Human leukocyte immunoglobulin-like receptors in health and disease

HDAC6 inhibition by ITF3756 modulates PD-L1 expression and monocyte phenotype: insights for a promising immune checkpoint blockade co-treatment therapy

Introduction

Tumor immunotherapy has revolutionized cancer treatment, particularly through the use of immune checkpoint inhibitors targeting the PD-L1/PD-1 axis. While PD-L1 expression on tumor cells is an established predictive biomarker for therapeutic response, emerging evidence highlights the importance of PD-L1 expression on myeloid cells, both in the periphery and within the tumor microenvironment (TME). This study explores the immunomodulatory effects of the selective HDAC6 inhibitor ITF3756 on monocytes and dendritic cells (DCs).

Methods

Monocytes were stimulated with the pro-inflammatory cytokine TNF-α and treated with ITF3756. PD-L1 and CD40 expression levels were assessed by flow cytometry. Transcriptomic and proteomic analyses were performed to characterize changes in gene and protein expression profiles. T cell proliferation was evaluated in co-culture assays. Additionally, the impact of ITF3756 was assessed in an in vivo murine model of colon cancer.

Results

ITF3756 effectively downregulated PD-L1 expression in TNF-α-activated monocytes and enhanced their costimulatory capacity by increasing CD40 expression. Transcriptomic and proteomic analyses revealed that ITF3756 counteracted TNF-α pathway activation and downregulated multiple inhibitory immune checkpoint molecules, promoting a less immunosuppressive phenotype. In co-culture assays, ITF3756-treated monocytes and DCs significantly enhanced T cell proliferation. In vivo, ITF3756 treatment led to reduced tumor growth in a colon cancer model.

Discussion

These findings demonstrate that selective HDAC6 inhibition by ITF3756 modulates myeloid cell functionality by diminishing inhibitory signals and promoting T cell activation. Thus, ITF3756 represents a promising immunomodulatory agent that could enhance the efficacy of immune checkpoint blockade in cancer immunotherapy.

Cooperation between inhibitory immune checkpoints of senescent cells with immunosuppressive network to promote immunosenescence and the aging process

The accumulation of senescent cells within tissues promotes the aging process by remodelling the functions of the immune system. For many years, it has been known that senescent cells secrete pro-inflammatory cytokines and chemokines, a phenotype called the senescence-associated secretory phenotype (SASP). Chemokines and colony-stimulating factors stimulate myelopoiesis and recruit myeloid cells into aging tissues. Interestingly, recent studies have demonstrated that senescent cells are not only secretory but they also express an increased level of ligand proteins for many inhibitory immune checkpoint receptors. These ligands represent "don't eat me" markers in senescent cells and moreover, they are able to induce an exhaustion of many immune cells, such as surveying natural killer (NK) cells, cytotoxic CD8+ T cells, and macrophages. The programmed cell death protein-1 (PD-1) and its ligand PD-L1 represent the best known inhibitory immune checkpoint pathway. Importantly, the activation of inhibitory checkpoint receptors, e.g., in chronic inflammatory states, can also induce certain immune cells to differentiate toward their immunosuppressive phenotype. This can be observed in myeloid derived suppressor cells (MDSC), tissue regulatory T cells (Treg), and M2 macrophages. Conversely, these immunosuppressive cells stimulate in senescent cells the expression of many ligand proteins for inhibitory checkpoint receptors. Paradoxically, senescent cells not only promote the pro-inflammatory state but they maintain it at a low-grade level by expressing ligands for inhibitory immune checkpoint receptors. Thus, the cooperation between senescent cells and immunosuppressive cells enhances the senescence state of immune cells, i.e., immune senescence/exhaustion, and cellular senescence within tissues via bystander effects.

