Biased signaling of G protein-coupled receptors - From a chemokine receptor CCR7 perspective

CCR7 affects the tumor microenvironment by regulating the activation of naïve CD8+ T cells to promote the proliferation of oral squamous cell carcinoma

BACKGROUND

Head and neck cancer is the sixth most common malignancy worldwide, and oral squamous cell carcinoma (OSCC) is the most common head and neck cancer, being one of the leading causes of cancer morbidity and mortality worldwide. CC Chemokine receptor 7(CCR7) is a multifunctional G protein-coupled trans-membrane chemokine that affects immune cell chemotaxis, migration, and cancer progression through its interaction with its ligands C-C motif chemokine ligand 19(CCL19) and C-C motif chemokine ligand 21(CCL21). Numerous studies have demonstrated the involvement of CCR7 in the malignant progression of a variety of cancers, reflecting the pro-cancer properties of CCR7. The Cancer Genome Atlas data suggests CCR7 has elevated expression in oral cancer. Specifically, CCR7 expression in tumor microenvironment (TME) may regulate the ability of some immune cells to engage in anti-tumor immune responses. Since CD8+ T cells have become a key immunotherapeutic target, the role of CCR7 in antitumor immune response of naïve CD8+ T cells in TME has not been thoroughly investigated.

METHODS

A CCR7 knockout mouse model was constructed, and the mechanism of ccr7 on the regulation of tumor microenvironment by naïve CD8+ T cells was verified under the guidance of single-cell RNA sequencing combined with in vivo animal experiments and in vitro cell experiments.

RESULTS

CCR7 is knocked out with impaired tumor growth and altered CD8+ T cell profiles, revealing the importance of this protein in OSCC.

CONCLUSIONS

Inhibition of CCR7 enhances CD8+ T cell activation, proliferation, and anti-tumor function, suggesting its potential as a therapeutic target.

NMR indicates the N-termini of PSGL1 and CCR7 bind competitively to the chemokine CCL21

Chemokines are from a family of secreted cytokines that direct the trafficking of immune cells to coordinate immune responses. Chemokines are involved in numerous disease states, including responding to infections, autoimmune disorders, and cancer metastasis. Ther are chemokines, like CCL21, that signal for cellular migration through the activation of G protein-coupled receptors, like CCR7, through interaction with the receptor's extracellular N-terminus, loops, and core of the receptor. CCL21 is involved in routine immune surveillance but can also attract metastasizing cancer cells to lymph nodes. P-selectin glycoprotein ligand 1 (PSGL1) has a role in cellular adhesion during chemotaxis and is a transmembrane signaling molecule. PSGL1 expression enhances chemotactic responses of T cells to CCL21. Here NMR studies indicate the binding sites on CCL21 for the N-termini or PSGL1 and CCR7 overlap, and binding of the N-termini of PSGL1 and CCR7 is competitive.

Heparin Specifically Interacts with Basic BBXB Motifs of the Chemokine CCL21 to Define CCR7 Signaling

Chemokines are critically involved in controlling directed leukocyte migration. Spatiotemporal secretion together with local retention processes establish and maintain local chemokine gradients that guide directional cell migration. Extracellular matrix proteins, particularly glycosaminoglycans (GAGs), locally retain chemokines through electrochemical interactions. The two chemokines CCL19 and CCL21 guide CCR7-expressing leukocytes, such as antigen-bearing dendritic cells and T lymphocytes, to draining lymph nodes to initiate adaptive immune responses. CCL21-in contrast to CCL19-is characterized by a unique extended C-terminus composed of highly charged residues to facilitate interactions with GAGs. Notably, both chemokines can trigger common, but also ligand-biased signaling through the same receptor. The underlying molecular mechanism of ligand-biased CCR7 signaling is poorly understood. Using a series of naturally occurring chemokine variants in combination with newly designed site-specific chemokine mutants, we herein assessed CCR7 signaling, as well as GAG interactions. We demonstrate that the charged chemokine C-terminus does not fully confer CCL21-biased CCR7 signaling. Besides the positively charged C-terminus, CCL21 also possesses specific BBXB motifs comprising basic amino acids. We show that CCL21 variants where individual BBXB motifs are mutated retain their capability to trigger G-protein-dependent CCR7 signaling, but lose their ability to interact with heparin. Moreover, we show that heparin specifically interacts with CCL21, but not with CCL19, and thereby competes with ligand-binding to CCR7 and prevents signaling. Hence, we provide evidence that soluble heparin, but not the other GAGs, complexes with CCL21 to define CCR7 signaling in a ligand-dependent manner.

