Entirely Carbohydrate-Based Vaccines: An Emerging Field for Specific and Selective Immune Responses

Total synthesis of a structurally complex zwitterionic hexasaccharide repeating unit of polysaccharide B from Bacteroides fragilis via one-pot glycosylation

Zwitterionic polysaccharides (ZPSs) present on the surface of a common gut commensal Bacteroides fragilis are endowed with unique immunological properties as they can directly bind to T-cells in the absence of protein conjugation. ZPSs are therefore considered to be potential antigens for the development of totally carbohydrate-based vaccines. Herein, we disclose the first total synthesis of a highly branched phosphorylated zwitterionic capsular polysaccharide repeating unit of Bacteroides fragilis. The hexasaccharide repeating unit bearing six different monosaccharides comprises three 1,2-cis-glycosidic linkages, a challenging 1,2-trans linkage in D-QuipNAc-β-(1→4)-D-Gal motif, and a 2-aminoethyl phosphonate appendage. The synthesis of target ZPS was accomplished utilizing an expeditious, highly stereoselective and convergent (1 + 2 + 2 + 1) one-pot glycosylation strategy. The striking features include efficient synthesis of rare deoxy amino sugars D- and L-quinovosamine, stereoselective installation of three 1,2-cis glycosidic linkages, glycosylation of D-quinovosamine donor with a sterically crowded, poorly reactive 4-OH galactose moiety, as well as late stage phosphorylation.

Are tumor-associated carbohydrates the missing link between the gut microbiome and response to immune checkpoint inhibitor treatment in cancer?

Immune checkpoint inhibitor therapy has dramatically improved survival in a significant subset of patients with several solid tumor types. Increasing the number of patients benefitting from this form of therapy is an important translational research goal. Correlations between the composition of the gut microbiome and response to immune checkpoint inhibitor therapy raised the possibility that direct modulation of the gut microbiome may significantly improve the clinical benefit of this treatment. Several lines of observations suggest that tumor-associated carbohydrates, including those recognized as blood group-related glycolipid antigens, such as the Forssman antigen, may be some of the key factors behind this clinical correlation. Such antigens are expressed in human cancer, humans often produce antibodies against those, and they can induce antibody directed cellular cytotoxicity. Importantly, these antibodies are often induced by antigens present in microbes of the gut. If identified, these antibodies could be boosted by appropriate vaccination techniques and thus enhance anti-tumor immunity with minimal side effects.

De Novo Synthetic Approach to 2,4-Diamino-2,4,6-trideoxyhexoses (DATDH): Bacterial and Rare Deoxy-Amino Sugars

A synthetic route to 2,4-diamino-2,4,6-trideoxysugar stereoisomers in 6-7 steps and 22-33% overall yield is described. A key step in this pathway is the carbonyl coupling of d- and l-threoninol or d- and l-allo-threoninol to a phthalimido-allene mediated by chiral iridium-H8-BINAP, which allows for installation of two new chiral centers in one, highly diastereoselective (>20:1 dr) step. This approach provides a more concise, diastereoselective, and versatile method to access these deoxy-amino sugars than is currently available.

A Hitchhiker's Guide to Problem Selection in Carbohydrate Synthesis

Oligosaccharides are ubiquitous in molecular biology and are used for functions ranging from governing protein folding to intercellular communication. Perhaps paradoxically, the exact role of the glycan in most of these settings is not well understood. One reason for this contradiction concerns the fact that carbohydrates often appear in heterogeneous form in nature. These mixtures complicate the isolation of pure material and characterization of structure-activity relationships. As a result, a major bottleneck in glycoscience research is the synthesis and modification of pure materials. While synthetic and chemoenzymatic methods have enabled access to homogeneous tool compounds, a central problem, particularly for newer synthetic chemists, is the matter of problem selection. This outlook aims to provide an entry level overview of fundamental principles in carbohydrate chemistry with an eye toward enabling solutions to frontier challenges.

Total Synthesis and Structural Studies of Zwitterionic Bacteroides fragilis Polysaccharide A1 Fragments

Zwitterionic polysaccharides (ZPSs) are exceptional carbohydrates, carrying both positively charged amine groups and negatively charged carboxylates, that can be loaded onto MHC-II molecules to activate T cells. It remains enigmatic, however, how these polysaccharides bind to these receptors, and to understand the structural features responsible for this "peptide-like" behavior, well-defined ZPS fragments are required in sufficient quantity and quality. We here present the first total synthesis of Bacteroides fragilis PS A1 fragments encompassing up to 12 monosaccharides, representing three repeating units. Key to our successful syntheses has been the incorporation of a C-3,C-6-silylidene-bridged "ring-inverted" galactosamine building block that was designed to act as an apt nucleophile as well as a stereoselective glycosyl donor. Our stereoselective synthesis route is further characterized by a unique protecting group strategy, built on base-labile protecting groups, which has allowed the incorporation of an orthogonal alkyne functionalization handle. Detailed structural studies have revealed that the assembled oligosaccharides take up a bent structure, which translates into a left-handed helix for larger PS A1 polysaccharides, presenting the key positively charged amino groups to the outside of the helix. The availability of the fragments and the insight into their secondary structure will enable detailed interaction studies with binding proteins to unravel the mode of action of these unique oligosaccharides at the atomic level.

Development in the Concept of Bacterial Polysaccharide Repeating Unit-Based Antibacterial Conjugate Vaccines

The surface of cells is coated with a dense layer of glycans, known as the cell glycocalyx. The complex glycans in the glycocalyx are involved in various biological events, such as bacterial pathogenesis, protection of bacteria from environmental stresses, etc. Polysaccharides on the bacterial cell surface are highly conserved and accessible molecules, and thus they are excellent immunological targets. Consequently, bacterial polysaccharides and their repeating units have been extensively studied as antigens for the development of antibacterial vaccines. This Review surveys the recent developments in the synthetic and immunological investigations of bacterial polysaccharide repeating unit-based conjugate vaccines against several human pathogenic bacteria. The major challenges associated with the development of functional carbohydrate-based antibacterial conjugate vaccines are also considered.

