mTOR- and HIF-1α-mediated aerobic glycolysis as metabolic basis for trained immunity

Glycolysis inhibition as a cancer treatment and its role in an anti-tumour immune response

Increased glycolysis is the main source of energy supply in cancer cells that use this metabolic pathway for ATP generation. Altered energy metabolism is a biochemical fingerprint of cancer cells that represents one of the "hallmarks of cancer". The immune system can prevent tumour growth by eliminating cancer cells but this editing process ultimately results in poorly immunogenic cells remaining allowing for unchallenged tumour growth. In this review we look at the glycolysis pathway as a target for cancer treatments. We also examine the interplay between the glycolysis modulation and the immune response as an anti-cancer therapy.

Inter-individual variability and genetic influences on cytokine responses to bacteria and fungi

Little is known about the inter-individual variation of cytokine responses to different pathogens in healthy individuals. To systematically describe cytokine responses elicited by distinct pathogens and to determine the effect of genetic variation on cytokine production, we profiled cytokines produced by peripheral blood mononuclear cells from 197 individuals of European origin from the 200 Functional Genomics (200FG) cohort in the Human Functional Genomics Project (http://www.humanfunctionalgenomics.org), obtained over three different years. We compared bacteria- and fungi-induced cytokine profiles and found that most cytokine responses were organized around a physiological response to specific pathogens, rather than around a particular immune pathway or cytokine. We then correlated genome-wide single-nucleotide polymorphism (SNP) genotypes with cytokine abundance and identified six cytokine quantitative trait loci (QTLs). Among them, a cytokine QTL at the NAA35-GOLM1 locus markedly modulated interleukin (IL)-6 production in response to multiple pathogens and was associated with susceptibility to candidemia. Furthermore, the cytokine QTLs that we identified were enriched among SNPs previously associated with infectious diseases and heart diseases. These data reveal and begin to explain the variability in cytokine production by human immune cells in response to pathogens.

Sharpening nature's tools for efficient tuberculosis control: A review of the potential role and development of host-directed therapies and strategies for targeted respiratory delivery

Centuries since it was first described, tuberculosis (TB) remains a significant global public health issue. Despite ongoing holistic measures implemented by health authorities and a number of new oral treatments reaching the market, there is still a need for an advanced, efficient TB treatment. An adjunctive, host-directed therapy designed to enhance endogenous pathways and hence compliment current regimens could be the answer. The integration of drug repurposing, including synthetic and naturally occurring compounds, with a targeted drug delivery platform is an attractive development option. In order for a new anti-tubercular treatment to be produced in a timely manner, a multidisciplinary approach should be taken from the outset including stakeholders from academia, the pharmaceutical industry, and regulatory bodies keeping the patient as the key focus. Pre-clinical considerations for the development of a targeted host-directed therapy are discussed here.

The Proteomic Landscape of Human Ex Vivo Regulatory and Conventional T Cells Reveals Specific Metabolic Requirements

Human CD4⁺CD25^hiFoxp3⁺CD127⁻ Treg and CD4⁺CD25⁻Foxp3⁻ Tconv cell functions are governed by their metabolic requirements. Here we report a comprehensive comparative analysis between ex vivo human Treg and Tconv cells that comprises analyses of the proteomic networks in subcellular compartments. We identified a dominant proteomic signature at the metabolic level that primarily impacted the highly-tuned balance between glucose and fatty-acid oxidation in the two cell types. Ex vivo Treg cells were highly glycolytic while Tconv cells used predominantly fatty-acid oxidation (FAO). When cultured in vitro, Treg cells engaged both glycolysis and FAO to proliferate, while Tconv cell proliferation mainly relied on glucose metabolism. Our unbiased proteomic analysis provides a molecular picture of the impact of metabolism on ex vivo human Treg versus Tconv cell functions that might be relevant for therapeutic manipulations of these cells.

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Ex vivo human Treg cells are highly glycolytic and proliferating

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Ex vivo human Tconv cells use fatty-acid oxidation (FAO) and are non-proliferating

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In vitro proliferation of human Treg cells requires both glycolysis and FAO

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In vitro proliferation of human Tconv cells relies mainly on glycolysis

Unravelling the nature of non-specific effects of vaccines-A challenge for innate immunologists

Epidemiological observations have shown that vaccines can influence morbidity and mortality more than can be ascribed to target-disease immunity. A growing number of immunological studies have helped identify possible biological mechanisms to explain these so-called nonspecific effects (NSE) of vaccines, including heterologous T-cell reactivity and innate immune memory or 'trained innate immunity', which involves epigenetic reprogramming of innate immune cells. Here, we review the epidemiological evidence for NSE as well as human, animal and in vitro immunological data that could explain these NSE, and discuss priorities for future epidemiologic and immunologic studies to further unravel the biology and optimize the benefits of current and new vaccines.

Expanded Glucose Import Capability Affords Staphylococcus aureus Optimized Glycolytic Flux during Infection

Acquisition of numerous virulence determinants affords Staphylococcus aureus greater pathogenicity than other skin-colonizing staphylococci in humans. Additionally, the metabolic adaptation of S. aureus to nonrespiratory conditions encountered during infection (e.g., hypoxia, nitric oxide, iron chelation) has been implicated as contributing to S. aureus virulence. Specifically, S. aureus has been shown to ferment glycolytic substrates in nonrespiratory environments encountered within the host. Here, we show that S. aureus has acquired unique carbohydrate transporters that facilitate the maximal uptake of host sugars and serve to support nonrespiratory growth in inflamed tissue. The carbohydrate substrates of 11 S. aureus transporters were identified, and at least four of their genes encode S. aureus glucose transporters (glcA, glcB, glcC, and glcU). Moreover, two transporter genes (glcA and glcC) are unique to S. aureus and contribute disproportionately to the nonrespiratory growth of S. aureus on glucose. Targeted inactivation of sugar transporters reduced glucose uptake and attenuated S. aureus in a murine model of skin and soft tissue infections. These data expand the evidence for metabolic adaptation of S. aureus to invasive infection and demonstrate the specific requirement for the fermentation of glucose over all other available carbohydrates. Ultimately, acquisition of foreign genes allows S. aureus to adopt a metabolic strategy resembling that of infiltrating host immune cells: high glycolytic flux coupled to lactate excretion.

