The CD85/LIR-1/ILT2 inhibitory receptor is expressed by all human T lymphocytes and down-regulates their functions

Increased donor inhibitory KIR are associated with reduced GVHD and improved survival following HLA-matched unrelated donor HCT in paediatric acute leukaemia

Killer immunoglobulin-like receptor (KIR) and KIR-ligand (KIRL) interactions play an important role in natural killer cell-mediated effects after haematopoietic stem cell transplantation (HCT). Previous work has shown that accounting for known KIR-KIRL interactions may identify donors with optimal NK cell-mediated alloreactivity in the adult transplant setting. Paediatric acute leukaemia patients were retrospectively analysed, and KIR-KIRL combinations and maximal inhibitory KIR ligand (IM-KIR) scores were determined. Clinical outcomes were examined using a series of graphs depicting clinical events and endpoints. The graph methodology demonstrated that prognostic variables significant in the occurrence of specific clinical endpoints remained significant for relevant downstream events. KIR-KIRL combinations were significantly predictive for reduced grade 3-4 aGVHD likelihood, in patients transplanted with increased inhibitory KIR gene content and IM-KIR = 5 scores. Improvements were also observed in associated outcomes for both ALL and AML patients, including relapse-free survival, GRFS and overall survival. This study demonstrates that NK cell KIR HLA interactions may be relevant to the paediatric acute leukaemia transplant setting. Reduction in aGVHD suggests KIR effects may extend beyond NK cells. Moving forward clinical trials utilizing donors with a higher iKIR should be considered for URD HCT in paediatric recipients with acute leukaemia to optimize clinical outcomes.

Human leukocyte immunoglobulin-like receptors in health and disease

Human leukocyte immunoglobulin (Ig)-like receptors (LILR) are a family of 11 innate immunomodulatory receptors, primarily expressed on lymphoid and myeloid cells. LILRs are either activating (LILRA) or inhibitory (LILRB) depending on their associated signalling domains (D). With the exception of the soluble LILRA3, LILRAs mediate immune activation, while LILRB1-5 primarily inhibit immune responses and mediate tolerance. Abnormal expression and function of LILRs is associated with a range of pathologies, including immune insufficiency (infection and malignancy) and overt immune responses (autoimmunity and alloresponses), suggesting LILRs may be excellent candidates for targeted immunotherapies. This review will discuss the biology and clinical relevance of this extensive family of immune receptors and will summarise the recent developments in targeting LILRs in disease settings, such as cancer, with an update on the clinical trials investigating the therapeutic targeting of these receptors.

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.

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.

Effect of HLA-G5 Immune Checkpoint Molecule on the Expression of ILT-2, CD27, and CD38 in Splenic B cells

The human leukocyte antigen G (HLA-G) is an immune checkpoint molecule with a complex network of interactions with several inhibitory receptors. Although the effect of HLA-G on T cells and NK cells is well studied, the effect of HLA-G on B cells is still largely elusive. B cells are of particular interest in the context of the HLA-G-ILT-2 interaction because the ILT-2 receptor is constitutively expressed on most B cells, whereas it is only present on some subsets of T and NK cells. To characterize the effect of HLA-G5 molecules on B cells, we studied splenic B cells derived from cytomegalovirus (CMV) sero-positive donors after CMV stimulation with antigens in the presence and absence of soluble HLA-G5. In the presence of HLA-G5, increased expression of the ITIM-bearing Ig-like transcript (ILT-2) was observed on B cells, but its expression was not affected by stimulation with CMV antigens. Moreover, it became evident that HLA-G5 exposure resulted in a decreased expression of CD27 and CD38 and, accordingly, in lower proportions of CD19+CD27+CD38+ and higher proportions of CD19+CD27-CD38- B cells. Taken together, our in vitro findings demonstrate that soluble HLA-G5 suppresses markers of B cell activation, suggesting that HLA-G5 has an impact on splenic B cell differentiation and activation. Based on these results, further investigation regarding the role of HLA-G as a prognostic factor and a potential therapeutic agent with respect to B cell function appears reasonable.

Extended loci histocompatibility matching in HSCT-Going beyond classical HLA

Unrelated haematopoietic stem cell transplantation (HSCT) has evolved from an experimental protocol to a potentially curative first-line treatment in a variety of haematologic malignancies. The continuous refinement of treatment protocols and supportive care paired with ongoing achievements in the technological field of histocompatibility testing enabled this transformation. Without a doubt, HLA matching is still the foremost criterion for donor selection in unrelated HSCT. However, HSCT-related treatment complications still occur frequently, often resulting in patients suffering severely or even dying as a consequence of such complications. Current literature indicates that other immune system modulating factors may play a role in the setting of HSCT. In this review, we discuss the current clinical evidence of a possible influence of nonclassical HLA antigens HLA-E, HLA-F, and HLA-G as well as the HLA-like molecules MICA and MICB, in HSCT.

Tumor infiltrating and peripheral CD4+ILT2+ T cells are a cytotoxic subset selectively inhibited by HLA-G in clear cell renal cell carcinoma patients

HLA-G

ILT2 has recently been positioned as a major immune checkpoint in urologic cancers. In clear cell renal cell carcinoma (ccRCC), tumor-infiltrating CD8⁺ T cells expressing ILT2 are a highly cytotoxic cell population, distinct from PD1⁺ T cells, and whose function is inhibited by HLA-G⁺ targets. Here we report that ILT2 receptor can also be expressed by CD4⁺ T cells in urologic cancer patients. In the course of deciphering the role of these ILT2⁺CD4⁺ T cells, we found a statistical association between the tumor context and these T cells, and a positive correlation between the levels of peripheral and intra-tumoral CD4⁺ILT2⁺ T cells. Phenotypic analyses revealed that CD4⁺ILT2⁺ T cells express memory T cell (CD27^-CD28^-CD57⁺) and cytotoxicity (Tbet⁺Perforin⁺KLRG1⁺NKp80⁺GPR56⁺) markers, consistent with a CD4⁺CTL phenotype. Functional assays showed that ccRCC-infiltrating CD4⁺ILT2⁺ T cells indeed have high cytolytic properties and therefore function as proper CD4⁺CTLs, but are selectively inhibited by HLA-G⁺ targets. Clinical relevance was provided by immunohistochemical analyses on ccRCC tumor lesions with HLA-G⁺ HLA class II⁺ tumor cells next to CD4⁺ T cell infiltrates. Our findings provide evidence supporting that ILT2⁺ T cells constitute a reservoir of intratumor cytotoxic T cells that is not targeted by the current checkpoint inhibitors, but could be by anti-HLA-G/anti-ILT2 antibodies as novel immunotherapy in HLA-G⁺ tumors.

