GITR Agonism Enhances Cellular Metabolism to Support CD8+ T-cell Proliferation and Effector Cytokine Production in a Mouse Tumor Model

GITR exacerbates lysophosphatidylcholine-induced macrophage pyroptosis in sepsis via posttranslational regulation of NLRP3

The NLRP3 inflammasome functions as an inflammatory driver, but its relationship with lipid metabolic changes in early sepsis remains unclear. Here, we found that GITR expression in monocytes/macrophages was induced by lysophosphatidylcholine (LPC) and was positively correlated with the severity of sepsis. GITR is a costimulatory molecule that is mainly expressed on T cells, but its function in macrophages is largely unknown. Our in vitro data showed that GITR enhanced LPC uptake by macrophages and specifically enhanced NLRP3 inflammasome-mediated macrophage pyroptosis. Furthermore, in vivo studies using either cecal ligation and puncture (CLP) or LPS-induced sepsis models demonstrated that LPC exacerbated sepsis severity/lethality, while conditional knockout of GITR in myeloid cells or NLRP3/caspase-1/IL-1β deficiency attenuated sepsis severity/lethality. Mechanistically, GITR specifically enhanced inflammasome activation by regulating the posttranslational modification (PTM) of NLRP3. GITR competes with NLRP3 for binding to the E3 ligase MARCH7 and recruits MARCH7 to induce deacetylase SIRT2 degradation, leading to decreasing ubiquitination but increasing acetylation of NLRP3. Overall, these findings revealed a novel role of macrophage-derived GITR in regulating the PTM of NLRP3 and systemic inflammatory injury, suggesting that GITR may be a potential therapeutic target for sepsis and other inflammatory diseases. GITR exacerbates LPC-induced macrophage pyroptosis in sepsis via posttranslational regulation of NLRP3. According to the model, LPC levels increase during the early stage of sepsis, inducing GITR expression on macrophages. GITR not only competes with NLRP3 for binding to the E3 ligase MARCH7 but also recruits MARCH7 to induce the degradation of the deacetylase SIRT2, leading to decreasing ubiquitination but increasing acetylation of NLRP3 and therefore exacerbating LPC-induced NLRP3 inflammasome activation, macrophage pyroptosis and systemic inflammatory injury.

Immunometabolism of CD8+ T cell differentiation in cancer

CD8+ cytotoxic T lymphocytes (CTLs) are central mediators of tumor immunity and immunotherapies. Upon tumor antigen recognition, CTLs differentiate from naive/memory-like toward terminally exhausted populations with more limited function against tumors. Such differentiation is regulated by both immune signals, including T cell receptors (TCRs), co-stimulation, and cytokines, and metabolism-associated processes. These immune signals shape the metabolic landscape via signaling, transcriptional and post-transcriptional mechanisms, while metabolic processes in turn exert spatiotemporal effects to modulate the strength and duration of immune signaling. Here, we review the bidirectional regulation between immune signals and metabolic processes, including nutrient uptake and intracellular metabolic pathways, in shaping CTL differentiation and exhaustion. We also discuss the mechanisms underlying how specific nutrient sources and metabolite-mediated signaling events orchestrate CTL biology. Understanding how metabolic programs and their interplay with immune signals instruct CTL differentiation and exhaustion is crucial to uncover tumor-immune interactions and design novel immunotherapies.

Association between Metabolic Reprogramming and Immune Regulation in Digestive Tract Tumors

BACKGROUND

The cancers of the digestive tract, including colorectal cancer (CRC), gastric cancer, and esophageal cancer, are part of the most common cancers as well as one of the most important leading causes of cancer death worldwide.

SUMMARY

Despite the emergence of immune checkpoint inhibitors (e.g., anti-CTLA-4 and anti-PD-1/PD-L1) in the past decade, offering renewed optimism in cancer treatment, only a fraction of patients derive benefit from these therapies. This limited efficacy may stem from tumor heterogeneity and the impact of metabolic reprogramming on both tumor cells and immune cells within the tumor microenvironment (TME). The metabolic reprogramming of glucose, lipids, amino acids, and other nutrients represents a pivotal hallmark of cancer, serving to generate energy, reducing equivalent and biological macromolecule, thereby fostering tumor proliferation and invasion. Significantly, the metabolic reprogramming of tumor cells can orchestrate changes within the TME, rendering patients unresponsive to immunotherapy.

KEY MESSAGES

In this review, we predominantly encapsulate recent strides on metabolic reprogramming among digestive tract cancer, especially CRC, in the TME with a focus on how these alterations influence anti-tumor immunity. Additionally, we deliberate on potential strategies to address these abnormities in metabolic pathways and the viability of combined therapy within the realm of anti-cancer immunotherapy.

The role of radiotherapy in tumor immunity and the potential of PET/CT in detecting the expression of PD-1/PD-L1

Upregulation of PD-1/PD-L1 allows cancer cells to escape from host immune systems by functionally inactivating T-cell immune surveillance. Clinical blockade strategies have resulted in an increased prevalence of patients with late-stage cancers. However, many cancer patients had limited or no response to current immunotherapeutic strategies. Therefore, how to improve the sensitivity of immunotherapy has become the focus of attention of many scholars. Radiotherapy plays a role in the recruitment of T cells in the tumor microenvironment, increases CD4 + and CD8 + T cells, and increases PD-L1 expression, resulting in the synergistically enhanced antitumor effect of irradiation and PD-L1 blockade. Radiotherapy can cause changes in tumor metabolism, especially glucose metabolism. Tumor glycolysis and tumor immune evasion are interdependent, glycolytic activity enhances PD-L1 expression on tumor cells and thus promotes anti-PD-L1 immunotherapy response. Therefore, the mechanism of radiotherapy affecting tumor immunity may be partly through intervention of tumor glucose metabolism. Furthermore, some authors had found that the uptake of 2'-deoxy-2'-[18F]fluoro-D-glucose(18F-FDG) was correlated with PD-1/PD-L1 expression. Positron emission tomography/computed tomography (PET/CT) is a non-invasive detection method for PD-1/PD-L1 expression and has several potential advantages over immunohistochemical (IHC), PET/CT can dynamically reflect the expression of PD-1/PD-L1 inside the tumor and further guide clinical treatment.