The bacterial pathogen Staphylococcus aureus causes a wide range of human infections that are costly and difficult to treat. S. aureus differs from closely related commensal staphylococci in its ability to flourish following the invasion of deeper tissue from the skin surface. There, S. aureus primarily uses glucose to grow under respiration-limiting conditions imposed by the immune system. It was previously unclear how S. aureus thrives in this environment when other Staphylococcus species cannot. Our results provide evidence that S. aureus has acquired an expanded repertoire of carbohydrate transporters. In particular, four glucose transporters contribute to efficient S. aureus growth during infection. Thus, S. aureus has evolved to maximize its glucose uptake abilities for enhanced glycolytic flux during tissue invasion. This dependence on glucose acquisition for S. aureus virulence may also explain links between serious infectious complications associated with diabetic patients exhibiting elevated blood glucose levels.

Anti-infective Activity of 2-Cyano-3-Acrylamide Inhibitors with Improved Drug-Like Properties against Two Intracellular Pathogens

Due to the rise of antibiotic resistance and the small number of effective antiviral drugs, new approaches for treating infectious diseases are urgently needed. Identifying targets for host-based therapies represents an emerging strategy for drug discovery. The ubiquitin-proteasome system is a central mode of signaling in the eukaryotic cell and may be a promising target for therapies that bolster the host's ability to control infection. Deubiquitinase (DUB) enzymes are key regulators of the host inflammatory response, and we previously demonstrated that a selective DUB inhibitor and its derivative promote anti-infective activities in host cells. To find compounds with anti-infective efficacy but improved toxicity profiles, we tested a library of predominantly 2-cyano-3-acrylamide small-molecule DUB inhibitors for anti-infective activity in macrophages against two intracellular pathogens: murine norovirus (MNV) and Listeria monocytogenes We identified compound C6, which inhibited DUB activity in human and murine cells and reduced intracellular replication of both pathogens with minimal toxicity in cell culture. Treatment with C6 did not significantly affect the ability of macrophages to internalize virus, suggesting that the anti-infective activity interferes with postentry stages of the MNV life cycle. Metabolic stability and pharmacokinetic assays showed that C6 has a half-life in mouse liver microsomes of ∼20 min and has a half-life of approximately 4 h in mice when administered intravenously. Our results provide a framework for targeting the host ubiquitin system in the development of host-based therapies for infectious disease. Compound C6 represents a promising tool with which to elucidate the role of DUBs in the macrophage response to infection.

Macrophage adaptation in airway inflammatory resolution

Bacterial and viral infections (exacerbations) are particularly problematic in those with underlying respiratory disease, including post-viral infection, asthma, chronic obstructive pulmonary disease and pulmonary fibrosis. Patients experiencing exacerbations tend to be at the more severe end of the disease spectrum and are often difficult to treat. Most of the unmet medical need remains in this patient group. Airway macrophages are one of the first cell populations to encounter airborne pathogens and, in health, exist in a state of reduced responsiveness due to interactions with the respiratory epithelium and specific factors found in the airway lumen. Granulocyte-macrophage colony-stimulating factor, interleukin-10, transforming growth factor-β, surfactant proteins and signalling via the CD200 receptor, for example, all raise the threshold above which airway macrophages can be activated. We highlight that following severe respiratory inflammation, the airspace microenvironment does not automatically re-set to baseline and may leave airway macrophages more restrained than they were at the outset. This excessive restraint is mediated in part by the clearance of apoptotic cells and components of extracellular matrix. This implies that one strategy to combat respiratory exacerbations would be to retune airway macrophage responsiveness to allow earlier bacterial recognition.

Inverse Correlation between IL-10 and HIF-1α in Macrophages Infected with Histoplasma capsulatum

Hypoxia-inducible factor (HIF)-1α is a transcription factor that regulates metabolic and immune response genes in the setting of low oxygen tension and inflammation. We investigated the function of HIF-1α in the host response to Histoplasma capsulatum because granulomas induced by this pathogenic fungus develop hypoxic microenvironments during the early adaptive immune response. In this study, we demonstrated that myeloid HIF-1α-deficient mice exhibited elevated fungal burden during the innate immune response (prior to 7 d postinfection) as well as decreased survival in response to a sublethal inoculum of H. capsulatum The absence of myeloid HIF-1α did not alter immune cell recruitment to the lungs of infected animals but was associated with an elevation of the anti-inflammatory cytokine IL-10. Treatment with mAb to IL-10 restored protective immunity to the mutant mice. Macrophages (Mϕs) constituted most IL-10-producing cells. Deletion of HIF-1α in neutrophils or dendritic cells did not alter fungal burden, thus implicating Mϕs as the pivotal cell in host resistance. HIF-1α was stabilized in Mϕs following infection. Increased activity of the transcription factor CREB in HIF-1α-deficient Mϕs drove IL-10 production in response to H. capsulatum IL-10 inhibited Mϕ control of fungal growth in response to the activating cytokine IFN-γ. Thus, we identified a critical function for Mϕ HIF-1α in tempering IL-10 production following infection. We established that transcriptional regulation of IL-10 by HIF-1α and CREB is critical for activation of Mϕs by IFN-γ and effective handling of H. capsulatum.

MicroRNA-138 suppresses proliferation, invasion and glycolysis in malignant melanoma cells by targeting HIF-1α

MicroRNAs (miRs) may induce mRNA degradation or inhibit protein translation by directly binding to the 3'-untranslational region of target mRNAs. It has been reported that miR-138 is downregulated in malignant melanoma (MM) cells. However, the role of miR-138 in MM cell proliferation, invasion and energy metabolism remains unknown. These were investigated using reverse transcription-quantitative polymerase chain reaction was used to evaluate the expression of miR-138 and the mRNA expression of hypoxia-inducible factor-1α (HIF-1α), as HIF-1α serves a crucial role in glycolysis, which is important for tumor growth. In addition, western blot analysis was used to detected the protein expression of HIF-1α, while MTT and Transwell assays evaluated cell proliferation and invasion, respectively. Furthermore, glucose consumption and lactic acid production were assessed. These tests were conducted using the normal human melanocyte cell line HM and the MM cell line WM451, which was transfected variously with scramble miR mimics, miR-138 mimics, miR-138 inhibitor, non-specific small interfering (si)RNA, HIF-1α siRNA, or co-transfected with miR-138 mimics and pc-DNA3.1(+)-HIF-1α plasmid. The results showed that miR-138 was significantly downregulated in MM WM451 cells compared to a normal melanocyte cell line HM. Overexpression of miR-138 significantly inhibited the proliferation and invasion of WM451 cells. These effects were similar to those induced by the siRNA-mediated knockdown of HIF-1α, a direct target of miR-138. Further investigation found that miR-138 negatively regulated the protein expression of HIF-1α in WM451 cells. Moreover, upregulation of miR-138 notably inhibited the glycolysis level, as demonstrated by reduced glucose consumption and lactic acid production, which could be reversed by the overexpression of HIF-1α. In summary, the present study demonstrated that miR-138 is able to inhibit proliferation, invasion and glycolysis in MM cells, potentially by directly targeting HIF-1α.

