Phenotypic switch of CD8(+) T cells reactivated under hypoxia toward IL-10 secreting, poorly proliferative effector cells

Harnessing CD8+ T cell dynamics in hepatitis B virus-associated liver diseases: Insights, therapies and future directions

Hepatitis B virus (HBV) infection playsa significant role in the etiology and progression of liver-relatedpathologies, encompassing chronic hepatitis, fibrosis, cirrhosis, and eventual hepatocellularcarcinoma (HCC). Notably, HBV infection stands as the primary etiologicalfactor driving the development of HCC. Given the significant contribution ofHBV infection to liver diseases, a comprehensive understanding of immunedynamics in the liver microenvironment, spanning chronic HBV infection,fibrosis, cirrhosis, and HCC, is essential. In this review, we focused on thefunctional alterations of CD8+ T cells within the pathogenic livermicroenvironment from HBV infection to HCC. We thoroughly reviewed the roles ofhypoxia, acidic pH, metabolic reprogramming, amino acid deficiency, inhibitory checkpointmolecules, immunosuppressive cytokines, and the gut-liver communication in shapingthe dysfunction of CD8+ T cells in the liver microenvironment. Thesefactors significantly impact the clinical prognosis. Furthermore, we comprehensivelyreviewed CD8+ T cell-based therapy strategies for liver diseases,encompassing HBV infection, fibrosis, cirrhosis, and HCC. Strategies includeimmune checkpoint blockades, metabolic T-cell targeting therapy, therapeuticT-cell vaccination, and adoptive transfer of genetically engineered CD8+ T cells, along with the combined usage of programmed cell death protein-1/programmeddeath ligand-1 (PD-1/PD-L1) inhibitors with mitochondria-targeted antioxidants.Given that targeting CD8+ T cells at various stages of hepatitis Bvirus-induced hepatocellular carcinoma (HBV + HCC) shows promise, we reviewedthe ongoing need for research to elucidate the complex interplay between CD8+ T cells and the liver microenvironment in the progression of HBV infection toHCC. We also discussed personalized treatment regimens, combining therapeuticstrategies and harnessing gut microbiota modulation, which holds potential forenhanced clinical benefits. In conclusion, this review delves into the immunedynamics of CD8+ T cells, microenvironment changes, and therapeuticstrategies within the liver during chronic HBV infection, HCC progression, andrelated liver diseases.

The cellular-centered view of hypoxia tumor microenvironment: Molecular mechanisms and therapeutic interventions

Cancer is a profoundly dynamic, heterogeneous and aggressive systemic ailment, with a coordinated evolution of various types of tumor niches. Hypoxia plays an indispensable role in the tumor micro-ecosystem, drastically enhancing the plasticity of cancer cells, fibroblasts and immune cells and orchestrating intercellular communication. Hypoxia-induced signals, particularly hypoxia-inducible factor-1α (HIF-1α), drive the reprogramming of genetic, transcriptional, and proteomic profiles. This leads to a spectrum of interconnected processes, including augmented survival of cancer cells, evasion of immune surveillance, metabolic reprogramming, remodeling of the extracellular matrix, and the development of resistance to conventional therapeutic modalities like radiotherapy and chemotherapy. Here, we summarize the latest research on the multifaceted effects of hypoxia, where a multitude of cellular and non-cellular elements crosstalk with each other and co-evolve in a synergistic manner. Additionally, we investigate therapeutic approaches targeting hypoxic niche, encompassing hypoxia-activated prodrugs, HIF inhibitors, nanomedicines, and combination therapies. Finally, we discuss some of the issues to be addressed and highlight the potential of emerging technologies in the treatment of cancer.

Intestinal tissue-resident memory T cells maintain distinct identity from circulating memory T cells after in vitro restimulation

Resident memory T (TRM) cells have been recently established as an important subset of memory T cells that provide early and essential protection against reinfection in the absence of circulating memory T cells. Recent findings showing that TRM expand in vivo after repeated antigenic stimulation indicate that these memory T cells are not terminally differentiated. This suggests an opportunity for in vitro TRM expansion to apply in an immunotherapy setting. However, it has also been shown that TRM may not maintain their identity and form circulating memory T cells after in vivo restimulation. Therefore, we set out to determine how TRM respond to antigenic activation in culture. Using Listeria monocytogenes and LCMV infection models, we found that TRM from the intraepithelial compartment of the small intestine expand in vitro after antigenic stimulation and subsequent resting in homeostatic cytokines. A large fraction of the expanded TRM retained their phenotype, including the expression of key TRM markers CD69 and CD103 (ITGAE). The optimal culture of TRM required low O2 pressure to maintain the expression of these and other TRM-associated molecules. Expanded TRM retained their effector capacity to produce cytokines after restimulation, but did not acquire a highly glycolytic profile indicative of effector T cells. The proteomic analysis confirmed TRM profile retention, including expression of TRM-related transcription factors, tissue retention factors, adhesion molecules, and enzymes involved in fatty acid metabolism. Collectively, our data indicate that limiting oxygen conditions supports in vitro expansion of TRM cells that maintain their TRM phenotype, at least in part, suggesting an opportunity for therapeutic strategies that require in vitro expansion of TRM.

A framework of transient hypercapnia to achieve an increased cerebral blood flow induced by nasal breathing during aerobic exercise

During exercise, cerebral blood flow (CBF) is expected to only increase to a maximal volume up to a moderate intensity aerobic effort, suggesting that CBF is expected to decline past 70 % of a maximal aerobic effort. Increasing CBF during exercise permits an increased cerebral metabolic activity that stimulates neuroplasticity and other key processes of cerebral adaptations that ultimately improve cognitive health. Recent work has focused on utilizing gas-induced exposure to intermittent hypoxia during aerobic exercise to maximize the improvements in cognitive function compared to those seen under normoxic conditions. However, it is postulated that exercising by isolating breathing only to the nasal route may provide a similar effect by stimulating a transient hypercapnic condition that is non-gas dependent. Because nasal breathing prevents hyperventilation during exercise, it promotes an increase in the partial arterial pressure of CO2. The rise in systemic CO2 stimulates hypercapnia and permits the upregulation of hypoxia-related genes. In addition, the rise in systemic CO2 stimulates cerebral vasodilation, promoting a greater increase in CBF than seen during normoxic conditions. While more research is warranted, nasal breathing might also promote benefits related to improved sleep, greater immunity, and body fat loss. Altogether, this narrative review presents a theoretical framework by which exercise-induced hypercapnia by utilizing nasal breathing during moderate-intensity aerobic exercise may promote greater health adaptations and cognitive improvements than utilizing oronasal breathing.

The multifaceted nature of IL-10: regulation, role in immunological homeostasis and its relevance to cancer, COVID-19 and post-COVID conditions

Interleukin-10 (IL-10) is a pleiotropic cytokine that has a fundamental role in modulating inflammation and in maintaining cell homeostasis. It primarily acts as an anti-inflammatory cytokine, protecting the body from an uncontrolled immune response, mostly through the Jak1/Tyk2 and STAT3 signaling pathway. On the other hand, IL-10 can also have immunostimulating functions under certain conditions. Given the pivotal role of IL-10 in immune modulation, this cytokine could have relevant implications in pathologies characterized by hyperinflammatory state, such as cancer, or infectious diseases as in the case of COVID-19 and Post-COVID-19 syndrome. Recent evidence proposed IL-10 as a predictor of severity and mortality for patients with acute or post-acute SARS-CoV-2 infection. In this context, IL-10 can act as an endogenous danger signal, released by tissues undergoing damage in an attempt to protect the organism from harmful hyperinflammation. Pharmacological strategies aimed to potentiate or restore IL-10 immunomodulatory action may represent novel promising avenues to counteract cytokine storm arising from hyperinflammation and effectively mitigate severe complications. Natural bioactive compounds, derived from terrestrial or marine photosynthetic organisms and able to increase IL-10 expression, could represent a useful prevention strategy to curb inflammation through IL-10 elevation and will be discussed here. However, the multifaceted nature of IL-10 has to be taken into account in the attempts to modulate its levels.

