Adaptive immune activation: glycosylation does matter

Changes in total plasma and serum N-glycome composition and patient-controlled analgesia after major abdominal surgery

Systemic inflammation participates to the complex healing process occurring after major surgery, thus directly affecting the surgical outcome and patient recovery. Total plasma N-glycome might be an indicator of inflammation after major surgery, as well as an anti-inflammatory therapy response marker, since protein glycosylation plays an essential role in the inflammatory cascade. Therefore, we assessed the effects of surgery on the total plasma N-glycome and the association with self-administration of postoperative morphine in two cohorts of patients that underwent major abdominal surgery. We found that plasma N-glycome undergoes significant changes one day after surgery and intensifies one day later, thus indicating a systemic physiological response. In particular, we observed the increase of bisialylated biantennary glycan, A2G2S[3,6]2, 12 hours after surgery, which progressively increased until 48 postoperative hours. Most changes occurred 24 hours after surgery with the decrease of most core-fucosylated biantennary structures, as well as the increase in sialylated tetraantennary and FA3G3S[3,3,3]3 structures. Moreover, we observed a progressive increase of sialylated triantennary and tetraantennary structures two days after surgery, with a concomitant decrease of the structures containing bisecting N-acetylglucosamine along with bi- and trisialylated triantennary glycans. We did not find any statistically significant association between morphine consumption and plasma N-glycome.

Label-Free Detection of Glycan-Protein Interactions for Array Development by Surface-Enhanced Raman Spectroscopy (SERS)

A glyco-array platform has been developed, in which glycans are attached to plasmonic nanoparticles through strain-promoted azide-alkyne cycloaddition. Glycan-protein binding events can then be detected in a label-free manner employing surface-enhanced Raman spectroscopy (SERS). As proof of concept, we have analyzed the binding of Gal1, Gal3, and influenza hemagglutinins (HAs) to various glycans and demonstrated that binding partners can be identified with high confidence. The attraction of SERS for optical sensing is that it can provide unique spectral signatures for glycan-protein complexes, confirm identity through statistical validation, and minimizes false positive results common to indirect methods. Furthermore, SERS is very sensitive and has multiplexing capabilities thereby allowing the simultaneous detection of multiple analytes.

Design of α-S-Neoglycopeptides Derived from MUC1 with a Flexible and Solvent-Exposed Sugar Moiety

The use of vaccines based on MUC1 glycopeptides is a promising approach to treat cancer. We present herein several sulfa-Tn antigens incorporated in MUC1 sequences that possess a variable linker between the carbohydrate (GalNAc) and the peptide backbone. The main conformations of these molecules in solution have been evaluated by combining NMR experiments and molecular dynamics simulations. The linker plays a key role in the modulation of the conformation of these compounds at different levels, blocking a direct contact between the sugar moiety and the backbone, promoting a helix-like conformation for the glycosylated residue and favoring the proper presentation of the sugar unit for molecular recognition events. The feasibility of these novel compounds as mimics of MUC1 antigens has been validated by the X-ray diffraction structure of one of these unnatural derivatives complexed to an anti-MUC1 monoclonal antibody. These features, together with potential lack of immune suppression, render these unnatural glycopeptides promising candidates for designing alternative therapeutic vaccines against cancer.

IgG Glycome in Colorectal Cancer

PURPOSE

Alternative glycosylation has significant structural and functional consequences on IgG and consequently also on cancer immunosurveillance. Because of technological limitations, the effects of highly heritable individual variations and the differences in the dynamics of changes in IgG glycosylation on colorectal cancer were never investigated before.

EXPERIMENTAL DESIGN

Using recently developed high-throughput UPLC technology for IgG glycosylation analysis, we analyzed IgG glycome composition in 760 patients with colorectal cancer and 538 matching controls. Effects of surgery were evaluated in 28 patients sampled before and three times after surgery. A predictive model was built using regularized logistic regression and evaluated using a 10-cross validation procedure. Furthermore, IgG glycome composition was analyzed in 39 plasma samples collected before initial diagnosis of colorectal cancer.

