Leukocyte Ig-Like receptor B1 restrains dendritic cell function through increased expression of the NF-κB regulator ABIN1/TNIP1

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.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

Tumor microenvironmental influences on dendritic cell and T cell function: A focus on clinically relevant immunologic and metabolic checkpoints

Cancer immunotherapy is fast becoming one of the most promising means of treating malignant disease. Cancer vaccines, adoptive cell transfer therapies, and immune checkpoint blockade have all shown varying levels of success in the clinical management of several cancer types in recent years. However, despite the clinical benefits often achieved by these regimens, an ongoing problem for many patients is the inherent or acquired resistance of their cancer to immunotherapy. It is now appreciated that dendritic cells and T lymphocytes both play key roles in antitumor immune responses and that the tumor microenvironment presents a number of barriers to the function of these cells that can ultimately limit the success of immunotherapy. In particular, the engagement of several immunologic and metabolic checkpoints within the hostile tumor microenvironment can severely compromise the antitumor functions of these important immune populations. This review highlights work from both preclinical and clinical studies that has shaped our understanding of the tumor microenvironment and its influence on dendritic cell and T cell function. It focuses on clinically relevant targeted and immunotherapeutic strategies that have emerged from these studies in an effort to prevent or overcome immune subversion within the tumor microenvironment. Emphasis is also placed on the potential of next-generation combinatorial regimens that target metabolic and immunologic impediments to dendritic cell and T lymphocyte function as strategies to improve antitumor immune reactivity and the clinical outcome of cancer immunotherapy going forward.

TNIP1 Inhibits Proliferation And Promotes Apoptosis In Clear Cell Renal Carcinoma Through Targeting C/Ebpβ

Background/Purpose

TNF-α-induced protein 3-interacting protein 1 (TNIP1) is active in various cancers, but its expression and function in renal cell carcinoma (RCC) have not been described. This study investigated the role of TNIP1 in clear cell renal cell carcinomas (ccRCC), which accounts for 75–80% of RCC and has a poor prognosis.

Methods

The expression of TNIP1 in human ccRCC tissues and cells was detected by real-time quantitative reverse transcription–polymerase chain reaction (qRT-PCR), Western blot (WB), and immunohistochemical (IHC) staining. Cell proliferation was assayed by a cell counting kit (CCK)-8 assay; cell cycle analysis and apoptosis assay were done by flow cytometry.

Results

TNIP1 is downregulated in both ccRCC human tissues and cells. Besides, TNIP1 downregulation promoted cell proliferation with more cell cycle entry, and inhibited apoptosis. TNIP1 downregulation was associated with increased of expression of the Bcl-2 anti-apoptosis gene and decreased expression of the Bax apoptosis-promoting gene and cleaved-caspase-3 by negatively regulating C/EBPβ expression.

Conclusion

TNIP1 acted as a tumor-inhibitor in ccRCC by targeting C/EBPβ. The results warrant study of TNIP1 as a potential diagnostic marker and therapeutic target of ccRCC.

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.

TNIP1 Polymorphisms with the Risk of Hepatocellular Carcinoma Based on Chronic Hepatitis B Infection in Chinese Han Population

Chronic hepatitis B virus (HBV) infection is an important etiology for the development of hepatocellular carcinoma (HCC). Tumor necrosis factor-α-induced protein 3-interacting protein 1 (TNIP1) is linked to specific inflammatory diseases as a novel type of endogenous inflammatory regulator. However, presently, rare information is found about the association between TNIP1 polymorphisms and HBV-induced HCC risk. In this case control study, we genotyped four single nucleotide polymorphisms (SNPs) in TNIP1 gene in 248 HCC patients and 242 chronic HBV carriers using Sequenom Mass-ARRAY technology. Genetic model and haplotype analysis were performed to evaluate the association between candidate SNPs polymorphisms and HBV-induced HCC susceptibility using Pearson's χ² test and unconditional logistic regression analysis. Overall, we found two risk alleles in TNIP1 for HBV-induced HCC in patients: the allele "G" of rs7708392 by genotype model ("G/C" vs. "C/C": OR 1.88, 95% CI 1.17-3, P = 0.009) and dominant model ("G/C-G/G" vs. "C/C": OR 1.69, 95% CI 1.08-2.65, P = 0.023), and the allele "C" of rs10036748 by genotype model ("C/T" vs. "T/T": OR 1.83, 95% CI 1.14-2.92, P = 0.012) and dominant model ("C/T-C/C" vs. "T/T": OR 1.65, 95% CI 1.05-2.59, P = 0.03). However, rs3792792 and rs4958881 polymorphisms didn't significantly correlate with the risk of HBV-induced HCC. Haplotype analysis showed no significant association between haplotypes and the HCC risk in HBV carriers. This study provides evidence for HBV-induced HCC susceptibility gene TNIP1 in the Chinese Han population.

The Toxoplasma gondii ME-49 strain upregulates levels of A20 that inhibit NF-κB activation and promotes apoptosis in human leukaemia T-cell lines

Background

Acute T-lymphocyte leukaemia is a form of haematological malignancy with abnormal activation of NF-κB pathway, which results in high expression of A20 and ABIN1, which constitute a negative feedback mechanism for the regulation of NF-κB activation. Clinical studies have found that acute T-lymphocyte leukaemia patients are susceptible to Toxoplasma gondii infection; however, the effect of T. gondii on the proliferation and apoptosis of human leukaemia T-cells remains unclear. Here, we used the T. gondii ME-49 strain to infect human leukaemia T-cell lines Jurkat and Molt-4, to explore the effect of T. gondii on proliferation and apoptosis, which is mediated by NF-κB in human leukaemia T-cells.

