The Fibronectin-ILT3 Interaction Functions as a Stromal Checkpoint that Suppresses Myeloid Cells

Epithelial-mesenchymal transition orchestrates tumor microenvironment: current perceptions and challenges

The epithelial-mesenchymal transition (EMT) is a critical process in cancer progression, facilitating tumor cells to develop invasive traits and augmenting their migratory capabilities. EMT is primed by tumor microenvironment (TME)-derived signals, whereupon cancer cells undergoing EMT in turn remodel the TME, thereby modulating tumor progression and therapeutic response. This review discusses the mechanisms by which EMT coordinates TME dynamics, including secretion of soluble factors, direct cell contact, release of exosomes and enzymes, as well as metabolic reprogramming. Recent evidence also indicates that cells undergoing EMT may differentiate into cancer-associated fibroblasts, thereby establishing themselves as functional constituents of the TME. Elucidating the relationship between EMT and the TME offers novel perspectives for therapeutic strategies to enhance cancer treatment efficacy. Although EMT-directed therapies present significant therapeutic potential, the current lack of effective targeting approaches-attributable to EMT complexity and its microenvironmental context dependency-underscores the necessity for mechanistic investigations and translational clinical validation.

LILRB4 specific overexpression in myeloid cells promotes tumor progression and immunosuppression in mouse models

Leukocyte immunoglobulin like receptor B4 (LILRB4) was considered to promote tumor progression and immunosuppression in various malignancies. As a murine homolog of LILRB4, gp49B has been employed in numerous mouse models to investigate the immunosuppressive properties of LILRB4. However, gp49B differs significantly from LILRB4 in its amino acid sequence and intracellular domains. In this study, we developed a conditional mouse model that overexpresses LILRB4 specifically in myeloid cells to investigate its effects on solid tumors and hematological malignancies. Our results showed that the physiological structure and overall immune system of LILRB4L/L; Cre mice were normal. LL2 tumors in LILRB4L/L; Cre mice exhibited increased size and weight, with elevated levels of immunosuppressive markers programmed cell death protein 1 (PD-1) and T cell immunoglobulin and mucin-domain containing-3 (TIM-3) on infiltrating CD3+ T cells, alongside a shift in tumor-associated macrophages (TAMs) from M1-type to M2-type. In the C1498 model, LILRB4 overexpression promoted tumor progression and metastasis, evidenced by increased bioluminescence and enhanced infiltration of monocytic myeloid-derived suppressor cells (M-MDSCs). Real-time PCR analysis showed upregulation of immunosuppressive mRNAs, including colony-stimulating factor 1 (CSF1), arginase1 (Arg1), macrophage galactose N-acetyl-galactosamine specific lectin 2 (Mgl2) and interleukin-1β (IL-1β) while downregulating pro-inflammatory markers like nitric oxide synthase 2 (Nos2). These findings indicate that LILRB4 fosters an immunosuppressive microenvironment that supports tumor progression. LILRB4L/L; Cre mice may serve as a promising tool for studying targeted LILRB4 tumor immunotherapy.

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.

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.

IGSF9 promotes tumor invasion and metastasis through GSK-3β/β-catenin mediated EMT in lung cancer

We previously reported that immunoglobulin superfamily member 9 (IGSF9) as a tumor specific immune checkpoint promoted the tumor immune escape, however, as an adhesion molecule, whether IGSF9 promotes tumor invasion and metastasis has not been reported. Here, the full length, the intracellular domain (ID) not extracellular domain (ECD) of IGSF9 could alter tumor cell morphology from a flat and polygonal shape to elongated strips, suggesting that IGSF9 signal pathway has the potential to mediate epithelial-to-mesenchymal transition (EMT). Real-time PCR and western blotting also showed that the mesenchymal markers were significantly up-regulated, and the epithelial markers were significantly down-regulated in IGSF9 and IGSF9-ID groups. Meanwhile, immunofluorescence showed that β-catenin was clearly translocated into the nucleus in IGSF9 and IGSF9-ID groups. The in vitro and in vivo data showed that IGSF9, IGSF9-ID and ECD could promote tumor invasion and metastasis. Mechanistically, IGSF9-ID could recruit GSK-3β to result in the accumulation and nuclear translocation of β-catenin to trigger EMT. Anti-IGSF9 could significantly inhibit the invasion and metastasis, and IGSF9 is an effective candidate for lung cancer therapy.