Harnessing the beneficial heterologous effects of vaccination

Clinical evidence strongly suggests that certain live vaccines, in particular bacille Calmette-Guérin (BCG) and measles vaccines, can reduce all-cause mortality, most probably through protection against non-targeted pathogens in addition to the targeted pathogen. The underlying mechanisms are currently unknown. We discuss how heterologous lymphocyte activation and innate immune memory could promote protection beyond the intended target pathogen and consider how vaccinologists could leverage heterologous immunity to improve outcomes in vulnerable populations, in particular the very young and the elderly.

New advances in invasive aspergillosis immunobiology leading the way towards personalized therapeutic approaches

Invasive aspergillosis (IA) remains a devastating disease in immune compromised patients despite significant advances in our understanding of fungal virulence and host defense mechanisms. In this review, we summarize important research advances in the fight against IA with particular focus on early events in the interactions between Aspergillus fumigatus and the host that occur in the respiratory tract. Advances in understanding mechanisms of immune effector cell recruitment, antifungal effector mechanisms, and how the dynamic host-fungal interaction alters the local microenvironment to effect outcomes are highlighted. These advances illustrate exciting new therapeutic opportunities, but also emphasize the importance of understanding each unique fungus-host interaction for improving patient outcomes.

Hypoxia and classical activation limits Mycobacterium tuberculosis survival by Akt-dependent glycolytic shift in macrophages

Cellular reactive oxygen species (ROS) is a major antibacterial defense mechanism used by macrophages upon activation. Exposure of Mycobacterium tuberculosis (Mtb)-infected macrophages to hypoxia is known to compromise the survival of the pathogen. Here we report that the hypoxia-induced control of intracellular Mtb load in RAW 264.7 macrophages was mediated by regulating the cellular ROS levels. We show that similar to classical activation, hypoxia incubation of macrophages resulted in decreased mitochondrial outer membrane potential (MOMP) and a concomitant increase in the cellular ROS levels. Mitochondrial depolarization and consequently higher ROS could be blocked by knocking down Akt using siRNAs, which acted by inhibiting the switch to glycolytic mode of metabolism, an essential adaptive response upon classical activation or hypoxic incubation of macrophages. Moreover, in the classically activated macrophages or in the macrophages under hypoxia incubation, supplementation with additional glucose had similar effects as Akt knockdown. Interestingly, in both the cases, the reversal of phenotype was linked with the ability of the mitochondrial F₀–F₁ ATP synthase activity to maintain the MOMP in the absence of oxidative phosphorylation. Both Akt knockdown and glucose supplementation were also able to rescue Mtb survival in these macrophages upon classical activation or hypoxia incubation. These results provide a framework for better understanding of how the interplay between oxygen supply, which is limiting in the human tubercular granulomas, and nutrient availability could together direct the outcome of infections in vivo.

MiR-186 inhibited aerobic glycolysis in gastric cancer via HIF-1α regulation

Deregulation of microRNAs in human malignancies has been well documented, among which microRNA-186 (miR-186) has an antiproliferative role in some carcinomas. Here we demonstrate that low expression of miR-186 facilitates aerobic glycolysis in gastric cancer. MiR-186 suppresses cell proliferation induced by hypoxia inducible factor 1 alpha (HIF-1α) in gastric cancer cell lines MKN45 and SGC7901. Cellular glycolysis, including cellular glucose uptake, lactate, ATP/ADP and NAD+/NADH ratios, are also inhibited by miR-186. The negative regulation of miR-186 on HIF-1α effects its downstream targets, including programmed death ligand 1 and two glycolytic key enzymes, hexokinase 2 and platelet-type phosphofructokinase. The antioncogenic effects of miR-186 are proved by in vivo xenograft tumor experiment. The results demonstrate that the miR-186/HIF-1α axis has an antioncogenic role in gastric cancer.

New insights into the multidimensional concept of macrophage ontogeny, activation and function

Macrophages have protective roles in immunity to pathogens, tissue development, homeostasis and repair following damage. Maladaptive immunity and inflammation provoke changes in macrophage function that are causative of disease. Despite a historical wealth of knowledge about macrophages, recent advances have revealed unknown aspects of their development and function. Following development, macrophages are activated by diverse signals. Such tissue microenvironmental signals together with epigenetic changes influence macrophage development, activation and functional diversity, with consequences in disease and homeostasis. We discuss here how recent discoveries in these areas have led to a multidimensional concept of macrophage ontogeny, activation and function. In connection with this, we also discuss how technical advances facilitate a new roadmap for the isolation and analysis of macrophages at high resolution.

Epigenetic Regulation of Adaptive NK Cell Diversification

Natural killer (NK) cells were previously considered to represent short-lived, innate lymphocytes. However, mouse models have revealed expansion and persistence of differentiated NK cell subsets in response to cytomegalovirus (CMV) infection, paralleling antigen-specific T cell differentiation. Congruently, analyses of humans have uncovered CMV-associated NK cell subsets characterized by epigenetic diversification processes that lead to altered target cell specificities and functional capacities. Here, focusing on responses to viruses, we review similarities and differences between mouse and human adaptive NK cells, identifying molecular analogies that may be key to transcriptional reprogramming and functional alterations. We discuss possible molecular mechanisms underlying epigenetic diversification and hypothesize that processes driving epigenetic diversification may represent a more widespread mechanism for fine-tuning and optimization of cellular immunity.

Molecular and epigenetic basis of macrophage polarized activation

Macrophages are unique cells for origin, heterogeneity and plasticity. At steady state most of macrophages are derived from fetal sources and maintained in adulthood through self-renewing. Despite sharing common progenitors, a remarkable heterogeneity characterized tissue-resident macrophages indicating that local signals educate them to express organ-specific functions. Macrophages are extremely plastic: chromatin landscape and transcriptional programs can be dynamically re-shaped in response to microenvironmental changes. Owing to their ductility, macrophages are crucial orchestrators of both initiation and resolution of immune responses and key supporters of tissue development and functions in homeostatic and pathological conditions. Herein, we describe current understanding of heterogeneity and plasticity of macrophages using the M1-M2 dichotomy as operationally useful simplification of polarized activation. We focused on the complex network of signaling cascades, metabolic pathways, transcription factors, and epigenetic changes that control macrophage activation. In particular, this network was addressed in sepsis, as a paradigm of a pathological condition determining dynamic macrophage reprogramming.

