses. Over the past three decades, our understanding of CD4 T cell differentiation has expanded and the initial paradigm of a dichotomic CD4 T cell family has been revisited to accommodate a constantly growing number of functionally distinct CD4 T helper and regulatory subpopulations. Of note, CD4 T cells with cytotoxic functions have also been described, initially in viral infections, autoimmune disorders and more recently also in cancer settings. Here, we provide an historical overview on the discovery and characterization of cytotoxic CD4 T cells, followed by a description of their mechanisms of cytotoxicity. We emphasize the relevance of these cells in disease conditions, particularly in cancer, and we provide insights on how to exploit these cells in immunotherapy.

Soluble CD137 is a novel serum marker of liver cirrhosis in patients with hepatitis C and alcohol-associated disease etiology

Defective T-cell functions play a role in the persistence of HCV infection. Activated T cells express CD137, which costimulates antivirus T-cell responses, and this activity is antagonized by soluble CD137 (sCD137). Here, we show that in sera of 81 patients with chronic HCV, sCD137 levels did not correlate with measures of viral infection, and did not decline after virus eradication using direct-acting antivirals. Thus, serum sCD137 was similar in patients infected with HCV and in uninfected controls. Of note, in HCV patients with liver cirrhosis and patients with mostly alcohol-associated liver cirrhosis, sCD137 was increased. A negative association of sCD137 and albumin existed in both cohorts. sCD137 concentrations were similar in hepatic and portal vein blood excluding the liver as the origin of higher levels. Recombinant sCD137 reduced Th1 and Th2 but not Th17 cell polarization in vitro, and accordingly lowered IFN-γ, TNF, and IL-13 in cell media. Serum sCD137 is associated with inflammatory states, and positively correlated with serum TNF in cirrhotic HCV patients following virus eradication. Our study argues against a role of sCD137 in HCV infection and suggests a function of sCD137 in liver cirrhosis, which yet has to be defined.

OX40L blockade cellular nanovesicles for autoimmune diseases therapy

Current clinical agents for autoimmunity disorders treatment often cause substantial adverse effects and safety concerns, owing to non-specific immune modulation. Due to the prominent contribution of effector T cells in pathogenesis of rheumatoid arthritis (RA) and inflammatory bowel disease (IBD), and preferential location of co-stimulatory receptor-ligand pair OX40-OX40L at the inflamed sites, selectively targeting autoaggressive T cells by blockade OX40-OX40L, might represent an alternative strategy. Herein, we developed a new strategy to antagonize OX40-OX40L interaction by engineering a cell membrane derived nanovesicles (NVs) expressing OX40 receptors (OX40 NVs), and explored their potential for autoimmune disorders therapy. OX40 NVs showed specific binding capability to inflamed HUVECs in vitro, it also possessed distinct arthritic-targeting capacity in RA inflamed joints, and preferential accumulation in IBD inflamed colon. OX40 NVs efficiently suppressed the progression of both RA and IBD diseases through reducing CD4⁺OX40⁺ T cells population, and proinflammatory cytokines (i.e., TNF-α and IL-1β), while reinforcing Tregs immune-suppressive effect, with superior therapeutic efficacy than anti-OX40L. Additionally, dexamethasone (DEX) loading can further enhance the potential of OX40 NVs for RA treatment. Owing to their preferential localization to inflamed sites, and potent immune-suppression ability, targeting OX40-OX40L blockade by OX40 NVs for autoimmune therapy is highly promising.

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.

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.

Targeting resistance to radiation-immunotherapy in cold HNSCCs by modulating the Treg-dendritic cell axis

BACKGROUND

Numerous trials combining radiation therapy (RT) and immunotherapy in head and neck squamous cell carcinoma (HNSCC) are failing. Using preclinical immune cold models of HNSCC resistant to RT-immune checkpoint inhibitors, we investigate therapeutic approaches of overcoming such resistance by examining the differential microenvironmental response to RT.

METHODS

We subjected two HPV-negative orthotopic mouse models of HNSCC to combination RT, regulatory T cells (Treg) depletion, and/or CD137 agonism. Tumor growth was measured and intratumorous and lymph node immune populations were compared among treatment groups. Human gene sets, genetically engineered mouse models DEREG and BATF3-/-, flow and time-of-flight cytometry, RNA-Seq, Treg adoptive transfer studies, and in vitro experiments were used to further evaluate the role of dendritic cells (DCs) and Tregs in these treatments.

