Factors Produced by Macrophages Eliminating Apoptotic Cells Demonstrate Pro-Resolutive Properties and Terminate Ongoing Inflammation

Extracellular vesicle as a next-generation drug delivery platform for rheumatoid arthritis therapy

Rheumatoid arthritis (RA) is a systemic autoimmune disorder characterized by chronic inflammation and progressive damage to connective tissue. It is driven by dysregulated cellular homeostasis, often leading to autoimmune destruction and permanent disability in severe cases. Over the past decade, various drug delivery systems have been developed to enable targeted therapies for disease prevention, reduction, or suppression. As an emerging therapeutic platform, extracellular vesicles (EVs) offer several advantages over conventional drug delivery systems, including biocompatibility and low immunogenicity. Consequently, an increasing number of studies have explored EV-based delivery systems in the treatment of RA, leveraging their natural ability to evade phagocytosis, prolong in vivo half-life, and minimize the immunogenicity of therapeutic agents. In this review, we first provide an in-depth overview of the pathogenesis of RA and the current treatment landscape. We then discuss the classification and biological properties of EVs, their potential therapeutic mechanisms, and the latest advancements in EVs as drug delivery platforms for RA therapy. We emphasize the significance of EVs as carriers in RA treatment and their potential to revolutionize therapeutic strategies. Furthermore, we examine key technological innovations and the future trajectory of EV research, focusing on the challenges and opportunities in translating these platforms into clinical practice. Our discussion aims to offer a comprehensive understanding of the current state and future prospects of EV-based therapeutics in RA.

Activin A activation of Smad3 mitigates innate inflammation in mouse models of psoriasis and sepsis

Phosphorylation of Smad3 is a critical mediator of TGF-β signaling, which plays an important role in regulating innate immune responses. However, whether Smad3 activation can be regulated in innate immune cells in TGF-β-independent contexts remains poorly understood. Here, we show that Smad3 is activated through the phosphorylation of its C-terminal residues (pSmad3C) in murine and human macrophages in response to bacterial and viral ligands, and this activation is mediated by activin A in a TGF-β-independent manner. Specifically, infectious ligands, such as LPS, induced secretion of activin A through the transcription factor STAT5 in macrophages, and activin A signaling in turn activated pSmad3C. This activin A/Smad3 axis controlled mitochondrial ATP production and ATP conversion into adenosine by CD73 in macrophages, enforcing an antiinflammatory mechanism. Consequently, mice with a deletion of activin A receptor 1b specifically in macrophages (Acvr1bfl/fl-Lyz2cre) succumbed more to sepsis as a result of uncontrolled inflammation and exhibited exacerbated skin disease in a mouse model of imiquimod-induced psoriasis. Thus, we have revealed a previously unrecognized natural brake to inflammation in macrophages that occurs through the activation of Smad3 in an activin A-dependent manner.

Clinically relevant cell culture model of inflammatory bowel diseases for identification of new therapeutic approaches

Inflammatory Bowel Diseases (IDB) are chronic disorders characterized by gut inflammation, mucosal damage, increased epithelial permeability and altered mucus layer. No accurate in vitro model exists to simulate these characteristics. In this context, drug development for IBD or intestinal inflammation requires in vivo evaluations to verify treatments efficacy. A new model with altered mucus layer composition; altered epithelial permeability and pro-inflammatory crosstalk between immune and epithelial cells will be developed to enhance in vitro models for studying IBD treatments. The effects of dextran sulfate sodium and/or lipopolysaccharides on intestinal permeability, cytokines synthesis (IL-6, IL-8, TNF-α and IL-1β), mucins (MUC2, MUC5AC) and tight junction proteins expression (Claudin-1, ZO-1 and Occludin) were investigated in a tri-coculture model combining differentiated Caco-2/HT29-MTX cells and THP-1 cells. Two anti-inflammatory agents were evaluated to assess the model's therapeutic strategy applicability (corticoids and pro-resolving factors). Two in vitro models have been developed. The first model, characterized by increased permeability of the epithelial layer and subsequent secretion of inflammatory cytokines, can reproduce the different phases of inflammation, and enables the evaluation of preventive treatments. The second model simulates the acute phase of inflammation and allows for the assessment of curative treatments. Both models demonstrated reversibility when treated with betamethasone and pro-resolving factors. These in vitro models are valuable for selecting therapeutic agents prior to their application in in vivo models. They enable the assessment of agents' anti-inflammatory effects and their ability to permeate the inflamed epithelial layer and interact with immune cells.

Low-Grade Chronic Inflammation: a Shared Mechanism for Chronic Diseases

Inflammation is an important physiological response of the organism to restore homeostasis upon pathogenic or damaging stimuli. However, the persistence of the harmful trigger or a deficient resolution of the process can evolve into a state of low-grade, chronic inflammation. This condition is strongly associated with the development of several increasingly prevalent and serious chronic conditions, such as obesity, cancer, and cardiovascular diseases, elevating overall morbidity and mortality worldwide. The current pandemic of chronic diseases underscores the need to address chronic inflammation, its pathogenic mechanisms, and potential preventive measures to limit its current widespread impact. The present review discusses the current knowledge and research gaps regarding the association between low-grade chronic inflammation and chronic diseases, focusing on obesity, cardiovascular diseases, digestive diseases, and cancer. We examine the state of the art in selected aspects of the topic and propose future directions and approaches for the field.

Resolution of chronic inflammation and cancer

Chronic inflammation poses challenges to effective cancer treatment. Although anti-inflammatory therapies have shown short-term benefits, their long-term implications may be unfavorable because they fail to initiate the necessary inflammatory responses. Recent research underscores the promise of specialized pro-resolving mediators, which play a role in modulating the cancer microenvironment by promoting the resolution of initiated inflammatory processes and restoring tissue hemostasis. This review addresses current insights into how inflammation contributes to cancer pathogenesis and explores recent strategies to resolve inflammation associated with cancer.

