LILRB4 on multiple myeloma cells promotes bone lesion by p-SHP2/NF-κB/RELT signal pathway.

BACKGROUND: Leukocyte Ig-like receptor B family 4 (LILRB4) as an immune checkpoint on myeloid cells is a potential target for tumor therapy. Extensive osteolytic bone lesion is the most characteristic feature of multiple myeloma. It is unclear whether ectopic LILRB4 on multiple myeloma regulates bone lesion. METHODS: The conditioned medium (CM) from LILRB4-WT and -KO cells was used to analyze the effects of LILRB4 on osteoclasts and osteoblasts. Xenograft, syngeneic and patient derived xenograft models were constructed, and micro-CT, H&E staining were used to observe the bone lesion. RNA-seq, cytokine array, qPCR, the activity of luciferase, Co-IP and western blotting were used to clarify the mechanism by which LILRB4 mediated bone damage in multiple myeloma. RESULTS: We comprehensively analyzed the expression of LILRB4 in various tumor tissue arrays, and found that LILRB4 was highly expressed in multiple myeloma samples. The patient's imaging data showed that the higher the expression level of LILRB4, the more serious the bone lesion in patients with multiple myeloma. The conditioned medium from LILRB4-WT not -KO cells could significantly promote the differentiation and maturation of osteoclasts. Xenograft, syngeneic and patient derived xenograft models furtherly confirmed that LILRB4 could mediate bone lesion of multiple myeloma. Next, cytokine array was performed to identify the differentially expressed cytokines, and RELT was identified and regulated by LILRB4. The overexpression or exogenous RELT could regenerate the bone damage in LILRB4-KO cells in vitro and in vivo. The deletion of LILRB4, anti-LILRB4 alone or in combination with bortezomib could significantly delay the progression of bone lesion of multiple myeloma. CONCLUSIONS: Our findings indicated that LILRB4 promoted the bone lesion by promoting the differentiation and mature of osteoclasts through secreting RELT, and blocking LILRB4 singling pathway could inhibit the bone lesion.

Fc gamma receptors promote antibody-induced LILRB4 internalization and immune regulation of monocytic AML.

The immune checkpoint leukocyte immunoglobulin-like receptor B4 (LILRB4) is found specifically on the cell surface of acute monocytic leukemia (monocytic AML), an aggressive and common subtype of AML. We have developed a humanized monoclonal IgG1 LILRB4-blocking antibody (h128-3), which improved immune regulation but reduced cell surface expression of LILRB4 in monocytic AML models by 40-60%. Interestingly, most of this effect was neutralized by mutation of the Fc region of the antibody (h128-3/N297A), which prevents interaction with Fc gamma receptors (FcγRs). This suggested that there is FcγR-dependent antigenic modulation underlying h128-3's effects, a mechanism known to alter the function of antibodies targeting B-cell malignancies. We disrupted the Fc-FcγR interaction pharmacologically and with stable CRISPR-Cas9-mediated genetic knockout of FcγRs in monocytic AML cell lines to investigate the role of FcγR-dependent antigenic modulation in the regulation of LILRB4 by h128-3. When FcγRI is inhibited or removed from the surface of monocytic AML cells, h128-3 cannot optimally perform its blocking function, resulting in activation of the LILRB4 inhibitory receptor and leading to a 15-25% decrease in T-cell-mediated cytotoxicity in vitro. In the absence of FcγRI, scaffolding by FcγRIIa allows h128-3 to maintain LILRB4-blocking function. Here we define a FcγR-dependent antigenic modulation mechanism underlying the function of an immunoreceptor blocking antibody for the first time in myeloid malignancy. This research will facilitate the development of safe, precision-targeted antibody therapeutics in myeloid malignancies with greater potency and efficacy.

LILRB3 Supports Immunosuppressive Activity of Myeloid Cells and Tumor Development.

