Differentially induced expression of C-type lectins in activated lymphocytes

Lectin-like Transcript-1 (LLT1) Expression in Oral Squamous Cell Carcinomas: Prognostic Significance and Relationship with the Tumor Immune Microenvironment

Lectin-like transcript-1 (LLT1) expression is detected in different cancer types and is involved in immune evasion. The present study investigates the clinical relevance of tumoral and stromal LLT1 expression in oral squamous cell carcinoma (OSCC), and relationships with the immune infiltrate into the tumor immune microenvironment (TIME). Immunohistochemical analysis of LLT1 expression was performed in 124 OSCC specimens, together with PD-L1 expression and the infiltration of CD20+, CD4+, and CD8+ lymphocytes and CD68+ and CD163+-macrophages. Associations with clinicopathological variables, prognosis, and immune cell densities were further assessed. A total of 41 (33%) OSCC samples showed positive LLT1 staining in tumor cells and 55 (44%) positive LLT1 in tumor-infiltrating lymphocytes (TILs). Patients harboring tumor-intrinsic LLT1 expression exhibited poorer survival, suggesting an immunosuppressive role. Conversely, positive LLT1 expression in TILs was significantly associated with better disease-specific survival, and also an immune-active tumor microenvironment highly infiltrated by CD8+ T cells and M1/M2 macrophages. Furthermore, the combination of tumoral and stromal LLT1 was found to distinguish three prognostic categories (favorable, intermediate, and adverse; p = 0.029, Log-rank test). Together, these data demonstrate the prognostic relevance of tumoral and stromal LLT1 expression in OSCC, and its potential application to improve prognosis prediction and patient stratification.

Long-Term Survival and Immune Response Dynamics in Melanoma Patients Undergoing TAPCells-Based Vaccination Therapy

Cancer vaccines present a promising avenue for treating immune checkpoint blockers (ICBs)-refractory patients, fostering immune responses to modulate the tumor microenvironment. We revisit a phase I/II trial using Tumor Antigen-Presenting Cells (TAPCells) (NCT06152367), an autologous antigen-presenting cell vaccine loaded with heat-shocked allogeneic melanoma cell lysates. Initial findings showcased TAPCells inducing lysate-specific delayed-type hypersensitivity (DTH) reactions, correlating with prolonged survival. Here, we extend our analysis over 15 years, categorizing patients into short-term (<36 months) and long-term (≥36 months) survivors, exploring novel associations between clinical outcomes and demographic, genetic, and immunologic parameters. Notably, DTHpos patients exhibit a 53.1% three-year survival compared to 16.1% in DTHneg patients. Extended remissions are observed in long-term survivors, particularly DTHpos/M1cneg patients. Younger age, stage III disease, and moderate immune events also benefit short-term survivors. Immunomarkers like increased C-type lectin domain family 2 member D on CD4+ T cells and elevated interleukin-17A were detected in long-term survivors. In contrast, toll-like receptor-4 D229G polymorphism and reduced CD32 on B cells are associated with reduced survival. TAPCells achieved stable long remissions in 35.2% of patients, especially M1cneg/DTHpos cases. Conclusions: Our study underscores the potential of vaccine-induced immune responses in melanoma, emphasizing the identification of emerging biological markers and clinical parameters for predicting long-term remission.

LLT1-CD161 Interaction in Cancer: Promises and Challenges

The success of immune checkpoint therapy in cancer has changed our way of thinking, promoting the design of future cancer treatments that places the immune system at the center stage. The knowledge gained on immune regulation and tolerance helped the identification of promising new clinical immune targets. Among them, the lectin-like transcript 1 (LLT1) is the ligand of CD161 (NKR-P1A) receptor expressed on natural killer cells and T cells. LLT1/CD161 interaction modulates immune responses but the exact nature of the signals delivered is still partially resolved. Investigation on the role of LLT1/CD161 interaction has been hampered by the lack of functional homologues in animal models. Also, some studies have been misled by the use of non-specific reagents. Recent studies and meta-analyses of single cell data are bringing new insights into the function of LLT1 and CD161 in human pathology and notably in cancer. The advances made on the characterization of the tumor microenvironment prompt us to integrate LLT1/CD161 interaction into the equation. This review recapitulates the key findings on the expression profile of LLT1 and CD161, their regulation, the role of their interaction in cancer development, and the relevance of targeting LLT1/CD161 interaction.