HLA-G and HLA-E Immune Checkpoints Are Widely Expressed in Ewing Sarcoma but Have Limited Functional Impact on the Effector Functions of Antigen-Specific CAR T Cells

Simple Summary

Solid cancers can effectively counteract immune attack by inhibitory checkpoints in the tumor microenvironment. Blockade of relevant immune checkpoints could be a useful tool for enhancing the efficacy of antitumor T cell therapies. Here, we studied the capacity of two nonclassical HLA molecules with known immunosuppressive function, HLA-G and HLA-E, to prevent antigen-specific immune effector functions of gene-engineered T cells against Ewing sarcoma. Inflammatory conditions and interactions of Ewing sarcoma cells with antitumor T cells reliably induced upregulation of the two molecules on the tumor cells. Moreover, as previously shown for HLA-G, HLA-E was detected in a high proportion of human Ewing sarcoma biopsies. However, artificial expression of either of the two molecules on Ewing sarcoma cells failed to reduce cytolytic and activation responses of antigen-specific T cells. We conclude that blockade of HLA-G and HLA-E immune checkpoints is not a promising strategy for enhancing T cell therapies in Ewing sarcoma.

Abstract

Immune-inhibitory barriers in the tumor microenvironment of solid cancers counteract effective T cell therapies. Based on our finding that Ewing sarcomas (EwS) respond to chimeric antigen receptor (CAR) gene-modified effector cells through upregulation of human leukocyte antigen G (HLA-G), we hypothesized that nonclassical HLA molecules, HLA-G and HLA-E, contribute to immune escape of EwS. Here, we demonstrate that HLA-G isotype G1 expression on EwS cells does not directly impair cytolysis by G_D2-specific CAR T cells (CART), whereas HLA-G1 on myeloid bystander cells reduces CART degranulation responses against EwS cells. HLA-E was induced in EwS cells by IFN-γ stimulation in vitro and by G_D2-specific CART treatment in vivo and was detected on tumor cells or infiltrating myeloid cells in a majority of human EwS biopsies. Interaction of HLA-E-positive EwS cells with G_D2-specific CART induced upregulation of HLA-E receptor NKG2A. However, HLA-E expressed by EwS tumor cells or by myeloid bystander cells both failed to reduce antitumor effector functions of CART. We conclude that non-classical HLA molecules are expressed in EwS under inflammatory conditions, but have limited functional impact on antigen-specific T cells, arguing against a relevant therapeutic benefit from combining CART therapy with HLA-G or HLA-E checkpoint blockade in this cancer.

Playing hide and seek: Tumor cells in control of MHC class I antigen presentation

MHC class I (MHC-I) molecules present a blueprint of the intracellular proteome to T cells allowing them to control infection or malignant transformation. As a response, pathogens and tumor cells often downmodulate MHC-I mediated antigen presentation to escape from immune surveillance. Although the fundamental rules of antigen presentation are known in detail, the players in this system are not saturated and new modules of regulation have recently been uncovered. Here, we update the understanding of antigen presentation by MHC-I molecules and how this can be exploited by tumors to prevent exposure of the intracellular proteome. This knowledge can provide new ways to improve immune responses against tumors and pathogens.

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.

Human Cytomegalovirus and Autoimmune Diseases: Where Are We?

Human cytomegalovirus (HCMV) is a ubiquitous double-stranded DNA virus belonging to the β-subgroup of the herpesvirus family. After the initial infection, the virus establishes latency in poorly differentiated myeloid precursors from where it can reactivate at later times to cause recurrences. In immunocompetent subjects, primary HCMV infection is usually asymptomatic, while in immunocompromised patients, HCMV infection can lead to severe, life-threatening diseases, whose clinical severity parallels the degree of immunosuppression. The existence of a strict interplay between HCMV and the immune system has led many to hypothesize that HCMV could also be involved in autoimmune diseases (ADs). Indeed, signs of active viral infection were later found in a variety of different ADs, such as rheumatological, neurological, enteric disorders, and metabolic diseases. In addition, HCMV infection has been frequently linked to increased production of autoantibodies, which play a driving role in AD progression, as observed in systemic lupus erythematosus (SLE) patients. Documented mechanisms of HCMV-associated autoimmunity include molecular mimicry, inflammation, and nonspecific B-cell activation. In this review, we summarize the available literature on the various ADs arising from or exacerbating upon HCMV infection, focusing on the potential role of HCMV-mediated immune activation at disease onset.

The SPPL3-Defined Glycosphingolipid Repertoire Orchestrates HLA Class I-Mediated Immune Responses

HLA class I (HLA-I) glycoproteins drive immune responses by presenting antigens to cognate CD8+ T cells. This process is often hijacked by tumors and pathogens for immune evasion. Because options for restoring HLA-I antigen presentation are limited, we aimed to identify druggable HLA-I pathway targets. Using iterative genome-wide screens, we uncovered that the cell surface glycosphingolipid (GSL) repertoire determines effective HLA-I antigen presentation. We show that absence of the protease SPPL3 augmented B3GNT5 enzyme activity, resulting in upregulation of surface neolacto-series GSLs. These GSLs sterically impeded antibody and receptor interactions with HLA-I and diminished CD8+ T cell activation. Furthermore, a disturbed SPPL3-B3GNT5 pathway in glioma correlated with decreased patient survival. We show that the immunomodulatory effect could be reversed through GSL synthesis inhibition using clinically approved drugs. Overall, our study identifies a GSL signature that inhibits immune recognition and represents a potential therapeutic target in cancer, infection, and autoimmunity.