RESULTS

We have found that colorectal cancer associates with decrease in IgG galactosylation, IgG sialylation and increase in core-fucosylation of neutral glycans with concurrent decrease of core-fucosylation of sialylated glycans. Although a model based on age and sex did not show discriminative power (AUC = 0.499), the addition of glycan variables into the model considerably increased the discriminative power of the model (AUC = 0.755). However, none of these differences were significant in the small set of samples collected before the initial diagnosis.

CONCLUSIONS

Considering the functional relevance of IgG glycosylation for both tumor immunosurveillance and clinical efficacy of therapy with mAbs, individual variation in IgG glycosylation may turn out to be important for prediction of disease course or the choice of therapy, thus warranting further, more detailed studies of IgG glycosylation in colorectal cancer. Clin Cancer Res; 22(12); 3078-86. ©2016 AACR.

Virus-like particles derived from Pichia pastoris-expressed dengue virus type 1 glycoprotein elicit homotypic virus-neutralizing envelope domain III-directed antibodies

Background

Four antigenically distinct serotypes (1–4) of dengue viruses (DENVs) cause dengue disease. Antibodies to any one DENV serotype have the potential to predispose an individual to more severe disease upon infection with a different DENV serotype. A dengue vaccine must elicit homotypic neutralizing antibodies to all four DENV serotypes to avoid the risk of such antibody-dependent enhancement in the vaccine recipient. This is a formidable challenge as evident from the lack of protective efficacy against DENV-2 by a tetravalent live attenuated dengue vaccine that has completed phase III trials recently. These trial data underscore the need to explore non-replicating subunit vaccine alternatives. Recently, using the methylotrophic yeast Pichia pastoris, we showed that DENV-2 and DENV-3 envelope (E) glycoproteins, expressed in absence of prM, implicated in causing severe dengue disease, self-assemble into virus-like particles (VLPs), which elicit predominantly virus-neutralizing antibodies and confer significant protection against lethal DENV challenge in an animal model. The current study extends this work to a third DENV serotype.

Results

We cloned and expressed DENV-1 E antigen in P. pastoris, and purified it to near homogeneity. Recombinant DENV-1 E underwent post-translational processing, namely, signal peptide cleavage and glycosylation. Purified DENV-1 E self-assembled into stable VLPs, based on electron microscopy and dynamic light scattering analysis. Epitope mapping with monoclonal antibodies revealed that the VLPs retained the overall antigenic integrity of the virion particles despite the absence of prM. Subtle changes accompanied the efficient display of E domain III (EDIII), which contains type-specific neutralizing epitopes. These VLPs were immunogenic, eliciting predominantly homotypic EDIII-directed DENV-1-specific neutralizing antibodies.

Conclusions

This work demonstrates the inherent potential of P. pastoris-expressed DENV-1 E glycoprotein to self-assemble into VLPs eliciting predominantly homotypic neutralizing antibodies. This work justifies an investigation of the last remaining serotype, namely, DENV-4, to assess if it also shares the desirable vaccine potential manifested by the remaining three DENV serotypes. Such efforts could make it possible to envisage the development of a tetravalent dengue vaccine based on VLPs of P. pastoris-expressed E glycoproteins of the four DENV serotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-016-0280-y) contains supplementary material, which is available to authorized users.

Carbohydrates as T-cell antigens with implications in health and disease

Glycosylation is arguably the most ubiquitous post-translational modification on proteins in microbial and mammalian cells. During the past few years, there has been intensive research demonstrating that carbohydrates, either in pure forms or in conjunction with proteins or lipids, evoke and modulate adaptive immune responses. We now know that carbohydrates can be directly recognized by T cells or participate in T-cell stimulation as components of T-cell epitopes. T-cell recognition of carbohydrate antigens takes place via their presentation by major histocompatibility complex pathways on antigen-presenting cells. In this review, we summarize studies on carbohydrates as T-cell antigens modulating adaptive immune responses. Through discussion of glycan-containing antigens, such as glycoproteins, glycolipids, zwitterionic polysaccharides and carbohydrate-based glycoconjugate vaccines, we will illustrate the key molecular and cellular interactions between carbohydrate antigens and T cells and the implications of these interactions in health and disease.

