Ig-like transcript 2 (ILT2)/leukocyte Ig-like receptor 1 (LIR1) inhibits TCR signaling and actin cytoskeleton reorganization

Geometric parameters that affect the behavior of logic-gated CAR T cells

Clinical applications of CAR-T cells are limited by the scarcity of tumor-specific targets and are often afflicted with the same on-target/off-tumor toxicities that plague other cancer treatments. A new promising strategy to enforce tumor selectivity is the use of logic-gated, two-receptor systems. One well-described application is termed Tmod™, which originally utilized a blocking inhibitory receptor directed towards HLA-I target antigens to create a protective NOT gate. Here we show that the function of Tmod blockers targeting non-HLA-I antigens is dependent on the height of the blocker antigen and is generally compatible with small, membrane-proximal targets. We compensate for this apparent limitation by incorporating modular hinge units to artificially extend or retract the ligand-binding domains relative to the effector cell surface, thereby modulating Tmod activator and blocker function. By accounting for structural differences between activator and blocker targets, we developed a set of simple geometric parameters for Tmod receptor design that enables targeting of blocker antigens beyond HLA-I, thereby broadening the applications of logic-gated cell therapies.

Tumor-Associated Macrophage Targeting of Nanomedicines in Cancer Therapy

The tumor microenvironment (TME) is pivotal in tumor growth and metastasis, aligning with the "Seed and Soil" theory. Within the TME, tumor-associated macrophages (TAMs) play a central role, profoundly influencing tumor progression. Strategies targeting TAMs have surfaced as potential therapeutic avenues, encompassing interventions to block TAM recruitment, eliminate TAMs, reprogram M2 TAMs, or bolster their phagocytic capabilities via specific pathways. Nanomaterials including inorganic materials, organic materials for small molecules and large molecules stand at the forefront, presenting significant opportunities for precise targeting and modulation of TAMs to enhance therapeutic efficacy in cancer treatment. This review provides an overview of the progress in designing nanoparticles for interacting with and influencing the TAMs as a significant strategy in cancer therapy. This comprehensive review presents the role of TAMs in the TME and various targeting strategies as a promising frontier in the ever-evolving field of cancer therapy. The current trends and challenges associated with TAM-based therapy in cancer are presented.

Soluble CD83 modulates human-monocyte-derived macrophages toward alternative phenotype, function, and metabolism

Alterations in macrophage (Mφ) polarization, function, and metabolic signature can foster development of chronic diseases, such as autoimmunity or fibrotic tissue remodeling. Thus, identification of novel therapeutic agents that modulate human Mφ biology is crucial for treatment of such conditions. Herein, we demonstrate that the soluble CD83 (sCD83) protein induces pro-resolving features in human monocyte-derived Mφ biology. We show that sCD83 strikingly increases the expression of inhibitory molecules including ILT-2 (immunoglobulin-like transcript 2), ILT-4, ILT-5, and CD163, whereas activation markers, such as MHC-II and MSR-1, were significantly downregulated. This goes along with a decreased capacity to stimulate alloreactive T cells in mixed lymphocyte reaction (MLR) assays. Bulk RNA sequencing and pathway analyses revealed that sCD83 downregulates pathways associated with pro-inflammatory, classically activated Mφ (CAM) differentiation including HIF-1A, IL-6, and cytokine storm, whereas pathways related to alternative Mφ activation and liver X receptor were significantly induced. By using the LXR pathway antagonist GSK2033, we show that transcription of specific genes (e.g., PPARG, ABCA1, ABCG1, CD36) induced by sCD83 is dependent on LXR activation. In summary, we herein reveal for the first time mechanistic insights into the modulation of human Mφ biology by sCD83, which is a further crucial preclinical study for the establishment of sCD83 as a new therapeutical agent to treat inflammatory conditions.

IMM47, a humanized monoclonal antibody that targets CD24, exhibits exceptional anti-tumor efficacy by blocking the CD24/Siglec-10 interaction and can be used as monotherapy or in combination with anti-PD1 antibodies for cancer immunotherapy

This study evaluates the anti-tumor mechanism of IMM47, a humanized anti-CD24 mAb. Biolayer interferometry, ELISA and flow cytometry methods were used to measure the IMM47 binding, affinity, ADCC, ADCP, ADCT and CDC activities. In vivo therapeutical efficacy was measured in transplanted mouse models. IMM47 significantly binds granulocytes but not human erythrocytes and blocks CD24's ability to bind to Siglec-10. IMM47 has strong ADCC, ADCT and ADCP activity against REH cells. IMM47's in vivo pharmacodynamics showed that IMM47 has strong anti-tumor effects in human siglec-10 transgenic mouse models with a memory immune response. IMM47 also has powerful synergistic therapeutic efficacy when combined with Tislelizumab, Opdivo and Keytruda, by blocking CD24/Siglec-10 interaction through macrophage antigen presentation with strong ADCC, ADCP, ADCT and CDC activities and with a safe profile. IMM47 binding to CD24 is independent of N-glycosylation modification of the extracellular domain.

Perspectives of targeting LILRB1 in innate and adaptive immune checkpoint therapy of cancer

Immune checkpoint blockade is a compelling approach in tumor immunotherapy. Blocking inhibitory pathways in T cells has demonstrated clinical efficacy in different types of cancer and may hold potential to also stimulate innate immune responses. A novel emerging potential target for immune checkpoint therapy is leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1). LILRB1 belongs to the superfamily of leukocyte immunoglobulin-like receptors and exerts inhibitory functions. The receptor is expressed by a variety of immune cells including macrophages as well as certain cytotoxic lymphocytes and contributes to the regulation of different immune responses by interaction with classical as well as non-classical human leukocyte antigen (HLA) class I molecules. LILRB1 has gained increasing attention as it has been demonstrated to function as a phagocytosis checkpoint on macrophages by recognizing HLA class I, which represents a 'Don't Eat Me!' signal that impairs phagocytic uptake of cancer cells, similar to CD47. The specific blockade of the HLA class I:LILRB1 axis may provide an option to promote phagocytosis by macrophages and also to enhance cytotoxic functions of T cells and natural killer (NK) cells. Currently, LILRB1 specific antibodies are in different stages of pre-clinical and clinical development. In this review, we introduce LILRB1 and highlight the features that make this immune checkpoint a promising target for cancer immunotherapy.

LILRB1+ immune cell infiltration identifies immunosuppressive microenvironment and dismal outcomes of patients with ovarian cancer

OBJECTIVE

Immune checkpoint inhibitors are commonly used in various types of cancer, but their efficacy in ovarian cancer (OC) is limited. Thus, identifying novel immune-related therapeutic targets is crucial. Leukocyte immunoglobulin-like receptor subfamily B1 (LILRB1), a key receptor of human leukocyte antigen G (HLA-G), is involved in immune tolerance, but its role in tumor immunity remains unclear.

METHODS

In this study, immunofluorescence was used to identify the location of LILRB1 in OC. The effect of LILRB1 expression on clinical outcomes in 217 patients with OC was analyzed retrospectively. A total of 585 patients with OC from the TCGA database were included to explore the relationship between LILRB1 and tumor microenvironment characteristics.

RESULTS

LILRB1 was found to be expressed in tumor cells (TCs) and immune cells (ICs). High LILRB1⁺ ICs, but not LILRB1⁺ TCs, were associated with advanced FIGO stage, shorter survival outcomes, and worse adjuvant chemotherapy responses in OC patients. LILRB1 expression was also associated with high M2 macrophage infiltration, reduced activation of dendritic cells, and dysfunction of CD8⁺ T cells, suggesting an immunosuppressive phenotype. The combination of LILRB1⁺ ICs and CD8⁺ T cell levels could be used to distinguish patients with different clinical survival results. Moreover, LILRB1⁺ ICs infiltration with CD8⁺ T cells absence indicated inferior responsiveness to anti-PD-1/PD-L1 therapy.

