Tim-3 mediates phagocytosis of apoptotic cells and cross-presentation. Blood. 2009;113:3821-3830. [PMID: 19224762 DOI: 10.1182/blood-2008-10-185884]

Antibody targeting of phosphatidylserine for the detection and immunotherapy of cancer

Phosphatidylserine (PS) is a negatively charged phospholipid in all eukaryotic cells that is actively sequestered to the inner leaflet of the cell membrane. Exposure of PS on apoptotic cells is a normal physiological process that triggers their rapid removal by phagocytic engulfment under noninflammatory conditions via receptors primarily expressed on immune cells. PS is aberrantly exposed in the tumor microenvironment and contributes to the overall immunosuppressive signals that antagonize the development of local and systemic antitumor immune responses. PS-mediated immunosuppression in the tumor microenvironment is further exacerbated by chemotherapy and radiation treatments that result in increased levels of PS on dying cells and necrotic tissue. Antibodies targeting PS localize to tumors and block PS-mediated immunosuppression. Targeting exposed PS in the tumor microenvironment may be a novel approach to enhance immune responses to cancer.

TIM-3 Regulates CD103+ Dendritic Cell Function and Response to Chemotherapy in Breast Cancer

Intratumoral CD103⁺ dendritic cells (DCs) are necessary for anti-tumor immunity. Here we evaluated the expression of immune regulators by CD103⁺ DCs in a murine model of breast cancer and identified expression of TIM-3 as a target for therapy. Anti-TIM-3 antibody improved response to paclitaxel chemotherapy in models of triple-negative and luminal B disease, with no evidence of toxicity. Combined efficacy was CD8⁺ T cell dependent and associated with increased granzyme B expression; however, TIM-3 expression was predominantly localized to myeloid cells in both human and murine tumors. Gene expression analysis identified upregulation of Cxcl9 within intratumoral DCs during combination therapy, and therapeutic efficacy was ablated by CXCR3 blockade, Batf3 deficiency, or Irf8 deficiency.

Erythrocyte efferocytosis modulates macrophages towards recovery after intracerebral hemorrhage

Macrophages are a source of both proinflammatory and restorative functions in damaged tissue through complex dynamic phenotypic changes. Here, we sought to determine whether monocyte-derived macrophages (MDMs) contribute to recovery after acute sterile brain injury. By profiling the transcriptional dynamics of MDMs in the murine brain after experimental intracerebral hemorrhage (ICH), we found robust phenotypic changes in the infiltrating MDMs over time and demonstrated that MDMs are essential for optimal hematoma clearance and neurological recovery. Next, we identified the mechanism by which the engulfment of erythrocytes with exposed phosphatidylserine directly modulated the phenotype of both murine and human MDMs. In mice, loss of receptor tyrosine kinases AXL and MERTK reduced efferocytosis of eryptotic erythrocytes and hematoma clearance, worsened neurological recovery, exacerbated iron deposition, and decreased alternative activation of macrophages after ICH. Patients with higher circulating soluble AXL had poor 1-year outcomes after ICH onset, suggesting that therapeutically augmenting efferocytosis may improve functional outcomes by both reducing tissue injury and promoting the development of reparative macrophage responses. Thus, our results identify the efferocytosis of eryptotic erythrocytes through AXL/MERTK as a critical mechanism modulating macrophage phenotype and contributing to recovery from ICH.

The tumor microenvironment: Thousand obstacles for effector T cells

The immune system is endowed with the capability to recognize and destroy transformed cells, but even in the presence of an immune infiltrate many tumors do progress. In the last decades new discoveries have shed light into (some of) the underlying mechanisms. Immune effector cells are not only under the influence of immune suppressive cell subsets, but also intrinsically regulated by immune check point molecules that under physiological condition avoid attach of healthy tissue. Moreover, tumor cells are modifying the surrounding microenvironment through secretion of immune modulators as well as via their own metabolism, thus further impairing the development of immune effector functions. Different approaches are currently being evaluated in the clinic to overcome those regulatory mechanisms and to unleash effector T cells.

High Tim-3 expression on AML blasts could enhance chemotherapy sensitivity

T-cell immunoglobulin and mucin domain-containing molecule3 (Tim-3) represents a novel mechanism of T-cell dysfunction and exhaustion. Tim-3 has also been identified in various solid tumors. However, the role of Tim-3 expression on blast cells in acute myeloid leukemia (AML) is not well understood. In this study, we aimed to explore the role of Tim-3 in patients with de novo AML, and the correlation between Tim-3 and clinicopathological prognosis. The study cohort consisted of 76 patients with de novo non-M3 AML. These patients’ bone marrow samples were collected and then bone marrow mononuclear cells (BMCs) were isolated for flow cytometry to detect Tim-3 expression on blasts. According to FAB type, 76 diagnosed AML patients included in this study were: M0 (n=2), M1 (n=16), M2 (n=20), M4 (n=20), M5 (n=16), and M6 (n=2). A positive expression (>20%) of Tim-3 was found in 87% (66/76) of patients with AML. The average percentage of Tim-3(+) blasts in these AML patients was 58.26 ± 29.23%. Moreover, the frequency of Tim-3 high expression was higher in M4 patients than that in other AML patients according to FAB type (P=0.004). Tim-3 high expression was also closely associated with inv(16) (P=0.01) and C/EBPA mutation (P=0.03). The mutations of the following six genes, i.e., FLT3-ITD, NPM1, C-KIT, IDH1/IDH2, DNMT3A, were independent of the Tim-3 expression. Additionally, it is more likely to find higher levels of Tim-3 in the low-risk group than in the intermediate- and high-risk groups (P=0.02). The expression of Tim-3 was positively correlated with CD13 (r=0.36, P=0.001), CD34 (r=0.41, P=0.000), and CD7 (r=0.27, P=0.02) in AML patients. AML patients with high Tim-3 expression achieved significantly high complete remission (CR) rate (P=0.01), while their Tim-3 expression significantly decreased after CR (P=0.01). Blockade of Tim-3 expression on AML blasts significantly reduced the Idarubicin (IDA)-mediated suppression of cell growth and reduction of cell apoptosis in vitro. Collectively, our study suggests that high Tim-3 expression on AML blasts could enhances chemotherapy sensitivity.

Cutting Edge: Anti-TIM-3 Treatment Exacerbates Pulmonary Inflammation and Fibrosis in Mice

Promising results of immune checkpoint inhibitors have indicated the use of immunotherapy against malignant tumors. However, they cause serious side effects, including autoimmune diseases and pneumonitis. T cell Ig and mucin domain (TIM)-3 is a new candidate immune checkpoint molecule; however, the potential toxicity associated with anti-TIM-3 treatment is unknown. In this study, we investigated the pathological contribution of anti-TIM-3 mAb in a bleomycin-induced lung inflammation and fibrosis model. Anti-TIM-3-treated mice showed more severe inflammation and peribronchiolar fibrosis compared with control IgG-treated mice. Anti-TIM-3 mAb was associated with increased numbers of myofibroblasts, collagen deposition, and TGF-β1 production in lungs. TIM-3 expression was only detected on alveolar macrophages that protect against fibrosis by apoptotic cell clearance. Treatment with anti-TIM-3 mAb inhibited the phagocytic ability of alveolar macrophages in vivo, resulting in the defective clearance of apoptotic cells in lungs. In summary, anti-TIM-3 mAb treatment might cause pneumonitis and it should be used with caution in clinical settings.