Efferocytosis: Unveiling its potential in autoimmune disease and treatment strategies

Efferocytosis is a crucial process whereby phagocytes engulf and eliminate apoptotic cells (ACs). This intricate process can be categorized into four steps: (1) ACs release "find me" signals to attract phagocytes, (2) phagocytosis is directed by "eat me" signals emitted by ACs, (3) phagocytes engulf and internalize ACs, and (4) degradation of ACs occurs. Maintaining immune homeostasis heavily relies on the efficient clearance of ACs, which eliminates self-antigens and facilitates the generation of anti-inflammatory and immunosuppressive signals that maintain immune tolerance. However, any disruptions occurring at any of the efferocytosis steps during apoptosis can lead to a diminished efficacy in removing apoptotic cells. Factors contributing to this inefficiency encompass dysregulation in the release and recognition of "find me" or "eat me" signals, defects in phagocyte surface receptors, bridging molecules, and other signaling pathways. The inadequate clearance of ACs can result in their rupture and subsequent release of self-antigens, thereby promoting immune responses and precipitating the onset of autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. A comprehensive understanding of the efferocytosis process and its implications can provide valuable insights for developing novel therapeutic strategies that target this process to prevent or treat autoimmune diseases.

Laminin-derived peptide, IKVAV, modulates macrophage phenotype through integrin mediation

Macrophages are highly plastic immune cells known to exist on a spectrum of phenotypes including pro-inflammatory (M1) or pro-healing (M2). Macrophages interact with extracellular matrix (ECM) ligands, such as fragments of collagen and laminin. Interaction of macrophages with ECM ligands is mediated through integrin receptors. However, the role of ECM ligands in directing macrophage function through integrins is not yet fully understood. Particularly, α2β1 has been implicated in modulating macrophage function, but complexity in mechanisms employed for integrin-ligation especially with laminin-derived peptides makes it challenging to understand macrophage-ECM interactions. We hypothesize that targeting α2β1 through laminin-derived peptide, IKVAV, will modulate macrophage phenotype. In this work we: i) investigated macrophage response to IKVAV in 2D and in a 3D platform, and ii) identified α2β1's role as it pertains to macrophage modulation via IKVAV. Soluble IKVAV treatment significantly reduced M1 markers and increased M2 markers via immunocytochemistry and gene expression. While the 3D ECM-mimicking PEG-IKVAV hydrogels did not have significant effects in modulating macrophage phenotype, we found that macrophage modulation via IKVAV is dependent on the concentration of peptide used and duration of exposure. To investigate integrin-ligand interactions for macrophages, α2β1 signaling was modulated by antagonists and agonists. We observed that blocking α2β1 reduces M1 activation. To understand integrin-ligand interactions and leveraging the therapeutic ability of macrophages in designing immunomodulatory solutions, it is critical to elucidate IKVAV's role in mediating macrophage phenotype.

[Strong as death or how efferocytotic macrophages promote the resolution of inflammation]

The resolution of inflammation is an active process leading to the restoration of tissue homeostasis. A critical step in the initiation of this process is the elimination of apoptotic immune cells by macrophages. This well-organized process, called efferocytosis, involves four different steps, namely the attraction of macrophages to the site where the cells die, the recognition of apoptotic cells, their internalization and their digestion leading to the activation of different metabolic pathways. All these steps are responsible for the reprogramming of macrophages towards a pro-resolving profile. Efferocytic macrophages produce several factors involved in the resolution of inflammation. These factors include lipids (i.e., specialized pro-resolving mediators such as lipoxins), and proteins (e.g., IL-10 or TGF-β). Here, we describe the different steps of efferocytosis and the mechanisms responsible for both macrophage reprogramming and the release of pro-resolving factors. These factors may represent a new therapeutic approach, called resolution therapy.

Efferocytosis: Current status and future prospects in the treatment of autoimmune diseases

Billions of apoptotic cells are swiftly removed from the human body daily. This clearance process is regulated by efferocytosis, an active anti-inflammatory process during which phagocytes engulf and remove apoptotic cells. However, impaired clearance of apoptotic cells is associated with the development of various autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease. In this review, we conducted a comprehensive search of relevant studies published from January 1, 2000, to the present, focusing on efferocytosis, autoimmune disease pathogenesis, regulatory mechanisms governing efferocytosis, and potential treatments targeting this process. Our review highlights the key molecules involved in different stages of efferocytosis-namely, the "find me," "eat me," and "engulf and digest" phases-while elucidating their relevance to autoimmune disease pathology. Furthermore, we explore the therapeutic potential of modulating efferocytosis to restore immune homeostasis and mitigate autoimmune responses. By providing theoretical underpinnings for the targeting of efferocytosis in the treatment of autoimmune diseases, this review contributes to the advancement of therapeutic strategies in this field.

Amelioration of experimental autoimmune encephalomyelitis by in vivo reprogramming of macrophages using pro-resolving factors

BACKGROUND

Reinstating inflammation resolution represents an innovative concept to regain inflammation control in diseases marked by chronic inflammation. While most therapeutics target inflammatory molecules and inflammatory effector cells and mediators, targeting macrophages to initiate inflammation resolution to control neuroinflammation has not yet been attempted. Resolution-phase macrophages are critical in the resolution process to regain tissue homeostasis, and are programmed through the presence and elimination of apoptotic leukocytes. Hence, inducing resolution-phase macrophages might represent an innovative therapeutic approach to control and terminate dysregulated neuroinflammation.

METHODS

Here, we investigated if the factors released by in vitro induced resolution-phase macrophages (their secretome) are able to therapeutically reprogram macrophages to control neuroinflammation in the model of experimental autoimmune encephalomyelitis (EAE).

RESULTS

We found that injection of the pro-resolutive secretome reduced demyelination and decreased inflammatory cell infiltration in the CNS, notably through the in vivo reprogramming of macrophages at the epigenetic level. Adoptive transfer experiments with in vivo or in vitro reprogrammed macrophages using such pro-resolutive secretome confirmed the stability and transferability of this acquired therapeutic activity.

CONCLUSIONS

Overall, our data confirm the therapeutic activity of a pro-resolution secretome in the treatment of ongoing CNS inflammation, via the epigenetic reprogramming of macrophages and open with that a new therapeutic avenue for diseases marked by neuroinflammation.