Regulation of Extracellular Vesicle-Mediated Immune Responses against Antigen-Specific Presentation

Extracellular vesicles (EVs) produced by various immune cells, including B and T cells, macrophages, dendritic cells (DCs), natural killer (NK) cells, and mast cells, mediate intercellular communication and have attracted much attention owing to the novel delivery system of molecules in vivo. DCs are among the most active exosome-secreting cells of the immune system. EVs produced by cancer cells contain cancer antigens; therefore, the development of vaccine therapy that does not require the identification of cancer antigens using cancer-cell-derived EVs may have significant clinical implications. In this review, we summarise the molecular mechanisms underlying EV-based immune responses and their therapeutic effects on tumour vaccination.

Nociception-Dependent CCL21 Induces Dorsal Root Ganglia Axonal Growth via CCR7-ERK Activation

While chemokines were originally described for their ability to induce cell migration, many studies show how these proteins also take part in many other cell functions, acting as adaptable messengers in the communication between a diversity of cell types. In the nervous system, chemokines participate both in physiological and pathological processes, and while their expression is often described on glial and immune cells, growing evidence describes the expression of chemokines and their receptors in neurons, highlighting their potential in auto- and paracrine signalling. In this study we analysed the role of nociception in the neuronal chemokinome, and in turn their role in axonal growth. We found that stimulating TRPV1⁺ nociceptors induces a transient increase in CCL21. Interestingly we also found that CCL21 enhances neurite growth of large diameter proprioceptors in vitro. Consistent with this, we show that proprioceptors express the CCL21 receptor CCR7, and a CCR7 neutralizing antibody dose-dependently attenuates CCL21-induced neurite outgrowth. Mechanistically, we found that CCL21 binds locally to its receptor CCR7 at the growth cone, activating the downstream MEK-ERK pathway, that in turn activates N-WASP, triggering actin filament ramification in the growth cone, resulting in increased axonal growth.

A Set of Experimentally Validated Decoys for the Human CC Chemokine Receptor 7 (CCR7) Obtained by Virtual Screening

We present a state-of-the-art virtual screening workflow aiming at the identification of novel CC chemokine receptor 7 (CCR7) antagonists. Although CCR7 is associated with a variety of human diseases, such as immunological disorders, inflammatory diseases, and cancer, this target is underexplored in drug discovery and there are no potent and selective CCR7 small molecule antagonists available today. Therefore, computer-aided ligand-based, structure-based, and joint virtual screening campaigns were performed. Hits from these virtual screenings were tested in a CCL19-induced calcium signaling assay. After careful evaluation, none of the in silico hits were confirmed to have an antagonistic effect on CCR7. Hence, we report here a valuable set of 287 inactive compounds that can be used as experimentally validated decoys.

Dendritic cell-targeting chemokines inhibit colorectal cancer progression

Aim

Recent progress in cancer immunotherapy has shown its promise and prompted researchers to develop novel therapeutic strategies. Dendritic cells (DCs) are professional antigen-presenting cells crucial for initiating adaptive anti-tumor immunity, therefore a promising target for cancer treatment. Here, anti-tumor activities of DC-targeting chemokines were explored in murine colorectal tumor models.

Methods

The correlation of chemokine messenger RNA (mRNA) expression with DC markers was analyzed using The Cancer Genome Atlas (TCGA) dataset. Murine colorectal tumor cell lines (CT26 and MC38) stably overexpressing mouse C-C motif chemokine ligand 3 (CCL3), CCL19, CCL21, and X-C motif chemokine ligand 1 (XCL1) were established by lentiviral transduction. The effect of chemokines on tumor cell proliferation/survival was evaluated in vitro by cell counting kit-8 (CCK-8) assay and colony formation assay. Syngeneic subcutaneous tumor models were used to study the effects of these chemokines on tumor growth. Ki-67 expression in tumors was examined by immunohistochemistry. Immune cells in the tumor microenvironment (TME) and lymph nodes were analyzed by flow cytometry.