CAR-Modified Vγ9Vδ2 T Cells Propagated Using a Novel Bisphosphonate Prodrug for Allogeneic Adoptive Immunotherapy

The benefits of CAR-T therapy could be expanded to the treatment of solid tumors through the use of derived autologous αβ T cell, but clinical trials of CAR-T therapy for patients with solid tumors have so far been disappointing. CAR-T therapy also faces hurdles due to the time and cost intensive preparation of CAR-T cell products derived from patients as such CAR-T cells are often poor in quality and low in quantity. These inadequacies may be mitigated through the use of third-party donor derived CAR-T cell products which have a potent anti-tumor function but a constrained GVHD property. Vγ9Vδ2 TCR have been shown to exhibit potent antitumor activity but not alloreactivity. Therefore, in this study, CAR-T cells were prepared from Vγ9Vδ2 T (CAR-γδ T) cells which were expanded by using a novel prodrug PTA. CAR-γδ T cells suppressed tumor growth in an antigen specific manner but only during a limited time window. Provision of GITR co-stimulation enhanced anti-tumor function of CAR-γδ T cells. Our present results indicate that, while further optimization of CAR-γδ T cells is necessary, the present results demonstrate that Vγ9Vδ2 T cells are potential source of 'off-the-shelf' CAR-T cell products for successful allogeneic adoptive immunotherapy.

Targeting GITR in cancer immunotherapy - there is no perfect knowledge

Glucocorticoid-induced TNFR-related protein (GITR) belongs to the TNFR superfamily (TNFRSF) and stimulates both the acquired and innate immunity. GITR is broadly expressed on immune cells, particularly regulatory T cells (Tregs) and natural killer (NK) cells. Given its potential to promote T effector function and impede Treg immune suppression, GITR is an attractive target for cancer immunotherapy. Preclinically, GITR agonists have demonstrated potent anti-tumor efficacy singly and in combination with a variety of agents, including PD-1 blockade. Multiple GITR agonists have been advanced into the clinic, although the experience with these agents has been disappointing. Recent mechanistic insights into the roles of antibody structure, valency, and Fc functionality in mediating anti-tumor efficacy may explain some of the apparent inconsistency or discordance between preclinical data and observed clinical efficacy.

Lipid metabolism reprogramming of CD8+ T cell and therapeutic implications in cancer

Effector, memory and exhaustion are three phenotypes of CD8⁺ T cell. In tumor microenvironment (TME), metabolism dysfunction of the three should take the blame for immune escape. Against background of CD8⁺ T cell in normal development, multiple determinants in TME, including nutrition competition, PD-1 signals and other cancer- CD8⁺ T cell interaction, cause metabolism reprograming, including failure in energy metabolism and other abnormal lipid metabolism. Further, incompatibility of different CD8⁺ T cell metabolism pattern results in unresponsiveness of immune checkpoint blockade (ICB). Therefore, combination of ICB and drugs aiming at abnormal lipid metabolism provides promising direction to improve cancer therapy.

Interactions of IDO and the Kynurenine Pathway with Cell Transduction Systems and Metabolism at the Inflammation-Cancer Interface

The mechanisms underlying a relationship between inflammation and cancer are unclear, but much emphasis has been placed on the role of tryptophan metabolism to kynurenine and downstream metabolites, as these make a substantial contribution to the regulation of immune tolerance and susceptibility to cancer. The proposed link is supported by the induction of tryptophan metabolism by indoleamine-2,3-dioxygenase (IDO) or tryptophan-2,3-dioxygenase (TDO), in response to injury, infection or stress. This review will summarize the kynurenine pathway and will then focus on the bi-directional interactions with other transduction pathways and cancer-related factors. The kynurenine pathway can interact with and modify activity in many other transduction systems, potentially generating an extended web of effects other than the direct effects of kynurenine and its metabolites. Conversely, the pharmacological targeting of those other systems could greatly enhance the efficacy of changes in the kynurenine pathway. Indeed, manipulating those interacting pathways could affect inflammatory status and tumor development indirectly via the kynurenine pathway, while pharmacological modulation of the kynurenine pathway could indirectly influence anti-cancer protection. While current efforts are progressing to account for the failure of selective IDO1 inhibitors to inhibit tumor growth and to devise means of circumventing the issue, it is clear that there are wider factors involving the relationship between kynurenines and cancer that merit detailed consideration as alternative drug targets.