Recent Advances in Targeting CD8 T-Cell Immunity for More Effective Cancer Immunotherapy

Recent advances in cancer treatment have emerged from new immunotherapies targeting T-cell inhibitory receptors, including cytotoxic T-lymphocyte associated antigen (CTLA)-4 and programmed cell death (PD)-1. In this context, anti-CTLA-4 and anti-PD-1 monoclonal antibodies have demonstrated survival benefits in numerous cancers, including melanoma and non-small-cell lung carcinoma. PD-1-expressing CD8⁺ T lymphocytes appear to play a major role in the response to these immune checkpoint inhibitors (ICI). Cytotoxic T lymphocytes (CTL) eliminate malignant cells through recognition by the T-cell receptor (TCR) of specific antigenic peptides presented on the surface of cancer cells by major histocompatibility complex class I/beta-2-microglobulin complexes, and through killing of target cells, mainly by releasing the content of secretory lysosomes containing perforin and granzyme B. T-cell adhesion molecules and, in particular, lymphocyte-function-associated antigen-1 and CD103 integrins, and their cognate ligands, respectively, intercellular adhesion molecule 1 and E-cadherin, on target cells, are involved in strengthening the interaction between CTL and tumor cells. Tumor-specific CTL have been isolated from tumor-infiltrating lymphocytes and peripheral blood lymphocytes (PBL) of patients with varied cancers. TCRβ-chain gene usage indicated that CTL identified in vitro selectively expanded in vivo at the tumor site compared to autologous PBL. Moreover, functional studies indicated that these CTL mediate human leukocyte antigen class I-restricted cytotoxic activity toward autologous tumor cells. Several of them recognize truly tumor-specific antigens encoded by mutated genes, also known as neoantigens, which likely play a key role in antitumor CD8 T-cell immunity. Accordingly, it has been shown that the presence of T lymphocytes directed toward tumor neoantigens is associated with patient response to immunotherapies, including ICI, adoptive cell transfer, and dendritic cell-based vaccines. These tumor-specific mutation-derived antigens open up new perspectives for development of effective second-generation therapeutic cancer vaccines.

Eutirucallin: A Lectin with Antitumor and Antimicrobial Properties

Eutirucallin is a lectin isolated from the latex of Euphorbia tirucalli, a plant known for its medical properties. The present study explores various characteristics of Eutirucallin including stability, cytotoxicity against tumor cells, antimicrobial and antiparasitic activities. Eutirucallin was stable from 2 to 40 days at 4°C, maintained hemagglutinating activity within a restricted range, and showed optimal activity at pH 7.0–8.0. Eutirucallin presented antiproliferative activity for HeLa, PC3, MDA-MB-231, and MCF-7 tumor cells but was not cytotoxic for non-tumorigenic cells such as macrophages and fibroblasts. Eutirucallin inhibited the Ehrlich ascites carcinoma in vivo and it was also observed that Eutirucallin inhibited 62.5% of Escherichia coli growth. Also, Eutirucallin showed to be effective when tested directly against Toxoplasma gondii infection in vitro. Therefore, this study sheds perspectives for pharmacological applications of Eutirucallin.

Expression of lectin-like transcript-1 in human tissues

Background: Receptor-ligand pairs of C-type lectin-like proteins have been shown to play an important role in cross talk between lymphocytes, as well as in immune responses within concrete tissues and structures, such as the skin or the germinal centres. The CD161-Lectin-like Transcript 1 (LLT1) pair has gained particular attention in recent years, yet a detailed analysis of LLT1 distribution in human tissue is lacking. One reason for this is the limited availability and poor characterisation of anti-LLT1 antibodies. Methods: We assessed the staining capabilities of a novel anti-LLT1 antibody clone (2H7), both by immunohistochemistry and flow cytometry, showing its efficiency at LLT1 recognition in both settings. We then analysed LLT1 expression in a wide variety of human tissues. Results: We found LLT1 expression in circulating B cells and monocytes, but not in lung and liver-resident macrophages. We found strikingly high LLT1 expression in immune-privileged sites, such as the brain, placenta and testes, and confirmed the ability of LLT1 to inhibit NK cell function. Conclusions: Overall, this study contributes to the development of efficient tools for the study of LLT1. Moreover, its expression in different healthy human tissues and, particularly, in immune-privileged sites, establishes LLT1 as a good candidate as a regulator of immune responses.

