O-glycosylated human MUC1 repeats are processed in vitro by immunoproteasomes

Aberrant Glycosylation as Immune Therapeutic Targets for Solid Tumors

Glycosylation occurs at all major types of biomolecules, including proteins, lipids, and RNAs to form glycoproteins, glycolipids, and glycoRNAs in mammalian cells, respectively. The carbohydrate moiety, known as glycans on glycoproteins and glycolipids, is diverse in their compositions and structures. Normal cells have their unique array of glycans or glycome which play pivotal roles in many biological processes. The glycan structures in cancer cells, however, are often altered, some having unique structures which are termed as tumor-associated carbohydrate antigens (TACAs). TACAs as tumor biomarkers are glycan epitopes themselves, or glycoconjugates. Some of those TACAs serve as tumor glyco-biomarkers in clinical practice, while others are the immune therapeutic targets for treatment of cancers. A monoclonal antibody (mAb) to GD2, an intermediate of sialic-acid containing glycosphingolipids, is an example of FDA-approved immune therapy for neuroblastoma indication in young adults and many others. Strategies for targeting the aberrant glycans are currently under development, and some have proceeded to clinical trials. In this review, we summarize the currently established and most promising aberrant glycosylation as therapeutic targets for solid tumors.

Identification of Flucloxacillin-Haptenated HLA-B*57:01 Ligands: Evidence of Antigen Processing and Presentation

Flucloxacillin is a β-lactam antibiotic associated with a high incidence of drug-induced liver reactions. Although expression of human leukocyte antigen (HLA)-B*57:01 increases susceptibility, little is known of the pathological mechanisms involved in the induction of the clinical phenotype. Irreversible protein modification is suspected to drive the reaction through the modification of peptides that are presented by the risk allele. In this study, the binding of flucloxacillin to immune cells was characterized and the nature of the peptides presented by HLA-B*57:01 was analyzed using mass spectrometric-based immunopeptidomics methods. Flucloxacillin modification of multiple proteins was observed, providing a potential source of neoantigens for HLA presentation. Of the peptides eluted from flucloxacillin-treated C1R-B*57:01 cells, 6 putative peptides were annotated as flucloxacillin-modified HLA-B*57:01 peptide ligands (data are available via ProteomeXchange with identifier PXD020137). To conclude, we have characterized naturally processed drug-haptenated HLA ligands presented on the surface of antigen presenting cells that may drive drug-specific CD8+ T-cell responses.

Does Antigen Glycosylation Impact the HIV-Specific T Cell Immunity?

It is largely unknown how post-translational protein modifications, including glycosylation, impacts recognition of self and non-self T cell epitopes presented by HLA molecules. Data in the literature indicate that O- and N-linked glycosylation can survive epitope processing and influence antigen presentation and T cell recognition. In this perspective, we hypothesize that glycosylation of viral proteins and processed epitopes contribute to the T cell response to HIV. Although there is some evidence for T cell responses to glycosylated epitopes (glyco-epitopes) during viral infections in the literature, this aspect has been largely neglected for HIV. To explore the role of glyco-epitope specific T cell responses in HIV infection we conducted in silico and ex vivo immune studies in individuals with chronic HIV infection. We found that in silico viral protein segments with potentially glycosylable epitopes were less frequently targeted by T cells. Ex vivo synthetically added glycosylation moieties generally masked T cell recognition of HIV derived peptides. Nonetheless, in some cases, addition of simple glycosylation moieties produced neo-epitopes that were recognized by T cells from HIV infected individuals. Herein, we discuss the potential importance of these observations and compare limitations of the employed technology with new methodologies that may have the potential to provide a more accurate assessment of glyco-epitope specific T cell immunity. Overall, this perspective is aimed to support future research on T cells recognizing glycosylated epitopes in order to expand our understanding on how glycosylation of viral proteins could alter host T cell immunity against viral infections.

Relevance of glycans in the interaction between T lymphocyte and the antigen presenting cell

The immunological synapse promotes receptors and ligands interaction in the contact interface between the T lymphocyte and the antigen presenting cell; glycosylation of the proteins involved in this biological process favors regulation of molecular interactions and development of the T lymphocyte effector response. Glycans in the immunological synapse influence cellular and molecular processes such as folding, expression, and structural stability of proteins, they also mediate ligand-receptor interaction and propagation of the intracellular signaling or inhibition of uncontrolled cellular activation that could lead to the development of autoimmunity, among others. It has been suggested that altered glycosylation of proteins that participate in the immunological synapse affects the signaling processes and cell proliferation, as well as exacerbation of the effector mechanisms of T cells that trigger systemic damage and autoimmunity. Understanding the role of glycans in the immune response has allowed for advances in the development of immunotherapies in different fields through the controlled and specific activation of the immune response. This review describes the structural and biological aspects of glycans associated with some molecules present in the immunological synapse, providing information that allows understanding the function of glycosylation in the interaction between the T lymphocyte and the antigen-presenting cell, as well as its impact on signaling and development regulation of T lymphocytes effector response.