Methods

The Tunel assay was used to detect cell apoptosis. Cell Counting Kit-8 was used to detect cell proliferation viability. The apoptosis level and the expression level of NF-κB related proteins in human leukaemia T-cells were detected by flow cytometry and Western blotting.

Results

Western blotting analyses revealed that the T. gondii ME-49 strain increased the expression of A20 and decreased both ABIN1 expression and NF-κB p65 phosphorylation. By constructing a lentiviral-mediated shRNA to knockdown the A20 gene in Jurkat T-cells and Molt-4 T-cells, the apoptosis levels of the two cell lines decreased after T. gondii ME-49 infection, and levels of NF-κB p65 phosphorylation and ABIN1 were higher than in the non-konckdown group. After knockingdown ABIN1 gene expression by constructing the lentiviral-mediated shRNA and transfecting the recombinant expression plasmid containing the ABIN1 gene into two cell lines, apoptosis levels and cleaved caspase-8 expression increased or decreased in response to T. gondii ME-49 infection, respectively.

Conclusions

Our data suggest that ABIN1 protects human leukaemia T-cells by allowing them to resist the apoptosis induced by T. gondii ME-49 and that the T. gondii ME-49 strain induces the apoptosis of human leukaemia T-cells via A20-mediated downregulation of ABIN1 expression.

TNIP1 reduction sensitizes keratinocytes to post-receptor signalling following exposure to TLR agonists

Cell level inflammatory signalling is a combination of initiation at cell membrane receptors and modulation by cytoplasmic regulatory proteins. For keratinocytes, the predominant cell type in the epidermis, this would include toll-like receptors (TLR) and cytoplasmic proteins that propagate or dampen post-receptor signalling. We previously reported that increased levels of tumor necrosis factor α induced protein 3-interacting protein 1 (TNIP1) in HaCaT keratinocytes leads to decreased expression of stress response and inflammation-associated genes. This finding suggested decreased TNIP1 levels, as seen in some cutaneous disease states, may produce the opposite effect, sensitizing cells to triggers of inflammatory signalling including those sensed by TLR. In this study of TNIP1-deficient HaCaT keratinocytes we examined intracellular signalling consequences especially those expected to produce gene expression changes downstream of TLR3 or TLR2/6 activation by Poly (I:C) or FSL-1, agonists modeling skin relevant pathogens. We found TNIP1-deficient keratinocytes are hyper-sensitive to TLR activation compared to control cells with a normal complement of TNIP1 and receiving the same agonist stimulation. TNIP1-deficient keratinocytes have increased levels of activated (phosphorylated) cytoplasmic mediators such as JNK and p38 and greater nuclear translocation of NF-κB and phospho-p38 when exposed to TLR ligands. This is consistent with significantly increased expression of several inflammatory cytokines and chemokines, such as IL-6 and IL-8. These results describe how decreased TNIP1 levels promote a hyper-sensitive state in HaCaT keratinocytes evidenced by increased activation of signalling molecules downstream of TLR agonists and increased expression of pro-inflammatory mediators. TNIP1 keratinocyte deficiency as reported for some skin diseases may predispose these cells to excessive inflammatory signalling upon exposure to viral or bacterial ligands for TLR.

MiR-30a increases MDSC differentiation and immunosuppressive function by targeting SOCS3 in mice with B-cell lymphoma

Myeloid-derived suppressor cells (MDSCs), including granulocytic (G)-MDSCs and monocytic (M)-MDSCs, play a critical role in tumor-induced T cell tolerance. MDSC immunosuppressive function and differentiation are significantly promoted in patients and B-cell lymphoma model mice. However, the mechanisms regulating these processes remain largely unclear. In the present study, we observed increased microRNA (miR)-30a expression both in G-MDSCs and in M-MDSCs from B cell lymphoma model mice. After transfection with miR-30a mimics, the differentiation and suppressive capacities of MDSCs were significantly increased via up-regulation of arginase-1. Moreover, we showed that the 3'-UTR of suppressor of cytokine signaling 3 (SOCS3) mRNA is a direct target of miR-30a. Decreased SOCS3 expression and activated Janus kinase-signal transducer and activator of transcription 3 signaling promote MDSC differentiation and suppressive activities. These findings provide new insights into the molecular mechanisms underlying MDSC expansion and function during B cell lymphoma development.

Immune regulator ABIN1 suppresses HIV-1 transcription by negatively regulating the ubiquitination of Tat

BACKGROUND

A20-binding inhibitor of NF-κB activation (ABIN1), an important immune regulator, was previously shown to be involved in HIV-1 replication. However, the reported studies done with overexpressed ABIN1 provided controversial results.

RESULTS

Here we identified ABIN1 as a suppressor of HIV-1 transcription since transient knockdown of ABIN1 led to increased HIV-1 replication both in transformed Jurkat T cell line and in primary human CD4+ T lymphocytes. Depletion of ABIN1 specifically enhanced the HIV-1 transcription from the integrated genome during viral life cycle, but not the earlier steps such as reverse transcription or integration. Immunoprecipitation assays revealed that ABIN1 specifically inhibits the proto-oncogene HDM2 catalyzed K63-linked polyubiquitination of Tat at Lys71, which is critical for the transactivation activity of Tat. The ubiquitin chain binding activity of ABIN1 carried by UBAN domain turned out to be essential for the inhibitory role of ABIN1. The results of immunofluorescence localization experiments suggested that ABIN1 may obstruct Tat ubiquitination by redistributing some of HDM2 from the nucleus to the cytoplasm.

CONCLUSIONS

Our findings have revealed ABIN1 as intrinsic suppressor of HIV-1 mRNA transcription by regulating the ubiquitination of Tat.