RESULTS

In MOC2 orthotopic tumors, we find no therapeutic benefit to targeting classically defined immunosuppressive myeloids, which increase with RT. In these radioresistant tumors, supplementing combination RT and Treg depletion with anti-CD137 agonism stimulates CD103+ DC activation in tumor-draining lymph nodes as characterized by increases in CD80+ and CCR7+ DCs, resulting in a CD8 T cell-dependent response. Simultaneously, Tregs are reprogrammed to an effector phenotype demonstrated by increases in interferonγ+, tumor necrosis factorα+, PI3K+, pAKT+ and Eomes+ populations as well as decreases in CTLA4+ and NRP-1+ populations. Tumor eradication is observed when RT is increased to an 8 Gy x 5 hypofractionated regimen and combined with anti-CD25+ anti-CD137 treatment. In a human gene set from oral squamous cell carcinoma tumors, high Treg number is associated with earlier recurrence.

CONCLUSIONS

Regulating Treg functionality and DC activation status within the lymph node is critical for generating a T cell effector response in these highly radioresistant tumors. These findings underscore the plasticity of Tregs and represent a new therapeutic opportunity for reprogramming the tumor microenvironment in HNSCCs resistant to conventional radioimmunotherapy approaches.

Tumor-specific cytolytic CD4 T cells mediate immunity against human cancer

CD4 T cells have been implicated in cancer immunity for their helper functions. Moreover, their direct cytotoxic potential has been shown in some patients with cancer. Here, by mining single-cell RNA-seq datasets, we identified CD4 T cell clusters displaying cytotoxic phenotypes in different human cancers, resembling CD8 T cell profiles. Using the peptide-MHCII-multimer technology, we confirmed ex vivo the presence of cytolytic tumor-specific CD4 T cells. We performed an integrated phenotypic and functional characterization of these cells, down to the single-cell level, through a high-throughput nanobiochip consisting of massive arrays of picowells and machine learning. We demonstrated a direct, contact-, and granzyme-dependent cytotoxic activity against tumors, with delayed kinetics compared to classical cytotoxic lymphocytes. Last, we found that this cytotoxic activity was in part dependent on SLAMF7. Agonistic engagement of SLAMF7 enhanced cytotoxicity of tumor-specific CD4 T cells, suggesting that targeting these cells might prove synergistic with other cancer immunotherapies.

Immune profiling and immunotherapeutic targets in pancreatic cancer

Background

Immunotherapeutic approaches for pancreatic ductal adenocarcinoma (PDAC) are less successful as compared to many other tumor types. In this study, comprehensive immune profiling was performed in order to identify novel, potentially actionable targets for immunotherapy.

Methods

Formalin-fixed paraffin embedded (FFPE) specimens from 68 patients were evaluated for expression of 395 immune-related markers (RNA-seq), mutational burden by complete exon sequencing of 409 genes, PD-L1 expression by immunohistochemistry (IHC), pattern of tumor infiltrating lymphocytes (TILs) infiltration by CD8 IHC, and PD-L1/L2 copy number by fluorescent in situ hybridization (FISH).

Results

The seven classes of actionable genes capturing myeloid immunosuppression, metabolic immunosuppression, alternative checkpoint blockade, CTLA-4 immune checkpoint, immune infiltrate, and programmed cell death 1 (PD-1) axis immune checkpoint, discerned 5 unique clinically relevant immunosuppression expression profiles (from most to least common): (I) combined myeloid and metabolic immunosuppression [affecting 25 of 68 patients (36.8%)], (II) multiple immunosuppressive mechanisms (29.4%), (III) PD-L1 positive (20.6%), (IV) highly inflamed PD-L1 negative (10.3%); and (V) immune desert (2.9%). The Wilcoxon rank-sum test was used to compare the PDAC cohort with a comparison cohort (n=1,416 patients) for the mean expressions of the 409 genes evaluated. Multiple genes including TIM3, VISTA, CCL2, CCR2, TGFB1, CD73, and CD39 had significantly higher mean expression versus the comparison cohort, while three genes (LAG3, GITR, CD38) had significantly lower mean expression.

Conclusions

This study demonstrates that a clinically relevant unique profile of immune markers can be identified in PDAC and be used as a roadmap for personalized immunotherapeutic decision-making strategies.