Results

Expression of the four chemokines was positively correlated with the two DC markers [integrin alpha X (ITGAX) and CLEC9A] in human colorectal tumor samples. Tumoral overexpression of DC-targeting chemokines had little or no effect on tumor cell proliferation/survival in vitro while significantly suppressing tumor growth in vivo. Fluorescence-activated cell sorting (FACS) analysis showed that CCL19, CCL21, and XCL1 boosted the ratios of DCs and T cells in CD45⁺ leukocytes while CCL3 increased the percentage of CD45⁺ leukocytes in total cells in MC38 tumor. XCL1 had an additional positive effect on antigen uptake by DCs in the TME and antigen transfer to tumor-draining lymph nodes.

Conclusions

CCL3, CCL19, CCL21, and XCL1 exhibited potent anti-tumor activities in vivo, although they might differentially regulate immune cells in the TME and antigen transfer to lymph nodes.

Chemokines in the Landscape of Cancer Immunotherapy: How They and Their Receptors Can Be Used to Turn Cold Tumors into Hot Ones?

Over the last decade, monoclonal antibodies to immune checkpoint inhibitors (ICI), also known as immune checkpoint blockers (ICB), have been the most successful approach for cancer therapy. Starting with mAb to cytotoxic T lymphocyte antigen 4 (CTLA-4) inhibitors in metastatic melanoma and continuing with blockers of the interactions between program cell death 1 (PD-1) and its ligand program cell death ligand 1 (PDL-1) or program cell death ligand 2 (PDL-2), that have been approved for about 20 different indications. Yet for many cancers, ICI shows limited success. Several lines of evidence imply that the limited success in cancer immunotherapy is associated with attempts to treat patients with "cold tumors" that either lack effector T cells, or in which these cells are markedly suppressed by regulatory T cells (Tregs). Chemokines are a well-defined group of proteins that were so named due to their chemotactic properties. The current review focuses on key chemokines that not only attract leukocytes but also shape their biological properties. CXCR3 is a chemokine receptor with 3 ligands. We suggest using Ig-based fusion proteins of two of them: CXL9 and CXCL10, to enhance anti-tumor immunity and perhaps transform cold tumors into hot tumors. Potential differences between CXCL9 and CXCL10 regarding ICI are discussed. We also discuss the possibility of targeting the function or deleting a key subset of Tregs that are CCR8+ by monoclonal antibodies to CCR8. These cells are preferentially abundant in several tumors and are likely to be the key drivers in suppressing anti-cancer immune reactivity.

CCL19 variants mediate chemotactic response via CCR7 in grass carp Ctenopharyngodon idella

CC chemokine ligand 19 (CCL19) plays a key role in the regulation of immune responses including homeostasis, inflammation, and immune tolerance. In this study, two variants of CCL19 homologues (CCL19a2 and CCL19b) and CCR7 were investigated in grass carp Ctenopharyngodon idella. The three genes were widely expressed in immune tissues and could be modulated by stimulation with LPS, PHA and poly(I:C), and infection with Flavobacterium columnare and grass carp reovirus. In an in vitro chemotaxis assay, the recombinant CCL19a2 and CCL19b were active to promote the migration of HEK293 T cells expressing CCR7 and leucocytes isolated from the gills, head kidney and spleen. Moreover, their chemotactive effects were validated in vivo. We found that the cells recruited by CCL19a2 and CCl19b are mainly monocytes/macrophages expressing high levels of IL-1β, IFN-γ, colony stimulating factor 1 receptor (CSF1R) and MHC II. Our work suggests that CCL19a2 and CCl19b are involved in recruitment of antigen presenting cells in fish.