Immunomodulatory nano-preparations for rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease (AD) caused by the aberrant attack of the immune system on its own joint tissues. Genetic and environmental factors are the main reasons of immune system impairment and high incidence of RA. Although there are medications on the market that lessen disease activity, there is no known cure for RA, and patients are at risk in varying degrees of systemic immunosuppression. By transporting (encapsulating or surface binding) RA-related self-antigens, nucleic acids, immunomodulators, or cytokines, tolerogenic nanoparticles-also known as immunomodulatory nano-preparations-have the potential to gently regulate local immune responses and ultimately induce antigen-specific immune tolerance. We review the recent advances in immunomodulatory nano-preparations for delivering self-antigen or self-antigen plus immunomodulator, simulating apoptotic cell avatars in vivo, acting as artificial antigen-presenting cells, and based on scaffolds and gels, to provide a reference for developing new immunotherapies for RA.

Apoptotic cell clearance components in inflammatory arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease of the synovial joints that affects ~1% of the human population. Joint swelling and bone erosion, hallmarks of RA, contribute to disability and, sometimes, loss of life. Mechanistically, disease is driven by immune dysregulation characterized by circulating autoantibodies, inflammatory mediators, tissue degradative enzymes, and metabolic dysfunction of resident stromal and recruited immune cells. Cell death by apoptosis has been therapeutically explored in animal models of RA due to the comparisons drawn between synovial hyperplasia and paucity of apoptosis in RA with the malignant transformation of cancer cells. Several efforts to induce cell death have shown benefits in reducing the development and/or severity of the disease. Apoptotic cells are cleared by phagocytes in a process known as efferocytosis, which differs from microbial phagocytosis in its "immuno-silent," or anti-inflammatory, nature. Failures in efferocytosis have been linked to autoimmune disease, whereas administration of apoptotic cells in RA models effectively inhibits inflammatory indices, likely though efferocytosis-mediated resolution-promoting mechanisms. However, the nature of signaling pathways elicited and the molecular identity of clearance mediators in RA are understudied. Furthermore, canonical efferocytosis machinery elements also play important non-canonical functions in homeostasis and pathology. Here, we discuss the roles of efferocytosis machinery components in models of RA and discuss their potential involvement in disease pathophysiology.

TGF-β uncouples glycolysis and inflammation in macrophages and controls survival during sepsis

Changes in metabolism of macrophages are required to sustain macrophage activation in response to different stimuli. We showed that the cytokine TGF-β (transforming growth factor-β) regulates glycolysis in macrophages independently of inflammatory cytokine production and affects survival in mouse models of sepsis. During macrophage activation, TGF-β increased the expression and activity of the glycolytic enzyme PFKL (phosphofructokinase-1 liver type) and promoted glycolysis but suppressed the production of proinflammatory cytokines. The increase in glycolysis was mediated by an mTOR-c-MYC-dependent pathway, whereas the inhibition of cytokine production was due to activation of the transcriptional coactivator SMAD3 and suppression of the activity of the proinflammatory transcription factors AP-1, NF-κB, and STAT1. In mice with LPS-induced endotoxemia and experimentally induced sepsis, the TGF-β-induced enhancement in macrophage glycolysis led to decreased survival, which was associated with increased blood coagulation. Analysis of septic patient cohorts revealed that the expression of PFKL, TGFBRI (which encodes a TGF-β receptor), and F13A1 (which encodes a coagulation factor) in myeloid cells positively correlated with COVID-19 disease. Thus, these results suggest that TGF-β is a critical regulator of macrophage metabolism and could be a therapeutic target in patients with sepsis.

ChemR23 activation reprograms macrophages toward a less inflammatory phenotype and dampens carcinoma progression

Introduction

Tumor Associated Macrophages (TAM) are a major component of the tumor environment and their accumulation often correlates with poor prognosis by contributing to local inflammation, inhibition of anti-tumor immune response and resistance to anticancer treatments. In this study, we thus investigated the anti-cancer therapeutic interest to target ChemR23, a receptor of the resolution of inflammation expressed by macrophages, using an agonist monoclonal antibody, αChemR23.

Methods

Human GM-CSF, M-CSF and Tumor Associated Macrophage (TAM)-like macrophages were obtained by incubation of monocytes from healthy donors with GM-CSF, M-CSF or tumor cell supernatants (Breast cancer (BC) or malignant pleural mesothelioma (MPM) cells). The effects of αChemR23 on macrophages were studied at the transcriptomic, protein and functional level. Datasets from The Cancer Genome Atlas (TCGA) were used to study CMKLR1 expression, coding for ChemR23, in BC and MPM tumors. In vivo, αChemR23 was evaluated on overall survival, metastasis development and transcriptomic modification of the metastatic niche using a model of resected triple negative breast cancer.

Results

We show that ChemR23 is expressed at higher levels in M-CSF and tumor cell supernatant differentiated macrophages (TAM-like) than in GM-CSF-differentiated macrophages. ChemR23 activation triggered by αChemR23 deeply modulates M-CSF and TAM-like macrophages including profile of cell surface markers, cytokine secretion, gene mRNA expression and immune functions. The expression of ChemR23 coding gene (CMKLR1) strongly correlates to TAM markers in human BC tumors and MPM and its histological detection in these tumors mainly corresponds to TAM expression. In vivo, treatment with αChemR23 agonist increased mouse survival and decreased metastasis occurrence in a model of triple-negative BC in correlation with modulation of TAM phenotype in the metastatic niche.

Conclusion

These results open an attractive opportunity to target TAM and the resolution of inflammation pathways through ChemR23 to circumvent TAM pro-tumoral effects.