Modulating Glycolysis to Improve Cancer Therapy

Cancer cells undergo metabolic reprogramming and switch to a 'glycolysis-dominant' metabolic profile to promote their survival and meet their requirements for energy and macromolecules. This phenomenon, also known as the 'Warburg effect,' provides a survival advantage to the cancer cells and make the tumor environment more pro-cancerous. Additionally, the increased glycolytic dependence also promotes chemo/radio resistance. A similar switch to a glycolytic metabolic profile is also shown by the immune cells in the tumor microenvironment, inducing a competition between the cancer cells and the tumor-infiltrating cells over nutrients. Several recent studies have shown that targeting the enhanced glycolysis in cancer cells is a promising strategy to make them more susceptible to treatment with other conventional treatment modalities, including chemotherapy, radiotherapy, hormonal therapy, immunotherapy, and photodynamic therapy. Although several targeting strategies have been developed and several of them are in different stages of pre-clinical and clinical evaluation, there is still a lack of effective strategies to specifically target cancer cell glycolysis to improve treatment efficacy. Herein, we have reviewed our current understanding of the role of metabolic reprogramming in cancer cells and how targeting this phenomenon could be a potential strategy to improve the efficacy of conventional cancer therapy.

Targeting T-cell metabolism to boost immune checkpoint inhibitor therapy

Immune checkpoint inhibitors (ICIs) have shown promising therapeutic effects in the treatment of advanced solid cancers, but their overall response rate is still very low for certain tumor subtypes, limiting their clinical scope. Moreover, the high incidence of drug resistance (including primary and acquired) and adverse effects pose significant challenges to the utilization of these therapies in the clinic. ICIs enhance T cell activation and reverse T cell exhaustion, which is a complex and multifactorial process suggesting that the regulatory mechanisms of ICI therapy are highly heterogeneous. Recently, metabolic reprogramming has emerged as a novel means of reversing T-cell exhaustion in the tumor microenvironment; there is increasing evidence that T cell metabolic disruption limits the therapeutic effect of ICIs. This review focuses on the crosstalk between T-cell metabolic reprogramming and ICI therapeutic efficacy, and summarizes recent strategies to improve drug tolerance and enhance anti-tumor effects by targeting T-cell metabolism alongside ICI therapy. The identification of potential targets for altering T-cell metabolism can significantly contribute to the development of methods to predict therapeutic responsiveness in patients receiving ICI therapy, which are currently unknown but would be of great clinical significance.

Metabolic modulation of immune checkpoints and novel therapeutic strategies in cancer

Cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) or programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1)-based immune checkpoint inhibitors (ICIs) have led to significant improvements in the overall survival of patients with certain cancers and are expected to benefit patients by achieving complete, long-lasting remissions and cure. However, some patients who receive ICIs either fail treatment or eventually develop immunotherapy resistance. The existence of such patients necessitates a deeper understanding of cancer progression, specifically nutrient regulation in the tumor microenvironment (TME), which includes both metabolic cross-talk between metabolites and tumor cells, and intracellular metabolism in immune and cancer cells. Here we review the features and behaviors of the TME and discuss the recently identified major immune checkpoints. We comprehensively and systematically summarize the metabolic modulation of tumor immunity and immune checkpoints in the TME, including glycolysis, amino acid metabolism, lipid metabolism, and other metabolic pathways, and further discuss the potential metabolism-based therapeutic strategies tested in preclinical and clinical settings. These findings will help to determine the existence of a link or crosstalk between tumor metabolism and immunotherapy, which will provide an important insight into cancer treatment and cancer research.

Downregulation of TCF1 in HIV Infection Impairs T-cell Proliferative Capacity by Disrupting Mitochondrial Function

Background

Despite the benefits of antiretroviral therapy (ART) for people with HIV, T-cell dysfunction cannot be fully restored. Metabolic dysregulation is associated with dysfunction of HIV-1-specific T-cells. Exploration of the factors regulating metabolic fitness can help reverse T-cell dysfunction and provide new insights into the underlying mechanism.

Methods

In this study, HIV-infected individuals and HIV-negative control individuals (NCs) were enrolled. T-cell factor (TCF)1 expression in cells was determined by quantitative reverse-transcriptase polymerase chain reaction and flow cytometry. Relevant microarray data from the GEO database were analyzed to explore the underlying mechanism. The effects of TCF1 on T-cell function and metabolic function were assessed in vitro.

Results

TCF7 mRNA expression in peripheral blood mononuclear cells was downregulated in rapid progressors compared with long-term non-progressors individuals and NCs. TCF1 expression on CD4+ and CD8+ T-cells was downregulated in treatment-naïve HIV-infected individuals compared with NCs. Interleukin (IL)2 production and proliferative capacity were impaired in TCF1 knockdown T-cells. Moreover, glycolytic capacity and mitochondrial respiratory function were decreased in TCF1 knockdown T-cells, and depolarized mitochondria were increased in TCF1 knockdown T-cells.

Conclusion

Downregulation of TCF1 in HIV infection impairs T-cell proliferative capacity by disrupting mitochondrial function. These findings highlight the metabolic regulation as a pivotal mechanism of TCF1 in the regulation of T-cell dysfunction.

Combination with Toll-like receptor 4 (TLR4) agonist reverses GITR agonism mediated M2 polarization of macrophage in Hepatocellular carcinoma

The glucocorticoid-induced tumor necrosis factor receptor (GITR) agonistic antibody (DTA-1) has been proved to elicit robust immune response in various kinds of tumors. However, only a few of the HCC patients could benefit from it, and the mechanism of DTA-1 resistance remains unknown. Here, we measured GITR expression in different immunocytes in HCC microenvironment, and we observed that tumor-infiltrating regulatory T cells (Ti-Tregs) significantly expressed GITR, which were associated with poor prognosis. Meanwhile, we analyzed the variation of tumor-infiltrating immune components and associated inflammation response after DTA-1 treatment in orthotopic liver cancer model of mice. Surprisingly, DTA-1 treatment reduced the infiltration of Tregs but failed to activate CD8⁺ T cells and elicit antitumor efficacy. In particular, DTA-1 treatment enforced alternative M2 polarization of macrophage, and macrophage depletion could enhance DTA-1-mediated antitumor efficacy in HCC. Mechanistically, macrophage M2 polarization attributed to the IL-4 elevation induced by Th2 immune activation in the treatment of DTA-1, resulting in DTA-1 resistance. Furthermore, Toll-like receptor 4 (TLR4) agonist could diminish the macrophage (M2) polarization and reverse the M2-mediated DTA-1 resistance, eliciting robust antitumor effect in HCC. Our finding demonstrated that the TLR4 agonist synergized with DTA-1 was a potential strategy for HCC treatment.