Hypoxia induces dichotomous and reversible attenuation of T cell responses through reactive oxygen species-dependent phenotype redistribution and delay in lymphoblast proliferation

As T cells transit between blood, lymphoid organs, and peripheral tissues, they experience varied levels of oxygen/hypoxia in inflamed tissues, skin, intestinal lining, and secondary lymphoid organs. Critical illness among COVID-19 patients is also associated with transient hypoxia and attenuation of T cell responses. Hypoxia is the fulcrum of altered metabolism, impaired functions, and cessation of growth of a subset of T cells. However, the restoration of normal T cell functions following transient hypoxia and kinetics of their phenotype-redistribution is not completely understood. Here, we sought to understand kinetics and reversibility of dichotomous T cell responses under sustained and transient hypoxia. We found that a subset of activated T cells accumulated as lymphoblasts under hypoxia. Further, T cells showed the normal expression of activation markers CD25 and CD69 and inflammatory cytokine secretion but a subset exhibited delayed cell proliferation under hypoxia. Increased levels of reactive oxygen species (ROS) in cytosol and mitochondria were seen during dichotomous and reversible attenuation of T cell response under hypoxia. Cell cycle analysis revealed maximum levels of cytosolic and mitochondrial ROS in dividing T cells (in S, G2, or M phase). Hypoxic T cells also showed specific attenuation of activation induced memory phenotype conversion without affecting naïve and activated T cells. Hypoxia-related attenuation of T cell proliferation was also found to be reversible in an allogeneic leukocyte specific mixed lymphocyte reaction assay. In summary, our results show that hypoxia induces a reversible delay in proliferation of a subset of T cells which is associated with obliteration of memory phenotype and specific increase in cytosolic/mitochondrial ROS levels in actively dividing subpopulation. Thus, the transient reoxygenation of hypoxic patients may restore normal T cell responses.

Phenotype switching in a global method for agent-based models of biological tissue

Agent-based models (ABMs) are an increasingly important tool for understanding the complexities presented by phenotypic and spatial heterogeneity in biological tissue. The resolution a modeler can achieve in these regards is unrivaled by other approaches. However, this comes at a steep computational cost limiting either the scale of such models or the ability to explore, parameterize, analyze, and apply them. When the models involve molecular-level dynamics, especially cell-specific dynamics, the limitations are compounded. We have developed a global method for solving these computationally expensive dynamics significantly decreases the computational time without altering the behavior of the system. Here, we extend this method to the case where cells can switch phenotypes in response to signals in the microenvironment. We find that the global method in this context preserves the temporal population dynamics and the spatial arrangements of the cells while requiring markedly less simulation time. We thus add a tool for efficiently simulating ABMs that captures key facets of the molecular and cellular dynamics in heterogeneous tissue.

Memory CD8+ T cells upregulate glycolysis and effector functions under limiting oxygen conditions

Memory CD8⁺ T cells are indispensable for maintaining long-term immunity against intracellular pathogens and tumors. Despite their presence at oxygen-deprived infected tissue sites or in tumors, the impact of local oxygen pressure on memory CD8⁺ T cells remains largely unclear. We sought to elucidate how oxygen pressure impacts memory CD8⁺ T cells arising after infection with Listeria monocytogenes-OVA. Our data revealed that reduced oxygen pressure during in vitro culture switched CD8⁺ T cell metabolism from oxidative phosphorylation to a glycolytic phenotype. Quantitative proteomic analysis showed that limiting oxygen conditions increased the expression of glucose transporters and components of the glycolytic pathway, while decreasing TCA cycle and mitochondrial respiratory chain proteins. The altered CD8⁺ T cell metabolism did not affect the expansion potential, but enhanced the granzyme B and IFN-γ production capacity. In vivo, memory CD8⁺ T cells cultured under low oxygen pressure provided protection against bacterial rechallenge. Taken together, our study indicates that strategies of cellular immune therapy may benefit from reducing oxygen during culture to develop memory CD8⁺ T cells with superior effector functions.

Metabolic Regulation of CD8+ T Cells: From Mechanism to Therapy

Significance: Cancer immunotherapy has yielded striking antitumor effects in many cancers, yet the proportion of benefited patients is still limited. As key mediators of tumor suppression, CD8⁺ T cells are crucial for cancer immunotherapy. It has been widely appreciated that the modulation of CD8⁺ T cell immunity could be an effective way to further improve the therapeutic benefit of immunotherapy. Recent Advances: Emerging evidence has underlined a close link between metabolism and immune functions, providing a metabolism-immune axis that is increasingly investigated for understanding CD8⁺ T cell regulation. On the other hand, growing findings have reported that tumors adopt multiple approaches to induce metabolic reprogramming of CD8⁺ T cells, leading to compromised immunotherapy. Critical Issues: CD8⁺ T cell metabolism in the tumor microenvironment (TME) is often adapted to diminish antitumor immune responses and thereby evade from immune surveillance. A better understanding of metabolic regulation of CD8⁺ T cells in the TME is believed to hold promise for opening a new therapeutic window to further improve the benefit of immunotherapy. We herein review the mechanistic understanding of how CD8⁺ T cell metabolism is reprogrammed in the TME, mainly focusing on the impact of nutrient availability and bioactive molecules secreted by surrounding cells. Future Directions: Future research should pay attention to tumor heterogeneity in the metabolic microenvironment and associated immune responses. It is also important to include the trending opinion of "precision medicine" in cancer immunotherapies to tailor metabolic interventions for individual patients in combination with immunotherapy treatments. Antioxid. Redox Signal. 37, 1234-1253.

Effects of hypoxia on antigen presentation and T cell-based immune recognition of HPV16-transformed cells

Attempts to develop a therapeutic vaccine against human papillomavirus (HPV)-induced malignancies have mostly not been clinically successful to date. One reason may be the hypoxic microenvironment present in most tumors, including cervical cancer. Hypoxia dysregulates the levels of human leukocyte antigen (HLA) class I molecules in different tumor entities, impacts the function of cytotoxic T cells, and leads to decreased protein levels of the oncoproteins E6 and E7 in HPV-transformed cells. Therefore, we investigated the effect of hypoxia on the presentation of HPV16 E6- and E7-derived epitopes in cervical cancer cells and its effect on epitope-specific T cell cytotoxicity. Hypoxia induced downregulation of E7 protein levels in all analyzed cell lines, as assessed by Western blotting. However, contrary to previous reports, no perturbation of antigen processing and presentation machinery (APM) components and HLA-A2 surface expression upon hypoxia treatment was detected by mass spectrometry and flow cytometry, respectively. Cytotoxicity assays performed in hypoxic conditions showed differential effects on the specific killing of HPV16-positive cervical cancer cells by epitope-specific CD8+ T cell lines in a donor- and peptide-specific manner. Effects of hypoxia on the expression of PD-L1 were ruled out by flow cytometry analysis. Altogether, our results under hypoxia show a decreased expression of E6 and E7, but an intact APM, and epitope- and donor-dependent effects on T cell cytotoxicity towards HPV16-positive target cells. This suggests that successful immunotherapies can be developed for hypoxic HPV-induced cervical cancer, with careful choice of target epitopes, and ideally in combination with hypoxia-alleviating measures.

Conducive target range of breast cancer: Hypoxic tumor microenvironment

Breast cancer is a kind of malignant tumor disease that poses a serious threat to human health. Its biological characteristics of rapid proliferation and delayed angiogenesis, lead to intratumoral hypoxia as a common finding in breast cancer. HIF as a transcription factor, mediate a series of reactions in the hypoxic microenvironment, including metabolic reprogramming, tumor angiogenesis, tumor cell proliferation and metastasis and other important physiological and pathological processes, as well as gene instability under hypoxia. In addition, in the immune microenvironment of hypoxia, both innate and acquired immunity of tumor cells undergo subtle changes to support tumor and inhibit immune activity. Thus, the elucidation of tumor microenvironment hypoxia provides a promising target for the resistance and limited efficacy of current breast cancer therapies. We also summarize the hypoxic mechanisms of breast cancer treatment related drug resistance, as well as the current status and prospects of latest related drugs targeted HIF inhibitors.