Mass spectrometry and the cellular surfaceome

The collection of exposed plasma membrane proteins, collectively termed the surfaceome, is involved in multiple vital cellular processes, such as the communication of cells with their surroundings and the regulation of transport across the lipid bilayer. The surfaceome also plays key roles in the immune system by recognizing and presenting antigens, with its possible malfunctioning linked to disease. Surface proteins have long been explored as potential cell markers, disease biomarkers, and therapeutic drug targets. Despite its importance, a detailed study of the surfaceome continues to pose major challenges for mass spectrometry-driven proteomics due to the inherent biophysical characteristics of surface proteins. Their inefficient extraction from hydrophobic membranes to an aqueous medium and their lower abundance compared to intracellular proteins hamper the analysis of surface proteins, which are therefore usually underrepresented in proteomic datasets. To tackle such problems, several innovative analytical methodologies have been developed. This review aims at providing an extensive overview of the different methods for surfaceome analysis, with respective considerations for downstream mass spectrometry-based proteomics.

Antitumor Properties of Epitope-Specific Engineered Vaccine in Murine Model of Melanoma

Finding new effective compounds of natural origin for composing anti-tumor vaccines is one of the main goals of antitumor research. Promising anti-cancer agents are the gastropodan hemocyanins-multimeric copper-containing glycoproteins used so far for therapy of different tumors. The properties of hemocyanins isolated from the marine snail Rapana thomasiana (RtH) and the terrestrial snail Helix aspersa (HaH) upon their use as carrier-proteins in conjugated vaccines, containing ganglioside mimotope GD3P4 peptide, were studied in the developed murine melanoma model. Murine melanoma cell line B16F10 was used for solid tumor establishment in C57BL/6 mice using various schemes of therapy. Protein engineering, flow cytometry, and cytotoxicity assays were also performed. The administration of the protein-engineered vaccines RtH-GD3P4 or HaH-GD3P4 under the three different regimens of therapy in the B16F10 murine melanoma model suppressed tumor growth, decreased tumor incidence, and prolonged the survival of treated animals. The immunization of experimental mice induced an infiltration of immunocompetent cells into the tumors and generated cytotoxic tumor-specific T cells in the spleen. The treatment also generates significantly higher levels of tumor-infiltrated M1 macrophages, compared to untreated tumor-bearing control mice. This study demonstrated a promising approach for cancer therapy having potential applications for cancer vaccine research.

The Shape of Nanostructures Encodes Immunomodulation of Carbohydrate Antigen and Vaccine Development

Gold nanoparticles (AuNPs) have shown remarkable potential for vaccine development, but the influence of the size and shape of nanoparticles modulating the T-cell-dependent carbohydrate antigen processing and immunomodulation is poorly investigated. Here, we described how different shapes and sizes of gold nanostructures carrying adjuvant modulate carbohydrate-based antigen processing in murine dendritic cells (mDCs) and subsequent T-cell activation produce a robust antibody response. As a prototype, CpG-adjuvant-coated spherical and rod- and star-shaped AuNPs were conjugated to the tripodal Tn-glycopeptide antigen to study their DC uptake and activation of T-cells in a DCs/T-cell co-culture assay. Our results showed that the spherical and star-shaped AuNPs displayed relatively weak receptor-mediated uptake and endosomal sequestration; however, they induced a high level of T helper-1 (Th1) biasing immune responses compared with rod-shaped AuNPs. Furthermore, the in vivo administration of AuNPs showed that the small spherical and star-shaped AuNPs induced an effective anti-Tn-glycopeptide immunoglobulin (IgG) antibody response compared with rod-shaped AuNPs. These results indicated that one could obtain superior carbohydrate vaccines by varying the shape and size parameters of nanostructures.

Glycoconjugate Nanoparticle-Based Systems in Cancer Immunotherapy: Novel Designs and Recent Updates

For many years, cell-surface glycans (in particular, Tumor-Associated Carbohydrate Antigens, TACAs) have been the target of both passive and active anticancer immunotherapeutic design. Recent advances in immunotherapy as a treatment for a variety of malignancies has revolutionized anti-tumor treatment regimens. Checkpoint inhibitors, Chimeric Antigen Receptor T-cells, Oncolytic virus therapy, monoclonal antibodies and vaccines have been developed and many approvals have led to remarkable outcomes in a subset of patients. However, many of these therapies are very selective for specific patient populations and hence the search for improved therapeutics and refinement of techniques for delivery are ongoing and fervent research areas. Most of these agents are directed at protein/peptide epitopes, but glycans-based targets are gaining in popularity, and a handful of approved immunotherapies owe their activity to oligosaccharide targets. In addition, nanotechnology and nanoparticle-derived systems can help improve the delivery of these agents to specific organs and cell types based on tumor-selective approaches. This review will first outline some of the historical beginnings of this research area and subsequently concentrate on the last 5 years of work. Based on the progress in therapeutic design, predictions can be made as to what the future holds for increasing the percentage of positive patient outcomes for optimized systems.

Engineering immunomodulatory nanoplatforms from commensal bacteria-derived polysaccharide A

Capsular zwitterionic polysaccharides (CZPs), typically found on the surfaces of commensal gut bacteria, are important immunomodulatory molecules due to their ability to produce a T-cell dependent immune response upon processing...

Glycosidase activated prodrugs for targeted cancer therapy

In this review glycosidase activated prodrugs that target cancer cells are discussed.