Engineering orthogonal human O-linked glycoprotein biosynthesis in bacteria

A major objective of synthetic glycobiology is to re-engineer existing cellular glycosylation pathways from the top down or construct non-natural ones from the bottom up for new and useful purposes. Here, we have developed a set of orthogonal pathways for eukaryotic O-linked protein glycosylation in Escherichia coli that installed the cancer-associated mucin-type glycans Tn, T, sialyl-Tn and sialyl-T onto serine residues in acceptor motifs derived from different human O-glycoproteins. These same glycoengineered bacteria were used to supply crude cell extracts enriched with glycosylation machinery that permitted cell-free construction of O-glycoproteins in a one-pot reaction. In addition, O-glycosylation-competent bacteria were able to generate an antigenically authentic Tn-MUC1 glycoform that exhibited reactivity with antibody 5E5, which specifically recognizes cancer-associated glycoforms of MUC1. We anticipate that the orthogonal glycoprotein biosynthesis pathways developed here will provide facile access to structurally diverse O-glycoforms for a range of important scientific and therapeutic applications.

Synthetic MUC1 breast cancer vaccine containing a Toll-like receptor 7 agonist exerts antitumor effects

Adjuvant immunotherapy has recently emerged as a potential treatment strategy for breast cancer. The tumor-associated protein mucin 1 (MUC1) has received increasing attention due to its high expression in numerous types of common tumors, in which MUC1 acts as a cancer antigen. However, the simple mixed composition of an adjuvant and a peptide is not a sufficient rationale for a MUC1 peptide-based vaccine. The present study developed a novel Toll-like receptor 7 (TLR7) agonist-conjugated MUC1 peptide vaccine (T7-MUC1), which elicited an effective immune response and a robust antitumor effect in a mouse breast cancer model. In vitro, T7-MUC1 significantly increased the release of cytokines in mouse bone marrow dendritic cells and spleen lymphocytes, and induced the dendritic cell-cytokine-induced killer response against tumor cells with high MUC1 expression. In vivo, it was observed that the 4T1 tumor weights in mice immunized with the T7-MUC1 conjugate were reduced by ≥70% compared with those in the control group. Furthermore, the therapeutic responses in vivo were attributed to the increase in specific humoral and cellular immunity, including high antibody titers, antibody-dependent cell-mediated cytotoxicity and cytotoxic T-lymphocyte activity. The percentages of CD3⁺/CD8⁺ T-cells were significantly higher in the T7-MUC1 treatment group compared with those in the control group. Therefore, the results of the present study suggested that the T7-MUC1 vaccine inhibited tumor growth in mice and thus may have potential as a therapeutic candidate in clinical trials for breast cancer immunotherapy.

Plant-Produced N-glycosylated Ag85A Exhibits Enhanced Vaccine Efficacy Against Mycobacterium tuberculosis HN878 Through Balanced Multifunctional Th1 T Cell Immunity

Tuberculosis (TB) is one of the deadliest infectious diseases worldwide and is caused by Mycobacterium tuberculosis (Mtb). An effective vaccine to prevent TB is considered the most cost-effective measure for controlling this disease. Many different vaccine antigen (Ag) candidates, including well-known and newly identified Ags, have been evaluated in clinical and preclinical studies. In this study, we took advantage of a plant system of protein expression using Nicotiana benthamiana to produce N-glycosylated antigen 85A (G-Ag85A), which is one of the most well-characterized vaccine Ag candidates in the field of TB vaccines, and compared its immunogenicity and vaccine efficacy with those of nonglycosylated Ag85A (NG-Ag85A) produced with an Escherichia coli system. Notably, G-Ag85A induced a more robust IFN-γ response than NG-Ag85A, which indicated that G-Ag85A is well recognized by the host immune system during Mtb infection. We subsequently compared the vaccine potential of G-Ag85A and NG-Ag85A by evaluating their immunological features and substantial protection efficacies. Interestingly, G-Ag85A yielded moderately enhanced long-term protective efficacy, as measured in terms of bacterial burden and lung inflammation. Strikingly, G-Ag85A-immunized mice showed a more balanced proportion of multifunctional Th1-biased immune responses with sustained IFN-γ response than did NG-Ag85A-immunized mice. Collectively, plant-derived G-Ag85A could induce protective and balanced Th1 responses and confer long-term protection against a hypervirulent Mtb Beijing strain infection, which indicated that plant-produced G-Ag85A might provide an excellent example for the production of an Mtb subunit vaccine Ag and could be an effective platform for the development of anti-TB vaccines.