CCR7 as a therapeutic target in Cancer

The CCR7 chemokine axis is comprised of chemokine ligand 21 (CCL21) and chemokine ligand 19 (CCL19) acting on chemokine receptor 7 (CCR7). This axis plays two important but apparently opposing roles in cancer. On the one hand, this axis is significantly engaged in the trafficking of a number of effecter cells involved in mounting an immune response to a growing tumour. This suggests therapeutic strategies which involve potentiation of this axis can be used to combat the spread of cancer. On the other hand, the CCR7 axis plays a significant role in controlling the migration of tumour cells towards the lymphatic system and metastasis and can thus contribute to the expansion of cancer. This implies that therapeutic strategies which involve decreasing signaling through the CCR7 axis would have a beneficial effect in preventing dissemination of cancer. This dichotomy has partly been the reason why this axis has not yet been exploited, as other chemokine axes have, as a therapeutic target in cancer. Recent report of a crystal structure for CCR7 provides opportunities to exploit this axis in developing new cancer therapies. However, it remains unclear which of these two strategies, potentiation or antagonism of the CCR7 axis, is more appropriate for cancer therapy. This review brings together the evidence supporting both roles of the CCR7 axis in cancer and examines the future potential of each of the two different therapeutic approaches involving the CCR7 axis in cancer.

CXCL12-PLGA/Pluronic Nanoparticle Internalization Abrogates CXCR4-Mediated Cell Migration

Chemokine-induced chemotaxis mediates physiological and pathological immune cell trafficking, as well as several processes involving cell migration. Among them, the role of CXCL12/CXCR4 signaling in cancer and metastasis is well known, and CXCR4 has been often targeted with small molecule-antagonists or short CXCL12-derived peptides to limit the pathological processes of cell migration and invasion. To reduce CXCR4-mediated chemotaxis, we adopted a different approach. We manufactured poly(lactic acid-co-glycolic acid) (PLGA)/Pluronic F127 nanoparticles through microfluidics-assisted nanoprecipitation and functionalized them with streptavidin to docking a biotinylated CXCL12 to be exposed on the nanoparticle surface. Our results show that CXCL12-decorated nanoparticles are non-toxic and do not induce inflammatory cytokine release in THP-1 monocytes cultured in fetal bovine and human serum-supplemented media. The cell internalization of our chemokine receptor-targeting particles increases in accordance with CXCR4 expression in FBS/medium. We demonstrated that CXCL12-decorated nanoparticles do not induce cell migration on their own, but their pre-incubation with THP-1 significantly decreases CXCR4⁺-cell migration, thereby antagonizing the chemotactic action of CXCL12. The use of biodegradable and immune-compatible chemokine-mimetic nanoparticles to reduce cell migration opens the way to novel antagonists with potential application in cancer treatments and inflammation.

Biased allosteric modulation of formyl peptide receptor 2 leads to distinct receptor conformational states for pro- and anti-inflammatory signaling

BACKGROUND AND PURPOSE

Formyl peptide receptor 2 (FPR2) is a Class A G protein-coupled receptor (GPCR) that interacts with multiple ligands and transduces both proinflammatory and anti-inflammatory signals. These ligands include weak agonists and modulators that are produced during inflammation. The present study investigates how prolonged exposure to FPR2 modulators influence receptor signaling.

EXPERIMENTAL APPROACH

Fluorescent biosensors of FPR2 were constructed based on single-molecule fluorescent resonance energy transfer (FRET) and used for measurement of ligand-induced receptor conformational changes. These changes were combined with FPR2-mediated signaling events and used as parameters for the conformational states of FPR2. Ternary complex models were developed to interpret ligand concentration-dependent changes in FPR2 conformational states.

KEY RESULTS

Incubation with Ac_2-26, an anti-inflammatory ligand of FPR2, decreased FRET intensity at picomolar concentrations. In comparison, WKYMVm (W-pep) and Aβ₄₂, both proinflammatory agonists of FPR2, increased FRET intensity. Preincubation with Ac_2-26 at 10 pM diminished W-pep-induced Ca²⁺ flux but potentiated W-pep-stimulated β-arrestin2 membrane translocation and p38 MAPK phosphorylation. The opposite effects were observed with 10 pM of Aβ₄₂. Neither Ac_2-26 nor Aβ₄₂ competed for W-pep binding at the picomolar concentrations.