A review of antibody-based immunotherapy clinical trials for adult acute myeloid leukemia (AML): monoclonal antibodies (mAbs) and beyond

INTRODUCTION

Antibody-based immunotherapies are a class of therapeutics under active investigation in clinical trials for the treatment of acute myeloid leukemia (AML). Our review provides a comprehensive examination of trials published to date, focusing on recurrent challenges and promising aspects of antibody-based therapeutics.

AREAS COVERED

We described antibody-based immunotherapies for AML, specifically, an overview of the most prominent antigen targets in published clinical trials investigating monoclonal antibodies, antibody-drug conjugates, bispecific antibodies, and chimeric antigen receptor therapies. Manuscripts and abstracts describing clinical trials investigating antibody-based therapies for AML published through December 2024, identified by searching Google Scholar and PubMed, were included.

EXPERT OPINION

Antibody-based immunotherapies for AML have encountered limitations, including imperfect target antigens with significant associated toxicity such as myelosuppression, in addition to challenges specific to the AML patient population. The majority of trials have targeted CD33, CD123, CD371 (CLL1/Clec12), and CD47. For successful implementation of antibody-based therapeutics in AML treatment, future directions require creative applications of antibody-based therapeutics specifically engineered to minimize limiting toxicities and tailoring of therapies for this unique patient population.

Assessing the impact of cell isolation method on B cell gene expression using next-generation sequencing

Transcriptional profiling of peripheral blood mononuclear cells (PBMCs) is a widely explored research approach across multiple fields. Cell populations of interest are generally isolated before analysis, especially if low-frequency cell populations are desired. B cells, in particular, make up approximately 5%-10% of total PBMCs in healthy individuals, thus, isolation of B cell populations is crucial for researchers investigating B cell malignancies. The most widely used cell isolation methods include negative or positive magnetic cell sorting (MCS) and fluorescence-activated cell sorting (FACS). In contrast to negative MCS, it is widely believed that positive MCS and FACS may affect gene expression due to the direct interaction of cell selection antibodies with surface markers. To the best of our knowledge, no specific studies have examined these effects within CD19+ B cell populations. To evaluate this, we have performed RNA sequencing (RNA-seq) on B cells isolated from four healthy donors using three distinct methods: positive and negative MCS using the EasySep StemCell Technologies kits and FACS, performed using the MACSQuant Tyto sorter (Miltenyi Biotec). We report significant gene expression changes following CD19-dependent B cell isolation via either positive MCS or FACS relative to negative MCS, including a general upregulation of genes associated with immune activity and receptor signaling and downregulation of RNA processing genes. These results suggest that B cell isolation methods should be taken into consideration when designing experiments or incorporating publicly available sequencing datasets into ongoing research studies, as they may significantly impact the reliability and interpretability of the findings.

LILRB4 as a novel immunotherapeutic target for multiple diseases

Immune checkpoints are critical for maintaining autoimmune homeostasis and are implicated in various autoimmune diseases, with their significance increasingly recognized. Investigating the functions and mechanisms of these checkpoints is essential for the development of more effective treatments. Leukocyte immunoglobulin-like receptor subfamily B member 4 (LILRB4) stands out as a unique immune checkpoint, with limited expression in most normal tissues but prominent presence in various hematological and solid tumors. It is also expressed on numerous immune and stromal cells, functioning as both a "Tumor Immune Checkpoint" and a "Tumor Stromal Immune Checkpoint." Due to its distinct expression profile, LILRB4 plays a pivotal role in tumors, autoimmune diseases, allergic reactions, and the maintenance of immune homeostasis during transplantation and pregnancy. A thorough understanding of its ligands, functions, mechanisms, and ongoing therapeutic strategies targeting LILRB4 will be crucial for the development of advanced therapeutic options. This review examines LILRB4 expression and function across multiple diseases and discusses therapeutic approaches targeting LILRB4 in various contexts. Additionally, the potential of combining current drugs with LILRB4-targeted therapies is explored. Challenges in developing LILRB4-targeting drugs are also addressed, offering valuable insights for future research.