Metabolic reprogramming through fatty acid transport protein 1 (FATP1) regulates macrophage inflammatory potential and adipose inflammation

Objective

A novel approach to regulate obesity-associated adipose inflammation may be through metabolic reprogramming of macrophages (MΦs). Broadly speaking, MΦs dependent on glucose are pro-inflammatory, classically activated MΦs (CAM), which contribute to adipose inflammation and insulin resistance. In contrast, MΦs that primarily metabolize fatty acids are alternatively activated MΦs (AAM) and maintain tissue insulin sensitivity. In actuality, there is much flexibility and overlap in the CAM-AAM spectrum in vivo dependent upon various stimuli in the microenvironment. We hypothesized that specific lipid trafficking proteins, e.g. fatty acid transport protein 1 (FATP1), would direct MΦ fatty acid transport and metabolism to limit inflammation and contribute to the maintenance of adipose tissue homeostasis.

Methods

Bone marrow derived MΦs (BMDMs) from Fatp1^−/− and Fatp1^+/+ mice were used to investigate FATP1-dependent substrate metabolism, bioenergetics, metabolomics, and inflammatory responses. We also generated C57BL/6J chimeric mice by bone marrow transplant specifically lacking hematopoetic FATP1 (Fatp1^B−/−) and controls Fatp1^B+/+. Mice were challenged by high fat diet (HFD) or low fat diet (LFD) and analyses including MRI, glucose and insulin tolerance tests, flow cytometric, histologic, and protein quantification assays were conducted. Finally, an FATP1-overexpressing RAW 264.7 MΦ cell line (FATP1-OE) and empty vector control (FATP1-EV) were developed as a gain of function model to test effects on substrate metabolism, bioenergetics, metabolomics, and inflammatory responses.

Results

Fatp1 is downregulated with pro-inflammatory stimulation of MΦs. Fatp1^−/− BMDMs and FATP1-OE RAW 264.7 MΦs demonstrated that FATP1 reciprocally controled metabolic flexibility, i.e. lipid and glucose metabolism, which was associated with inflammatory response. Supporting our previous work demonstrating the positive relationship between glucose metabolism and inflammation, loss of FATP1 enhanced glucose metabolism and exaggerated the pro-inflammatory CAM phenotype. Fatp1^B−/− chimeras fed a HFD gained more epididymal white adipose mass, which was inflamed and oxidatively stressed, compared to HFD-fed Fatp1^B+/+ controls. Adipose tissue macrophages displayed a CAM-like phenotype in the absence of Fatp1. Conversely, functional overexpression of FATP1 decreased many aspects of glucose metabolism and diminished CAM-stimulated inflammation in vitro. FATP1 displayed acyl-CoA synthetase activity for long chain fatty acids in MΦs and modulated lipid mediator metabolism in MΦs.

Conclusion

Our findings provide evidence that FATP1 is a novel regulator of MΦ activation through control of substrate metabolism. Absence of FATP1 exacerbated pro-inflammatory activation in vitro and increased local and systemic components of the metabolic syndrome in HFD-fed Fatp1^B−/− mice. In contrast, gain of FATP1 activity in MΦs suggested that Fatp1-mediated activation of fatty acids, substrate switch to glucose, oxidative stress, and lipid mediator synthesis are potential mechanisms. We demonstrate for the first time that FATP1 provides a unique mechanism by which the inflammatory tone of adipose and systemic metabolism may be regulated.

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FATP1-mediated activation of fatty acids is a novel approach to limit inflammation.

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Fatp1 deficiency primed macrophages for pro-inflammatory activation.

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Lack of Fatp1 led to greater HFD-induced adipose inflammation.

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Fatp1^−/− adipose tissue macrophages were classically activated.

Long-term activation of the innate immune system in atherosclerosis

Efforts to reverse the pathologic consequences of vulnerable plaques are often stymied by the complex treatment resistant pro-inflammatory environment within the plaque. This suggests that pro-atherogenic stimuli, such as LDL cholesterol and high fat diets may impart longer lived signals on (innate) immune cells that persist even after reversing the pro-atherogenic stimuli. Recently, a series of studies challenged the traditional immunological paradigm that innate immune cells cannot display memory characteristics. Epigenetic reprogramming in these myeloid cell subsets, after exposure to certain stimuli, has been shown to alter the expression of genes upon re-exposure. This phenomenon has been termed trained innate immunity or innate immune memory. The changed responses of 'trained' innate immune cells can confer nonspecific protection against secondary infections, suggesting that innate immune memory has likely evolved as an ancient mechanism to protect against pathogens. However, dysregulated processes of immunological imprinting mediated by trained innate immunity may also be detrimental under certain conditions as the resulting exaggerated immune responses could contribute to autoimmune and inflammatory diseases, such as atherosclerosis. Pro-atherogenic stimuli most likely cause epigenetic modifications that persist for prolonged time periods even after the initial stimulus has been removed. In this review we discuss the concept of trained innate immunity in the context of a hyperlipidemic environment and atherosclerosis. According to this idea the epigenome of myeloid (progenitor) cells is presumably modified for prolonged periods of time, which, in turn, could evoke a condition of continuous immune cell over-activation.

Trained immunity: A program of innate immune memory in health and disease

The general view that only adaptive immunity can build immunological memory has recently been challenged. In organisms lacking adaptive immunity, as well as in mammals, the innate immune system can mount resistance to reinfection, a phenomenon termed "trained immunity" or "innate immune memory." Trained immunity is orchestrated by epigenetic reprogramming, broadly defined as sustained changes in gene expression and cell physiology that do not involve permanent genetic changes such as mutations and recombination, which are essential for adaptive immunity. The discovery of trained immunity may open the door for novel vaccine approaches, new therapeutic strategies for the treatment of immune deficiency states, and modulation of exaggerated inflammation in autoinflammatory diseases.

Temporal proteomic profiling of Chlamydia trachomatis-infected HeLa-229 human cervical epithelial cells

Chlamydia trachomatis is the leading causative agent of bacterial sexually transmitted infections worldwide which can lead to female pelvic inflammatory disease and infertility. A greater understanding of host response during chlamydial infection is essential to design intervention technique to reduce the increasing incidence rate of genital chlamydial infection. In this study, we investigated proteome changes in epithelial cells during C. trachomatis infection by using an isobaric tags for relative and absolute quantitation (iTRAQ) labeling technique coupled with a liquid chromatography-tandem mass spectrometry (LC-MS(3) ) analysis. C. trachomatis (serovar D, MOI 1)-infected HeLa-229 human cervical carcinoma epithelial cells (at 2, 4 and 8 h) showed profound modifications of proteome profile which involved 606 host proteins. MGST1, SUGP2 and ATXN10 were among the top in the list of the differentially upregulated protein. Through pathway analysis, we suggested the involvement of eukaryotic initiation factor 2 (eIF2) and mammalian target of rapamycin (mTOR) in host cells upon C. trachomatis infection. Network analysis underscored the participation of DNA repair mechanism during C. trachomatis infection. In summary, intense modifications of proteome profile in C. trachomatis-infected HeLa-229 cells indicate complex host-pathogen interactions at early phase of chlamydial infection.