The potential role of HLA-G in the pathogenesis of HBV infection: Immunosuppressive or immunoprotective?

The non-classical human leukocyte antigens (HLA)-G could be generally considered as a potent tolerogenic molecule, which modulates immune responses. HLA-G due to the immunosuppressive properties may play an important role in the pathogenesis of infections related to the liver. HLA-G may display two distinct activities in the pathological conditions so that it could be protective in the autoimmune and inflammatory diseases or could be suppressive of the immune system in the infections or cancers. HLA-G might be used as a novel therapeutic target for liver diseases in the future. Indeed, new therapeutic agents targeting HLA-G expression or antibodies which block HLA-G activity are being developed and tested. However, further consideration of the HLA-G function in liver disease is required. This review aims to summarize the role of HLA-G in the liver of patients with HBV infection.

Roles of HLA-G in the Maternal-Fetal Immune Microenvironment

During pregnancy, the maternal uterus and fetus form a special microenvironment at the maternal-fetal interface to support fetal development. Extravillous trophoblasts (EVTs), differentiated from the fetus, invade into the decidua and interact with maternal cells. Human leukocyte antigen (HLA)-G is a non-classical MHC-I molecule that is expressed abundantly and specifically on EVTs in physiological conditions. Soluble HLA-G (sHLA-G) is also found in maternal blood, amniotic fluid, and cord blood. The abnormal expression and polymorphisms of HLA-G are related to adverse pregnancy outcomes such as preeclampsia (PE) and recurrent spontaneous abortion (RSA). Here we summarize current findings about three main roles of HLA-G during pregnancy, namely its promotion of spiral artery remodeling, immune tolerance, and fetal growth, all resulting from its interaction with immune cells. These findings are not only of great significance for the treatment of pregnancy-related diseases but also provide clues to tumor immunology research since HLA-G functions as a checkpoint in tumors.

Zoledronate decreases CTLA-4 in vivo and in vitro independently of its action on bone resorption

Acute phase response (APR) following intravenous zoledronate (ZOL) administration is related to activation and increased proliferation of γδ T cells, attributed to the molecular mechanism of action of nitrogen-containing bisphosphonates (N-BPs). ZOL, however, has also been reported to inhibit the proliferation of regulatory T cells in vitro and to reduce the expression of Cytotoxic T-Lymphocyte Antigen-4 (CTLA-4), a negative regulator of T cell activation that is increased in patients with autoimmune diseases. There are, however, no data on the relationship between ZOL treatment and soluble(s)CTLA-4 either in vivo in relevant patient populations or in vitro with the use of assays relevant to the mechanism of action of N-BPs. The objectives of the present study were firstly, to characterize the ZOL-induced APR in patients with inflammatory rheumatic diseases (IRDs) and its relationship with changes in circulating sCTLA-4 and secondly, to investigate the effects of ZOL on CTLA-4 production and expression by peripheral blood mononuclear cells (PBMCs). We studied 10 postmenopausal women with IRDs treated with intravenous ZOL 5 mg. Five women experienced APR (APR+) associated with significant decreases in blood lymphocytes and increases in granulocytes and serum CRP. Serum sCTLA-4 values were increased in all patients before ZOL administration and decreased significantly 72 h after the ZOL infusion (from 30.0 ± 2.9 to 6.3 ± 1.8 ng/ml; p < 0.001) with no differences between APR+ and APR- patients. Consistent with the results of the in vivo study, ZOL (1 μM) decreased the production of sCTLA-4 by 87% and 57% after 3 and 5 days in cultures of peripheral blood mononuclear cells (PBMCs) in vitro, respectively, and inhibited the expression of both cytoplasmic and membrane-bound CTLA-4. Our results reveal a novel immunoregulatory action of ZOL that is not related to its action on bone resorption but might be associated with reported clinically significant extraskeletal outcomes of ZOL treatment.

LILRB3 (ILT5) is a myeloid cell checkpoint that elicits profound immunomodulation

Despite advances in identifying the key immunoregulatory roles of many of the human leukocyte immunoglobulin-like receptor (LILR) family members, the function of the inhibitory molecule LILRB3 (ILT5, CD85a, LIR3) remains unclear. Studies indicate a predominant myeloid expression; however, high homology within the LILR family and a relative paucity of reagents have hindered progress toward identifying the function of this receptor. To investigate its function and potential immunomodulatory capacity, a panel of LILRB3-specific monoclonal antibodies (mAbs) was generated. LILRB3-specific mAbs bound to discrete epitopes in Ig-like domain 2 or 4. LILRB3 ligation on primary human monocytes by an agonistic mAb resulted in phenotypic and functional changes, leading to potent inhibition of immune responses in vitro, including significant reduction in T cell proliferation. Importantly, agonizing LILRB3 in humanized mice induced tolerance and permitted efficient engraftment of allogeneic cells. Our findings reveal powerful immunosuppressive functions of LILRB3 and identify it as an important myeloid checkpoint receptor.