Reprogramming the tumor microenvironment by genome editing for precision cancer therapy

The tumor microenvironment (TME) is essential for immune escape by tumor cells. It plays essential roles in tumor development and metastasis. The clinical outcomes of tumors are often closely related to individual differences in the patient TME. Therefore, reprogramming TME cells and their intercellular communication is an attractive and promising strategy for cancer therapy. TME cells consist of immune and nonimmune cells. These cells need to be manipulated precisely and safely to improve cancer therapy. Furthermore, it is encouraging that this field has rapidly developed in recent years with the advent and development of gene editing technologies. In this review, we briefly introduce gene editing technologies and systematically summarize their applications in the TME for precision cancer therapy, including the reprogramming of TME cells and their intercellular communication. TME cell reprogramming can regulate cell differentiation, proliferation, and function. Moreover, reprogramming the intercellular communication of TME cells can optimize immune infiltration and the specific recognition of tumor cells by immune cells. Thus, gene editing will pave the way for further breakthroughs in precision cancer therapy.

New Developments in T Cell Immunometabolism and Implications for Cancer Immunotherapy

Despite rapid advances in the field of immunotherapy, the elimination of established tumors has not been achieved. Many promising new treatments such as adoptive cell therapy (ACT) fall short, primarily due to the loss of T cell effector function or the failure of long-term T cell persistence. With the availability of new tools and advancements in technology, our understanding of metabolic processes has increased enormously in the last decade. Redundancy in metabolic pathways and overlapping targets that could address the plasticity and heterogenous phenotypes of various T cell subsets have illuminated the need for understanding immunometabolism in the context of multiple disease states, including cancer immunology. Herein, we discuss the developing field of T cell immunometabolism and its crucial relevance to improving immunotherapeutic approaches. This in-depth review details the metabolic pathways and preferences of the antitumor immune system and the state of various metabolism-targeting therapeutic approaches.

Metabolic Implications of Immune Checkpoint Proteins in Cancer

Expression of immune checkpoint proteins restrict immunosurveillance in the tumor microenvironment; thus, FDA-approved checkpoint inhibitor drugs, specifically PD-1/PD-L1 and CTLA-4 inhibitors, promote a cytotoxic antitumor immune response. Aside from inflammatory signaling, immune checkpoint proteins invoke metabolic reprogramming that affects immune cell function, autonomous cancer cell bioenergetics, and patient response. Therefore, this review will focus on the metabolic alterations in immune and cancer cells regulated by currently approved immune checkpoint target proteins and the effect of costimulatory receptor signaling on immunometabolism. Additionally, we explore how diet and the microbiome impact immune checkpoint blockade therapy response. The metabolic reprogramming caused by targeting these proteins is essential in understanding immune-related adverse events and therapeutic resistance. This can provide valuable information for potential biomarkers or combination therapy strategies targeting metabolic pathways with immune checkpoint blockade to enhance patient response.

The therapeutic implications of immunosuppressive tumor aerobic glycolysis

In 2011, Hanahan and Weinberg added "Deregulating Cellular Energetics" and "Avoiding Immune Destruction" to the six previous hallmarks of cancer. Since this seminal paper, there has been a growing consensus that these new hallmarks are not mutually exclusive but rather interdependent. The following review summarizes how founding genetic events for tumorigenesis ultimately increase tumor cell glycolysis, which not only supports the metabolic demands of malignancy but also provides an immunoprotective niche, promoting malignant cell proliferation, maintenance and progression. The mechanisms by which altered metabolism contributes to immune impairment are multifactorial: (1) the metabolic demands of proliferating tumor cells and activated immune cells are similar, thus creating a situation where immune cells may be in competition for key nutrients; (2) the metabolic byproducts of aerobic glycolysis directly inhibit antitumor immunity while promoting a regulatory immune phenotype; and (3) the gene programs associated with the upregulation of glycolysis also result in the generation of immunosuppressive cytokines and metabolites. From this perspective, we shed light on important considerations for the development of new classes of agents targeting cancer metabolism. These types of therapies can impair tumor growth but also pose a significant risk of stifling antitumor immunity.

