Synthesis and Evaluation of GM2-Monophosphoryl Lipid A Conjugate as a Fully Synthetic Self-Adjuvant Cancer Vaccine

Design, Synthesis, and Bioactivity Evaluation of a TF-Based Cancer Vaccine Candidate Using Lipid A Mimetics As a Built-In Adjuvant

This study describes the design and synthesis of five TF-based cancer vaccine candidates using a lipid A mimetic as the carrier and a built-in adjuvant. All synthesized conjugates elicited robust and consistent TF-specific immune responses in mice without external adjuvants. Immunological studies subsequently conducted in wild-type and TLR4 knockout C57BL/6 mice demonstrated that the activation of TLR4 was the main reason that the synthesized lipid A mimetics increased the TF-specific immune responses. All antisera induced by these conjugates can specifically recognize, bind to, and induce the lysis of TF-positive cancer cells. Moreover, representative conjugates 2 and 3 could effectively reduce the growth of tumors and prolong the survival time of mice in vivo, and the efficacies were better than glycoprotein TF-CRM197 with alum adjuvant. Lipid A mimetics could therefore be a promising platform for the development of new carbohydrate-based vaccine carriers with self-adjuvanting properties for the treatment of cancer.

Monophosphoryl Lipid A-Rhamnose Conjugates as a New Class of Vaccine Adjuvants

Adjuvant is an integral part of all vaccine formulations but only a few adjuvants with limited efficacies or application scopes are available. Thus, developing more robust and diverse adjuvants is necessary. To this end, a new class of adjuvants having α- and β-rhamnose (Rha) attached to the 1- and 6'-positions of monophosphoryl lipid A (MPLA) was designed, synthesized, and immunologically evaluated in mice. The results indicated a synergistic effect of MPLA and Rha, two immunostimulators that function via interacting with toll-like receptor 4 and recruiting endogenous anti-Rha antibodies, respectively. All the tested MPLA-Rha conjugates exhibited potent adjuvant activities to promote antibody production against both protein and carbohydrate antigens. Overall, MPLA-α-Rha exhibited better activities than MPLA-β-Rha, and 6'-linked conjugates were slightly better than 1-linked ones. Particularly, MPLA-1-α-Rha and MPLA-6'-α-Rha were the most effective adjuvants in promoting IgG antibody responses against protein antigen keyhole limpet hemocyanin and carbohydrate antigen sTn, respectively.

Glycovaccinology: The design and engineering of carbohydrate-based vaccine components

Vaccines remain one of the most important pillars in preventative medicine, providing protection against a wide array of diseases by inducing humoral and/or cellular immunity. Of the many possible candidate antigens for subunit vaccine development, carbohydrates are particularly appealing because of their ubiquitous presence on the surface of all living cells, viruses, and parasites as well as their known interactions with both innate and adaptive immune cells. Indeed, several licensed vaccines leverage bacterial cell-surface carbohydrates as antigens for inducing antigen-specific plasma cells secreting protective antibodies and the development of memory T and B cells. Carbohydrates have also garnered attention in other aspects of vaccine development, for example, as adjuvants that enhance the immune response by either activating innate immune responses or targeting specific immune cells. Additionally, carbohydrates can function as immunomodulators that dampen undesired humoral immune responses to entire protein antigens or specific, conserved regions on antigenic proteins. In this review, we highlight how the interplay between carbohydrates and the adaptive and innate arms of the immune response is guiding the development of glycans as vaccine components that act as antigens, adjuvants, and immunomodulators. We also discuss how advances in the field of synthetic glycobiology are enabling the design, engineering, and production of this new generation of carbohydrate-containing vaccine formulations with the potential to prevent infectious diseases, malignancies, and complex immune disorders.