CD137 (4-1BB) stimulation leads to metabolic and functional reprogramming of human monocytes/macrophages enhancing their tumoricidal activity

Immunotherapies have heralded a new era in the cancer treatment. In addition to checkpoint inhibitors, agonistic antibodies against co-stimulatory immune receptors hold the potential to invoke efficient antitumor immunity. Targeting CD137 has gained momentum based on its ability to drive NK- and T-cell-based responses. CD137-engaging mAbs have already entered clinical trials for different types of tumors showing promising results. Despite the efforts to translate CD137-mediated immunotherapy into clinical practice, little remains known regarding the role of CD137 in human monocytes/macrophages.We found CD137 being expressed on monocytes of healthy controls and at even higher levels in patients with multiple myeloma or CLL. CD137^HI(GH) monocytes displayed a distinct phenotypic, transcriptomic, and metabolic profile. They possessed an increased phagocytic capacity enabling superior antibody-dependent phagocytosis (ADPC) of multiple myeloma and lymphoma cells that were treated with anti-CD38 or anti-CD20 mAbs. Triggering CD137 promoted both metabolic and tumoricidal activity in an extracellular signal-regulated kinase (ERK)-dependent fashion. In addition, we observed a phenotypic, transcriptomic, and functional skewing towards a M1-like phenotype.Overall, we introduce CD137 as a positive immune checkpoint on human monocytes/macrophages, which can have therapeutic implications especially in view of synergistic effects when combining CD137 agonists with tumor-targeting antibodies.

4-1BB co-stimulation further enhances anti-PD-1-mediated reinvigoration of exhausted CD39+ CD8 T cells from primary and metastatic sites of epithelial ovarian cancers

BACKGROUND

Responses to immunotherapy vary between different cancer types and sites. Here, we aimed to investigate features of exhaustion and activation in tumor-infiltrating CD8 T cells at both the primary and metastatic sites in epithelial ovarian cancer.

METHODS

Tumor tissues and peripheral blood were obtained from 65 patients with ovarian cancer. From these samples, we isolated tumor-infiltrating lymphocytes (TILs) and peripheral blood mononuclear cells. These cells were used for immunophenotype using multicolor flow cytometry, gene expression profile using RNA sequencing and ex vivo functional restoration assays.

RESULTS

We found that CD39+ CD8 TILs were enriched with tumor-specific CD8 TILs, and that the activation status of these cells was determined by the differential programmed cell death protein 1 (PD-1) expression level. CD39+ CD8 TILs with high PD-1 expression (PD-1high) exhibited features of highly tumor-reactive and terminally exhausted phenotypes. Notably, PD-1high CD39+ CD8 TILs showed similar characteristics in terms of T-cell exhaustion and activation between the primary and metastatic sites. Among co-stimulatory receptors, 4-1BB was exclusively overexpressed in CD39+ CD8 TILs, especially on PD-1high cells, and 4-1BB-expressing cells displayed immunophenotypes indicating higher degrees of T-cell activation and proliferation, and less exhaustion, compared with cells not expressing 4-1BB. Importantly, 4-1BB agonistic antibodies further enhanced the anti-PD-1-mediated reinvigoration of exhausted CD8 TILs from both primary and metastatic sites.

CONCLUSION

Severely exhausted PD-1high CD39+ CD8 TILs displayed a distinctly heterogeneous exhaustion and activation status determined by differential 4-1BB expression levels, providing rationale and evidence for immunotherapies targeting co-stimulatory receptor 4-1BB in ovarian cancers.

The emerging role of co-stimulatory molecules and their agonistic mAb-based combination therapies in melanoma

Although anti-PD-1/L1 and anti-CTLA-4 antibodies, the validated immune checkpoint blockades, can elicit durable long-lasting antitumor immunity and improve the clinical outcomes of melanoma treatment, there are still a fraction of patients who did not receive therapeutic benefits as expected. In addition to findings of blocking the co-inhibitory pathways, the preclinical and clinical evidence suggests that triggering the co-stimulatory pathways through agonists such as CD137, OX40, CD40, GITR and CD27 may be a rational next step for melanoma therapy. In this review, we discuss the progress of studies on these co-stimulatory molecules in terms of their promising therapeutic effects and underlying antitumor mechanisms, and provide a review of the possible combinations that orchestrate the interplay of co-stimulatory agonistic mAbs and other therapies for treating melanoma, including inhibitory immune checkpoint mAbs, adoptive T cell therapy, chemotherapy and radiotherapy. We also briefly present the limitations and challenges involved in these co-stimulatory agonistic mAb-based combination strategies for melanoma patients.