The existing T cell-centered immune checkpoint blockade therapies have been successful in treating some but not all patients with cancer. Immunosuppressive myeloid cells, including myeloid-derived suppressor cells (MDSC), that inhibit antitumor immunity and support multiple steps of tumor development are recognized as one of the major obstacles in cancer treatment. Leukocyte Ig-like receptor subfamily B3 (LILRB3), an immune inhibitory receptor containing tyrosine-based inhibitory motifs (ITIM), is expressed solely on myeloid cells. However, it is unknown whether LILRB3 is a critical checkpoint receptor in regulating the activity of immunosuppressive myeloid cells, and whether LILRB3 signaling can be blocked to activate the immune system to treat solid tumors. Here, we report that galectin-4 and galectin-7 induce activation of LILRB3 and that LILRB3 is functionally expressed on immunosuppressive myeloid cells. In some samples from patients with solid cancers, blockade of LILRB3 signaling by an antagonistic antibody inhibited the activity of immunosuppressive myeloid cells. Anti-LILRB3 also impeded tumor development in myeloid-specific LILRB3 transgenic mice through a T cell-dependent manner. LILRB3 blockade may prove to be a novel approach for immunotherapy of solid cancers.

Mapping the protein-protein interactome in the tumor immune microenvironment.

The cell-to-cell communication primarily occurs through cell-surface and secreted proteins, which form a sophisticated network that coordinates systemic immune function. Uncovering these protein-protein interactions (PPIs) is indispensable for understanding the molecular mechanism and elucidating immune system aberrances under diseases. Traditional biological studies typically focus on a limited number of PPI pairs due to the relative low throughput of commonly used techniques. Encouragingly, classical methods have advanced, and many new systems tailored for large-scale protein-protein screening have been developed and successfully utilized. These high-throughput PPI investigation techniques have already made considerable achievements in mapping the immune cell interactome, enriching PPI databases and analysis tools, and discovering therapeutic targets for cancer and other diseases, which will definitely bring unprecedented insight into this field.

The Metabolism and Immune Environment in Diffuse Large B-Cell Lymphoma.

Cells utilize different metabolic processes to maintain their growth and differentiation. Tumor cells have made some metabolic changes to protect themselves from malnutrition. These metabolic alterations affect the tumor microenvironment and macroenvironment. Developing drugs targeting these metabolic alterations could be a good direction. In this review, we briefly introduce metabolic changes/regulations of the tumor macroenvironment and microenvironment and summarize potential drugs targeting the metabolism in diffuse large B-cell lymphoma.

Neutrophils as key regulators of tumor immunity that restrict immune checkpoint blockade in liver cancer.

OBJECTIVE: Liver cancer is a deadly malignancy associated with high mortality and morbidity. Less than 20% of patients with advanced liver cancer respond to a single anti-PD-1 treatment. The high heterogeneity of neutrophils in the tumor immune microenvironment in liver cancer may contribute to resistance to immune checkpoint blockade (ICB). However, the underlying mechanism remains largely unknown. METHODS: We established an orthotopic liver cancer model by using transposable elements to integrate the oncogenes Myc and KrasG12D into the genome in liver cells from conditional Trp53 null/null mice (pTMK/Trp53-/-). Flow cytometry and immunohistochemistry were used to assess the changes in immune cells in the tumor microenvironment. An ex vivo coculture assay was performed to test the inhibitory effects of tumor-associated neutrophils (TANs) on CD8+ T cells. The roles of neutrophils, T cells, and NK cells were validated through antibody-mediated depletion. The efficacy of the combination of neutrophil depletion and ICB was evaluated. RESULTS: Orthotropic pTMK/Trp53-/- mouse liver tumors displayed a moderate response to anti-Ly6G treatment but not PD-1 blockade. Depletion of neutrophils increased the infiltration of CD8+ T cells and decreased the number of exhausted T cells in the tumor microenvironment. Furthermore, depletion of either CD8+ T or NK cells abrogated the antitumor efficacy of anti-Ly6G treatment. Moreover, the combination of anti-Ly6G with anti-PD-L1 enhanced the infiltration of cytotoxic CD8+ T cells and thereafter resulted in a significantly greater decrease in tumor burden. CONCLUSIONS: Our data suggest that TANs may contribute to the resistance of liver cancer to ICB, and combining TAN depletion with T cell immunotherapy synergistically increases antitumor efficacy.

IgG4-related ophthalmic disease masquerading as ciliary body tumors and scleritis in both eyes: a case report.