Efferocytes release extracellular vesicles to resolve inflammation and tissue injury via prosaposin-GPR37 signaling

Macrophages release soluble mediators following efferocytic clearance of apoptotic cells to facilitate intercellular communication and promote the resolution of inflammation. However, whether inflammation resolution is modulated by extracellular vesicles (EVs) and vesicular mediators released by efferocytes is not known. We report that efferocyte-derived EVs express prosaposin, which binds to macrophage GPR37 to increase expression of the efferocytosis receptor Tim4 via an ERK-AP1-dependent signaling axis, leading to increased macrophage efferocytosis efficiency and accelerated resolution of inflammation. Neutralization and knockdown of prosaposin or blocking GRP37 abrogates the pro-resolution effects of efferocyte-derived EVs in vivo. Administration of efferocyte-derived EVs in a murine model of atherosclerosis is associated with an increase in lesional macrophage efferocytosis efficiency and a decrease in plaque necrosis and lesional inflammation. Thus, we establish a critical role for efferocyte-derived vesicular mediators in increasing macrophage efferocytosis efficiency and accelerating the resolution of inflammation and tissue injury.

Human adenovirus lung disease: outbreaks, models of immune-response-driven acute lung injury and pandemic potential

PURPOSE OF REVIEW

An overview of epidemic, human adenovirus (HAdV) lung infections with proposed studies of the viral/host immune response interface to better understand mechanisms of immunopathogenesis, for development of improved responses to a potential HAdV pandemic.

RECENT FINDINGS

Emergent HAdV strains 7, 3, 4, 14 are the most common types associated with infection outbreaks. Recent outbreaks have revealed increased community spread, beyond epidemic group settings. The ongoing circulation of these virulent HAdV strains might allow for further HAdV adaptation, with increased HAdV spread and disease severity in the population that could theoretically result in expansion to a pandemic level.

SUMMARY

Public health screening has revealed spread of HAdV outbreak strains to the general community. Despite expanded awareness of viral respiratory diseases during the SARS-CoV-2 pandemic, there has been limited, systematic monitoring of HAdV infection in the population. The shift in clinical laboratories to a focus on molecular diagnostics and away from classical methods of viral characterization has reduced the distribution of outbreak HAdV strains to the research community to study mechanisms of pathogenesis. This change risks reduced development of new preventive and therapeutic strategies that could be needed in the event of more widespread HAdV epidemics.

Multiple Shades of Gray-Macrophages in Acute Allograft Rejection

Long-term results following solid organ transplantation do not mirror the excellent short-term results achieved in recent decades. It is therefore clear that current immunosuppressive maintenance protocols primarily addressing the adaptive immune system no longer meet the required clinical need. Identification of novel targets addressing this shortcoming is urgently needed. There is a growing interest in better understanding the role of the innate immune system in this context. In this review, we focus on macrophages, which are known to prominently infiltrate allografts and, during allograft rejection, to be involved in the surge of the adaptive immune response by expression of pro-inflammatory cytokines and direct cytotoxicity. However, this active participation is janus-faced and unspecific targeting of macrophages may not consider the different subtypes involved. Under this premise, we give an overview on macrophages, including their origins, plasticity, and important markers. We then briefly describe their role in acute allograft rejection, which ranges from sustaining injury to promoting tolerance, as well as the impact of maintenance immunosuppressants on macrophages. Finally, we discuss the observed immunosuppressive role of the vitamin-like compound tetrahydrobiopterin and the recent findings that suggest the innate immune system, particularly macrophages, as its target.

Mucosal healing and inflammatory bowel disease: Therapeutic implications and new targets

Mucosal healing (MH) is vital in maintaining homeostasis within the gut and protecting against injury and infections. Multiple factors and signaling pathways contribute in a dynamic and coordinated manner to maintain intestinal homeostasis and mucosal regeneration/repair. However, when intestinal homeostasis becomes chronically disturbed and an inflammatory immune response is constitutively active due to impairment of the intestinal epithelial barrier autoimmune disease results, particularly inflammatory bowel disease (IBD). Many proteins and signaling pathways become dysregulated or impaired during these pathological conditions, with the mechanisms of regulation just beginning to be understood. Consequently, there remains a relative lack of broadly effective therapeutics that can restore MH due to the complexity of both the disease and healing processes, so tissue damage in the gastrointestinal tract of patients, even those in clinical remission, persists. With increased understanding of the molecular mechanisms of IBD and MH, tissue damage from autoimmune disease may in the future be ameliorated by developing therapeutics that enhance the body’s own healing response. In this review, we introduce the concept of mucosal healing and its relevance in IBD as well as discuss the mechanisms of IBD and potential strategies for altering these processes and inducing MH.

Cellular mechanisms underlying the impairment of macrophage efferocytosis

The phagocytosis and clearance of dying cells by macrophages, a process termed efferocytosis, is essential for both maintaining homeostasis and promoting tissue repair after infection or sterile injury. If not removed in a timely manner, uncleared cells can undergo secondary necrosis, and necrotic cells lose membrane integrity, release toxic intracellular components, and potentially induce inflammation or autoimmune diseases. Efferocytosis also initiates the repair process by producing a wide range of pro-reparative factors. Accumulating evidence has revealed that macrophage efferocytosis defects are involved in the development and progression of a variety of inflammatory and autoimmune diseases. The underlying mechanisms of efferocytosis impairment are complex, disease-dependent, and incompletely understood. In this review, we will first summarize the current knowledge about the normal signaling and metabolic processes of macrophage efferocytosis and its importance in maintaining tissue homeostasis and repair. We then will focus on analyzing the molecular and cellular mechanisms underlying efferocytotic abnormality (impairment) in disease or injury conditions. Next, we will discuss the potential molecular targets for enhanced efferocytosis in animal models of disease. To provide a balanced view, we will also discuss some deleterious effects of efferocytosis.

IFN-γ and TGF-β, Crucial Players in Immune Responses: A Tribute to Howard Young

Interferon gamma (IFN-γ) and transforming growth factor beta (TGF-β), both pleiotropic cytokines, have been long studied and described as critical mediators of the immune response, notably in T cells. One of the investigators who made seminal and critical discoveries in the field of IFN-γ biology is Dr. Howard Young. In this review, we provide an overview of the biology of IFN-γ as well as its role in cancer and autoimmunity with an emphasis on Dr. Young's critical work in the field. We also describe how Dr. Young's work influenced our own research studying the role of TGF-β in the modulation of immune responses.