A Stable Gold Nanoparticle-Based Vaccine for the Targeted Delivery of Tumor-Associated Glycopeptide Antigens

We have developed a novel antigen delivery system based on polysaccharide-coated gold nanoparticles (AuNPs) targeted to antigen presenting cells (APCs) expressing Dectin-1. AuNPs were synthesized de-novo using yeast-derived β-1,3-glucans (B13G) as the reductant and passivating agent in a microwave-catalyzed procedure yielding highly uniform and serum-stable particles. These were further functionalized with both a peptide and a specific glycosylated form from the tandem repeat sequence of mucin 4 (MUC4), a glycoprotein overexpressed in pancreatic tumors. The glycosylated sequence contained the Thomsen-Friedenreich disaccharide, a pan-carcinoma, Tumor-Associated Carbohydrate Antigen (TACA), which has been a traditional target for antitumor vaccine design. These motifs were prepared with a cathepsin B protease cleavage site (Gly-Phe-Leu-Gly), loaded on the B13G-coated particles and these constructs were examined for Dectin-1 binding, APC processing and presentation in a model in vitro system and for immune responses in mice. We showed that these particles elicit strong in vivo immune responses through the production of both high-titer antibodies and priming of antigen-recognizing T-cells. Further examination showed that a favorable antitumor balance of expressed cytokines was generated, with limited expression of immunosuppressive Il-10. This system is modular in that any range of antigens can be conjugated to our particles and efficiently delivered to APCs expressing Dectin-1.

Total Synthesis of the Phosphorylated Zwitterionic Trisaccharide Repeating Unit of Photorhabdus temperata cinerea 3240

Herein, we report the total synthesis of the phosphorylated zwitterionic trisaccharide repeating unit of Photorhabdus temperata subsp. cinerea 3240. The efficient route involves regio- and stereoselective assembly of trisaccharide with rare deoxyamino sugar AAT at the nonreducing end, late stage oxidation, and installation of a phosphate linker on the trisaccharide. The total synthesis was completed via a longest linear sequence of 24 steps in 6.5% overall yield.

A brief insight to the role of glyconanotechnology in modern day diagnostics and therapeutics

Carbohydrate-protein and carbohydrate-carbohydrate interactions are very important for various biological processes. Although the magnitude of these interactions is low compared to that of protein-protein interaction, the magnitude can be boosted by multivalent approach known as glycocluster effect. Nanoparticle platform is one of the best ways to present diverse glycoforms in multivalent manner and thus, the field of glyconanotechnology has emerged as an important field of research considering their potential applications in diagnostics and therapeutics. Considerable advances in the field have been achieved through development of novel techniques, use of diverse metallic and non-metallic cores for better efficacy and application of ever-increasing number of carbohydrate ligands for site-specific interaction. The present review encompasses the recent developments in the area of glyconanotechnology and their future promise as diagnostic and therapeutic tools.

Carbohydrate-Based Macromolecular Biomaterials

Carbohydrates are the most abundant and one of the most important biomacromolecules in Nature. Except for energy-related compounds, carbohydrates can be roughly divided into two categories: Carbohydrates as matter and carbohydrates as information. As matter, carbohydrates are abundantly present in the extracellular matrix of animals and cell walls of various plants, bacteria, fungi, etc., serving as scaffolds. Some commonly found polysaccharides are featured as biocompatible materials with controllable rigidity and functionality, forming polymeric biomaterials which are widely used in drug delivery, tissue engineering, etc. As information, carbohydrates are usually referred to the glycans from glycoproteins, glycolipids, and proteoglycans, which bind to proteins or other carbohydrates, thereby meditating the cell-cell and cell-matrix interactions. These glycans could be simplified as synthetic glycopolymers, glycolipids, and glycoproteins, which could be afforded through polymerization, multistep synthesis, or a semisynthetic strategy. The information role of carbohydrates can be demonstrated not only as targeting reagents but also as immune antigens and adjuvants. The latter are also included in this review as they are always in a macromolecular formulation. In this review, we intend to provide a relatively comprehensive summary of carbohydrate-based macromolecular biomaterials since 2010 while emphasizing the fundamental understanding to guide the rational design of biomaterials. Carbohydrate-based macromolecules on the basis of their resources and chemical structures will be discussed, including naturally occurring polysaccharides, naturally derived synthetic polysaccharides, glycopolymers/glycodendrimers, supramolecular glycopolymers, and synthetic glycolipids/glycoproteins. Multiscale structure-function relationships in several major application areas, including delivery systems, tissue engineering, and immunology, will be detailed. We hope this review will provide valuable information for the development of carbohydrate-based macromolecular biomaterials and build a bridge between the carbohydrates as matter and the carbohydrates as information to promote new biomaterial design in the near future.

Total Synthesis of the Repeating Unit of Bacteroides fragilis Zwitterionic Polysaccharide A1

Zwitterionic polysaccharides isolated from commensal bacteria are endowed with unique immunological properties and are emerging as immunotherapeutic agents as well as vaccine carriers. Reported herein is a total synthesis of the repeating unit of Bacteroides fragilis zwitterionic polysaccharide A1 (PS A1). The structurally complex tetrasaccharide unit contains a rare sugar 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (AAT) and two consecutive 1,2-cis glycosidic linkages. The repeating unit was efficiently assembled by rapid synthesis of d-galactosamine and AAT building blocks from cheap and abundant d-mannose via a one-pot S_N2 displacement of 2,4-bistriflates and installation of all of the glycosidic bonds in a highly stereoselective manner. The total synthesis involves a longest linear sequence of 17 steps with 3.47% overall yield.