Extracellular vesicles produced by immunomodulatory cells harboring OX40 ligand and 4-1BB ligand enhance antitumor immunity

Genetically modified tumor cells harboring immunomodulators may be used as therapeutic vaccines to stimulate antitumor immunity. The therapeutic benefit of these tumor vaccines is extensively investigated and mechanisms by which they boost antitumor response may be further explored. Tumor cells are large secretors of extracellular vesicles (EVs). These EVs are able to vehiculate RNA and proteins to target cells, and engineered EVs also vehiculate recombinant proteins. In this study, we explore immunomodulatory properties of EVs derived from antitumor vaccines expressing the TNFSF ligands 4-1BBL and OX40L, modulating immune response mediated by immune cells and eliminating tumors. Our results suggest that the EVs secreted by genetically modified tumor cells harboring TNFSF ligands can induce T cell proliferation, inhibit the transcription factor FoxP3, associated with the maintenance of Treg phenotype, and enhance antitumor activity mediated by immune cells. The immunomodulatory extracellular vesicles have potential to be further engineered for developing new approaches for cancer therapy.

Functional effects of chimeric antigen receptor co-receptor signaling domains in human regulatory T cells

Antigen-specific regulatory T cells (Tregs) engineered with chimeric antigen receptors (CARs) are a potent immunosuppressive cellular therapy in multiple disease models and could overcome shortcomings of polyclonal Treg therapy. CAR therapy was initially developed with conventional T cells, which have different signaling requirements than do Tregs. To date, most of the CAR Treg studies used second-generation CARs, encoding a CD28 or 4-1BB co-receptor signaling domain and CD3ζ, but it was not known if this CAR design was optimal for Tregs. Using a human leukocyte antigen–A2–specific CAR platform and human Tregs, we compared 10 CARs with different co-receptor signaling domains and systematically tested their function and CAR-stimulated gene expression profile. Tregs expressing a CAR encoding CD28wt were markedly superior to all other CARs tested in an in vivo model of graft-versus-host disease. In vitro assays revealed stable expression of Helios and an ability to suppress CD80 expression on dendritic cells as key in vitro predictors of in vivo function. This comprehensive study of CAR signaling domain variants in Tregs can be leveraged to optimize CAR design for use in antigen-specific Treg therapy.

Regulatory T cell therapy: Current and future design perspectives

Regulatory T cells (Tregs) maintain immune equilibrium by suppressing immune responses through various multistep contact dependent and independent mechanisms. Cellular therapy using polyclonal Tregs in transplantation and autoimmune diseases has shown promise in preclinical models and clinical trials. Although novel approaches have been developed to improve specificity and efficacy of antigen specific Treg based therapies, widespread application is currently restricted. To date, design-based approaches to improve the potency and persistence of engineered chimeric antigen receptor (CAR) Tregs are limited. Here, we describe currently available Treg based therapies, their advantages and limitations for implementation in clinical studies. We also examine various strategies for improving CAR T cell design that can potentially be applied to CAR Tregs, such as identifying co-stimulatory signalling domains that enhance suppressive ability, determining optimal scFv affinity/avidity, and co-expression of accessory molecules. Finally, we discuss the importance of tailoring CAR Treg design to suit the individual disease.

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

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

Combination immunotherapy with anti-PD-L1 antibody and depletion of regulatory T cells during acute viral infections results in improved virus control but lethal immunopathology

Combination immunotherapy (CIT) is currently applied as a treatment for different cancers and is proposed as a cure strategy for chronic viral infections. Whether such therapies are efficient during an acute infection remains elusive. To address this, inhibitory receptors were blocked and regulatory T cells depleted in acutely Friend retrovirus-infected mice. CIT resulted in a dramatic expansion of cytotoxic CD4+ and CD8+ T cells and a subsequent reduction in viral loads. Despite limited viral replication, mice developed fatal immunopathology after CIT. The pathology was most severe in the gastrointestinal tract and was mediated by granzyme B producing CD4+ and CD8+ T cells. A similar post-CIT pathology during acute Influenza virus infection of mice was observed, which could be prevented by vaccination. Melanoma patients who developed immune-related adverse events under immune checkpoint CIT also presented with expanded granzyme-expressing CD4+ and CD8+ T cell populations. Our data suggest that acute infections may induce immunopathology in patients treated with CIT, and that effective measures for infection prevention should be applied.