Resolution therapy: Harnessing efferocytic macrophages to trigger the resolution of inflammation

Several chronic inflammatory diseases are associated with non-resolving inflammation. Conventional anti-inflammatory drugs fail to completely cure these diseases. Resolution pharmacology is a new therapeutic approach based on the use of pro-resolving mediators that accelerate the resolution phase of inflammation by targeting the productive phase of inflammation. Indeed, pro-resolving mediators prevent leukocyte recruitment and induce apoptosis of accumulated leukocytes. This approach is now called resolution therapy with the introduction of complex biological drugs and cell-based therapies. The main objective of resolution therapy is to specifically reduce the duration of the resolution phase to accelerate the return to homeostasis. Under physiological conditions, macrophages play a critical role in the resolution of inflammation. Indeed, after the removal of apoptotic cells (a process called efferocytosis), macrophages display anti-inflammatory reprogramming and subsequently secrete multiple pro-resolving factors. These factors can be used as resolution therapy. Here, we review the different mechanisms leading to anti-inflammatory reprogramming of macrophages after efferocytosis and the pro-resolving factors released by these efferocytic macrophages. We classify these mechanisms in three different categories: macrophage reprogramming induced by apoptotic cell-derived factors, by molecules expressed by apoptotic cells (i.e., "eat-me" signals), and induced by the digestion of apoptotic cell-derived materials. We also evoke that macrophage reprogramming may result from cooperative mechanisms, for instance, implicating the apoptotic cell-induced microenvironment (including cellular metabolites, specific cytokines or immune cells). Then, we describe a new drug candidate belonging to this resolution therapy. This candidate, called SuperMApo, corresponds to the secretome of efferocytic macrophages. We discuss its production, the pro-resolving factors present in this drug, as well as the results obtained in experimental models of chronic (e.g., arthritis, colitis) and acute (e.g., peritonitis or xenogeneic graft-versus-host disease) inflammatory diseases.

DCs unchained: Whetting dendritic-cell appetite boosts wound healing

Apoptotic-cell uptake (efferocytosis) by dendritic cells (DCs) has been mainly linked to their antigen presentation property. In a recent issue of Nature, Maschalidi et al. identified a break to efferocytosis in DCs, the inhibition of which improves skin debris cleansing after a wound, accelerating healing.

Targeting SLC7A11 improves efferocytosis by dendritic cells and wound healing in diabetes

Chronic non-healing wounds are a major complication of diabetes, which affects 1 in 10 people worldwide. Dying cells in the wound perpetuate the inflammation and contribute to dysregulated tissue repair^1-3. Here we reveal that the membrane transporter SLC7A11 acts as a molecular brake on efferocytosis, the process by which dying cells are removed, and that inhibiting SLC7A11 function can accelerate wound healing. Transcriptomics of efferocytic dendritic cells in mouse identified upregulation of several SLC7 gene family members. In further analyses, pharmacological inhibition of SLC7A11, or deletion or knockdown of Slc7a11 using small interfering RNA enhanced efferocytosis in dendritic cells. Slc7a11 was highly expressed in dendritic cells in skin, and single-cell RNA sequencing of inflamed skin showed that Slc7a11 was upregulated in innate immune cells. In a mouse model of excisional skin wounding, inhibition or loss of SLC7A11 expression accelerated healing dynamics and reduced the apoptotic cell load in the wound. Mechanistic studies revealed a link between SLC7A11, glucose homeostasis and diabetes. SLC7A11-deficient dendritic cells were dependent on aerobic glycolysis using glucose derived from glycogen stores for increased efferocytosis; also, transcriptomics of efferocytic SLC7A11-deficient dendritic cells identified increased expression of genes linked to gluconeogenesis and diabetes. Further, Slc7a11 expression was higher in the wounds of diabetes-prone db/db mice, and targeting SLC7A11 accelerated their wound healing. The faster healing was also linked to the release of the TGFβ family member GDF15 from efferocytic dendritic cells. In sum, SLC7A11 is a negative regulator of efferocytosis, and removing this brake improves wound healing, with important implications for wound management in diabetes.

Weathering the Storm: Harnessing the Resolution of Inflammation to Limit COVID-19 Pathogenesis

The resolution of inflammation is a temporally and spatially coordinated process that in its innate manifestations, primarily involves neutrophils and macrophages. The shutdown of infection or injury-induced acute inflammation requires termination of neutrophil accumulation within the affected sites, neutrophil demise, and clearance by phagocytes (efferocytosis), such as tissue-resident and monocyte-derived macrophages. This must be followed by macrophage reprogramming from the inflammatory to reparative and consequently resolution-promoting phenotypes and the production of resolution-promoting lipid and protein mediators that limit responses in various cell types and promote tissue repair and return to homeostatic architecture and function. Recent studies suggest that these events, and macrophage reprogramming to pro-resolving phenotypes in particular, are not only important in the acute setting, but might be paramount in limiting chronic inflammation, autoimmunity, and various uncontrolled cytokine-driven pathologies. The SARS-CoV-2 (COVID-19) pandemic has caused a worldwide health and economic crisis. Severe COVID-19 cases that lead to high morbidity are tightly associated with an exuberant cytokine storm that seems to trigger shock-like pathologies, leading to vascular and multiorgan failures. In other cases, the cytokine storm can lead to diffuse alveolar damage that results in acute respiratory distress syndrome (ARDS) and lung failure. Here, we address recent advances on effectors in the resolution of inflammation and discuss how pro-resolution mechanisms with particular emphasis on macrophage reprogramming, might be harnessed to limit the universal COVID-19 health threat.