Recent advances on smart glycoconjugate vaccines in infections and cancer

Vaccination is one of the greatest achievements in biomedical research preventing death and morbidity in many infectious diseases through the induction of pathogen-specific humoral and cellular immune responses. Currently, no effective vaccines are available for pathogens with a highly variable antigenic load, such as the human immunodeficiency virus or to induce cellular T-cell immunity in the fight against cancer. The recent SARS-CoV-2 outbreak has reinforced the relevance of designing smart therapeutic vaccine modalities to ensure public health. Indeed, academic and private companies have ongoing joint efforts to develop novel vaccine prototypes for this virus. Many pathogens are covered by a dense glycan-coat, which form an attractive target for vaccine development. Moreover, many tumor types are characterized by altered glycosylation profiles that are known as "tumor-associated carbohydrate antigens". Unfortunately, glycans do not provoke a vigorous immune response and generally serve as T-cell-independent antigens, not eliciting protective immunoglobulin G responses nor inducing immunological memory. A close and continuous crosstalk between glycochemists and glycoimmunologists is essential for the successful development of efficient immune modulators. It is clear that this is a key point for the discovery of novel approaches, which could significantly improve our understanding of the immune system. In this review, we discuss the latest advancements in development of vaccines against glycan epitopes to gain selective immune responses and to provide an overview on the role of different immunogenic constructs in improving glycovaccine efficacy.

Prophylactic Cancer Vaccines Engineered to Elicit Specific Adaptive Immune Response

Vaccines have been used to prevent and eradicate different diseases for over 200 years, and new vaccine technologies have the potential to prevent many common illnesses. Cancer, despite many advances in therapeutics, is still the second leading causes of death in the United States. Prophylactic, or preventative, cancer vaccines have the potential to reduce cancer prevalence by initiating a specific immune response that will target cancer before it can develop. Cancer vaccines can include many different components, such as peptides and carbohydrates, and be fabricated for delivery using a variety of means including through incorporation of stabilizing chemicals like polyethylene glycol (PEG) and pan-DR helper T-lymphocyte epitope (PADRE), fusion with antigen-presenting cells (APCs), microneedle patches, and liposomal encapsulation. There are currently five cancer vaccines used in the clinic, protecting against either human papillomavirus (HPV) or hepatitis B virus (HBV), and preventing several different types of cancer including cervical and oral cancer. Prophylactic cancer vaccines can promote three different types of adaptive responses: humoral (B cell, or antibody-mediated), cellular (T cell) or a combination of the two types. Each vaccine has its advantages and challenges at eliciting an adaptive immune response, but these prophylactic cancer vaccines in development have the potential to prevent or delay tumor development, and reduce the incidence of many common cancers.

Exploratory N-Protecting Group Manipulation for the Total Synthesis of Zwitterionic Shigella sonnei Oligosaccharides

Shigella sonnei surface polysaccharides are well-established protective antigens against this major cause of diarrhoeal disease. They also qualify as unique zwitterionic polysaccharides (ZPSs) featuring a disaccharide repeating unit made of two 1,2-trans linked rare aminodeoxy sugars, a 2-acetamido-2-deoxy-l-altruronic acid (l-AltpNAcA) and a 2-acetamido-4-amino-2,4,6-trideoxy-d-galactopyranose (AAT). Herein, the stereoselective synthesis of S. sonnei oligosaccharides comprising two, three and four repeating units is reported for the first time. Several sets of up to seven protecting groups were explored, shedding light on the singular conformational behavior of protected altrosamine and altruronic residues. A disaccharide building block equipped with three distinct N-protecting groups and featuring the uronate moiety already in place was designed to accomplish the iterative high yielding glycosylation at the axial 4-OH of the altruronate component and achieve the challenging full deprotection step. Key to the successful route was the use of a diacetyl strategy whereby the N-acetamido group of the l-AltpNAcA is masked in the form of an imide.

Glycoproteogenomics: Setting the Course for Next-generation Cancer Neoantigen Discovery for Cancer Vaccines

Molecular-assisted precision oncology gained tremendous ground with high-throughput next-generation sequencing (NGS), supported by robust bioinformatics. The quest for genomics-based cancer medicine set the foundations for improved patient stratification, while unveiling a wide array of neoantigens for immunotherapy. Upfront pre-clinical and clinical studies have successfully used tumor-specific peptides in vaccines with minimal off-target effects. However, the low mutational burden presented by many lesions challenges the generalization of these solutions, requiring the diversification of neoantigen sources. Oncoproteogenomics utilizing customized databases for protein annotation by mass spectrometry (MS) is a powerful tool toward this end. Expanding the concept toward exploring proteoforms originated from post-translational modifications (PTMs) will be decisive to improve molecular subtyping and provide potentially targetable functional nodes with increased cancer specificity. Walking through the path of systems biology, we highlight that alterations in protein glycosylation at the cell surface not only have functional impact on cancer progression and dissemination but also originate unique molecular fingerprints for targeted therapeutics. Moreover, we discuss the outstanding challenges required to accommodate glycoproteomics in oncoproteogenomics platforms. We envisage that such rationale may flag a rather neglected research field, generating novel paradigms for precision oncology and immunotherapy.

Natural and synthetic carbohydrate-based vaccine adjuvants and their mechanisms of action

Modern subunit vaccines based on homogeneous antigens offer more precise targeting and improved safety compared with traditional whole-pathogen vaccines. However, they are also less immunogenic and require an adjuvant to increase the immunogenicity of the antigen and potentiate the immune response. Unfortunately, few adjuvants have sufficient potency and low enough toxicity for clinical use, highlighting the urgent need for new, potent and safe adjuvants. Notably, a number of natural and synthetic carbohydrate structures have been used as adjuvants in clinical trials, and two have recently been approved in human vaccines. However, naturally derived carbohydrate adjuvants are heterogeneous, difficult to obtain and, in some cases, unstable. In addition, their molecular mechanisms of action are generally not fully understood, partly owing to the lack of tools to elucidate their immune-potentiating effects, thus hampering the rational development of optimized adjuvants. To address these challenges, modification of the natural product structure using synthetic chemistry emerges as an attractive approach to develop well-defined, improved carbohydrate-containing adjuvants and chemical probes for mechanistic investigation. This Review describes selected examples of natural and synthetic carbohydrate-based adjuvants and their application in synthetic self-adjuvanting vaccines, while also discussing current understanding of their molecular mechanisms of action.