Maternal and fetal T cells in term pregnancy and preterm labor

Pregnancy is a state of immunological balance during which the mother and the developing fetus must tolerate each other while maintaining sufficient immunocompetence to ward off potential threats. The site of closest contact between the mother and fetus is the decidua, which represents the maternal-fetal interface. Many of the immune cell subsets present at the maternal-fetal interface have been well described; however, the importance of the maternal T cells in this compartment during late gestation and its complications, such as preterm labor and birth, has only recently been established. Moreover, pioneer and recent studies have indicated that fetal T cells are activated in different subsets of preterm labor and may elicit distinct inflammatory responses in the amniotic cavity, leading to preterm birth. In this review, we describe the established and proposed roles for maternal T cells at the maternal-fetal interface in normal term parturition, as well as the demonstrated contributions of such cells to the pathological process of preterm labor and birth. We also summarize the current knowledge of and proposed roles for fetal T cells in the pathophysiology of the preterm labor syndrome. It is our hope that this review provides a solid conceptual framework highlighting the importance of maternal and fetal T cells in late gestation and catalyzes new research questions that can further scientific understanding of these cells and their role in preterm labor and birth, the leading cause of neonatal mortality and morbidity worldwide.

Cytometry-based analysis of HLA-G functions according to ILT2 expression

HLA-G was described as a molecule inhibiting NK and T cells functions through its receptor, ILT2. However, most functional studies of HLA-G were so far performed on heterogeneous immune populations and regardless of ILT2 expression. This may lead to an underestimation of the effect of HLA-G. Thus, considering the immune subpopulations sensitive to HLA-G remained an important issue in the field. Here we present a new cytometry assay to evaluate HLA-G effects on both NK and CD8⁺ T cell cytotoxic functions. Using flow cytometry allows for the comparison of HLA-G function on multiple subsets and multiple functions in the same time. In particular, we sharpen the analysis by specifically studying the immune subpopulations expressing HLA-G receptor ILT2. We focused our work on: IFN-gamma production and cytotoxicity (CD107a expression) by CD8⁺ T cells and NK cells expressing or not ILT2. We compared the expression of these markers in presence of target cells, expressing or not HLA-G1, and added a blocking antibody to reverse HLA-G inhibition. This new method allows for the discrimination of cell subsets responding and non-responding to HLA-G1 in one tube. We confirm that HLA-G-specifically inhibits the ILT2⁺ CD8⁺ T cell and ILT2⁺ NK cell subsets but not ILT2-negative ones. By blocking HLA-G/ILT2 interaction using an anti-ILT2 antibody we restored the cytotoxicity level, corroborating the specific inhibition of HLA-G1. We believe that our methodology enables to investigate HLA-G immune functions easily and finely towards other immune cell lineages or expressing other receptors, and might be applied in several pathological contexts, such as cancer and transplantation.

CD8+PD-1-ILT2+ T Cells Are an Intratumoral Cytotoxic Population Selectively Inhibited by the Immune-Checkpoint HLA-G

Only some cancer patients respond to the immune-checkpoint inhibitors being used in the clinic, and other therapeutic targets are sought. Here, we investigated the HLA-G/ILT2 checkpoint in clear-cell renal-cell carcinoma (ccRCC) patients and focused on tumor-infiltrating CD8⁺ T lymphocytes (TIL) expressing the HLA-G receptor ILT2. Using transcriptomics and flow cytometry, we characterized both peripheral blood and tumor-infiltrating CD8⁺ILT2⁺ T cells from cancer patients as late-differentiated CD27^-CD28^-CD57⁺ cytotoxic effectors. We observed a clear dichotomy between CD8⁺ILT2⁺ and CD8⁺PD-1⁺ TIL subsets. These subsets, which were sometimes present at comparable frequencies in TIL populations, barely overlapped phenotypically and were distinguished by expression of exclusive sets of surface molecules that included checkpoint molecules and activating and inhibitory receptors. CD8⁺ILT2⁺ TILs displayed a more mature phenotype and higher expression of cytotoxic molecules. In ex vivo functional experiments with both peripheral blood T cells and TILs, CD8⁺ILT2⁺ T cells displayed significantly higher cytotoxicity and IFNγ production than their ILT2^- (peripheral blood mononuclear cells, PBMC) and PD-1⁺ (TILs) counterparts. HLA-G expression by target cells specifically inhibited CD8⁺ILT2⁺ T-cell cytotoxicity, but not that of their CD8⁺ILT2^- (PBMC) or CD8⁺PD-1⁺ (TIL) counterparts, an effect counteracted by blocking the HLA-G/ILT2 interaction. CD8⁺ILT2⁺ TILs may therefore constitute an untapped reservoir of fully differentiated cytotoxic T cells within the tumor microenvironment, independent of the PD1⁺ TILs targeted by immune therapies, and specifically inhibited by HLA-G. These results emphasize the potential of therapeutically targeting the HLA-G/ILT2 checkpoint in HLA-G⁺ tumors, either concomitantly with anti-PD-1/PD-L1 or in cases of nonresponsiveness to anti-PD-1/PD-L1.

The MHC class I-LILRB1 signalling axis as a promising target in cancer therapy

Immune checkpoint inhibitors are among the newest, cutting-edge methods for the treatment of cancer. Currently, they primarily influence T cell adaptive immunotherapy targeting the PD-1/PD-L1 and CTLA-4/B7 signalling pathways. These inhibitors fight cancer by reactivating the patient's own adaptive immune system, with good results in many cancers. With the discovery of the "Don't Eat Me" molecule, CD47, antibody-based drugs that target the macrophage-related innate immunosuppressive signalling pathway, CD47-SIRPα, have been developed and have achieved stunning results in the laboratory and the clinic, but there remain unexplained instances of tumour immune escape. While investigating the immunological tolerance of cancer to anti-CD47 antibodies, a second "Don't Eat Me" molecule on tumour cells, beta 2 microglobulin (β2m), a component of MHC class I, was described. Some tumour cells reduce their surface expression of MHC class I to escape T cell recognition. However, other tumour cells highly express β2m complexed with the MHC class I heavy chain to send a "Don't Eat Me" signal by binding to leucocyte immunoglobulin-like receptor family B, member 1 (LILRB1) on macrophages, leading to a loss of immune surveillance. Investigating the mechanisms underlying this immunosuppressive MHC class I-LILRB1 signalling axis in tumour-associated macrophages will be useful in developing therapies to restore macrophage function and control MHC class I signalling in patient tumours. The goal is to promote adaptive immunity while suppressing the innate immune response to tumours. This work will identify new therapeutic targets for the development of pharmaceutical-based tumour immunotherapy.