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.

Leukocyte immunoglobulin-like receptor B4 (LILRB4) in acute myeloid leukemia: From prognostic biomarker to immunotherapeutic target

ABSTRACT

Leukocyte immunoglobulin-like receptor (LILR) B4 (also known as ILT3/CD85k) is an immune checkpoint protein that is highly expressed in solid tumors and hematological malignancies and plays a significant role in the pathophysiology of cancer. LILRB4 is highly expressed in acute myeloid leukemia (AML), and this phenotype is associated with adverse patient outcomes. Its differential expression in tumors compared to normal tissues, its presence in tumor stem cells, and its multifaceted roles in tumorigenesis position it as a promising therapeutic target in AML. Currently, several immunotherapies targeting LILRB4 are undergoing clinical trials. This review summarizes advancements made in the study of LILRB4 in AML, focusing on its structure, ligands, expression, and significance in normal tissues and AML; its protumorigenic effects and mechanisms in AML; and the application of LILRB4-targeted therapies in AML. These insights highlight the potential advantages of LILRB4 as an immunotherapeutic target in the context of AML.

Cell Populations in Human Breast Cancers are Molecularly and Biologically Distinct with Age

Aging is associated with increased breast cancer risk and outcomes are worse for the oldest and youngest patients, regardless of subtype. It is not known how cells in the breast tumor microenvironment are impacted by age and how they might contribute to age-related disease pathology. Here, we discover age-associated differences in cell states and interactions in human estrogen receptor-positive (ER+) and triple-negative breast cancers (TNBC) using new computational analyses of existing single-cell gene expression data. Age-specific program enrichment (ASPEN) analysis reveals age-related changes, including increased tumor cell epithelial-mesenchymal transition, cancer-associated fibroblast inflammatory responses, and T cell stress responses and apoptosis in TNBC. ER+ breast cancer is dominated by increased cancer cell estrogen receptor 1 (ESR1) and luminal cell activity, reduced immune cell metabolism, and decreased vascular and extracellular matrix (ECM) remodeling with age. Cell interactome analysis reveals candidate signaling pathways that drive many of these cell states. This work lays a foundation for discovery of age-adapted therapeutic interventions for breast cancer.

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.

In vitro screening methods of novel immune checkpoint inhibitors related to T cell infiltration and anti-PD-1 resistance

Immune checkpoint blockade-based cancer immunotherapy is an effective tool for cancer treatment. PD-1/PD-L1 blockade, however, is limited by a low response rate and adaptive resistance. A growing body of studies has shown that the high stromal content dense with extracellular matrix plays a significant role in immune checkpoint blockade resistance as well as T cell exclusion. In addition to physically obstructing immune cell infiltration, the extracellular matrix (ECM) may also interact with T cell receptors to indirectly impair their effector function and lead to anti-PD-1 resistance. Anti-PD-1 resistance may thus be overcome by rupturing the physical barrier related negative immune regulation, which may improve T cell infiltration and the efficacy of cancer immunotherapy. Here, we offer two straightforward methods based on flow cytometry and confocal microscopy to evaluate the effectiveness of an inhibitor targeting the novel "stromal checkpoint" DDR1/collagen, which aims to facilitate T cell migration and infiltration of tumor spheres by overcoming collagen barriers. With minor variations, the same method can be easily modified to test the inhibitors that target other immune checkpoints, and the extracellular matrix-associated drug targets that mediate anti-PD-1 resistance.

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.

