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Exciting progress in the field of cancer immunotherapy has renewed the urgency of the need for basic studies of immunoregulation in both adaptive cell lineages and innate cell lineages. Here we found a central role for major histocompatibility complex (MHC) class I in controlling the phagocytic function of macrophages. Our results demonstrated that expression of the common MHC class I component β 2 -microglobulin (β2M) by cancer cells directly protected them from phagocytosis. We further showed that this protection was mediated by the inhibitory receptor LILRB1, whose expression was upregulated on the surface of macrophages, including tumor-associated macrophages. Disruption of either MHC class I or LILRB1 potentiated phagocytosis of tumor cells both in vitro and in vivo , which defines the MHC class I–LILRB1 signaling axis as an important regulator of the effector function of innate immune cells, a potential biomarker for therapeutic response to agents directed against the signal-regulatory protein CD47 and a potential target of anti-cancer immunotherapy. Host cells display ‘don’t eat me’ signals to protect themselves from phagocytosis. Maute and colleagues identify a novel ‘don’t eat me’ system based on recognition of MHC class I by the phagocyte-expressed inhibitory molecule LILRB1.

The Plasmodium species that cause malaria are obligate intracellular parasites, and disease symptoms occur when these parasites replicate in human blood. Despite the risk of immune detection, the parasite delivers proteins that bind to host receptors on the cell surfaces of infected erythrocytes. In the causative parasite of the most deadly form of malaria in humans, Plasmodium falciparum , RIFINs form the largest family of surface proteins displayed by erythrocytes 1 . Some RIFINs can bind to inhibitory immune receptors, and these RIFINs act as targets for unusual antibodies that contain a LAIR1 ectodomain 2 – 4 or as ligands for LILRB1 5 . RIFINs stimulate the activation of and signalling by LILRB1 5 , which could potentially lead to the dampening of human immune responses. Here, to understand how RIFINs activate LILRB1-mediated signalling, we determine the structure of a RIFIN bound to LILRB1. We show that this RIFIN mimics the natural activating ligand of LILRB1, MHC class I, in its LILRB1-binding mode. A single mutation in the RIFIN disrupts the complex, blocks LILRB1 binding of all tested RIFINs and abolishes signalling in a reporter assay. In a supported lipid bilayer system, which mimics the activation of natural killer (NK) cells by antibody-dependent cell-mediated cytotoxicity, both RIFIN and MHC are recruited to the immunological synapse of NK cells and reduce the activation of NK cells, as measured by the mobilization of perforin. Therefore, LILRB1-binding RIFINs mimic the binding mode of the natural ligand of LILRB1 and suppress the function of NK cells. The structure of a RIFIN–LILRB1 complex reveals that a subset of RIFINs of Plasmodium falciparum mimics the binding mode of the natural ligand of human LILRB1 and suppress the function of natural killer cells in humans.

Multiple myeloma (MM) is a hematologic malignancy characterized by uncontrolled proliferation of plasma cells in the bone marrow. MM patients with aggressive progression have poor survival, emphasizing the urgent need for identifying new therapeutic targets. Here, we show that the leukocyte immunoglobulin-like receptor B1 (LILRB1), a transmembrane receptor conducting negative immune response, is a top-ranked gene associated with poor prognosis in MM patients. LILRB1 deficiency inhibits MM progression in vivo by enhancing the ferroptosis of MM cells. Mechanistic studies reveal that LILRB1 forms a complex with the low-density lipoprotein receptor (LDLR) and LDLR adapter protein 1 (LDLRAP1) to facilitate LDL/cholesterol uptake. Loss of LILRB1 impairs cholesterol uptake but activates the de novo cholesterol synthesis pathway to maintain cellular cholesterol homeostasis, leading to the decrease of anti-ferroptotic metabolite squalene. Our study uncovers the function of LILRB1 in regulating cholesterol metabolism and protecting MM cells from ferroptosis, implicating LILRB1 as a promising therapeutic target for MM patients. Patients with multiple myeloma need new therapeutic targets. The authors identify the transmembrane receptor LILRB1 as a potential target as it protects myeloma cells from ferroptosis by facilitating cholesterol uptake and maintaining cholesterol homeostasis and squalene levels.