Effect of cytomegalovirus infection and leukocyte immunoglobulin like receptor B1 polymorphisms on receptor expression in peripheral blood mononuclear cells

Leukocyte immunoglobulin like receptor B1 (LILRB1) plays a significant role in a number of infectious, autoimmune, cardiovascular, and oncologic disorders. LILRB1 expression varies between individuals and may be associated with polymorphisms on the regulatory region of the LILRB1 gene, as well as to previous cytomegalovirus infection. In this study, the contribution of these two factors to LILRB1 expression in peripheral blood mononuclear cells of healthy young adults was analyzed. LILRB1 expression in NK cells, T cells, B cells and monocytes was significantly stronger in individuals who had had cytomegalovirus infection than in those who had not (P < 0.001, P < 0.001, P < 0.01, and P < 0.001, respectively). Overall, no differences in LILRB1 expression were observed between individuals with and without GAA haplotypes of the LILRB1 regulatory region. However, when analyzed according to cytomegalovirus infection status, significant differences in LILRB1+ NK cells were observed. A higher proportion of LILRB1+ cells was found in GAA+ than in GAA- individuals who had not been infected (P < 0.01), whereas GAA- individuals had a larger proportion of LILRB1+ cells than GAA+ individuals who were cytomegalovirus positive (P < 0.01). In conclusion, cytomegalovirus infection has a major effect on LILRB1 expression in NK and other mononuclear cells and polymorphisms in the LILRB1 regulatory region appear to have a modulatory influence over this effect.

Ig-Like Transcript 2 (ILT2) Blockade and Lenalidomide Restore NK Cell Function in Chronic Lymphocytic Leukemia

One of the cardinal features of chronic lymphocytic leukemia (CLL) is its association with a profound immunosuppression. NK cell function is markedly impaired in CLL patients, who show a significant dysregulation of the expression of activating and inhibitory receptors. Here, we analyzed the role of the novel inhibitory receptor Ig-like transcript 2 (ILT2, also termed LIR-1, LILRB1) in the regulation of NK cells in CLL. Our results show that ILT2 expression was significantly decreased on leukemic cells and increased on NK cells of CLL patients, particularly in those with advanced disease and with bad prognostic features, such as those carrying chromosome del(11q). The immunomodulatory drug lenalidomide may regulate the expression of ILT2 and its ligands in CLL since it significantly increased the expression of ILT2 and partially reestablished the expression of its ligands on leukemic cells. Furthermore, lenalidomide significantly increased the activation and proliferation of NK cells, which was strongly enhanced by ILT2 blockade. Combining ILT2 blockade and lenalidomide activated NK cell cytotoxicity resulting in increased elimination of leukemic cells from CLL patients. Overall, we describe herein the role of an inhibitory receptor involved in the suppression of NK cell activity in CLL, which is restored by ILT2 blockade in combination with lenalidomide, suggesting that it may be an interesting therapeutic strategy to be explored in this disease.

Signatures of CD8+ T cell dysfunction in AML patients and their reversibility with response to chemotherapy

BACKGROUND

Our understanding of phenotypic and functional signatures of CD8+ T cell dysfunction in acute myeloid leukemia (AML) is limited. Deciphering these deranged T cell functional states and how they are impacted by induction chemotherapy is essential for incorporation of novel immune-based strategies to restore and maintain antileukemia immunity.

METHODS

We utilized high-dimensional immunophenotyping, gene expression, and functional studies to characterize peripheral blood and bone marrow CD8+ T cells in 72 AML patients at diagnosis and after induction chemotherapy.

RESULTS

Our data suggest that multiple aspects of deranged T cell function are operative in AML at diagnosis, with exhaustion and senescence being the dominant processes. Following treatment, the phenotypic and transcriptional profile of CD8+ T cells diverged between responders and nonresponders. Response to therapy correlated with upregulation of costimulatory, and downregulation of apoptotic and inhibitory, T cell signaling pathways, indicative of restoration of T cell function. In functional studies, AML blasts directly altered CD8+ T cell viability, expansion, co-signaling and senescence marker expression. This CD8+ T cell dysfunction was in part reversible upon PD-1 blockade or OX40 costimulation in vitro.

CONCLUSION

Our findings highlight the uniqueness of AML in sculpting CD8+ T cell responses and the plasticity of their signatures upon chemotherapy response, providing a compelling rationale for integration of novel immunotherapies to augment antileukemia immunity.

FUNDING

This work was supported by the Leukemia & Lymphoma Society grant no. 6449-13; NIH grants UM1-CA186691 and R01-HL110907-01; the American Society for Blood and Marrow Transplantation New Investigator Award/Gabrielle's Angel Foundation; the Vienna Fund for Innovative Cancer Research; and by fellowships from the Wenner-Gren Foundation and the Swedish Society for Medical Research.

Signatures of CD8+ T cell dysfunction in AML patients and their reversibility with response to chemotherapy

BACKGROUND

Our understanding of phenotypic and functional signatures of CD8+ T cell dysfunction in acute myeloid leukemia (AML) is limited. Deciphering these deranged T cell functional states and how they are impacted by induction chemotherapy is essential for incorporation of novel immune-based strategies to restore and maintain antileukemia immunity.

METHODS

We utilized high-dimensional immunophenotyping, gene expression, and functional studies to characterize peripheral blood and bone marrow CD8+ T cells in 72 AML patients at diagnosis and after induction chemotherapy.