Costimulation Blockade in Transplantation

T cells play a pivotal role in orchestrating immune responses directed against a foreign (allogeneic) graft. For T cells to become fully activated, the T-cell receptor (TCR) must interact with the major histocompatibility complex (MHC) plus peptide complex on antigen-presenting cells (APCs), followed by a second "positive" costimulatory signal. In the absence of this second signal, T cells become anergic or undergo deletion. By blocking positive costimulatory signaling, T-cell allo-responses can be aborted, thus preventing graft rejection and promoting long-term allograft survival and possibly tolerance (Alegre ML, Najafian N, Curr Mol Med 6:843-857, 2006; Li XC, Rothstein DM, Sayegh MH, Immunol Rev 229:271-293, 2009). In addition, costimulatory molecules can provide negative "coinhibitory" signals that inhibit T-cell activation and terminate immune responses; strategies to promote these pathways can also lead to graft tolerance (Boenisch O, Sayegh MH, Najafian N, Curr Opin Organ Transplant 13:373-378, 2008). However, T-cell costimulation involves an incredibly complex array of interactions that may act simultaneously or at different times in the immune response and whose relative importance varies depending on the different T-cell subsets and activation status. In transplantation, the presence of foreign alloantigen incites not only destructive T effector cells but also protective regulatory T cells, the balance of which ultimately determines the fate of the allograft (Lechler RI, Garden OA, Turka LA, Nat Rev Immunol 3:147-158, 2003). Since the processes of alloantigen-specific rejection and regulation both require activation of T cells, costimulatory interactions may have opposing or synergistic roles depending on the cell being targeted. Such complexities present both challenges and opportunities in targeting T-cell costimulatory pathways for therapeutic purposes. In this chapter, we summarize our current knowledge of the various costimulatory pathways in transplantation and review the current state and challenges of harnessing these pathways to promote graft tolerance (summarized in Table 10.1).

Friend retrovirus studies reveal complex interactions between intrinsic, innate and adaptive immunity

Approximately 4.4% of the human genome is comprised of endogenous retroviral sequences, a record of an evolutionary battle between man and retroviruses. Much of what we know about viral immunity comes from studies using mouse models. Experiments using the Friend virus (FV) model have been particularly informative in defining highly complex anti-retroviral mechanisms of the intrinsic, innate and adaptive arms of immunity. FV studies have unraveled fundamental principles about how the immune system controls both acute and chronic viral infections. They led to a more complete understanding of retroviral immunity that begins with cellular sensing, production of type I interferons, and the induction of intrinsic restriction factors. Novel mechanisms have been revealed, which demonstrate that these earliest responses affect not only virus replication, but also subsequent innate and adaptive immunity. This review on FV immunity not only surveys the complex host responses to a retroviral infection from acute infection to chronicity, but also highlights the many feedback mechanisms that regulate and counter-regulate the various arms of the immune system. In addition, the discovery of molecular mechanisms of immunity in this model have led to therapeutic interventions with implications for HIV cure and vaccine development.

Allergen-specific immunotherapy enhances CD8+ CD25+ CD137+ regulatory T cells and decreases nasal nitric oxide

BACKGROUND

4-1BB (CD137), a member of the inducible tumor necrosis factor receptor (TNFR) family, is expressed on regulatory T (Treg) cells and regulates Treg cells to control allergic inflammation. Pam3CSK4, a synthetic TLR2 ligand that can expand CD8⁺ Treg function, is a promising adjuvant for allergen immunotherapy (IT). We examined whether Dermatophagoides pteronyssinus (Der p) IT and Pam3CSK4 could enhance CD8⁺  CD25⁺  CD137⁺ Treg suppressive function to decrease nasal nitric oxide (nNO) levels.

METHODS

Nasal symptom scores, nNO levels, PBMCs, and inferior turbinate biopsies were obtained from 40 mite-sensitive perennial allergic rhinitis (PAR) patients before and after one year of Der p IT and 30 non-allergic control subjects. CD137 expression on CD8⁺  CD25⁺ T cells and suppressive function of CD8⁺  CD25⁺  CD137⁺ Tregs was measured using flow cytometry. Cytokine levels were analyzed by ELISA. Inducible nitric oxide synthase production by nasal epithelial cells after co-culturing with CD8⁺  CD25⁺  CD137⁺ T cells was analyzed by Western blotting.

RESULTS

Der p IT improved nasal symptom scores, decreased nNO levels, and increased CD137 expression on CD8⁺ T cells in PBMCs and nasal mucosa. Pam3CSK4 expanded the CD8⁺  CD25⁺  CD137⁺ population in PBMCs. Pam3CSK4-stimulated CD8⁺  CD25⁺  CD137⁺ Tregs induced IL-10 and TGF-β and suppressed CD4⁺  CD25- T-cell proliferation mainly by cell contact inhibition. CD8⁺  CD25⁺  CD137⁺ Tregs cultured with nasal epithelial cells suppressed Der p 2-induced iNOS production. Silencing CD137 in sorted CD8⁺  CD25⁺ T cells decreased Pam3CSK4-activated Foxp3 expression.

CONCLUSION

Der p IT expanded CD8⁺  CD25⁺  CD137⁺ Tregs and decreased nNO levels. Induced CD137 expression on CD8⁺  CD25⁺ Tregs by Pam3CSK4 stimulation may help suppress allergic inflammation during IT.