CD19 CAR-T cells have established a new standard for relapsed/refractory B-cell malignancies. However, the treatment fails in 50% of patients, often due to CD19 antigen loss. Alternative immunotherapies targeting other antigens are being tested but show limited efficacy, especially in cases of lineage switching or loss of B-cell phenotype, highlighting the need for novel targets. Herein, we identified leukocyte-immunoglobulin-like-receptor-B1 (LILRB1, CD85j) as a novel target for CAR-T cells through cell surface proteomics on patient-derived samples of high-risk B-cell acute lymphoblastic leukemia (B-ALL). LILRB1, an immune inhibitory receptor, is normally expressed only on monocytes and B-cells. We observed stable LILRB1 expression in B-ALL and B-cell non-Hodgkin lymphoma (B-NHL), even after CD20/CD19-based immunotherapies. LILRB1 CAR-T cells showed antigen-specific antitumor activity in vitro against B-ALL/B-NHL cells, including those resistant to CD19 CAR-T-cells, and in vivo in B-ALL xenografts. Additionally, we identified LILRB1 in monocytic acute myeloid leukemia (AML) and demonstrated LILRB1 CAR-T cell cytotoxicity against AML cell lines in vitro and in vivo. These findings establish LILRB1 as a novel target for cancer immunotherapy and show evidence for the preclinical efficacy of LILRB1 CAR-T cells against haematological malignancies, including cases resistant to previous lines of immunotherapy, thus holding promise for further clinical development.

Immune checkpoint blockades (ICBs) have revolutionized cancer therapy through unleashing anti-tumor adaptive immunity. Despite that, they are usually effective only in a small subset of patients and relapse can occur in patients who initially respond to the treatment. Recent breakthroughs in this field have identified innate immune checkpoints harnessed by cancer cells to escape immunosurveillance from innate immunity. MHC1 appears to be such a molecule expressed on cancer cells which can transmit a negative signal to innate immune cells through interaction with leukocyte immunoglobulin like receptor B1 (LILRB1). The review aims to summarize the current understanding of MHC1/LILRB1 axis on mediating cancer immune evasion with an emphasis on the therapeutic potential to block this axis for cancer therapy. Nevertheless, one should note that this field is still in its infancy and more studies are warranted to further verify the effectiveness and safety in clinical as well as the potential to combine with existing immune checkpoints.

Tumor immune escape is associated with both, the expression of immune checkpoint molecules on peripheral immune cells and soluble forms of the human leukocyte antigen-G (HLA-G) in the blood, which are consequently discussed as clinical biomarker for disease status and outcome of cancer patients. HLA-G preferentially interacts with the inhibitory receptor immunoglobulin-like transcript (ILT) receptor-2 in the blood and can be secreted as free soluble molecules (sHLA-G) or via extracellular vesicles (EV). To investigate the contribution of these two forms to the expression of checkpoint molecules in peripheral blood, we primed peripheral blood mononuclear cells with purified soluble sHLA-G1 protein, or EV preparations derived from SUM149 cells transfected with membrane-bound HLA-G1 or control vector prior to anti-CD3/CD28 T cell activation. Our study demonstrated that priming of PBMC with sHLA-G1 protein prior to 48 h activation resulted in enhanced frequencies of ILT-2 expressing CD8 T cells, and in an upregulation of immune checkpoint molecules CTLA-4, PD-1, TIM-3, and CD95 exclusively on ILT-2 positive CD8 T cells. In contrast, when PBMC were primed with EV (containing HLA-G1 or not) upregulation of CTLA-4, PD-1, TIM-3, and CD95 occurred exclusively on ILT-2 negative CD8 T cells. Taken together, our data suggest that priming with sHLA-G forms induces a pronounced immunosuppressive/exhausted phenotype and that priming with sHLA-G1 protein or EV derived from HLA-G1 positive or negative SUM149 cells affects CD8 T cells complementary by targeting either the ILT-2 positive or negative subpopulation, respectively, after T cell activation.

Human leukocyte antigen E (HLA-E) communicates cellular health to natural killer (NK) cells through presentation of peptides derived from the leader sequence of classical major histocompatibility complex class I (MHC-I), inhibiting NK cell activation and lysis of healthy cells. Besides this canonical role, HLA-E can also present peptides from pathogens such as Mycobacterium tuberculosis (Mtb) to T cells and can inhibit phagocytosis by engaging with LILRB1/2. To identify additional HLA-E binding surface molecules, we utilized a CRISPR/Cas9 activation screen with HLA-E tetramers, which identified Stabilin (STAB)1 and STAB2 as novel interactors. This interaction depended on the nature of the peptide/HLA-E complex, whereby high affinity peptides did not permit the interaction while low affinity peptides did. Functionally, expression of STAB1 or STAB2 on THP-1 monocytes increased phagocytic uptake of HLA-E coated microbeads. These results provide the first evidence of an interaction between Stabilin receptors and specific HLA-E conformations.