CONCLUSIONS AND IMPLICATIONS

The results support the presence of two allosteric binding sites on FPR2, each for Ac_2-26 and Aβ₄₂, with high and low affinities. Sequential binding of the two allosteric ligands at increasing concentrations induce different conformational changes in FPR2, providing a novel mechanism by which biased allosteric modulators alter receptor conformations and generate pro- and anti-inflammatory signals.

Understanding the mechanisms that facilitate specificity, not redundancy, of chemokine-mediated leukocyte recruitment

Chemokines (chemotactic cytokines) and their receptors are critical to recruitment and positioning of cells during development and the immune response. The chemokine system has long been described as redundant for a number of reasons, where multiple chemokine ligands can bind to multiple receptors and vice versa. This apparent redundancy has been thought to be a major reason for the failure of drugs targeting chemokines during inflammatory disease. We are now beginning to understand that chemokine biology is in fact based around a high degree of specificity, where each chemokine and receptor plays a particular role in the immune response. This specificity hypothesis is supported by a number of recent studies designed to address this problem. This review will detail these studies and the mechanisms that produce this specificity of function with an emphasis on the emerging role of chemokine–glycosaminoglycan interactions.

Targeting Chemokine-Glycosaminoglycan Interactions to Inhibit Inflammation

Leukocyte migration into tissues depends on the activity of chemokines that form concentration gradients to guide leukocytes to a specific site. Interaction of chemokines with their specific G protein-coupled receptors (GPCRs) on leukocytes induces leukocyte adhesion to the endothelial cells, followed by extravasation of the leukocytes and subsequent directed migration along the chemotactic gradient. Interaction of chemokines with glycosaminoglycans (GAGs) is crucial for extravasation in vivo. Chemokines need to interact with GAGs on endothelial cells and in the extracellular matrix in tissues in order to be presented on the endothelium of blood vessels and to create a concentration gradient. Local chemokine retention establishes a chemokine gradient and prevents diffusion and degradation. During the last two decades, research aiming at reducing chemokine activity mainly focused on the identification of inhibitors of the interaction between chemokines and their cognate GPCRs. This approach only resulted in limited success. However, an alternative strategy, targeting chemokine-GAG interactions, may be a promising approach to inhibit chemokine activity and inflammation. On this line, proteins derived from viruses and parasites that bind chemokines or GAGs may have the potential to interfere with chemokine-GAG interactions. Alternatively, chemokine mimetics, including truncated chemokines and mutant chemokines, can compete with chemokines for binding to GAGs. Such truncated or mutated chemokines are characterized by a strong binding affinity for GAGs and abrogated binding to their chemokine receptors. Finally, Spiegelmers that mask the GAG-binding site on chemokines, thereby preventing chemokine-GAG interactions, were developed. In this review, the importance of GAGs for chemokine activity in vivo and strategies that could be employed to target chemokine-GAG interactions will be discussed in the context of inflammation.

Concepts of GPCR-controlled navigation in the immune system

G‐protein–coupled receptor (GPCR) signaling is essential for the spatiotemporal control of leukocyte dynamics during immune responses. For efficient navigation through mammalian tissues, most leukocyte types express more than one GPCR on their surface and sense a wide range of chemokines and chemoattractants, leading to basic forms of leukocyte movement (chemokinesis, haptokinesis, chemotaxis, haptotaxis, and chemorepulsion). How leukocytes integrate multiple GPCR signals and make directional decisions in lymphoid and inflamed tissues is still subject of intense research. Many of our concepts on GPCR‐controlled leukocyte navigation in the presence of multiple GPCR signals derive from in vitro chemotaxis studies and lower vertebrates. In this review, we refer to these concepts and critically contemplate their relevance for the directional movement of several leukocyte subsets (neutrophils, T cells, and dendritic cells) in the complexity of mouse tissues. We discuss how leukocyte navigation can be regulated at the level of only a single GPCR (surface expression, competitive antagonism, oligomerization, homologous desensitization, and receptor internalization) or multiple GPCRs (synergy, hierarchical and non‐hierarchical competition, sequential signaling, heterologous desensitization, and agonist scavenging). In particular, we will highlight recent advances in understanding GPCR‐controlled leukocyte navigation by intravital microscopy of immune cells in mice.