LLT1 and CD161 Expression in Human Germinal Centers Promotes B Cell Activation and CXCR4 Downregulation

Germinal centers (GCs) are microanatomical structures critical for the development of high-affinity Abs and B cell memory. They are organized into two zones, light and dark, with coordinated roles, controlled by local signaling. The innate lectin-like transcript 1 (LLT1) is known to be expressed on B cells, but its functional role in the GC reaction has not been explored. In this study, we report high expression of LLT1 on GC-associated B cells, early plasmablasts, and GC-derived lymphomas. LLT1 expression was readily induced via BCR, CD40, and CpG stimulation on B cells. Unexpectedly, we found high expression of the LLT1 ligand, CD161, on follicular dendritic cells. Triggering of LLT1 supported B cell activation, CD83 upregulation, and CXCR4 downregulation. Overall, these data suggest that LLT1–CD161 interactions play a novel and important role in B cell maturation within the GC in humans.

Expression of Lectin-Like Transcript 1, the Ligand for CD161, in Rheumatoid Arthritis

Objectives

Precursor Th17 lineage cells expressing CD161 are implicated in Rheumatoid Arthritis (RA) pathogenesis. CD4+CD161+ T-cells accumulate in RA joints and may acquire a non classical Th1 phenotype. The endogenous ligand for CD161 is lectin-like transcript 1 (LLT1). CD161/LLT1 ligation may co-stimulate T-cell IFN-γ production. We investigated the presence and identity of LLT1-expressing cells in RA synovial fluid (SF) and synovial tissue (ST). We also assessed levels of soluble LLT1 (sLLT1) in different phases of RA development.

Methods

Paired samples of peripheral blood mononuclear cells (MC) and SFMC (n = 14), digested ST cells (n = 4) and ST paraffin sections (n = 6) from late-stage RA were analyzed for LLT1 expression by flow cytometry and immunohistochemistry. sLLT1 was measured using a sandwich ELISA. Sera and SF from late-stage RA (n = 26), recently diagnosed RA patients (n = 39), seropositive arthralgia patients (SAP, n = 31), spondyloarthropathy patients (SpA, n = 26) and healthy controls (HC, n = 31) were assayed.

Results

In RA SF, LLT1 was expressed by a small proportion of monocytes. In RA ST, LLT1-expressing cells were detected in the lining, sublining layer and in areas with infiltrates. The LLT1 staining pattern overlapped with the CD68 staining pattern. FACS analysis of digested ST confirmed LLT1 expression by CD68+ cells. Elevated systemic sLLT1 was found in all patient groups.

Conclusions

In RA joints, LLT1 is expressed by cells of the monocyte/macrophage lineage. Serum levels of sLLT1 were increased in all patient groups (patients with early- and late-stage RA, seropositive arthralgia and spondyloarthropathy) when compared to healthy subjects.

Gene expression responses to Riemerella anatipestifer infection in the liver of ducks

Riemerella anatipestifer is one of the most economically important pathogens of farm ducks worldwide. The molecular mechanisms that underlie its pathogenesis, particularly the host response to R. anatipestifer infection, are poorly understood. The differentially expressed gene profile of duck livers at 24 h following R. anatipestifer infection was therefore investigated using suppression subtractive hybridizaton analysis. A total of 45 differentially expressed genes were identified, which primarily included genes for proteins involved in acute-phase response, inflammatory response, immune response, wound healing and iron homeostasis. For the expression level of 20 genes from those 45 analysed by quantitative reverse transcriptase-polymerase chain reaction at 8, 24 and 48 h post infection, significant differences were observed among the three time points of measurements. The result from this study revealed a gene expression profile of duck liver during R. anatipestifer infection, and those genes with a role in the immune response and wound healing deserving further investigation to elucidate their respective roles during infection.

Natural killer cell subsets in man and rodents

NK cells are important contributors to the early immune defence against infected or transformed cells. They are rapidly activated in response to cytokines, whereby they exert their effector functions. NK cell responses are controlled by a multitude of receptors, which are expressed by subpopulations of NK cells with distinct phenotypes and functionalities. Direct comparisons between species are often difficult because of differences in the expression of NK cell receptors and other markers. In addition, NK cells change their phenotype and effector functions during differentiation, by tissue-specific factors, or upon activation, complicating interpretations. We will here review the similarities and differences between the major NK cell subsets in man and two well-characterized rodent models.