Trained immunity: a new avenue for tuberculosis vaccine development

Adaptive immunity towards tuberculosis (TB) has been extensively studied for many years. In addition, in recent years the profound contribution of innate immunity to host defence against this disease has become evident. The discovery of pattern recognition receptors, which allow innate immunity to tailor its response to different infectious agents, has challenged the view that this arm of immunity is nonspecific. Evidence is now accumulating that innate immunity can remember a previous exposure to a microorganism and respond differently during a second exposure. Although the specificity and memory of innate immunity cannot compete with the highly sophisticated adaptive immune response, its contribution to host defence against infection and to vaccine-induced immunity should not be underestimated and needs to be explored. Here, we present the concept of trained immunity and discuss how this may contribute to new avenues for control of TB.

Glucose Metabolism in T Cells and Monocytes: New Perspectives in HIV Pathogenesis

Activation of the immune system occurs in response to the recognition of foreign antigens and receipt of optimal stimulatory signals by immune cells, a process that requires energy. Energy is also needed to support cellular growth, differentiation, proliferation, and effector functions of immune cells. In HIV-infected individuals, persistent viral replication, together with inflammatory stimuli contributes to chronic immune activation and oxidative stress. These conditions remain even in subjects with sustained virologic suppression on antiretroviral therapy. Here we highlight recent studies demonstrating the importance of metabolic pathways, particularly those involving glucose metabolism, in differentiation and maintenance of the activation states of T cells and monocytes. We also discuss how changes in the metabolic status of these cells may contribute to ongoing immune activation and inflammation in HIV- infected persons and how this may contribute to disease progression, establishment and persistence of the HIV reservoir, and the development of co-morbidities. We provide evidence that other viruses such as Epstein-Barr and Flu virus also disrupt the metabolic machinery of their host cells. Finally, we discuss how redox signaling mediated by oxidative stress may regulate metabolic responses in T cells and monocytes during HIV infection.

An Immunological Perspective on Neonatal Sepsis

Despite concerted international efforts, mortality from neonatal infections remains unacceptably high in some areas of the world, particularly for premature infants. Recent developments in flow cytometry and next-generation sequencing technologies have led to major discoveries over the past few years, providing a more integrated understanding of the developing human immune system in the context of its microbial environment. We review these recent findings, focusing on how in human newborns incomplete maturation of the immune system before a full term of gestation impacts on their vulnerability to infection. We also discuss some of the clinical implications of this research in guiding the design of more-accurate age-adapted diagnostic and preventive strategies for neonatal sepsis.

Monocyte-mediated defense against bacteria, fungi, and parasites

Circulating blood monocytes are a heterogeneous leukocyte population that contributes critical antimicrobial and regulatory functions during systemic and tissue-specific infections. These include patrolling vascular tissue for evidence of microbial invasion, infiltrating peripheral tissues and directly killing microbial invaders, conditioning the inflammatory milieu at sites of microbial tissue invasion, and orchestrating the activation of innate and adaptive immune effector cells. The central focus of this review is the in vivo mechanisms by which monocytes and their derivative cells promote microbial clearance and immune regulation. We include an overview of murine models to examine monocyte functions during microbial challenges and review our understanding of the functional roles of monocytes and their derivative cells in host defense against bacteria, fungi, and parasites.

Innate immune reconstitution with suppression of HIV-1

Progressive HIV-1 infection leads to both profound immune suppression and pathologic inflammation in the majority of infected individuals. While adaptive immune dysfunction, as evidenced by CD4⁺ T cell depletion and exhaustion, has been extensively studied, less is known about the functional capacity of innate immune cell populations in the context of HIV-1 infection. Given the broad susceptibility to opportunistic infections and the dysregulated inflammation observed in progressive disease, we hypothesized that there would be significant changes in the innate cellular responses. Using a cohort of patients with multiple samplings before and after antiretroviral therapy (ART) initiation, we demonstrated increased responses to innate immune stimuli following viral suppression, as measured by the production of inflammatory cytokines. Plasma viral load itself had the strongest association with this change in innate functional capacity. We further identified epigenetic modifications in the TNFA promoter locus in monocytes that are associated with viremia, suggesting a molecular mechanism for the observed changes in innate immune function following initiation of ART. These data indicate that suppression of HIV-1 viremia is associated with changes in innate cellular function that may in part determine the restoration of protective immune responses.

Macrophages and Iron Metabolism

Iron is a transition metal that due to its inherent ability to exchange electrons with a variety of molecules is essential to support life. In mammals, iron exists mostly in the form of heme, enclosed within an organic protoporphyrin ring and functioning primarily as a prosthetic group in proteins. Paradoxically, free iron also has the potential to become cytotoxic when electron exchange with oxygen is unrestricted and catalyzes the production of reactive oxygen species. These biological properties demand that iron metabolism is tightly regulated such that iron is available for core biological functions while preventing its cytotoxic effects. Macrophages play a central role in establishing this delicate balance. Here, we review the impact of macrophages on heme-iron metabolism and, reciprocally, how heme-iron modulates macrophage function.

The cells that mediate innate immune memory and their functional significance in inflammatory and infectious diseases

Immunological memory mediated by antigen-specific T and B cells is the foundation of adaptive immunity and is fundamental to the heightened and rapid protective immune response induced by vaccination or following re-infection with the same pathogen. While the innate immune system has classically been considered to be non-specific and devoid of memory, it now appears that it can be trained following exposure to microbes or their products and that this may confer a form of memory on innate immune cells. The evidence for immunological memory outside of T and B cells has been best established for natural killer (NK) cells, where it has been known for decades that NK cells have heighten responses following immunological re-challenge. Furthermore, recent studies have demonstrated that monocyte/macrophages, and probably dendritic cells, can be re-programmed through epigenetic modification, following exposure to pathogens or their products, resulting in heighted responses following a second stimulation. Unlike antigen-specific memory of the adaptive immune system, the second stimulation does not have to be with the same pathogen or antigen. Indirect evidence for this comes from reports on the non-specific beneficial effect of certain live vaccines, such as Bacillus Calmette Guerin (BCG) against unrelated childhood infectious diseases. It also appears that certain pathogen or pathogen-derived molecules can prime immune cells, especially macrophages, to secrete more anti-inflammatory and less pro-inflammatory cyokines, thus opening up the possibility of exploiting innate immune training as a new therapeutic approach for inflammatory diseases.