Hypoxia Is a Dominant Remodeler of the Effector T Cell Surface Proteome Relative to Activation and Regulatory T Cell Suppression

Immunosuppressive factors in the tumor microenvironment (TME) impair T cell function and limit the antitumor immune response. T cell surface receptors and surface proteins that influence interactions and function in the TME are proven targets for cancer immunotherapy. However, how the entire surface proteome remodels in primary human T cells in response to specific suppressive factors in the TME remains to be broadly and systematically characterized. Here, using a reductionist cell culture approach with primary human T cells and stable isotopic labeling with amino acids in cell culture–based quantitative cell surface capture glycoproteomics, we examined how two immunosuppressive TME factors, regulatory T cells (Tregs) and hypoxia, globally affect the activated CD8⁺ surface proteome (surfaceome). Surprisingly, coculturing primary CD8⁺ T cells with Tregs only modestly affected the CD8⁺ surfaceome but did partially reverse activation-induced surfaceomic changes. In contrast, hypoxia drastically altered the CD8⁺ surfaceome in a manner consistent with both metabolic reprogramming and induction of an immunosuppressed state. The CD4⁺ T cell surfaceome similarly responded to hypoxia, revealing a common hypoxia-induced surface receptor program. Our surfaceomics findings suggest that hypoxic environments create a challenge for T cell activation. These studies provide global insight into how Tregs and hypoxia remodel the T cell surfaceome and we believe represent a valuable resource to inform future therapeutic efforts to enhance T cell function.

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Quantitative surface proteomics of primary human T cells

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Activation, regulatory T cells, and hypoxia induce bidirectional surfaceome changes

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Hypoxia dramatically remodels the primary T cell surface proteome

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Both regulatory T cells and hypoxia downregulate nutrient transporter expression

Multifaceted Interplay between Hormones, Growth Factors and Hypoxia in the Tumor Microenvironment

Simple Summary

Hormones and growth factors impact many processes in the cell. Moreover, these molecules influence tumor growth, as does a lack of oxygen (hypoxia) that characterizes cancer progression. Proteins that are stabilized by low oxygen tension, known as hypoxia-inducible factors (HIFs), help tumor cells to adapt to their environment. Of note, hormones and growth factors regulate the activity of HIFs toward malignant aggressiveness, including the resistance to therapy. In this review, we summarize the current knowledge regarding the role of hormones and growth factors in cancer development with a particular focus on their interplay with hypoxia and HIFs and comment on how these factors influence the response to cancer immunotherapy.

Abstract

Hormones and growth factors (GFs) are signaling molecules implicated in the regulation of a variety of cellular processes. They play important roles in both healthy and tumor cells, where they function by binding to specific receptors on target cells and activating downstream signaling cascades. The stages of tumor progression are influenced by hormones and GF signaling. Hypoxia, a hallmark of cancer progression, contributes to tumor plasticity and heterogeneity. Most solid tumors contain a hypoxic core due to rapid cellular proliferation that outgrows the blood supply. In these circumstances, hypoxia-inducible factors (HIFs) play a central role in the adaptation of tumor cells to their new environment, dramatically reshaping their transcriptional profile. HIF signaling is modulated by a variety of factors including hormones and GFs, which activate signaling pathways that enhance tumor growth and metastatic potential and impair responses to therapy. In this review, we summarize the role of hormones and GFs during cancer onset and progression with a particular focus on hypoxia and the interplay with HIF proteins. We also discuss how hypoxia influences the efficacy of cancer immunotherapy, considering that a hypoxic environment may act as a determinant of the immune-excluded phenotype and a major hindrance to the success of adoptive cell therapies.

18F-FMISO PET Imaging Identifies Hypoxia and Immunosuppressive Tumor Microenvironments and Guides Targeted Evofosfamide Therapy in Tumors Refractory to PD-1 and CTLA-4 Inhibition

PURPOSE

Hypoxia is a common characteristic of many tumor microenvironments, and it has been shown to promote suppression of anti-tumor immunity. Despite strong biological rationale, longitudinal correlation of hypoxia and response to immunotherapy has not been investigated.

EXPERIMENTAL DESIGN

In this study, we probed the tumor and its surrounding microenvironment with ¹⁸F-FMISO PET imaging to non-invasively quantify tumor hypoxia in vivo prior to and during PD-1 and CTLA-4 checkpoint blockade in preclinical models of breast and colon cancer.

RESULTS

Longitudinal imaging identified hypoxia as an early predictive biomarker of therapeutic response (prior to anatomic changes in tumor volume) with a decreasing standard uptake value (SUV) ratio in tumors that effectively respond to therapy. PET signal correlated with ex vivo markers of tumor immune response including cytokines (Ifng, Gzmb, and Tnf), damage-associated molecular pattern receptors (Tlr2/4) and immune cell populations (macrophages, dendritic cells, and cytotoxic T cells). Responding tumors were marked by increased inflammation that were spatially distinct from hypoxic regions, providing a mechanistic understanding of the immune signaling pathways activated. To exploit image-guided combination therapy, hypoxia signal from PET imaging was used to guide the addition of a hypoxia targeted treatment to non-responsive tumors, which ultimately provided therapeutic synergy and rescued response as determined by longitudinal changes in tumor volume.

CONCLUSIONS

The results generated from this work provide an immediately translatable paradigm for measuring and targeting hypoxia to increase response to immune checkpoint therapy and using hypoxia imaging to guide combinatory therapies.

Quantitative Analyses Reveal How Hypoxia Reconfigures the Proteome of Primary Cytotoxic T Lymphocytes

Metabolic and nutrient-sensing pathways play an important role in controlling the efficacy of effector T cells. Oxygen is a critical regulator of cellular metabolism. However, during immune responses T cells must function in oxygen-deficient, or hypoxic, environments. Here, we used high resolution mass spectrometry to investigate how the proteome of primary murine CD8⁺ cytotoxic T lymphocytes (CTLs) is reconfigured in response to hypoxia in vitro. We identified and quantified over 7,600 proteins and discovered that hypoxia increased the abundance of a selected number of proteins in CTLs. This included glucose transporters, metabolic enzymes, transcription factors, cytolytic effector molecules, checkpoint receptors and adhesion molecules. While some of these proteins may augment the effector functions of CTLs, others may limit their cytotoxicity. Moreover, we determined that hypoxia could inhibit IL-2-induced proliferation cues and antigen-induced pro-inflammatory cytokine production in CTLs. These data provide a comprehensive resource for understanding the magnitude of the CTL response to hypoxia and emphasise the importance of oxygen-sensing pathways for controlling CD8⁺ T cells. Additionally, this study provides new understanding about how hypoxia may promote the effector function of CTLs, while contributing to their dysfunction in some contexts.

Stem cell-like memory T cells: The generation and application

Stem cell-like memory T cells (Tscm), are a newly defined memory T cell subset with characteristics of long life span, consistent self-renewing, rapid differentiation into effector T cells, and apoptosis resistance. These features indicate that Tscm have great therapeutic or preventive purposes, including being applied in chimeric Ag receptor-engineered T cells, TCR gene-modified T cells, and vaccines. However, the little knowledge about Tscm development restrains their applications. Strength and duration of TCR signaling, cytokines and metabolism in the T cells during activation all influence the Tscm development via regulating transcriptional factors and cell signaling pathways. Here, we summarize the molecular and cellular pathways involving Tscm differentiation, and its clinical application for cancer immunotherapy and prevention.

Hypoxia and heat stress affect epithelial integrity in a Caco-2/HT-29 co-culture

Hypoxia and hyperthermia, which can be induced by high environmental temperature or strenuous exercise, are two common stressors that affect intestinal epithelial integrity and lead to multiple clinical symptoms. In this study, we developed an in-vitro intestinal monolayer model using two human colonic epithelial cell lines, Caco-2 and HT-29, co-cultured in Transwell inserts, and investigated the effects of heat treatment and/or hypoxia on the epithelial barrier function. The monolayer with a ratio of 9:1 (Caco-2:HT-29) showed high trans-epithelial electrical resistance (TEER), low Lucifer Yellow permeability and high mucin production. Hyperthermia and/or hypoxia exposure (2 h) triggered heat shock and oxidative stress responses. HSP-70 and HSF-1 protein levels were up-regulated by hyperthermia, which were further enhanced when hyperthermia was combined with hypoxia. Increased HIF-1α protein expression and Nrf2 nuclear translocation was only caused by hypoxia. Hyperthermia and/or hypoxia exposure disrupted the established monolayer by increasing paracellular permeability, decreasing ZO-1, claudin-3 and occludin protein/mRNA expression, while enhancing E-cadherin protein expression. Tight junction protein distribution in the monolayer was also modulated by the hyperthermia and/or hypoxia exposure. In addition, transcription levels of mucin genes, MUC-2 and MUC-5AC, were increased after 2 h of hyperthermia and/or hypoxia exposure. In conclusion, this Caco-2/HT-29 cell model is valid and effective for studying detrimental effects of hyperthermia and/or hypoxia on intestinal barrier function and related heat shock and oxidative stress pathways and can be used to investigate possible interventions to reverse hyperthermia and/or hypoxia-induced intestinal epithelial injury.