ATG-101 Is a Tetravalent PD-L1×4-1BB Bispecific Antibody That Stimulates Antitumor Immunity through PD-L1 Blockade and PD-L1-Directed 4-1BB Activation

Immune checkpoint inhibitors (ICI) have transformed cancer treatment. However, only a minority of patients achieve a profound response. Many patients are innately resistant while others acquire resistance to ICIs. Furthermore, hepatotoxicity and suboptimal efficacy have hampered the clinical development of agonists of 4-1BB, a promising immune-stimulating target. To effectively target 4-1BB and treat diseases resistant to ICIs, we engineered ATG-101, a tetravalent "2+2″ PD-L1×4-1BB bispecific antibody. ATG-101 bound PD-L1 and 4-1BB concurrently, with a greater affinity for PD-L1, and potently activated 4-1BB+ T cells when cross-linked with PD-L1-positive cells. ATG-101 activated exhausted T cells upon PD-L1 binding, indicating a possible role in reversing T-cell dysfunction. ATG-101 displayed potent antitumor activity in numerous in vivo tumor models, including those resistant or refractory to ICIs. ATG-101 greatly increased the proliferation of CD8+ T cells, the infiltration of effector memory T cells, and the ratio of CD8+ T/regulatory T cells in the tumor microenvironment (TME), rendering an immunologically "cold" tumor "hot." Comprehensive characterization of the TME after ATG-101 treatment using single-cell RNA sequencing further revealed an altered immune landscape that reflected increased antitumor immunity. ATG-101 was well tolerated and did not induce hepatotoxicity in non-human primates. According to computational semimechanistic pharmacology modeling, 4-1BB/ATG-101/PD-L1 trimer formation and PD-L1 receptor occupancy were both maximized at around 2 mg/kg of ATG-101, providing guidance regarding the optimal biological dose for clinical trials. In summary, by localizing to PD-L1-rich microenvironments and activating 4-1BB+ immune cells in a PD-L1 cross-linking-dependent manner, ATG-101 safely inhibits growth of ICI resistant and refractory tumors.

SIGNIFICANCE

The tetravalent PD-L1×4-1BB bispecific antibody ATG-101 activates 4-1BB+ T cells in a PD-L1 cross-linking-dependent manner, minimizing the hepatotoxicity of existing 4-1BB agonists and suppressing growth of ICI-resistant tumors. See related commentary by Ha et al., p. 1546.

ILT2 and ILT4 Drive Myeloid Suppression via Both Overlapping and Distinct Mechanisms

Solid tumors are dense three-dimensional (3D) multicellular structures that enable efficient receptor-ligand trans interactions via close cell-cell contact. Immunoglobulin-like transcript (ILT)2 and ILT4 are related immune-suppressive receptors that play a role in the inhibition of myeloid cells within the tumor microenvironment. The relative contribution of ILT2 and ILT4 to immune inhibition in the context of solid tumor tissue has not been fully explored. We present evidence that both ILT2 and ILT4 contribute to myeloid inhibition. We found that although ILT2 inhibits myeloid cell activation in the context of trans-engagement by MHC-I, ILT4 efficiently inhibits myeloid cells in the presence of either cis- or trans-engagement. In a 3D spheroid tumor model, dual ILT2/ILT4 blockade was required for the optimal activation of myeloid cells, including the secretion of CXCL9 and CCL5, upregulation of CD86 on dendritic cells, and downregulation of CD163 on macrophages. Humanized mouse tumor models showed increased immune activation and cytolytic T-cell activity with combined ILT2 and ILT4 blockade, including evidence of the generation of immune niches, which have been shown to correlate with clinical response to immune-checkpoint blockade. In a human tumor explant histoculture system, dual ILT2/ILT4 blockade increased CXCL9 secretion, downregulated CD163 expression, and increased the expression of M1 macrophage, IFNγ, and cytolytic T-cell gene signatures. Thus, we have revealed distinct contributions of ILT2 and ILT4 to myeloid cell biology and provide proof-of-concept data supporting the combined blockade of ILT2 and ILT4 to therapeutically induce optimal myeloid cell reprogramming in the tumor microenvironment.