Earlier infantile immune maturation is related to higher DTP vaccine responses in children

There are large inter-individual variations in vaccine-specific antibody responses in children. We sought to investigate whether early-life environmental factors and/or adaptive immune maturation were related to diphtheria–tetanus–pertussis (DTP) vaccine-specific antibody levels at 18 months of age. In the prospective FARMFLORA birth-cohort, including both farming and non-farming families, children were immunized with DTP vaccine at 3, 5 and 12 months of age. DTP vaccine-induced antibody levels were measured in plasma at 18 months of age. Infants' blood samples obtained at birth, 3–5 days, 4, 18 and 36 months and at 8 years of age were analyzed for total CD4⁺ T- and B-cell counts, proportions of naïve and memory T and B cells, and fractions of putative regulatory T cells by flow cytometry. Multivariate factor analysis was used to examine associations between immune variables and vaccine responses. The most apparent multivariate pattern was that higher anti-DTP antibody titers at 18 months of age were associated with lower infantile total counts of T and B cells in the blood. Furthermore, lower infantile total T- and B-cell blood counts were associated with higher proportions of circulating CD45RO⁺ memory T cells and to lower proportions of α4β7⁺ naïve T cells later in childhood. The multivariate findings were corroborated in univariate correlation analyses. Sex, delivery mode and dairy farm exposure were unrelated to the magnitude of DTP-specific antibody responses. Our results thus suggest that children with a more mature/activated infantile adaptive immunity respond with higher vaccine-induced anti-DTP antibody levels at 18 months of age.

Trained immunity: A smart way to enhance innate immune defence

The innate arm of the immune system is generally viewed as primitive and non-specific and - in contrast to the adaptive immune arm - not to possess memory. However in plants and invertebrate animals that lack adaptive immunity, innate immunity will exhibit a prolonged enhanced functional state after adequate priming. A similar enhancement of function of the innate immunity has occasionally been described in vertebrates, including humans. Over the past few years we have studied this phenomenon in greater detail and we have coined the term 'Trained (innate) immunity' (TI). TI can be induced by a variety of stimuli, of which we have studied BCG and β-glucan in greater detail. The non-specific protective effects of BCG that have been observed in vaccination studies in the literature are probably due to TI. Monocytes and macrophages are among the main cells of the innate immune arm that can be trained. We have discovered that both BCG (via NOD2 signalling) and β-glucan (via dectin-1) induce epigenetic reprogramming, in particular stable changes in histone trimethylation at H3K4. These epigenetic changes lead to cellular activation, enhanced cytokine production and a change in the metabolic state of the cell with a shift from oxidative phosphorylation to aerobic glycolysis. TI is not only important for host defence and vaccine responses, but most probably also for diseases like atherosclerosis. Modulation of TI is a promising area for new treatments.

Broad defects in the energy metabolism of leukocytes underlie immunoparalysis in sepsis

The acute phase of sepsis is characterized by a strong inflammatory reaction. At later stages in some patients, immunoparalysis may be encountered, which is associated with a poor outcome. By transcriptional and metabolic profiling of human patients with sepsis, we found that a shift from oxidative phosphorylation to aerobic glycolysis was an important component of initial activation of host defense. Blocking metabolic pathways with metformin diminished cytokine production and increased mortality in systemic fungal infection in mice. In contrast, in leukocytes rendered tolerant by exposure to lipopolysaccharide or after isolation from patients with sepsis and immunoparalysis, a generalized metabolic defect at the level of both glycolysis and oxidative metabolism was apparent, which was restored after recovery of the patients. Finally, the immunometabolic defects in humans were partially restored by therapy with recombinant interferon-γ, which suggested that metabolic processes might represent a therapeutic target in sepsis.

HIF-1 at the crossroads of hypoxia, inflammation, and cancer

The complex cross-talk of intricate intercellular signaling networks between the tumor and stromal cells promotes cancer progression. Hypoxia is one of the most common conditions encountered within the tumor microenvironment that drives tumorigenesis. Most responses to hypoxia are elicited by a family of transcription factors called hypoxia-inducible factors (HIFs), which induce expression of a diverse set of genes that assist cells to adapt to hypoxic environments. Among the three HIF protein family members, the role of HIF-1 is well established in cancer progression. HIF-1 functions as a signaling hub to coordinate the activities of many transcription factors and signaling molecules that impact tumorigenesis. This mini review discusses the complex role of HIF-1 and its context-dependent partners under various cancer-promoting events including inflammation and generation of cancer stem cells, which are implicated in tumor metastasis and relapse. In addition, the review highlights the importance of therapeutic targeting of HIF-1 for cancer prevention.

Genomic landscape of the individual host response and outcomes in sepsis: a prospective cohort study

BACKGROUND

Effective targeted therapy for sepsis requires an understanding of the heterogeneity in the individual host response to infection. We investigated this heterogeneity by defining interindividual variation in the transcriptome of patients with sepsis and related this to outcome and genetic diversity.

METHODS

We assayed peripheral blood leucocyte global gene expression for a prospective discovery cohort of 265 adult patients admitted to UK intensive care units with sepsis due to community-acquired pneumonia and evidence of organ dysfunction. We then validated our findings in a replication cohort consisting of a further 106 patients. We mapped genomic determinants of variation in gene transcription between patients as expression quantitative trait loci (eQTL).

FINDINGS

We discovered that following admission to intensive care, transcriptomic analysis of peripheral blood leucocytes defines two distinct sepsis response signatures (SRS1 and SRS2). The presence of SRS1 (detected in 108 [41%] patients in discovery cohort) identifies individuals with an immunosuppressed phenotype that included features of endotoxin tolerance, T-cell exhaustion, and downregulation of human leucocyte antigen (HLA) class II. SRS1 was associated with higher 14 day mortality than was SRS2 (discovery cohort hazard ratio (HR) 2·4, 95% CI 1·3-4·5, p=0·005; validation cohort HR 2·8, 95% CI 1·5-5·1, p=0·0007). We found that a predictive set of seven genes enabled the classification of patients as SRS1 or SRS2. We identified cis-acting and trans-acting eQTL for key immune and metabolic response genes and sepsis response networks. Sepsis eQTL were enriched in endotoxin-induced epigenetic marks and modulated the individual host response to sepsis, including effects specific to SRS group. We identified regulatory genetic variants involving key mediators of gene networks implicated in the hypoxic response and the switch to glycolysis that occurs in sepsis, including HIF1α and mTOR, and mediators of endotoxin tolerance, T-cell activation, and viral defence.