The role of inhibitory immune checkpoint receptors in the pathogenesis of Alzheimer's disease

There is mounting evidence that microglial cells have a key role in the pathogenesis of Alzheimer's disease (AD). In AD pathology, microglial cells not only are unable to remove β-amyloid (Aβ) plaques and invading pathogens but also are involved in synaptic pruning, chronic neuroinflammation, and neuronal degeneration. Microglial cells possess many different inhibitory immune checkpoint receptors, such as PD-1, LILRB2-4, Siglecs, and SIRPα receptors, which can be targeted by diverse cell membrane-bound and soluble ligand proteins to suppress the functions of microglia. Interestingly, in the brains of AD patients there are elevated levels of many of the inhibitory ligands acting via these inhibitory checkpoint receptors. For instance, Aβ oligomers, ApoE4, and fibronectin are able to stimulate the LILRB2-4 receptors. Increased deposition of sialoglycans, e.g., gangliosides, inhibits microglial function via Siglec receptors. AD pathology augments the accumulation of senescent cells, which are known to possess a high level of PD-L1 proteins, and thus, they can evade immune surveillance. A decrease in the expression of SIRPα receptor in microglia and its ligand CD47 in neurons enhances the phagocytic pruning of synapses in AD brains. Moreover, cerebral neurons contain inhibitory checkpoint receptors which can inhibit axonal growth, reduce synaptic plasticity, and impair learning and memory. It seems that inappropriate inhibitory immune checkpoint signaling impairs the functions of microglia and neurons thus promoting AD pathogenesis. KEY MESSAGES: Microglial cells have a major role in the pathogenesis of AD. A decline in immune activity of microglia promotes AD pathology. Microglial cells and neurons contain diverse inhibitory immune checkpoint receptors. The level of ligands for inhibitory checkpoint receptors is increased in AD pathology. Impaired signaling of inhibitory immune checkpoint receptors promotes AD pathology.

The LILRB family in hematologic malignancies: prognostic associations, mechanistic considerations, and therapeutic implications

The leukocyte immunoglobulin-like receptor B (LILRB) proteins, characterized by their transmembrane nature and canonical immunoreceptor tyrosine-based inhibitory motifs (ITIM) signaling, play a pivotal role in maintaining immune homeostasis and are implicated in the pathogenesis of various disease states. This comprehensive review will focus on the intricate involvement of the LILRB family in hematologic malignancies. These receptors have emerged as valuable diagnostic and prognostic biomarkers in leukemia, lymphoma, and myeloma. Beyond their prognostic implications, LILRBs actively shape the immune microenvironment and directly influence the disease pathogenesis of hematologic malignancies. Furthermore, their identification as potential therapeutic targets offer a promising avenue for precision medicine strategies in the treatment of these disorders. Currently, multiple LILRB directed therapies are in the preclinical and clinical trial pipelines. This review underscores the multifaceted role of the LILRB family in hematologic malignancies, highlighting their significance from diagnostic and prognostic perspectives to their broader impact on disease pathophysiology and as valuable therapeutic targets.

Characterization of Freshly Isolated Human Peripheral Blood B Cells, Monocytes, CD4+ and CD8+ T Cells, and Skin Mast Cells by Quantitative Transcriptomics