Modulation of Macrophage Immunometabolism: A New Approach to Fight Infections

Macrophages are essential innate immune cells that contribute to host defense during infection. An important feature of macrophages is their ability to respond to extracellular cues and to adopt different phenotypes and functions in response to these stimuli. The evidence accumulated in the last decade has highlighted the crucial role of metabolic reprogramming during macrophage activation in infectious context. Thus, understanding and manipulation of macrophage immunometabolism during infection could be of interest to develop therapeutic strategies. In this review, we focus on 5 major metabolic pathways including glycolysis, pentose phosphate pathway, fatty acid oxidation and synthesis, tricarboxylic acid cycle and amino acid metabolism and discuss how they sustain and regulate macrophage immune function in response to parasitic, bacterial and viral infections as well as trained immunity. At the end, we assess whether some drugs including those used in clinic and in development can target macrophage immunometabolism for potential therapy during infection with an emphasis on SARS-CoV2 infection.

Repolarization of Unbalanced Macrophages: Unmet Medical Need in Chronic Inflammation and Cancer

Monocytes and their tissue counterpart macrophages (MP) constitute the front line of the immune system. Indeed, they are able to rapidly and efficiently detect both external and internal danger signals, thereby activating the immune system to eradicate the disturbing biological, chemical, or physical agents. They are also in charge of the control of the immune response and account for the repair of the damaged tissues, eventually restoring tissue homeostasis. The balance between these dual activities must be thoroughly controlled in space and time. Any sustained unbalanced response of MP leads to pathological disorders, such as chronic inflammation, or favors cancer development and progression. In this review, we take advantage of our expertise in chronic inflammation, especially in rheumatoid arthritis, and in cancer, to highlight the pivotal role of MP in the physiopathology of these disorders and to emphasize the repolarization of unbalanced MP as a promising therapeutic strategy to control these diseases.

Pro-Resolving Factor Administration Limits Cancer Progression by Enhancing Immune Response Against Cancer Cells

Cancers are consequences of cellular dysfunction leading to an aberrant cellular multiplication and proliferation, subsequently yielding metastasis formation. Inflammatory reaction, with immune cell recruitment, is the main defense against precancerous lesions. However, an inflammatory environment also favors cancer cell progression, with cancer cell evasion from immune surveillance, leading to cancer development. Current therapeutic strategies enhance this natural immune response in order to restore immunosurveillance. The variety of these strategies is a predominant source of inflammatory mediators used by cancer cells to grow, differentiate, and migrate, therefore encouraging metastasis formation. For this reason, during cancer progression, limiting inflammation appears to be an innovative strategy to avoid the escape of cancer cells and potentially enhance the efficacy of antitumor therapies. Thus, this study aims to investigate the impact of administering pro-resolving factors (SuperMApo® drug candidate), which are inducers of inflammation resolution, in the framework of cancer treatment. We have observed that administering pro-resolving mediators issued from apoptotic cell efferocytosis by macrophages controlled peritoneal cancer progression by limiting cancer cell dissemination to the blood and mesenteric lymph nodes. This observation has been linked to an increase of macrophage mobilization in both peritoneal cavity and mesenteric lymph nodes. This control is associated to a restricted immunosuppressive myeloid cell circulation and to an IFN-γ-specific anti-tumor T-cell response. Altogether, these results suggest that administering proresolving factors could provide a new additional therapeutic alternative to control cancer progression.

Pro-Resolving Factors Released by Macrophages After Efferocytosis Promote Mucosal Wound Healing in Inflammatory Bowel Disease

Nonresolving inflammation is a critical driver of several chronic inflammatory diseases, including inflammatory bowel diseases (IBD). This unresolved inflammation may result from the persistence of an initiating stimulus or from the alteration of the resolution phase of inflammation. Elimination of apoptotic cells by macrophages (a process called efferocytosis) is a critical step in the resolution phase of inflammation. Efferocytosis participates in macrophage reprogramming and favors the release of numerous pro-resolving factors. These pro-resolving factors exert therapeutic effects in experimental autoimmune arthritis. Here, we propose to evaluate the efficacy of pro-resolving factors produced by macrophages after efferocytosis, a secretome called SuperMApo, in two IBD models, namely dextran sodium sulfate (DSS)-induced and T cell transfer-induced colitis. Reintroducing these pro-resolving factors was sufficient to decrease clinical, endoscopic and histological colitis scores in ongoing naive T cell-transfer-induced colitis and in DSS-induced colitis. Mouse primary fibroblasts isolated from the colon demonstrated enhanced healing properties in the presence of SuperMApo, as attested by their increased migratory, proliferative and contractive properties. This was confirmed by the use of human fibroblasts isolated from patients with IBD. Exposure of an intestinal epithelial cell (IEC) line to these pro-resolving factors increased their proliferative properties and IEC acquired the capacity to capture apoptotic cells. The improvement of wound healing properties induced by SuperMApo was confirmed in vivo in a biopsy forceps-wound colonic mucosa model. Further in vivo analysis in naive T cell transfer-induced colitis model demonstrated an improvement of intestinal barrier permeability after administration of SuperMApo, an intestinal cell proliferation and an increase of α-SMA expression by fibroblasts, as well as a reduction of the transcript coding for fibronectin (Fn1). Finally, we identified TGF-β, IGF-I and VEGF among SuperMApo as necessary to favor mucosal healing and confirmed their role both in vitro (using neutralizing antibodies) and in vivo by depleting these factors from efferocytic macrophage secretome using antibody-coated microbeads. These growth factors only explained some of the beneficial effects induced by factors released by efferocytic macrophages. Overall, the administration of pro-resolving factors released by efferocytic macrophages limits intestinal inflammation and enhance tissue repair, which represents an innovative treatment of IBD.

Apoptotic Cells for Therapeutic Use in Cytokine Storm Associated With Sepsis- A Phase Ib Clinical Trial

Background

Sepsis has no proven specific pharmacologic treatment and reported mortality ranges from 30%–45%. The primary aim of this phase IB study was to determine the safety profile of Allocetra™-OTS (early apoptotic cell) infusion in subjects presenting to the emergency room with sepsis. The secondary aims were to measure organ dysfunction, intensive care unit (ICU) and hospital stays, and mortality. Exploratory endpoints included measuring immune modulator agents to elucidate the mechanism of action.