Antibody-mediated targeting of human microglial leukocyte Ig-like receptor B4 attenuates amyloid pathology in a mouse model

Microglia help limit the progression of Alzheimer's disease (AD) by constraining amyloid-β (Aβ) pathology, effected through a balance of activating and inhibitory intracellular signals delivered by distinct cell surface receptors. Human leukocyte Ig-like receptor B4 (LILRB4) is an inhibitory receptor of the immunoglobulin (Ig) superfamily that is expressed on myeloid cells and recognizes apolipoprotein E (ApoE) among other ligands. Here, we find that LILRB4 is highly expressed in the microglia of patients with AD. Using mice that accumulate Aβ and carry a transgene encompassing a portion of the LILR region that includes LILRB4, we corroborated abundant LILRB4 expression in microglia wrapping around Aβ plaques. Systemic treatment of these mice with an anti-human LILRB4 monoclonal antibody (mAb) reduced Aβ load, mitigated some Aβ-related behavioral abnormalities, enhanced microglia activity, and attenuated expression of interferon-induced genes. In vitro binding experiments established that human LILRB4 binds both human and mouse ApoE and that anti-human LILRB4 mAb blocks such interaction. In silico modeling, biochemical, and mutagenesis analyses identified a loop between the two extracellular Ig domains of LILRB4 required for interaction with mouse ApoE and further indicated that anti-LILRB4 mAb may block LILRB4-mApoE by directly binding this loop. Thus, targeting LILRB4 may be a potential therapeutic avenue for AD.

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.

Tumoral and stromal hMENA isoforms impact tertiary lymphoid structure localization in lung cancer and predict immune checkpoint blockade response in patients with cancer

BACKGROUND

Tertiary Lymphoid Structures (TLS) correlate with positive outcomes in patients with NSCLC and the efficacy of immune checkpoint blockade (ICB) in cancer. The actin regulatory protein hMENA undergoes tissue-specific splicing, producing the epithelial hMENA11a linked to favorable prognosis in early NSCLC, and the mesenchymal hMENAΔv6 found in invasive cancer cells and pro-tumoral cancer-associated fibroblasts (CAFs). This study investigates how hMENA isoforms in tumor cells and CAFs relate to TLS presence, localization and impact on patient outcomes and ICB response.

METHODS

Methods involved RNA-SEQ on NSCLC cells with depleted hMENA isoforms. A retrospective observational study assessed tissues from surgically treated N0 patients with NSCLC, using immunohistochemistry for tumoral and stromal hMENA isoforms, fibronectin, and TLS presence. ICB-treated patient tumors were analyzed using Nanostring nCounter and GeoMx spatial transcriptomics. Multiparametric flow cytometry characterized B cells and tissue-resident memory T cells (TRM). Survival and ICB response were estimated in the cohort and validated using bioinformatics pipelines in different datasets.

FINDINGS

Findings indicate that hMENA11a in NSCLC cells upregulates the TLS regulator LTβR, decreases fibronectin, and favors CXCL13 production by TRM. Conversely, hMENAΔv6 in CAFs inhibits LTβR-related NF-kB pathway, reduces CXCL13 secretion, and promotes fibronectin production. These patterns are validated in N0 NSCLC tumors, where hMENA11ahigh expression, CAF hMENAΔv6low, and stromal fibronectinlow are associated with intratumoral TLS, linked to memory B cells and predictive of longer survival. The hMENA isoform pattern, fibronectin, and LTβR expression broadly predict ICB response in tumors where TLS indicates an anti-tumor immune response.

INTERPRETATION

This study uncovers hMENA alternative splicing as an unexplored contributor to TLS-related Tumor Immune Microenvironment (TIME) and a promising biomarker for clinical outcomes and likely ICB responsiveness in N0 patients with NSCLC.

FUNDING

This work is supported by AIRC (IG 19822), ACC (RCR-2019-23669120), CAL.HUB.RIA Ministero Salute PNRR-POS T4, "Ricerca Corrente" granted by the Italian Ministry of Health.

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.

Immune approaches beyond traditional immune checkpoint inhibitors for advanced renal cell carcinoma

Renal cell carcinoma (RCC), especially clear cell RCC, is generally considered an immunotherapy-responsive cancer. Recently, the prognosis for patients with locally advanced and metastatic RCC has significantly improved with the regulatory approvals of anti-PD-1/PD-L1/CTLA-4 immune checkpoint inhibitor (ICI)-based regimens. Yet in most cases, RCC will remain initially unresponsive to treatment or will develop resistance over time. Hence, there remains an unmet need to understand what leads to ICI resistance and to develop novel immune and nonimmune treatments to enhance the response to ICIs. In this review, we highlight recently published studies and the latest clinical studies investigating the next generation of immune approaches to locally advanced and metastatic RCC beyond traditional ICIs. These trials include cytokines, gut microbiota-based therapies, novel immune checkpoint agents, vaccines, and chimeric antigen receptor T cells. These agents are being evaluated as monotherapy or in combination with traditional ICIs and will hopefully provide improved outcomes to patients with RCC soon.

