Metabolic mechanisms of tumor resistance to T cell effector function

Signaling pathways and targeted therapies in lung squamous cell carcinoma: mechanisms and clinical trials

Lung cancer is the leading cause of cancer-related death across the world. Unlike lung adenocarcinoma, patients with lung squamous cell carcinoma (LSCC) have not benefitted from targeted therapies. Although immunotherapy has significantly improved cancer patients' outcomes, the relatively low response rate and severe adverse events hinder the clinical application of this promising treatment in LSCC. Therefore, it is of vital importance to have a better understanding of the mechanisms underlying the pathogenesis of LSCC as well as the inner connection among different signaling pathways, which will surely provide opportunities for more effective therapeutic interventions for LSCC. In this review, new insights were given about classical signaling pathways which have been proved in other cancer types but not in LSCC, including PI3K signaling pathway, VEGF/VEGFR signaling, and CDK4/6 pathway. Other signaling pathways which may have therapeutic potentials in LSCC were also discussed, including the FGFR1 pathway, EGFR pathway, and KEAP1/NRF2 pathway. Next, chromosome 3q, which harbors two key squamous differentiation markers SOX2 and TP63 is discussed as well as its related potential therapeutic targets. We also provided some progress of LSCC in epigenetic therapies and immune checkpoints blockade (ICB) therapies. Subsequently, we outlined some combination strategies of ICB therapies and other targeted therapies. Finally, prospects and challenges were given related to the exploration and application of novel therapeutic strategies for LSCC.

IL-36β Promotes CD8+ T Cell Activation and Antitumor Immune Responses by Activating mTORC1

Cytokine-amplified functional CD8⁺ T cells ensure effective eradication of tumors. Interleukin 36α (IL-36α), IL-36β, and IL-36γ share the same receptor complex, composed of the IL-36 receptor (IL-36R), and IL-1RAcP. Recently, we revealed that IL-36γ greatly promoted CD8⁺ T cell activation, contributing to antitumor immune responses. However, the underlying mechanism of IL-36-mediated CD8⁺ T cell activation remains understood. In the current study, we proved that IL-36β had the same effect on CD8⁺ T cell as IL-36γ, and uncovered that IL-36β significantly activated mammalian target of rapamycin complex 1 (mTORC1) of CD8⁺ T cells. When mTORC1 was inhibited by rapamycin, IL-36β-stimulated CD8⁺ T cell activation and expansion was drastically downregulated. Further, we elucidated that IL-36β-mediated mTORC1 activation was dependent on the pathway of phosphatidylinositol 3 kinase (PI3K)/Akt, IκB kinase (IKK) and myeloid differentiation factor 88 (MyD88). Inhibition of PI3K or IKK by inhibitor, or deficiency of MyD88, respectively, suppressed mTORC1 signal, causing arrest of CD8⁺ T cell activation. Additionally, it was validated that IL-36β significantly promoted mTORC1 activation and antitumor function of CD8⁺ tumor-infiltrating lymphocytes (TILs) in vivo, resulting in inhibition of tumor growth and prolongation of survival of tumor-bearing mice. Taken together, we substantiated that IL-36β could promote CD8⁺ T cell activation through activating mTORC1 dependent on PI3K/Akt, IKK and MyD88 pathways, leading to enhancement of antitumor immune responses, which laid the foundations for applying IL-36β into tumor immunotherapy.

Filling the Tank: Keeping Antitumor T Cells Metabolically Fit for the Long Haul

Discoveries in tumor immunology and subsequent clinical advances in cancer immunotherapy have revealed that the immune system is not oblivious to tumor progression but heavily interacts with developing neoplasia and malignancy. A major factor preventing immune destruction is the establishment of a highly immunosuppressive tumor microenvironment (TME), which provides architecture to the tumor, supports indirect means of immunosuppression such as the recruitment of tolerogenic cells like regulatory T cells and myeloid-derived suppressor cells (MDSC), and represents a zone of metabolically dearth conditions. T-cell activation and consequent effector function are cellular states characterized by extreme metabolic demands, and activation in the context of insufficient metabolic substrates results in anergy or regulatory differentiation. Thus, T cells must endure both immunosuppression (co-inhibitory molecule ligation, regulatory T cells, and suppressive cytokines) but also a sort of metabolic suppression in the TME. Here I will review the general features of the TME, identify the metabolic demands of activated effector T cells, discuss the known metabolic checkpoints associated with intratumoral T cells, and propose strategies for generating superior antitumor T cells, whether in vitro for adoptive cell therapy or through in vivo reinvigoration of the existing immune response. Cancer Immunol Res; 4(12); 1001-6. ©2016 AACR.