Efficacy of cancer vaccines in selected gynaecological breast and ovarian cancers: A 20-year systematic review and meta-analysis

BACKGROUND

Therapeutic cancer vaccination is an area of interest, even though promising efficacy has not been demonstrated so far.

DESIGN

A systematic review and meta-analysis was conducted to evaluate vaccines' efficacy on breast cancer (BC) and ovarian cancer (OC) patients. Our search was based on the PubMed electronic database, from 1st January 2000 to 4th February 2020.

OBJECTIVE

response rate (ORR) was the primary end-point of interest, while progression-free survival (PFS), overall survival (OS) and toxicity were secondary end-points. Analysis was performed separately for BC and OC patients. Pooled ORRs were estimated by fixed or random effects models, depending on the detected degree of heterogeneity, for all studies with more than five patients. Subgroup analyses by vaccine type and treatment schema as well as sensitivity analyses, were implemented.

RESULTS

Among 315 articles initially identified, 67 were eligible for our meta-analysis (BC: 46, 1698 patients; OC: 32, 426 patients; where both BC/OC in 11). Dendritic-cell and peptide vaccines were found in more studies, 6/10 BC and 10/13 OC studies, respectively. In our primary BC analysis (21 studies; 428 patients), the pooled ORR estimate was 9% (95%CI[5%,13%]). The primary OC analysis (12 studies; 182 patients), yielded pooled ORR estimate of 4% (95%CI[1%,7%]). Similar were the results derived in sensitivity analyses. No statistically significant differences were detected by vaccine type or treatment schema. Median PFS was 2.6 months (95% confidence interval (CI)[1.9,2.9]) and 13.0 months (95%CI[8.5,16.3]) for BC and OC respectively, while corresponding median OS was 24.8 months (95%CI[15.0,46.0]) and 39.0 months (95%CI[31.0,49.0]). In almost all cases, the observed toxicity was only moderate.

CONCLUSION

Despite their modest results in terms of ORR, therapeutic vaccines in the last 20 years display relatively long survival rates and low toxicity. Since a plethora of different approaches have been tested, a better understanding of the underlying mechanisms is needed in order to further improve vaccine efficacy.

Chemical synthesis and immunological evaluation of entirely carbohydrate conjugate Globo H-PS A1

An anticancer, entirely carbohydrate conjugate, Globo H-polysaccharide A1 (Globo H-PS A1), was chemically prepared and immunologically evaluated in C57BL/6 mice. Tumor associated carbohydrate antigen Globo H hexasaccharide was synthesized in an overall 7.8% yield employing a convergent [3 + 3] strategy that revealed an anomeric aminooxy group used for conjugation to oxidized PS A1 via an oxime linkage. Globo H-PS A1, formulated with adjuvants monophosphoryl lipid A and TiterMax® Gold. After immunization an antigen specific immune response was observed in ELISA with anti-Globo H IgG/IgM antibodies. Specificity of the corresponding antibodies was determined by FACS showing cell surface binding to Globo H-positive cancer cell lines MCF-7 and OVCAR-5. The anti-Globo H antibodies also exhibited complement-dependent cellular cytotoxicity against MCF-7 and OVCAR-5 cells.

Using the Past to Maximize the Success Probability of Future Anti-Viral Vaccines

Rapid obtaining of safe, effective, anti-viral vaccines has recently risen to the top of the international agenda. To maximize the success probability of future anti-viral vaccines, the anti-viral vaccines successful in the past are summarized here by virus type and vaccine type. The primary focus is on viruses with both single-stranded RNA genomes and a membrane envelope, given the pandemic past of influenza viruses and coronaviruses. The following conclusion is reached, assuming that success of future strategies is positively correlated with strategies successful in the past. The primary strategy, especially for emerging pandemic viruses, should be development of vaccine antigens that are live-attenuated viruses; the secondary strategy should be development of vaccine antigens that are inactivated virus particles. Support for this conclusion comes from the complexity of immune systems. These conclusions imply the need for a revision in current strategic planning.

Carbohydrate Conjugates in Vaccine Developments

Vaccines are powerful tools that can activate the immune system for protection against various diseases. As carbohydrates can play important roles in immune recognition, they have been widely applied in vaccine development. Carbohydrate antigens have been investigated in vaccines against various pathogenic microbes and cancer. Polysaccharides such as dextran and β-glucan can serve as smart vaccine carriers for efficient antigen delivery to immune cells. Some glycolipids, such as galactosylceramide and monophosphoryl lipid A, are strong immune stimulators, which have been studied as vaccine adjuvants. In this review, we focus on the current advances in applying carbohydrates as vaccine delivery carriers and adjuvants. We will discuss the examples that involve chemical modifications of the carbohydrates for effective antigen delivery, as well as covalent antigen-carbohydrate conjugates for enhanced immune responses.

Carbohydrates: Potential Sweet Tools Against Cancer

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Cancer, one of the most devastating degenerative diseases nowadays, is one of the main targets in Medicinal Chemistry and Pharmaceutical industry. Due to the significant increase in the incidence of cancer within world population, together with the complexity of such disease, featured with a multifactorial nature, access to new drugs targeting different biological targets connected to cancer is highly necessary.

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Among the vast arsenal of compounds exhibiting antitumor activities, this review will cover the use of carbohydrate derivatives as privileged scaffolds. Their hydrophilic nature, together with their capacity of establishing selective interactions with biological receptors located on cell surface, involved in cell-to-cell communication processes, has allowed the development of an ample number of new templates useful in cancer treatment.