CONCLUSIONS

Tumor-infiltrating LILRB1⁺ ICs could be applied as an independent clinical prognosticator and a predictive biomarker for therapy responsiveness to OC. Further studies targeting the LILRB1 pathway should be conducted in the future.

A LILRB1 variant with a decreased ability to phosphorylate SHP-1 leads to autoimmune diseases

Inborn errors of immunity are known to cause not only immunodeficiencies and allergies but also autoimmunity. Leukocyte immunoglobulin-like receptor B1 (LILRB1) is a receptor on leukocytes playing a role in regulating immune responses. No phenotypes have been reported to be caused by germline mutations in LILRB1. We aimed to identify the causative variant in a three-generation family with nine members suffering from one of the three autoimmune diseases—Graves’ disease, Hashimoto's thyroiditis, or systemic lupus erythematosus. Whole-genome linkage study revealed a locus on chromosome 19q13.4 with the maximum LOD score of 2.71. Whole-exome sequencing identified a heterozygous missense variant, c.479G > A (p. G160E) in LILRB1, located within the chromosomal-linked region, in all nine affected members. The variant has never been previously reported. Jurkat cells transfected with the mutant LILRB1, compared with those with the wild-type LILRB1, showed decreased phosphorylation of both LILRB1 and its downstream protein, SHP-1. Flow cytometry was used to study immunophenotype and revealed that LILRB1 was significantly lower on the surface of activated regulatory T lymphocytes (Treg) cells of patients. Single-cell RNA sequencing showed substantially increased M1-like monocytes in peripheral blood mononuclear cells of affected individuals. This study, for the first time, implicates LILRB1 as a new disease gene for autoimmunity.

BND-22, a first-in-class humanized ILT2-blocking antibody, promotes antitumor immunity and tumor regression

BACKGROUND

Cancer immunotherapy has revolutionized cancer treatment. However, considering the limited success of immunotherapy to only some cancer types and patient cohorts, there is an unmet need for developing new treatments that will result in higher response rates in patients with cancer. Immunoglobulin-like transcript 2 (ILT2), a LILRB family member, is an inhibitory receptor expressed on a variety of immune cells including T cells, natural killer (NK) cells and different myeloid cells. In the tumor microenvironment, binding of class I MHC (in particular HLA-G) to ILT2 on immune cells mediates a strong inhibitory effect, which manifests in inhibition of antitumor cytotoxicity of T and NK cells, and prevention of phagocytosis of the tumor cells by macrophages.

METHODS

We describe here the development and characteristics of BND-22, a novel, humanized monoclonal antibody that selectively binds to ILT2 and blocks its interaction with classical MHC I and HLA-G. BND-22 was evaluated for its binding and blocking characteristics as well as its ability to increase the antitumor activity of macrophages, T cells and NK cells in various in vitro, ex vivo and in vivo systems.

RESULTS

Collectively, our data suggest that BND-22 enhances activity of both innate and adaptive immune cells, thus generating robust and comprehensive antitumor immunity. In humanized mice models, blocking ILT2 with BND-22 decreased the growth of human tumors, hindered metastatic spread to the lungs, and prolonged survival of the tumor-bearing mice. In addition, BND-22 improved the antitumor immune response of approved therapies such as anti-PD-1 or anti-EGFR antibodies.

CONCLUSIONS

BND-22 is a first-in-human ILT2 blocking antibody which has demonstrated efficient antitumor activity in various preclinical models as well as a favorable safety profile. Clinical evaluation of BND-22 as a monotherapy or in combination with other therapeutics is under way in patients with cancer.

TRIAL REGISTRATION NUMBER

NCT04717375.

Immune Checkpoint Inhibitors in Cancer Therapy—How to Overcome Drug Resistance?

Simple Summary

Immune checkpoint inhibitors (ICIs) are an important strategy in cancer therapy. However, with the widespread clinical use of ICIs, people gradually found that ICIs may not be effective enough to eliminate tumor tissue for certain patients. The resistance to ICI treatment makes some patients unable to benefit from their antitumor effects. Therefore, it is vital to understand their antitumor and drug resistance mechanisms to better narrow the ICI-resistant patient population. This review outlines the antitumor action sites and mechanisms of different types of ICIs and lists the main reason of ICI resistance based on recent studies. Finally, we propose current and future solutions for resistance to ICIs.

Abstract

Immune checkpoint inhibitors (ICIs), antagonists used to remove tumor suppression of immune cells, have been widely used in clinical settings. Their high antitumor effect makes them crucial for treating cancer after surgery, radiotherapy, chemotherapy, and targeted therapy. However, with the advent of ICIs and their use by a large number of patients, more clinical data have gradually shown that some cancer patients still have resistance to ICI treatment, which makes some patients unable to benefit from their antitumor effect. Therefore, it is vital to understand their antitumor and drug resistance mechanisms. In this review, we focused on the antitumor action sites and mechanisms of different types of ICIs. We then listed the main possible mechanisms of ICI resistance based on recent studies. Finally, we proposed current and future solutions for the resistance of ICIs, providing theoretical support for improving their clinical antitumor effect.

Robust In Vitro Pharmacology of Tmod, a Synthetic Dual-Signal Integrator for Cancer Cell Therapy

Progress toward improved solid-tumor treatment has long been hindered by the lack of truly tumor-specific targets. We have developed an approach to T cell therapy based on a dual-receptor system called Tmod™ that addresses this problem. The Tmod system exploits one of the few common genetic differences between tumor and normal cells: loss of heterozygosity (LOH). It utilizes the basic mechanistic logic that evolved in early vertebrates to mediate self vs. non-self discrimination, where an activation stimulus is blocked by self-ligands. Tmod constructs employ a chimeric antigen receptor (CAR) or T cell receptor (TCR) as activator component and a modified LIR-1 inhibitory receptor (blocker) to achieve high selectivity based on expression of the blocker antigen (Ag). Here we explore the in vitro pharmacology of a blocker directed at the HLA-A*02 Ag paired with either a mesothelin CAR or an HLA-A*11-restricted KRAS peptide TCR. While more sensitive to receptor expression changes on effector cells, we show that Tmod response is well-buffered against variations in Ag levels on target cells. In addition, the data reveal at least two distinguishable pharmacologic mechanisms of Tmod blocker function: (1) reducing activator sensitivity and (2) decreasing activation magnitude.

HLA-G and Other Immune Checkpoint Molecules as Targets for Novel Combined Immunotherapies

HLA-G is an HLA-class Ib molecule that is involved in the establishment of tolerance at the maternal/fetal interface during pregnancy. The expression of HLA-G is highly restricted in adults, but the de novo expression of this molecule may be observed in different hematological and solid tumors and is related to cancer progression. Indeed, tumor cells expressing high levels of HLA-G are able to suppress anti-tumor responses, thus escaping from the control of the immune system. HLA-G has been proposed as an immune checkpoint (IC) molecule due to its crucial role in tumor progression, immune escape, and metastatic spread. We here review data available in the literature in which the interaction between HLA-G and other IC molecules is reported, in particular PD-1, CTLA-4, and TIM-3, but also IDO and TIGIT. Clinical trials using monoclonal antibodies against HLA-G and other IC are currently ongoing with cancer patients where antibodies and inhibitors of PD-1 and CTLA-4 showed encouraging results. With this background, we may envisage that combined therapies using antibodies targeting HLA-G and another IC may be successful for clinical purposes. Indeed, such immunotherapeutic protocols may achieve a better rescue of effective anti-tumor immune response, thus improving the clinical outcome of patients.

