This study was supported in parts by research funding from the Swiss National Science Foundation (grant number 310030_189144), the Thurgauische Stiftung für Wissenschaft und Forschung, and the State Secretariat for Education, Research and Innovation to DFL.

Dendritic cells (DCs) are potent and versatile professional antigen-presenting cells and central for the induction of adaptive immunity. The ability to migrate and transport peripherally acquired antigens to draining lymph nodes for subsequent cognate T cell priming is a key feature of DCs. Consequently, DC-based immunotherapies are used to elicit tumor-antigen specific T cell responses in cancer patients. Understanding chemokine-guided DC migration is critical to explore DCs as cellular vaccines for immunotherapeutic approaches. Currently, research is hampered by the lack of appropriate human cellular model systems to effectively study spatio-temporal signaling and CCR7-driven migration of human DCs. Here, we report that the previously established human neoplastic cell line CAL-1 expresses the human DC surface antigens CD11c and HLA-DR together with co-stimulatory molecules. Importantly, if exposed for three days to GM-CSF, CAL-1 cells induce the endogenous expression of the chemokine receptor CCR7 upon encountering the clinically approved TLR7/8 agonist Resiquimod R848 and readily migrate along chemokine gradients. Further, we demonstrate that CAL-1 cells can be genetically modified to express fluorescent (GFP)-tagged reporter proteins to study and visualize signaling or can be gene-edited using CRISPR/Cas9. Hence, we herein present the human CAL-1 cell line as versatile and valuable cellular model system to effectively study human DC migration and signaling.

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, K1303.26, 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.

The chemokine receptor CCR7 plays a pivotal role in health and disease. In particular, CCR7 controls homing of antigen-bearing dendritic cells and T cells to lymph nodes, where adaptive immune responses are initiated. However, CCR7 also guides T cells to inflamed synovium and thereby contributes to rheumatoid arthritis and promotes cancer cell migration and metastasis formation. Nanobodies have recently emerged as versatile tools to study G-protein-coupled receptor functions and are being tested in diagnostics and therapeutics. In this study, we designed a strategy to engineer novel nanobodies recognizing human CCR7. We generated a nanobody library based on a solved crystal structure of the nanobody Nb80 recognizing the β2-adrenergic receptor (β2AR) and by specifically randomizing two segments within complementarity determining region 1 (CDR1) and CDR3 of Nb80 known to interact with β2AR. We fused the nanobody library to one half of split-YFP in order to identify individual nanobody clones interacting with CCR7 fused to the other half of split-YFP using bimolecular fluorescence complementation. We present three novel nanobodies, termed Nb1, Nb5, and Nb38, that recognize human CCR7 without interfering with G-protein-coupling and downstream signaling. Moreover, we were able to follow CCR7 trafficking upon CCL19 triggering using Nb1, Nb5, and Nb38.

Chemokine receptors are considered to belong to the group of G protein-coupled receptors that use the first transmembrane domain as signal anchor sequence for membrane insertion instead of a cleavable N-terminal signal sequence. Chemokine recognition is determined by the N-termini of chemokine receptors. Here, we show that the chemokine receptor CCR7, which is essential for directed migration of adaptive immune cells, possesses a 24 amino acids long N-terminal signal sequence that is unique among chemokine receptors. This sequence is cleaved off the mature human and mouse protein. Introducing single point mutations in the hydrophobic core h-region or in the polar C-terminal segment (c-region) of the signal sequence to interfere with its cleavage retained CCR7 in the ER and prevented its surface expression. Furthermore, we demonstrate the correct topology of the 35 amino acids short extracellular N-tail of CCR7 in a deletion mutant lacking the natural signal sequence. This signal sequence deletion mutant of CCR7 is fully functional as it efficiently binds its ligand, elicits chemokine-induced calcium mobilization, and directs cell migration. However, we show that the signal sequence promotes efficient recruitment of the GPCR to ER exit sites, thereby controlling efficient ER to Golgi trafficking of CCR7 on its way to reach the plasma membrane.