Pathophysiological roles and applications of glycosphingolipids in the diagnosis and treatment of cancer diseases

Glycosphingolipids (GSLs) are major amphiphilic glycolipids present on the surface of living cell membranes. They have important biological functions, including maintaining plasma membrane stability, regulating signal transduction, and mediating cell recognition and adhesion. Specific GSLs and related enzymes are abnormally expressed in many cancer diseases and affect the malignant characteristics of tumors. The regulatory roles of GSLs in signaling pathways suggest that they are involved in tumor pathogenesis. GSLs have therefore been widely studied as diagnostic markers of cancer diseases and important targets of immunotherapy. This review describes the tumor-related biological functions of GSLs and systematically introduces recent progress in using diverse GSLs and related enzymes to diagnose and treat tumor diseases. Development of drugs and biomarkers for personalized cancer therapy based on GSL structure is also discussed. These advances, combined with recent progress in the preparation of GSLs derivatives through synthetic biology technologies, suggest a strong future for the use of customized GSL libraries in treating human diseases.

NOD-scid IL2rγnull mice lacking TLR4 support human immune system development and the study of human-specific innate immunity

Agents that induce inflammation have been used since the 18th century for the treatment of cancer. The inflammation induced by agents such as Toll-like receptor agonists is thought to stimulate tumor-specific immunity in patients and augment control of tumor burden. While NOD-scid IL2rγnull mice lack murine adaptive immunity (T cells and B cells), these mice maintain a residual murine innate immune system that responds to Toll-like receptor agonists. Here we describe a novel NOD-scid IL2rγnull mouse lacking murine TLR4 that fails to respond to lipopolysaccharide. NSG-Tlr4null mice support human immune system engraftment and enable the study of human-specific responses to TLR4 agonists in the absence of the confounding effects of a murine response. Our data demonstrate that specific stimulation of TLR4 activates human innate immune systems and delays the growth kinetics of a human patient-derived xenograft melanoma tumor.

Immunomodulatory glycomedicine: Introducing next generation cancer glycovaccines

Cancer remains a leading cause of death worldwide due to the lack of safer and more effective therapies. Cancer vaccines developed from neoantigens are an emerging strategy to promote protective and therapeutic anti-cancer immune responses. Advances in glycomics and glycoproteomics have unveiled several cancer-specific glycosignatures, holding tremendous potential to foster effective cancer glycovaccines. However, the immunosuppressive nature of tumours poses a major obstacle to vaccine-based immunotherapy. Chemical modification of tumour associated glycans, conjugation with immunogenic carriers and administration in combination with potent immune adjuvants constitute emerging strategies to address this bottleneck. Moreover, novel vaccine vehicles have been optimized to enhance immune responses against otherwise poorly immunogenic cancer epitopes. Nanovehicles have shown increased affinity for antigen presenting cells (APCs) in lymph nodes and tumours, while reducing treatment toxicity. Designs exploiting glycans recognized by APCs have further enhanced the delivery of antigenic payloads, improving glycovaccine's capacity to elicit innate and acquired immune responses. These solutions show potential to reduce tumour burden, while generating immunological memory. Building on this rationale, we provide a comprehensive overview on emerging cancer glycovaccines, emphasizing the potential of nanotechnology in this context. A roadmap towards clinical implementation is also delivered foreseeing advances in glycan-based immunomodulatory cancer medicine.

Self-Adjuvanting Protein Vaccine Conjugated with a Novel Synthetic TLR4 Agonist on Virus-Like Liposome Induces Potent Immunity against SARS-CoV-2

Exploring potent adjuvants and new vaccine strategies is crucial for the development of protein vaccines. In this work, we synthesized a new TLR4 agonist, structurally simplified lipid A analogue GAP112, as a potent built-in adjuvant to improve the immunogenicity of SARS-CoV-2 spike RBD protein. The new TLR4 agonist GAP112 was site-selectively conjugated on the N-terminus of RBD to construct an adjuvant-protein conjugate vaccine in a liposomal formulation. It is the first time that a TLR4 agonist is site-specifically and quantitatively conjugated to a protein antigen. Compared with an unconjugated mixture of GAP112/RBD, a two-dose immunization of the GAP112-RBD conjugate vaccine strongly activated innate immune cells, elicited a 223-fold increase in RBD-specific antibodies, and markedly enhanced T-cell responses. Antibodies induced by GAP112-RBD also effectively cross-neutralized SARS-CoV-2 variants (Delta/B.1.617.2 and Omicron/B.1.1.529). This conjugate strategy provides an effective method to greatly enhance the immunogenicity of antigen in protein vaccines against SARS-CoV-2 and other diseases.