Esophageal, gastric and colorectal cancers: Looking beyond classical serological biomarkers towards glycoproteomics-assisted precision oncology

Esophageal (OC), gastric (GC) and colorectal (CRC) cancers are amongst the digestive track tumors with higher incidence and mortality due to significant molecular heterogeneity. This constitutes a major challenge for patients' management at different levels, including non-invasive detection of the disease, prognostication, therapy selection, patient's follow-up and the introduction of improved and safer therapeutics. Nevertheless, important milestones have been accomplished pursuing the goal of molecular-based precision oncology. Over the past five years, high-throughput technologies have been used to interrogate tumors of distinct clinicopathological natures, generating large-scale biological datasets (e.g. genomics, transcriptomics, and proteomics). As a result, GC and CRC molecular subtypes have been established to assist patient stratification in the clinical settings. However, such molecular panels still require refinement and are yet to provide targetable biomarkers. In parallel, outstanding advances have been made regarding targeted therapeutics and immunotherapy, paving the way for improved patient care; nevertheless, important milestones towards treatment personalization and reduced off-target effects are also to be accomplished. Exploiting the cancer glycoproteome for unique molecular fingerprints generated by dramatic alterations in protein glycosylation may provide the necessary molecular rationale towards this end. Therefore, this review presents functional and clinical evidences supporting a reinvestigation of classical serological glycan biomarkers such as sialyl-Tn (STn) and sialyl-Lewis A (SLe^A) antigens from a tumor glycoproteomics perspective. We anticipate that these glycobiomarkers that have so far been employed in non-invasive cancer prognostication may hold unexplored value for patients' management in precision oncology settings.

Various Tastes of Sugar: The Potential of Glycosylation in Targeting and Modulating Human Immunity via C-Type Lectin Receptors

C-type lectin receptors (CLRs) are important in several immune regulatory processes. These receptors recognize glycans expressed by host cells or by pathogens. Whereas pathogens are recognized through their glycans, which leads to protective immunity, aberrant cellular glycans are now increasingly recognized as disease-driving factors in cancer, auto-immunity, and allergy. The vast variety of glycan structures translates into a wide spectrum of effects on the immune system ranging from immune suppression to hyper-inflammatory responses. CLRs have distinct expression patterns on antigen presenting cells (APCs) controlling their role in immunity. CLRs can also be exploited to selectively target specific APCs, modulate immune responses and enhance antigen presentation. Here we will discuss the role of glycans and their receptors in immunity as well as potential strategies for immune modulation. A special focus will be given to different dendritic cell subsets as these APCs are crucial orchestrators of immune responses in infections, cancer, auto-immunity and allergies. Furthermore, we will highlight the potential use of nanoscale lipid bi-layer structures (liposomes) in targeted immunotherapy.

Going Native: Synthesis of Glycoproteins and Glycopeptides via Native Linkages To Study Glycan-Specific Roles in the Immune System

Glycosylation plays a myriad of roles in the immune system: Certain glycans can interact with specific immune receptors to kickstart a pro-inflammatory response, whereas other glycans can do precisely the opposite and ameliorate the immune response. Specific glycans and glycoforms can themselves become the targets of the adaptive immune system, leading to potent antiglycan responses that can lead to the killing of altered self- or pathogenic species. This hydra-like set of roles glycans play is of particular importance in cancer immunity, where it influences the anticancer immune response, likely playing pivotal roles in tumor survival or clearance. The complexity of carbohydrate biology requires synthetic access to glycoproteins and glycopeptides that harbor homogeneous glycans allowing the probing of these systems with high precision. One particular complicating factor in this is that these synthetic structures are required to be as close to the native structures as possible, as non-native linkages can themselves elicit immune responses. In this Review, we discuss examples and current strategies for the synthesis of natively linked single glycoforms of peptides and proteins that have enabled researchers to gain new insights into glycoimmunology, with a particular focus on the application of these reagents in cancer immunology.

Antigens reversibly conjugated to a polymeric glyco-adjuvant induce protective humoral and cellular immunity