HLA-G: Too Much or Too Little? Role in Cancer and Autoimmune Disease

HLA-G is a non-classical HLA class I molecule with immunomodulatory properties. It was initially described at the maternal-fetal interface, and it was later found that this molecule was constitutively expressed on certain immuneprivileged tissues, such as cornea, endothelial and erythroid precursors, and thymus. The immunosuppressive effect of HLA-G is exerted through the interaction with its cognate receptors, expressed on immunocompetent cells, like ILT2, expressed on NK, B, T cells and APCs; ILT4, on APCs; KIR, found on the surface of NK cells; and finally, the co-receptor CD8. Because of these immunomodulatory functions, HLA-G has been involved in several processes, amongst which organ transplantation, viral infections, cancer progression, and autoimmunity. HLA-G neo-expression on tumors has been recently described in several types of malignancies. In fact, tumor progression is tightly linked to the presence of the molecule, as it exerts its tolerogenic function, inhibiting the cells of the immune system and favoring tumor escape. Several polymorphisms in the 3’UTR region condition changes in HLA-G expression (14bp and +3142C/G, among others), which have been associated with both the development and outcome of patients with different tumor types. Also, in recent years, several studies have shown that HLA-G plays an important role in the control of autoimmune diseases. The ability of HLA-G to limit the progression of these diseases has been confirmed and, in fact, levels of the molecule and several of its polymorphisms have been associated with increased susceptibility to the development of autoimmune diseases, as well as increased disease severity. Thus, modulating HLA-G expression in target tissues of oncology patients or patients with autoimmune diseases may be potential therapeutic approaches to treat these pathological conditions.

LILRB3 supports acute myeloid leukemia development and regulates T-cell antitumor immune responses through the TRAF2-cFLIP-NF-κB signaling axis

Leukocyte immunoglobulin-like receptor B (LILRB), a family of immune checkpoint receptors, contributes to acute myeloid leukemia (AML) development, but the specific mechanisms triggered by activation or inhibition of these immune checkpoints in cancer is largely unknown. Here we demonstrate that the intracellular domain of LILRB3 is constitutively associated with the adaptor protein TRAF2. Activated LILRB3 in AML cells leads to recruitment of cFLIP and subsequent NF-κB upregulation, resulting in enhanced leukemic cell survival and inhibition of T-cell-mediated anti-tumor activity. Hyperactivation of NF-κB induces a negative regulatory feedback loop mediated by A20, which disrupts the interaction of LILRB3 and TRAF2; consequently the SHP-1/2-mediated inhibitory activity of LILRB3 becomes dominant. Finally, we show that blockade of LILRB3 signaling with antagonizing antibodies hampers AML progression. LILRB3 thus exerts context-dependent activating and inhibitory functions, and targeting LILRB3 may become a potential therapeutic strategy for AML treatment.

Leukocyte immunoglobulin-like receptor subfamily B: therapeutic targets in cancer

Inhibitory leukocyte immunoglobulin-like receptors (LILRBs 1–5) transduce signals via intracellular immunoreceptor tyrosine-based inhibitory motifs that recruit phosphatases to negatively regulate immune activation. The activation of LILRB signaling in immune cells may contribute to immune evasion. In addition, the expression and signaling of LILRBs in cancer cells especially in certain hematologic malignant cells directly support cancer development. Certain LILRBs thus have dual roles in cancer biology—as immune checkpoint molecules and tumor-supporting factors. Here, we review the expression, ligands, signaling, and functions of LILRBs, as well as therapeutic development targeting them. LILRBs may represent attractive targets for cancer treatment, and antagonizing LILRB signaling may prove to be effective anti-cancer strategies.

COVID-19: Integrating the Complexity of Systemic and Pulmonary Immunopathology to Identify Biomarkers for Different Outcomes

In the last few months, the coronavirus disease 2019 (COVID-19) pandemic has affected millions of people worldwide and has provoked an exceptional effort from the scientific community to understand the disease. Clinical evidence suggests that severe COVID-19 is associated with both dysregulation of damage tolerance caused by pulmonary immunopathology and high viral load. In this review article, we describe and discuss clinical studies that show advances in the understanding of mild and severe illness and we highlight major points that are critical for improving the comprehension of different clinical outcomes. The understanding of pulmonary immunopathology will contribute to the identification of biomarkers in an attempt to classify mild, moderate, severe and critical COVID-19 illness. The interface of pulmonary immunopathology and the identification of biomarkers are critical for the development of new therapeutic strategies aimed to reduce the systemic and pulmonary hyperinflammation in severe COVID-19.

Camouflage strategies for therapeutic exosomes evasion from phagocytosis

Background

Even though exosome-based therapy has been shown to be able to control the progression of different pathologies, the data revealed by pharmacokinetic studies warn of the low residence time of exogenous exosomes in circulation that can hinder the clinical translation of therapeutic exosomes. The macrophages related to the organs of the mononuclear phagocytic system are responsible primarily for the rapid clearance and retention of exosomes, which strongly limits the amount of exosomal particles available to reach the target tissue, accumulate in it and release with high efficiency its therapeutic cargo in acceptor target cells to exert the desired biological effect.

Aim of review

Endowing exosomes with surface modifications to evade the immune system is a plausible strategy to contribute to the suppression of exosomal clearance and increase the efficiency of their targeted content delivery. Here, we summarize the current evidence about the mechanisms underlying the recognition and sequestration of therapeutic exosomes by phagocytic cells. Also, we propose different strategies to generate 'invisible' exosomes for the immune system, through the incorporation of different anti-phagocytic molecules on the exosomes’ surface that allow increasing the circulating half-life of therapeutic exosomes with the purpose to increase their bioavailability to reach the target tissue, transfer their therapeutic molecular cargo and improve their efficacy profile.

Key scientific concepts of review

Macrophage-mediated phagocytosis are the main responsible behind the short half-life in circulation of systemically injected exosomes, hindering their therapeutic effect. Exosomes ‘Camouflage Cloak’ strategy using antiphagocytic molecules can contribute to the inhibition of exosomal clearance, hence, increasing the on-target effect. Some candidate molecules that could exert an antiphagocytic role are CD47, CD24, CD44, CD31, β2M, PD-L1, App1, and DHMEQ. Pre- and post-isolation methods for exosome engineering are compatible with the loading of therapeutic cargo and the expression of antiphagocytic surface molecules.

HLA-G: Function, polymorphisms and pathology

HLA-G immune modulatory genes and molecules are presently being studied by a widespread number of research groups. In the present study, we do not aim to be exhaustive since the number of manuscripts published every year is overwhelming. Instead, our aim is pointing out facts about HLA-G function, polymorphism and pathology that have been confirmed by several different researchers, together with exposing aspects that may have been overlooked or not sufficiently remarked in this productive field of study. On the other hand, we question whether performing mainly studies on HLA-G and disease associations is going to give a clear answer in the future, since 40 years of study of classical HLA molecules association with disease has still given no definite answer on this issue.