Glycoconjugates: Synthesis, Functional Studies, and Therapeutic Developments

Glycoconjugates are major constituents of mammalian cells that are formed via covalent conjugation of carbohydrates to other biomolecules like proteins and lipids and often expressed on the cell surfaces. Among the three major classes of glycoconjugates, proteoglycans and glycoproteins contain glycans linked to the protein backbone via amino acid residues such as Asn for N-linked glycans and Ser/Thr for O-linked glycans. In glycolipids, glycans are linked to a lipid component such as glycerol, polyisoprenyl pyrophosphate, fatty acid ester, or sphingolipid. Recently, glycoconjugates have become better structurally defined and biosynthetically understood, especially those associated with human diseases, and are accessible to new drug, diagnostic, and therapeutic developments. This review describes the status and new advances in the biological study and therapeutic applications of natural and synthetic glycoconjugates, including proteoglycans, glycoproteins, and glycolipids. The scope, limitations, and novel methodologies in the synthesis and clinical development of glycoconjugates including vaccines, glyco-remodeled antibodies, glycan-based adjuvants, glycan-specific receptor-mediated drug delivery platforms, etc., and their future prospectus are discussed.

MUC1 Specific Immune Responses Enhanced by Coadministration of Liposomal DDA/MPLA and Lipoglycopeptide

Mucin 1 (MUC1), a well-known tumor-associated antigen and attractive target for tumor immunotherapy, is overexpressed in most human epithelial adenomas with aberrant glycosylation. However, its low immunogenicity impedes the development of MUC1-targeted antitumor vaccines. In this study, we investigated three liposomal adjuvant systems containing toll-like receptor 4 (TLR4) agonist monophosphoryl lipid A (MPLA) and auxiliary lipids of different charges: cationic lipid dimethyldioctadecylammonium (DDA), neutral lipid distearoylglycerophosphocholine (DSPC) or anionic lipid dioleoylphosphatidylglycerol (DOPG), respectively. ELISA assay evidenced that the positively charged DDA/MPLA liposomes are potent immune activators, which induced remarkable levels of anti-MUC1 antibodies and exhibited robust Th1-biased immune responses. Importantly, the antibodies induced by DDA/MPLA liposomes efficiently recognized and killed MUC1-positive tumor cells through complement-mediated cytotoxicity. In addition, antibody titers in mice immunized with P2-MUC1 vaccine were significantly higher than those from mice immunized with P1-MUC1 or MUC1 vaccine, which indicated that the lipid conjugated on MUC1 antigen also played important role for immunomodulation. This study suggested that the liposomal DDA/MPLA with lipid-MUC1 is a promising antitumor vaccine, which can be used for the immunotherapy of various epithelial carcinomas represented by breast cancer.

Built-in adjuvants for use in vaccines

Vaccine refers to biological products that are produced using various pathogenic microorganisms for inoculation. The goal of vaccination is to induce a robust immune response against a specific antigen, thus preventing the organism from getting infected. In vaccines, adjuvants have been widely employed to enhance immunity against specific antigens. An ideal adjuvant should be stable, biodegradable, and low cost, not induce system rejection and promote an immune response. Various adjuvant components have been investigated across diverse applications. Typically, adjuvants are employed to meet the following objectives: (1) to improve the effectiveness of immunization with vaccines for specific populations, such as newborns and the elderly; (2) enhance the immunogenicity of highly purified or recombinant antigens; (3) allow immunization with a smaller dose of the vaccine, reducing drug dosage. In the present review, we primarily focus on chemically synthesized compounds that can be used as built-in adjuvants. We elaborate the classification of these compounds based on the induced immune activation mechanism and summarize their application in various vaccine types.