Fully effective vaccines for complex infections must elicit a diverse repertoire of antibodies (humoral immunity) and CD8⁺ T-cell responses (cellular immunity). Here, we present a synthetic glyco-adjuvant named p(Man-TLR7), which, when conjugated to antigens, elicits robust humoral and cellular immunity. p(Man-TLR7) is a random copolymer composed of monomers that either target dendritic cells (DCs) via mannose-binding receptors or activate DCs via Toll-like receptor 7 (TLR7). Protein antigens are conjugated to p(Man-TLR7) via a self-immolative linkage that releases chemically unmodified antigen after endocytosis, thus amplifying antigen presentation to T cells. Studies with ovalbumin (OVA)-p(Man-TLR7) conjugates demonstrate that OVA-p(Man-TLR7) generates greater humoral and cellular immunity than OVA conjugated to polymers lacking either mannose targeting or TLR7 ligand. We show significant enhancement of Plasmodium falciparum-derived circumsporozoite protein (CSP)-specific T-cell responses, expansion in the breadth of the αCSP IgG response and increased inhibition of sporozoite invasion into hepatocytes with CSP-p(Man-TLR7) when compared with CSP formulated with MPLA/QS-21-loaded liposomes-the adjuvant used in the most clinically advanced malaria vaccine. We conclude that our antigen-p(Man-TLR7) platform offers a strategy to enhance the immunogenicity of protein subunit vaccines.

Synthesis of a Self-Adjuvanting MUC1 Vaccine via Diselenide-Selenoester Ligation-Deselenization

Access to lipopeptide-based vaccines for immunological studies remains a significant challenge owing to the amphipathic nature of the molecules, which makes them difficult to synthesize and purify to homogeneity. Here, we describe the application of a new peptide ligation technology, the diselenide-selenoester ligation (DSL), to access self-adjuvanting glycolipopeptide vaccines. We show that rapid ligation of glyco- and lipopeptides is possible via DSL in mixed organic solvent-aqueous buffer and, when coupled with deselenization chemistry, affords rapid and efficient access to a vaccine candidate possessing a MUC1 glycopeptide epitope and the lipopeptide adjuvant Pam₂Cys. This construct was shown to elicit MUC1-specific antibody and cytotoxic T lymphocyte responses in the absence of any other injected lipids or adjuvants. The inclusion of the helper T cell epitope PADRE both boosted the antibody response and resulted in elevated cytokine production.

Synthesis and Immunological Evaluation of a Multicomponent Cancer Vaccine Candidate Containing a Long MUC1 Glycopeptide

A fully synthetic MUC1-based cancer vaccine was designed and chemically synthesized containing an endogenous helper T-epitope (MHC class II epitope). The vaccine elicited robust IgG titers that could neutralize cancer cells by antibody-dependent cell-mediated cytotoxicity (ADCC). It also activated cytotoxic T-lymphocytes. Collectively, the immunological data demonstrate engagement of helper T-cells in immune activation. A synthetic methodology was developed for a penta-glycosylated MUC1 glycopeptide, and antisera of mice immunized by the new vaccine recognized such a structure. Previously reported fully synthetic MUC1-based cancer vaccines that elicited potent immune responses employed exogenous helper T-epitopes derived from microbes. It is the expectation that the use of the newly identified endogenous helper T-epitope will be more attractive, because it will activate cognate CD4+ T-cells that will provide critical tumor-specific help intratumorally during the effector stage of tumor rejection and will aid in the generation of sustained immunological memory.

Synergistic effects of dendritic cell targeting and laser-microporation on enhancing epicutaneous skin vaccination efficacy

Due to its unique immunological properties, the skin is an attractive target tissue for allergen-specific immunotherapy. In our current work, we combined a dendritic cell targeting approach with epicutaneous immunization using an ablative fractional laser to generate defined micropores in the upper layers of the skin. By coupling the major birch pollen allergen Bet v 1 to mannan from S. cerevisiae via mild periodate oxidation we generated hypoallergenic Bet-mannan neoglycoconjugates, which efficiently targeted CD14⁺ dendritic cells and Langerhans cells in human skin explants. Mannan conjugation resulted in sustained release from the skin and retention in secondary lymphoid organs, whereas unconjugated antigen showed fast renal clearance. In a mouse model, Bet-mannan neoglycoconjugates applied via laser-microporated skin synergistically elicited potent humoral and cellular immune responses, superior to intradermal injection. The induced antibody responses displayed IgE-blocking capacity, highlighting the therapeutic potential of the approach. Moreover, application via micropores, but not by intradermal injection, resulted in a mixed TH1/TH17-biased immune response. Our data clearly show that applying mannan-neoglycoconjugates to an organ rich in dendritic cells using laser-microporation is superior to intradermal injection. Due to their low IgE binding capacity and biodegradability, mannan neoglycoconjugates therefore represent an attractive formulation for allergen-specific epicutaneous immunotherapy.