Metabolic Reprogramming in the Tumor Microenvironment With Immunocytes and Immune Checkpoints

Immune checkpoint inhibitors (ICIs), Ipilimumab, Nivolumab, Pembrolizumab and Atezolizumab, have been applied in anti-tumor therapy and demonstrated exciting performance compared to conventional treatments. However, the unsatisfactory response rates, high recurrence and adaptive resistance limit their benefits. Metabolic reprogramming appears to be one of the crucial barriers to immunotherapy. The deprivation of required nutrients and altered metabolites not only promote tumor progression but also confer dysfunction on immune cells in the tumor microenvironment (TME). Glycolysis plays a central role in metabolic reprogramming and immunoregulation in the TME, and many therapies targeting glycolysis have been developed, and their combinations with ICIs are in preclinical and clinical trials. Additional attention has been paid to the role of amino acids, lipids, nucleotides and mitochondrial biogenesis in metabolic reprogramming and clinical anti-tumor therapy. This review attempts to describe reprogramming metabolisms within tumor cells and immune cells, from the aspects of glycolysis, amino acid metabolism, lipid metabolism, nucleotide metabolism and mitochondrial biogenesis and their impact on immunity in the TME, as well as the significance of targeting metabolism in anti-tumor therapy, especially in combination with ICIs. In particular, we highlight the expression mechanism of programmed cell death (ligand) 1 [PD-(L)1] in tumor cells and immune cells under reprogramming metabolism, and discuss in detail the potential of targeting key metabolic pathways to break resistance and improve the efficacy of ICIs based on results from current preclinical and clinical trials. Besides, we draw out biomarkers of potential predictive value in ICIs treatment from a metabolic perspective.

Interplay of Immunometabolism and Epithelial-Mesenchymal Transition in the Tumor Microenvironment

Epithelial–mesenchymal transition (EMT) and metabolic reprogramming in cancer cells are the key hallmarks of tumor metastasis. Since the relationship between the two has been well studied, researchers have gained increasing interest in the interplay of cancer cell EMT and immune metabolic changes. Whether the mutual influences between them could provide novel explanations for immune surveillance during metastasis is worth understanding. Here, we review the role of immunometabolism in the regulatory loop between tumor-infiltrating immune cells and EMT. We also discuss the challenges and perspectives of targeting immunometabolism in cancer treatment.

Metabolic checkpoints and novel approaches for immunotherapy against cancer

While immunotherapy has achieved unprecedented success in conquering cancer, the majority of patients develop primary or acquired resistance to immunotherapy, largely in part due to the complicated metabolic networks in the tumor microenvironment. The microenvironmental metabolic networks are woven by a set of metabolic checkpoints, and accumulating evidence indicates that these metabolic checkpoints orchestrate antitumor immunity and immunotherapy. Metabolic checkpoints can regulate T cell development, differentiation and function, orchestrate metabolic competition between tumor cells and infiltrating T cells, and respond to the metabolic stress imposed on the infiltrating T cells. Furthermore, metabolic checkpoints and pathways can modulate the expression profiles of immune checkpoint receptors and ligands and vice versa. Therefore, repurposing interventions targeting metabolic checkpoints might synergize with immunotherapy, and promising approaches to reprogram the metabolic environment are much more warranted. In this review, we summarize recent researches on the metabolic checkpoints and discuss how these metabolic checkpoints regulate antitumor immunity and the promising approaches to modulate these metabolic checkpoints in the combination therapy. A comprehensive and objective understanding of the metabolic checkpoints might help the research and development of novel approaches to antitumor immunotherapy.

New emerging targets in cancer immunotherapy: the role of GITR

In the last decade, immunotherapies have revolutionised anticancer treatment. However, there is still a number of patients that do not respond or acquire resistance to these treatments. Despite several efforts to combine immunotherapy with other strategies like chemotherapy, or other immunotherapy, there is an 'urgent' need to better understand the immune landscape of the tumour microenvironment. New promising approaches, in addition to blocking co-inhibitory pathways, such those cytotoxic T-lymphocyte-associated protein 4 and programmed cell death protein 1 mediated, consist of activating co-stimulatory pathways to enhance antitumour immune responses. Among several new targets, glucocorticoid-induced TNFR-related gene (GITR) activation can promote effector T-cell function and inhibit regulatory T-cell (Treg) function. Preclinical data on GITR-agonist monoclonal antibodies (mAbs) demonstrated antitumour activity in vitro and in vivo enhancing CD8⁺ and CD4⁺ effector T-cell activity and depleting tumour-infiltrating Tregs. Phase I clinical trials reported a manageable safety profile of GITR mAbs. However, monotherapy seems not to be effective, whereas responses have been reported in combination therapy, in particular adding PD-1 blockade. Several clinical studies are ongoing and results are awaited to further develop GITR-stimulating treatments.

Triple-modality therapy maximizes antitumor immune responses in a mouse model of mesothelioma

Malignant pleural mesothelioma (MPM) is an intractable disease with an extremely poor prognosis. Our clinical protocol for MPM of subablative radiotherapy (RT) followed by radical surgery achieved better survival compared to other multimodal treatments, but local relapse and metastasis remain a problem. This subablative RT elicits an antitumoral immune response that is limited by the immunosuppressive microenvironment generated by regulatory T (T_reg) cells. The antitumor effect of immunotherapy to simultaneously modulate the immune activation and the immune suppression after subablative RT has not been investigated in MPM. Herein, we demonstrated a rationale to combine interleukin-15 (IL-15) superagonist (IL-15SA) and glucocorticoid-induced tumor necrosis factor receptor-related protein (GITR) agonist (DTA-1) with subablative RT in mesothelioma. IL-15SA boosted the systemic expansion of specific antitumoral memory CD8⁺ T cells that were induced by RT in mice. Their effect, however, was limited by the up-regulation and activation of T_reg cells in the radiated tumor microenvironment. Hence, selective depletion of intratumoral T_reg cells through DTA-1 enhanced the benefit of subablative RT in combination with IL-15SA. The addition of surgical resection of the radiated tumor in combination with IL-15SA and DTA-1 maximized the benefit of RT and was accompanied by a reproducible abscopal response in a concomitant tumor model. These data support the development of clinical trials in MPM to test such treatment options for patients with locally advanced or metastatic tumors.