Hypoxia-modulatory nanomaterials to relieve tumor hypoxic microenvironment and enhance immunotherapy: Where do we stand?

The past several years have witnessed the blooming of emerging immunotherapy, as well as their therapeutic potential in remodeling the immune system. Nevertheless, with the development of biological mechanisms in oncology, it has been demonstrated that hypoxic tumor microenvironment (TME) seriously impairs the therapeutic outcomes of immunotherapy. Hypoxia, caused by Warburg effect and insufficient oxygen delivery, has been considered as a primary construction element of TME and drawn tremendous attention in cancer therapy. Multiple hypoxia-modulatory theranostic agents have been facing many obstacles and challenges while offering initial therapeutic effect. Inspired by versatile nanomaterials, great efforts have been devoted to design hypoxia-based nanoplatforms to preserve drug activity, reduce systemic toxicity, provide adequate oxygenation, and eventually ameliorate hypoxic-tumor management. Besides these, recently, some curative and innovative hypoxia-related nanoplatforms have been applied in synergistic immunotherapy, especially in combination with immune checkpoint blockade (ICB), immunomodulatory therapeutics, cancer vaccine therapy and immunogenic cell death (ICD) effect. Herein, the paramount impact of hypoxia on tumor immune escape was initially described and discussed, followed by a comprehensive overview on the design tactics of multimodal nanoplatforms based on hypoxia-enabled theranostic agents. A variety of nanocarriers for relieving tumor hypoxic microenvironment were also summarized. On this basis, we presented the latest progress in the use of hypoxia-modulatory nanomaterials for synergistic immunotherapy and highlighted current challenges and plausible promises in this area in the near future. STATEMENT OF SIGNIFICANCE: Cancer immunotherapy, emerging as a novel treatment to eradicate malignant tumors, has achieved a measure of success in clinical popularity and transition. However, over the last decades, hypoxia-induced tumor immune escape has attracted enormous attention in cancer treatment. Limitations of free targeting agents have paved the path for the development of multiple nanomaterials with the hope of boosting immunotherapy. In this review, the innovative design tactics and multifunctional nanocarriers for hypoxia alleviation are summarized, and the smart nanomaterial-assisted hypoxia-modulatory therapeutics for synergistic immunotherapy and versatile biomedical applications are especially highlighted. In addition, the challenges and prospects of clinical transformation are further discussed.

Hypoxia-inducible factor activity promotes antitumor effector function and tissue residency by CD8+ T cells

Adoptive T cell therapies (ACTs) hold great promise in cancer treatment, but low overall response rates in patients with solid tumors underscore remaining challenges in realizing the potential of this cellular immunotherapy approach. Promoting CD8+ T cell adaptation to tissue residency represents an underutilized but promising strategy to improve tumor-infiltrating lymphocyte (TIL) function. Here, we report that deletion of the HIF negative regulator von Hippel-Lindau (VHL) in CD8+ T cells induced HIF-1α/HIF-2α-dependent differentiation of tissue-resident memory-like (Trm-like) TILs in mouse models of malignancy. VHL-deficient TILs accumulated in tumors and exhibited a core Trm signature despite an exhaustion-associated phenotype, which led to retained polyfunctionality and response to αPD-1 immunotherapy, resulting in tumor eradication and protective tissue-resident memory. VHL deficiency similarly facilitated enhanced accumulation of chimeric antigen receptor (CAR) T cells with a Trm-like phenotype in tumors. Thus, HIF activity in CD8+ TILs promotes accumulation and antitumor activity, providing a new strategy to enhance the efficacy of ACTs.

Metabolic and Mitochondrial Functioning in Chimeric Antigen Receptor (CAR)-T Cells

Chimeric antigen receptor (CAR) T-cell therapy has revolutionized adoptive cell therapy with impressive therapeutic outcomes of >80% complete remission (CR) rates in some haematological malignancies. Despite this, CAR T cell therapy for the treatment of solid tumours has invariably been unsuccessful in the clinic. Immunosuppressive factors and metabolic stresses in the tumour microenvironment (TME) result in the dysfunction and exhaustion of CAR T cells. A growing body of evidence demonstrates the importance of the mitochondrial and metabolic state of CAR T cells prior to infusion into patients. The different T cell subtypes utilise distinct metabolic pathways to fulfil their energy demands associated with their function. The reprogramming of CAR T cell metabolism is a viable approach to manufacture CAR T cells with superior antitumour functions and increased longevity, whilst also facilitating their adaptation to the nutrient restricted TME. This review discusses the mitochondrial and metabolic state of T cells, and describes the potential of the latest metabolic interventions to maximise CAR T cell efficacy for solid tumours.

Metabolic regulation of T cells in the tumor microenvironment by nutrient availability and diet

Recent advances in immunotherapies such as immune checkpoint blockade (ICB) and chimeric antigen receptor T cells (CAR-T) for the treatment of cancer have generated excitement over their ability to yield durable, and potentially curative, responses in a multitude of cancers. These findings have established that the immune system is capable of eliminating tumors and led us to a better, albeit still incomplete, understanding of the mechanisms by which tumors interact with and evade destruction by the immune system. Given the central role of T cells in immunotherapy, elucidating the cell intrinsic and extrinsic factors that govern T cell function in tumors will facilitate the development of immunotherapies that establish durable responses in a greater number of patients. One such factor is metabolism, a set of fundamental cellular processes that not only sustains cell survival and proliferation, but also serves as a means for cells to interpret their local environment. Nutrient sensing is critical for T cells that must infiltrate into a metabolically challenging tumor microenvironment and expand under these harsh conditions to eliminate cancerous cells. Here we introduce T cell exhaustion with respect to cellular metabolism, followed by a discussion of nutrient availability at the tumor and organismal level in relation to T cell metabolism and function to provide rationale for the study and targeting of metabolism in anti-tumor immune responses.

Tumor Hypoxia as a Barrier in Cancer Therapy: Why Levels Matter

Simple Summary

Hypoxia is a common feature of solid tumors and associated with poor outcome in most cancer types and treatment modalities, including radiotherapy, chemotherapy, surgery and, most likely, immunotherapy. Emerging strategies, such as proton therapy and combination therapies with radiation and hypoxia targeted drugs, provide new opportunities to overcome the hypoxia barrier and improve therapeutic outcome. Hypoxia is heterogeneously distributed both between and within tumors and shows large variations across patients not only in prevalence, but importantly, also in level. To best exploit the emerging strategies, a better understanding of how individual hypoxia levels from mild to severe affect tumor biology is vital. Here, we discuss our current knowledge on this topic and how we should proceed to gain more insight into the field.

Abstract

Hypoxia arises in tumor regions with insufficient oxygen supply and is a major barrier in cancer treatment. The distribution of hypoxia levels is highly heterogeneous, ranging from mild, almost non-hypoxic, to severe and anoxic levels. The individual hypoxia levels induce a variety of biological responses that impair the treatment effect. A stronger focus on hypoxia levels rather than the absence or presence of hypoxia in our investigations will help development of improved strategies to treat patients with hypoxic tumors. Current knowledge on how hypoxia levels are sensed by cancer cells and mediate cellular responses that promote treatment resistance is comprehensive. Recently, it has become evident that hypoxia also has an important, more unexplored role in the interaction between cancer cells, stroma and immune cells, influencing the composition and structure of the tumor microenvironment. Establishment of how such processes depend on the hypoxia level requires more advanced tumor models and methodology. In this review, we describe promising model systems and tools for investigations of hypoxia levels in tumors. We further present current knowledge and emerging research on cellular responses to individual levels, and discuss their impact in novel therapeutic approaches to overcome the hypoxia barrier.