RESULTS

Our data suggest that multiple aspects of deranged T cell function are operative in AML at diagnosis, with exhaustion and senescence being the dominant processes. Following treatment, the phenotypic and transcriptional profile of CD8+ T cells diverged between responders and nonresponders. Response to therapy correlated with upregulation of costimulatory, and downregulation of apoptotic and inhibitory, T cell signaling pathways, indicative of restoration of T cell function. In functional studies, AML blasts directly altered CD8+ T cell viability, expansion, co-signaling and senescence marker expression. This CD8+ T cell dysfunction was in part reversible upon PD-1 blockade or OX40 costimulation in vitro.

CONCLUSION

Our findings highlight the uniqueness of AML in sculpting CD8+ T cell responses and the plasticity of their signatures upon chemotherapy response, providing a compelling rationale for integration of novel immunotherapies to augment antileukemia immunity.

FUNDING

This work was supported by the Leukemia & Lymphoma Society grant no. 6449-13; NIH grants UM1-CA186691 and R01-HL110907-01; the American Society for Blood and Marrow Transplantation New Investigator Award/Gabrielle's Angel Foundation; the Vienna Fund for Innovative Cancer Research; and by fellowships from the Wenner-Gren Foundation and the Swedish Society for Medical Research.

LILRB1 polymorphisms influence posttransplant HCMV susceptibility and ligand interactions

UL18 is a human CMV (HCMV) MHC class I (MHCI) homolog that efficiently inhibits leukocyte immunoglobulin-like receptor subfamily B member 1 (LILRB1)+ NK cells. We found an association of LILRB1 polymorphisms in the regulatory regions and ligand-binding domains with control of HCMV in transplant patients. Naturally occurring LILRB1 variants expressed in model NK cells showed functional differences with UL18 and classical MHCI, but not with HLA-G. The altered functional recognition was recapitulated in binding assays with the binding domains of LILRB1. Each of 4 nonsynonymous substitutions in the first 2 LILRB1 immunoglobulin domains contributed to binding with UL18, classical MHCI, and HLA-G. One of the polymorphisms controlled addition of an N-linked glycan, and that mutation of the glycosylation site altered binding to all ligands tested, including enhancing binding to UL18. Together, these findings indicate that specific LILRB1 alleles that allow for superior immune evasion by HCMV are restricted by mutations that limit LILRB1 expression selectively on NK cells. The polymorphisms also maintained an appropriate interaction with HLA-G, fitting with a principal role of LILRB1 in fetal tolerance.

Inhibiting HLA-G restores IFN-γ and TNF-α producing T cell in pleural Tuberculosis

Human Leukocyte Antigen-G (HLA-G), a non-classical, class Ib molecule, has been shown to mediate immunoregulatory functions by inducing apoptosis, inhibits cytotoxicity and differentiation by modulating cytokine secretion. Due to its immune-suppressive function, it facilitates tolerance in feto-maternal interface and transplantation. In contrary, it favours immune evasion of microbes and tumors by inhibiting immune and inflammatory responses. In Tuberculosis (TB), we previously reported differential expression of HLA-G and its receptor Ig-like transcript -2 (ILT-2) in disseminated vs. localized Tuberculosis. The present study explores the impact of HLA-G inhibition on the function of T cells and monocytes, in TB Pleural Effusion (PE), a localized form of TB. Blocking of HLA-G resulted in significant increase in IFN-γ and TNF-α production by CD3⁺ T cells. Additionally, we observed that HLA-G influences the apoptosis and cytotoxic effect of T cells from TB- PE patients. Next, we checked the impact of interaction between HLA-G and ILT-4 receptor in monocytes derived from TB-PE patients upon blocking and observed significant increase in IFN-γ production. The present study reveals for the first time HLA-G mediated suppression of Th1 cytokines, especially, IFN-γ and TNF-α in TB-PE patients.

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.

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.

HLA-G: At the Interface of Maternal-Fetal Tolerance

During pregnancy, semiallogeneic fetal extravillous trophoblasts (EVT) invade the uterine mucosa without being rejected by the maternal immune system. Several mechanisms were initially proposed by Peter Medawar half a century ago to explain this apparent violation of the laws of transplantation. Then, three decades ago, an unusual human leukocyte antigen (HLA) molecule was identified: HLA-G. Uniquely expressed in EVT, HLA-G has since become the center of the present understanding of fetus-induced immune tolerance. Despite slow progress in the field, the last few years have seen an explosion in our knowledge of HLA-G biology. Here, we critically review new insights into the mechanisms controlling the expression and function of HLA-G at the maternal-fetal interface, and discuss their relevance for fetal tolerance.

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.

Latent Cytomegalovirus Infection in Rheumatoid Arthritis and Increased Frequencies of Cytolytic LIR-1+CD8+ T Cells

Objective

Leukocyte immunoglobulin‐like receptor 1 (LIR‐1) is up‐regulated by cytomegalovirus (CMV), which in turn, has been associated with premature aging and more severe joint disease in patients with rheumatoid arthritis (RA). The aim of this study was to investigate the expression and functional significance of LIR‐1 in CMV‐positive RA patients.

Methods

We determined the phenotype, cytolytic potential, CMV‐specific proliferation, and HLA–G–triggered, LIR‐1–mediated inhibition of interferon‐γ secretion of LIR‐1+ T cells in RA patients and healthy controls.

Results

We found increased frequencies of CD8+ T cells with CMV pp65–specific T cell receptors in CMV‐positive RA patients as compared to CMV‐positive healthy controls. CMV‐specific CD8+ T cells in these patients were preferentially LIR‐1+ and exhibited a terminally differentiated polyfunctional phenotype. The numbers of LIR‐1+CD8+ T cells increased with age and disease activity, and showed high levels of reactivity to CMV antigens. Ligation of LIR‐1 with soluble HLA–G molecules in vitro confirmed an inhibitory role of the molecule when expressed on CD8+ T cells in RA patients.