Molecular Mechanism of Tumor Cell Immune Escape Mediated by CD24/Siglec-10

Tumor immune escape is an important part of tumorigenesis and development. Tumor cells can develop a variety of immunosuppressive mechanisms to combat tumor immunity. Exploring tumor cells that escape immune surveillance through the molecular mechanism of related immunosuppression in-depth is helpful to develop the treatment strategies of targeted tumor immune escape. The latest studies show that CD24 on the surface of tumor cells interacts with Siglec-10 on the surface of immune cells to promote the immune escape of tumor cells. It is necessary to comment on the molecular mechanism of inhibiting the activation of immune cells through the interaction between CD24 on tumor cells and Siglec-10 on immune cells, and a treatment strategy of tumors through targeting CD24 on the surface of tumor cells or Siglec-10 on immune cells.

Correlation between MDSC and Immune Tolerance in Transplantation: Cytokines, Pathways and Cell-cell Interaction

MDSCs play an important role in the induction of immune tolerance. Cytokines and chemokines (GM-CSF, IL-6) contributed to the expansion, accumulation of MDSCs, and MDSCs function through iNOS, arginase and PD-L1. MDSCs are recruited and regulated through JAK/STAT, mTOR and Raf/MEK/ERK signaling pathways. MDSCs' immunosuppressive functions were realized through Tregs-mediated pathways and their direct suppression of immune cells. All of the above contribute to the MDSC-related immune tolerance in transplantation. MDSCs have huge potential in prolonging graft survival and reducing rejection through different ways and many other factors worthy to be further investigated are also introduced.

Leukocyte Immunoglobulin-Like Receptors (LILRs) on Human Neutrophils: Modulators of Infection and Immunity

Neutrophils have a crucial role in defense against microbes. Immune receptors allow neutrophils to sense their environment, with many receptors functioning to recognize signs of infection and to promote antimicrobial effector functions. However, the neutrophil response must be tightly regulated to prevent excessive inflammation and tissue damage, and regulation is achieved by expression of inhibitory receptors that can raise activation thresholds. The leukocyte immunoglobulin-like receptor (LILR) family contain activating and inhibitory members that can up- or down-regulate immune cell activity. New ligands and functions for LILR continue to emerge. Understanding the role of LILR in neutrophil biology is of general interest as they can activate and suppress antimicrobial responses of neutrophils and because several human pathogens exploit these receptors for immune evasion. This review focuses on the role of LILR in neutrophil biology. We focus on the current knowledge of LILR expression on neutrophils, the known functions of LILR on neutrophils, and how these receptors may contribute to shaping neutrophil responses during infection.

IL-13-regulated Macrophage Polarization during Granuloma Formation in an In Vitro Human Sarcoidosis Model

The mechanisms underlying abnormal granuloma formation in patients with sarcoidosis are complex and remain poorly understood. A novel in vitro human granuloma model was used to determine the molecular mechanisms of granuloma genesis in patients with sarcoidosis in response to putative disease-causing mycobacterial antigens. Peripheral blood mononuclear cells (PBMCs) from patients with active sarcoidosis and from normal, disease-free control subjects were incubated for 7 days with purified protein derivative-coated polystyrene beads. Molecular responses, as reflected by differential expression of genes, extracellular cytokine patterns, and cell surface receptor expression, were analyzed. Unbiased systems biology approaches were used to identify signaling pathways engaged during granuloma formation. Model findings were compared with human lung and mediastinal lymph node gene expression profiles. Compared with identically treated PBMCs of control subjects (n = 5), purified protein derivative-treated sarcoidosis PBMCs (n = 6) were distinguished by the formation of cellular aggregates resembling granulomas. Ingenuity Pathway Analysis of differential expression gene patterns identified molecular pathways that are primarily regulated by IL-13, which promotes alternatively activated (M2) macrophage polarization. M2 polarization was further demonstrated by immunohistochemistry performed on the in vitro sarcoidosis granuloma-like structures. IL-13-regulated gene pathways were confirmed in human sarcoidosis lung and mediastinal lymph node tissues. The in vitro human sarcoidosis granuloma model provides novel insights into early granuloma formation, particularly IL-13 regulation of molecular networks that regulate M2 macrophage polarization. M2 macrophages are predisposed to aggregation and multinucleated giant cell formation, which are characteristic features of sarcoidosis granulomas. Clinical trial registered with www.clinicaltrials.gov (NCT01857401).

CD24 signalling through macrophage Siglec-10 is a target for cancer immunotherapy

Ovarian cancer and triple-negative breast cancer are among the most lethal diseases affecting women, with few targeted therapies and high rates of metastasis. Cancer cells are capable of evading clearance by macrophages through the overexpression of anti-phagocytic surface proteins called 'don't eat me' signals-including CD471, programmed cell death ligand 1 (PD-L1)2 and the beta-2 microglobulin subunit of the major histocompatibility class I complex (B2M)3. Monoclonal antibodies that antagonize the interaction of 'don't eat me' signals with their macrophage-expressed receptors have demonstrated therapeutic potential in several cancers4,5. However, variability in the magnitude and durability of the response to these agents has suggested the presence of additional, as yet unknown 'don't eat me' signals. Here we show that CD24 can be the dominant innate immune checkpoint in ovarian cancer and breast cancer, and is a promising target for cancer immunotherapy. We demonstrate a role for tumour-expressed CD24 in promoting immune evasion through its interaction with the inhibitory receptor sialic-acid-binding Ig-like lectin 10 (Siglec-10), which is expressed by tumour-associated macrophages. We find that many tumours overexpress CD24 and that tumour-associated macrophages express high levels of Siglec-10. Genetic ablation of either CD24 or Siglec-10, as well as blockade of the CD24-Siglec-10 interaction using monoclonal antibodies, robustly augment the phagocytosis of all CD24-expressing human tumours that we tested. Genetic ablation and therapeutic blockade of CD24 resulted in a macrophage-dependent reduction of tumour growth in vivo and an increase in survival time. These data reveal CD24 as a highly expressed, anti-phagocytic signal in several cancers and demonstrate the therapeutic potential for CD24 blockade in cancer immunotherapy.

Ig-like transcript 2 (ILT2) suppresses T cell function in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is associated with a profound dysregulation of the immune system. Loss of T cell function is frequently caused in cancer by sustained signaling of inhibitory receptors. Here, we analyzed the role of the novel inhibitory receptor Ig-like transcript 2 (ILT2) in the pathogenesis of CLL. We observed that ILT2 expression was markedly reduced on leukemic cells, whereas it was increased on CD8 and CD4 T cells from CLL patients, particularly in those patients harboring chromosome 11q deletion, which includes the ATM gene. A deep dysregulation of ILT2 ligands expression in leukemia cells was also observed. ILT2 impaired the activation and proliferation of CD4 and CD8 T cells in CLL patients, but it had no effect in leukemic cells. ILT2 downregulated the production of IL-2 by CD4 T cells of CLL patients and induced the expression of cytokines that promote the survival of leukemic cells, such as IFN-γ, by T cells. Importantly, ILT2 blockade restored the activation, proliferation and cytokine production of T cells. In conclusion, we describe a novel immune inhibitory pathway that is upregulated in CLL and delineate a new potential target to be explored in this disease.

Autoantibody-Positive Healthy Individuals Display Unique Immune Profiles That May Regulate Autoimmunity

Objective

Antinuclear antibodies (ANAs) are detected in ∼18% of females, yet autoimmune disease develops in only 5–8%. Immunologic differences between ANA‐positive healthy individuals and patients with systemic lupus erythematosus (SLE) may elucidate the regulatory mechanisms by which ANA‐positive individuals avoid transition to clinical autoimmune disease.