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.

Reprogramming the Tumor Microenvironment to Improve Immunotherapy: Emerging Strategies and Combination Therapies

Emerging immunotherapeutic approaches have revolutionized the treatment of multiple malignancies. Immune checkpoint blockers (ICBs) have enabled never-before-seen success rates in durable tumor control and enhanced survival benefit in patients with advanced cancers. However, this effect is not universal, resulting in responder and nonresponder populations not only between, but also within solid tumor types. Although ICBs are thought to be most effective against tumors with more genetic mutations and higher antigen loads, this is not always the case for all cancers or for all patients within a cancer subtype. Furthermore, debilitating and sometimes deadly immune-related adverse events (irAEs) have resulted from aberrant activation of T-cell responses following immunotherapy. Thus, we must identify new ways to overcome resistance to ICB-based immunotherapies and limit irAEs. In fact, preclinical and clinical data have identified abnormalities in the tumor microenvironment (TME) that can thwart the efficacy of immunotherapies such as ICBs. Here, we will discuss how reprogramming various facets of the TME (blood vessels, myeloid cells, and regulatory T cells [Tregs]) may overcome TME-instigated resistance mechanisms to immunotherapy. We will discuss clinical applications of this strategic approach, including the recent successful phase III trial combining bevacizumab with atezolizumab and chemotherapy for metastatic nonsquamous non-small cell lung cancer that led to rapid approval by the U.S. Food and Drug Administration of this regimen for first-line treatment. Given the accelerated testing and approval of ICBs combined with various targeted therapies in larger numbers of patients with cancer, we will discuss how these concepts and approaches can be incorporated into clinical practice to improve immunotherapy outcomes.

Chimeric antigen receptor-engineered regulatory T lymphocytes: promise for immunotherapy of autoimmune disease

Regulatory T lymphocytes (Tregs) exist as natural ideal immunosuppressors in the immune system. Autologous or allogeneic Treg transfusion therapy has been carried out in animal models and humans as a new strategy for treating autoimmune disease. Recent studies have shown that Tregs can be engineered with chimeric antigen receptors to be antigen-specific, which are more effective than polyclonal Tregs with fewer target limitations and a lack of major histocompatibility complex restriction. This review describes the potential for applying chimeric antigen receptor-engineered regulatory T cells in autoimmune diseases.

Single-Cell Lymphocyte Heterogeneity in Advanced Cutaneous T-cell Lymphoma Skin Tumors

PURPOSE

The heterogeneity of tumor cells presents a major challenge to cancer diagnosis and therapy. Cutaneous T-cell lymphomas (CTCL) are a group of T lymphocyte malignancies that primarily affect skin. Lack of highly specific markers for malignant lymphocytes prevents early diagnosis, while only limited treatment options are available for patients with advanced stage CTCL. Droplet-based single-cell transcriptome analysis of CTCL skin biopsies opens avenues for dissecting patient-specific T lymphocyte heterogeneity, providing a basis for identifying specific markers for diagnosis and cure of CTCL.

EXPERIMENTAL DESIGN

Single-cell RNA-sequencing was performed by Droplet-based sequencing (10X Genomics), focusing on 14,056 CD3⁺ lymphocytes (448 cells from normal and 13,608 cells from CTCL skin samples) from skin biopsies of 5 patients with advanced-stage CTCL and 4 healthy donors. Protein expression of identified genes was validated in advanced stage CTCL skin tumors by immunohistochemistry and confocal immunofluorescence microscopy.

RESULTS

Our analysis revealed a large inter- and intratumor gene expression heterogeneity in the T lymphocyte subset, as well as a common gene expression signature in highly proliferating lymphocytes that was validated in multiple advanced-stage skin tumors. In addition, we established the immunologic state of reactive lymphocytes and found heterogeneity in effector and exhaustion programs across patient samples.

CONCLUSIONS

Single-cell analysis of CTCL skin tumor samples reveals patient-specific landscapes of malignant and reactive lymphocytes within the local microenvironment of each tumor, giving an unprecedented view of lymphocyte heterogeneity and identifying tumor-specific molecular signatures, with important implications for diagnosis and personalized disease treatment.