Control of NK Cell Activation by Immune Checkpoint Molecules

The development of cancer and chronic infections is facilitated by many subversion mechanisms, among which enhanced expression of immune checkpoints molecules, such as programmed death-1 (PD-1) and cytotoxic T lymphocyte-associated antigen 4 (CTLA-4), on exhausted T cells. Recently, immune checkpoint inhibitors have shown remarkable efficiency in the treatment of a number of cancers. However, expression of immune checkpoints on natural killer (NK) cells and its functional consequences on NK cell effector functions are much less explored. In this review, we focus on the current knowledge on expression of various immune checkpoints in NK cells, how it can alter NK cell-mediated cytotoxicity and cytokine production. Dissecting the role of these inhibitory mechanisms in NK cells is critical for the full understanding of the mode of action of immunotherapies using checkpoint inhibitors in the treatment of cancers and chronic infections.

Translational Implication of Galectin-9 in the Pathogenesis and Treatment of Viral Infection

The interaction between galectin-9 and its receptor, Tim-3, triggers a series of signaling events that regulate immune responses. The expression of galectin-9 has been shown to be increased in a variety of target cells of many different viruses, such as hepatitis C virus (HCV), hepatitis B virus (HBV), herpes simplex virus (HSV), influenza virus, dengue virus (DENV), and human immunodeficiency virus (HIV). This enhanced expression of galectin-9 following viral infection promotes significant changes in the behaviors of the virus-infected cells, and the resulting events tightly correlate with the immunopathogenesis of the viral disease. Because the human immune response to different viral infections can vary, and the lack of appropriate treatment can have potentially fatal consequences, understanding the implications of galectin-9 is crucial for developing better methods for monitoring and treating viral infections. This review seeks to address how we can apply the current understanding of galectin-9 function to better understand the pathogenesis of viral infection and better treat viral diseases.

Clinical Significance of T-Cell Immunoglobulin Mucin 3 Expression on Peripheral Blood Mononuclear Cells in Pediatric Acute Immune Thrombocytopenia

T-cell immunoglobulin mucin 3 (TIM-3) is a transmembrane protein that plays an important role in several autoimmune diseases. The relationship between TIM-3 and excessive immune responses in immune thrombocytopenia (ITP) is still unknown. In this study, we evaluated the relationship between the expression of TIM-3 on peripheral blood mononuclear cells in patients with ITP and the disease severity. The frequency of lymphocyte and monocyte subsets and their TIM-3 expression were evaluated in patients with acute ITP (n = 45) and in healthy control (n = 20) using flow cytometry. Based on bleeding severity, patients were classified into 3 subgroups as mild (n = 12), moderate (n = 25), and severe (n = 8) bleeding. T-helper lymphocytes was found to be significantly decreased in the severe bleeding group compared to the mild and moderate bleeding groups, while CD56^high natural killer (NK) cells were significantly expanded in severe bleeding group. In contrast, classical, intermediate, and nonclassical monocytes, natural killer T lymphocyte (NKT), and CD56^dim NK cells showed no significant changes among different patient groups. This alteration of lymphocyte and monocyte subsets was associated with significant decrease in TIM-3 expression on CD56^high NK cells, T-helper lymphocytes, NKT cells, and nonclassical monocytes in patients with ITP compared to the controls. Lower level of TIM-3 was found in severe bleeding group compared to mild and moderate bleeding groups. These results indicate that TIM-3 may be involved in the pathogenesis of ITP which subsequently can represent an opportunity for new therapeutic plan, moreover. This may have a prognostic value for disease severity.

Lag-3, Tim-3, and TIGIT: Co-inhibitory Receptors with Specialized Functions in Immune Regulation

Co-inhibitory receptors, such as CTLA-4 and PD-1, have an important role in regulating T cell responses and have proven to be effective targets in the setting of chronic diseases where constitutive co-inhibitory receptor expression on T cells dampens effector T cell responses. Unfortunately, many patients still fail to respond to therapies that target CTLA-4 and PD-1. The next wave of co-inhibitory receptor targets that are being explored in clinical trials include Lag-3, Tim-3, and TIGIT. These receptors, although they belong to the same class of receptors as PD-1 and CTLA-4, exhibit unique functions, especially at tissue sites where they regulate distinct aspects of immunity. Increased understanding of the specialized functions of these receptors will inform the rational application of therapies that target these receptors to the clinic.

Immunomodulatory Monoclonal Antibodies in Combined Immunotherapy Trials for Cutaneous Melanoma

In the last few years, there has been a twist in cancer treatment toward immunotherapy thanks to the impressive results seen in advanced patients from several tumor pathologies. Cutaneous melanoma is a highly mutated and immunogenic tumor that has been a test field for the development of immunotherapy. However, there is still a way on the road to achieving complete and long-lasting responses in most patients. It is desirable that immunotherapeutic strategies induce diverse immune reactivity specific to tumor antigens, including the so-called neoantigens, as well as the blockade of immunosuppressive mechanisms. In this review, we will go through the role of promising monoclonal antibodies in cancer immunotherapy with immunomodulatory function, especially blocking of the inhibitory immune checkpoints CTLA-4 and PD-1, in combination with different immunotherapeutic strategies such as vaccines. We will discuss the rational basis for these combinatorial approaches as well as different schemes currently under study for cutaneous melanoma in the clinical trials arena. In this way, the combination of "push and release" immunomodulatory therapies can contribute to achieving a more robust and durable antitumor immune response in patients.

A TIM-3 Oligonucleotide Aptamer Enhances T Cell Functions and Potentiates Tumor Immunity in Mice

T cell immunoglobulin-3 (TIM-3) is a negative regulator of interferon-γ (IFN-γ) secreting CD4⁺ T cells and CD8⁺ T cytotoxic cells. Recent studies have highlighted the role of TIM-3 as an important mediator of CD8⁺ T cell exhaustion in the setting of chronic viral infections and cancer. In murine tumor models, antibody blockade of TIM-3 with anti-TIM-3 antibodies as monotherapy has no or minimal antitumor activity, suggesting that TIM-3 signaling exerts an accessory or amplifying effect in keeping immune responses in check. Using a combined bead and cell-based systemic evolution of ligands by exponential enrichment (SELEX) protocol, we have isolated nuclease-resistant oligonucleotide aptamer ligands that bind to cell-associated TIM-3 with high affinity and specificity. A trimeric form of the TIM-3 aptamer blocked the interaction of TIM-3 with Galectin-9, reduced cell death, and enhanced survival, proliferation, and cytokine secretion in vitro. In tumor-bearing mice, the aptamer delayed tumor growth as monotherapy and synergized with PD-1 antibody in prolonging the survival of the tumor-bearing mice. Both in vitro and in vivo, the trimeric aptamer displayed superior activity compared to the currently used RMT3-23 monoclonal antibody. This study suggests that multi-valent aptamers could represent an alternative platform to generate potent ligands to manipulate the function of TIM-3 and other immune modulatory receptors.