Metabolic and epigenetic regulation of T-cell exhaustion

Current immunotherapies yield remarkable clinical outcomes by boosting the power of host immunity in cancer cell elimination and viral clearance. However, after prolonged antigen exposure, CD8⁺ T cells differentiate into a special differentiation state known as T-cell exhaustion, which poses one of the major hurdles to antiviral and antitumor immunity during chronic viral infection and tumour development. Growing evidence indicates that exhausted T cells undergo metabolic insufficiency with altered signalling cascades and epigenetic landscapes, which dampen effector immunity and cause poor responsiveness to immune-checkpoint-blockade therapies. How metabolic stress affects T-cell exhaustion remains unclear; therefore, in this Review, we summarize current knowledge of how T-cell exhaustion occurs, and discuss how metabolic insufficiency and prolonged stress responses may affect signalling cascades and epigenetic reprogramming, thus locking T cells into an exhausted state via specialized differentiation programming.

Differential gene expression of tumor-infiltrating CD8+ T cells in advanced versus early-stage colorectal cancer and identification of a gene signature of poor prognosis

Background

Cytotoxic CD8⁺ T cell-mediated response is the most important arm of adaptive immunity, which dictates the capacity of the host immune response in eradicating tumor cells. Due to tumor intrinsic and/or extrinsic factors, the density and function of CD8⁺ tumor-infiltrating lymphocytes (TILs) could be compromised, leading to poor prognosis and survival.

Methods

Using RNA-Seq, transcriptomes of sorted CD3⁺CD8⁺ TILs from treatment-naïve colorectal cancer (CRC) patients at advanced stages (III and IV) were compared with those from patients with early stages (I and II). A signature referred to as ‘poor prognosis CD8 gene signature (ppCD8sig)’ was identified and analyzed in The Cancer Genome Atlas CRC dataset. Scores for the ppCD8sig were calculated and classified as high, intermediate and low, and its prognostic significance was assessed using multivariate analysis and Cox proportional hazard model. Densities of CD3⁺ and CD8⁺ T cell infiltration in tumors from patients with high and low ppCD8sig scores were assessed by flow cytometry and immunostaining.

Results

Genes related to epigenetic regulation and response to hypoxia were upregulated in CD8⁺ TILs from patients with advanced stages, while genes related to T cell activation, cell proliferation and cell cycle were downregulated. Patients with high ppCD8sig score had poorer disease-specific survival (DSS) and shorter progression-free interval (PFI). The ppCD8sig was an independent prognostic indicator for DSS (HR 1.83, 95% CI 1.40 to 2.38, p<0.0001) and PFI (HR 1.42, 95% CI 1.04 to 1.93, p=0.026). Additionally, patients with high ppCD8sig score were more likely to have advanced stages (χ² p<0.0001) and residual disease after primary therapy (χ² p=0.046). Patients with high ppCD8sig score had reduced levels of CD3⁺ and CD8⁺ TILs and low Immunoscores (IS), compared to patients with low ppCD8sig score.

Conclusions

Our data provided insights into the altered regulation of biological mechanisms and signaling pathways in CD8⁺ TILs during CRC progression, and revealed a gene signature as an independent prognostic indicator. Patients with high ppCD8sig score had lower levels of TILs and low IS. These data further confirm the prognostic value of the identified ppCD8sig and potentially highlight its clinical relevance.

An Experimentally Defined Hypoxia Gene Signature in Glioblastoma and Its Modulation by Metformin

Glioblastoma multiforme (GBM) is the most common and aggressive primary brain tumor, characterized by a high degree of intertumoral heterogeneity. However, a common feature of the GBM microenvironment is hypoxia, which can promote radio- and chemotherapy resistance, immunosuppression, angiogenesis, and stemness. We experimentally defined common GBM adaptations to physiologically relevant oxygen gradients, and we assessed their modulation by the metabolic drug metformin. We directly exposed human GBM cell lines to hypoxia (1% O₂) and to physioxia (5% O₂). We then performed transcriptional profiling and compared our in vitro findings to predicted hypoxic areas in vivo using in silico analyses. We observed a heterogenous hypoxia response, but also a common gene signature that was induced by a physiologically relevant change in oxygenation from 5% O₂ to 1% O₂. In silico analyses showed that this hypoxia signature was highly correlated with a perinecrotic localization in GBM tumors, expression of certain glycolytic and immune-related genes, and poor prognosis of GBM patients. Metformin treatment of GBM cell lines under hypoxia and physioxia reduced viable cell number, oxygen consumption rate, and partially reversed the hypoxia gene signature, supporting further exploration of targeting tumor metabolism as a treatment component for hypoxic GBM.

Hypoxia regulates the differentiation and anti-tumor effector functions of γδT cells in oral cancer

Hypoxia within the tumor microenvironment (TME) is a key factor contributing to immunosuppression in tumors, co-relating with poor treatment outcome and decreased overall survival in advanced oral cancer (OC) patients. Vδ2 is a dominant subset of gamma delta T cells (γδT cells) present in the peripheral blood which exhibits potent anti-tumor cytotoxicity and is evolving as a key player of anti-cancer cellular therapy. However, the fate of γδT cells in hypoxic oral tumors remains elusive. In the present study, we compared the effect of hypoxia (1% O₂ ) and normoxia (21% O₂ ) on the expansion, proliferation, activation status, cytokine secretion and cytotoxicity of γδT cells isolated from OC patients and healthy individuals. Hypoxia-exposed γδT cells exhibited reduced cytotoxicity against oral tumor cells. Our data demonstrated that hypoxia reduces the calcium efflux and the expression of degranulation marker CD107a in γδT cells, which explains the decreased anti-tumor cytotoxicity of γδT cells observed under hypoxia. Hypoxia-exposed γδT cells differentiated to γδT17 [γδ T cells that produce interleukin (IL)-17] cells, which corroborated our observations of increased γδT17 cells observed in the oral tumors. Co-culture of γδT cells with CD8 T cells in the presence of hypoxia showed that programmed cell death ligand 1 (PD-L1)^high γδT cells brought about apoptosis of programmed cell death 1 (PD-1)^high CD8 T cells which could be significantly reversed upon blocking PD-1. Thus, future immunotherapeutic treatment modality for oral cancer may use a combined approach of blocking the PD-1/PD-L1 signaling and targeting hypoxia-inducible factor 1α, which may help in reversing hypoxia-induced immunosuppression.

Profiles of Immune Infiltration in Bladder Cancer and its Clinical Significance: an Integrative Genomic Analysis

Tumor-infiltrating immune cells are closely related to the prognosis of bladder cancer. Analysis of tumor infiltrating immune cells is usually based on immunohistochemical analysis. Since many immune cell marker proteins are not specific for different immune cells, which may induce misleading or incomplete. CIBERSORT is an algorithm to estimate specific cell types in a mixed cell population using gene expression data. In this study, the CIBERSORT algorithm was used to identify the immune cell infiltration signatures. The gene expression profiles, mutation data, and clinical data were collected from The Cancer Genome Atlas (TCGA) database. Unsupervised consensus clustering was used to acquire the immune cell infiltration subtypes of bladder cancer based on the fractions of 22 immune cell types. Four immune cell clusters with different immune infiltrate and mutation characteristics were identified. In addition, this stratification has a prognostic relevance, with cluster 2 having the best outcome, cluster 1 the worst. These clusters showed distinct mRNA expression patterns. The characteristic genes in subtype cluster 1 were mainly involved in cell division, those in subtype cluster 2 were mainly related in antigen processing and presentation, those in subtype cluster 3 were mainly involved in epidermal cell differentiation, and those in subtype cluster 4 were mainly related in the humoral immune response. These differences may affect the development of the bladder cancer, the sensitivity to treatment as well as the prognosis. Through further validation, this study may contribute to the development of personalized therapy and precision medical treatments.