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Their intrinsic water solubility has allowed their use as of pro-drug carriers for accessing more efficiently the pharmaceutical targets. The preparation of glycoconjugates in which the carbohydrate is tethered to a pharmacophore has also allowed a better permeation of the drug through cellular membranes, in which selective interactions with the carbohydrate motifs are involved. In this context, the design of multivalent structures (e.g. gold nanoparticles) has been demonstrated to enhance crucial interactions with biological receptors like lectins, glycoproteins that can be involved in cancer progression.

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Moreover, the modification of the carbohydrate structural motif, by incorporation of metal complexes, or by replacing their endocyclic oxygen, or carbon atoms with heteroatoms has led to new antitumor agents.

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Such diversity of sugar-based templates with relevant antitumor activity will be covered in this review.

Glycoconjugate vaccines: some observations on carrier and production methods

Glycoconjugate vaccines use protein carriers to improve the immune response to polysaccharide antigens. The protein component allows the vaccine to interact with T cells, providing a stronger and longer-lasting immune response than a polysaccharide interacting with B cells alone. Whilst in theory the mere presence of a protein component in a vaccine should be sufficient to improve vaccine efficacy, the extent of improvement varies. In the present review, a comparison of the performances of vaccines developed with and without a protein carrier are presented. The usefulness of analytical tools for macromolecular integrity assays, in particular nuclear magnetic resonance, circular dichroism, analytical ultracentrifugation and SEC coupled to multi-angle light scattering (MALS) is indicated. Although we focus mainly on bacterial capsular polysaccharide-protein vaccines, some consideration is also given to research on experimental cancer vaccines using zwitterionic polysaccharides which, unusually for polysaccharides, are able to invoke T-cell responses and have been used in the development of potential all-polysaccharide-based cancer vaccines.A general trend of improved immunogenicity for glycoconjugate vaccines is described. Since the immunogenicity of a vaccine will also depend on carrier protein type and the way in which it has been linked to polysaccharide, the effects of different carrier proteins and production methods are also reviewed. We suggest that, in general, there is no single best carrier for use in glycoconjugate vaccines. This indicates that the choice of carrier protein is optimally made on a case-by-case basis, based on what generates the best immune response and can be produced safely in each individual case.Abbreviations: AUC: analytical ultracentrifugation; BSA: bovine serum albumin; CD: circular dichroism spectroscopy; CPS: capsular polysaccharide; CRM197: Cross Reactive Material 197; DT: diphtheria toxoid; Hib: Haemophilius influenzae type b; MALS: multi-angle light scattering; Men: Neisseria menigitidis; MHC-II: major histocompatibility complex class II; NMR: nuclear magnetic resonance spectroscopy; OMP: outer membrane protein; PRP: polyribosyl ribitol phosphate; PSA: Polysaccharide A1; Sa: Salmonella; St.: Streptococcus; SEC: size exclusion chromatography; Sta: Staphylococcus; TT: tetanus toxoid; ZPS: zwitterionic polysaccharide(s).

Synthesis of glycoimmunogen Tn-Thr-PS A1 via hydrazone bond and stability optimization of PS A1 monosaccharide mimics under vaccine development conditions

Previously, our group constructed several immunogens utilizing oxime linkage to conjugate a T-cell stimulatory zwitterionic polysaccharide PS A1 and tumor associated carbohydrate antigens (TACAs) in acetate buffer. Here, a semi-synthetic immunogen was synthesized using hydrazone conjugation between PS A1 and a glycopeptide hydrazide (α-d-GalNAc-l-Thr-NH-NH2) with an excellent loading in PBS buffer. To get robust immune response, the retention of zwitterionic character of PS A1 under vaccine construction conditions is essential. In this regard, the stability of embedded pyruvate acetal moiety in tetrasaccharide repeating unit of PS A1 can validate the retention of the dual charges. Therefore, rather than utilizing this highly immunogenic PS A1 fully, stability studies were performed with synthetic 1-thiophenyl-4,6-O-pyruvate acetal-d-galactopyranose in varying acetate buffer pHs and time intervals. Furthermore, 1-propyl-d-galactofuranose was synthesized to mimick the d-Galf of PS A1 to examine regioselective hydrazone and oxime formation with α-d-GalNAc-l-Thr-NH-NH2 and α-d-GalNAc-ONH2 moieties respectively.

Synthetic carbohydrate-based vaccines: challenges and opportunities

Glycoconjugate vaccines based on bacterial capsular polysaccharides (CPS) have been extremely successful in preventing bacterial infections. The glycan antigens for the preparation of CPS based glycoconjugate vaccines are mainly obtained from bacterial fermentation, the quality and length of glycans are always inconsistent. Such kind of situation make the CMC of glycoconjugate vaccines are difficult to well control. Thanks to the advantage of synthetic methods for carbohydrates syntheses. The well controlled glycan antigens are more easily to obtain, and them are conjugated to carrier protein to from the so-call homogeneous fully synthetic glycoconjugate vaccines. Several fully glycoconjugate vaccines are in different phases of clinical trial for bacteria or cancers. The review will introduce the recent development of fully synthetic glycoconjugate vaccine.

Antibody recognition of bacterial surfaces and extracellular polysaccharides

Because of the ongoing increase in antibiotic-resistant microbes, new strategies such as therapeutic antibodies and effective vaccines are required. Bacterial carbohydrates are known to be particularly antigenic, and several monoclonal antibodies that target bacterial polysaccharides have been generated, with more in current development. This review examines the known 3D crystal structures of anti-bacterial antibodies and the structural basis for carbohydrate recognition and explores the potential mechanisms for antibody-dependent bacterial cell death. Understanding the key interactions between an antibody and its polysaccharide target on the surface of bacteria or in biofilms can provide essential information for the development of more specific and effective antibody therapeutics as well as carbohydrate-based vaccines.