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.

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.

Anti-glycan antibodies: roles in human disease

Carbohydrate-binding antibodies play diverse and critical roles in human health. Endogenous carbohydrate-binding antibodies that recognize bacterial, fungal, and other microbial carbohydrates prevent systemic infections and help maintain microbiome homeostasis. Anti-glycan antibodies can have both beneficial and detrimental effects. For example, alloantibodies to ABO blood group carbohydrates can help reduce the spread of some infectious diseases, but they also impose limitations for blood transfusions. Antibodies that recognize self-glycans can contribute to autoimmune diseases, such as Guillain-Barre syndrome. In addition to endogenous antibodies that arise through natural processes, a variety of vaccines induce anti-glycan antibodies as a primary mechanism of protection. Some examples of approved carbohydrate-based vaccines that have had a major impact on human health are against pneumococcus, Haemophilus influeanza type b, and Neisseria meningitidis. Monoclonal antibodies specifically targeting pathogen associated or tumor associated carbohydrate antigens (TACAs) are used clinically for both diagnostic and therapeutic purposes. This review aims to highlight some of the well-studied and critically important applications of anti-carbohydrate antibodies.

Exendin 4-Hapten Conjugate Capable of Binding with Endogenous Antibodies for Peptide Half-life Extension and Exerting Long-Acting Hypoglycemic Activity

Hapten-specific endogenous antibodies are naturally occurring antibodies present in human blood. Herein, we investigated a new strategy in which small-molecule haptens were utilized as naturally occurring antibody binders for peptide half-life extension. The glucagon-like peptide 1 receptor agonist exendin 4 was site-specifically functionalized with the dinitrophenyl (DNP) hapten at the C-terminus via sortase A-mediated ligation. The resulting Ex4-DNP conjugates retained GLP-1 receptor activation potency in vitro and had a similar in vivo acute glucose-lowering effect comparable to that of native Ex4. Pharmacokinetic studies and hypoglycemic duration tests demonstrated that the Ex4-DNP conjugates displayed significantly elongated half-lives and improved long-acting antidiabetic activity in the presence of endogenous anti-DNP antibodies. In chronic treatment studies, once-daily administration of optimal conjugate 7 demonstrated more beneficial effects without prominent toxicity compared with Ex4. This strategy provides a new approach and represents an alternative to the well-established peptide-Fc fusion strategy to improve the peptide half-life and the therapeutic efficacy.

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.

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

Synthesis of monophosphoryl lipid A using 2-naphtylmethyl ethers as permanent protecting groups

Lipid A, which is a conserved component of lipopolysaccharides of gram-negative bacteria, has attracted considerable interest for the development of immuno-adjuvants. Most approaches for lipid A synthesis rely on the use of benzyl ethers as permanent protecting groups. Due to the amphiphilic character of lipid A, these compounds aggregate during the hydrogenation step to remove benzyl ethers, resulting in a sluggish reaction and by-product formation. To address this problem, we have developed a synthetic approach based on the use of 2-naphtylmethyl ether (Nap) ethers as permanent protecting group for hydroxyls. At the end of a synthetic sequence, multiple of these protecting groups can readily be removed by oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Di-allyl N,N-diisopropylphosphoramidite was employed to install the phosphate ester and the resulting allyl esters were cleaved using palladium tetrakistriphenylphosphine. The synthetic strategy allows late stage introduction of different fatty acids at the amines of the target compound, which is facilitated by Troc and Fmoc as orthogonal amino-protecting groups.