Methods

Healthy individuals (n = 790) were screened for autoantibodies specific for 11 antigens associated with lupus, systemic sclerosis, and Sjögren's syndrome. From this screening, 31 European American ANA‐positive healthy individuals were selected and demographically matched to ANA‐negative controls and SLE patients. Serum cytokine profiles, leukocyte subset frequency, and reactivity were analyzed by multiplex assays, immunophenotyping, and phosphospecific flow cytometry.

Results

Of 790 individuals screened, 57 (7%) were ANA‐positive. The majority of proinflammatory cytokines, including interferon‐γ (IFNγ), tumor necrosis factor, interleukin‐17 (IL‐17), and granulocyte colony‐stimulating factor, exhibited a stepwise increase in serum levels from ANA‐negative controls to ANA‐positive healthy individuals to SLE patients (P < 0.0001). IFNα, IFNβ, IL‐12p40, and stem cell factor/c‐Kit ligand were increased in SLE patients only (P < 0.05). B lymphocyte stimulator (BlyS) was elevated in SLE patients but decreased in ANA‐positive individuals (P < 0.001). Further, IL‐1 receptor antagonist (IL‐1Ra) was down‐regulated in SLE patients only (P < 0.0001). ANA‐positive individuals had increased frequencies of monocytes, memory B cells, and plasmablasts and increased levels of pSTAT‐1 and pSTAT‐3 following IFNα stimulation compared with ANA‐negative controls (P < 0.05).

Conclusion

ANA‐positive healthy individuals exhibit dysregulation in multiple immune pathways yet differ from SLE patients by the absence of elevated IFNs, BLyS, IL‐12p40, and stem cell factor/c‐Kit ligand. Further, severely decreased levels of IL‐1Ra in SLE patients compared with ANA‐positive individuals may contribute to disease development. These results highlight the importance of IFN‐related pathways and regulatory elements in SLE pathogenesis.

LILRB receptor-mediated regulation of myeloid cell maturation and function

The leukocyte immunoglobulin-like receptor (LILR) family comprises a set of paired immunomodulatory receptors expressed among human myeloid and lymphocyte cell populations. While six members of LILR subfamily A (LILRA) associate with membrane adaptors to signal via immunoreceptor tyrosine-based activating motifs (ITAM), LILR subfamily B (LILRB) members signal via multiple cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIM). Ligand specificity of some LILR family members has been studied in detail, but new perspective into the immunoregulatory aspects of this receptor family in human myeloid cells has been limited. LILRB receptors and the murine ortholog, paired immunoglobulin-like receptor B (PIRB), have been shown to negatively regulate maturation pathways in myeloid cells including mast cells, neutrophils, dendritic cells, as well as B cells. Our laboratory further demonstrated in mouse models that PIRB regulated functional development of myeloid-derived suppressor cell and the formation of a tumor-permissive microenvironment. Based on observations from the literature and our own studies, our laboratory is focusing on how LILRs modulate immune homeostasis of human myeloid cells and how these pathways may be targeted in disease states. Integrity of this pathway in tumor microenvironments, for example, permits a myeloid phenotype that suppresses antitumor adaptive immunity. This review presents the evidence supporting a role of LILRs as myeloid cell regulators and ongoing efforts to understand the functional immunology surrounding this family.

Immune Checkpoint Function of CD85j in CD8 T Cell Differentiation and Aging

Aging is associated with an increased susceptibility to infection and a failure to control latent viruses thought to be driven, at least in part, by alterations in CD8 T cell function. The aging T cell repertoire is characterized by an accumulation of effector CD8 T cells, many of which express the negative regulatory receptor CD85j. To define the biological significance of CD85j expression on CD8 T cells and to address the question whether presence of CD85j in older individuals is beneficial or detrimental for immune function, we examined the specific attributes of CD8 T cells expressing CD85j as well as the functional role of CD85j in antigen-specific CD8 T cell responses during immune aging. Here, we show that CD85j is mainly expressed by terminally differentiated effector (TEMRAs) CD8 T cells, which increase with age, in cytomegalovirus (CMV) infection and in males. CD85j⁺ CMV-specific cells demonstrate clonal expansion. However, TCR diversity is similar between CD85j⁺ and CD85j⁻ compartments, suggesting that CD85j does not directly impact the repertoire of antigen-specific cells. Further phenotypic and functional analyses revealed that CD85j identifies a specific subset of CMV-responsive CD8 T cells that coexpress a marker of senescence (CD57) but retain polyfunctional cytokine production and expression of cytotoxic mediators. Blocking CD85j binding enhanced proliferation of CMV-specific CD8 T cells upon antigen stimulation but did not alter polyfunctional cytokine production. Taken together, these data demonstrate that CD85j characterizes a population of “senescent,” but not exhausted antigen-specific effector CD8 T cells and indicates that CD85j is an important checkpoint regulator controlling expansion of virus-specific T cells during aging. Inhibition of CD85j activity may be a mechanism to promote stronger CD8 T cell effector responses during immune aging.

Inhibitory leukocyte immunoglobulin-like receptors: Immune checkpoint proteins and tumor sustaining factors

Inhibitory leukocyte immunoglobulin-like receptors (LILRBs 1-5) transduce signals via intracellular immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that recruit protein tyrosine phosphatase non-receptor type 6 (PTPN6 or SHP-1), protein tyrosine phosphatase non-receptor type 11 (PTPN11 or SHP-2), or Src homology 2 domain-containing inositol phosphatase (SHIP), leading to negative regulation of immune cell activation. Certain of these receptors also play regulatory roles in neuronal activity and osteoclast development. The activation of LILRBs on immune cells by their ligands may contribute to immune evasion by tumors. Recent studies found that several members of LILRB family are expressed by tumor cells, notably hematopoietic cancer cells, and may directly regulate cancer development and relapse as well as the activity of cancer stem cells. LILRBs thus have dual concordant roles in tumor biology - as immune checkpoint molecules and as tumor-sustaining factors. Importantly, the study of knockout mice indicated that LILRBs do not affect hematopoiesis and normal development. Therefore LILRBs may represent ideal targets for tumor treatment. This review aims to summarize current knowledge on expression patterns, ligands, signaling, and functions of LILRB family members in the context of cancer development.

Leukocyte Ig-Like Receptors - A Model for MHC Class I Disease Associations

MHC class I (MHC-I) polymorphisms are associated with the outcome of some viral infections and autoimmune diseases. MHC-I proteins present antigenic peptides and are recognized by receptors on natural killer cells and cytotoxic T lymphocytes, thus enabling the immune system to detect self-antigens and eliminate targets lacking self or expressing foreign antigens. Recognition of MHC-I, however, extends beyond receptors on cytotoxic leukocytes. Members of the leukocyte Ig-like receptor (LILR) family are expressed on monocytic cells and can recognize both classical and non-classical MHC-I alleles. Despite their relatively broad specificity when compared to the T cell receptor or killer Ig-like receptors, variations in the strength of LILR binding between different MHC-I alleles have recently been shown to correlate with control of HIV infection. We suggest that LILR recognition may mediate MHC-I disease association in a manner that does not depend on a binary discrimination of self/non-self by cytotoxic cells. Instead, the effects of LILR activity following engagement by MHC-I may represent a “degrees of self” model, whereby strength of binding to different alleles determines the degree of influence exerted by these receptors on immune cell functions. LILRs are expressed by myelomonocytic cells and lymphocytes, extending their influence across antigen-presenting cell subsets including dendritic cells, macrophages, and B cells. They have been identified as important players in the response to infection, inflammatory diseases, and cancer, with recent literature to indicate that MHC-I recognition by these receptors and consequent allelic effects could extend an influence beyond the immune system.