Selectively Charged and Zwitterionic Analogues of the Smallest Immunogenic Structure of Streptococcus Pneumoniae Type 14

Zwitterionic polysaccharides (ZPs) have been shown in recent years to display peculiar immunological properties, thus attracting the interest of the carbohydrate research community. To fully elucidate the mechanisms underlying these properties and exploit the potential of this kind of structures, in depth studies are still required. In this context, the preparation of two cationic, an anionic, as well as two zwitterionic tetrasaccharide analogues of the smallest immunogenic structure of Streptococcus pneumoniae type 14 (SP14) capsular polysaccharide are presented. By exploiting a block strategy, the negative charge has been installed on the non-reducing end of the lactose unit of the tetrasaccharide and the positive charge either on the non-reducing end of the lactosamine moiety or on an external linker. These structures have then been tested by competitive ELISA, showing that the structural variations we made do not modify the affinity of the neutral compound to binding to a specific antibody. However, lower efficacies than the natural SP14 compound were observed. The results obtained, although promising, point to the need to further elongate the polysaccharide structure, which is likely too short to cover the entire epitopes.

Total Synthesis of the Congested, Bisphosphorylated Morganella morganii Zwitterionic Trisaccharide Repeating Unit

Zwitterionic polysaccharides (ZPSs) activate T-cell-dependent immune responses by major histocompatibility complex class II presentation. Herein, we report the first synthesis of a Morganella morganii ZPS repeating unit as an enabling tool in the synthesis of novel ZPS materials. The repeating unit incorporates a 1,2-cis-α-glycosidic bond; the problematic 1,2-trans-galactosidic bond, Gal-β-(1 → 3)-GalNAc; and phosphoglycerol and phosphocholine residues which have not been previously observed together as functional groups on the same oligosaccharide. The successful third-generation approach leverages a first in class glycosylation of a phosphoglycerol-functionalized acceptor. To install the phosphocholine unit, a highly effective phosphocholine donor was synthesized.

Developments in Carbohydrate-Based Cancer Therapeutics

Cancer cells of diverse origins express extracellular tumor-specific carbohydrate antigens (TACAs) because of aberrant glycosylation. Overexpressed TACAs on the surface of tumor cells are considered biomarkers for cancer detection and have always been prioritized for the development of novel carbohydrate-based anti-cancer vaccines. In recent years, progress has been made in developing synthetic, carbohydrate-based antitumor vaccines to improve immune responses associated with targeting these specific antigens. Tumor cells also exhaust more energy for proliferation than normal cells, by consuming excessive amounts of glucose via overexpressed sugar binding or transporting receptors located in the cellular membrane. Furthermore, inspired by the Warburg effect, glycoconjugation strategies of anticancer drugs have gained considerable attention from the scientific community. This review highlights a small cohort of recent efforts which have been made in carbohydrate-based cancer treatments, including vaccine design and the development of glycoconjugate prodrugs, glycosidase inhibiting iminosugars, and early cancer diagnosis.

Chemical Synthesis of Rare, Deoxy-Amino Sugars Containing Bacterial Glycoconjugates as Potential Vaccine Candidates

Bacteria often contain rare deoxy amino sugars which are absent in the host cells. This structural difference can be harnessed for the development of vaccines. Over the last fifteen years, remarkable progress has been made toward the development of novel and efficient protocols for obtaining the rare sugar building blocks and their stereoselective assembly to construct conjugation ready bacterial glycans. In this review, we discuss the total synthesis of a variety of rare sugar containing bacterial glycoconjugates which are potential vaccine candidates.

Efficient syntheses and anti-cancer activity of xenortides A-D including ent/epi-stereoisomers

A one-pot, two-step, total synthesis of naturally occurring xenortides A, B, C and D, (Xens A-D) isolated from the bacterium Xenorhabdus nematophila, and an entire complementary set of stereoisomers, has been achieved. Compounds were synthesized utilizing an isocyanide-based Ugi 4-CR followed by facile N-Boc deprotection. The reaction sequence took advantage of the chiral pool of N-Boc protected amino acids (l-Leu/Val and d-Leu/Val) with aryl isocyanides, phenyl acetaldehyde and methylamine giving the desired Xens A-D (A and B >98% ee) and all subsequent stereoisomers in reasonable yields upon deprotection followed by separation of diastereomers. Also, detailed mechanistic insights for diastereoselectivity of (-)-Xen A, as a model in the Ugi 4-CR, has been described. Moreover, for the first time, this focused library was screened for cytotoxicity against a panel of epithelial cancer cell lines as well as normal cell lines with an MTT proliferation assay. The structure-activity relationship (SAR) study demonstrated that tryptamides Xen B and D were more active than phenylethylamides Xen A and C. Furthermore, (-)-Xen B (IC50 = 19-25 μM) and ent-(+)-Xen D (IC50 = 21-26 μM) gave the highest cytotoxicity and they were also found to be non-toxic toward normal cells. Importantly, the SAR results indicate that the stereochemistry at C8 and C11 in (-)-Xen B and ent-(+)-Xen D play a critical role in cytotoxic activity.

An innovative and efficient route to the synthesis of metal-based glycoconjugates: proof-of-concept and potential applications

With a view to developing more efficient strategies to the functionalization of metallodrugs with carbohydrates, we here report on an innovative and efficient synthetic route to generate gold(iii) glycoconjugates in high yields and purity. The method is based on the initial synthesis of the zinc(ii)-dithiocarbamato intermediate [Zn^II(SSC-Inp-GlcN)₂] (Inp = isonipecotic moiety; GlcN = amino-glucose) followed by the transfer of the glucoseisonipecoticdithiocarbamato ligand to the gold(iii) center via transmetallation reaction between the zinc(ii) intermediate and K[Au^IIIBr₄] in 1 : 2 stoichiometric ratio, yielding the corresponding glucose-functionalized gold(iii)-dithiocarbamato derivative [Au^IIIBr₂(SSC-Inp-GlcN)]. No protection/deprotection of the amino-glucose scaffold and no chromatographic purification were needed. The synthetic protocol was optimized for glucose precursors bearing the amino function at either the C² or the C⁶ position, and works in the case of both α and β anomers. The application of the synthetic strategy was also successfully extended to other metal ions of biomedical interest, such as gold(i) and platinum(ii), to obtain [Au^I(SSC-Inp-GlcN)(PPh₃)] and [Pt^II(SSC-Inp-GlcN)₂], respectively. All compounds were fully characterized by elemental analysis, mid- and far-IR, mono- and multidimensional NMR spectroscopy, and, where possible, X-ray crystallography. Results and potential applications are here discussed.