Quantitative transcriptomics offers a new way to obtain a detailed picture of freshly isolated cells. By direct isolation, the cells are unaffected by in vitro culture, and the isolation at cold temperatures maintains the cells relatively unaltered in phenotype by avoiding activation through receptor cross-linking or plastic adherence. Simultaneous analysis of several cell types provides the opportunity to obtain detailed pictures of transcriptomic differences between them. Here, we present such an analysis focusing on four human blood cell populations and compare those to isolated human skin mast cells. Pure CD19+ peripheral blood B cells, CD14+ monocytes, and CD4+ and CD8+ T cells were obtained by fluorescence-activated cell sorting, and KIT+ human connective tissue mast cells (MCs) were purified by MACS sorting from healthy skin. Detailed information concerning expression levels of the different granule proteases, protease inhibitors, Fc receptors, other receptors, transcription factors, cell signaling components, cytoskeletal proteins, and many other protein families relevant to the functions of these cells were obtained and comprehensively discussed. The MC granule proteases were found exclusively in the MC samples, and the T-cell granzymes in the T cells, of which several were present in both CD4+ and CD8+ T cells. High levels of CD4 were also observed in MCs and monocytes. We found a large variation between the different cell populations in the expression of Fc receptors, as well as for lipid mediators, proteoglycan synthesis enzymes, cytokines, cytokine receptors, and transcription factors. This detailed quantitative comparative analysis of more than 780 proteins of importance for the function of these populations can now serve as a good reference material for research into how these entities shape the role of these cells in immunity and tissue homeostasis.

Heterogeneous immune landscapes and macrophage dynamics in primary and lung metastatic adenoid cystic carcinoma of the head and neck

Introduction

Recurrent or metastatic adenoid cystic carcinoma (ACC) of the head and neck is rare and highly aggressive. Due to the ineffectiveness of immune checkpoint therapies, this study aims to investigate the tumor immune microenvironment of primary tumor tissues and lung metastatic tissues and to comprehend the challenges of immunotherapy.

Methods

We analyzed RNA sequencing data and constructed immune landscapes from 25 primary tumors and 34 lung metastases. The data were then validated by immunohistochemistry and single-cell sequencing analysis.

Results

Compared to adjacent normal tissues, both primary and lung metastatic ACC showed low immune infiltration. Lung metastases had higher immune infiltration levels and antigen presentation scores but also higher T cell exclusion and dysfunction scores. Single-cell sequencing data and immunohistochemistry revealed abundant immunosuppressive tumor-associated macrophages in lung metastases. Patients with high M2 macrophage infiltration had shorter lung metastasis-free survival.

Discussion

Primary and lung metastatic ACC exhibit heterogeneous tumor immune microenvironments. Higher immune cell infiltration in lung metastases is countered by the presence of suppressive tumor-associated macrophages, which may limit effective anti-tumor responses.

Leukocyte immunoglobulin-like receptor B4: A keystone in immune modulation and therapeutic target in cancer and beyond

Leukocyte immunoglobulin-like receptor B4 (LILRB4) significantly impacts immune regulation and the pathogenesis and progression of various cancers. This review discusses LILRB4's structural attributes, expression patterns in immune cells, and molecular mechanisms in modulating immune responses. We describe the influence of LILRB4 on T cells, dendritic cells, NK cells, and macrophages, and its dual role in stimulating and suppressing immune activities. The review discusses the current research on LILRB4's involvement in acute myeloid leukemia, chronic lymphocytic leukemia, and solid tumors, such as colorectal cancer, pancreatic cancer, non-small cell lung cancer, hepatocellular carcinoma, and extramedullary multiple myeloma. The review also describes LILRB4's role in autoimmune disorders, infectious diseases, and other conditions. We evaluate the recent advancements in targeting LILRB4 using monoclonal antibodies and peptide inhibitors and their therapeutic potential in cancer treatment. Together, these studies underscore the need for further research on LILRB4's interactions in the tumor microenvironment and highlight its importance as a therapeutic target in oncology and for future clinical innovations.

Inhibitory immune checkpoints suppress the surveillance of senescent cells promoting their accumulation with aging and in age-related diseases