Comparative modeling and docking of chemokine-receptor interactions with Rosetta

Chemokine receptors are a subset of G protein-coupled receptors defined by the distinct property of binding small protein ligands in the chemokine family. Chemokine receptors recognize their ligands by a mechanism that is distinct from other class A GPCRs that bind peptides or small molecules. For this reason, structural information on other ligand-GPCR interactions are only indirectly relevant to understanding the chemokine receptor interface. Additionally, the experimentally determined structures of chemokine-GPCR complexes represent less than 3% of the known interactions of this complex, multi-ligand/multi-receptor network. To enable predictive modeling of the remaining 97% of interactions, a general in silico protocol was designed to utilize existing chemokine receptor crystal structures, co-crystal structures, and NMR ensembles of chemokines bound to receptor fragments. This protocol was benchmarked on the ability to predict each of the three published co-crystal structures, while being blinded to the target structure. Averaging ensembles selected from the top-ranking models reproduced up to 84% of the intermolecular contacts found in the crystal structure, with the lowest Cα-RMSD of the complex at 3.3 Å. The chemokine receptor N-terminus, unresolved in crystal structures, was included in the modeling and recapitulates contacts with known sulfotyrosine binding pockets seen in structures derived from experimental NMR data. This benchmarking experiment suggests that realistic homology models of chemokine-GPCR complexes can be generated by leveraging current structural data.

Arrestin-independent constitutive endocytosis of GPR125/ADGRA3

The orphan receptor GPR125 (ADGRA3) belongs to subgroup III of the adhesion G protein−coupled receptor (aGPCR) family. aGPCRs, also known as class B2 GPCRs, share basic structural and functional properties with other GPCRs. Many of them couple to G proteins and activate G protein−dependent and −independent signaling pathways, but little is known about aGPCR internalization and β‐arrestin recruitment. GPR125 was originally described as a spermatogonial stem cell marker and studied for its role in Wnt signaling and cell polarity. Here, using cell‐based assays and confocal microscopy, we show that GPR125 is expressed on the cell surface and undergoes constitutive endocytosis in a β‐arrestin−independent, but clathrin‐dependent manner, as indicated by colocalization with transferrin receptor 1, an early endosome marker. These data support that the constitutive internalization of GPR125 contributes to its biological functions by controlling receptor surface expression and accessibility for ligands. Our study sheds light on a new property of aGPCRs, namely internalization; a property described to be important for signal propagation, signal termination, and desensitization of class A (rhodopsin‐like) and B1 (VIP/secretin) GPCRs.

Biased Signaling of CCL21 and CCL19 Does Not Rely on N-Terminal Differences, but Markedly on the Chemokine Core Domains and Extracellular Loop 2 of CCR7

Chemokine receptors play important roles in the immune system and are linked to several human diseases. Targeting chemokine receptors have so far shown very little success owing to, to some extent, the promiscuity of the immune system and the high degree of biased signaling within it. CCR7 and its two endogenous ligands display biased signaling and here we investigate the differences between the two ligands, CCL21 and CCL19, with respect to their biased activation of CCR7. We use bystander bioluminescence resonance energy transfer (BRET) based signaling assays and Transwell migration assays to determine (A) how swapping of domains between the two ligands affect their signaling patterns and (B) how receptor mutagenesis impacts signaling. Using chimeric ligands we find that the chemokine core domains are central for determining signaling outcome as the lack of β-arrestin-2 recruitment displayed by CCL21 is linked to its core domain and not N-terminus. Through a mutagenesis screen, we identify the extracellular domains of CCR7 to be important for both ligands and show that the two chemokines interact differentially with extracellular loop 2 (ECL-2). By using in silico modeling, we propose a link between ECL-2 interaction and CCR7 signal transduction. Our mutagenesis study also suggests a lysine in the top of TM3, K130^3.26, to be important for G protein signaling, but not β-arrestin-2 recruitment. Taken together, the bias in CCR7 between CCL19 and CCL21 relies on the chemokine core domains, where interactions with ECL-2 seem particularly important. Moreover, TM3 selectively regulates G protein signaling as found for other chemokine receptors.