Emerging roles of protein mannosylation in inflammation and infection

Proteins are frequently modified by complex carbohydrates (glycans) that play central roles in maintaining the structural and functional integrity of cells and tissues in humans and lower organisms. Mannose forms an essential building block of protein glycosylation, and its functional involvement as components of larger and diverse α-mannosidic glycoepitopes in important intra- and intercellular glycoimmunological processes is gaining recognition. With a focus on the mannose-rich asparagine (N-linked) glycosylation type, this review summarises the increasing volume of literature covering human and non-human protein mannosylation, including their structures, biosynthesis and spatiotemporal expression. The review also covers their known interactions with specialised host and microbial mannose-recognising C-type lectin receptors (mrCLRs) and antibodies (mrAbs) during inflammation and pathogen infection. Advances in molecular mapping technologies have recently revealed novel immuno-centric mannose-terminating truncated N-glycans, termed paucimannosylation, on human proteins. The cellular presentation of α-mannosidic glycoepitopes on N-glycoproteins appears tightly regulated; α-mannose determinants are relative rare glycoepitopes in physiological extracellular environments, but may be actively secreted or leaked from cells to transmit potent signals when required. Simultaneously, our understanding of the molecular basis on the recognition of mannosidic epitopes by mrCLRs including DC-SIGN, mannose receptor, mannose binding lectin and mrAb is rapidly advancing, together with the functional implications of these interactions in facilitating an effective immune response during physiological and pathophysiological conditions. Ultimately, deciphering these complex mannose-based receptor-ligand interactions at the detailed molecular level will significantly advance our understanding of immunological disorders and infectious diseases, promoting the development of future therapeutics to improve patient clinical outcomes.

Synthesis of glycoaminooxy acid and N-oxyamide-linked glycolipids

Synthesis of orthogonally protected glycoaminooxy acid and fully deprotected N-oxyamide-linked novel glycolipids is reported.

N–O linkage in carbohydrates and glycoconjugates

The synthesis and chemical and physicochemical properties as well as biological and medical applications of various hydroxylamine-functionalized carbohydrate derivatives are summarized.

Mycobacterial infection induces a specific human innate immune response

The innate immune system provides the first response to infection and is now recognized to be partially pathogen-specific. Mycobacterium tuberculosis (MTB) is able to subvert the innate immune response and survive inside macrophages. Curiously, only 5-10% of otherwise healthy individuals infected with MTB develop active tuberculosis (TB). We do not yet understand the genetic basis underlying this individual-specific susceptibility. Moreover, we still do not know which properties of the innate immune response are specific to MTB infection. To identify immune responses that are specific to MTB, we infected macrophages with eight different bacteria, including different MTB strains and related mycobacteria, and studied their transcriptional response. We identified a novel subset of genes whose regulation was affected specifically by infection with mycobacteria. This subset includes genes involved in phagosome maturation, superoxide production, response to vitamin D, macrophage chemotaxis, and sialic acid synthesis. We suggest that genetic variants that affect the function or regulation of these genes should be considered candidate loci for explaining TB susceptibility.

Extended O-GlcNAc on HLA Class-I-Bound Peptides

We report unexpected mass spectrometric observations of glycosylated human leukocyte antigen (HLA) class I-bound peptides. Complemented by molecular modeling, in vitro enzymatic assays, and oxonium ion patterns, we propose that the observed O-linked glycans carrying up to five monosaccharides are extended O-GlcNAc's rather than GalNAc-initiated O-glycans. A cytosolic O-GlcNAc modification is normally terminal and does not extend to produce a polysaccharide, but O-GlcNAc on an HLA peptide presents a special case because the loaded HLA class I complex traffics through the endoplasmic reticulum and Golgi apparatus on its way to the cell membrane and is hence exposed to glycosyltransferases. We also report for the first time natural HLA class I presentation of O- and N-linked glycopeptides derived from membrane proteins. HLA class I peptides with centrally located oligosaccharides have been shown to be immunogenic and may thus be important targets for immune surveillance.