The accumulation of pro-inflammatory senescent cells within tissues is a common hallmark of the aging process and many age-related diseases. This modification has been called the senescence-associated secretory phenotype (SASP) and observed in cultured cells and in cells isolated from aged tissues. Currently, there is a debate whether the accumulation of senescent cells within tissues should be attributed to increased generation of senescent cells or to a defect in their elimination from aging tissues. Emerging studies have revealed that senescent cells display an increased expression of several inhibitory immune checkpoint ligands, especially those of the programmed cell death protein-1 (PD-1) ligand-1 (PD-L1) proteins. It is known that the PD-L1 ligands, especially those of cancer cells, target the PD-1 receptor of cytotoxic CD8+ T and natural killer (NK) cells disturbing their functions, e.g., evoking a decline in their cytotoxic activity and promoting their exhaustion and even apoptosis. An increase in the level of the PD-L1 protein in senescent cells was able to suppress their immune surveillance and inhibit their elimination by cytotoxic CD8+ T and NK cells. Senescent cells are known to express ligands for several inhibitory immune checkpoint receptors, i.e., PD-1, LILRB4, NKG2A, TIM-3, and SIRPα receptors. Here, I will briefly describe those pathways and examine whether these inhibitory checkpoints could be involved in the immune evasion of senescent cells with aging and age-related diseases. It seems plausible that an enhanced inhibitory checkpoint signaling can prevent the elimination of senescent cells from tissues and thus promote the aging process.

Fifty years of HLA-associated type 1 diabetes risk: history, current knowledge, and future directions

More than 50 years have elapsed since the association of human leukocyte antigens (HLA) with type 1 diabetes (T1D) was first reported. Since then, methods for identification of HLA have progressed from cell based to DNA based, and the number of recognized HLA variants has grown from a few to tens of thousands. Current genotyping methodology allows for exact identification of all HLA-encoding genes in an individual's genome, with statistical analysis methods evolving to digest the enormous amount of data that can be produced at an astonishing rate. The HLA region of the genome has been repeatedly shown to be the most important genetic risk factor for T1D, and the original reported associations have been replicated, refined, and expanded. Even with the remarkable progress through 50 years and over 5,000 reports, a comprehensive understanding of all effects of HLA on T1D remains elusive. This report represents a summary of the field as it evolved and as it stands now, enumerating many past and present challenges, and suggests possible paradigm shifts for moving forward with future studies in hopes of finally understanding all the ways in which HLA influences the pathophysiology of T1D.

IOS-1002, a Stabilized HLA-B57 Open Format, Exerts Potent Anti-Tumor Activity

HLA-B27 and HLA-B57 are associated with autoimmunity and long-term viral control and protection against HIV and HCV infection; however, their role in cancer immunity remains unknown. HLA class I molecules interact with innate checkpoint receptors of the LILRA, LILRB and KIR families present in diverse sets of immune cells. Here, we demonstrate that an open format (peptide free conformation) and expression- and stability-optimized HLA-B57-B2m-IgG4_Fc fusion protein (IOS-1002) binds to human leukocyte immunoglobulin-like receptor B1 and B2 (LILRB1 and LILRB2) and to killer immunoglobulin-like receptor 3DL1 (KIR3DL1). In addition, we show that the IgG4 Fc backbone is required for engagement to Fcγ receptors and potent activation of macrophage phagocytosis. IOS-1002 blocks the immunosuppressive ITIM and SHP1/2 phosphatase signaling cascade, reduces the expression of immunosuppressive M2-like polarization markers of macrophages and differentiation of monocytes to myeloid-derived suppressor cells, enhances tumor cell phagocytosis in vitro and potentiates activation of T and NK cells. Lastly, IOS-1002 demonstrates efficacy in an ex vivo patient-derived tumor sample tumoroid model. IOS-1002 is a first-in-class multi-target and multi-functional human-derived HLA molecule that activates anti-tumor immunity and is currently under clinical evaluation.

