Glycan recognition by human blood mononuclear cells with an emphasis on dendritic cells

Synthesis of bodipy-labeled bacterial polysaccharides and their interaction with human dendritic cells

In this report, we describe the fluorescent labeling of bacterial polysaccharides (Escherichia coli O86:B7, Escherichia coli O19ab, Pseudomonas aeruginosa O10a10b, and Shigella flexneri 2b) at the "natural" amino group of their phosphoethanolamine moiety. Two protocols for labeling are compared: 1) on a scale of a few mg of the polysaccharide, with a dialysis procedure for purification from excessive reagents; and 2) on a scale of 0.1 mg of the polysaccharide, with a simple precipitation procedure instead of dialysis. The microscale version is sufficient for comfortable cytofluorometric analysis. The resulting probes were found to specifically bind to human dendritic cells in a dose-dependent manner. The used limited set of polysaccharides did not allow us even to get close to understanding which dendritic cell-associated lectins and which cognate polysaccharide epitopes are involved in recognition, but the proposed microscale protocol allows to generate a library of fluorescent probes for further mapping of the polysaccharide specificity of the dendritic cells.

Tolerogenic Immunotherapy: Targeting DC Surface Receptors to Induce Antigen-Specific Tolerance

Dendritic cells (DCs) are well-established as major players in the regulation of immune responses. They either induce inflammatory or tolerogenic responses, depending on the DC-subtype and stimuli they receive from the local environment. This dual capacity of DCs has raised therapeutic interest for their use to modify immune-activation via the generation of tolerogenic DCs (tolDCs). Several compounds such as vitamin D3, retinoic acid, dexamethasone, or IL-10 and TGF-β have shown potency in the induction of tolDCs. However, an increasing interest exists in defining tolerance inducing receptors on DCs for new targeting strategies aimed to develop tolerance inducing immunotherapies, on which we focus particular in this review. Ligation of specific cell surface molecules on DCs can result in antigen presentation to T cells in the presence of inhibitory costimulatory molecules and tolerogenic cytokines, giving rise to regulatory T cells. The combination of factors such as antigen structure and conformation, delivery method, and receptor specificity is of paramount importance. During the last decades, research provided many tools that can specifically target various receptors on DCs to induce a tolerogenic phenotype. Based on advances in the knowledge of pathogen recognition receptor expression profiles in human DC subsets, the most promising cell surface receptors that are currently being explored as possible targets for the induction of tolerance in DCs will be discussed. We also review the different strategies that are being tested to target DC receptors such as antigen-carbohydrate conjugates, antibody-antigen fusion proteins and antigen-adjuvant conjugates.

40 years of glyco-polyacrylamide in glycobiology

Polyacrylamide conjugates of glycans have long been widely used in many research areas of glycobiology, mainly for immobilizing glycans in solid-phase assays and as multivalent inhibitors. Pending biotin tag allows immobilizing Glyc-PAA quantitatively on any surface, and acts as a tracer for detection of carbohydrate-binding proteins. However, the scope of already realized capabilities of these probes is immeasurably richer than those listed above. This review is not so much about routine as about less common, but not less significant applications. Also, the data on the glycopolymers themselves, their molecular weight, size and polymer chain flexibility are presented, as well as the methods of synthesis, clusterisation and entropy factor in their interaction with proteins.

An innovative immunotherapeutic strategy for ovarian cancer: CLEC10A and glycomimetic peptides

BACKGROUND

Receptors specific for the sugar N-acetylgalactosamine (GalNAc) include the human type II, C-type lectin receptor macrophage galactose-type lectin/C-type lectin receptor family member 10A (MGL/CLEC10A/CD301) that is expressed prominently by human peripheral immature dendritic cells, dendritic cells in the skin, alternatively-activated (M2a) macrophages, and to lesser extents by several other types of tissues. CLEC10A is an endocytic receptor on antigen-presenting cells and has been proposed to play an important role in maturation of dendritic cells and initiation of an immune response. In this study, we asked whether a peptide that binds in the GalNAc-binding site of CLEC10A would serve as an effective tool to activate an immune response against ovarian cancer.

METHODS

A 12-mer sequence emerged from a screen of a phage display library with a GalNAc-specific lectin. The peptide, designated svL4, and a shorter peptide consisting of the C-terminal 6 amino acids, designated sv6D, were synthesized as tetravalent structures based on a tri-lysine core. In silico and in vitro binding assays were developed to evaluate binding of the peptides to GalNAc-specific receptors. Endotoxin-negative peptide solutions were administered by subcutaneous injection and biological activity of the peptides was determined by secretion of cytokines and the response of peritoneal immune cells in mice. Anti-cancer activity was studied in a murine model of ovarian cancer.

RESULTS

The peptides bound to recombinant human CLEC10A with high avidity, with half-maximal binding in the low nanomolar range. Binding to the receptor was Ca²⁺-dependent. Subcutaneous injection of low doses of peptides into mice on alternate days resulted in several-fold expansion of populations of mature immune cells within the peritoneal cavity. Peptide sv6D effectively suppressed development of ascites in a murine ovarian cancer model as a monotherapy and in combination with the chemotherapeutic drug paclitaxel or the immunotherapeutic antibody against the receptor PD-1. Toxicity, including antigenicity and release of cytotoxic levels of cytokines, was not observed.

CONCLUSION

sv6D is a functional ligand for CLEC10A and induces maturation of immune cells in the peritoneal cavity. The peptide caused a highly significant extension of survival of mice with implanted ovarian cancer cells with a favorable toxicity and non-antigenic profile.