An HIF-1α/VEGF-A Axis in Cytotoxic T Cells Regulates Tumor Progression

Cytotoxic T cells infiltrating tumors are thought to utilize HIF transcription factors during adaptation to the hypoxic tumor microenvironment. Deletion analyses of the two key HIF isoforms found that HIF-1α, but not HIF-2α, was essential for the effector state in CD8⁺ T cells. Furthermore, loss of HIF-1α in CD8⁺ T cells reduced tumor infiltration and tumor cell killing, and altered tumor vascularization. Deletion of VEGF-A, an HIF target gene, in CD8⁺ T cells accelerated tumorigenesis while also altering vascularization. Analyses of human breast cancer showed inverse correlations between VEGF-A expression and CD8⁺ T cell infiltration, and a link between T cell infiltration and vascularization. These data demonstrate that the HIF-1α/VEGF-A axis is an essential aspect of tumor immunity.

Pharmacological Modulation of Proton Channel Hv1 in Cancer Therapy: Future Perspectives

The pharmacological modulation of the immunosuppressive tumor microenvironment has emerged as a relevant component for cancer therapy. Several approaches aiming to deplete innate and adaptive suppressive populations, to circumvent the impairment in antigen presentation, and to ultimately increase the frequency of activated tumor-specific T cells are currently being explored. In this review, we address the potentiality of targeting the voltage-gated proton channel, Hv1, as a novel strategy to modulate the tumor microenvironment. The function of Hv1 in immune cells such as macrophages, neutrophils, dendritic cells, and T cells has been associated with the maintenance of NADPH oxidase activity and the generation of reactive oxygen species, which are required for the host defense against pathogens. We discuss evidence suggesting that the Hv1 proton channel could also be important for the function of these cells within the tumor microenvironment. Furthermore, as summarized here, tumor cells express Hv1 as a primary mechanism to extrude the increased amount of protons generated metabolically, thus maintaining physiologic values for the intracellular pH. Therefore, because this channel might be relevant for both tumor cells and immune cells supporting tumor growth, the pharmacological inhibition of Hv1 could be an innovative approach for cancer therapy. With that focus, we analyzed the available compounds that inhibit Hv1, highlighted the need to develop better drugs suitable for patients, and commented on the future perspectives of targeting Hv1 in the context of cancer therapy.

Metabolic regulation of natural killer cells

Natural killer (NK) cells have key roles in anti-viral and anti-tumour immune responses. Recent research demonstrates that cellular metabolism is an important determinant for the function of pro-inflammatory immune cells, including activated NK cells. The mammalian target of rapamcyin (mTOR) complex 1 (mTORC1) has been identified as a key metabolic regulator that promotes glycolytic metabolism in multiple immune cell subsets. Glycolysis is integrally linked to pro-inflammatory immune responses such that activated NK cells and effector T-cell subsets are reliant on sufficient glucose availability for maximal effector function. This article will discuss the regulation of cellular metabolism in NK cells as compared with that of T lymphocytes and discuss the implications for NK cell responses to viral infection and cancer.

mTORC1-dependent metabolic reprogramming is a prerequisite for NK cell effector function

The mammalian target of rapamycin complex 1 (mTORC1) is a key regulator of cellular metabolism and also has fundamental roles in controlling immune responses. Emerging evidence suggests that these two functions of mTORC1 are integrally linked. However, little is known regarding mTORC1 function in controlling the metabolism and function of NK cells, lymphocytes that play key roles in antiviral and antitumor immunity. This study investigated the hypothesis that mTORC1-controlled metabolism underpins normal NK cell proinflammatory function. We demonstrate that mTORC1 is robustly stimulated in NK cells activated in vivo and in vitro. This mTORC1 activity is required for the production of the key NK cell effector molecules IFN-γ, which is important in delivering antimicrobial and immunoregulatory functions, and granzyme B, a critical component of NK cell cytotoxic granules. The data reveal that NK cells undergo dramatic metabolic reprogramming upon activation, upregulating rates of glucose uptake and glycolysis, and that mTORC1 activity is essential for attaining this elevated glycolytic state. Directly limiting the rate of glycolysis is sufficient to inhibit IFN-γ production and granzyme B expression. This study provides the highly novel insight that mTORC1-mediated metabolic reprogramming of NK cells is a prerequisite for the acquisition of normal effector functions.