Identification of gene expression profiles and immune cell infiltration signatures between low and high tumor mutation burden groups in bladder cancer

Bladder cancer is one of the most commonly diagnosed tumors and is results from the accumulation of somatic mutations in the DNA. Tumor mutation burden (TMB) has been associated with cancer immunotherapeutic response. In this study, we attempted to explore the correlation between TMB and cancer prognosis. Identify the different expressed genes and immune cell infiltration signatures between low and high TMB group. Mutation data, gene expression profiles and clinical data were downloaded from The Cancer Genome Atlas (TCGA) database. Patients were divided into high and low TMB groups, allowing differentially expressed genes (DEGs) to be identified. Functional enrichment and protein-protein interaction (PPI) network analysis were used to identify the functions of the DEGs. And immune cell infiltration signatures were evaluated by CIBERSORT algorithm. These results shown that high TMB was significantly associated with prognosis. We obtained a list of TMB related genes which may influence the infiltrations of immune cells. We also found a higher proportion of CD8 T cells, CD4 T cells and NK cells in the high TMB group. Our data suggest that higher TMB tends to promote the infiltrations of T cells and NK cells and patients with higher TMB may achieve a more favorable prognosis in bladder cancer.

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through hypoxia-inducible factor 1α

BACKGROUND

CD8+ type 2 cytotoxic T (TC2) cells undergo transcriptional reprogramming to IL-13 production in the presence of IL-4 to become potent, steroid-insensitive, pathogenic effector cells in asthmatic patients and in mice in a model of experimental asthma. However, no studies have described the effects of hypoxia exposure on TC2 cell differentiation.

OBJECTIVE

We determined the effects of hypoxia exposure on IL-13-producing CD8+ TC2 cells.

METHODS

CD8+ transgenic OT-1 cells differentiated with IL-2 and IL-4 (TC2 cells) were exposed to normoxia (21% oxygen) or hypoxia (3% oxygen), and IL-13 production in vitro was monitored. After differentiation under these conditions, cells were adoptively transferred into CD8-deficient mice, and lung allergic responses, including airway hyperresponsiveness to inhaled methacholine, were assessed. The effects of pharmacologic inhibitors of hypoxia-inducible factor (HIF) 1α and HIF-2α were determined, as were responses in HIF-1α-deficient OT-1 cells.

RESULTS

Under hypoxic conditioning, CD8+ TC2 cell differentiation was significantly enhanced, with increased numbers of IL-13+ T cells and increased production of IL-13 in vitro. Adoptive transfer of TC2 cells differentiated under hypoxic conditioning restored lung allergic responses in sensitized and challenged CD8-deficient recipients to a greater degree than seen in recipients of TC2 cells differentiated under normoxic conditioning. Pharmacologic inhibition of HIF-1α or genetic manipulation to reduce HIF-1α expression reduced the hypoxia-enhanced differentiation of TC2 cells, IL-13 production, and the capacity of transferred cells to restore lung allergic responses in vivo. IL-4-dependent, hypoxia-mediated increases in HIF-1α and TC2 cell differentiation were shown to be mediated through activation of Janus kinase 1/3 and GATA-3.

CONCLUSIONS

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through HIF-1α activation. These findings coupled with the known insensitivity of CD8+ T cells to corticosteroids suggests that activation of the IL-4-HIF-1α-IL-13 axis might play a role in the development of steroid-refractory asthma.

Hypoxia Selectively Impairs CAR-T Cells In Vitro

Hypoxia is a major characteristic of the solid tumor microenvironment. To understand how chimeric antigen receptor-T cells (CAR-T cells) function in hypoxic conditions, we characterized CD19-specific and BCMA-specific human CAR-T cells generated in atmospheric (18% oxygen) and hypoxic (1% oxygen) culture for expansion, differentiation status, and CD4:CD8 ratio. CAR-T cells expanded to a much lower extent in 1% oxygen than in 18% oxygen. Hypoxic CAR-T cells also had a less differentiated phenotype and a higher CD4:CD8 ratio than atmospheric CAR-T cells. CAR-T cells were then added to antigen-positive and antigen-negative tumor cell lines at the same or lower oxygen level and characterized for cytotoxicity, cytokine and granzyme B secretion, and PD-1 upregulation. Atmospheric and hypoxic CAR-T cells exhibited comparable cytolytic activity and PD-1 upregulation; however, cytokine production and granzyme B release were greatly decreased in 1% oxygen, even when the CAR-T cells were generated in atmospheric culture. Together, these data show that at solid tumor oxygen levels, CAR-T cells are impaired in expansion, differentiation and cytokine production. These effects may contribute to the inability of CAR-T cells to eradicate solid tumors seen in many patients.

Intratumoral Hypoxia Reduces IFN-γ-Mediated Immunity and MHC Class I Induction in a Preclinical Tumor Model

Tumor hypoxia occurs because of an increased demand for oxygen by the rapidly growing tumor cells, together with reduction in the oxygen supply due to malformed and nonfunctional tumor vasculature. The effects of tumor hypoxia on radiotherapy (RT) are well known; however, recent findings suggest it may also suppress immunotherapy, although the mechanisms governing this observation remain undetermined. Our laboratory and others have shown that IFN-γ conditions the tumor milieu and is important for the efficacy of RT. Thus, we hypothesized that hypoxia could inhibit IFN-γ–mediated antitumor responses, resulting in decreased RT efficacy. This inhibition could involve the production and/or the cellular response to IFN-γ. To test this, we used murine tumor cell lines B16F0 and Colon38. We observed that hypoxia inhibited upregulation of IFN-γ–dependent MHC class I expression by tumor cells along with the gene expression of IFN-γ–dependent chemokines CXCL9 and CXCL10, essential for immune cell infiltration. Furthermore, CD8⁺ T cells, an important source of IFN-γ, which mediate effector antitumor responses, had reduced ability to proliferate and generate IFN-γ under hypoxic conditions in vitro. Interestingly, reoxygenation restored the cytokine-producing capability of these cells. Studies performed in vivo using a mouse tumor model and the hypoxia marker EF5 demonstrated that RT could reverse the hypoxia within treated tumors. This study has identified a unique mechanism of hypoxia-induced immune suppression involving the downregulation of IFN-γ production and cellular responsiveness to this essential cytokine. These results suggest that therapies that target and reduce tumor hypoxia can potentially boost antitumor immune responses.

Hypoxia and mesenchymal stromal cells as key drivers of initial fracture healing in an equine in vitro fracture hematoma model

Fractures in horses–whether simple fractures with just one clean break, or incomplete greenstick with stress fractures, or complications such as shattered bones can all be either minimal or even catastrophic. Thus, improvement in fracture healing is a hallmark in equine orthopedics. The fracture healing process implements a complex sequence of events including the initial inflammatory phase removing damaged tissue, re-establishment of vessels and mesenchymal stromal cells, a soft and hard callus phase closing the fracture gap as well as the remodeling phase shaping the bone to a scar-free tissue. Detailed knowledge on processes in equine fracture healing in general and on the initial phase in particular is apparently very limited. Therefore, we generated equine in vitro fracture hematoma models (FH models) to study time-dependent changes in cell composition and RNA-expression for the most prominent cells in the FH model (immune cells, mesenchymal stromal cells) under conditions most closely adapted to the in vivo situation (hypoxia) by using flow cytometry and qPCR. In order to analyze the impact of mesenchymal stromal cells in greater detail, we also incubated blood clots without the addition of mesenchymal stromal cells under the same conditions as a control. We observed a superior survival capacity of mesenchymal stromal cells over immune cells within our FH model maintained under hypoxia. Furthermore, we demonstrate an upregulation of relevant angiogenic, osteogenic and hypoxia-induced markers within 48 h, a time well-known to be crucial for proper fracture healing.