Tim-3 and its role in regulating anti-tumor immunity

Immunotherapy is being increasingly recognized as a key therapeutic modality to treat cancer and represents one of the most exciting treatments for the disease. Fighting cancer with immunotherapy has revolutionized treatment for some patients and therapies targeting the immune checkpoint molecules such as CTLA-4 and PD-1 have achieved durable responses in melanoma, renal cancer, Hodgkin's diseases and lung cancer. However, the success rate of these treatments has been low and a large number of cancers, including colorectal cancer remain largely refractory to CTLA-4 and PD-1 blockade. This has provided impetus to identify other co-inhibitory receptors that could be exploited to enhance response rates of current immunotherapeutic agents and achieve responses to the cancers that are refectory to immunotherapy. Tim-3 is a co-inhibitory receptor that is expressed on IFN-g-producing T cells, FoxP3+ Treg cells and innate immune cells (macrophages and dendritic cells) where it has been shown to suppress their responses upon interaction with their ligand(s). Tim-3 has gained prominence as a potential candidate for cancer immunotherapy, where it has been shown that in vivo blockade of Tim-3 with other check-point inhibitors enhances anti-tumor immunity and suppresses tumor growth in several preclinical tumor models. This review discusses the recent findings on Tim-3, the role it plays in regulating immune responses in different cell types and the rationale for targeting Tim-3 for effective cancer immunotherapy.

Molecular Mechanisms of Phagosome Formation

Phagocytosis refers to the active process that allows cells to take up large particulate material upon binding to surface receptors. The discovery of phagocytosis in 1883 by Elie Metchnikoff, leading to the concept that specialized cells are implicated in the defense against microbes, was one of the starting points of the field of immunology. After more than a century of research, phagocytosis is now appreciated to be a widely used process that enables the cellular uptake of a remarkable variety of particles, including bacteria, fungi, parasites, viruses, dead cells, and assorted debris and solid materials. Uptake of foreign particles is performed almost exclusively by specialized myeloid cells, commonly termed "professional phagocytes": neutrophils, monocytes, macrophages, and dendritic cells. Phagocytosis of microbes not only stops or at least restricts the spread of infection but also plays an important role in regulating the innate and adaptive immune responses. Activation of the myeloid cells upon phagocytosis leads to the secretion of cytokines and chemokines that convey signals to a variety of immune cells. Moreover, foreign antigens generated by the degradation of microbes following phagocytosis are loaded onto the major histocompatibility complex for presentation to specific T lymphocytes. However, phagocytosis is not restricted to professional myeloid phagocytes; an expanding diversity of cell types appear capable of engulfing apoptotic bodies and debris, playing a critical role in tissue remodeling and in the clearance of billions of effete cells every day.

Functional annotation of the T-cell immunoglobulin mucin family in birds

T‐cell immunoglobulin and mucin (TIM) family molecules are cell membrane proteins, preferentially expressed on various immune cells and implicated in recognition and clearance of apoptotic cells. Little is known of their function outside human and mouse, and nothing outside mammals. We identified only two TIM genes (chTIM) in the chicken genome, putative orthologues of mammalian TIM1 and TIM4, and cloned the respective cDNAs. Like mammalian TIM1, chTIM1 expression was restricted to lymphoid tissues and immune cells. The gene chTIM4 encodes at least five splice variants with distinct expression profiles that also varied between strains of chicken. Expression of chTIM4 was detected in myeloid antigen‐presenting cells, and in γδ T cells, whereas mammalian TIM4 is not expressed in T cells. Like the mammalian proteins, chTIM1 and chTIM4 fusion proteins bind to phosphatidylserine, and are thereby implicated in recognition of apoptotic cells. The chTIM4–immunoglobulin fusion protein also had co‐stimulatory activity on chicken T cells, suggesting a function in antigen presentation.

Engulfment signals and the phagocytic machinery for apoptotic cell clearance

The clearance of apoptotic cells is an essential process for tissue homeostasis. To this end, cells undergoing apoptosis must display engulfment signals, such as ‘find-me' and ‘eat-me' signals. Engulfment signals are recognized by multiple types of phagocytic machinery in phagocytes, leading to prompt clearance of apoptotic cells. In addition, apoptotic cells and phagocytes release tolerogenic signals to reduce immune responses against apoptotic cell-derived self-antigens. Here we discuss recent advances in our knowledge of engulfment signals, the phagocytic machinery and the signal transduction pathways for apoptotic cell engulfment.

TIM-3 as a Target for Cancer Immunotherapy and Mechanisms of Action

Cancer immunotherapy has produced impressive clinical results in recent years. Despite the success of the checkpoint blockade strategies targeting cytotoxic T lymphocyte antigen 4 (CTLA-4) and programmed death receptor 1 (PD-1), a large portion of cancer patients have not yet benefited from this novel therapy. T cell immunoglobulin and mucin domain 3 (TIM-3) has been shown to mediate immune tolerance in mouse models of infectious diseases, alloimmunity, autoimmunity, and tumor Immunity. Thus, targeting TIM-3 emerges as a promising approach for further improvement of current immunotherapy. Despite a large amount of experimental data showing an immune suppressive function of TIM-3 in vivo, the exact mechanisms are not well understood. To enable effective targeting of TIM-3 for tumor immunotherapy, further in-depth mechanistic studies are warranted. These studies will also provide much-needed insight for the rational design of novel combination therapy with other checkpoint blockers. In this review, we summarize key evidence supporting an immune regulatory role of TIM-3 and discuss possible mechanisms of action.

Tim-3 is a Marker of Plasmacytoid Dendritic Cell Dysfunction during HIV Infection and Is Associated with the Recruitment of IRF7 and p85 into Lysosomes and with the Submembrane Displacement of TLR9

In chronic diseases, such as HIV infection, plasmacytoid dendritic cells (pDCs) are rendered dysfunctional, as measured by their decreased capacity to produce IFN-α. In this study, we identified elevated levels of T cell Ig and mucin-domain containing molecule-3 (Tim-3)-expressing pDCs in the blood of HIV-infected donors. The frequency of Tim-3-expressing pDCs correlated inversely with CD4 T cell counts and positively with HIV viral loads. A lower frequency of pDCs expressing Tim-3 produced IFN-α or TNF-α in response to the TLR7 agonists imiquimod and Sendai virus and to the TLR9 agonist CpG. Thus, Tim-3 may serve as a biomarker of pDC dysfunction in HIV infection. The source and function of Tim-3 was investigated on enriched pDC populations from donors not infected with HIV. Tim-3 induction was achieved in response to viral and artificial stimuli, as well as exogenous IFN-α, and was PI3K dependent. Potent pDC-activating stimuli, such as CpG, imiquimod, and Sendai virus, induced the most Tim-3 expression and subsequent dysfunction. Small interfering RNA knockdown of Tim-3 increased IFN-α secretion in response to activation. Intracellular Tim-3, as measured by confocal microscopy, was dispersed throughout the cytoplasm prior to activation. Postactivation, Tim-3 accumulated at the plasma membrane and associated with disrupted TLR9 at the submembrane. Tim-3-expressing pDCs had reduced IRF7 levels. Furthermore, intracellular Tim-3 colocalized with p85 and IRF7 within LAMP1⁺ lysosomes, suggestive of a role in degradation. We conclude that Tim-3 is a biomarker of dysfunctional pDCs and may negatively regulate IFN-α, possibly through interference with TLR signaling and recruitment of IRF7 and p85 into lysosomes, enhancing their degradation.