Increased CCR7loPD-1hiCXCR5+CD4+ T Cells in Peripheral Blood Mononuclear Cells Are Correlated with Immune Activation in Patients with Chronic HBV Infection

T follicular helper cells (Tfh cells) affect essential immune pathogenesis in chronic hepatitis B virus (HBV) infection. The CCR7^loPD-1^hi Tfh subset has a partial Tfh effector phenotype and is associated with active Tfh differentiation, whereas the CCR7^hiPD-1^lo Tfh subset is a resting phenotype. We recruited 20 healthy volunteers and 77 patients with chronic HBV infection, including those in the immune tolerant (IT) phase (n=19), immune clearance (IC) phase (n=20), low replicative (LR) phase (n=18), and reactivation (RA) phase (n=20). The expression of CD4, CXCR5, PD-1, and CCR7 was detected in T cells from peripheral blood by flow cytometry. The frequency of the CCR7^loPD-1^hi T subset was significantly higher in the patients than in the healthy controls (14.92±4.87% vs 12.23±2.95%, p=0.018). The frequency of this Tfh subset in the IC group (18.42%±3.08) was increased compared with the IT group (11.94±2.87%, p=0.001) and LR group (13.65±4.93%, p=0.031) and was higher in the RA group than in the IT group (16.03±5.37% vs 11.94±2.87%, p=0.030). We observed a weak positive correlation between the CCR7^loPD-1^hi Tfh subset population and the alanine transaminase (ALT) level (r=0.370, p=0.001). The CCR7^loPD-1^h Tfh subset in the chronic HBV-infected patients was elevated to various degrees among the different immune phases. CCR7^loPD-1^hiCXCR5⁺CD4⁺ T cells are correlated with the immune status of chronic HBV infection patients and may be developed as a potential indicator for antiviral treatment.

Identification of Cosalane as an Inhibitor of Human and Murine CC-Chemokine Receptor 7 Signaling via a High-Throughput Screen

CC-chemokine receptor 7 (CCR7) is a G protein-coupled receptor expressed on a variety of immune cells. CCR7 plays a critical role in the migration of lymphocytes into secondary lymphoid tissues. CCR7 expression, however, has been linked to numerous disease states. Due to its therapeutic relevance and absence of available CCR7 inhibitors, we undertook a high-throughput screen (HTS) to identify small-molecule antagonists of the receptor. Here, we describe a robust HTS approach using a commercially available β-galactosidase enzyme fragment complementation system and confirmatory transwell chemotaxis assays. This work resulted in the identification of several compounds with activity against CCR7. The most potent of these was subsequently determined to be cosalane, a cholesterol derivative previously designed as a therapeutic for human immunodeficiency virus. Cosalane inhibited both human and murine CCR7 in response to both CCL19 and CCL21 agonists at physiologic concentrations. Furthermore, cosalane produced durable inhibition of the receptor following a cellular incubation period with subsequent washout. Overall, our work describes the development of an HTS-compatible assay, completion of a large HTS campaign, and demonstration for the first time that cosalane is a validated CCR7 antagonist. These efforts could pave the way for new approaches to address CCR7-associated disease processes.