Regulation of tumor immunity and immunotherapy by the tumor collagen extracellular matrix

It has been known for decades that the tumor extracellular matrix (ECM) is dysfunctional leading to loss of tissue architecture and promotion of tumor growth. The altered ECM and tumor fibrogenesis leads to tissue stiffness that act as a physical barrier to immune cell infiltration into the tumor microenvironment (TME). It is becoming increasingly clear that the ECM plays important roles in tumor immune responses. A growing body of data now indicates that ECM components also play a more active role in immune regulation when dysregulated ECM components act as ligands to interact with receptors on immune cells to inhibit immune cell subpopulations in the TME. In addition, immunotherapies such as checkpoint inhibitors that are approved to treat cancer are often hindered by ECM changes. In this review we highlight the ways by which ECM alterations affect and regulate immunity in cancer. More specifically, how collagens and major ECM components, suppress immunity in the complex TME. Finally, we will review how our increased understanding of immune and immunotherapy regulation by the ECM is leading towards novel disruptive strategies to overcome immune suppression.

The extracellular matrix - immune microenvironment crosstalk in cancer therapy: Challenges and opportunities

Targeting the tumour immune microenvironment (TIME) by cancer immunotherapy has led to improved patient outcomes. However, response to these treatments is heterogeneous and cancer-type dependant. The therapeutic activity of classical cancer therapies such as chemotherapy, radiotherapy, and surgical oncology is modulated by alterations of the TIME. A major regulator of immune cell function and resistance to both immune and classical therapies is the extracellular matrix (ECM). Concurrently, cancer therapies reshape the TIME as well as the ECM, causing both pro- and anti-tumour responses. Accordingly, the TIME-ECM crosstalk presents attractive opportunities to improve therapy outcomes. Here, we review the molecular crosstalk between the TIME and the ECM in cancer and its implications in cancer progression and clinical intervention. Additionally, we discuss examples and future directions of ECM and TIME co-targeting in combination with oncological therapies including surgery, chemotherapy, and radiotherapy.

Enhancing immunotherapy response in melanoma: myeloid-derived suppressor cells as a therapeutic target

Despite the remarkable success of immune checkpoint inhibitors (ICIs) in melanoma treatment, resistance to them remains a substantial clinical challenge. Myeloid-derived suppressor cells (MDSCs) represent a heterogeneous population of myeloid cells that can suppress antitumor immune responses mediated by T and natural killer cells and promote tumor growth. They are major contributors to ICI resistance and play a crucial role in creating an immunosuppressive tumor microenvironment. Therefore, targeting MDSCs is considered a promising strategy to improve the therapeutic efficacy of ICIs. This Review describes the mechanism of MDSC-mediated immune suppression, preclinical and clinical studies on MDSC targeting, and potential strategies for inhibiting MDSC functions to improve melanoma immunotherapy.

Prognostic impact of LILRB4 expression on tumor-infiltrating cells in resected non-small cell lung cancer

BACKGROUND

Leukocyte immunoglobulin-like receptor subfamily B member 4 (LILRB4/ILT3) is an up-and-coming molecule that promotes immune evasion. We have previously reported that LILRB4 facilitates myeloid-derived suppressor cells (MDSCs)-mediated tumor metastasis in mice. This study aimed to investigate the impact of the LILRB4 expression levels on tumor-infiltrating cells on the prognosis of non-small cell lung cancer (NSCLC) patients.

METHODS

We immunohistochemically evaluated the LILRB4 expression levels of completely resected 239 NSCLC specimens. Whether the blocking of LILRB4 on human PBMC-derived CD33⁺ MDSCs inhibited the migration ability of lung cancer cells was also examined using transwell migration assay.