Potential influences of complement factor H in autoimmune inflammatory and thrombotic disorders

Complement system homeostasis is important for host self-protection and anti-microbial immune surveillance, and recent research indicates roles in tissue development and remodelling. Complement also appears to have several points of interaction with the blood coagulation system. Deficiency and altered function due to gene mutations and polymorphisms in complement effectors and regulators, including Factor H, have been associated with familial and sporadic autoimmune inflammatory - thrombotic disorders, in which autoantibodies play a part. These include systemic lupus erythematosus, rheumatoid arthritis, atypical haemolytic uremic syndrome, anti-phospholipid syndrome and age-related macular degeneration. Such diseases are generally complex - multigenic and heterogeneous in their symptoms and predisposition/susceptibility. They usually need to be triggered by vascular trauma, drugs or infection and non-complement genetic factors also play a part. Underlying events seem to include decline in peripheral regulatory T cells, dendritic cell, and B cell tolerance, associated with alterations in lymphoid organ microenvironment. Factor H is an abundant protein, synthesised in many cell types, and its reported binding to many different ligands, even if not of high affinity, may influence a large number of molecular interactions, together with the accepted role of Factor H within the complement system. Factor H is involved in mesenchymal stem cell mediated tolerance and also contributes to self-tolerance by augmenting iC3b production and opsonisation of apoptotic cells for their silent dendritic cell engulfment via complement receptor CR3, which mediates anti-inflammatory-tolerogenic effects in the apoptotic cell context. There may be co-operation with other phagocytic receptors, such as complement C1q receptors, and the Tim glycoprotein family, which specifically bind phosphatidylserine expressed on the apoptotic cell surface. Factor H is able to discriminate between self and nonself surfaces for self-protection and anti-microbe defence. Factor H, particularly as an abundant platelet protein, may also modulate blood coagulation, having an anti-thrombotic role. Here, we review a number of interaction pathways in coagulation and in immunity, together with associated diseases, and indicate where Factor H may be expected to exert an influence, based on reports of the diversity of ligands for Factor H.

Efferocytosis Signaling in the Regulation of Macrophage Inflammatory Responses

Since the pioneering work of Elie Metchnikoff and the discovery of cellular immunity, the phagocytic clearance of cellular debris has been considered an integral component of resolving inflammation and restoring function of damaged and infected tissues. We now know that the phagocytic clearance of dying cells (efferocytosis), particularly by macrophages and other immune phagocytes, has profound consequences on innate and adaptive immune responses in inflamed tissues. These immunomodulatory effects result from an array of molecular signaling events between macrophages, dying cells, and other tissue-resident cells. In recent years, many of these molecular pathways have been identified and studied in the context of tissue inflammation, helping us better understand the relationship between efferocytosis and inflammation. We review specific types of efferocytosis-related signals that can impact macrophage immune responses and discuss their relevance to inflammation-related diseases.

Modulators of the Balance between M1 and M2 Macrophages during Pregnancy

Macrophages are a subset of mononuclear phagocytes of the innate immune system with high plasticity and heterogeneity. At the maternal–fetal interface, macrophages are present in all stages of pregnancy and involved in a variety of activities, including regulation of immune cell activities, decidualization, placental cell invasion, angiogenesis, parturition, and postpartum uterine involution. The activation state and function of uterine–placental macrophages are largely dependent on the local tissue microenvironment. However, disruption of the uterine microenvironment can have profound effects on macrophage activity and subsequently impact pregnancy outcome. Thus, appropriately and timely regulated macrophage polarization has been considered a key determinant of successful pregnancy. Targeting macrophage polarization might be an efficient strategy for maintaining maternal–fetal immune homeostasis and a normal pregnancy. Here, we will review the latest findings regarding the modulators regulating macrophage polarization in healthy pregnancies and pregnancy complications, which might provide a basis for macrophage-centered therapeutic strategies.

Tim3/Gal9 interactions between T cells and monocytes result in an immunosuppressive feedback loop that inhibits Th1 responses in osteosarcoma patients

The Tim3/Gal9 pathway is associated with immunosuppression and worse clinical outcome in multiple cancers. To illustrate the specific mechanism of Tim3/Gal9 interaction in osteosarcoma, we examined expression, function, and regulation of Tim3/Gal9 in various cells from osteosarcoma patients. Data showed that CD4⁺ T cells, CD8⁺ T cells, and monocytes from both peripheral blood and tumor of osteosarcoma patients contained high frequencies of Tim3⁺ cells, while the Gal9 expression was primarily found in regulatory T cells (Tregs) from osteosarcoma patients and was elevated compared to that in non-cancer controls. The Tim3⁺ CD4⁺ and CD8⁺ T cells presented lower proliferation capacity compared to their Tim3^- counterparts, which could be reverted by blocking Tim3 or Gal9. Interestingly, purified Tim3⁺ CD4⁺ T cells secreted more interferon gamma (IFNγ) than purified Tim3^- CD4⁺ T cells, but IFNγ production by Tim3⁺ CD4⁺ T cells was vulnerable to Gal9-mediated suppression. In monocytes, Tim3 expression was associated with high interleukin (IL)-10 and low IL-12 cytokine secretion profile. Exogenous recombinant Gal9, as well as CD4⁺CD25⁺ Treg supernatant, further decreased IL-12 expression in monocytes. In CD4⁺ T cell-monocyte coculture experiments, Tim3⁺ monocytes inhibited IFNγ expression from total CD4⁺ T cells and the development of IFNγ response in naive CD4⁺ T cells. Blocking the Tim3/Gal9 pathway reverted these effects. Together, these results suggested that in osteosarcoma patients, Tim3 expression did not directly mediate immune suppression, but the interaction between Tim3⁺ T cells and monocytes, naive CD4⁺ T cells, and Gal9-expressing CD4⁺CD25⁺ Tregs could resulting in progressive suppression of Th1 responses.

Tim-3, Lag-3, and TIGIT

Co-inhibitory receptors play a key role in regulating T cell responses and maintaining immune homeostasis. Their inhibitory function prevents autoimmune responses but also restricts the ability of T cells to mount effective immune responses against tumors or persistent pathogens. T cells express a module of co-inhibitory receptors, which display great diversity in expression, structure, and function. Here, we focus on the co-inhibitory receptors Tim-3, Lag-3, and TIGIT and how they regulate T cell function, maintenance of self-tolerance, their role in regulating ongoing T cell responses at peripheral tissues, and their synergistic effects in regulating autoimmunity and antitumor responses.