Rationale for Combining Radiotherapy and Immune Checkpoint Inhibition for Patients With Hypoxic Tumors

In order to compensate for the increased oxygen consumption in growing tumors, tumors need angiogenesis and vasculogenesis to increase the supply. Insufficiency in this process or in the microcirculation leads to hypoxic tumor areas with a significantly reduced pO2, which in turn leads to alterations in the biology of cancer cells as well as in the tumor microenvironment. Cancer cells develop more aggressive phenotypes, stem cell features and are more prone to metastasis formation and migration. In addition, intratumoral hypoxia confers therapy resistance, specifically radioresistance. Reactive oxygen species are crucial in fixing DNA breaks after ionizing radiation. Thus, hypoxic tumor cells show a two- to threefold increase in radioresistance. The microenvironment is enriched with chemokines (e.g., SDF-1) and growth factors (e.g., TGFβ) additionally reducing radiosensitivity. During recent years hypoxia has also been identified as a major factor for immune suppression in the tumor microenvironment. Hypoxic tumors show increased numbers of myeloid derived suppressor cells (MDSCs) as well as regulatory T cells (Tregs) and decreased infiltration and activation of cytotoxic T cells. The combination of radiotherapy with immune checkpoint inhibition is on the rise in the treatment of metastatic cancer patients, but is also tested in multiple curative treatment settings. There is a strong rationale for synergistic effects, such as increased T cell infiltration in irradiated tumors and mitigation of radiation-induced immunosuppressive mechanisms such as PD-L1 upregulation by immune checkpoint inhibition. Given the worse prognosis of patients with hypoxic tumors due to local therapy resistance but also increased rate of distant metastases and the strong immune suppression induced by hypoxia, we hypothesize that the subgroup of patients with hypoxic tumors might be of special interest for combining immune checkpoint inhibition with radiotherapy.

Regulation of T cell antitumor immune response by tumor induced metabolic stress

Adaptive T cell immune response is essential for tumor growth control. The efficacy of immune checkpoint inhibitors is regulated by intratumoral immune response. The tumor microenvironment has a major role in adaptive immune response tuning. Tumor cells generate a particular metabolic environment in comparison to other tissues. Tumors are characterized by glycolysis, hypoxia, acidosis, amino acid depletion and fatty acid metabolism modification. Such metabolic changes promote tumor growth, impair immune response and lead to resistance to therapies. This review will detail how these modifications strongly affect CD8 and CD4 T cell functions and impact immunotherapy efficacy.

Myeloma escape after stem cell transplantation is a consequence of T-cell exhaustion and is prevented by TIGIT blockade

Autologous stem cell transplantation (SCT) remains a standard of care for multiple myeloma (MM) patients and prolongs progression-free survival. A small cohort of patients achieve long-term control of disease, but the majority of patients ultimately relapse, and the mechanisms permitting disease progression remain unclear. In this study, we used a preclinical model of autologous SCT for myeloma where the disease either progressed (MM relapsed) or was controlled. In the bone marrow (BM), inhibitory receptor expression on CD8⁺ T cells correlated strongly with myeloma progression after transplant. In conjunction, the costimulatory/adhesion receptor CD226 (DNAM-1) was markedly downregulated. Interestingly, DNAM-1^- CD8⁺ T cells in MM-relapsed mice had an exhausted phenotype, characterized by upregulation of multiple inhibitory receptors, including T-cell immunoglobulin and ITIM domains (TIGIT) and programmed cell death protein 1 (PD-1) with decreased T-bet and increased eomesodermin expression. Immune checkpoint blockade using monoclonal antibodies against PD-1 or TIGIT significantly prolonged myeloma control after SCT. Furthermore, CD8⁺ T cells from MM-relapsed mice exhibited high interleukin-10 (IL-10) secretion that was associated with increased TIGIT and PD-1 expression. However, while donor-derived IL-10 inhibited myeloma control post-SCT, this was independent of IL-10 secretion by or signaling to T cells. Instead, the donor myeloid compartment, including colony-stimulating factor 1 receptor-dependent macrophages and an IL-10-secreting dendritic cell population in the BM, promoted myeloma progression. Our findings highlight PD-1 or TIGIT blockade in conjunction with SCT as a potent combination therapy in the treatment of myeloma.

Culturing CTLs under Hypoxic Conditions Enhances Their Cytolysis and Improves Their Anti-tumor Function

Cytotoxic T lymphocytes (CTLs) used in immunotherapy are typically cultured under atmospheric O₂ pressure but encounter hypoxic conditions inside tumors. Activating CTLs under hypoxic conditions has been shown to improve their cytotoxicity in vitro, but the mechanism employed and the implications for immunotherapy remain unknown. We activated and cultured OT-I CD8 T cells at either 1% or 20% O₂. Hypoxic CTLs survived, as well as normoxic ones, in vitro but killed OVA-expressing B16 melanoma cells more efficiently. Hypoxic CTLs contained similar numbers of cytolytic granules and released them as efficiently but packaged more granzyme-B in each granule without producing more perforin. We imaged CTL distribution and motility inside B16-OVA tumors using confocal and intravital 2-photon microscopy and observed no obvious differences. However, mice treated with hypoxic CTLs exhibited better tumor regression and survived longer. Thus, hypoxic CTLs may perform better in tumor immunotherapy because of higher intrinsic cytotoxicity rather than improved migration inside tumors.

Engineering Chimeric Antigen Receptor T-Cells for Racing in Solid Tumors: Don't Forget the Fuel

T-cells play a critical role in tumor immunity. Indeed, the presence of tumor-infiltrating lymphocytes is a predictor of favorable patient prognosis for many indications and is a requirement for responsiveness to immune checkpoint blockade therapy targeting programmed cell death 1. For tumors lacking immune infiltrate, or for which antigen processing and/or presentation has been downregulated, a promising immunotherapeutic approach is chimeric antigen receptor (CAR) T-cell therapy. CARs are hybrid receptors that link the tumor antigen specificity and affinity of an antibody-derived single-chain variable fragment with signaling endodomains associated with T-cell activation. CAR therapy targeting CD19 has yielded extraordinary clinical responses against some hematological tumors. Solid tumors, however, remain an important challenge to CAR T-cells due to issues of homing, tumor vasculature and stromal barriers, and a range of obstacles in the tumor bed. Protumoral immune infiltrate including T regulatory cells and myeloid-derived suppressor cells have been well characterized for their ability to upregulate inhibitory receptors and molecules that hinder effector T-cells. A critical role for metabolic barriers in the tumor microenvironment (TME) is emerging. High glucose consumption and competition for key amino acids by tumor cells can leave T-cells with insufficient energy and biosynthetic precursors to support activities such as cytokine secretion and lead to a phenotypic state of anergy or exhaustion. CAR T-cell expansion protocols that promote a less differentiated phenotype, combined with optimal receptor design and coengineering strategies, along with immunomodulatory therapies that also promote endogenous immunity, offer great promise in surmounting immunometabolic barriers in the TME and curing solid tumors.

[Brain tumor immunotherapy: Illusion or hope?]

Immunotherapy has proven efficient for many tumors and is now part of standard of care in many indications. What is the picture for brain tumors? The recent development of anti-CTLA-4 and PD1 immune checkpoint inhibitors, which have the ability to restore T lymphocytes activity, has gathered enthusiasm and is now paving the way towards more complex models of immune system manipulation. These models include, among others, vaccination and adoptive T cell transfer technologies. Complementary to those strategies, molecules capable of reshaping the immune tumor microenvironment are currently being investigated in early phase trials. Indeed, the tumor bed is hostile to anti-tumor immune responses due to many escape mechanisms, and this is particularly true in the context of brain tumors, a master in eliciting immunosuppressive cells and molecules. The goal of this review is to describe the hopes and challenges of brain tumors immunotherapy and to propose an inventory of the current clinical research with specific focus on the therapies targeting the tumor microenvironment.

Molecular mechanisms involved in dendritic cell dysfunction in cancer

Dendritic cells (DC) play a pivotal role in the tumor microenvironment (TME). As the primary antigen-presenting cells in the tumor, DCs modulate anti-tumor responses by regulating the magnitude and duration of infiltrating cytotoxic T lymphocyte responses. Unfortunately, due to the immunosuppressive nature of the TME, as well as the inherent plasticity of DCs, tumor DCs are often dysfunctional, a phenomenon that contributes to immune evasion. Recent progresses in our understanding of tumor DC biology have revealed potential molecular targets that allow us to improve tumor DC immunogenicity and cancer immunotherapy. Here, we review the molecular mechanisms that drive tumor DC dysfunction. We discuss recent advances in our understanding of tumor DC ontogeny, tumor DC subset heterogeneity, and factors in the tumor microenvironment that affect DC recruitment, differentiation, and function. Finally, we describe potential strategies to optimize tumor DC function in the context of cancer therapy.