BACKGROUND: To report a rare case of IgG4-related ophthalmic disease (IgG4-ROD) manifesting as intraocular masses and scleritis in both eyes in a 61-year-old male and to investigate the changes in multimodal imaging features of the lesion sites and helper T-cell type 1 (Th 1)/Th 2/Th 17 cytokine levels in the aqueous humor. CASE PRESENTATION: A patient with IgG4-ROD seemingly manifested with an intraocular tumor in the left eye and sequentially, with an inflammatory mass in the ciliary body and scleritis in the right eye. The patient complained of vision loss of 6 months duration in the left eye at his first visit. With a preliminary diagnosis of an intraocular tumor, enucleation of the left eyeball and histopathological examination were performed. Approximately 3 months later, the patient started to experience headache, eye pain, and declining vision in the right eye. Ophthalmic imaging revealed a ciliary mass and scleritis. Th 1/Th 2/Th 17 cytokine levels and multimodal imaging findings were analyzed before and after corticosteroid treatment. Histopathological examination and immunohistochemistry (IHC) of the enucleated left eye demonstrated lymphoplasmacytic infiltration with an IgG4+/IgG+ cell ratio of approximately 40%, pointing to the diagnosis of probable IgG4-ROD. Long-term treatment with corticosteroids led to significant improvement in the signs and symptoms of the left eye. Th 1/Th 2/Th 17 cytokine profile monitoring of the aqueous humor and multimodal imaging of the right eye showed gradual regression of the mass and attenuation of ocular inflammation during treatment. CONCLUSIONS: Patients with an atypical presentation of IgG4-ROD, such as intraocular masses and scleritis, are likely to experience a significant delay in diagnosis. This case demonstrates the significance of IgG4-ROD in the differential diagnosis of intraocular tumors and ocular inflammation. IgG4-RD is a newly diagnosed disease with multi-organ involvement and little is known about its pathogenesis, particularly in the eye. The present case will open new challenges in the clinico-pathological diagnosis and research of this disease. Combined investigations of multimodal imaging and cytokine level detection of intraocular fluid provide a new and effective way to monitor disease progression.

Cell atlas of the immune microenvironment in gastrointestinal cancers: Dendritic cells and beyond.

Gastrointestinal (GI) cancers occur in the alimentary tract and accessory organs. They exert a global burden with high morbidity and mortality. Inside the tumor microenvironment, dendritic cells (DCs) are the most efficient antigen-presenting cells and are necessary for adaptive immune responses such as T and B-cell maturation. However, the subsets of DCs revealed before were mostly based on flow cytometry and bulk sequencing. With the development of single-cell RNA sequencing (scRNA-seq), the tumor and microenvironment heterogeneity of GI cancer has been illustrated. In this review, we summarize the classification and development trajectory of dendritic cells at the single-cell level in GI cancer. Additionally, we focused on the interaction of DCs with T cells and their effect on the response to immunotherapy. Specifically, we focused on the newly identified tumor-infiltrating dendritic cells and discuss their potential function in antitumor immunity.

Myeloid checkpoints for cancer immunotherapy.

Myeloid checkpoints are receptors on the myeloid cell surface which can mediate inhibitory signals to modulate anti-tumor immune activities. They can either inhibit cellular phagocytosis or suppress T cells and are thus involved in the pathogenesis of various diseases. In the tumor microenvironment, besides killing tumor cells by phagocytosis or activating anti-tumor immunity by tumor antigen presentation, myeloid cells could execute pro-tumor efficacies through myeloid checkpoints by interacting with counter-receptors on other immune cells or cancer cells. In summary, myeloid checkpoints may be promising therapeutic targets for cancer immunotherapy.

Liver tumour immune microenvironment subtypes and neutrophil heterogeneity.