Chemokine receptors are seven transmembrane-domain receptors belonging to class A of G-protein-coupled receptors (GPCRs). The receptors together with their chemokine ligands constitute the chemokine system, which is essential for directing cell migration and plays a crucial role in a variety of physiologic and pathologic processes. Given the importance of orchestrating cell migration, it is vital that chemokine receptor signaling is tightly regulated to ensure appropriate responses. Recent studies highlight a key role for cholesterol in modulating chemokine receptor activities. The steroid influences the spatial organization of GPCRs within the membrane bilayer, and consequently can tune chemokine receptor signaling. The effects of cholesterol on the organization and function of chemokine receptors and GPCRs in general include direct and indirect effects (Fig. 1). Here, we review how cholesterol and some key metabolites modulate functions of the chemokine system in multiple ways. We emphasize the role of cholesterol in chemokine receptor oligomerization, thereby promoting the formation of a signaling hub enabling integration of distinct signaling pathways at the receptor-membrane interface. Moreover, we discuss the role of cholesterol in stabilizing particular receptor conformations and its consequence for chemokine binding. Finally, we highlight how cholesterol accumulation, its deprivation, or cholesterol metabolites contribute to modulating cell orchestration during inflammation, induction of an adaptive immune response, as well as to dampening an anti-tumor immune response.

Spatially distinct pools of the small GTPase Cdc42 were observed, but the major focus of research so far has been to investigate its signaling at the plasma membrane. We recently showed that the Golgi pool of Cdc42 is relevant for cell polarity and that it is regulated by GM130, a Golgi matrix protein. Loss of GM130 abrogated cell polarity and consistent with the notion that polarity is frequently impaired in cancer, we found that GM130 is downregulated in colorectal cancer. Whether the loss of GM130 solely affects polarity, or whether it affects other processes relevant for tumorigenesis remains unclear. In a panel of breast cancer cells lines, we investigated the consequences of GM130 depletion on traits of relevance for tumor progression, such as survival, proliferation, adhesion, migration and invasion. We show that cellular assays that depend on polarity, such as chemotaxis and wound scratch assays, are only of limited use to investigate the role of polarity modulators in cancer. Depletion of GM130 increases cellular velocity and increases the invasiveness of breast cancer cells, therefore supporting the view that alterations of polarity contribute to tumor progression.

The CC-chemokine receptor 7 (CCR7) coordinates the migration of cancer cells as well as immune cells towards lymphatic organs where its two ligands CCL19 and CCL21 are constitutively expressed. Here we provide a topological model of CCR7, which belongs to the class A of G-protein coupled, seven-transmembrane spanning receptors, and describe how CCR7 expression is regulated. We focus on its role in cancer cell migration and metastasis formation and discuss how cancer cells can utilize CCR7 or its ligands to escape from immune surveillance.

Prostaglandin E2 (PGE2) is the most abundant eicosanoid and a very potent lipid mediator. PGE2 is produced predominantly from arachidonic acid by its tightly regulated cyclooxygenases (COX) and prostaglandin E synthases (PGES). Secreted PGE2 acts in an autocrine or paracrine manner through its four cognate G protein coupled receptors EP1 to EP4. Under physiological conditions, PGE2 is key in many biological functions, such as regulation of immune responses, blood pressure, gastrointestinal integrity, and fertility. Deregulated PGE2 synthesis or degradation is associated with severe pathological conditions like chronic inflammation, Alzheimer's disease, or tumorigenesis. Therefore, pharmacological inhibition of COX enzymes and PGE2 receptor antagonism is of great therapeutic interest.