Tumor necrosis factor receptor-2 (TNFR2): an overview of an emerging drug target

INTRODUCTION

Tumor necrosis factor (TNF) receptor 2 (TNFR2) is one of two receptors of the cytokines, TNF and lymphotoxin-α. TNFR1 is a strong inducer of proinflammatory activities. TNFR2 has proinflammatory effects too, but it also elicits strong anti-inflammatory activities and has protective effects on oligodendrocytes, cardiomyocytes, and keratinocytes. The protective and anti-inflammatory effects of TNFR2 may explain why TNF inhibitors failed to be effective in diseases such as heart failure or multiple sclerosis, where TNF has been strongly implicated as a driving force. Stimulatory and inhibitory TNFR2 targeting hence attracts considerable interest for the treatment of autoimmune diseases and cancer. Areas covered: Based on a brief description of the pathophysiological importance of the TNF-TNFR1/2 system, we discuss the potential applications of TNFR2 targeting therapies. We also debate TNFR2 activation as a way forward in the search for TNFR2-specific agents. Expert opinion: The use of TNFR2 to target regulatory T-cells is attractive, but this approach is just one amongst many suitable targets. With respect to its preference for Treg stimulation and protection of non-immune cells, TNFR2 is more unique and thus offers opportunities for translational success.

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

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

CD73 expression on effector T cells sustained by TGF-β facilitates tumor resistance to anti-4-1BB/CD137 therapy

Agonist antibodies (Ab) directed against costimulatory molecules on the surface of antigen-primed T cells are in various stages of pre-clinical and clinical trials, albeit with limited therapeutic benefit as single agents. The underlying mechanisms of action remain incompletely understood. Here, we demonstrate an inhibitory role of ecto-enzyme CD73 for agonistic anti-4-1BB/CD137 Ab therapy. In particular, anti-4-1BB treatment preferentially drives CD73⁻ effector T cell response for tumor inhibition. Anti-CD73 neutralizing Ab further improves anti-4-1BB therapy associated with enhanced anti-tumor T cell immunity. However, the TGF-β-rich tumor milieu confers resistance to anti-4-1BB therapy by sustaining CD73 expression primarily on infiltrating CD8⁺ T cells across several tumor models. TGF-β blockade results in downregulation of CD73 expression on infiltrating T cells and sensitizes resistant tumors to agonistic anti-4-1BB therapy. Thus, our findings identify a mechanism of action for more effective clinical targeting of 4-1BB or likely other costimulatory molecules.

Targeting the immune-stimulatory receptor 4-1BB has only yielded modest benefit in cancer treatment. In this study, the authors show that CD73 expression on effector T cells sustained by TGF-β drives tumor resistance to anti-4-1BB therapy and therefore TGF- β blockade can be used to overcome such resistance.

Reprogramming the Tumor Microenvironment to Improve Immunotherapy: Emerging Strategies and Combination Therapies

Emerging immunotherapeutic approaches have revolutionized the treatment of multiple malignancies. Immune checkpoint blockers (ICBs) have enabled never-before-seen success rates in durable tumor control and enhanced survival benefit in patients with advanced cancers. However, this effect is not universal, resulting in responder and nonresponder populations not only between, but also within solid tumor types. Although ICBs are thought to be most effective against tumors with more genetic mutations and higher antigen loads, this is not always the case for all cancers or for all patients within a cancer subtype. Furthermore, debilitating and sometimes deadly immune-related adverse events (irAEs) have resulted from aberrant activation of T-cell responses following immunotherapy. Thus, we must identify new ways to overcome resistance to ICB-based immunotherapies and limit irAEs. In fact, preclinical and clinical data have identified abnormalities in the tumor microenvironment (TME) that can thwart the efficacy of immunotherapies such as ICBs. Here, we will discuss how reprogramming various facets of the TME (blood vessels, myeloid cells, and regulatory T cells [Tregs]) may overcome TME-instigated resistance mechanisms to immunotherapy. We will discuss clinical applications of this strategic approach, including the recent successful phase III trial combining bevacizumab with atezolizumab and chemotherapy for metastatic nonsquamous non-small cell lung cancer that led to rapid approval by the U.S. Food and Drug Administration of this regimen for first-line treatment. Given the accelerated testing and approval of ICBs combined with various targeted therapies in larger numbers of patients with cancer, we will discuss how these concepts and approaches can be incorporated into clinical practice to improve immunotherapy outcomes.