Immune checkpoint inhibitors for cancer treatment

During immune responses antigen-specific T cells are regulated by several mechanisms, including through inhibitory receptors and regulatory T cells, to avoid excessive or persistent immune responses. These regulatory mechanisms, which are called 'immune checkpoints', suppress T cell responses, particularly in patients with chronic viral infections and cancer where viral antigens or tumor antigens persist for a long time and contribute to T cell exhaustion. Among these regulatory mechanisms, cytotoxic T lymphocyte associated protein-4 (CTLA-4) and programmed cell death 1 (PD-1) are the most well-known receptors and both have been targeted for drug development. As a result, anti-CTLA-4 and anti-PD-1 (or anti-PD-L1) antibodies were recently developed as immune checkpoint inhibitors for use in cancer treatments. In this review we describe several receptors that function as immunological checkpoints as well as the pharmaceuticals that target them.

The miR-125a-3p Inhibits TIM-3 Expression in AML Cell Line HL-60 In Vitro

Acute Myeloid Leukemia is a cancer of leukemic stem cells (LSCs) with a rapid progression. It is characterized by overproduction of immature myeloid cells in bone marrow which crowds out normal hematopoietic stem cells (HSC). TIM-3, an immune regulatory molecule, is an LSC specific surface marker in AML with high expression on these cells compared to HSCs. Studies have indicated that micro RNAs (miRNAs) may play an important role in either cancer progression or suppression. Based on bioinformatics assessments, we have predicted that miR-125a-3p could be a miRNA with high suppressive activity on TIM-3 expression. The purpose of this study was to investigate the inhibitory effect of miR-125a-3p on TIM-3 gene expression in an AML cell line, HL-60, in vitro. HL-60 cells were cultured in RPMI 1640 supplied with 10 % FBS. TIM-3 expression was induced on the cells using phorbol miristate acetate. The cells were transfected with miR-125-3p for 24 h and the gene and protein expression of TIM-3 were measured using q-RT-PCR and flow-cytometery methods, respectively. The results of this study showed that miR-125a-3p has a strong silencing effect on TIM-3 gene and protein expression on HL-60 cell line. Based to our results, miR125a-3p can strongly silence TIM-3 expression in AML cell line. Thus, our results have confirmed the bioinformatics prediction of suppressive effect of miR-125a-3p on TIM-3with Mirwalk and Target Scan softwares.

Combination Therapy with Anti-PD-1, Anti-TIM-3, and Focal Radiation Results in Regression of Murine Gliomas

PURPOSE

Checkpoint molecules like programmed death-1 (PD-1) and T-cell immunoglobulin mucin-3 (TIM-3) are negative immune regulators that may be upregulated in the setting of glioblastoma multiforme. Combined PD-1 blockade and stereotactic radiosurgery (SRS) have been shown to improve antitumor immunity and produce long-term survivors in a murine glioma model. However, tumor-infiltrating lymphocytes (TIL) can express multiple checkpoints, and expression of ≥2 checkpoints corresponds to a more exhausted T-cell phenotype. We investigate TIM-3 expression in a glioma model and the antitumor efficacy of TIM-3 blockade alone and in combination with anti-PD-1 and SRS.

EXPERIMENTAL DESIGN

C57BL/6 mice were implanted with murine glioma cell line GL261-luc2 and randomized into 8 treatment arms: (i) control, (ii) SRS, (iii) anti-PD-1 antibody, (iv) anti-TIM-3 antibody, (v) anti-PD-1 + SRS, (vi) anti-TIM-3 + SRS, (vii) anti-PD-1 + anti-TIM-3, and (viii) anti-PD-1 + anti-TIM-3 + SRS. Survival and immune activation were assessed.

RESULTS

Dual therapy with anti-TIM-3 antibody + SRS or anti-TIM-3 + anti-PD-1 improved survival compared with anti-TIM-3 antibody alone. Triple therapy resulted in 100% overall survival (P < 0.05), a significant improvement compared with other arms. Long-term survivors demonstrated increased immune cell infiltration and activity and immune memory. Finally, positive staining for TIM-3 was detected in 7 of 8 human GBM samples.

CONCLUSIONS

This is the first preclinical investigation on the effects of dual PD-1 and TIM-3 blockade with radiation. We also demonstrate the presence of TIM-3 in human glioblastoma multiforme and provide preclinical evidence for a novel treatment combination that can potentially result in long-term glioma survival and constitutes a novel immunotherapeutic strategy for the treatment of glioblastoma multiforme. Clin Cancer Res; 23(1); 124-36. ©2016 AACR.

TIM-3 Regulates Distinct Functions in Macrophages

The transmembrane protein TIM-3 is a type I protein expressed by sub-types of lymphoid cells, such as lymphocytes Th1, Th17, Tc1, NK, as well as in myeloid cells. Scientific evidence indicates that this molecule acts as a negative regulator of T lymphocyte activation and that its expression is modified in viral infections or autoimmune diseases. In addition to evidence from lymphoid cells, the function of TIM-3 has been investigated in myeloid cells, such as monocytes, macrophages, and dendritic cells (DC), where studies have demonstrated that it can regulate cytokine production, cell activation, and the capture of apoptotic bodies. Despite these advances, the function of TIM-3 in myeloid cells and the molecular mechanisms that this protein regulates are not yet fully understood. This review examines the most recent evidence concerning the function of TIM-3 when expressed in myeloid cells, primarily macrophages, and the potential impact of that function on the field of basic immunology.

Critical role of CCL22/CCR4 axis in the maintenance of immune homeostasis during apoptotic cell clearance by splenic CD8α(+) CD103(+) dendritic cells

Macrophages and dendritic cells (DCs) in murine spleen are essential for the maintenance of immune homeostasis by elimination of blood-borne foreign particles and organisms. It has been reported that splenic DCs, especially CD8α(+) CD103(+) DCs, are responsible for tolerance to apoptosis-associated antigens. However, the molecular mechanism by which these DCs maintain immune homeostasis by blood-borne apoptotic cell clearance remains elusive. Here, we found that the CCL22/CCR4 axis played a critical role in the maintenance of immune homeostasis during apoptotic cell clearance by splenic CD8α(+) CD103(+) DCs. The present results revealed that systemic administration of apoptotic cells rapidly induced a large number of CCL22 and CCR4(+) regulatory T (Treg) cells in the spleen of C57BL/6J mice. Further study demonstrated that CD8α(+) CD103(+) DCs dominantly produce much higher CCL22 than CD8α(+) CD103(-) DCs. Moreover, the transient deletion of CD8α(+) CD103(+) DCs caused a decrease in CCL22 levels together with CCR4(+) Treg cell percentage. Subsequently, the levels of some pro-inflammatory cytokines, such as interleukin-17 and interferon-γ in the spleen with the absence of CD8α(+) CD103(+) DCs increased in response to the administration of apoptotic cells. Hence, intravenous injection of apoptotic cells induced a subsequent increase in CCL22 expression and CCR4(+) Treg cells, which contribute to the maintenance of immune homeostasis at least partially by splenic CD8α(+) CD103(+) DCs.