BACKGROUND. The expression of the scavenger receptor for advanced glycation end products (RAGE) and various ligands of RAGE correlate significantly with cancer progression. However, the mechanism of RAGE/sRAGE-induced cancer cell activation and ligand usage remain largely unknown.METHODS. Androgen-independent, highly invasive, as well as androgen-dependent, non-invasive human prostate carcinoma (CaP) cells were investigated for their interaction with the soluble form of RAGE (sRAGE). Using neutralizing antibodies and soluble proteins, the ligand for RAGE was identified on CaP cells and ligand binding with sRAGE was biochemically characterized.RESULTS. Both androgen-independent, highly invasive and androgen-dependent, non-invasive CaP cells interacted with immobilized sRAGE in a surprisingly strong manner. Using C-terminal truncation variants of RAGE we identified the V domain being responsible for the adhesion of CaP cells to sRAGE. Moreover, we demonstrate that this adhesion cannot be blocked by S100B or neutralizing antibodies against beta integrins, or amphoterin. However, the Cap cell-RAGE interaction was inhibited with either AGE-modified proteins, or with neutralizing antibodies against AGE or RAGE. Despite similar binding kinetics between AGE-modified BSA and different RAGE domains, only applying an excess of sRAGE, but not the VC1 or V domain of RAGE, was able to block the CaP cell-RAGE interaction.CONCLUSIONS. We identified AGEs as the ligand for RAGE on both invasive and non-invasive prostate cancer cells.

Biodegradable microparticles (MP) represent a promising and efficient delivery system for parenteral vaccination. Recently, MP have also been explored as tool for the ex vivo antigen loading of professional antigen-presenting cells such as dendritic cells (DC) to be used as cellular vaccines. The purpose of this study was to investigate various polycationic coatings on poly(lactide-co-glycolide) (PLGA) MP, with regard to their effect on phenotypic and functional maturation of monocyte-derived DC (MoDC) that had previously been loaded with the MP in vitro. The preparation and concomitant coating of the PLGA was performed by means of a solvent extraction/evaporation method using a recently developed microextrusion-based technique. The polyelectrolytes tested for MP coating encompassed aminodextran, chitosan, poly(ethylene imine) (PEI), poly(l-lysine) and protamine. Uncoated and differently coated PLGA MP were fed to immature MoDC, which ingested efficiently the different MP types irrespective of their surface coating. The MP-loaded immature MoDC were then matured with the help of a cytokine/PGE-2 maturation cocktail. Here, the presence of the ingested MP did not affect the MoDC maturation in terms of expression of the surface markers CD80, CD83, CD86, HLA-DR and MMR, irrespective of the MP surface coating. Importantly, none of the PLGA MP types alone induced significant maturation of MoDC in the absence of the maturation cocktail. MP-loaded and subsequently matured MoDC expressed high levels of the chemokine receptor CCR7, whose functional activity was evidenced by the migration of MoDC towards CCL21, irrespective of the presence of ingested MP. Further, MP-loaded and subsequently matured MoDC also secreted comparable amounts of IL-10 and IL-12p70, irrespective of the presence of ingested MP except for PEI-coated PLGA MP, which enhanced significantly the secretion of IL-12p70 in mature MoDC. In conclusion, phenotypic and functional maturation of MoDC by means of a maturation cocktail remained unchanged irrespective of the presence of previously ingested differently coated PLGA MP. This offers interesting perspectives for using these particulate systems together with entrapped antigens for ex vivo loading of MoDC in view of cellular immunotherapy.