Targeted antigen delivery by an anti-class II MHC VHH elicits focused αMUC1(Tn) immunity

Unusual patterns of glycosylation on the surface of transformed cells contribute to immune modulation and metastasis of malignant tumors. Active immunization against them requires effective antigen presentation, which is complicated by a lack of access to tumor-specific posttranslational modifications through standard genetic approaches and by the low efficiency of passive antigen sampling. We found that antigen targeted to antigen presenting cells via class II MHC products can elicit a robust immune response against MUC1(Tn) bearing a defined tumor-associated glycoform, Tn. The two-component vaccine construct was prepared by sortase-mediated protein ligation of a synthetic MUC1(Tn) fragment to a class II MHC-binding single-domain antibody fragment (VHH7) as targeting moiety. We show that VHH7 targets antigen presenting cells in vivo, and when conjugated to MUC1(Tn) can elicit a strong αMUC1(Tn) immune response in mice. The resulting sera preferentially recognized the MUC1 epitope with the tumor-associated carbohydrate antigen Tn and were capable of killing cancer cells in a complement-mediated cytotoxicity assay. Immunoglobulin isotype analysis and cytokine release assays suggested a favorable Th1 response. A single boost 12 months after primary immunization triggered a recall response of the same quality, suggesting that long-term αMUC1(Tn) memory had been achieved.

Genetically engineered mucin mouse models for inflammation and cancer

Mucins are heavily O-glycosylated proteins primarily produced by glandular and ductal epithelial cells, either in membrane-tethered or secretory forms, for providing lubrication and protection from various exogenous and endogenous insults. However, recent studies have linked their aberrant overexpression with infection, inflammation, and cancer that underscores their importance in tissue homeostasis. In this review, we present current status of the existing mouse models that have been developed to gain insights into the functional role(s) of mucins under physiological and pathological conditions. Knockout mouse models for membrane-associated (Muc1 and Muc16) and secretory mucins (Muc2) have helped us to elucidate the role of mucins in providing effective and protective barrier functions against pathological threats, participation in disease progression, and improved our understanding of mucin interaction with biotic and abiotic environmental components. Emphasis is also given to available transgenic mouse models (MUC1 and MUC7), which has been exploited to understand the context-dependent regulation and therapeutic potential of human mucins during inflammation and cancer.

Immunological Evaluation of Recent MUC1 Glycopeptide Cancer Vaccines

Aberrantly glycosylated mucin 1 (MUC1) is a recognized tumor-specific antigen on epithelial cell tumors. A wide variety of MUC1 glycopeptide anti-cancer vaccines have been formulated by many research groups. Some researchers have used MUC1 alone as an immunogen whereas other groups used different antigenic carrier proteins such as bovine serum albumin or keyhole limpet hemocyanin for conjugation with MUC1 glycopeptide. A variety of adjuvants have been used with MUC1 glycopeptides to improve their immunogenicity. Fully synthetic multicomponent vaccines have been synthesized by incorporating different T helper cell epitopes and Toll-like receptor agonists. Some vaccine formulations utilized liposomes or nanoparticles as vaccine delivery systems. In this review, we discuss the immunological evaluation of different conjugate or synthetic MUC1 glycopeptide vaccines in different tumor or mouse models that have been published since 2012.

A Bitter Sweet Symphony: Immune Responses to Altered O-glycan Epitopes in Cancer

The appearance of aberrant glycans on the tumor cell surface is one of the emerging hallmarks of cancer. Glycosylation is an important post-translation modification of proteins and lipids and is strongly affected by oncogenesis. Tumor-associated glycans have been extensively characterized regarding their composition and tumor-type specific expression patterns. Nevertheless whether and how tumor-associated glycans contribute to the observed immunomodulatory actions by tumors has not been extensively studied. Here, we provide a detailed overview of the current knowledge on how tumor-associated O-glycans affect the anti-tumor immune response, thereby focusing on truncated O-glycans present on epithelial tumors and mucins. These tumor-associated O-glycans and mucins bind a variety of lectin receptors on immune cells to facilitate the subsequently induction of tolerogenic immune responses. We, therefore, postulate that tumor-associated glycans not only support tumor growth, but also actively contribute to immune evasion.

O-Glycosylation of a Secretory Granule Membrane Enzyme Is Essential for Its Endocytic Trafficking

Peptidylglycine α-amidating monooxygenase (PAM) (EC 1.14.17.3) catalyzes peptide amidation, a crucial post-translational modification, through the sequential actions of its monooxygenase (peptidylglycine α-hydroxylating monooxygenase) and lyase (peptidyl-α-hydroxyglycine α-amidating lyase (PAL)) domains. Alternative splicing generates two different regions that connect the protease-resistant catalytic domains. Inclusion of exon 16 introduces a pair of Lys residues, providing a site for controlled endoproteolytic cleavage of PAM and the separation of soluble peptidylglycine α-hydroxylating monooxygenase from membrane-associated PAL. Exon 16 also includes two O-glycosylation sites. PAM-1 lacking both glycosylation sites (PAM-1/OSX; where OSX is O-glycan-depleted mutant of PAM-1) was stably expressed in AtT-20 corticotrope tumor cells. In PAM-1/OSX, a cleavage site for furin-like convertases was exposed, generating a shorter form of membrane-associated PAL. The endocytic trafficking of PAM-1/OSX differed dramatically from that of PAM-1. A soluble fragment of the cytosolic domain of PAM-1 was produced in the endocytic pathway and entered the nucleus; very little soluble fragment of the cytosolic domain was produced from PAM-1/OSX. Internalized PAM-1/OSX was rapidly degraded; unlike PAM-1, very little internalized PAM-1/OSX was detected in multivesicular bodies. Blue native PAGE analysis identified high molecular weight complexes containing PAM-1; the ability of PAM-1/OSX to form similar complexes was markedly diminished. By promoting the formation of high molecular weight complexes, O-glycans may facilitate the recycling of PAM-1 through the endocytic compartment.