Key mechanisms governing resolution of lung inflammation

Innate immunity normally provides excellent defence against invading microorganisms. Acute inflammation is a form of innate immune defence and represents one of the primary responses to injury, infection and irritation, largely mediated by granulocyte effector cells such as neutrophils and eosinophils. Failure to remove an inflammatory stimulus (often resulting in failed resolution of inflammation) can lead to chronic inflammation resulting in tissue injury caused by high numbers of infiltrating activated granulocytes. Successful resolution of inflammation is dependent upon the removal of these cells. Under normal physiological conditions, apoptosis (programmed cell death) precedes phagocytic recognition and clearance of these cells by, for example, macrophages, dendritic and epithelial cells (a process known as efferocytosis). Inflammation contributes to immune defence within the respiratory mucosa (responsible for gas exchange) because lung epithelia are continuously exposed to a multiplicity of airborne pathogens, allergens and foreign particles. Failure to resolve inflammation within the respiratory mucosa is a major contributor of numerous lung diseases. This review will summarise the major mechanisms regulating lung inflammation, including key cellular interplays such as apoptotic cell clearance by alveolar macrophages and macrophage/neutrophil/epithelial cell interactions. The different acute and chronic inflammatory disease states caused by dysregulated/impaired resolution of lung inflammation will be discussed. Furthermore, the resolution of lung inflammation during neutrophil/eosinophil-dominant lung injury or enhanced resolution driven via pharmacological manipulation will also be considered.

The future of cancer treatment: immunomodulation, CARs and combination immunotherapy

In the past decade, advances in the use of monoclonal antibodies (mAbs) and adoptive cellular therapy to treat cancer by modulating the immune response have led to unprecedented responses in patients with advanced-stage tumours that would otherwise have been fatal. To date, three immune-checkpoint-blocking mAbs have been approved in the USA for the treatment of patients with several types of cancer, and more patients will benefit from immunomodulatory mAb therapy in the months and years ahead. Concurrently, the adoptive transfer of genetically modified lymphocytes to treat patients with haematological malignancies has yielded dramatic results, and we anticipate that this approach will rapidly become the standard of care for an increasing number of patients. In this Review, we highlight the latest advances in immunotherapy and discuss the role that it will have in the future of cancer treatment, including settings for which testing combination strategies and 'armoured' CAR T cells are recommended.

Do not let death do us part: 'find-me' signals in communication between dying cells and the phagocytes

The turnover and clearance of cells is an essential process that is part of many physiological and pathological processes. Improper or deficient clearance of apoptotic cells can lead to excessive inflammation and autoimmune disease. The steps involved in cell clearance include: migration of the phagocyte toward the proximity of the dying cells, specific recognition and internalization of the dying cell, and degradation of the corpse. The ability of phagocytes to recognize and react to dying cells to perform efficient and immunologically silent engulfment has been well-characterized in vitro and in vivo. However, how apoptotic cells themselves initiate the corpse removal and also influence the cells within the neighboring environment during clearance was less understood. Recent exciting observations suggest that apoptotic cells can attract phagocytes through the regulated release of 'find-me' signals. More recent studies also suggest that these find-me signals can have additional roles outside of phagocyte attraction to help orchestrate engulfment. This review will discuss our current understanding of the different find-me signals released by apoptotic cells, how they may be relevant in vivo, and their additional roles in facilitating engulfment.

G protein α12 (Gα12) is a negative regulator of kidney injury molecule-1-mediated efferocytosis

Kidney injury molecule-1 (KIM-1) is a receptor for the "eat me" signal, phosphatidylserine, on apoptotic cells. The specific upregulation of KIM-1 by injured tubular epithelial cells (TECs) enables them to clear apoptotic cells (also known as efferocytosis), thereby protecting from acute kidney injury. Recently, we uncovered that KIM-1 binds directly to the α-subunit of heterotrimeric G₁₂ protein (Gα₁₂) and inhibits its activation by reactive oxygen species during renal ischemia-reperfusion injury (Ismail OZ, Zhang X, Wei J, Haig A, Denker BM, Suri RS, Sener A, Gunaratnam L. Am J Pathol 185: 1207-1215, 2015). Here, we investigated the role that Gα₁₂ plays in KIM-1-mediated efferocytosis by TECs. We showed that KIM-1 remains bound to Gα₁₂ and suppresses its activity during phagocytosis. When we silenced Gα₁₂ expression using small interefering RNA, KIM-1-mediated engulfment of apoptotic cells was increased significantly; in contrast overexpression of constitutively active Gα₁₂ (QLGα₁₂) resulted in inhibition of efferocytosis. Inhibition of RhoA, a key effector of Gα₁₂, using a chemical inhibitor or expression of dominant-negative RhoA, had the same effect as inhibition of Gα₁₂ on efferocytosis. Consistent with this, silencing Gα₁₂ suppressed active RhoA in KIM-1-expressing cells. Finally, using primary TECs from Kim-1^+/+ and Kim-1^-/- mice, we confirmed that engulfment of apoptotic cells requires KIM-1 expression and that silencing Gα₁₂ enhanced efferocytosis by primary TECs. Our data reveal a previously unknown role for Gα₁₂ in regulating efferocytosis and that renal TECs require KIM-1 to mediate this process. These results may have therapeutic implications given the known harmful role of Gα₁₂ in acute kidney injury.

Immunological landscape and immunotherapy of hepatocellular carcinoma

Advanced hepatocellular carcinoma (HCC) is a serious therapeutic challenge and targeted therapies only provide a modest benefit in terms of overall survival. Novel approaches are urgently needed for the treatment of this prevalent malignancy. Evidence demonstrating the antigenicity of tumour cells, the discovery that immune checkpoint molecules have an essential role in immune evasion of tumour cells, and the impressive clinical results achieved by blocking these inhibitory receptors, are revolutionizing cancer immunotherapy. Here, we review the data on HCC immunogenicity, the mechanisms for HCC immune subversion and the different immunotherapies that have been tested to treat HCC. Taking into account the multiplicity of hyperadditive immunosuppressive forces acting within the HCC microenvironment, a combinatorial approach is advised. Strategies include combinations of systemic immunomodulation and gene therapy, cell therapy or virotherapy.

Downregulation of T cell immunoglobulin and mucin protein 3 in the pathogenesis of intracranial aneurysm

Evidence has shown that inflammation acts as a critical contributor to the pathogenesis of intracranial aneurysm (IA), a potentially devastating clinical problem. T cell immunoglobulin and mucin protein 3 (Tim-3) is a negative regulatory molecule and plays important roles in the inflammation process. In the current study, we investigated the expression of Tim-3 and its correlation with tumor necrosis factor alpha (TNF-α) in IA patients. Data showed that both messenger RNA (mRNA) level and protein level of Tim-3 were significantly decreased in CD4+ T cells and CD8+ T cells from IA patients than from healthy controls (P < 0.001). However, expression of Tim-3 was not altered in monocytes between patients and healthy donors. Further analyses revealed that patients with ruptured aneurysm had significantly lower level of Tim-3 in CD8+ T cells than those with un-ruptured aneurysm. In addition, a negative correlation between serum level of TNF-α and the expression of Tim-3 in CD4+ T cells was observed in IA patients. Similar correlation was also identified in CD8+ T cells from IA patients. Our study suggests that Tim-3 may participate in the development and progression of IA by probably its negative regulation on TNF-α.