Background : Dendritic cell (DC)-based immunotherapy is a promising approach to augment tumor antigen-specific T cell responses in cancer patients. However, tumor escape with down-regulation or complete loss of target antigens may limit the susceptibility of tumor cells to the immune attack. Concomitant generation of T cell responses against several immunodominant antigens may circumvent this potential drawback. In this trial, we determined the immunostimulatory capacity of autologous DC pulsed with multiple T cell epitopes derived from four different prostate-specific antigens in patients with advanced hormone-refractory prostate cancer. Patients and methods : Autologous DC of HLA-A*0201 + patients with hormone-refractory prostate cancer were loaded with antigenic peptides derived from prostate stem cell antigen (PSCA 14–22 ), prostatic acid phosphatase (PAP 299–307 ), prostate-specific membrane antigen (PSMA 4–12 ), and prostate-specific antigen (PSA 154–163 ). DC were intradermally applied six times at biweekly intervals followed—in the case of an enhanced immune response—by monthly booster injections. Immune monitoring during the time of ongoing vaccinations (12–59 weeks) included ex vivo ELISPOT measurements, MHC tetramer analysis and in vitro cytotoxicity assays. Results : Of the initial six patients, three qualified for long-term multi-epitope DC vaccination. This regime was tolerated well by all three patients. The vaccination elicited significant cytotoxic T cell responses against all prostate-specific antigens tested. In addition, memory T cell responses against the control peptides derived from influenza matrix protein and tetanus toxoid were efficiently boosted. Clinically, the long-term DC vaccination was associated with an increase in PSA doubling time. Conclusions : DC-based multi-epitope immunotherapy with repeated boosting in men with hormone-refractory prostate carcinoma is feasible and generates efficient cellular antitumor responses.

Dendritic cell (DC)-based immunotherapy has been hampered by the lack of suitable methods for antigen delivery. Here, we use biodegradable poly(d,l-lactide-co-glycolide) microspheres (PLGA-MS) as carriers of peptides and proteins for antigen delivery to human monocyte-derived DC (MoDC). Compared to soluble proteins, MHC classes I and II-restricted presentation of PLGA-MS-encapsulated proteins and peptides by MoDC was markedly prolonged and proteins were presented 50-fold more efficiently on class I molecules. The vaccination of mice with DC loaded with PLGA-MS-encapsulated proteins raised strong and persisting cytotoxic T cell responses. In conclusion, antigen delivery via PLGA-MS markedly enhanced the duration of antigen presentation by human MoDC and the potency of DC-based vaccination.

Dendritic cells (DC) are increasingly explored as cellular vaccines for tumor immunotherapy. In most reported DC-based cancer vaccine trials, DC have been pulsed with soluble tumor antigen-derived peptide ligands of MHC molecules. Considering that the half-life of peptide/MHC complexes on the cell surface is relatively short and that soluble exogenous protein antigens cannot be efficiently processed via the MHC class I-processing pathway, the current vaccination procedure is not optimal for the induction of strong T cell responses aiming at tumor rejection. Recently, we have shown that antigen presentation can be prolonged when synthetic peptides were encapsulated in biodegradable poly(d,l-lactide-co-glycolide) (PLGA) microspheres (MS) for uptake by DC. In the present study, we investigated the phenotypic and functional consequences of MS uptake by human monocyte-derived dendritic cells (MoDC) in vitro. We found that immature MoDC that were prepared in serum free media suitable for clinical application were able to phagocytose high numbers of MS, while matured MoDC showed a reduced capacity for phagocytosis of MS. The ingestion of MS did not change the cell surface expression of CD80, CD83, CD86 and HLA-DR of immature and mature DC, suggesting that MS uptake did not induce DC maturation but that maturation by cytokines or LPS was unaltered in the presence of MS. Furthermore, MS-loaded mature MoDC expressed normal levels of the chemokine receptor CCR7 and migrated as efficiently towards CCL19 or CCL21 as unloaded MoDC. DC viability and the secretion of TNF-α and IL-12 was not significantly changed by MS loading. Taken together, our data indicate that PLGA-MS loading has no negative effects on the pivotal properties of MoDC in vitro. It should therefore be feasible to further develop this antigen loading strategy for clinical use in immunotherapy against viral infections and tumors.