RESULTS

The LILRB4 ^high group, in which patients with a high LILRB4 expression level on tumor-infiltrating cells, showed a shorter overall survival (OS) (p = 0.013) and relapse-free survival (RFS) (p = 0.0017) compared to the LILRB4 ^low group. Multivariate analyses revealed that a high LILRB4 expression was an independent factor for postoperative recurrence, poor OS and RFS. Even in the cohort background aligned by propensity score matching, OS (p = 0.023) and RFS (p = 0.0046) in the LILRB4 ^high group were shorter than in the LILRB4 ^low group. Some of the LILRB4 positive cells were positive for MDSC markers, CD33 and CD14. Transwell migration assay demonstrated that blocking LILRB4 significantly inhibited the migration of human lung cancer cells cocultured with CD33⁺ MDSCs.

CONCLUSION

Together, signals through LILRB4 on tumor-infiltrating cells, including MDSCs, play an essential role in promoting tumor evasion and cancer progression, impacting the recurrence and poor prognosis of patients with resected NSCLC.

LILRB4/gp49B Co-Localizes with Integrin via Fibronectin at Focal Adhesion Sites on Mast Cells

Mast cells protect a host from invasion by infectious agents and environmental allergens through activation of innate and adaptive immune receptors, their excessive activation being tightly regulated by inhibitory receptors, such as leukocyte immunoglobulin-like receptor (LILR)B4 (gp49B in mice). However, the regulatory mechanism of LILRB4/gp49B expressed on mast cells remains to be clarified in relation to their recently identified ligand, fibronectin (FN), a direct activator of integrins and an indirect stimulator of high-affinity Fc receptor for IgE (FcεRI). Confocal microscopic analysis suggested that gp49B is spatially close to integrin β₁ on non-adhered bone marrow-derived mast cells (BMMCs). Their spatial relatedness increases further at robust focal adhesion sites on cells adhering to immobilized FN. However, the confocal fluorescence signal of the α subunit of FcεRI was found to be correlated to neither gp49B nor integrin β₁ on non-adherent and adherent BMMCs. Stimulation of FcεRI with an immobilized antigen caused FcεRIα signals to accumulate in an inside area surrounded by robust focal adhesion with a concomitant slight increase in the signal correlation of FcεRIα and integrin β₁, accompanied by a less significant increase of the FcεRIα and gp49 correlation. Thus, activating and inhibitory FN receptors integrin and gp49B, respectively, were co-localized via FN at robust focal adhesion sites on BMMCs, while FcεRI was not close to gp49B spatially.

Antibody therapies for the treatment of acute myeloid leukemia: exploring current and emerging therapeutic targets

INTRODUCTION

Acute myeloid leukemia (AML) is the most common and deadly type of leukemia affecting adults. It is typically managed with rounds of non-targeted chemotherapy followed by hematopoietic stem cell transplants, but this is only possible in patients who can tolerate these harsh treatments and many are elderly and frail. With the identification of novel tumor-specific cell surface receptors, there is great conviction that targeted antibody therapies will soon become available for these patients.

AREAS COVERED

In this review, we describe the current landscape of known target receptors for monospecific and bispecific antibody-based therapeutics for AML. Here, we characterize each of the receptors and targeted antibody-based therapeutics in development, illustrating the rational design behind each therapeutic compound. We then discuss the bispecific antibodies in development and how they improve immune surveillance of AML. For each therapeutic, we also summarize the available pre-clinical and clinical data, including data from discontinued trials.

EXPERT OPINION

One antibody-based therapeutic has already been approved for AML treatment, the CD33-targeting antibody-drug conjugate, gemtuzumab ozogamicin. Many more are currently in pre-clinical and clinical studies. These antibody-based therapeutics can perform tumor-specific, elaborate cytotoxic functions and there is growing confidence they will soon lead to personalized, safe AML treatment options that induce durable remissions.