INTERPRETATION

Our integrated genomics approach advances understanding of heterogeneity in sepsis by defining subgroups of patients with different immune response states and prognoses, as well as revealing the role of underlying genetic variation. Our findings provide new insights into the pathogenesis of sepsis and create opportunities for a precision medicine approach to enable targeted therapeutic intervention to improve sepsis outcomes.

FUNDING

European Commission, Medical Research Council (UK), and the Wellcome Trust.

Akt-mTORC1 signaling regulates Acly to integrate metabolic input to control of macrophage activation

Macrophage activation/polarization to distinct functional states is critically supported by metabolic shifts. How polarizing signals coordinate metabolic and functional reprogramming, and the potential implications for control of macrophage activation, remains poorly understood. Here we show that IL-4 signaling co-opts the Akt-mTORC1 pathway to regulate Acly, a key enzyme in Ac-CoA synthesis, leading to increased histone acetylation and M2 gene induction. Only a subset of M2 genes is controlled in this way, including those regulating cellular proliferation and chemokine production. Moreover, metabolic signals impinge on the Akt-mTORC1 axis for such control of M2 activation. We propose that Akt-mTORC1 signaling calibrates metabolic state to energetically demanding aspects of M2 activation, which may define a new role for metabolism in supporting macrophage activation.

Fungal Chitin Induces Trained Immunity in Human Monocytes during Cross-talk of the Host with Saccharomyces cerevisiae

The immune system is essential to maintain the mutualistic homeostatic interaction between the host and its micro- and mycobiota. Living as a commensal,Saccharomyces cerevisiaecould potentially shape the immune response in a significant way. We observed thatS. cerevisiaecells induce trained immunity in monocytes in a strain-dependent manner through enhanced TNFα and IL-6 production upon secondary stimulation with TLR ligands, as well as bacterial and fungal commensals. Differential chitin content accounts for the differences in training properties observed among strains, driving induction of trained immunity by increasing cytokine production and direct antimicrobial activity bothin vitroandin vivo These chitin-induced protective properties are intimately associated with its internalization, identifying a critical role of phagosome acidification to facilitate microbial digestion. This study reveals how commensal and passenger microorganisms could be important in promoting health and preventing mucosal diseases by modulating host defense toward pathogens and thus influencing the host microbiota-immune system interactions.

Cutting Edge: Mycobacterium tuberculosis Induces Aerobic Glycolysis in Human Alveolar Macrophages That Is Required for Control of Intracellular Bacillary Replication

Recent advances in immunometabolism link metabolic changes in stimulated macrophages to production of IL-1β, a crucial cytokine in the innate immune response to Mycobacterium tuberculosis. To investigate this pathway in the host response to M. tuberculosis, we performed metabolic and functional studies on human alveolar macrophages, human monocyte-derived macrophages, and murine bone marrow-derived macrophages following infection with the bacillus in vitro. M. tuberculosis infection induced a shift from oxidative phosphorylation to aerobic glycolysis in macrophages. Inhibition of this shift resulted in decreased levels of proinflammatory IL-1β and decreased transcription of PTGS2, increased levels of anti-inflammatory IL-10, and increased intracellular bacillary survival. Blockade or absence of IL-1R negated the impact of aerobic glycolysis on intracellular bacillary survival, demonstrating that infection-induced glycolysis limits M. tuberculosis survival in macrophages through induction of IL-1β. Drugs that manipulate host metabolism may be exploited as adjuvants for future therapeutic and vaccination strategies.

Glioma Stem Cells and Their Microenvironments: Providers of Challenging Therapeutic Targets

Malignant gliomas are aggressive brain tumors with limited therapeutic options, possibly because of highly tumorigenic subpopulations of glioma stem cells. These cells require specific microenvironments to maintain their “stemness,” described as perivascular and hypoxic niches. Each of those niches induces particular signatures in glioma stem cells (e.g., activation of Notch signaling, secretion of VEGF, bFGF, SDF1 for the vascular niche, activation of HIF2α, and metabolic reprogramming for hypoxic niche). Recently, accumulated knowledge on tumor-associated macrophages, possibly delineating a third niche, has underlined the role of immune cells in glioma progression, via specific chemoattractant factors and cytokines, such as macrophage-colony stimulation factor (M-CSF). The local or myeloid origin of this new component of glioma stem cells niche is yet to be determined. Such niches are being increasingly recognized as key regulators involved in multiple stages of disease progression, therapy resistance, immune-escaping, and distant metastasis, thereby substantially impacting the future development of frontline interventions in clinical oncology. This review focuses on the microenvironment impact on the glioma stem cell biology, emphasizing GSCs cross talk with hypoxic, perivascular, and immune niches and their potential use as targeted therapy.

T Cells and Cancer: How Metabolism Shapes Immunity

Tumor microenvironment is characterized by a consistent reduction in oxygen and blood-borne nutrients that significantly affects the metabolism of distinct cell subsets. Immune cells populating malignant lesions need to activate alternative pathways to overcome tumor-prolonged nutrient deprivation. In particular, the metabolic switch occurring in transforming tissues dramatically impacts on tumor-infiltrating T cell biology. Remarkably, the recruitment and activation of T cell within cancers are instrumental for effective antitumor response. Therefore, T cell metabolic adaptation acts as crucial checkpoint hijacked by tumors to dampen antitumor immunity.

Natural killer cell memory in infection, inflammation and cancer

Immunological memory can be defined as a quantitatively and qualitatively enhanced immune response upon rechallenge. For natural killer (NK) cells, two main types of memory exist. First, similarly to T cells and B cells, NK cells can exert immunological memory after encounters with stimuli such as haptens or viruses, resulting in the generation of antigen-specific memory NK cells. Second, NK cells can remember inflammatory cytokine milieus that imprint long-lasting non-antigen-specific NK cell effector function. The basic concepts derived from studying NK cell memory provide new insights about innate immunity and could lead to novel strategies to improve treatments for infectious diseases and cancer.

Initiation and perpetuation of NLRP3 inflammasome activation and assembly

The NLRP3 (NOD-like receptor family, pyrin domain containing 3) inflammasome is a multiprotein complex that orchestrates innate immune responses to infection and cell stress through activation of caspase-1 and maturation of inflammatory cytokines pro-interleukin-1β (pro-IL-1β) and pro-IL-18. Activation of the inflammasome during infection can be protective, but unregulated NLRP3 inflammasome activation in response to non-pathogenic endogenous or exogenous stimuli can lead to unintended pathology. NLRP3 associates with mitochondria and mitochondrial molecules, and activation of the NLRP3 inflammasome in response to diverse stimuli requires cation flux, mitochondrial Ca(2+) uptake, and mitochondrial reactive oxygen species accumulation. It remains uncertain whether NLRP3 surveys mitochondrial integrity and senses mitochondrial damage, or whether mitochondria simply serve as a physical platform for inflammasome assembly. The structure of the active, caspase-1-processing NLRP3 inflammasome also requires further clarification, but recent studies describing the prion-like properties of ASC have advanced the understanding of how inflammasome assembly and caspase-1 activation occur while raising new questions regarding the propagation and resolution of NLRP3 inflammasome activation. Here, we review the mechanisms and pathways regulating NLRP3 inflammasome activation, discuss emerging concepts in NLRP3 complex organization, and expose the knowledge gaps hindering a comprehensive understanding of NLRP3 activation.