CCL19 with CCL21-tail displays enhanced glycosaminoglycan binding with retained chemotactic potency in dendritic cells

CCL19 is more potent than CCL21 in inducing chemotaxis of human dendritic cells (DC). This difference is attributed to 1) a stronger interaction of the basic C-terminal tail of CCL21 with acidic glycosaminoglycans (GAGs) in the environment and 2) an autoinhibitory function of this C-terminal tail. Moreover, different receptor docking modes and tissue expression patterns of CCL19 and CCL21 contribute to fine-tuned control of CCR7 signaling. Here, we investigate the effect of the tail of CCL21 on chemokine binding to GAGs and on CCR7 activation. We show that transfer of CCL21-tail to CCL19 (CCL19^CCL21-tail ) markedly increases binding of CCL19 to human dendritic cell surfaces, without impairing CCL19-induced intracellular calcium release or DC chemotaxis, although it causes reduced CCR7 internalization. The more potent chemotaxis induced by CCL19 and CCL19^CCL21-tail compared to CCL21 is not transferred to CCL21 by replacing its N-terminus with that of CCL19 (CCL21^CCL19-N-term ). Measurements of cAMP production in CHO cells uncover that CCL21-tail transfer (CCL19^CCL21-tail ) negatively affects CCL19 potency, whereas removal of CCL21-tail (CCL21^tailless ) increases signaling compared to full-length CCL21, indicating that the tail negatively affects signaling via cAMP. Similar to chemokine-driven calcium mobilization and chemotaxis, the potency of CCL21 in cAMP is not improved by transfer of the CCL19 N-terminus to CCL21 (CCL21^CCL19-N-term ). Together these results indicate that ligands containing CCL21 core and C-terminal tail (CCL21 and CCL21^CCL19-N-term ) are most restricted in their cAMP signaling; a phenotype attributed to a stronger GAG binding of CCL21 and defined structural differences between CCL19 and CCL21.

Chlamydia abortus Pmp18.1 Induces IL-1β Secretion by TLR4 Activation through the MyD88, NF-κB, and Caspase-1 Signaling Pathways

The polymorphic membrane protein D (Pmp18D) is a 160-kDa outer membrane protein that is conserved and plays an important role in Chlamydia abortus pathogenesis. We have identified an N-terminal fragment of Pmp18D (designated Pmp18.1) as a possible subunit vaccine antigen. In this study, we evaluated the vaccine potential of Pmp18.1 by investigating its ability to induce innate immune responses in dendritic cells and the signaling pathway(s) involved in rPmp18.1-induced IL-1β secretion. We next investigated the immunomodulatory impact of VCG, in comparison with the more established Th1-promoting adjuvants, CpG and FL, on rPmp18.1-mediated innate immune activation. Finally, the effect of siRNA targeting TLR4, MyD88, NF-κB p50, and Caspase-1 mRNA in DCs on IL-1β cytokine secretion was also investigated. Bone marrow-derived dendritic cells (BMDCs) were stimulated with rPmp18.1 in the presence or absence of VCG or CpG or FL and the magnitude of cytokines produced was assessed using a multiplex cytokine ELISA assay. Expression of costimulatory molecules and Toll-like receptors (TLRs) was analyzed by flow cytometry. Quantitation of intracellular levels of myeloid differentiation factor 88 (MyD88), nuclear factor kappa beta (NF-κB p50/p65), and Caspase-1 was evaluated by Western immunoblotting analysis while NF-κB p65 nuclear translocation was assessed by confocal microscopy. The results showed DC stimulation with rPmp18.1 provoked the secretion of proinflammatory cytokines and upregulated expression of TLRs and co-stimulatory molecules associated with DC maturation. These responses were significantly (p ≤ 0.001) enhanced by VCG but not CpG or FL. In addition, rPmp18.1 activated the expression of MyD88, NF-κB p50, and Caspase-1 as well as the nuclear expression of NF-κB p65 in treated DCs. Furthermore, targeting TLR4, MyD88, NF-κB p50, and Caspase-1 mRNA in BMDCs with siRNA significantly reduced their expression levels, resulting in decreased IL-1β cytokine secretion, strongly suggesting their involvement in the rPmp18.1-induced IL-1β cytokine secretion. Taken together, these results indicate that C. abortus Pmp18.1 induces IL-1β secretion by TLR4 activation through the MyD88, NF-κB as well as the Caspase-1 signaling pathways and may be a potential C. abortus vaccine candidate. The vaccine potential of Pmp18.1 will subsequently be evaluated in an appropriate animal model, using VCG as an immunomodulator, following immunization and challenge.