Conclusion

We propose that latent CMV infection in the context of a chronic autoimmune response induces the recently described “chronic infection phenotype” in CD8+ T cells, which retains anti‐infectious effector features while exhibiting autoreactive cytolytic potential. This response is likely dampened by LIR‐1 to avoid overwhelming immunopathologic changes in the setting of the autoimmune disease RA. The known deficiency of soluble HLA–G in RA and the observed association of LIR‐1 expression with disease activity suggest, however, that LIR‐1+ T cells are insufficiently controlled in RA and are still likely to be involved in the pathogenesis of the disease.

Mouse models for studies of HLA-G functions in basic science and pre-clinical research

HLA-G was described originally as a tolerogenic molecule that allows the semiallogeneic fetus to escape from recognition by the maternal immune response. This review will discuss different steps in the study of HLA-G expression and functions in vivo, starting with analyses of expression of the HLA-G gene and its receptors in transgenic mice, and continuing with applications of HLA-G and its receptors in prevention of allograft rejection, transplantation tolerance, and controlling the development of infection. Humanized mouse models have been discussed for developing in vivo studies of HLA-G in physiological and pathological conditions. Collectively, animal models provide an opportunity to evaluate the importance of the interaction between HLA-G and its receptors in terms of its ability to regulate immune responses during maternal-fetal tolerance, survival of allografts, tumor-escape mechanisms, and development of infections when both HLA-G and its receptors are expressed. In addition, in vivo studies on HLA-G also offer novel approaches to achieve a reproducible transplantation tolerance and to develop personalized medicine to prevent allograft rejection.

TLR8 regulation of LILRA3 in monocytes is abrogated in human immunodeficiency virus infection and correlates to CD4 counts and virus loads

BACKGROUND

LILRA3 is an immunostimulatory molecule which can conditionally induce the proliferation of cytotoxic cells. LILRA3 has a deletion genotype which is associated with multiple immune disorders. In this study, we wanted to analyze the regulation of LILRA3 and its significance in the context of HIV infection.

RESULTS

We analyzed a panel of TLR agonists and found that ssRNA40, a TLR8 agonist, is a potent inducer of LILRA3 in healthy individuals. However, this regulation is much diminished in HIV. Comparison of TLR8 to TLR4 induction of LILRA3 indicated that LPS induces less LILRA3 than ssRNA40 among healthy controls, but not HIV patients. Levels of LILRA3 induction correlated to virus load and CD4 counts in untreated patients. Recombinant LILRA3 can induce a host of proinflammatory genes which include IL-6 and IL-1α, as well as alter the expression of MHC and costimulatory molecules in monocytes and B-cells.

CONCLUSION

Our experiments point towards a beneficial role for LILRA3 in virus infections, especially in ssRNA viruses, like HIV, that engage TLR8. However, the potentially beneficial role of LILRA3 is abrogated during a HIV infection. We believe that more work has to be done to study the role of LILRA3 in infectious diseases and that there is a potential for exploring the use of LILRA3 in the treatment of virus infections.

Increased frequency of ILT2-expressing CD56(dim)CD16(+) NK cells correlates with disease severity of pulmonary tuberculosis

The functional role of ILT2 in anti-tuberculosis immunity remains to be elucidated. In this study, we investigated expression and functions of ILT2 on NK cells during TB infection. The frequency of CD56(dim)CD16(+) NK cells that expressed ILT2 was significantly elevated in patients with active pulmonary TB as compared with tuberculin-positive healthy controls (p < 0.0001). TB patients with Mycobacterium tuberculosis smear/culture-positive result had significantly higher frequency of ILT2-expressing CD56(dim)CD16(+) NK cells than those with M. tuberculosis smear/culture-negative result (p < 0.0001), suggesting that ILT2 expression on CD56(dim)CD16(+) NK cells correlated with disease severity of pulmonary TB. ILT2-expressing CD56(dim) NK cells had a functional defect, as evidenced by reduced expression of CD107a and IFN-γ. Spontaneous apoptosis in ILT2(+)CD56(dim) NK cells was higher than in ILT2(-) cells. Blocking of ILT2 signaling resulted in increased expression of CD107a on CD56(dim)CD16(+) NK cells. It is concluded that ILT2 has an inhibitory role on NK cells in patients with active TB.

HLA-G as a tolerogenic molecule in transplantation and pregnancy

HLA-G is a nonclassical HLA class I molecule. In allogeneic situations such as pregnancy or allograft transplantation, the expression of HLA-G has been related to a better acceptance of the fetus or the allograft. Thus, it seems that HLA-G is crucially involved in mechanisms shaping an allogeneic immune response into tolerance. In this contribution we focus on (i) how HLA-G is involved in transplantation and human reproduction, (ii) how HLA-G is regulated by genetic and microenvironmental factors, and (iii) how HLA-G can offer novel perspectives with respect to therapy.

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.

Do inhibitory immune receptors play a role in the etiology of autoimmune disease?

Inhibitory receptors are thought to be important in balancing immune responses. The general assumption is that lack of inhibition predisposes for autoimmune diseases. As reviewed here, various experimental and clinical data support this assumption. However, in humans genetic evidence implicates only a limited number of inhibitory receptors. GWAS have established common variation in a few inhibitory receptor genes, such as FCγRIIB, PD-1 and CTLA-4 as risk factors. The question arises whether inhibitory receptor function is a major determinant of autoimmune disease. In this respect, the finding that genetic variation in CSK and PTPN22 is strongly associated with multiple autoimmune diseases is of interest. We propose a model in which the molecules encoded by these genes are downstream of inhibitory receptors. We conclude that common genetic variation of inhibitory receptors, with few exceptions, is not a determining factor for autoimmunity in humans. However, common downstream signaling pathways are.

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.