Carbohydrate-based vaccines for oncotherapy

Cancer is still one of the most serious threats to human worldwide. Aberrant patterns of glycosylation on the surface of cancer cells, which are correlated with various cancer development stages, can differentiate the abnormal tissues from the healthy ones. Therefore, tumor-associated carbohydrate antigens (TACAs) represent the desired targets for cancer immunotherapy. However, these carbohydrate antigens may not able to evoke powerful immune response to combat with cancer for their poor immunogenicity and immunotolerance. Different approaches have been developed to address these problems. In this review, we want to summarize the latest advances in TACAs based anticancer vaccines.

Parasite Carbohydrate Vaccines

Vaccination is an efficient means of combating infectious disease burden globally. However, routine vaccines for the world's major human parasitic diseases do not yet exist. Vaccines based on carbohydrate antigens are a viable option for parasite vaccine development, given the proven success of carbohydrate vaccines to combat bacterial infections. We will review the key components of carbohydrate vaccines that have remained largely consistent since their inception, and the success of bacterial carbohydrate vaccines. We will then explore the latest developments for both traditional and non-traditional carbohydrate vaccine approaches for three of the world's major protozoan parasitic diseases-malaria, toxoplasmosis, and leishmaniasis. The traditional prophylactic carbohydrate vaccine strategy is being explored for malaria. However, given that parasite disease biology is complex and often arises from host immune responses to parasite antigens, carbohydrate vaccines against deleterious immune responses in host-parasite interactions are also being explored. In particular, the highly abundant glycosylphosphatidylinositol molecules specific for Plasmodium, Toxoplasma, and Leishmania spp. are considered exploitable antigens for this non-traditional vaccine approach. Discussion will revolve around the application of these protozoan carbohydrate antigens for vaccines currently in preclinical development.

Technological Microbiology: Development and Applications

Over thousands of years, modernization could be predicted for the use of microorganisms in the production of foods and beverages. However, the current accelerated pace of new food production is due to the rapid incorporation of biotechnological techniques that allow the rapid identification of new molecules and microorganisms or even the genetic improvement of known species. At no other time in history have microorganisms been so present in areas such as agriculture and medicine, except as recognized villains. Currently, however, beneficial microorganisms such as plant growth promoters and phytopathogen controllers are required by various agricultural crops, and many species are being used as biofactories of important pharmacological molecules. The use of biofactories does not end there: microorganisms have been explored for the synthesis of diverse chemicals, fuel molecules, and industrial polymers, and strains environmentally important due to their biodecomposing or biosorption capacity have gained interest in research laboratories and in industrial activities. We call this new microbiology Technological Microbiology, and we believe that complex techniques, such as heterologous expression and metabolic engineering, can be increasingly incorporated into this applied science, allowing the generation of new and improved products and services.

Engineering of CHO Cells for the Production of Recombinant Glycoprotein Vaccines with Xylosylated N-glycans

Xylose is a general component of O-glycans in mammals. Core-xylosylation of N-glycans is only found in plants and helminth. Consequently, xylosylated N-glycans cause immunological response in humans. We have used the F-protein of the human respiratory syncytial virus (RSV), one of the main causes of respiratory tract infection in infants and elderly, as a model protein for vaccination. The RSV-F protein was expressed in CHO-DG44 cells, which were further modified by co-expression of β1,2-xylosyltransferase from Nicotiana tabacum. Xylosylation of RSV-F N-glycans was shown by monosaccharide analysis and MALDI-TOF mass spectrometry. In immunogenic studies with a human artificial lymph node model, the engineered RSV-F protein revealed improved vaccination efficacy.

A Leishmania murine model to evaluate the immunomodulatory properties of Pythium insidiosum proteins

Pythium insidiosum immunomodulatory vaccine (PiV) has been tested in clinical and experimental pythiosis. Previous data showed that P. insidiosum immunogens have the ability to switch the Th2 immune response, normally in place during pythiosis, to a curative Th1 response. Pythiosis cannot be reproduced in experimental rodents with the exception of rabbits, and thus thorough evaluation of PiV´s immunomodulatory properties has been limited by the lack of a compatible inbred mouse model. In this study, we took advantage of the murine BALB/c Leishmania infection model, where infected mice produce a Th2 response, to evaluate the PiV Th2 to Th1 immunomodulatory potential. Twenty-one days following challenge with L. major, large cutaneous granulomas developed in control mice, consistent with the expected Th2 response. In contrast, Leishmania-induced cutaneous lesions in PiV-immunized mice were minimal or absent. Flow cytometry analysis of spleen cells from mice immunized with PiV and subsequently challenged with L. major displayed more CD4+ and CD8+ cells than the control group. Moreover, spleen cells from mice that were immunized with PiV then challenged with L. major secreted high levels of IFN-γ, with a moderate IL-2, IL-4, and IL-10 mixed cytokine profile upon in vitro re-stimulation with PiV. Anti-P. insidiosum IgG1 in immunized animals was present at low titers suggesting a minor immunological role for this Ig isotype in this model. Our preliminary data showed that BALB/c mice challenged with L. major represent an attractive model in which to study PiV´s immunomodulatory properties.