Interaction of the LILRB1 inhibitory receptor with HLA class Ia dimers

Leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1) has been reported to interact with a wide spectrum of HLA class I (HLA-I) molecules, albeit with different affinities determined by allelic polymorphisms and conformational features. HLA-G dimerization and the presence of intracellular Cys residues in HLA-B7 have been shown to be critical for their recognition by LILRB1. We hypothesized that dimerization of classical HLA class Ia molecules, previously detected in exosomes, might enhance their interaction with LILRB1. A soluble LILRB1-Fc fusion protein and a sensitive cellular reporter system expressing a LILRB1-ζ chimera were employed to assess receptor interaction with different HLA class Ia molecules transfected in the human lymphoblastoid 721.221 cell line. Under these conditions, intracellular Cys residues and HLA-I dimerization appeared associated with increased LILRB1 recognition. On the other hand, a marginal interaction of LILRB1 with primary monocytic cells, irrespective of their high HLA-I expression, was enhanced by type I interferon (IFN). This effect appeared disproportionate to the cytokine-induced increase of surface HLA-I expression and was accompanied by detection of HLA class Ia dimers. Altogether, the results support that a regulated assembly of these noncanonical HLA-I conformers during the immune response may enhance the avidity of their interaction with LILRB1.

Surveillance of cell and tissue perturbation by receptors in the LRC

The human leukocyte receptor complex (LRC) encompasses several sets of genes with a common evolutionary origin and which form a branch of the immunoglobulin superfamily (IgSF). Comparisons of LRC genes both within and between species calls for a high degree of plasticity. The drive for this unprecedented level of variation is not known, but it relates in part to interaction of several LRC products with polymorphic human leukocyte antigen (HLA) class I molecules. However, the range of other proposed ligands for LRC products indicates a dynamic set of receptors that have adapted to detect target molecules relating to numerous cellular pathways. Several receptors in the complex bind a molecular signature in collagenous ligands. Others detect a variety of motifs relating to pathogens in addition to cellular stress, attesting to the opportunistic versatility of LRC receptors.

Overexpression of CD85j in TNBC patients inhibits Cetuximab-mediated NK-cell ADCC but can be restored with CD85j functional blockade

Clinical studies suggest that triple negative breast cancer (TNBC) patients with epidermal growth factor receptor (EGFR)-expressing tumors could benefit from therapy with Cetuximab, which targets EGFR. NK cells are the primary effectors of antibody (Ab)-dependent cell-mediated cytotoxicity (ADCC) and thus play a role in Ab-based therapies. We have previously described diminished levels of Cetuximab-mediated ADCC in vitro in patients with advanced breast cancer. Here, we investigated the potential causes of this NK-cell functional deficiency. We characterized NK-cell activating/inhibitory receptors in the peripheral blood of breast cancer patients and found CD85j inhibitory receptor overexpression. The capacity of NK cells to perform Cetuximab-triggered ADCC against TNBC cells correlated inversely with CD85j expression, even in the presence of the stimulatory cytokines IL-2 or IL-15. Hence, patients expressing high levels of CD85j had an impaired ability to lyse TNBC cells in the presence of Cetuximab. We also found that CD85j overexpression was associated with HLA-I and soluble HLA-G expression by tumors. A CD85j functional blockade with a CD85j antagonist Ab restored ADCC levels in breast cancer patients and reverted this negative effect. Our data suggest that strategies that overcome the hurdles of immune activation could improve Cetuximab clinical efficacy.

Increased expression of human leucocyte antigen class I free heavy chains on monocytes of patients with spondyloarthritis and cells transfected with HLA-B27

Human leucocyte antigen (HLA)-B27 expression is correlated with spondyloarthritis (SpA), but its role in disease pathogenesis remains unclear. The aim of the study was to determine whether HLA-B27 free heavy chain (FHC) contributes to SpA pathogenesis. Flow cytometry was used to analyse the FHC expression on CD3+ and CD14+ cells in the peripheral blood (PB) and synovial fluid (SF) from SpA patients, healthy controls, and rheumatoid arthritis (RA) patients. Human monocytic U937 cell lines stably expressing enhanced green fluorescence protein (EGFP)/HLA-B27, EGFP/HLA-A2 or EGFP alone were created to further investigate the relation between HLA-B27 and FHC expression. The relative FHC level on CD14+ PB cells was significantly higher in SpA patients than in controls, but lower than on the SF cells of SpA patients. No significant correlation was found for relative FHC expression with HLA-B27 or β2-microglobulin expression. HLA-B27-transfected U937 cells expressed higher FHC levels than either EGFP/HLA-A2- or EGFP-transfected cells. HLA class I FHC expression was significantly increased on monocytes of SpA patients and HLA-B27-transfected cells, implying that FHC, perhaps mostly derived from HLA-B27, plays an important role in SpA pathogenesis.

Downregulation of immunoglobulin-like transcript-4 (ILT4) in patients with psoriatic arthritis

OBJECTIVE

The immunoglobulin-like transcript-4 (ILT4) is an inhibitory receptor that modulates the activity of innate immune agents. We determined the expression of ILT4 and analysed the relationship with the expression of costimulatory proteins and tumor necrosis factor-α (TNF-α) production in monocytes from patients with psoriatic arthritis (PsA) starting anti-TNF treatment.

METHODS

Peripheral blood monocytes from 15 healthy controls and from 16 patients with PsA were activated in vitro by CD40 ligand (CD40L) and analyzed for ILT4, CD40, CD80 and CD86 expression, and spontaneous lipopolysaccharide (LPS)-induced TNF-α production by flow cytometry, before and after treatment with adalimumab.

RESULTS

The percentage of ILT4-negative monocytes was greater in PsA patients compared to controls and negatively correlated with DAS44. Normal monocytes treated with sera of PsA patients showed a reduced expression of ILT4 compared with monocytes exposed to sera from controls. CD40, CD80 and CD86 expression was higher in patients compared to controls. Both spontaneous and LPS-induced TNF-α production was restricted to ILT4-negative monocytes and was greater in PsA patients compared to controls. Finally, twelve weeks-treatment with adalimumab resulted in a significant increase of ILT4 expression and a decrease of costimulatory molecules expression in PsA patients, compared to pre-therapy levels.

CONCLUSIONS

These data support the possibility that changes in the immunophenotype of monocytes play a role in the pathogenesis of PSA. Thus, modulation of the expression of ILT4 may represent an enticing new therapeutic target.

Association of the LILRA3 deletion with B-NHL and functional characterization of the immunostimulatory molecule

LILRA3 is the sole soluble member of the LILR family. Previous studies from our group had shown that a 6.7 kb genetic deletion of LILRA3 is associated with MS and Sjögren's syndrome. An impairment of the immune response leads to a predisposition for B-NHL, so we wanted to study whether the deletion of LILRA3 is also a risk factor for B-NHL, as well as the function of LILRA3. We discovered that the frequency of the homozygous LILRA3 deletion was significantly higher in B-NHL (6%) than in blood donors (3%) (P = 0.03). We detected binding of fluorochrome-conjugated recombinant LILRA3 to monocytes and B-cells. Incubation of PBMCs with recombinant LILRA3 induced proliferation of CD8(+) T-cells and NK cells, as determined by CFSE staining. Using a transwell system, we demonstrated that LILRA3-stimulated lymphocyte proliferation was mediated by monocytes and required both cell contact and soluble factors. Secretion of IL-6, IL-8, IL-1β and IL-10 in the cell supernatant was stimulated by LILRA3. We conclude that LILRA3 is an immunostimulatory molecule, whose deficiency is associated with higher frequency of B-NHL.