Modification of Asparagine-Linked Glycan Density for the Design of Hepatitis B Virus Virus-Like Particles with Enhanced Immunogenicity

The small envelope proteins (HBsAgS) derived from hepatitis B virus (HBV) represent the antigenic components of the HBV vaccine and are platforms for the delivery of foreign antigenic sequences. To investigate structure-immunogenicity relationships for the design of improved immunization vectors, we have generated biochemically modified virus-like particles (VLPs) exhibiting glycoengineered HBsAgS. For the generation of hypoglycosylated VLPs, the wild-type (WT) HBsAgS N146 glycosylation site was converted to N146Q; for constructing hyperglycosylated VLPs, potential glycosylation sites were introduced in the HBsAgS external loop region at positions T116 and G130 in addition to the WT site. The introduced T116N and G130N sites were utilized as glycosylation anchors resulting in the formation of hyperglycosylated VLPs. Mass spectroscopic analyses showed that the hyperglycosylated VLPs carry the same types of glycans as WT VLPs, with minor variations regarding the degree of fucosylation, bisecting N-acetylglucosamines, and sialylation. Antigenic fingerprints for the WT and hypo- and hyperglycosylated VLPs using a panel of 19 anti-HBsAgS monoclonal antibodies revealed that 15 antibodies retained their ability to bind to the different VLP glyco-analogues, suggesting that the additional N-glycans did not shield extensively for the HBsAgS-specific antigenicity. Immunization studies with the different VLPs showed a strong correlation between N-glycan abundance and antibody titers. The T116N VLPs induced earlier and longer-lasting antibody responses than did the hypoglycosylated and WT VLPs. The ability of nonnative VLPs to promote immune responses possibly due to differences in their glycosylation-related interaction with cells of the innate immune system illustrates pathways for the design of immunogens for superior preventive applications.

IMPORTANCE

The use of biochemically modified, nonnative immunogens represents an attractive strategy for the generation of modulated or enhanced immune responses possibly due to differences in their interaction with immune cells. We have generated virus-like particles (VLPs) composed of hepatitis B virus envelope proteins (HBsAgS) with additional N-glycosylation sites. Hyperglycosylated VLPs were synthesized and characterized, and the results demonstrated that they carry the same types of glycans as wild-type VLPs. Comparative immunization studies demonstrated that the VLPs with the highest N-glycan density induce earlier and longer-lasting antibody immune responses than do wild-type or hypoglycosylated VLPs, possibly allowing reduced numbers of vaccine injections. The ability to modulate the immunogenicity of an immunogen will provide opportunities to develop optimized vaccines and VLP delivery platforms for foreign antigenic sequences, possibly in synergy with the use of suitable adjuvanting compounds.

Glycocalyx-Mimicking Nanoparticles for Stimulation and Polarization of Macrophages via Specific Interactions

Malignant tumors develop multiple mechanisms to impair and escape from antitumor immune responses, of which tumor-associated macrophages that often show immunosuppressive phenotype (M2), play a critical role in tumor-induced immunosuppression. Therefore, strategies that can reverse M2 phenotype and even enhance immune-stimulation function of macrophage would benefit tumor immunotherapy. In this paper, self-assembled glyco-nanoparticles (glyco-NPs), as artificial glycocalyx, have been found to be able to successfully induce the polarization of mouse primary peritoneal macrophages from M2 to inflammatory type (M1). The polarization change was evidenced by the decreased expression of cell surface signaling molecules CD206 and CD23, and the increased expression of CD86. Meanwhile, secretion of cytokines supported this polarization change as well. More importantly, this phenomenon is observed not only in vitro, but also in vivo. As far as we known, this is the first report about macrophage polarization being induced by synthetic nanomaterials. Moreover, preparation, characterization of these glyco-NPs and their interaction with the macrophages are also demonstrated.