The heterogeneity of the tumour immune microenvironment (TIME), organized by various immune and stromal cells, is a major contributing factor of tumour metastasis, relapse and drug resistance1-3, but how different TIME subtypes are connected to the clinical relevance in liver cancer remains unclear. Here we performed single-cell RNA-sequencing (scRNA-seq) analysis of 189 samples collected from 124 patients and 8 mice with liver cancer. With more than 1 million cells analysed, we stratified patients into five TIME subtypes, including immune activation, immune suppression mediated by myeloid or stromal cells, immune exclusion and immune residence phenotypes. Different TIME subtypes were spatially organized and associated with chemokine networks and genomic features. Notably, tumour-associated neutrophil (TAN) populations enriched in the myeloid-cell-enriched subtype were associated with an unfavourable prognosis. Through in vitro induction of TANs and ex vivo analyses of patient TANs, we showed that CCL4+ TANs can recruit macrophages and that PD-L1+ TANs can suppress T cell cytotoxicity. Furthermore, scRNA-seq analysis of mouse neutrophil subsets revealed that they are largely conserved with those of humans. In vivo neutrophil depletion in mouse models attenuated tumour progression, confirming the pro-tumour phenotypes of TANs. With this detailed cellular heterogeneity landscape of liver cancer, our study illustrates diverse TIME subtypes, highlights immunosuppressive functions of TANs and sheds light on potential immunotherapies targeting TANs.

Blocking LAIR1 signaling in immune cells inhibits tumor development.

The current immune checkpoint blockade therapy has been successful in treating some cancers but not others. New molecular targets and therapeutic approaches of cancer immunology need to be identified. Leukocyte associated immunoglobulin like receptor 1 (LAIR1) is an immune inhibitory receptor expressing on most immune cell types. However, it remains a question whether we can specifically and actively block LAIR1 signaling to activate immune responses for cancer treatment. Here we report the development of specific antagonistic anti-LAIR1 monoclonal antibodies and studied the effects of LAIR1 blockade on the anti-tumor immune functions. The anti-LAIR1 antagonistic antibody stimulated the activities of T cells, natural killer cells, macrophages, and dendritic cells in vitro. The single-cell RNA sequencing analysis of intratumoral immune cells in syngeneic human LAIR1 transgenic mice treated with control or anti-LAIR1 antagonist antibodies indicates that LAIR1 signaling blockade increased the numbers of CD4 memory T cells and inflammatory macrophages, but decreased those of pro-tumor macrophages, regulatory T cells, and plasmacytoid dendritic cells. Importantly, the LAIR1 blockade by the antagonistic antibody inhibited the activity of immunosuppressive myeloid cells and reactivated T cells from cancer patients in vitro and impeded tumor metastasis in a humanized mouse model. Blocking LAIR1 signaling in immune cells represents a promising strategy for development of anti-cancer immunotherapy.

LILRB4, an immune checkpoint on myeloid cells.

Leukocyte immunoglobulin-like receptor B4 (LILRB4) is an inhibitory receptor in the LILR family mainly expressed on normal and malignant human cells of myeloid origin. By binding to ligands, LILRB4 is activated and subsequently recruits adaptors to cytoplasmic immunoreceptor tyrosine inhibitory motifs to initiate different signaling cascades, thus playing an important role in physiological and pathological conditions, including autoimmune diseases, microbial infections, and cancers. In normal myeloid cells, LILRB4 regulates intrinsic cell activation and differentiation. In disease-associated or malignant myeloid cells, LILRB4 is significantly correlated with disease severity or patient survival and suppresses T cells, thereby participating in the pathogenesis of various diseases. In summary, LILRB4 functions as an immune checkpoint on myeloid cells and may be a promising therapeutic target for various human immune diseases, especially for cancer immunotherapy.

LncRNA LPAL2/miR-1287-5p/EGFR Axis Modulates TED-Derived Orbital Fibroblast Activation Through Cell Adhesion Factors.