Synthesis of a Liposomal MUC1 Glycopeptide-Based Immunotherapeutic and Evaluation of the Effect of l-Rhamnose Targeting on Cellular Immune Responses

Generation of a CD8(+) response to extracellular antigen requires processing of the antigen by antigen presenting cells (APC) and cross-presentation to CD8(+) T cell receptors via MHC class I molecules. Cross-presentation is facilitated by efficient antigen uptake followed by immune-complex-mediated maturation of the APCs. We hypothesize that improved antigen uptake of a glycopeptide sequence containing a CD8(+) T cell epitope could be achieved by delivering it on a liposome surface decorated with an immune complex-targeting ligand, an l-Rhamnose (Rha) epitope. We synthesized a 20-amino-acid glycopeptide TSAPDT(GalNAc)RPAPGSTAPPAHGV from the variable number tandem repeat region of the tumor marker MUC1 containing an N-terminal azido moiety and a tumor-associated α-N-acetyl galactosamine (GalNAc) at the immunogenic DTR motif. The MUC1 antigen was attached to Pam3Cys, a Toll-like receptor-2 ligand via copper(I)-catalyzed azido-alkyne cycloaddition (CuAAc) chemistry. The Rha-decorated liposomal Pam3Cys-MUC1-Tn 4 vaccine was evaluated in groups of C57BL/6 mice. Some groups were previously immunized to generate anti-Rha antibodies. Anti-Rha antibody expressing mice that received the Rha liposomal vaccine showed higher cellular immunogenicity compared to the control group while maintaining a strong humoral response.

Synthesis and immunological evaluation of MUC1 glycopeptide conjugates bearing N-acetyl modified STn derivatives as anticancer vaccines

Unnatural STn disaccharides with N-acetyl modifications were incorporated into a 20-amino acid MUC1 tandem repeat sequence. The modified STn-MUC1 glycopeptide–protein conjugates showed high immunogenicity.

Effects of the multiple O-glycosylation states on antibody recognition of the immunodominant motif in MUC1 extracellular tandem repeats

The conformational impact of the clusteredO-glycans strongly influences recognition by antibodies of the cancer-relevant epitope in the MUC1 extracellular tandem repeat domain.

Synthesis and cell-selective antitumor properties of amino acid conjugated tumor-associated carbohydrate antigen-coated gold nanoparticles

The Thomsen Friedenreich antigen (TFag) disaccharide is a tumor-associated carbohydrate antigen (TACA) found primarily on carcinoma cells and rarely expressed in normal tissue. The TFag has been shown to interact with Galectin-3 (Gal-3), one in a family of β-galactoside binding proteins. Galectins have a variety of cellular functions, and Gal-3 has been shown to be the sole galectin with anti-apoptotic activity. We have previously prepared gold nanoparticles (AuNP) coated with the TFag in various presentations as potential anti-adhesive therapeutic tools or antitumor vaccine platforms. Here we describe the synthesis of TFag-glycoamino acid conjugates attached to gold nanoparticles through a combined alkane/PEG linker, where the TFag was attached to either a serine or threonine amino acid. Particles were fully characterized by a host of biophysical techniques, and along with a control particle carrying hydroxyl-terminated linker units, were evaluated in both Gal-3 positive and negative cell lines. We show that the particles bearing the saccharides selectively inhibited tumor cell growth of the Gal-3 positive cells significantly more than the Gal-3 negative cells. In addition, the threonine-attached TF particles were more potent than the serine-attached constructs. These results support the use of AuNP as antitumor therapeutic platforms, targeted against cell lines that express specific lectins that interact with TFag.

Glycan-mediated modification of the immune response

Aberrantly glycosylated tumor antigens represent promising targets for the development of anti-cancer vaccines, yet how glycans influence immune responses is poorly understood. Recent studies have demonstrated that GalNAc-glycosylation enhances antigen uptake by dendritic cells as well as CD4⁺ T-cell and humoral responses, but prevents CD8⁺ T-cell activation. Here, we briefly discuss the relevance of glycans as candidate targets for anti-cancer vaccines.