How Chemotherapy Increases the Risk of Systemic Candidiasis in Cancer Patients: Current Paradigm and Future Directions

Candida albicans is a fungal commensal and a major colonizer of the human skin, as well as of the gastrointestinal and genitourinary tracts. It is also one of the leading causes of opportunistic microbial infections in cancer patients, often presenting in a life-threatening, systemic form. Increased susceptibility to such infections in cancer patients is attributed primarily to chemotherapy-induced depression of innate immune cells and weakened epithelial barriers, which are the body’s first-line defenses against fungal infections. Moreover, classical chemotherapeutic agents also have a detrimental effect on components of the adaptive immune system, which further play important roles in the antifungal response. In this review, we discuss the current paradigm regarding the mechanisms behind the increased risk of systemic candidiasis in cancer patients. We also highlight some recent findings, which suggest that chemotherapy may have more extensive effects beyond the human host, in particular towards C. albicans itself and the bacterial microbiota. The extent to which these additional effects contribute towards the development of candidiasis in chemotherapy-treated patients remains to be investigated.

GSK3 Deficiencies in Hematopoietic Stem Cells Initiate Pre-neoplastic State that Is Predictive of Clinical Outcomes of Human Acute Leukemia

Initial pathway alternations required for pathogenesis of human acute myeloid leukemia (AML) are poorly understood. Here we reveal that removal of glycogen synthase kinase-3α (GSK-3α) and GSK-3β dependency leads to aggressive AML. Although GSK-3α deletion alone has no effect, GSK-3β deletion in hematopoietic stem cells (HSCs) resulted in a pre-neoplastic state consistent with human myelodysplastic syndromes (MDSs). Transcriptome and functional studies reveal that each GSK-3β and GSK-3α uniquely contributes to AML by affecting Wnt/Akt/mTOR signaling and metabolism, respectively. The molecular signature of HSCs deleted for GSK-3β provided a prognostic tool for disease progression and survival of MDS patients. Our study reveals that GSK-3α- and GSK-3β-regulated pathways can be responsible for stepwise transition to MDS and subsequent AML, thereby providing potential therapeutic targets of disease evolution.

Immunometabolism governs dendritic cell and macrophage function

Recent studies on intracellular metabolism in dendritic cells (DCs) and macrophages provide new insights on the functioning of these critical controllers of innate and adaptive immunity. Both cell types undergo profound metabolic reprogramming in response to environmental cues, such as hypoxia or nutrient alterations, but importantly also in response to danger signals and cytokines. Metabolites such as succinate and citrate have a direct impact on the functioning of macrophages. Immunogenicity and tolerogenicity of DCs is also determined by anabolic and catabolic processes, respectively. These findings provide new prospects for therapeutic manipulation in inflammatory diseases and cancer.

Metabolic Reprogramming of Immune Cells in Cancer Progression

Immune cells play a key role in host defense against infection and cancer. Upon encountering danger signals, these cells undergo activation leading to a modulation in their immune functions. However, recent studies reveal that immune cells upon activation also show distinct metabolic changes that impact their immune functions. Such metabolic reprogramming and its functional effects are well known for cancer cells. Given that immune cells have emerged as crucial players in cancer progression, it is important to understand whether immune cells also undergo metabolic reprogramming in tumors and how this might affect their contribution in cancer progression. This emerging aspect of tumor-associated immune cells is reviewed here, discussing metabolic reprogramming of different immune cell types, the key pathways involved, and its impact on tumor progression.

The Evolving Roles of Memory Immune Cells in Transplantation

Memory cells are the products of immune responses but also exert significant impact on subsequent immunity and immune tolerance, thus placing them in a unique position in transplant research. Memory cells are heterogeneous, including not only memory T cells but also memory B cells and innate memory cells. Memory cells are a critical component of protective immunity against invading pathogens, especially in immunosuppressed patients, but they also mediate graft loss and tolerance resistance. Recent studies suggest that some memory cells unexpectedly act as regulatory cells, promoting rather than hindering transplant survival. This functional diversity makes therapeutic targeting of memory cells a challenging task in transplantation. In this article, we highlight recent advances in our understanding of memory cells, focusing on diversity of memory cells and mechanisms involved in their induction and functions. We also provide a broad overview on the challenges and opportunities in targeting memory cells in the induction of transplant tolerance.

The Cellular and Molecular Basis of Translational Immunometabolism

The immune response requires major changes to metabolic processes, and indeed, energy metabolism and functional activation are fully integrated in immune cells to determine their ability to divide, differentiate, and carry out effector functions. Immune cell metabolism has therefore become an attractive target area for therapeutic purposes. A neglected aspect in the translation of immunometabolism is the critical connection between systemic and cellular metabolism. Here, we discuss the importance of understanding and manipulating the integration of systemic and immune cell metabolism through in-depth analysis of immune cell phenotype and function in human metabolic diseases and, in parallel, of the effects of conventional metabolic drugs on immune cell differentiation and function. We examine how the recent identification of selective metabolic programs operating in distinct immune cell subsets and functions has the potential to deliver tools for cell- and function-specific immunometabolic targeting.

Immune System Disorders and Epigenetics

Our understanding of epigenetics in complex diseases is rapidly advancing and increasingly influencing the practice of medicine. Much is known about disruption of chromatin-modifying enzymes in malignant disease, but knowledge of irregular epigenetics in immune-driven disorders is just emerging. Epigenetic factors, such as DNA or histone modifications, are indispensable for precise gene expression in diverse immune cell types. Thus a disruption of epigenetic landscapes likely has a large impact on immune homeostasis. Moreover, the low concordance rates for most autoimmune diseases suggest that epigenetics contribute to immune tolerance disturbance. Here we review the important role of epigenetics for initiation, maintenance, tolerance, and training of immune responses. We discuss evolving evidence that DNA/histone modifications and chromatin-modifying enzymes are altered in immune-based diseases. Furthermore, we explore the potential of small molecules targeting epigenetic machinery, some of which are already used in oncology, as a way to reset the immune response in disease.