Immunometabolism Modulation in Therapy

The study of cancer biology should be based around a comprehensive vision of the entire tumor ecosystem, considering the functional, bioenergetic and metabolic state of tumor cells and those of their microenvironment, and placing particular importance on immune system cells. Enhanced understanding of the molecular bases that give rise to alterations of pathways related to tumor development can open up new therapeutic intervention opportunities, such as metabolic regulation applied to immunotherapy. This review outlines the role of various oncometabolites and immunometabolites, such as TCA intermediates, in shaping pro/anti-inflammatory activity of immune cells such as MDSCs, T lymphocytes, TAMs and DCs in cancer. We also discuss the extraordinary plasticity of the immune response and its implication in immunotherapy efficacy, and highlight different therapeutic intervention possibilities based on controlling the balanced systems of specific metabolites with antagonistic functions.

The Complex Integration of T-cell Metabolism and Immunotherapy

Immune oncology approaches of adoptive cell therapy and immune checkpoint blockade aim to activate T cells to eliminate tumors. Normal stimulation of resting T cells induces metabolic reprogramming from catabolic and oxidative metabolism to aerobic glycolysis in effector T cells, and back to oxidative metabolism in long-lived memory cells. These metabolic reprogramming events are now appreciated to be essential aspects of T-cell function and fate. Here, we review these transitions, how they are disrupted by T-cell interactions with tumors and the tumor microenvironment, and how they can inform immune oncology to enhance T-cell function against tumors. SIGNIFICANCE: T-cell metabolism plays a central role in T-cell fate yet is altered in cancer in ways that can suppress antitumor immunity. Here, we discuss challenges and opportunities to stimulate effector T-cell metabolism and improve cancer immunotherapy.

Immunometabolism in the Tumor Microenvironment

Advances in immunotherapy have underscored the importance of antitumor immune responses in controlling cancer. However, the tumor microenvironment (TME) imposes several obstacles to the proper function of immune cells, including a metabolically challenging and immunosuppressive microenvironment. The increased metabolic activity of tumor cells can lead to the depletion of key nutrients required by immune cells and the accumulation of byproducts that hamper antitumor immunity. Furthermore, the presence of suppressive immune cells, such as regulatory T cells and myeloid-derived suppressor cells, and the expression of immune inhibitory receptors can negatively impact immune cell metabolism and function. This review summarizes the metabolic reprogramming that is characteristic of various immune cell subsets, discusses how the metabolism and function of immune cells are shaped by the TME, and highlights how therapeutic interventions aimed at improving the metabolic fitness of immune cells and alleviating the metabolic constraints in the TME can boost antitumor immunity.

The Roles of Immunoregulatory Networks in Severe Drug Hypersensitivity

The immunomodulatory effects of regulatory T cells (Tregs) and co-signaling receptors have gained much attention, as they help balance immunogenic and immunotolerant responses that may be disrupted in autoimmune and infectious diseases. Drug hypersensitivity has a myriad of manifestations, which ranges from the mild maculopapular exanthema to the severe Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN), and drug reaction with eosinophilia and systemic symptoms/drug-induced hypersensitivity syndrome (DRESS/DIHS). While studies have identified high-risk human leukocyte antigen (HLA) allotypes, the presence of the HLA allotype at risk is not sufficient to elicit drug hypersensitivity. Recent studies have suggested that insufficient regulation by Tregs may play a role in severe hypersensitivity reactions. Furthermore, immune checkpoint inhibitors, such as anti-CTLA-4 or anti-PD-1, in cancer treatment also induce hypersensitivity reactions including SJS/TEN and DRESS/DIHS. Taken together, mechanisms involving both Tregs as well as coinhibitory and costimulatory receptors may be crucial in the pathogenesis of drug hypersensitivity. In this review, we summarize the currently implicated roles of co-signaling receptors and Tregs in delayed-type drug hypersensitivity in the hope of identifying potential pharmacologic targets.

Role of GLUT-1 in the Upregulation of PD-L1 Expression After Radiotherapy and Association of PD-L1 with Favourable Overall Survival in Hypopharyngeal Cancer

Purpose

The alteration of tumor immunity after radiotherapy (RT) has been widely studied in recent years. However, the mechanism through which RT mediates tumor immunity and the involvement of glycolysis in this mediation in hypopharyngeal cancer remain unclear. This study investigated whether RT regulates programmed cell death ligand 1(PD-L1) partly via glucose transporter 1(GLUT-1) expression and whether PD-L1 expression predicts overall survival (OS) in patients with hypopharyngeal cancer.

Methods

The expression of PD-L1 and Glut-1, and the numbers of CD4+, CD8+ T cells were detected by immunohistochemical analysis on 47 pre-RT and 25 post-RT specimens of hypopharyngeal cancer. Changes in these indicators before and after RT were compared, and their association with the OS of patients was analyzed. Moreover, we used siRNA-GLUT-1 to inhibit GLUT-1 expression and examined whether GLUT-1 was a key factor involved in the mediation of PD-L1 expression by RT in vitro.

Results

In the multivariate analysis, patients with higher PD-L1 expression (p=0.037), higher CD4+ T cell infiltration (p=0.016) and earlier clinical stage (p=0.019) had favourable OS. The expression of PD-L1, and the CD4+ and CD8+ T cells was markedly increased following RT. PD-L1 expression was correlated with Glut-1 pre-RT (p=0.002), but not after RT (p=0.051). The expression of PD-L1 in FaDu cells was upregulated after RT, especially at 96h after RT in vitro. However, the expression of PD-L1 in siRNA-GLUT-1 FaDu cells was markedly decreased at 96h after RT compared with that measured in FaDu cells.