Potential immunotherapy targets in recurrent cervical cancer

OBJECTIVE

Our objective was to characterize the intra and peritumoral immune profile in recurrent cervical cancers to identify rational immunotherapy targets.

METHODS

Archival pelvic exenteration specimens were examined using a validated multiplex immuno-fluorescent panel of antibodies against cluster of differentiation 8 (CD8), cluster of differentiation 68 (CD68), forkhead box P3 (FoxP3), programmed cell death protein 1 (PD1), and programmed death-ligand 1 (PD-L1, N=28). Clinical data were abstracted from the electronic medical record.

RESULTS

Cytotoxic T cells, macrophages, and regulatory T cells were found in higher densities in peritumoral stroma (CD8+ density 497.7 vs 83.5, p<0.0001, CD68+ density 345.0 vs 196.7, p=0.04, FoxP3+ density 214.5 vs 35.6, p<0.0001). Antigen experienced T cells (PD1+) were higher in peritumoral compared to tumor tissue (median normalized fluorescence intensity 0.05 vs 0.0085, p<0.001). Although there was a higher median density of intratumoral cytotoxic T cells and macrophages compared to regulatory T cells (median density CD8+ 83.5 vs 35.6, p<0.05, median density 196.7 vs 35.6, p<0.05), the presence of macrophages correlated with the presence of regulatory T cells in tumors (r=0.58, p=0.001).

CONCLUSIONS

While cytotoxic T cells are present in tumor tissue to varying degrees, their density is lower than in peritumoral stroma, suggesting intratumoral exclusion or destruction of T cells. Higher densities of intratumoral macrophages compared to regulatory T cells suggest macrophages may be important contributors to the immunosuppressive tumor environment. Future directions for combination therapy include altering T cell trafficking and targeting tumor associated macrophages (TAMs) to enhance intratumoral activated T cell density and effect a more robust immune response.

Radiation-induced immune responses: mechanisms and therapeutic perspectives

Recent advancement in the radiotherapy technology has allowed conformal delivery of high doses of ionizing radiation precisely to the tumors while sparing large volume of the normal tissues, which have led to better clinical responses. Despite this technological advancement many advanced tumors often recur and they do so within the previously irradiated regions. How could tumors recur after receiving such high ablative doses of radiation? In this review, we outlined how radiation can elicit anti-tumor responses by introducing some of the cytokines that can be induced by ionizing radiation. We then discuss how tumor hypoxia, a major limiting factor responsible for failure of radiotherapy, may also negatively impact the anti-tumor responses. In addition, we highlight how there may be other populations of immune cells including regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and tumor-associated macrophages (TAMs) that can be recruited to tumors interfering with the anti-tumor immunity. Finally, the impact of irradiation on tumor hypoxia and the immune responses according to different radiotherapy regimen is also delineated. It is indeed an exciting time to see that radiotherapy is being combined with immunotherapy in the clinic and we hope that this review can add an excitement to the field.

Hypoxia and antitumor CD8+ T cells: An incompatible alliance?

T Lymphocytes face pathologically low O₂ tensions within the tumor bed at which they will have to function in order to impact on the malignancy. Recent studies highlighting the importance of O₂ and hypoxia-inducible factors for CD8⁺ T-cell function and fate must now be integrated into tumor immunology concepts if immunotherapies are to progress. Here, we discuss, reinterpret, and reconcile the many apparent contradictions in these data and we propose that O₂ is a master regulator of the CD8⁺ T-cell response. Certain T cell functions are enhanced, others suppressed, but on balance, hypoxia is globally detrimental to the antitumor response.

Decitabine Treatment of Glioma-Initiating Cells Enhances Immune Recognition and Killing

Malignant gliomas are aggressive brain tumours with very poor prognosis. The majority of glioma cells are differentiated (glioma-differentiated cells: GDCs), whereas the smaller population (glioma-initiating cells, GICs) is undifferentiated and resistant to conventional therapies. Therefore, to better target this pool of heterogeneous cells, a combination of diverse therapeutic approaches is envisaged. Here we investigated whether the immunosensitising properties of the hypomethylating agent decitabine can be extended to GICs. Using the murine GL261 cell line, we demonstrate that decitabine augments the expression of the death receptor FAS both on GDCs and GICs. Interestingly, it had a higher impact on GICs and correlated with an enhanced sensitivity to FASL-mediated cell death. Moreover, the expression of other critical molecules involved in cognate recognition by cytotoxic T lymphocytes, MHCI and ICAM-1, was upregulated by decitabine treatment. Consequently, T-cell mediated killing of both GDCs and GICs was enhanced, as was T cell proliferation after reactivation. Overall, although GICs are described to resist classical therapies, our study shows that hypomethylating agents have the potential to enhance glioma cell recognition and subsequent destruction by immune cells, regardless of their differentiation status. These results support the development of combinatorial treatment modalities including epigenetic modulation together with immunotherapy in order to treat heterogenous malignancies such as glioblastoma.

Deciphering CD137 (4-1BB) signaling in T-cell costimulation for translation into successful cancer immunotherapy

CD137 (4-1BB, TNF-receptor superfamily 9) is a surface glycoprotein of the TNFR family which can be induced on a variety of leukocyte subsets. On T and NK cells, CD137 is expressed following activation and, if ligated by its natural ligand (CD137L), conveys polyubiquitination-mediated signals via TNF receptor associated factor 2 that inhibit apoptosis, while enhancing proliferation and effector functions. CD137 thus behaves as a bona fide inducible costimulatory molecule. These functional properties of CD137 can be exploited in cancer immunotherapy by systemic administration of agonist monoclonal antibodies, which increase anticancer CTLs and enhance NK-cell-mediated antibody-dependent cell-mediated cytotoxicity. Reportedly, anti-CD137 mAb and adoptive T-cell therapy strongly synergize, since (i) CD137 expression can be used to select the T cells endowed with the best activities against the tumor, (ii) costimulation of the lymphocyte cultures to be used in adoptive T-cell therapy can be done with CD137 agonist antibodies or CD137L, and (iii) synergistic effects upon coadministration of T cells and antibodies are readily observed in mouse models. Furthermore, the signaling cytoplasmic tail of CD137 is a key component of anti-CD19 chimeric antigen receptors that are used to redirect T cells against leukemia and lymphoma in the clinic. Ongoing phase II clinical trials with agonist antibodies and the presence of CD137 sequence in these successful chimeric antigen receptors highlight the importance of CD137 in oncoimmunology.

Low ambient oxygen prevents atherosclerosis

Large population studies have shown that living at higher altitudes, which lowers ambient oxygen exposure, is associated with reduced cardiovascular disease mortality. However, hypoxia has also been reported to promote atherosclerosis by worsening lipid metabolism and inflammation. We sought to address these disparate reports by reducing the ambient oxygen exposure of ApoE-/- mice. We observed that long-term adaptation to 10% O2 (equivalent to oxygen content at ∼5000 m), compared to 21% O2 (room air at sea level), resulted in a marked decrease in aortic atherosclerosis in ApoE-/- mice. This effect was associated with increased expression of the anti-inflammatory cytokine interleukin-10 (IL-10), known to be anti-atherogenic and regulated by hypoxia-inducible transcription factor-1α (HIF-1α). Supporting these observations, ApoE-/- mice that were deficient in IL-10 (IL10-/- ApoE-/- double knockout) failed to show reduced atherosclerosis in 10% oxygen. Our study reveals a specific mechanism that can help explain the decreased prevalence of ischemic heart disease in populations living at high altitudes and identifies ambient oxygen exposure as a potential factor that could be modulated to alter pathogenesis. Key messages: Chronic low ambient oxygen exposure decreases atherosclerosis in mice. Anti-inflammatory cytokine IL-10 levels are increased by low ambient O2. This is consistent with the established role of HIF-1α in IL10 transactivation. Absence of IL-10 results in the loss of the anti-atherosclerosis effect of low O2. This mechanism may contribute to decreased atherosclerosis at high altitudes.