Immune and anticancer responses elicited by fully synthetic aberrantly glycosylated MUC1 tripartite vaccines modified by a TLR2 or TLR9 agonist

The mucin MUC1 is overexpressed and aberrantly glycosylated by many epithelial cancer cells manifested by truncated O-linked saccharides. Although tumor-associated MUC1 has generated considerable attention because of its potential for the development of a therapeutic cancer vaccine, it has been difficult to design constructs that consistently induce cytotoxic T-lymphocytes (CTLs) and ADCC-mediating antibodies specific for the tumor form of MUC1. We have designed, chemically synthesized, and immunologically examined vaccine candidates each composed of a glycopeptide derived from MUC1, a promiscuous Thelper peptide, and a TLR2 (Pam3 CysSK4 ) or TLR9 (CpG-ODN 1826) agonist. It was found that the Pam3 CysSK4 -containing compound elicits more potent antigenic and cellular immune responses, resulting in a therapeutic effect in a mouse model of mammary cancer. It is thus shown, for the first time, that the nature of an inbuilt adjuvant of a tripartite vaccine can significantly impact the quality of immune responses elicited against a tumor-associated glycopeptide. The unique adjuvant properties of Pam3 CysSK4 , which can reduce the suppressive function of regulatory T cells and enhance the cytotoxicity of tumor-specific CTLs, are likely responsible for the superior properties of the vaccine candidate 1.

Adaptive immune activation: glycosylation does matter

Major histocompatibility complex (MHC) class I and II are glycoproteins that can present antigenic peptides at the cell surface for recognition and activation of circulating T lymphocytes. Here, the importance of the modification of protein antigens by glycans on cellular uptake, proteolytic processing, presentation by MHC and subsequent T-cell priming is reviewed. Antigen glycosylation is important for a number of diseases and vaccine design. All of the key proteins involved in antigen recognition and the orchestration of downstream effector functions are glycosylated. The influence of protein glycosylation on immune function and disease is covered.

Microvesicle cargo of tumor-associated MUC1 to dendritic cells allows cross-presentation and specific carbohydrate processing

Tumor-associated glycoproteins are a group of antigens with high immunogenic interest: The glycoforms generated by the aberrant glycosylation are tumor-specific and the novel glycoepitopes exposed can be targets of tumor-specific immune responses. The MUC1 antigen is one of the most relevant tumor-associated glycoproteins. In cancer, MUC1 loses polarity and becomes overexpressed and hypoglycosylated. Changes in glycan moieties contribute to MUC1 immunogenicity and can modify the interactions of tumor cells with antigen-presenting cells such as dendritic cells that would affect the overall antitumor immune response. Here, we show that the form of the MUC1 antigen, i.e., soluble or as microvesicle cargo, influences MUC1 processing in dendritic cells. In fact, MUC1 carried by microvesicles translocates from the endolysosomal/HLA-II to the HLA-I compartment and is presented by dendritic cells to MUC1-specific CD8(+) T cells stimulating IFN-γ responses, whereas the soluble MUC1 is retained in the endolysosomal/HLA-II compartment independently by the glycan moieties and by the modality of internalization (receptor-mediated or non-receptor mediated). MUC1 translocation to the HLA-I compartment is accompanied by deglycosylation that generates novel MUC1 glycoepitopes. Microvesicle-mediated transfer of tumor-associated glycoproteins to dendritic cells may be a relevant biologic mechanism in vivo contributing to define the type of immunogenicity elicited. Furthermore, these results have important implications for the design of glycoprotein-based immunogens for cancer immunotherapy.

MUC1-specific cytotoxic T lymphocytes in cancer therapy: induction and challenge

MUC1 glycoprotein is often found overexpressed and hypoglycosylated in tumor cells from numerous cancer types. Since its discovery MUC1 has been an attractive target for antitumor immunotherapy. Indeed, in vitro and in vivo experiments have shown T-cell-specific responses against MUC1 in an HLA-restricted and HLA-unrestricted manner, although some animal models have highlighted the possible development of tolerogenic responses against this antigen. These observations permit the development of new T-cell vaccine strategies capable of inducing an MUC1-specific cytotoxic T cell response in cancer patients. Some of these strategies are now being tested in clinical trials against different types of cancer. To date, encouraging clinical responses have been observed with some MUC1 vaccines in phase II/III clinical trials. This paper compiles knowledge regarding MUC1 as a promising tumor antigen for antitumor therapeutic vaccines applicable to numerous cancers. We also summarize the results of MUC1-vaccine-based clinical trials.