So far, the pathogenic significance and use for diagnosis of antiganglioside GM1 antibodies (anti-GM1) are unclear. We therefore compared serum IgM and IgG antimonosialo ganglioside GM1 levels of 33 patients with presumed immune-mediated neuropathies, 100 patients with various other central or peripheral neurological disorders, and 110 controls by ELISA. We also measured the complement-activating capacity of anti-GM1 by C5b-9-GM1-ELISA to evaluate its value to distinguish between pathogenic and nonpathogenic autoantibodies. Low levels of anti-GM1 were observed in all disease categories and in controls (healthy blood donors). Twenty-four of the controls including the 10 with the highest serum IgM or IgG anti-GM1 were examined for neurological disorders in a double-blind checkup study. In the patients, elevated IgM anti-GM1 levels were predominantly found in those with neuropathies (NP), but barely in patients with central nervous system disease (CNSD). We found elevated IgG anti-GM1 levels predominantly in patients with NP of inflammatory origin (multifocal motor neuropathy, chronic inflammatory demyelinating polyneuropathy or Guillain-Barré syndrome), rarely in patients with NP of noninflammatory origin or CNSD, but not in the control disease group myasthenia gravis (MG). Median levels of IgM-, IgG-, (IgM+IgG)-, and C5b-9-binding anti-GM1 were significantly higher in patients with inflammatory NP as compared to the controls (p < 0.025). In addition, median levels of IgG- and (IgM+IgG)-anti-GM1 were significantly higher in inflammatory NP versus CNSD. Elevated complement-binding activity was associated with low or elevated IgM and/or IgG anti-GM1. Nevertheless, there was a significant correlation between anti-GM1 level (IgM+IgG) and the respective complement-activating capacity (r = 0.758; n = 243). Estimation of anti-GM1 and their respective complement-activating capacity may be helpful in the diagnosis of inflammatory neuropathies. However, neither an elevated anti-GM1 level nor an increased C5b-9 binding seems specific for a given disease category (e.g. peripheral nerve disease) nor a disease process (e.g. demyelination or inflammation).

Abstract:The presence of naturally occurring anti‐Galα1–3Gal (anti‐αGal) antibodies in human serum is believed to be a major factor in the hyperacute rejection of discordant organ xenografts such as the pig‐to‐human combination. Galα1–3Gal epitopes are expressed on pig tissues and the binding of anti‐αGal leads to endothelial cell activation and complement‐mediated, hyperacute graft rejection. One possible method to overcome this problem is to absorb anti‐αGal antibodies from the plasma of the xenograft recipient using a suitable immunoabsorbent or to interfere with their binding to tissues and thus prevent their cytotoxic activity by the intravenous injection of soluble antigen. We describe here the use of new synthetic antigens containing the Galα1–3Gal disaccharide (Bdi) epitope. Soluble conjugates of the Bdi with polyacrylamide (PAA‐Bdi) were used as coating antigens for an anti‐αGal ELISA as well as for in vitro inhibition of the cytotoxicity of anti‐αGal. An immunoabsorbent consisting of PAA‐Bdi coupled to macroporous glass (Sorbent Bdi) was tested for absorption of anti‐αGal from human serum.Anti‐αGal IgM, IgG and IgA could be detected by the anti‐αGal ELISA and were specifically absorbed by Sorbent Bdi with absorption efficiencies ranging from 70 to 50% for anti‐αGal IgG and 60 to 25% for anti‐αGal IgM. A comparison of the anti‐αGal absorption by Sorbent Bdi and rabbit red blood cells revealed a qualitatively (isotype distribution) and quantitatively similar pattern. Nonspecific absorption by Sorbent Bdi was low, as detected by the reduction of anti‐A trisaccharide antibodies. The cytotoxic effect of human serum on pig kidney (PK15) cells was almost totally inhibited by the addition of synthetic B disaccharide or by adsorption of the serum through immunoaffinity columns of PAA‐Bdi. We conclude that the newly developed, synthetic αGal1–3Gal antigens are suitable for the detection and immunoabsorption or inhibition of anti‐αGal antibodies.