Systematic and site-specific analysis of N-sialoglycosylated proteins on the cell surface by integrating click chemistry and MS-based proteomics

Glycoproteins on the cell surface are ubiquitous and essential for cells to interact with the extracellular matrix, communicate with other cells, and respond to environmental cues. Although surface sialoglycoproteins can dramatically impact cell properties and represent different cellular statuses, global and site-specific analysis of sialoglycoproteins only on the cell surface is extraordinarily challenging. An effective method integrating metabolic labeling, copper-free click chemistry and mass spectrometry-based proteomics was developed to globally and site-specifically analyze surface N-sialoglycoproteins. Surface sialoglycoproteins metabolically labeled with a functional group were specifically tagged through copper-free click chemistry, which is ideal because it is quick, specific and occurs under physiological conditions. Sequentially tagged sialoglycoproteins were enriched for site-specific identification by mass spectrometry. Systematic and quantitative analysis of the surface N-sialoglycoproteome in cancer cells with distinctive invasiveness demonstrated many N-sialoglycoproteins up-regulated in invasive cells, the majority of which contained cell adhesion-related domains. This method is very effective to globally and site-specifically analyze N-sialoglycoproteins on the cell surface, and will have extensive applications in the biological and biomedical research communities. Site-specific information regarding surface sialoglycoproteins can serve as biomarkers for disease detection, targets for vaccine development and drug treatment.

Carbohydrates on Proteins: Site-Specific Glycosylation Analysis by Mass Spectrometry

Glycosylation on proteins adds complexity and versatility to these biologically vital macromolecules. To unveil the structure-function relationship of glycoproteins, glycopeptide-centric analysis using mass spectrometry (MS) has become a method of choice because the glycan is preserved on the glycosylation site and site-specific glycosylation profiles of proteins can be readily determined. However, glycopeptide analysis is still challenging given that glycopeptides are usually low in abundance and relatively difficult to detect and the resulting data require expertise to analyze. Viewing the urgent need to address these challenges, emerging methods and techniques are being developed with the goal of analyzing glycopeptides in a sensitive, comprehensive, and high-throughput manner. In this review, we discuss recent advances in glycoprotein and glycopeptide analysis, with topics covering sample preparation, analytical separation, MS and tandem MS techniques, as well as data interpretation and automation.

Lipophilic Muramyl Dipeptide-Antigen Conjugates as Immunostimulating Agents

Muramyl dipeptide (MDP) is the smallest peptidoglycan fragment capable of triggering the innate immune system through interaction with the intracellular NOD2 receptor. To develop synthetic vaccine modalities composed of an antigenic entity (typically a small peptide) and a molecular adjuvant with well-defined activity, we previously assembled covalent MDP-antigen conjugates. Although these were found to be capable of stimulating the NOD2 receptor and were processed by dendritic cells (DCs) leading to effective antigen presentation, DC maturation--required for an apt immune response--could not be achieved with these conjugates. To improve the efficacy of these vaccine modalities, we equipped the MDP moiety with lipophilic tails, well-known modifications to enhance the immune-stimulatory activity of MDPs. Herein we report the design and synthesis of a lipophilic MDP-antigen conjugate and show that it is a promising vaccine modality capable of stimulating the NOD2 receptor, maturing DCs, and delivering antigen cargo into the MHC-I cross-presentation pathway.