Crystal structures of the two membrane-proximal Ig-like domains (D3D4) of LILRB1/B2: alternative models for their involvement in peptide-HLA binding

Leukocyte immunoglobulin-like receptors (LILRs), also called CD85s, ILTs, or LIRs, are important mediators of immune activation and tolerance that contain tandem immunoglobulin (Ig)-like folds. There are 11 (in addition to two pseudogenes) LILRs in total, two with two Ig-like domains (D1D2) and the remaining nine with four Ig-like domains (D1D2D3D4). Thus far, the structural features of the D1D2 domains of LILR proteins are well defined, but no structures for the D3D4 domains have been reported. This is a very important field to be studied as it relates to the unknown functions of the D3D4 domains, as well as their relative orientation to the D1D2 domains on the cell surface. Here, we report the crystal structures of the D3D4 domains of both LILRB1 and LILRB2. The two Ig-like domains of both LILRB1-D3D4 and LILRB2-D3D4 are arranged at an acute angle (∼60°) to form a bent structure, resembling the structures of natural killer inhibitory receptors. Based on these two D3D4 domain structures and previously reported D1D2/HLA I complex structures, two alternative models of full-length (four Ig-like domains) LILR molecules bound to HLA I are proposed.

Natural killer reprogramming in cutaneous T-cell lymphomas: Facts and hypotheses

To better understand the pathogenesis of Sézary cells, distinguish them from reactive skin-infiltrating T-cells and improve disease treatment, efforts have been made to identify molecular targets deregulated by the malignant process. From immunophenotypic analysis and subtractive differential expression experiments to pan-genomic studies, many approaches have been used to identify markers of the disease. During the last decade several natural killer (NK) cell markers have been found aberrantly expressed at the surface of Sézary cells. In particular, KIR3DL2/CD158k, expressed by less than 2% of healthy individuals CD4⁺ T-cells, is an excellent marker to identify and follow the tumor burden in the blood of Sézary syndrome patients. It may also represent a valuable target for specific immunotherapy. Other products of the NK cluster on chromosome 19q13 have been detected on Sézary cells, raising the hypothesis of an NK reprogramming process associated with the malignant transformation that may induce survival functions.

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.

6.7-kbp deletion in LILRA3 (ILT6) gene is associated with later onset of the multiple sclerosis in a Polish population

Recently published studies have implicated the deletion polymorphism in LILRA3 gene, as being associated with multiple sclerosis (MS). A total of 309 patients diagnosed with MS and 379 unrelated healthy volunteers were typed for 6.7-kbp deletion in LILRA3 gene. Simultaneously, presence or absence of HLA-DRB1(∗)1501 allele was established to assess the possibility of interaction between LILRA3 deletion and HLA-DRB1(∗)1501 status. In contrast to previous reports, we did not find any association of LILRA3 deletion with MS susceptibility. Also, the HLA-DRB1(∗)1501 stratification analysis showed no LILRA3 association with the disease. However, we observed that patients negative for the deletion may begin to suffer from MS significantly earlier than patients who are positive (p = 0.014). Similarly to the most European populations we found significantly higher frequency of HLA-DRB1(∗)1501 allele in cases than we found in controls (27.0% vs. 12.5%; p < 0.0001, OR = 2.6, 95%CI = 1.96-3.42).

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 emerging role of leukocyte immunoglobulin-like receptors (LILRs) in HIV-1 infection

LILRs represent a group of immunomodulatory molecules that regulate the functional properties of professional APCs and influence immune activation in a variety of disease contexts. Many members of the LILR family recognize peptide/MHC class I complexes as their physiological ligands, and increasing evidence suggests that such interactions are prominently influenced by polymorphisms in HLA class I alleles or sequence variations in the presented antigenic peptides. Emerging data show that LILRs are involved in multiple, different aspects of HIV-1 disease pathogenesis and may critically influence spontaneous HIV-1 disease progression. Here, we review recent progress in understanding the role of LILR during HIV-1 infection by focusing on the dynamic interplay between LILR and HLA class I molecules in determining HIV-1 disease progression, the effects of HIV-1 mutational escape on LILR-mediated immune recognition, the contribution of LILR to HIV-1-associated immune dysfunction, and the unique expression patterns of LILR on circulating myeloid DCs from elite controllers, a small subset of HIV-1-infected patients with natural control of HIV-1 replication. Obtaining a more complete understanding of LILR-mediated immune regulation during HIV-1 infection may ultimately allow for improved strategies to treat or prevent HIV-1-associated disease manifestations.

Lymphocyte cell-cycle inhibition by HLA-G is mediated by phosphatase SHP-2 and acts on the mTOR pathway

Human leukocyte antigen G (HLA-G) is involved in regulating T-cell responses through its interaction with inhibitory receptors belonging to the immunoglobulin-like transcript family (ILT). In this context, we investigated the pathways involved in the control of cell-cycle entry of T cells following HLA-G interaction with its inhibitory receptor. We show that HLA-G acts through its interaction with the LILRB1 receptor expressed on T lymphocytes. Both HLA-G and LILRB1 antibodies block the inhibitory effect of HLA-G and restore T-cell proliferation. The interaction of HLA-G with T lymphocytes is associated with phosphorylation of SHP-2 phosphatase, but not SHP-1. In addition, in activated T cells, their incubation with HLA-G is not associated with a decrease in the TCR or CD28 downstream pathways, but is associated with dephosphorylation of the mTOR molecule and p70S6K. In contrast, Akt, which acts upstream of mTOR, is not affected by HLA-G. The inhibition of SHP-2 by NSC-87877(5 µM), a chemical inhibitor of SHP-2, or the use of siRNA, abrogates dephosphorylation of mTOR and impairs the overexpression of p27^kip in the presence of HLA-G. Together, these results indicate that HLA-G is associated with activation of phosphatase SHP-2, which inhibits the mTOR pathway and favors the inhibition of the cell-cycle entry of human-activated T cells.