Human leukocyte antigen (HLA)-G is a nonclassical HLA class I molecule that has an immunosuppressive effect mediated by binding to immune inhibitory leukocyte immunoglobulin-like receptors (LILR) B1 and LILRB2. A conventional HLA-G isoform, HLA-G1, forms a heterotrimeric complex composed of a heavy chain (α1-α3 domains), β2-microglobulin (β2m) and a cognate peptide. One of the other isoforms, HLA-G2, lacks a α2 domain or β2m to form a nondisulfide-linked homodimer, and its ectodomain specifically binds to LILRB2 expressed in human monocytes, macrophages, and dendritic cells. The administration of the ectodomain of HLA-G2, designated the soluble HLA-G2 homodimer, showed significant immunosuppressive effects in mouse models of rheumatoid arthritis and systemic lupus erythematosus, presumably by binding to a mouse ortholog of LILRB2, paired immunoglobulin-like receptor B. However, the refolded soluble HLA-G2 homodimer used in these studies tends to aggregate and degrade; thus, its stability for clinical use has been a concern. In the present study, we improved the stability of the refolded soluble HLA-G2 homodimer via a site-directed PEGylation method. PEGylation at an original free cysteine residue, Cys42, resulted in increased lyophilization and thermal and serum stability. Furthermore, the PEGylated soluble HLA-G2 homodimer could better suppress atopic symptoms in mice than the non-PEGylated homodimer. These results suggest that PEGylated soluble HLA-G2 homodimers could be candidates for immunosuppressive biologics that specifically target LILRB2-positive myelomonocytic antigen-presenting cells.

Background Leukocyte immunoglobulin-like receptor subfamily B (LILRB), including 5 subtypes, is a group of inhibitory receptors in the immune system. The LILRB family is known to be involved in the tumor progression of various cancer types, especially liver cancer. However, the expression patterns and prognostic values of LILRB family members in liver cancer tissues remain unclear. Methods We used the Oncomine database, GEPIA database, Kaplan–Meier Plotter, Timer, and TISIDB to assess the expression and prognostic value of the LILRB family in liver cancer patients. We also verified the expression of the LILRB family in tumor tissues and tumor-free liver tissues at the protein level by using immunohistochemistry. The STRING website was used to explore the interaction between the LILRB family and their related genes. The DAVID database was used to perform the gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Flow cytometry was used to assess the infiltrated NK cells in liver cancer tissues. Results Our study revealed that the mRNA expression of LILRB1, LILRB2, LILRB3, and LILRB5 was downregulated, while compared with normal tissues, the mRNA expression of LILRB4 was upregulated in liver cancer tissues. Survival analysis revealed that LILRB2 and LILRB5 mRNA expression levels were significantly positively associated with overall survival (OS) and disease-free survival (DSS) and that the mRNA expression of all LILRB family members was significantly positively correlated with recurrence-free survival (RFS) and progression-free survival (PFS). Next, we further found that the mRNA expression of all LILRB family members was significantly associated with the infiltration of B cells, CD8 + T cells, CD4 + T cells, macrophages, neutrophils, and dendritic cells in liver cancer. Finally, GO and KEGG analyses found that the LILRB family and its related genes were involved in antigen processing and presentation and natural killer cell-mediated cytotoxicity pathways. Conclusions Our study suggested that LILRB family expression was associated with the prognosis of liver cancer patients and infiltrated immune cells. The LILRB family might be involved in antigen processing and presentation and natural killer cell-mediated cytotoxicity pathways.

Problem. Natural killer (NK) cells are the most abundant leukocyte population in the uterus. The interactions of the maternal NK expression of killer cell immunoglobulin-like receptors (KIRs) and human inhibitory receptor Ig-like transcript (ILT) with fetal HLA determine the activation of NK cells and pregnancy outcomes. Moreover, dNK cells release numerous angiogenic factors including VEGF. Our previous study showed that sildenafil citrate (SC) significantly decreased peripheral blood NK (pbNK) cell activity and improved intrauterine blood flow, which correlated with a successful pregnancy outcome. Thus, in this study, we investigated whether SC influenced the expression of KIR or ILT receptors on induced decidual NK (idNK), the apoptosis of cells, and VEGF-A production in the culture supernatants of idNK cells. Method of Study. pbNK cells from 24 healthy women and 23 women with RPL were converted to idNK cells under hypoxia, IL-15, and TGF-β conditions. The cultures were prepared with or without SC. Changes in KIR2DL1 (CD158a), NKG2A (CD159a), ILT-2 (CD85j), and ILT-4 (CD85d) expression on CD56+CD16- cells and their apoptosis were determined via flow cytometry. VEGF-A level was established in culture supernatants with the ELISA method. Results. KIR2DL1 and ILT-2 expression on idNK cells was higher in healthy women than in RPL patients. Sildenafil enhanced NKG2A expression in RPL patients. VEGF concentration was higher in fertile woman idNK cell cultures. idNK cells were more sensitive for necrosis in RPL than in fertile women. SC did not influence VEGF production or idNK cell apoptosis. Conclusions. A combination of hypoxia, IL-15, and AZA promotes the conversion of pbNK into idNK cells CD56+CD16--expressing KIR receptors and produces VEGF. Alterations in KIR2DL1 and ILT-2 expression as well as impaired VEGF production were associated with RPL. SC affects NKG2A expression on RPL idNK cells. SC had no effect on VEGF release or idNK cell apoptosis.