Glycans Instructing Immunity: The Emerging Role of Altered Glycosylation in Clinical Immunology

Protein glycosylation is an important epigenetic modifying process affecting expression, localization, and function of numerous proteins required for normal immune function. Recessive germline mutations in genes responsible for protein glycosylation processes result in congenital disorders of glycosylation and can have profound immunologic consequences. Genetic mutations in immune signaling pathways that affect glycosylation sites have also been shown to cause disease. Sugar supplementation and in vivo alteration of glycans by medication holds therapeutic promise for some of these disorders. Further understanding of how changes in glycosylation alter immunity may provide novel treatment approaches for allergic disease, immune dysregulation, and immunodeficiency in the future.

N-Glycosylation Fingerprinting of Viral Glycoproteins by xCGE-LIF

The ongoing threat of pathogens, increasing resistance against antibiotics, and the risk of fast spreading of infectious diseases in a global community resulted in an intensified development of vaccines. Antigens used for vaccination comprise a wide variety of macromolecules including glycoproteins, lipopolysaccharides, and complex carbohydrates. For all of these antigens the sugar composition plays a crucial role for immunogenicity and protective efficacy of the vaccine. Here, we provide a protocol for N-glycosylation fingerprinting utilizing high performance multiplexed capillary gel electrophoresis with laser-induced fluorescence detection (xCGE-LIF) technology. The method described, enables to analyze the N-glycosylation of specific proteins out of a complex sample or even the total of all N-glycans contained in such a sample. The protocol is exemplarily demonstrated for N-glycosylation fingerprinting of cell culture-derived influenza A and B viruses and their major antigens, the membrane glycoproteins hemagglutinin and neuraminidase.

Design, automated synthesis and immunological evaluation of NOD2-ligand-antigen conjugates

The covalent attachment of an innate immune system stimulating agent to an antigen can provide active vaccine modalities capable of eliciting a potent immune response against the incorporated antigen. Here we describe the design, automated synthesis and immunological evaluation of a set of four muramyl dipeptide-peptide antigen conjugates. Muramyl dipeptide (MDP) represents a well-known ligand for the intracellular NOD2 receptor and our study shows that covalently linking an MDP-moiety to an antigenic peptide can lead to a construct that is capable of stimulating the NOD2 receptor if the ligand is attached at the anomeric center of the muramic acid. The constructs can be processed by dendritic cells (DCs) and the conjugation does not adversely affect the presentation of the incorporated SIINFEKL epitope on MHC-I molecules. However, stimulation of the NOD2 receptor in DCs was not sufficient to provide a strong immunostimulatory signal.

Glycans in immune recognition and response

Glycans at the forefront of cells facilitate immune recognition processes. Cancer cells commonly present altered cell surface glycosylation, especially manifested in the expression of sialic acid at the termini of glycolipids and glycoproteins. Although tumor-associated carbohydrate antigens (TACAs) result in expression of altered-self, most such carbohydrates do not elicit strong humoral responses. Various strategies had been devised to elicit increased immunogenicity of such TACA aiming for potent immunotherapeutic antibodies or cancer vaccines. However some carbohydrates are immunogenic in humans and hold potential for novel glycotherapies. N-Glycolylneuraminic acid (Neu5Gc) is a foreign immunogenic sugar in humans originating from the diet (e.g., red meat) and subsequently expressed on the cell surface, especially accumulating on carcinoma. Consequently, the human immune system detects this non-self carbohydrate generating a broad anti-Neu5Gc antibody response. The co-existence of Neu5Gc/anti-Neu5Gc within humans spurs chronic inflammation mediated disease, including cancer. Concurrently, anti-Neu5Gc antibodies hold potential for novel targeted therapy. αGal is another foreign immunogenic carbohydrate antigen in humans and all humans have circulating anti-Gal antibodies. This review aims to describe the immunogenicity of Neu5Gc and its implications for human diseases, highlighting differences and similarities with αGal and its potential for novel targeted theranostics.

Adaptable synthesis of C-lactosyl glycoclusters and their binding properties with galectin-3

The synthesis of mono- to tetravalent C-β-lactosyl glycoclusters has been achieved in good yield. The K_D values of glycoclusters against galectin-3 were tested by SPR assay, and the structure–activity relationship has been summarized in detail.