Conclusion

Patients with high PD-L1 expression and CD4+ T cell infiltration may have favourable OS in hypopharyngeal cancer. RT may increase PD-L1 expression and alter tumor immunity. The expression of PD-L1 was correlated with Glut-1, and inhibition of GLUT-1 expression may decrease the expression of PD-L1. GLUT-1 may participate in the alteration of tumor immunity after RT.

Metabolic Consequences of T-cell Costimulation in Anticancer Immunity

T-cell functional behavior and performance are closely regulated by nutrient availability and the control of metabolism within the T cell. T cells have distinct energetic and anabolic needs when nascently activated, actively proliferating, in naïveté, or in a resting, memory state. As a consequence, bioenergetics are key for T cells to mount adequate immune responses in health and disease. Solid tumors are particularly hostile metabolic environments, characterized by low glucose concentration, hypoxia, and low pH. These metabolic conditions in the tumor are known to hinder antitumor immune responses of T cells by limiting nutrient availability and energetic efficiency. In such immunosuppressive environments, artificial modulation of glycolysis, mitochondrial respiratory capabilities, and fatty acid β-oxidation are known to enhance antitumor performance. Reportedly, costimulatory molecules, such as CD28 and CD137, are important regulators of metabolic routes in T cells. In this sense, different costimulatory signals and cytokines induce diverse metabolic changes that critically involve mitochondrial mass and function. For instance, the efficacy of chimeric antigen receptors (CAR) encompassing costimulatory domains, agonist antibodies to costimulatory receptors, and checkpoint inhibitors depends on the associated metabolic events in immune cells. Here, we review the metabolic changes that costimulatory receptors can promote in T cells and the potential consequences for cancer immunotherapy. Our focus is mostly on discoveries regarding the physiology and pharmacology of IL15, CD28, PD-1, and CD137 (4-1BB).

Metabolism of immune cells in cancer

Through the successes of checkpoint blockade and adoptive cellular therapy, immunotherapy has become an established treatment modality for cancer. Cellular metabolism has emerged as a critical determinant of the viability and function of both cancer cells and immune cells. In order to sustain prodigious anabolic needs, tumours employ a specialized metabolism that differs from untransformed somatic cells. This metabolism leads to a tumour microenvironment that is commonly acidic, hypoxic and/or depleted of critical nutrients required by immune cells. In this context, tumour metabolism itself is a checkpoint that can limit immune-mediated tumour destruction. Because our understanding of immune cell metabolism and cancer metabolism has grown significantly in the past decade, we are on the cusp of being able to unravel the interaction of cancer cell metabolism and immune metabolism in therapeutically meaningful ways. Although there are metabolic processes that are seemingly fundamental to both cancer and responding immune cells, metabolic heterogeneity and plasticity may serve to distinguish the two. As such, understanding the differential metabolic requirements of the diverse cells that comprise an immune response to cancer offers an opportunity to selectively regulate immune cell function. Such a nuanced evaluation of cancer and immune metabolism can uncover metabolic vulnerabilities and therapeutic windows upon which to intervene for enhanced immunotherapy.

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.

Co-Stimulatory Receptors in Cancers and Their Implications for Cancer Immunotherapy

Immune checkpoint inhibitors (ICIs), including anti-PD-1 and anti-CTLA-4 therapeutic agents, are now approved by the Food and Drug Administration for treatment of various types of cancer. However, the therapeutic efficacy of ICIs varies among patients and cancer types. Moreover, most patients do not develop durable antitumor responses after ICI therapy due to an ephemeral reversal of T-cell dysfunction. As co-stimulatory receptors play key roles in regulating the effector functions of T cells, activating co-stimulatory pathways may improve checkpoint inhibition efficacy, and lead to durable antitumor responses. Here, we review recent advances in our understating of co-stimulatory receptors in cancers, providing the necessary groundwork for the rational design of cancer immunotherapy.

Immunometabolism and Its Potential to Improve the Current Limitations of Immunotherapy

The last century of research in tumor immunology has culminated in the advent of immunotherapy, most notably immune checkpoint inhibitors. These drugs have shown encouraging results across a multitude of malignancies and have shifted the paradigm of cancer treatment. However, no more than 40% of patients treated with these immune checkpoint blockade inhibitors respond. Thus, resistance is a barrier to therapy that remains poorly understood. All cells require energy and biosynthetic precursors for survival, growth, and functioning, where multiple metabolic pathways allow for flexibility in how nutrients are utilized. A defining hallmark of many cancers is altered cellular metabolism, creating an imbalanced demand for nutrients within the tumor microenvironment. Immunometabolism is increasingly understood to be vital to the functions and phenotypes of a myriad of immune cell subsets. In tumors, the high demand for nutrients by the tumor drives competition between tumor cells and infiltrating immune cells, culminating in dysfunctional immune responses. This chapter discusses the recent successes in cancer immunotherapy and highlights challenges to therapy. We also outline the major metabolic processes involved in the generation of an immune response, how this can become dysregulated in the context of the tumor microenvironment, and how this contributes to resistance to immunotherapy. Finally, we explore the potential for targeting immunometabolic pathways to improve immunotherapy, and examine current trials targeting various aspects of metabolism in an attempt to improve the outcomes from immunotherapy.