Functional consequences of interactions between human NKR-P1A and its ligand LLT1 expressed on activated dendritic cells and B cells

Lectin-like transcript-1 (LLT1) (also named osteoclast inhibitory lectin or CLEC2D) is a ligand for the human NKR-P1A (CD161) receptor, present on NK cells and T cells. To further understand the physiological relevance of this interaction, we developed mAbs against LLT1, characterized the expression pattern of LLT1, and explored the functional consequence of LLT1 engagement of the NKR-P1A receptor on NK cells and T cells. LLT1 is expressed on TLR-activated plasmacytoid dendritic, TLR-activated monocyte-derived dendritic cells, and on B cells stimulated through TLR9, surface Ig, or CD40. Interactions between NKR-P1A on NK cells and LLT1 on target cells inhibit NK cell-mediated cytotoxicity and cytokine production and can inhibit TNF-alpha production by TCR-activated NKR-P1A(+) CD8(+) T cells. In contrast, NKR-P1A failed to inhibit or augment the TCR-dependent activation of NKR-P1A-bearing CD4(+) T cells. Expression of LLT1 on activated dendritic cells and B cells suggests that it might regulate the cross-talk between NK cells and APCs.

Malignant glioma cells counteract antitumor immune responses through expression of lectin-like transcript-1

Glioblastoma, one of the most lethal tumors, is paradigmatic for tumor-associated immunosuppression. Lectin-like transcript-1 (LLT1) is a newly identified ligand for the inhibitory natural killer (NK) cell receptor CD161. Here, we report that glioma cells express LLT1 mRNA and protein in vitro and in vivo, whereas expression levels in normal brain are low. LLT1 expression in human gliomas increases with the WHO grade of malignancy. We further show that transforming growth factor-beta (TGF-beta) up-regulates the expression of LLT1 in glioma cells. Small interfering RNA (siRNA)-mediated down-regulation of LLT1 in LNT-229 and LN-428 cells promotes their lysis by NK cells. Thus, LLT1 acts as a mediator of immune escape and contributes to the immunosuppressive properties of glioma cells.

Cutting edge: lectin-like transcript 1 is a ligand for the CD161 receptor

Human NK cells and subsets of T cells or NKT cells express the orphan C-type lectin receptor CD161 (NKR-P1A) of unknown function. In contrast to rodents that possess several NKR-P1 genes coding for either activating or inhibitory receptors, the nature of signals delivered by the single human NKR-P1A receptor is still to be clarified. In this article, we show that the lectin-like transcript 1 (LLT1) molecule is a ligand for the CD161 receptor. Engagement of CD161 on NK cells with LLT1 expressed on target cells inhibited NK cell-mediated cytotoxicity and IFN-gamma secretion. Conversely, LLT1/CD161 interaction in the presence of a TCR signal enhanced IFN-gamma production by T cells. These findings identify a novel ligand/receptor pair that differentially regulate NK and T cell functions.

Phosphorylation of galectin-3 contributes to malignant transformation of human epithelial cells via modulation of unique sets of genes

Galectin-3 is a multifunctional beta-galactoside-binding protein implicated in apoptosis, malignant transformation, and tumor progression. The mechanisms by which galectin-3 contributes to malignant progression are not fully understood. In this study, we found that the introduction of wild-type galectin-3 into nontumorigenic, galectin-3-null BT549 human breast epithelial cells conferred tumorigenicity and metastatic potential in nude mice, and that galectin-3 expressed by the cells was phosphorylated. In contrast, BT549 cells expressing galectin-3 incapable of being phosphorylated (Ser6-->Glu Ser6-->Ala) were nontumorigenic. A microarray analysis of 10,000 human genes, comparing BT549 transfectants expressing wild-type and those expressing phosphomutant galectin-3, identified 188 genes that were differentially expressed (>2.5-fold). Genes affected by introduction of wild-type phosphorylated but not phosphomutant galectin-3 included those involved in oxidative stress, a novel noncaspase lysosomal apoptotic pathway, cell cycle regulation, transcriptional activation, cytoskeleton remodeling, cell adhesion, and tumor invasion. The reliability of the microarray data was validated by real-time reverse transcription-PCR (RT-PCR) and by Western blot analysis, and clinical relevance was evaluated by real-time RT-PCR screening of a panel of matched pairs of breast tumors. Differentially regulated genes in breast cancers that are also predicted to be associated with phospho-galectin-3 in transformed BT549 cells include C-type lectin 2, insulin-like growth factor-binding protein 5, cathepsins L2, and cyclin D1. These data show the functional diversity of galectin-3 and suggest that phosphorylation of the protein is necessary for regulation (directly or indirectly) of unique sets of genes that play a role in malignant transformation.