Ways to enhance lymphocyte trafficking into tumors and fitness of tumor infiltrating lymphocytes

The tumor is a hostile microenvironment for T lymphocytes. Indeed, irregular blood flow, and endothelial cell (EC) anergy that characterize most solid tumors hamper leukocyte adhesion, extravasation, and infiltration. In addition, hypoxia and reprograming of energy metabolism within cancer cells transform the tumor mass in a harsh environment that limits survival and effector functions of T cells, regardless of being induced in vivo by vaccination or adoptively transferred. In this review, we will summarize on recent advances in our understanding of the characteristics of tumor-associated neo-angiogenic vessels as well as of the tumor metabolism that may impact on T cell trafficking and fitness of tumor infiltrating lymphocytes. In particular, we will focus on how advances in knowledge of the characteristics of tumor ECs have enabled identifying strategies to normalize the tumor-vasculature and/or overcome EC anergy, thus increasing leukocyte-vessel wall interactions and lymphocyte infiltration in tumors. We will also focus on drugs acting on cells and their released molecules to transiently render the tumor microenvironment more suitable for tumor infiltrating T lymphocytes, thus increasing the therapeutic effectiveness of both active and adoptive immunotherapies.

[The systemic evaluation and clinical significance of immunological function for advanced lung cancer patients]

背景与目的

真实评价免疫功能对明确肿瘤的发生发展及给予适时治疗具有重要意义。本研究旨在系统评价晚期肺癌患者免疫功能及意义。

方法

计数晚期肺癌患者和健康人外周血免疫细胞数；用流式细胞仪测定免疫细胞亚群比例和细胞内IL-4、INF-γ及穿孔素、颗粒酶水平；用MTT法评价淋巴细胞对肿瘤细胞株的抑制率及其增殖活性。

结果

晚期肺癌患者组T、B、NK细胞绝对数及亚群比例均显著低于健康组（P < 0.05）；但患者组的调节性T细胞（4.00±1.84）%明显高于健康组（1.27±0.78）%（P < 0.05）。患者组的CD8⁺T细胞中IFN-γ、穿孔素及颗粒酶阳性率均显著低于健康组（P < 0.05）；而IL-4正好相反。患者组的免疫细胞增殖能力、PPD阳性率及对瘤细胞株的抑制率显著低于健康组（P < 0.05）。

结论

晚期肺癌患者免疫功能较健康人明显低下。

Failure at the effector phase: immune barriers at the level of the melanoma tumor microenvironment

The clinical investigation of numerous therapeutic cancer vaccine strategies has resulted in relative disappointment. Whereas a minority of patients have indeed experienced clinical benefit, the majority of patients show disease progression even in cases in which induction of functional tumor antigen-specific T-cell responses as measured in the blood is easily detected. This observation has led to interrogation of the tumor microenvironment for potential mechanisms of tumor resistance to the effector phase of the antitumor T-cell response. Poor chemokine-mediated trafficking of effector cells and the action of negative regulatory pathways that inhibit T-cell function have been identified as key limiting factors. Important negative regulatory pathways include T-cell anergy from insufficient B7 costimulation, extrinsic suppression by regulatory T-cell populations, direct inhibition through inhibitory ligands such as PD-L1, and metabolic dysregulation such as through the activity of indoleamine 2,3-dioxygenase. Recognition of these evasion mechanisms has pointed toward new therapeutic approaches for cancer immunotherapy.

Current approaches in dendritic cell generation and future implications for cancer immunotherapy

The discovery of tumor-associated antigens, which are either selectively or preferentially expressed by tumors, together with an improved insight in dendritic cell biology illustrating their key function in the immune system, have provided a rationale to initiate dendritic cell-based cancer immunotherapy trials. Nevertheless, dendritic cell vaccination is in an early stage, as methods for preparing tumor antigen presenting dendritic cells and improving their immunostimulatory function are continuously being optimized. In addition, recent improvements in immunomonitoring have emphasized the need for careful design of this part of the trials. Still, valuable proofs-of-principle have been obtained, which favor the use of dendritic cells in subsequent, more standardized clinical trials. Here, we review the recent developments in clinical DC generation, antigen loading methods and immunomonitoring approaches for DC-based trials.