Recent Progress on the Role of Fibronectin in Tumor Stromal Immunity and Immunotherapy

As a major component of the stromal microenvironment of various solid tumors, the extracellular matrix (ECM) has attracted increasing attention in cancer-related studies. ECM in the tumor stroma not only provides an external barrier and framework for tumor cell adhesion and movement, but also acts as an active regulator that modulates the tumor microenvironment, including stromal immunity. Fibronectin (Fn), as a core component of the ECM, plays a key role in the assembly and remodeling of the ECM. Hence, understanding the role of Fn in the modulation of tumor stromal immunity is of great importance for cancer immunotherapy. Hence, in-depth studies on the underlying mechanisms of Fn in tumors are urgently needed to clarify the current understanding and issues and to identify new and specific targets for effective diagnosis and treatment purposes. In this review, we summarize the structure and role of Fn, its potent derivatives in tumor stromal immunity, and their biological effects and mechanisms in tumor development. In addition, we discuss the novel applications of Fn in tumor treatment. Therefore, this review can provide prospective insight into Fn immunotherapeutic applications in tumor treatment.

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.

Extracellular matrix-natural killer cell interactome: an uncharted territory in health and disease

Extracellular matrix (ECM) constantly undergoes remodeling to maintain the tissue homeostasis and an impaired ECM remodeling is a hallmark of many diseases, including cancer, infections, and inflammatory disorders. ECM has recently become recognized to regulate the immune response in peripheral tissues. Most immune cells express a diverse array of ECM receptors that, upon engagement by their cognate ECM ligands, can regulate their movement and effector functions. Natural killer (NK) cells are innate lymphocytes capable of mounting a swift cytotoxic immunity against cancer and virally infected cells using germline-encoded activating and inhibitory receptors. Regulation of NK cell effector function by ECM proteins in peripheral tissues is an emerging field with major implications for maintaining tolerance in normal tissues and controlling solid cancers, viral infections, and inflammatory diseases. The development of novel therapeutics targeting ECM-NK cell interplay represents a promising strategy to promote health and combat many diseases affecting solid organs.

Host and microbiome features of secondary infections in lethal covid-19

Secondary infections contribute significantly to covid-19 mortality but driving factors remain poorly understood. Autopsies of 20 covid-19 cases and 14 controls from the first pandemic wave complemented with microbial cultivation and RNA-seq from lung tissues enabled description of major organ pathologies and specification of secondary infections. Lethal covid-19 segregated into two main death causes with either dominant diffuse alveolar damage (DAD) or secondary pneumonias. The lung microbiome in covid-19 showed a reduced biodiversity and increased prototypical bacterial and fungal pathogens in cases of secondary pneumonias. RNA-seq distinctly mirrored death causes and stratified DAD cases into subgroups with differing cellular compositions identifying myeloid cells, macrophages and complement C1q as strong separating factors suggesting a pathophysiological link. Together with a prominent induction of inhibitory immune-checkpoints our study highlights profound alterations of the lung immunity in covid-19 wherein a reduced antimicrobial defense likely drives development of secondary infections on top of SARS-CoV-2 infection.

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Covid-19 autopsy cohort complemented with microbial cultivation and deep sequencing

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Major death causes stratify into DAD and secondary pneumonias

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Prototypical bacterial and fungal agents are found in secondary pneumonias

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Macrophages and C1q stratify DAD subgroups and indicate immune impairment in lungs

Immune checkpoints in osteosarcoma: Recent advances and therapeutic potential

Osteosarcoma is the most common primary malignant bone tumor and is associated with a high risk of recurrence and distant metastasis. Effective treatment for osteosarcoma, especially advanced osteosarcoma, has stagnated over the past four decades. The advent of immune checkpoint inhibitor (ICI) has transformed the treatment paradigm for multiple malignant tumor types and indicated a potential therapeutic strategy for osteosarcoma. In this review, we discuss recent advances in immune checkpoints, including programmed cell death protein-1 (PD-1), programmed cell death protein ligand-1 (PD-L1), and cytotoxic T lymphocyte-associated antigen-4 (CTLA-4), and their related ICIs for osteosarcoma treatment. We present the main existing mechanisms of resistance to ICIs therapy in osteosarcoma. Moreover, we summarize the current strategies for improving the efficacy of ICIs in osteosarcoma and address the potential predictive biomarkers of ICIs treatment in osteosarcoma.