Methods

Ten patients presenting to the emergency room at the Hadassah Medical Center with sepsis were enrolled in this phase Ib clinical study. Enrolled patients were males and females aged 51–83 years, who had a Sequential Organ Failure Assessment (SOFA) score ≥2 above baseline and were septic due to presumed infection. Allocetra™-OTS was administered as a single dose (day +1) or in two doses of 140×10⁶ cells/kg on (day +1 and +3), following initiation of standard-of-care (SOC) treatment for septic patients. Safety was evaluated by serious adverse events (SAEs) and adverse events (AEs). Organ dysfunction, ICU and hospital stays, and mortality, were compared to historical controls. Immune modulator agents were measured using Luminex^® multiplex analysis.

Results

All 10 patients had mild-to-moderate sepsis with SOFA scores ranging from 2–6 upon entering the study. No SAEs and no related AEs were reported. All 10 study subjects survived, while matched historical controls had a mortality rate of 27%. The study subjects exhibited rapid resolution of organ dysfunction and had significantly shorter ICU stays compared to matched historical controls (p<0.0001). All patients had both elevated pro- and anti-inflammatory cytokines, chemokines, and additional immune modulators that gradually decreased following treatment.

Conclusion

Administration of apoptotic cells to patients with mild-to-moderate sepsis was safe and had a significant immuno-modulating effect, leading to early resolution of the cytokine storm.

Clinical Trial Registration

ClinicalTrials.gov Identifier: NCT03925857. (https://clinicaltrials.gov/ct2/show/study/NCT03925857).

Eicosanoid regulation of debris-stimulated metastasis

Cancer therapy, such as chemotherapy, induces tumor cell death (“debris”), which can stimulate metastasis. Chemotherapy-generated debris upregulates soluble epoxide hydrolase (sEH) and the prostaglandin E₂ receptor 4 (EP4), which triggers a macrophage-derived storm of proinflammatory and proangiogenic lipid autacoid and cytokine mediators. Although sEH inhibitors and EP4 antagonists are in clinical development for multiple inflammatory diseases, their combined role in cancer is unknown. Here, we show that the synergistic antitumor activity of sEH and EP4 inhibition suppresses hepato-pancreatic tumor growth, without overt toxicity, via macrophage phagocytosis of debris and counterregulation of a debris-stimulated cytokine storm. Thus, stimulating the resolution of inflammation via combined inhibition of sEH and EP4 may be an approach for preventing metastatic progression driven by cancer therapy.

Cancer therapy reduces tumor burden via tumor cell death (“debris”), which can accelerate tumor progression via the failure of inflammation resolution. Thus, there is an urgent need to develop treatment modalities that stimulate the clearance or resolution of inflammation-associated debris. Here, we demonstrate that chemotherapy-generated debris stimulates metastasis by up-regulating soluble epoxide hydrolase (sEH) and the prostaglandin E₂ receptor 4 (EP4). Therapy-induced tumor cell debris triggers a storm of proinflammatory and proangiogenic eicosanoid-driven cytokines. Thus, targeting a single eicosanoid or cytokine is unlikely to prevent chemotherapy-induced metastasis. Pharmacological abrogation of both sEH and EP4 eicosanoid pathways prevents hepato-pancreatic tumor growth and liver metastasis by promoting macrophage phagocytosis of debris and counterregulating a protumorigenic eicosanoid and cytokine storm. Therefore, stimulating the clearance of tumor cell debris via combined sEH and EP4 inhibition is an approach to prevent debris-stimulated metastasis and tumor growth.

High Na+ Environments Impair Phagocyte Oxidase-Dependent Antibacterial Activity of Neutrophils

Infection and inflammation can augment local Na⁺ abundance. These increases in local Na⁺ levels boost proinflammatory and antimicrobial macrophage activity and can favor polarization of T cells towards a proinflammatory Th17 phenotype. Although neutrophils play an important role in fighting intruding invaders, the impact of increased Na⁺ on the antimicrobial activity of neutrophils remains elusive. Here we show that, in neutrophils, increases in Na⁺ (high salt, HS) impair the ability of human and murine neutrophils to eliminate Escherichia coli and Staphylococcus aureus. High salt caused reduced spontaneous movement, degranulation and impaired production of reactive oxygen species (ROS) while leaving neutrophil viability unchanged. High salt enhanced the activity of the p38 mitogen-activated protein kinase (p38/MAPK) and increased the interleukin (IL)-8 release in a p38/MAPK-dependent manner. Whereas inhibition of p38/MAPK did not result in improved neutrophil defense, pharmacological blockade of the phagocyte oxidase (PHOX) or its genetic ablation mimicked the impaired antimicrobial activity detected under high salt conditions. Stimulation of neutrophils with phorbol-12-myristate-13-acetate (PMA) overcame high salt-induced impairment in ROS production and restored antimicrobial activity of neutrophils. Hence, we conclude that high salt-impaired PHOX activity results in diminished antimicrobial activity. Our findings suggest that increases in local Na⁺ represent an ionic checkpoint that prevents excessive ROS production of neutrophils, which decreases their antimicrobial potential and could potentially curtail ROS-mediated tissue damage.

Specialized Pro-Resolving Mediators Mitigate Cancer-Related Inflammation: Role of Tumor-Associated Macrophages and Therapeutic Opportunities

Inflammation is a fundamental physiological response orchestrated by innate immune cells to restore tissue homeostasis. Specialized pro-resolving mediators (SPMs) are involved in active resolution of inflammation but when inflammation is incomplete, chronic inflammation creates a favorable environment that fuels carcinogenesis and cancer progression. Conventional cancer therapy also strengthens cancer-related inflammation by inducing massive tumor cell death that activate surrounding immune-infiltrating cells such as tumor-associated macrophages (TAMs). Macrophages are key actors of both inflammation and its active resolution due to their plastic phenotype. In line with this high plasticity, macrophages can be hijacked by cancer cells to support tumor progression and immune escape, or therapy resistance. Impaired resolution of cancer-associated inflammation supported by TAMs may thus reinforces tumor progression. From this perspective, recent evidence suggests that stimulating macrophage's pro-resolving functions using SPMs can promote inflammation resolution in cancer and improve anticancer treatments. Thus, TAMs' re-education toward an antitumor phenotype by using SPMs opens a new line of attack in cancer treatment. Here, we review SPMs' anticancer capacities with special attention regarding their effects on TAMs. We further discuss how this new therapeutic approach could be envisioned in cancer therapy.