S100A9 protein is a novel ligand for the CD85j receptor and its interaction is implicated in the control of HIV-1 replication by NK cells

Background

The reportedly broad expression of CD85j across different immune cell types suggests an importance for this molecule in the human immune system. Previous reports have shown that this receptor interacts with several HLA class-I molecules, as well as with some viral proteins. We have demonstrated that the subset of CD85j + Natural Killer (NK) cells efficiently controls human immunodeficiency virus type 1 (HIV-1) replication in monocyte-derived dendritic cells (MDDC) in vitro and this led us to hypothesize that the CD85j + NK cell-mediated anti-HIV activity in MDDC is specifically dependent on the interaction between the CD85j receptor and unknown non-HLA class-I ligand(s).

Results

In this study, we focused our efforts on the identification of these non-described ligands for CD85j. We found that the CD85j receptor interacts with a calcium-binding proteins of the S100 family; namely, S100A9. We further demonstrated that HIV-1 infection of MDDC induces a modulation of S100A9 expression on surface of the MDDC, which potentially influences the anti-HIV-1 activity of human NK cells through a mechanism involving CD85j ligation. Additionally, we showed that stimulation of NK cells with exogenous S100A9 enhances the control of HIV-1 infection in CD4+ T cells.

Conclusions

Our data show that S100A9 protein, through ligation with CD85j, can stimulate the anti-HIV-1 activity of NK cells.

HLA-dependent tumour development: a role for tumour associate macrophages?

HLA abnormalities on tumour cells for immune escape have been widely described. In addition, cellular components of the tumour microenvironment, in particular myeloid derived suppressor cells (MDSC) and alternatively activated M2 tumour-associated macrophages (TAMs), are involved in tumour promotion, progression, angiogenesis and suppression of anti-tumour immunity. However, the role of HLA in these activities is poorly understood. This review details MHC class I characteristics and describes MHC class I receptors functions. This analysis established the basis for a reflection about the crosstalk among the tumour cells, the TAMs and the cells mediating an immune response.The tumour cells and TAMs exploit MHC class I molecules to modulate the surrounding immune cells. HLA A, B, C and G molecules down-regulate the macrophage myeloid activation through the interaction with the inhibitory LILRB receptors. HLA A, B, C are able to engage inhibitory KIR receptors negatively regulating the Natural Killer and cytotoxic T lymphocytes function while HLA-G induces the secretion of pro-angiogenic cytokines and chemokine thanks to an activator KIR receptor expressed by a minority of peripheral NK cells. The open conformer of classical MHC-I is able to interact with LILRA receptors described as being associated to the Th2-type cytokine response, triggering a condition for the M2 like TAM polarization. In addition, HLA-E antigens on the surface of the TAMs bind the inhibitory receptor CD94/NKG2A expressed by a subset of NK cells and activated cytotoxic T lymphocytes protecting from the cytolysis.Furthermore MHC class II expression by antigen presenting cells is finely regulated by factors provided with immunological capacities. Tumour-associated macrophages show an epigenetically controlled down-regulation of the MHC class II expression induced by the decoy receptor DcR3, a member of the TNFR, which further enhances the M2-like polarization. BAT3, a positive regulator of MHC class II expression in normal macrophages, seems to be secreted by TAMs, consequently lacking its intracellular function, it looks like acting as an immunosuppressive factor.In conclusion HLA could cover a considerable role in tumour-development orchestrated by tumour-associated macrophages.

Cis association of leukocyte Ig-like receptor 1 with MHC class I modulates accessibility to antibodies and HCMV UL18

Leukocyte Ig-like receptor (LIR) 1 (CD85j/ILT2/LILRB1) is an inhibitory receptor with broad specificity for MHC class I (MHC-I) and the human CMV MHC-I homologue UL18. LIR-1 can inhibit NK cells through the conventional interaction with MHC-I expressed on a target cell (in trans) but the nature and the effects of LIR-1 interactions with MHC-I in cis are not well understood. Here we show that MHC-I expressed in cis has an impact on the detection of LIR-1 with various antibodies. We found the cis interaction alters recognition by only one of two antibodies known to block functional trans recognition by LIR-1 on NK cells. Specifically, we observed an enhancement of recognition with GHI/75 in the presence of various MHC-I alleles on 721.221 cells. We found that blocking the LIR-1 contact site with anti-MHC-I antibodies decreased detection of LIR-1 with GHI/75. We also observed a decrease in GHI/75 following acid denaturation of MHC-I. Finally, disruption of LIR-1 cis interactions with MHC-I significantly enhanced UL18-Fc binding to NK92 cells and enhanced the relative inhibition of NK92 cells by HLA-G. These results have implications for LIR-1 function in scenarios such as infection when MHC-I levels on effector cells may be increased by IFNs.

Impact of the NK cell receptor LIR-1 (ILT-2/CD85j/LILRB1) on cytotoxicity against multiple myeloma

The role of different receptors in natural-killer- (NK-) cell-mediated cytotoxicity against multiple myeloma (MM) cells is unknown. We investigated if an enhancement of NK-cell-mediated cytotoxicity against MM could be reached by blocking of the inhibitory leukocyte immunoglobulin-like receptor 1 (LIR-1). Our investigations revealed high levels of LIR-1 expression not only on the NK cell line NK-92, but also on myeloma cells (MOLP-8, RPMI8226) as well as on a lymphoblastoid cell line (LBCL; IM-9). Subsequent cytotoxicity assays were designed to show the isolated effects of LIR-1 blocking on either the effector or the tumor side to rule out receptor-receptor interactions. Although NK-92 was shown to be capable of myeloma cell lysis, inhibition of LIR-1 on NK-92 did not enhance cytotoxicity. Targeting the receptor on MM and LBCL did not also alter NK-92-mediated lysis. We come to the conclusion that LIR-1 alone does not directly influence NK-cell-mediated cytotoxicity against myeloma. To our knowledge, this work provides the first investigation of the inhibitory capability of LIR-1 in NK-92-mediated cytotoxicity against MM and the first functional evaluation of LIR-1 on MM and LBCL.

Signaling pathways in aged T cells - a reflection of T cell differentiation, cell senescence and host environment

With increasing age, the ability of the immune system to protect against new antigenic challenges or to control chronic infections erodes. Decline in thymic function and cumulating antigenic experiences of acute and chronic infections threaten T cell homeostasis, but insufficiently explain the failing immune competence and the increased susceptibility for autoimmunity. Alterations in signaling pathways in the aging T cells account for many of the age-related defects. Signaling threshold calibrations seen with aging frequently built on mechanisms that are operational in T cell development and T cell differentiation or are adaptations to the changing environment in the aging host. Age-related changes in transcription of receptors and signaling molecules shift the balance towards inhibitory pathways, most dominantly seen in CD8 T cells and to a lesser degree in CD4 T cells. Prominent examples are the expression of negative regulatory receptors of the CD28 and the TNF receptor superfamilies as well the expression of various cytoplasmic and nuclear dual-specific phosphatases.