Identification of TIM-3 as a Leukemic Stem Cell Surface Molecule in Primary Acute Myeloid Leukemia

Acute myeloid leukemia (AML) originates from self-renewing leukemic stem cells (LSCs), an ultimate therapeutic target in AML. Eradication of LSCs should be a critical and efficient therapeutic approach for the cure of AML. T-cell immunoglobulin mucin-3 (TIM-3) is expressed in most types of AML LSCs, but not in normal hematopoietic stem cells (HSCs); therefore, TIM-3 would be one of the promising therapeutic targets to specifically kill AML LSCs, sparing normal HSCs. In xenograft models reconstituted with human AML LSCs or human normal HSCs, an anti-human TIM-3 mouse antibody with cytotoxic activities exerts a potent anti-leukemic effect by targeting AML LSCs but does not affect normal human hematopoiesis in vivo. Here, we would like to introduce the recent studies on TIM-3 in normal and malignant hematopoiesis.

Negative immune checkpoints on T lymphocytes and their relevance to cancer immunotherapy

The term 'inhibitory checkpoint' refers to the broad spectrum of co-receptors expressed by T cells that negatively regulate T cell activation thus playing a crucial role in maintaining peripheral self-tolerance. Co-inhibitory receptor ligands are highly expressed by a variety of malignancies allowing evasion of anti-tumour immunity. Recent studies demonstrate that manipulation of these co-inhibitory pathways can remove the immunological brakes that impede endogenous immune responses against tumours. Antibodies that block the interactions between co-inhibitory receptors and their ligands have delivered very promising clinical responses, as has been shown by recent successful trials targeting the CTLA-4 and PD-1 pathways. In this review, we discuss the mechanisms of action and expression pattern of co-inhibitory receptors on different T cells subsets, emphasising differences between CD4(+) and CD8(+) T cells. We also summarise recent clinical findings utilising immune checkpoint blockade.

TIM-3 Suppresses Anti-CD3/CD28-Induced TCR Activation and IL-2 Expression through the NFAT Signaling Pathway

TIM-3 (T cell immunoglobulin and mucin-domain containing protein 3) is a member of the TIM family of proteins that is preferentially expressed on Th₁ polarized CD4⁺ and CD8⁺ T cells. Recent studies indicate that TIM-3 serves as a negative regulator of T cell function (i.e. T cell dependent immune responses, proliferation, tolerance, and exhaustion). Despite having no recognizable inhibitory signaling motifs, the intracellular tail of TIM-3 is apparently indispensable for function. Specifically, the conserved residues Y265/Y272 and surrounding amino acids appear to be critical for function. Mechanistically, several studies suggest that TIM-3 can associate with interleukin inducible T cell kinase (ITK), the Src kinases Fyn and Lck, and the p85 phosphatidylinositol 3-kinase (PI3K) adaptor protein to positively or negatively regulate IL-2 production via NF-κB/NFAT signaling pathways. To begin to address this discrepancy, we examined the effect of TIM-3 in two model systems. First, we generated several Jurkat T cell lines stably expressing human TIM-3 or murine CD28-ECD/human TIM-3 intracellular tail chimeras and examined the effects that TIM-3 exerts on T cell Receptor (TCR)-mediated activation, cytokine secretion, promoter activity, and protein kinase association. In this model, our results demonstrate that TIM-3 inhibits several TCR-mediated phenotypes: i) NF-kB/NFAT activation, ii) CD69 expression, and iii) suppression of IL-2 secretion. To confirm our Jurkat cell observations we developed a primary human CD8⁺ cell system that expresses endogenous levels of TIM-3. Upon TCR ligation, we observed the loss of NFAT reporter activity and IL-2 secretion, and identified the association of Src kinase Lck, and PLC-γ with TIM-3. Taken together, our results support the conclusion that TIM-3 is a negative regulator of TCR-function by attenuating activation signals mediated by CD3/CD28 co-stimulation.

An Apoptotic 'Eat Me' Signal: Phosphatidylserine Exposure

Apoptosis and the clearance of apoptotic cells are essential processes in animal development and homeostasis. For apoptotic cells to be cleared, they must display an 'eat me' signal, most likely phosphatidylserine (PtdSer) exposure, which prompts phagocytes to engulf the cells. PtdSer, which is recognized by several different systems, is normally confined to the cytoplasmic leaflet of the plasma membrane by a 'flippase'; apoptosis activates a 'scramblase' that quickly exposes PtdSer on the cell surface. The molecules that flip and scramble phospholipids at the plasma membrane have recently been identified. Here we discuss recent findings regarding the molecular mechanisms of apoptotic PtdSer exposure and the clearance of apoptotic cells.

Distinct Trafficking of Cell Surface and Endosomal TIM-1 to the Immune Synapse

The T cell costimulatory molecule TIM-1 (T cell/transmembrane, mucin and immunoglobulin domain protein 1) sorts mainly to endosomes in lymphoid cells. At difference from the cell surface protein, endosomal TIM-1 translocates to the immune synapse (IS), where it can contribute to antigen-dependent T cell costimulation. TIM-1 ligands increase the amount of cell surface protein, preventing its traffic to the IS. The bipolar sorting of TIM-1 observed during IS formation is determined by differences in its subcellular location, and probably modulates antigen-driven immune responses.

Clearance of Apoptotic Cells and Pyrenocytes

Apoptotic cells are engulfed and digested by macrophages to maintain homeostasis in animals. If dead cells are not engulfed swiftly, they undergo secondary necrosis and release intracellular components that activate the immune system. Apoptotic cells are efficiently cleared due to phosphatidylserine (PtdSer) exposed on the cell surface that acts as an "eat me" signal. PtdSer is exposed through the activation of phospholipid scramblase and the inactivation of phospholipid flippase, which are both caspase-mediated events. Macrophages express a variety of molecules to recognize PtdSer, and use a sophisticated mechanism to engulf apoptotic cells. In red blood cells, the nucleus is lost when it is extruded as a pyrenocyte during definitive erythropoiesis. These pyrenocytes (nuclei surrounded by plasma membrane) also expose PtdSer on their surface and are efficiently engulfed by macrophages in a PtdSer-dependent manner. Macrophages transfer the engulfed apoptotic cell or pyrenocyte into lysosomes, where the components of the dead cell or pyrenocyte are degraded. If lysosomes cannot digest the DNA from apoptotic cells or pyrenocytes, the undigested DNA accumulates in the lysosome and activates macrophages to produce type I interferon (IFN) via a STING-dependent pathway; in embryos, this causes severe anemia. Here, we discuss how macrophages clear apoptotic cells and pyrenocytes.