Novel insights into macrophage diversity in rheumatoid arthritis synovium

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease affecting joints and causing progressive damage and disability. Macrophages are of critical importance in the initiation and perpetuation of synovitis in RA, they can function as antigen presenting cells leading to T-cell dependent B-cell activation, assume a variety of inflammatory cell states with the production of destructive cytokines, but also contribute to tissue homeostasis/repair. The recent development of high-throughput technologies, including bulk and single cells RNA-sequencing, has broadened our understanding of synovial cell diversity, and opened novel perspectives to the discovery of new potential therapeutic targets in RA. In this review, we will focus on the relationship between the synovial macrophage infiltration and clinical disease severity and response to treatment. We will then provide a state-of-the-art picture of the biological roles of synovial macrophages and distinct macrophage subsets described in RA. Finally, we will review the effects of approved conventional and biologic drugs on the synovial macrophage component and highlight the therapeutic potential of future strategies to re-program macrophage phenotypes in RA.

Mini-Review: The Administration of Apoptotic Cells for Treating Rheumatoid Arthritis: Current Knowledge and Clinical Perspectives

Rheumatoid arthritis (RA) is a chronic immune-mediated disease managed by conventional synthetic drugs, such as methotrexate (MTX), and targeted drugs including biological agents. Cell-based therapeutic approaches are currently developed in RA, mainly mesenchymal stroma cell-based approaches. Early-stage apoptotic cells possess direct and indirect anti-inflammatory properties. During the elimination of dying cells (a process called efferocytosis), specific mechanisms operate to control immune responses. There are compelling evidences in experimental models of arthritis indicating that apoptotic cell administration may benefit joint inflammation, and may even have therapeutic effects on arthritis. Additionally, it has been demonstrated that apoptotic cells could be administered with standard treatments of RA, such as MTX or TNF inhibitors (TNFi), given even a synergistic response with TNFi. Interestingly, apoptotic cell infusion has been successfully experienced to prevent acute graft-vs.-host disease after hematopoietic cell transplantation in patients with hematologic malignancies, with a good safety profile. In this mini-review, the apoptotic cell-based therapy development in arthritis is discussed, as well as its transfer in the short-term to an innovative treatment for patients with RA. The use of apoptotic cell-derived factors, including secretome or phosphatidylserine-containing liposomes, in RA are also discussed.

Apoptotic Cells induce Proliferation of Peritoneal Macrophages

The interaction of macrophages with apoptotic cells is required for efficient resolution of inflammation. While apoptotic cell removal prevents inflammation due to secondary necrosis, it also alters the macrophage phenotype to hinder further inflammatory reactions. The interaction between apoptotic cells and macrophages is often studied by chemical or biological induction of apoptosis, which may introduce artifacts by affecting the macrophages as well and/or triggering unrelated signaling pathways. Here, we set up a pure cell death system in which NIH 3T3 cells expressing dimerizable Caspase-8 were co-cultured with peritoneal macrophages in a transwell system. Phenotype changes in macrophages induced by apoptotic cells were evaluated by RNA sequencing, which revealed an unexpectedly dominant impact on macrophage proliferation. This was confirmed in functional assays with primary peritoneal macrophages and IC-21 macrophages. Moreover, inhibition of apoptosis during Zymosan-induced peritonitis in mice decreased mRNA levels of cell cycle mediators in peritoneal macrophages. Proliferation of macrophages in response to apoptotic cells may be important to increase macrophage numbers in order to allow efficient clearance and resolution of inflammation.

Resolution of Inflammation and Gut Repair in IBD: Translational Steps Towards Complete Mucosal Healing

Despite significant recent therapeutic advances, complete mucosal healing remains a difficult treatment target for many patients with inflammatory bowel diseases (IBD) to achieve. Our review focuses on the translational concept of promoting resolution of inflammation and repair as a necessary adjunctive step to reach this goal. We explore the roles of inflammatory cell apoptosis and efferocytosis to promote resolution, the new knowledge of gut monocyte-macrophage populations and their secreted prorepair mediators, and the processes of gut epithelial repair and regeneration to bridge this gap. We discuss the need and rationale for this vision and the tangible steps toward integrating proresolution therapies in IBD.

Human primary neutrophil mRNA does not contaminate human resolving macrophage mRNA after efferocytosis

The ingestion of apoptotic corpses by macrophages, a process called efferocytosis, is a crucial step in inflammation resolution, since it alters macrophage phenotype toward a pro-resolving profile to foil inflammation and to favor tissue repair. Up to now, the resolving macrophages remain poorly characterized, especially in humans. Global investigations, like RNA sequencing, would be very helpful to unravel some features of these elusive cells. Nonetheless, these inquiries may be challenging in a single-species model, since the fate of ingested mRNA remains unknown and may hinder any subsequent mRNA investigations in the phagocyte. A full human model consisting of primary human neutrophil and primary human monocyte-derived macrophage co-culture was set up several decades ago to mimic in vitro the efferocytosis process. However, to our knowledge, this model has not been characterized as a suitable model to perform global mRNA investigations. Indeed, the extent of ingested neutrophil mRNA contamination has not been assessed in resolving macrophages. This work answers to this crucial question. Indeed, based on the protocols presented in this article, we demonstrate that neutrophil mRNA is severely degraded and is not able to cross-contaminate resolving macrophage mRNA, contrary to apoptotic human peripheral blood derived mononuclear cell (PBMC) or apoptotic leukemic Jurkat cell mRNA. Moreover, this allogenic co-culture system does not favor neither neutrophil activation nor macrophage pro-inflammatory cytokine release. Collectively, we highlight that this model of primary human neutrophil and primary human monocyte-derived macrophage co-culture is the best model for mRNA investigations in human resolving macrophages to help improving our knowledge on these crucial cells.