CONTEXT: The activation of orbital fibroblasts, the prime targets in thyroid eye disease (TED), is central to its underlying pathogenesis. OBJECTIVE: We aimed to investigate the mechanism of TED orbital fibroblast activation from the perspective of noncoding RNA regulation. METHODS: Immunofluorescence (IF) staining was applied to evaluate the fibrotic changes in target cells. Cell proliferation was evaluated by 5-ethoxy 2-deoxyuridine and colony-formation assays. Collagen I concentration was determined by enzyme-linked immunosorbent assay. Human microarray analysis was performed on 3 TED and 3 healthy control orbital tissue samples. RESULTS: Bioinformatics analysis showed that cell adhesion signaling factors were differentially expressed in TED tissues, including intercellular adhesion molecule (ICAM)-1, ICAM-4, vascular cell adhesion molecule, and CD44, which were all upregulated in diseased orbital tissues. Long noncoding RNA LPAL2 level was also upregulated in orbital tissues and positively correlated with ICAM-1 and ICAM-4 expression. Stimulation of the TED orbital fibroblasts by transforming growth factor-ß1 (TGF-ß1) significantly increased the expression of ICAM-1, ICAM-4, and LPAL2. Knockdown of LPAL2 in orbital fibroblasts inhibited TGF-ß1-induced increases in cell adhesion factor levels and orbital fibroblast activation. Microarray profiling was performed on TED and normal orbital tissues to identify differentially expressed microRNAs, and miR-1287-5p was remarkably reduced within diseased orbital samples. miR-1287-5p was directly bound to the epidermal growth factor receptor (EGFR) 3' untranslated region and LPAL2, and LPAL2 modulated EGFR/protein kinase B (AKT) signaling through targeting miR-1287-5p. CONCLUSION: The LPAL2/miR-1287-5p axis modulated TGF-ß1-induced increases in cell adhesion factor levels and TED orbital fibroblast activation through EGFR/AKT signaling.

Silencing of LINE-1 retrotransposons is a selective dependency of myeloid leukemia.

Transposable elements or transposons are major players in genetic variability and genome evolution. Aberrant activation of long interspersed element-1 (LINE-1 or L1) retrotransposons is common in human cancers, yet their tumor-type-specific functions are poorly characterized. We identified MPHOSPH8/MPP8, a component of the human silencing hub (HUSH) complex, as an acute myeloid leukemia (AML)-selective dependency by epigenetic regulator-focused CRISPR screening. Although MPP8 is dispensable for steady-state hematopoiesis, MPP8 loss inhibits AML development by reactivating L1s to induce the DNA damage response and cell cycle exit. Activation of endogenous or ectopic L1s mimics the phenotype of MPP8 loss, whereas blocking retrotransposition abrogates MPP8-deficiency-induced phenotypes. Expression of AML oncogenic mutations promotes L1 suppression, and enhanced L1 silencing is associated with poor prognosis in human AML. Hence, while retrotransposons are commonly recognized for their cancer-promoting functions, we describe a tumor-suppressive role for L1 retrotransposons in myeloid leukemia.

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.

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

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

Leukocyte immunoglobulin-like receptor B1 and B4 (LILRB1 and LILRB4): Highly sensitive and specific markers of acute myeloid leukemia with monocytic differentiation.

BACKGROUND: Acute myeloid leukemia (AML) with monocytic differentiation (M-AML) remains a diagnostic challenge largely due to lack of sensitive and specific markers for immature monocytes. The immunoglobulin-like inhibitory receptors, LILRB1 and LILRB4, are expressed on monocytes but have not yet been systematically evaluated in the clinical setting. METHODS: We evaluated the diagnostic performance of LILRB1 and LILRB4 as monocytic markers for both immature and mature monocytes in comparison to other myelomonocytic markers including CD14, CD15, CD33, CD36, and CD64 in eight cases of control bone marrow (BM, 5) and peripheral blood (PB, 3), 64 cases of (M-AML), and 57 cases of AML without monocytic differentiation (NM-AML) by flow cytometric immunophenotyping. RESULTS: In control BM, LILRB1 and LILRB4 were consistently expressed on monocytes at all stages of maturation, from CD34+ /CD14- monocytic precursors to CD14-/dim+ maturing and CD14+ mature monocytes. In M-AML, LILRB1 and LILRB4 were consistently expressed on monocytes, regardless of the degree of maturity, from CD14-/dim+ monoblasts/promonocytes to CD14+ mature monocytes but were not expressed on myeloblasts. The diagnostic performances as a monocytic marker assessed by sensitivity/specificity were 100%/100% for LILRB1/LILRB4, 100%/82% for CD11b, 80%/100% for CD14, 100%/81% for CD64, 100%/58% for CD15/CD33, and 89%/97% for CD36/CD64. CONCLUSION: The co-expression of LILRB1/LILRB4 outperformed other myelomonocytic markers as a highly sensitive and specific marker for monocytes at all stages of maturation and could reliably distinguish M-AML from NM-AML. LILRB4 additionally represents a novel therapeutic target for treating M-AML.