Chemical Strategies to Boost Cancer Vaccines

Personalized cancer vaccines (PCVs) are reinvigorating vaccine strategies in cancer immunotherapy. In contrast to adoptive T-cell therapy and checkpoint blockade, the PCV strategy modulates the innate and adaptive immune systems with broader activation to redeploy antitumor immunity with individualized tumor-specific antigens (neoantigens). Following a sequential scheme of tumor biopsy, mutation analysis, and epitope prediction, the administration of neoantigens with synthetic long peptide (SLP) or mRNA formulations dramatically improves the population and activity of antigen-specific CD4+ and CD8+ T cells. Despite the promising prospect of PCVs, there is still great potential for optimizing prevaccination procedures and vaccine potency. In particular, the arduous development of tumor-associated antigen (TAA)-based vaccines provides valuable experience and rational principles for augmenting vaccine potency which is expected to advance PCV through the design of adjuvants, delivery systems, and immunosuppressive tumor microenvironment (TME) reversion since current personalized vaccination simply admixes antigens with adjuvants. Considering the broader application of TAA-based vaccine design, these two strategies complement each other and can lead to both personalized and universal therapeutic methods. Chemical strategies provide vast opportunities for (1) exploring novel adjuvants, including synthetic molecules and materials with optimizable activity, (2) constructing efficient and precise delivery systems to avoid systemic diffusion, improve biosafety, target secondary lymphoid organs, and enhance antigen presentation, and (3) combining bioengineering methods to innovate improvements in conventional vaccination, "smartly" re-educate the TME, and modulate antitumor immunity. As chemical strategies have proven versatility, reliability, and universality in the design of T cell- and B cell-based antitumor vaccines, the union of such numerous chemical methods in vaccine construction is expected to provide new vigor and vitality in cancer treatment.

Past, Present, and Future of Anticancer Nanomedicine

This review aims to summarize the methods that have been used till today, highlight methods that are currently being developed, and predict the future roadmap for anticancer therapy. In the beginning of this review, established approaches for anticancer therapy, such as conventional chemotherapy, hormonal therapy, monoclonal antibodies, and tyrosine kinase inhibitors are summarized. To counteract the side effects of conventional chemotherapy and to increase limited anticancer efficacy, nanodrug- and stem cell-based therapies have been introduced. However, current level of understanding and strategies of nanodrug and stem cell-based therapies have limitations that make them inadequate for clinical application. Subsequently, this manuscript reviews methods with fewer side effects compared to those of the methods mentioned above which are currently being investigated and are already being applied in the clinic. The newer strategies that are already being clinically applied include cancer immunotherapy, especially T cell-mediated therapy and immune checkpoint inhibitors, and strategies that are gaining attention include the manipulation of the tumor microenvironment or the activation of dendritic cells. Tumor-associated macrophage repolarization is another potential strategy for cancer immunotherapy, a method which activates macrophages to immunologically attack malignant cells. At the end of this review, we discuss combination therapies, which are the future of cancer treatment. Nanoparticle-based anticancer immunotherapies seem to be effective, in that they effectively use nanodrugs to elicit a greater immune response. The combination of these therapies with others, such as photothermal or tumor vaccine therapy, can result in a greater anticancer effect. Thus, the future of anticancer therapy aims to increase the effectiveness of therapy using various therapies in a synergistic combination rather than individually.

Comparative immunological studies of tumor-associated Lewis X, Lewis Y, and KH-1 antigens