Hypothesis: Tim-3/galectin-9, a new pathway for leukemia stem cells survival by promoting expansion of myeloid-derived suppressor cells and differentiating into tumor-associated macrophages

Despite the improvements in chemotherapy, about 60 % of acute myeloid leukemia (AML) remission patients still relapse. Leukemic stem cells (LSCs) are the main causes for the relapse and refractory. T cell immunoglobulin mucin-3 (TIM-3), a specific surface molecule expressed on LSCs in most types of AML, is a candidate for AML LSC-targeted therapies. It is important to know how this molecule functions in the maintenance of LSCs and suppression of anti-tumor immunity. Recent data have shown that Tim-3 which expresses on T cells can suppress immune responses indirectly by inducing expansion of myeloid-derived suppressor cells (MDSCs). MDSCs at the leukemia site can also differentiate into tumor-associated macrophages (TAMs). TAMs can promote proliferation and survival of LSCs by the diversion of adaptive immunity and the facilitation of extracellular matrix remodeling, angiogenesis, and lymphangiogenesis. Our previous study in AML patient bone marrow samples showed CD68(+) macrophages around AML clone. Based on the known evidence and our experimental findings, we hypothesize that Tim-3, which specifically expresses on LSCs, is beneficial for LSCs survival and AML progression by promoting expansion of MDSCs and differentiating into TAMs at the leukemia site.

Beyond CTLA-4 and PD-1, the Generation Z of Negative Checkpoint Regulators

In the last two years, clinical trials with blocking antibodies to the negative checkpoint regulators CTLA-4 and PD-1 have rekindled the hope for cancer immunotherapy. Multiple negative checkpoint regulators protect the host against autoimmune reactions but also restrict the ability of T cells to effectively attack tumors. Releasing these brakes has emerged as an exciting strategy for cancer treatment. Conversely, these pathways can be manipulated to achieve durable tolerance for treatment of autoimmune diseases and transplantation. In the future, treatment may involve combination therapy to target multiple cell types and stages of the adaptive immune responses. In this review, we describe the current knowledge on the recently discovered negative checkpoint regulators, future targets for immunotherapy.

KIM-1-/TIM-1-mediated phagocytosis links ATG5-/ULK1-dependent clearance of apoptotic cells to antigen presentation

Phagocytosis of apoptotic cells by both professional and semi-professional phagocytes is required for resolution of organ damage and maintenance of immune tolerance. KIM-1/TIM-1 is a phosphatidylserine receptor that is expressed on epithelial cells and can transform the cells into phagocytes. Here, we demonstrate that KIM-1 phosphorylation and association with p85 results in encapsulation of phagosomes by lipidated LC3 in multi-membrane organelles. KIM-1-mediated phagocytosis is not associated with increased ROS production, and NOX inhibition does not block LC3 lipidation. Autophagy gene expression is required for efficient clearance of apoptotic cells and phagosome maturation. KIM-1-mediated phagocytosis leads to pro-tolerogenic antigen presentation, which suppresses CD4 T-cell proliferation and increases the percentage of regulatory T cells in an autophagy gene-dependent manner. Taken together, these data reveal a novel mechanism of epithelial biology linking phagocytosis, autophagy and antigen presentation to regulation of the inflammatory response.

Cross-Presentation of Cell-Associated Antigens by MHC Class I in Dendritic Cell Subsets

Dendritic cells (DCs) have the unique ability to pick up dead cells carrying antigens in tissue and migrate to the lymph nodes where they can cross-present cell-associated antigens by MHC class I to CD8⁺ T cells. There is strong in vivo evidence that the mouse XCR1⁺ DCs subset acts as a key player in this process. The intracellular processes underlying cross-presentation remain controversial and several pathways have been proposed. Indeed, a wide number of studies have addressed the cellular process of cross-presentation in vitro using a variety of sources of antigen and antigen-presenting cells. Here, we review the in vivo and in vitro evidence supporting the current mechanistic models and disscuss their physiological relevance to the cross-presentation of cell-associated antigens by DCs subsets.

Emerging and Novel Functions of Complement Protein C1q

Complement protein C1q, the recognition molecule of the classical pathway, performs a diverse range of complement and non-complement functions. It can bind various ligands derived from self, non-self, and altered self and modulate the functions of immune and non-immune cells including dendritic cells and microglia. C1q involvement in the clearance of apoptotic cells and subsequent B cell tolerance is more established now. Recent evidence appears to suggest that C1q plays an important role in pregnancy where its deficiency and dysregulation can have adverse effects, leading to preeclampsia, missed abortion, miscarriage or spontaneous loss, and various infections. C1q is also produced locally in the central nervous system, and has a protective role against pathogens and possible inflammatory functions while interacting with aggregated proteins leading to neurodegenerative diseases. C1q role in synaptic pruning, and thus CNS development, its anti-cancer effects as an immune surveillance molecule, and possibly in aging are currently areas of extensive research.

Increased Tim-3 expression on peripheral T lymphocyte subsets and association with higher disease activity in systemic lupus erythematosus

Background

Both the T cell immunoglobulin domain- and mucin domain-containing molecule-3 (Tim-3) and the death receptor Fas contribute to the pathogenesis of various autoimmune diseases, including systemic lupus erythematosus (SLE). The aim of the present study was to determine whether Tim-3 and Fas are co-expressed on certain peripheral T lymphocyte subsets, and whether this expression is associated with greater disease activity in SLE.

Methods

Peripheral blood mononuclear cells were isolated from 46 patients newly diagnosed with SLE and 28 age- and sex-matched healthy controls (HCs). Expression of Tim-3 and Fas on T subsets was analyzed by flow cytometry, while mRNA levels of the Tim-3 ligand galectin-9 and Fas ligand FasL were assayed using real-time RT-PCR.

Results

The proportions of CD3⁺CD4⁺ and CD3⁺CD4^- T cells expressing Tim-3⁺ and Tim⁺Fas⁺ were significantly higher in patients than in HCs (p < 0.05), while the proportions of these subtypes expressing Fas were similar for the two groups. Patients with active SLE, as defined by their score on the SLE Disease Activity Index, had lower proportions of CD3⁺CD4⁺ T cells and higher proportions of CD3⁺CD4⁺Tim-3⁺ and CD3⁺CD4⁺Tim-3⁺Fas⁺ T cells than did patients with stable SLE. Serum levels of complement C3 and C4 proteins, considered as a marker of SLE activity, correlated negatively with proportions of CD3⁺CD4⁺ and CD3⁺CD4^- T cells expressing Tim-3.

Conclusions

Expression of Tim-3 and co-expression of Tim-3 and Fas on certain peripheral T subsets are associated with disease activity in SLE patients. Future research should examine whether the same is true of other T subsets implicated in SLE, and should explore the potential role(s) of Tim-3 in the disease pathway.

Virtual slides

http://www.diagnosticpathology.diagnomx.eu/vs/1855527845145188