Co-localization of Fibronectin Receptors LILRB4/gp49B and Integrin on Dendritic Cell Surface

A myeloid immune checkpoint, leukocyte immunoglobulin-like receptor (LILR) B4 (B4, also known as ILT3/CD85k in humans and gp49B in mice) is expressed on dendritic cells (DCs). However, a mode of regulation of DCs by B4/gp49B is not identified yet in relation to the ligand(s) as well as to the counteracting, activation-type receptor. Our recent identification of the physiological/pathological ligand for B4/gp49B as the fibronectin (FN) N-terminal 30-kDa domain poses the question of the relationship between B4/gp49B and a classical FN receptor/cellular activator, integrin, on DCs. Here we showed that FN is not constitutively tethered on the surface of bone marrow-derived cultured DCs (BMDCs) or splenic DCs, even though the FN receptor integrin and gp49B are co-expressed on these cells. Confocal laser scanning microscopic analysis, however, revealed weak correlation of fluorescent signals between gp49B and integrin β₁, suggesting their partial co-localization on the BMDC surface even in the absence of FN. We found that the plating of BMDCs onto immobilized FN induced tyrosine phosphorylation of focal adhesion kinase (FAK) and spleen tyrosine kinase (Syk). In the absence of gp49B, while the FAK phosphorylation level was virtually unchanged, that of phosphorylation of Syk was markedly augmented. These results suggested that the immobilized FN induced a crosstalk between gp49B and integrin in terms of the intracellular signaling of BMDCs, in which gp49B suppressed the integrin-mediated pro-inflammatory cascade. Our observations may provide a clue for elucidating the mechanism of the therapeutic efficacy of B4/gp49B blocking in autoimmune disease and cancer.

Myeloid immune checkpoint ILT3/LILRB4/gp49B can co-tether fibronectin with integrin on macrophages

LILRB4 (B4, also known as ILT3/CD85k) is an immune checkpoint of myeloid-lineage cells, albeit its mode of function remains obscure. Our recent identification of a common ligand for both human B4 and its murine ortholog gp49B as the fibronectin (FN) N-terminal 30-kDa domain poses the question of how B4/gp49B regulate cellular activity upon recognition of FN in the plasma and/or the extracellular matrix. Since FN in the extracellular matrix is tethered by FN-binding integrins, we hypothesized that B4/gp49B would tether FN in cooperation with integrins on the cell surface, thus they should be in close vicinity to integrins spatially. This scenario suggests a mode of function of B4/gp49B by which the FN-induced signal is regulated. FN pull-down complex was found to contain gp49B and integrin β1 in bone marrow-derived macrophages. The confocal fluorescent signals of the three molecules on the intrinsically FN-tethering macrophages were correlated to each other. When FN-poor macrophages adhered to culture plate, the gp49-integrin β1 signal correlation increased at the focal adhesion, supporting the notion that gp49B and integrin β1 become spatially closer to each other there. While adherence of RAW264.7 and THP-1 cells to immobilized FN induced phosphorylation of spleen tyrosine kinase, whose level was augmented under B4/gp49B deficiency. Thus, we concluded that B4/gp49B can co-tether fibronectin in cooperation with integrin in the cis configuration on the same cell, forming a B4/gp49B-FN-integrin triplet as a regulatory unit of focal adhesion-dependent proinflammatory signal in macrophages.

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.

Hepatocellular Carcinoma Immunotherapy

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and the third leading cause of cancer-related death worldwide. Single-agent anti-PD-1 immune checkpoint inhibitors (ICIs) demonstrated promising efficacy in early-phase trials, a finding that was not confirmed in phase III studies. The combination of atezolizumab (an anti-PD-L1 ICI) with bevacizumab (an anti-VEGF antibody) was approved as first-line therapy in 2020, however, with significant improvement in response rate, progression-free survival, and overall survival in comparison with the previous standard of care, sorafenib. Numerous ongoing clinical trials are assessing ICIs in combination with each other or with targeted agents, and also in earlier stages with local therapies. This review summarizes the latest concepts in the use of ICIs for the management of HCC. Expected final online publication date for the Annual Review of Medicine, Volume 73 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.