Peritumoral administration of DRibbles-pulsed antigen-presenting cells enhances the antitumor efficacy of anti-GITR and anti-PD-1 antibodies via an antigen presenting independent mechanism

Background

TNF receptor family agonists and checkpoint blockade combination therapies lead to minimal tumor clearance of poorly immunogenic tumors. Therefore, a need to enhance the efficacy of this combination therapy arises. Antigen-presenting cells (APCs) present antigen to T cells and steer the immune response through chemokine and cytokine secretion. DRibbles (DR) are tumor-derived autophagosomes containing tumor antigens and innate inflammatory adjuvants.

Methods

Using preclinical murine lung and pancreatic cancer models, we assessed the triple combination therapy of GITR agonist and PD-1 blocking antibodies with peritumoral injections of DRibbles-pulsed-bone marrow cells (BMCs), which consisted mainly of APCs, or CD103+ cross-presenting dendritic cells (DCs). Immune responses were assessed by flow cytometry. FTY720 was used to prevent T-cell egress from lymph nodes to assess lymph node involvement, and MHC-mismatched-BMCs were used to assess the necessity of antigen presentation by the peritumorally-injected DR-APCs.

Results

Tritherapy increased survival and cures in tumor-bearing mice compared to combined antibody therapy or peritumoral DR-BMCs alone. Peritumorally-injected BMCs remained within the tumor for at least 14 days and tritherapy efficacy was dependent on both CD4+ and CD8+ T cells. Although the overall percent of tumor-infiltrating T cells remained similar, tritherapy increased the ratio of effector CD4+ T cells-to-regulatory T cells, CD4+ T-cell cytokine production and proliferation, and CD8+ T-cell cytolytic activity in the tumor. Despite tritherapy-induced T-cell activation and cytolytic activity in lymph nodes, this T-cell activation was not required for tumor regression and enhanced survival. Replacement of DR-BMCs with DR-pulsed-DCs in the tritherapy led to similar antitumor effects, whereas replacement with DRibbles was less effective but delayed tumor growth. Interestingly, peritumoral administration of DR-pulsed MHC-mismatched-APCs in the tritherapy led to similar antitumor effects as MHC-matched-APCs, indicating that the observed enhanced antitumor effect was mediated independently of antigen presentation by the administered APCs.

Conclusions

Overall, these results demonstrate that peritumoral DR-pulsed-BMC/DC administration synergizes with GITR agonist and PD-1 blockade to locally modulate and sustain tumor effector T-cell responses independently of T cell priming and perhaps through innate inflammatory modulations mediated by the DRibbles adjuvant. We offer a unique approach to modify the tumor microenvironment to benefit T-cell-targeted immunotherapies.

Latest Advances in Targeting the Tumor Microenvironment for Tumor Suppression

The tumor bulk is composed of a highly heterogeneous population of cancer cells, as well as a large variety of resident and infiltrating host cells, extracellular matrix proteins, and secreted proteins, collectively known as the tumor microenvironment (TME). The TME is essential for driving tumor development by promoting cancer cell survival, migration, metastasis, chemoresistance, and the ability to evade the immune system responses. Therapeutically targeting tumor-associated macrophages (TAMs), cancer-associated fibroblasts (CAFs), regulatory T-cells (T-regs), and mesenchymal stromal/stem cells (MSCs) is likely to have an impact in cancer treatment. In this review, we focus on describing the normal physiological functions of each of these cell types and their behavior in the cancer setting. Relying on the specific surface markers and secreted molecules in this context, we review the potential targeting of these cells inducing their depletion, reprogramming, or differentiation, or inhibiting their pro-tumor functions or recruitment. Different approaches were developed for this targeting, namely, immunotherapies, vaccines, small interfering RNA, or small molecules.

Immunity, Hypoxia, and Metabolism-the Ménage à Trois of Cancer: Implications for Immunotherapy

It is generally accepted that metabolism is able to shape the immune response. Only recently we are gaining awareness that the metabolic crosstalk between different tumor compartments strongly contributes to the harsh tumor microenvironment (TME) and ultimately impairs immune cell fitness and effector functions. The major aims of this review are to provide an overview on the immune system in cancer; to position oxygen shortage and metabolic competition as the ground of a restrictive TME and as important players in the anti-tumor immune response; to define how immunotherapies affect hypoxia/oxygen delivery and the metabolic landscape of the tumor; and vice versa, how oxygen and metabolites within the TME impinge on the success of immunotherapies. By analyzing preclinical and clinical endeavors, we will discuss how a metabolic characterization of the TME can identify novel targets and signatures that could be exploited in combination with standard immunotherapies and can help to predict the benefit of new and traditional immunotherapeutic drugs.

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.

Treg programming and therapeutic reprogramming in cancer

Overcoming the immunosuppressive tumour microenvironment is the major challenge impeding cancer immunotherapy today. Regulatory T-cells (Tregs) are prevalent in nearly all cancers and, as immunosuppressive regulators of immune responses, they are the principal opponents of cancer immunotherapy. However, disabling Tregs systemically causes severe autoimmune toxicity, hastening the need for more selective methods to target intratumoural Tregs. In this review, we discuss a burgeoning new modality to specifically target tumour-infiltrating Tregs (TI-Tregs) by reprogramming their functionality from immunosuppressive to immune stimulatory within tumours. As the basis for therapeutic selectivity of TI-Tregs, we will focus on the defining features of Tregs within cancer: their highly activated state controlled by the engagement of key surface receptors, their distinct metabolic programme, and their unique transcriptional programme. By identifying proteins and pathways that distinguish TI-Tregs from other Tregs in the body, as well as from the beneficial antitumour effector T-cells within tumours, we highlight mechanisms to selectively reprogramme TI-Tregs for the treatment of cancer.