The Potential Role of the Leucocyte Immunoglobulin-Like Receptors in Kidney Transplant Rejection: A Mini Review

Antibody-mediated rejection (ABMR) remains one of the main causes of long-term graft failure after kidney transplantation, despite the development of powerful immunosuppressive therapy. A detailed understanding of the complex interaction between recipient-derived immune cells and the allograft is therefore essential. Until recently, ABMR mechanisms were thought to be solely caused by adaptive immunity, namely, by anti-human leucocyte antigen (HLA) donor-specific antibody. However recent reports support other and/or additive mechanisms, designating monocytes/macrophages as innate immune contributors of ABMR histological lesions. In particular, in mouse models of experimental allograft rejection, monocytes/macrophages are readily able to discriminate non-self via paired immunoglobulin receptors (PIRs) and thus accelerate rejection. The human orthologs of PIRs are leukocyte immunoglobulin-like receptors (LILRs). Among those, LILRB3 has recently been reported as a potential binder of HLA class I molecules, shedding new light on LILRB3 potential as a myeloid mediator of allograft rejection. In this issue, we review the current data on the role of LILRB3 and discuss the potential mechanisms of its biological functions.

Identification of the hybrid gene LILRB5-3 by long-read sequencing and implication of its novel signaling function

Leukocyte immunoglobulin (Ig)-like receptors (LILRs) on human chromosome 19q13.4 encode 11 immunoglobulin superfamily receptors, exhibiting genetic diversity within and between human populations. Among the LILR genes, the genomic region surrounding LILRB3 and LILRA6 has yet to be fully characterized due to their significant sequence homology, which makes it difficult to differentiate between them. To examine the LILRB3 and LILRA6 genomic region, a tool named JoGo-LILR CN Caller, which can call copy number from short-read whole genome sequencing (srWGS) data, was applied to an extensive international srWGS dataset comprising 2,504 samples. During this process, a previously unreported loss of both LILRB3 and LILRA6 was detected in three samples. Using long-read sequencing of these samples, we have discovered a novel large deletion (33,692 bp) in the LILRB3 and LILRA6 genomic regions in the Japanese population. This deletion spanned three genes, LILRB3, LILRA6, and LILRB5, resulting in LILRB3 exons 12-13 being located immediately downstream of LILRB5 exons 1-12 with the loss of LILRA6, suggesting the potential expression of a hybrid gene between LILRB5 and LILRB3 (LILRB5-3). Transcription and subsequent translation of the LILRB5-3 hybrid gene were also verified. The hybrid junction was located within the intracellular domain, resulting in an LILRB5 extracellular domain fused to a partial LILRB3 intracellular domain with three immunoreceptor tyrosine-based inhibitory motifs (ITIMs), suggesting that LILRB5-3 acquired a novel signaling function. Further application of the JoGo-LILR tool to srWGS samples suggested the presence of the LILRB5-3 hybrid gene in the CEU population. Our findings provide insight into the genetic and functional diversity of the LILR family.

LILRB4 Checkpoint for Immunotherapy: Structure, Mechanism and Disease Targets

LILRB4, a myeloid inhibitory receptor belonging to the family of leukocyte immunoglobulin-like receptors (LILRs/LIRs), plays a pivotal role in the regulation of immune tolerance. LILRB4 primarily mediates suppressive immune responses by transmitting inhibitory signals through immunoreceptor tyrosine-based inhibitory motifs (ITIMs). This immune checkpoint molecule has gained considerable attention due to its potent regulatory functions. Its ability to induce effector T cell dysfunction and promote T suppressor cell differentiation has been demonstrated, indicating the therapeutic potential of LILRB4 for modulating excessive immune responses, particularly in autoimmune diseases or the induction of transplant tolerance. Additionally, through intervening with LILRB4 molecules, immune system responsiveness can be adjusted, representing significant value in areas such as cancer treatment. Thus, LILRB4 has emerged as a key player in addressing autoimmune diseases, transplant tolerance induction, and other medical issues. In this review, we provide a comprehensive overview of LILRB4, encompassing its structure, expression, and ligand molecules as well as its role as a tolerance receptor. By exploring the involvement of LILRB4 in various diseases, its significance in disease progression is emphasized. Furthermore, we propose that the manipulation of LILRB4 represents a promising immunotherapeutic strategy and highlight its potential in disease prevention, treatment and diagnosis.