LILRB4-targeting Antibody-Drug Conjugates for the Treatment of Acute Myeloid Leukemia.

Acute myeloid leukemia (AML) is the most common and aggressive blood cancer in adults. In particular, significant unmet medical needs exist for effective treatment strategies for acute myelomonocytic leukemia (M4) and acute monocytic leukemia (M5) AML subtypes. Antibody-drug conjugates (ADC) are a promising drug class for AML therapy, as demonstrated by the FDA-approved anti-CD33 ADC, gemtuzumab ozogamicin (Mylotarg). However, CD33 is expressed in normal hematopoietic stem cells, highlighting the critical need to identify AML-specific targets to minimize the risk of potential adverse effects. We have demonstrated that the leukocyte immunoglobulin-like receptor subfamily B4 (LILRB4) is expressed at significantly higher levels on monocytic M4 and M5 AML cells than on normal counterparts. Here, we test whether LILRB4 is a promising ADC target to kill monocytic AML cells while sparing healthy counterparts. To this end, we generated ADCs from a humanized anti-LILRB4 mAb and the antimitotic payload, monomethyl auristatin F. The conjugates constructed were characterized and evaluated for LILRB4-specific cell killing potency, toxicity to progenitor cells, pharmacokinetics, and therapeutic efficacy. Our ADC linker technology platform efficiently generated homogeneous anti-LILRB4 ADCs with defined drug-to-antibody ratios. The homogeneous anti-LILRB4 ADCs demonstrated the capacity for LILRB4-mediated internalization, suitable physicochemical properties, and high cell killing potency against LILRB4-positive AML cells. Importantly, our data indicate that these ADCs spare normal progenitor cells. One of our homogeneous conjugates exerted a remarkable therapeutic effect and no significant toxicity in a xenograft mouse model of disseminated human AML. Our findings highlight the clinical potential of anti-LILRB4 ADCs in monocytic AML therapy.

Antagonistic anti-LILRB1 monoclonal antibody regulates antitumor functions of natural killer cells.

BACKGROUND: Current immune checkpoint blockade strategies have been successful in treating certain types of solid cancer. However, checkpoint blockade monotherapies have not been successful against most hematological malignancies including multiple myeloma and leukemia. There is an urgent need to identify new targets for development of cancer immunotherapy. LILRB1, an immunoreceptor tyrosine-based inhibitory motif-containing receptor, is widely expressed on human immune cells, including B cells, monocytes and macrophages, dendritic cells and subsets of natural killer (NK) cells and T cells. The ligands of LILRB1, such as major histocompatibility complex (MHC) class I molecules, activate LILRB1 and transduce a suppressive signal, which inhibits the immune responses. However, it is not clear whether LILRB1 blockade can be effectively used for cancer treatment. METHODS: First, we measured the LILRB1 expression on NK cells from cancer patients to determine whether LILRB1 upregulated on NK cells from patients with cancer, compared with NK cells from healthy donors. Then, we developed specific antagonistic anti-LILRB1 monoclonal antibodies and studied the effects of LILRB1 blockade on the antitumor immune function of NK cells, especially in multiple myeloma models, in vitro and in vivo xenograft model using non-obese diabetic (NOD)-SCID interleukin-2Rγ-null mice. RESULTS: We demonstrate that percentage of LILRB1+ NK cells is significantly higher in patients with persistent multiple myeloma after treatment than that in healthy donors. Further, the percentage of LILRB1+ NK cells is also significantly higher in patients with late-stage prostate cancer than that in healthy donors. Significantly, we showed that LILRB1 blockade by our antagonistic LILRB1 antibody increased the tumoricidal activity of NK cells against several types of cancer cells, including multiple myeloma, leukemia, lymphoma and solid tumors, in vitro and in vivo. CONCLUSIONS: Our results indicate that blocking LILRB1 signaling on immune effector cells such as NK cells may represent a novel strategy for the development of anticancer immunotherapy.