C-type lectin-like receptors on myeloid cells

Host defence against pathogens requires the recognition of conserved microbial molecules, or 'pathogen-associated molecular patterns' (PAMPs), by their receptors termed 'pattern recognition receptors' (PRRs), represented most notably by toll-like receptors (TLRs) and C-type lectins. The 'non-classical' C-type lectins (these that lack the residues involved in calcium binding, required for carbohydrate binding) are traditionally thought of as being restricted to natural killer (NK) or T cells, playing important roles in immune surveillance. In recent years, however, a growing number of these receptors have been identified on myeloid cells, both of human and mouse origin. In contrast to their NK counterparts that primarily control cellular activation through recognition of major histocompatibility antigen (MHC) class I and related molecules, the myeloid-expressed receptors appear to have a far more diverse range of functions and ligands, including those of exogenous origin. Some of C-type lectin-like molecules possess activating/inhibitory signalling motifs that trigger downstream signalling events, suggesting the role for these receptors as positive/negative regulators of granulocyte and monocyte functions. With the exception of a few myeloid NK-like lectins, the natural ligands for most of these receptors remain unidentified, making it difficult to define their functions in normal physiological, inflammatory or pathological conditions. Importantly, in some cases, these novel C-type lectin-like lectins, encoded by genes from the same gene cluster, can act as receptor/ligand pairs, additionally contributing to the regulation of myeloid cell functions or their interaction with other (like NK) cell types. However, the relevance and importance of such interactions still needs to be assessed. Although few of the myeloid-expressed C-type lectins have been characterized in detail, we review here each of these receptors and highlight their prospective roles in innate and adaptive immunity.

Role for NKG2-A and NKG2-C surface receptors in chronic CD4+ T-cell responses

The participation of CD94 and NKG2 gene family members in the function of NK cells and CD8+ cytolytic cells has recently been addressed in detail. However, the role that these molecules play in the key CD4+ regulatory cells remains largely unexplored. This study has examined the expression and regulation of CD94 and NKG2 genes in purified human peripheral CD4+ cells stimulated with several agents. We found a constitutive expression of NKG2-E in CD94-depleted resting peripheral CD4+ cells, whereas inductions of NKG2-A and NKG2-C required chronic cell activation and occurred after expression of CD94. We found that CD3-mediated stimulation induces the expression of CD94 first by day 5 of culture, followed by NKG2-A by day 15 and finally NKG2-C, which is not detected until 20 days after repeated stimulation. This pattern of gene expression differs sharply from that observed in purified CD8+ T cells, where mRNA from all NKG2 gene family members are detected after 5 days of stimulation. Selective activation of TCR V beta 2-bearing cells with toxic shock syndrome toxin-1 superantigen reveals that mRNA induction of NKG2-A and NKG2-C genes is significantly influenced by the presence of cytokines (IL-10 and TGF-beta) and by the restimulation of the cells. In addition, the occupancy of the CD94/NKG2-A receptor expressed on these superantigen-stimulated CD4+ T lymphocytes abrogates TNF-alpha and IFN-gamma production, whereas NKG2-C enhances production of these cytokines. Taken together our results reveal strict gene regulatory mechanisms for CD94 and NKG2 gene expression on CD4+ cells that are different from those governing the expression of these same genes in CD8+ cells. The results suggest that these genes also participate in chronic CD4+ T-cell responses.

Immune functions encoded by the natural killer gene complex

There has been marked progress in our understanding of the role of natural killer (NK) cells in immune responses, mainly due to the identification of NK-cell receptors and their ligands. The genes encoding many NK-cell receptors are located in the NK-gene complex (NKC). Here, we review the properties of NKC-encoded receptors, and provide a genomic and conceptual framework for an insight into NK-cell function and biology.

C-type lectin receptors on dendritic cells and Langerhans cells

Dendritic cells and Langerhans cells are specialized for the recognition of pathogens and have a pivotal role in the control of immunity. As guardians of the immune system, they are present in essentially every organ and tissue, where they operate at the interface of innate and acquired immunity. Recently, several C-type lectin and lectin-like receptors have been characterized that are expressed abundantly on the surface of these professional antigen-presenting cells. It is now becoming clear that lectin receptors not only serve as antigen receptors but also regulate the migration of dendritic cells and their interaction with lymphocytes.