The adaptor protein Crk controls activation and inhibition of natural killer cells

Natural killer (NK) cell inhibitory receptors recruit tyrosine phosphatases to prevent activation, induce phosphorylation and dissociation of the small adaptor Crk from cytoskeleton scaffold complexes, and maintain NK cells in a state of responsiveness to subsequent activation events. How Crk contributes to inhibition is unknown. We imaged primary NK cells over lipid bilayers carrying IgG1 Fc to stimulate CD16 and human leukocyte antigen (HLA)-E to inhibit through receptor CD94-NKG2A. HLA-E alone induced Crk phosphorylation in NKG2A(+) NK cells. At activating synapses with Fc alone, Crk was required for the movement of Fc microclusters and their ability to trigger activation signals. At inhibitory synapses, HLA-E promoted central accumulation of both Fc and phosphorylated Crk and blocked the Fc-induced buildup of F-actin. We propose a unified model for inhibitory receptor function: Crk phosphorylation prevents essential Crk-dependent activation signals and blocks F-actin network formation, thereby reducing constraints on subsequent engagement of activation receptors.

Curcumin induces maturation-arrested dendritic cells that expand regulatory T cells in vitro and in vivo

Dendritic cells (DC) and regulatory T cells (T(regs) ) are vital to the development of transplant tolerance. Curcumin is a novel biological agent extracted from Curcuma longa (turmeric), with anti-inflammatory and anti-oxidant activity mediated via nuclear factor (NF)-κB inhibition. We investigated the immunomodulatory effects of curcumin on human monocyte-derived and murine DC. Human monocyte-derived DC (hu-Mo-DC) were generated in the presence (CurcDC) or absence (matDC) of 25 µM curcumin, and matured using lipopolysaccharide (1 µg/ml). DC phenotype and allostimulatory capacity was assessed. CD11c(+) DC were isolated from C57BL/6 mice, pretreated with curcumin and injected into BALB/c mice, followed by evaluation of in vivo T cell populations and alloproliferative response. Curcumin induced DC differentiation towards maturation-arrest. CurcDC demonstrated minimal CD83 expression (<2%), down-regulation of CD80 and CD86 (50% and 30%, respectively) and reduction (10%) in both major histocompatibility complex (MHC) class II and CD40 expression compared to matDC. CurcDC also displayed decreased RelB and interleukin (IL)-12 mRNA and protein expression. Functionally, CurcDC allostimulatory capacity was decreased by up to 60% (P < 0·001) and intracellular interferon (IFN-γ) expression in the responding T cell population were reduced by 50% (P < 0·05). T cell hyporesponsiveness was due to generation of CD4(+) CD25(hi) CD127(lo) forkhead box P3 (FoxP3)(+) T(regs) that exerted suppressive functions on naïve syngeneic T cells, although the effect was not antigen-specific. In mice, in vivo infusion of allogeneic CurcDC promoted development of FoxP3(+) T(regs) and reduced subsequent alloproliferative capacity. Curcumin arrests maturation of DC and induces a tolerogenic phenotype that subsequently promotes functional FoxP3(+) T(regs) in vitro and in vivo.

The role of HLA-G in immunity and hematopoiesis

The non-classical HLA class I molecule HLA-G was initially shown to play a major role in feto-maternal tolerance. Since this discovery, it has been established that HLA-G is a tolerogenic molecule which participates to the control of the immune response. In this review, we summarize the recent advances on (1) the multiple structures of HLA-G, which are closely associated with their role in the inhibition of NK cell cytotoxicity, (2) the factors that regulate the expression of HLA-G and its receptors, (3) the mechanism of action of HLA-G at the immunological synapse and through trogocytosis, and (4) the generation of suppressive cells through HLA-G. Moreover, we also review recent findings on the non-immunological functions of HLA-G in erythropoiesis and angiogenesis.

Proper regrafting of Ig-like transcript 2 after trogocytosis allows a functional cell-cell transfer of sensitivity

The acquisition by T cells of exogenous ligands originally expressed by APC has been already described. However, reports essentially focused on the outward signaling of acquired ligands and their effects on surroundings cells. We investigated the function of transferred receptors (not ligands) on the T cells that acquired them (not on cells they interact with). We show that inhibitory Ig-like transcript 2 receptors efficiently transfer from monocytes to autologous T cells by trogocytosis and integrate within the plasma membrane of the acquirer T cells. Furthermore, the acquired receptors can access compatible signaling machinery within acquirer T cells and use it to signal and alter the functions of their new host cells. These data are a formal demonstration that a transferred molecule may send signals to its new host cell. We also provide evidence that sensitivity to modulatory molecules can be acquired from other cells and introduce the notion of intercellular transfer of sensitivities.

Up-regulation of cytolytic functions of human Vδ2-γ T lymphocytes through engagement of ILT2 expressed by tumor target cells

In humans, the majority of peripheral blood γδ T cells expresses Vγ9Vδ2 T-cell receptors (TCR) and recognize nonpeptidic phosphorylated antigens. In contrast, most tissue-derived γδ T cells, which are located mainly in spleen and epithelia, preferentially use Vδ1 or Vδ3 chains paired with diverse Vγ chains to form their TCR. Our knowledge about the antigenic specificity and costimulation requirements of human Vδ2(-) γδ T cells remains limited. In an attempt to address this important issue, we characterized the specificity of a monoclonal antibody (mAb 256), screened for its ability to specifically inhibit cytolytic responses of several human Vδ2(-) γδ T-cell clones against transformed B cells. We show that mAb 256 does not target a TCR ligand but blocks key interactions between non-TCR molecules on effector γδ T cells and ILT2 molecule, expressed by tumor targets. In line with the previously reported specificity of this NK receptor for classic and nonclassic major histocompatibility complex (MHC) class I molecules, blockade of MHC class I/ILT2 interactions using MHC class I- or ILT2-specific mAbs and ILT2-Fc molecules inhibited tumor-induced activation of Vγ8Vδ3 T-cell clones. Therefore, this study describes a new cytotoxic T lymphocyte activation pathway involving MHC class I engagement on γδ T cells.

Implications of the polymorphism of HLA-G on its function, regulation, evolution and disease association

The HLA-G gene displays several peculiarities that are distinct from those of classical HLA class I genes. The unique structure of the HLA-G molecule permits a restricted peptide presentation and allows the modulation of the cells of the immune system. Although polymorphic sites may potentially influence all biological functions of HLA-G, those present at the promoter and 3′ untranslated regions have been particularly studied in experimental and pathological conditions. The relatively low polymorphism observed in the MHC-G coding region both in humans and apes may represent a strong selective pressure for invariance, whereas, in regulatory regions several lines of evidence support the role of balancing selection. Since HLA-G has immunomodulatory properties, the understanding of gene regulation and the role of polymorphic sites on gene function may permit an individualized approach for the future use of HLA-G for therapeutic purposes.

LILRB1 polymorphism and surface phenotypes of natural killer cells

Leukocyte Ig-like receptor (LIR)-1 is an inhibitory receptor that binds a broad range of class I HLA molecules and is encoded by the LILRB1 gene within the leukocyte receptor complex. In contrast to uniform expression on monocytes and B cells, LIR-1 expression on natural killer (NK) cells varies considerably between individuals. To investigate how polymorphism is related to the observed patterns of expression, we analyzed the LILRB1 gene and its transcriptional activity in a group of individuals with various levels of expression on NK cells. We found that LILRB1 transcription is correlated with surface protein expression on NK cells. In a cohort of 24 donors, we found high expression on NK cells to be associated with three linked SNPs (AGG verses GAA) within the putative regulatory region. We also identified several new protein variants and observed variants with P, T, T, and I at positions 68, 95, 142, and 155, respectively, more frequently in donors with low expression on NK cells. These results suggest that there is a significant degree of diversity within the LILRB1 locus and that it influences expression patterns on NK cells. These genetic differences may underpin variation in individual immune responses involving LIR-1 on NK cells.