Regulatory T cells in retroviral infections

Tight regulation of immune responses is not only critical for preventing autoimmune diseases but also for preventing immunopathological damage during infections in which overactive immune responses may be more harmful for the host than the pathogen itself. Regulatory T cells (Tregs) play a critical role in this regulation, which was discovered using the Friend retrovirus (FV) mouse model. Subsequent FV studies revealed basic biological information about Tregs, including their suppressive activity on effector cells as well as the molecular mechanisms of virus-induced Treg expansion. Treg suppression not only limits immunopathology but also prevents complete elimination of pathogens contributing to chronic infections. Therefore, Tregs play a complex role in the pathogenesis of persistent retroviral infections. New therapeutic concepts to reactivate effector T-cell responses in chronic viral infections by manipulating Tregs also came from work with the FV model. This knowledge initiated many studies to characterize the role of Tregs in HIV pathogenesis in humans, where a complex picture is emerging. On one hand, Tregs suppress HIV-specific effector T-cell responses and are themselves targets of infection, but on the other hand, Tregs suppress HIV-induced immune hyperactivation and thus slow the infection of conventional CD4⁺ T cells and limit immunopathology. In this review, the basic findings from the FV mouse model are put into perspective with clinical and basic research from HIV studies. In addition, the few Treg studies performed in the simian immunodeficiency virus (SIV) monkey model will also be discussed. The review provides a comprehensive picture of the diverse role of Tregs in different retroviral infections and possible therapeutic approaches to treat retroviral chronicity and pathogenesis by manipulating Treg responses.

Regulatory T cells (Tregs) play a very complex role in retroviral infections, and the balance of beneficial versus detrimental effects from Tregs can change between the acute and chronic phase of infection. Therefore, the development of therapeutics to treat chronic retroviral infections via modulation of Tregs requires detailed information regarding both the positive and negative contributions of Tregs in a particular phase of a specific infection. Here, we review the molecular mechanisms that initiate and control Treg responses in retroviral infections as well as the target cells that are functionally manipulated by Tregs. Basic findings from the Friend retrovirus mouse model that initiated this area of research are put into perspective with clinical and basic research from HIV studies. The targeted manipulation of Treg responses holds a bright future for enhancing immune responses to infections, vaccine responses, and for cure or functional cure of chronic retroviral infections.

A novel biologic platform elicits profound T cell costimulatory activity and antitumor immunity in mice

Combination immunotherapies utilizing complementary modalities that target distinct tumor attributes or immunosuppressive mechanisms, or engage different arms of the antitumor immune response, can elicit greater therapeutic efficacy than the component monotherapies. Increasing the number of agents included in a therapeutic cocktail can further increase efficacy, however, this approach poses numerous challenges for clinical translation. Here, a novel platform to simplify combination immunotherapy by covalently linking immunotherapeutic agonists to the costimulatory receptors CD134 and CD137 into a single heterodimeric drug, "OrthomAb", is shown. This reagent not only retains costimulatory T cell activity, but also elicits unique T cell functions that are not programmed by either individual agonist, and preferentially expands effector T cells over Tregs. Finally, in an aggressive melanoma model OrthomAb elicits better therapeutic efficacy compared to the unlinked agonists. This demonstration that two drugs can be combined into one provides a framework for distilling complex combination drug cocktails into simpler delivery platforms.

An Immunotherapeutic CD137 Agonist Releases Eomesodermin from ThPOK Repression in CD4 T Cells

Agonists to the TNF/TNFR costimulatory receptors CD134 (OX40) and CD137 (4-1BB) elicit antitumor immunity. Dual costimulation with anti-CD134 plus anti-CD137 is particularly potent because it programs cytotoxic potential in CD8⁺ and CD4⁺ T cells. Cytotoxicity in dual-costimulated CD4 T cells depends on the T-box transcription factor eomesodermin (Eomes), which we report is induced via a mechanism that does not rely on IL-2, in contrast to CD8⁺ CTL, but rather depends on the CD8 T cell lineage commitment transcription factor Runx3, which supports Eomes expression in mature CD8⁺ CTLs. Further, Eomes and Runx3 were indispensable for dual-costimulated CD4 T cells to mediate antitumor activity in an aggressive melanoma model. Runx3 is also known to be expressed in standard CD4 Th1 cells where it fosters IFN-γ expression; however, the CD4 T cell lineage commitment factor ThPOK represses transcription of Eomes and other CD8 lineage genes, such as Cd8a Hence, CD4 T cells can differentiate into Eomes⁺ cytotoxic CD4⁺CD8⁺ double-positive T cells by terminating ThPOK expression. In contrast, dual-costimulated CD4 T cells express Eomes, despite the continued expression of ThPOK and the absence of CD8α, indicating that Eomes is selectively released from ThPOK repression. Finally, although Eomes was induced by CD137 agonist, but not CD134 agonist, administered individually, CD137 agonist failed to induce CD134^-/- CD4 T cells to express Eomes or Runx3, indicating that both costimulatory pathways are required for cytotoxic Th1 programming, even when only CD137 is intentionally engaged with a therapeutic agonist.