Combination of physical activity, nutrition, or other metabolic factors and vaccine response

A number of lifestyle factors that reduce cancer risk in the primary prevention setting may be potential new targets for use in combination with cancer vaccines. This review discusses the modulation of energy balance (physical activity, calorie restriction, and obesity prevention), and the supplementation with natural and synthetic analogs of vitamins A and E, as potential interventions for use in combination with cancer vaccines. Additionally, the pharmacologic manipulation of nutrient metabolism in the tumor microenvironment (e.g., arachidonic acid, arginine, tryptophan, and glucose metabolism) is discussed. This review includes a brief overview of the role of each agent in primary cancer prevention; outlines the effects of these agents on immune function, specifically adaptive and/or anti-tumor immune mechanisms, when known; and discusses the potential use of these interventions in combination with therapeutic cancer vaccines. Modulation of energy balance through exercise and strategies targeting nutrient metabolism in the tumor microenvironment represent the most promising interventions to partner with therapeutic cancer vaccines. Additionally, the use of vitamin E succinate and the retinoid X receptor-directed rexinoids in combination with cancer vaccines offer promise. In summary, a number of energy balance- and nutrition-related interventions are viable candidates for further study in combination with cancer vaccines.

Immune resistance orchestrated by the tumor microenvironment

It is now little disputed that most if not all cancer cells express antigens that can be recognized by specific CD8(+) T lymphocytes. However, a central question in the field of anti-tumor immunity is why such antigen-expressing tumors are not spontaneously eliminated by the immune system. While in some cases, this lack of rejection may be due to immunologic ignorance, induction of anti-tumor T-cell responses in many patients has been detected in the peripheral blood, either spontaneously or in response to vaccination, without accompanying tumor rejection. These observations argue for the importance of barriers downstream from initial T-cell priming that need to be addressed to translate immune responses into clinical tumor regression. Recent data suggest that the proper trafficking of effector T cells into the tumor microenvironment may not always occur. T cells that do effectively home to tumor metastases are often found to be dysfunctional, pointing toward immunosuppressive mechanisms in the tumor microenvironment. T-cell anergy due to insufficient B7 costimulation, extrinsic suppression by regulatory cell populations, inhibition by ligands such as programmed death ligand-1, metabolic dysregulation by enzymes such as indoleamine-2,3-dioxygenase, and the action of soluble inhibitory factors such as transforming growth factor-beta have all been clearly implicated in generating this suppressive microenvironment. Identification of these downstream processes points to new therapeutic targets that should be manipulated to facilitate the effector phase of anti-tumor immune responses in concert with vaccination or T-cell adoptive transfer.

Immune suppression in the tumor microenvironment

The identification of tumor-expressed antigens that can be recognized by specific T lymphocytes has made it possible both to study the properties of T cells participating in anti-tumor immune responses in patients and also to develop antigen-specific immunotherapies as a treatment modality. Interestingly, moves toward intervention have proceeded at a faster pace than have investigations toward understanding. In melanoma in particular, many clinical trials of active immunization have been performed, and many of these have shown increases in tumor antigen-specific T cells circulating in the blood. However, clinical responses have been infrequent, arguing that mechanisms of resistance downstream from initial T cell priming may be dominant in many cases. In fact, may patients show spontaneous generation of immune effector cells and/or antibodies, implying that the priming phase has occurred already in such individuals even without vaccination. Recent attention has turned toward mechanisms of immune evasion at the effector phase of the anti-tumor immune response, predominantly within the tumor microenvironment. Evidence is accumulating that T cell-intrinsic hyporesponsiveness or anergy, extrinsic suppression by regulatory cell populations, inhibitory ligands such as PD-L1, soluble factors such as TGF-beta, and the activity of nutrient-catabolizing enzymes such as indoleamine 2,3-dioxygenase (IDO), may contribute to immune escape in different settings. Murine preclinical models have shown that interfering with each of these processes can translate into T cell-mediated tumor control. Clinical studies to estimate the frequency of specific immune evasion mechanisms in individual patients, to correlate specific events with clinical outcome, and to develop strategies to counter resistance mechanisms should receive a high priority.