Tumor-associated carbohydrate antigens Lewis X (Lex), Lewis Y (Ley), and KH-1 are useful targets for cancer immunotherapy. In this regard, an insight into the structure-immunogenicity relationships of these antigens is important but this has not been systematically investigated yet. In the current study, Lex, Ley, and KH-1 antigens with a lactose unit at the reducing end as a spacer were synthesized and coupled with keyhole limpet hemocyanin (KLH) protein. Immunological evaluations of the resultant conjugates revealed that they all could elicit robust immune responses whilst the Ley conjugate could provoke the highest titers of total and IgG antibodies. The binding assays of their antisera to each antigen and to cancer cells showed that each antiserum had extensive cross-reaction with all three antigens as protein conjugates and strong but somewhat antigen-selective binding towards MCF-7 cancer cell. Moreover, none of these antisera had obvious binding to SKMEL-28 cancer cell that does not express Lex, Ley and KH-1. The results of assays of these antisera to mediate complement-dependent cytotoxicity (CDC) to MCF-7 and SKMEL-28 cancer cells were very similar to the results of binding assays. Thus, it was concluded that all three antigens could form effective conjugate vaccines whereas the Ley conjugate induced the most robust immune responses and the antiserum of Lex had the highest binding and cytotoxicity to target cancer cells. In addition, as the antibodies induced by each antigen had extensive cross-reaction with other two antigens, either Lex or Ley or the two combined can be utilized to formulate effective conjugate vaccines for cancer immunotherapy. Another paradigm-shifting discovery of this study is that the presentation of Lex, Ley, and KH-1 antigens on cancer cell can be different from that in synthetic conjugates, which should be taken into consideration during the design and optimization of related cancer vaccines or immunotherapies.

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.

Preparation and in vivo evaluation of glyco-gold nanoparticles carrying synthetic mycobacterial hexaarabinofuranoside

A number of bacterial glycans are specific markers for the detection and the serological identification of microorganisms and are also widely used as antigenic components of vaccines. The use of gold nanoparticles as carriers for glyco-epitopes is becoming an important alternative to the traditional conjugation with proteins and synthetic polymers. In this study, we aimed to prepare and evaluate in vivo glyco-gold nanoparticles (glyco-GNPs) bearing the terminal-branched hexaarabinofuranoside fragment (Ara₆) of arabinan domains of lipoarabinomannan and arabinogalactan, which are principal polysaccharides of the cell wall of Mycobacterium tuberculosis, the causative agent of tuberculosis. In particular, we were interested whether the antibodies generated against Ara₆-GNPs would recognize the natural saccharides on the cell surface of different mycobacterial strains. Two synthetic Ara₆ glycosides with amino-functionalized spacer aglycons differing in length and hydrophilicity were directly conjugated with spherical gold nanoparticles (d = 15 nm) to give two sets of glyco-GNPs, which were used for the immunization of rabbits. Dot assays revealed cross-reactions between the two obtained antisera with the hexaarabinofuranoside and the 2-aminoethyl aglycon used for the preparation of glyco-GNPs. Both antisera contained high titers of antibodies specific for Mycobacteria as shown by enzyme-linked immunosorbent assay using M. bovis and M. smegmatis cells as antigens while there was only a weak response to M. phlei cells and no interaction with E. coli cells. The results obtained suggest that glyco-GNPs are promising agents for the generation of anti-mycobacterial antibodies.

Synthesis of Lewis Y Analogues and Their Protein Conjugates for Structure-Immunogenicity Relationship Studies of Lewis Y Antigen

Analogues of cancer-associated Lewis Y (Le^y) antigen with varying structures at the reducing end were synthesized by a highly efficient strategy involving one-pot preactivation-based iterative glycosylation to obtain the key tetra-/pentasaccharide intermediates, which was followed by stereoselective fucosylation. After global deprotection, these oligosaccharides were coupled with carrier protein keyhole limpet hemocyanin. The resultant glycan-protein conjugates were subjected to immunological studies in mice. It was disclosed that the conjugate of the pentasaccharide analogue of Lewis Y antigen was more immunogenic than that of the hexasaccharide analogue, but the antisera of both conjugates could indiscriminately recognize each carbohydrate hapten. These results suggested that the short Lewis Y analogue may be utilized to develop functional conjugate cancer vaccines. More importantly, the results also proved that the reducing-end glucose residue in the hexasaccharide analogue of Lewis Y was probably not involved in its interaction with the immune system, whose discovery can have a broad impact on the design of new cancer vaccines.

Vaccinations for Colorectal Cancer: Progress, Strategies, and Novel Adjuvants

Although cancer is a leading cause of death, significant breakthroughs have been made in its treatment in recent years. In particular, increasingly effective cancer vaccines are being developed, including some for colorectal cancer. There are also currently a variety of compounds that can act as adjuvants, such as signalling molecules called cytokines. Other adjuvants target and inhibit the specific mechanisms by which cancers evade the immune system. One of them is a galectin inhibitor, which targets galectins—proteins produced by cancer cells that can cause the death of immune cells. Likewise, immune checkpoint inhibitors affect immune checkpoints—natural host proteins that usually control inflammation but can be exploited by cancers to weaken the body’s defences. Equally, regulatory T cells may contribute to the progression of cancer by inhibiting the functions of other T cells. The main advantages of cancer vaccines include their low toxicity and their ability to strengthen the immune system. Nevertheless, significant limitations include their slow effects and their inability to treat cancer at times due to immunosuppression. Ultimately, ongoing trials provide hope for the development of more effective methods of immunotherapeutic inoculation that can target a greater variety of cancers.

Recent Advances in Toll Like Receptor-Targeting Glycoconjugate Vaccines

Many malignant cell surface carbohydrates resulting from abnormal glycosylation patterns of certain diseases can serve as antigens for the development of vaccines against these diseases. However, carbohydrate antigens are usually poorly immunogenic by themselves, thus they need to be covalently coupled with immunologically active carrier molecules to be functional. The most well established and commonly used carriers are proteins. In recent years, the use of toll-like receptor (TLR) ligands to formulate glycoconjugate vaccines has gained significant attention because TLR ligands can serve not only as carrier molecules but also as built-in adjuvants to form fully synthetic and self-adjuvanting conjugate vaccines, which have several advantages over carbohydrate-protein conjugates and formulated mixtures with external adjuvants. This article reviews recent progresses in the development of conjugate vaccines based on TLR ligands. Two major classes of TLR ligands, lipopeptides and lipid A derivatives will be covered with more focus on monophosohoryl lipid A (MPLA) and related analogs, which are TLR4 ligands demonstrated to be able to provoke T cell-dependent, adaptive immune responses. Corresponding conjugate vaccines have shown promising application potentials to multiple diseases including cancer.

Engineering a new generation of carbohydrate-based vaccines

Recent advances in chemical synthesis, conjugation chemistry, engineered biosynthesis, and formulation design have spawned a new generation of vaccines that incorporate carbohydrate antigens. By providing better immunity against a variety of pathogens or malignant cells and lowering the cost of production, these developments overcome many of the limitations associated with conventional vaccines involving polysaccharides. Moreover, the resulting vaccine candidates are shedding light on how the immune system responds to carbohydrates and providing mechanistic insight that can help guide future vaccine design. Here, we review recent engineering efforts to develop and manufacture carbohydrate-based vaccines that are efficacious, durable, and cost-effective.

Interplay of Carbohydrate and Carrier in Antibacterial Glycoconjugate Vaccines

Bacterial infections are a serious health concern and are responsible for millions of illnesses and deaths each year in communities around the world. Vaccination is an important public health measure for reducing and eliminating this burden, and regions with comprehensive vaccination programs have achieved significant reductions in infection and mortality. This is often accomplished by immunization with bacteria-derived carbohydrates, typically in conjunction with other biomolecules, which induce immunological memory and durable protection against bacterial human pathogens. For many species, however, vaccines are currently unavailable or have suboptimal efficacy characterized by short-lived memory and incomplete protection, especially among at-risk populations. To address this challenge, new tools and techniques have emerged for engineering carbohydrates and conjugating them to carrier molecules in a tractable and scalable manner. Collectively, these approaches are yielding carbohydrate-based vaccine designs with increased immunogenicity and protective efficacy, thereby opening up new opportunities for this important class of antigens. In this chapter we detail the current understanding of how carbohydrates interact with the immune system to provide immunity; how glycoengineering, especially in the context of glycoconjugate vaccines, can be used to modify and enhance immune responses; and current trends and strategies being pursued for the rational design of next-generation glycosylated antibacterial vaccines. Graphical Abstract.