Cancer associated aberrant protein O-glycosylation can modify antigen processing and immune response

Aberrant glycosylation of mucins and other extracellular proteins is an important event in carcinogenesis and the resulting cancer associated glycans have been suggested as targets in cancer immunotherapy. We assessed the role of O-linked GalNAc glycosylation on antigen uptake, processing, and presentation on MHC class I and II molecules. The effect of GalNAc O-glycosylation was monitored with a model system based on ovalbumin (OVA)-MUC1 fusion peptides (+/- glycosylation) loaded onto dendritic cells co-cultured with IL-2 secreting OVA peptide-specific T cell hybridomas. To evaluate the in vivo response to a cancer related tumor antigen, Balb/c or B6.Cg(CB)-Tg(HLA-A/H2-D)2Enge/J (HLA-A2 transgenic) mice were immunized with a non-glycosylated or GalNAc-glycosylated MUC1 derived peptide followed by comparison of T cell proliferation, IFN-γ release, and antibody induction. GalNAc-glycosylation promoted presentation of OVA-MUC1 fusion peptides by MHC class II molecules and the MUC1 antigen elicited specific Ab production and T cell proliferation in both Balb/c and HLA-A2 transgenic mice. In contrast, GalNAc-glycosylation inhibited the presentation of OVA-MUC1 fusion peptides by MHC class I and abolished MUC1 specific CD8+ T cell responses in HLA-A2 transgenic mice. GalNAc glycosylation of MUC1 antigen therefore facilitates uptake, MHC class II presentation, and antibody response but might block the antigen presentation to CD8+ T cells.

Sialyl-tn in cancer: (how) did we miss the target?

Sialyl-Tn antigen (STn) is a short O-glycan containing a sialic acid residue α2,6-linked to GalNAcα-O-Ser/Thr. The biosynthesis of STn is mediated by a specific sialyltransferase termed ST6GalNAc I, which competes with O-glycans elongating glycosyltransferases and prevents cancer cells from exhibiting longer O-glycans. While weakly expressed by fetal and normal adult tissues, STn is expressed by more than 80% of human carcinomas and in all cases, STn detection is associated with adverse outcome and decreased overall survival for the patients. Because of its pan-carcinoma expression associated with an adverse outcome, an anti-cancer vaccine, named Theratope, has been designed towards the STn epitope. In spite of the great enthusiasm around this immunotherapy, Theratope failed on Phase III clinical trial. However, in lieu of missing this target, one should consider to revise the Theratope design and the actual facts. In this review, we highlight the many lessons that can be learned from this failure from the immunological standpoint, as well as from the drug design and formulation and patient selection. Moreover, an irrefutable knowledge is arising from novel immunotherapies targeting other carbohydrate antigens and STn carrier proteins, such as MUC1, that will warrantee the future development of more successful anti-STn immunotherapy strategies.

The sweet side of tumor immunotherapy

Carbohydrate signatures on tumor cells have functional implications in tumor growth and metastasis and constitute valuable tools in cancer diagnosis and immunotherapy. Increasing data regarding the mechanisms by which they are recognized by the immune system are facilitating the design of more efficient immunotherapeutic protocols based on cancer-associated glycan structures. Recent molecular and proteomic studies revealed that carbohydrates are recognized, not only by B cells and antibodies, but also by cells from the innate arm of immunity, as well as by T cells, and are able to induce specific T-cell immunity and cytotoxicity. In this review, we discuss and update the different strategies targeting tumor-associated carbohydrate antigens that are being evaluated for antitumor immunotherapy, an approach that will be highly relevant, especially when combined with other strategies, in the future fight against cancer.

A focused immune response targeting the homotypic binding domain of the carcinoembryonic antigen blocks the establishment of tumor foci in vivo

Metastatic forms of cancers remain the main cause of death in cancer patients. In this study, we demonstrate that directing a sustained antibody response towards the homotypic binding function of CEA interferes with the implantation and development of tumor foci in CEA-expressing transgenic (CEA.Tg) mice. Specifically, vaccinating CEA.Tg mice with a recombinant, altered self-form of the CEA Ig V-like N domain led to the production of circulating IgG1 and IgG2a antibodies that inhibited CEA-mediated adhesion of murine carcinoma expressing CEA (MC38.CEA) and mediated antibody-dependent lysis of tumor cells. Moreover, vaccinated CEA.Tg mice were resistant to the development of tumor nodules in the lungs and the peritoneal cavity, suggesting that mounting a focused antibody response to the CEA N domain may represent a simple therapeutic strategy to control the establishment of metastatic foci in cancer patients.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, published in 1999, on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Immune recognition of tumor-associated mucin MUC1 is achieved by a fully synthetic aberrantly glycosylated MUC1 tripartite vaccine

The mucin MUC1 is typically aberrantly glycosylated by epithelial cancer cells manifested by truncated O-linked saccharides. The resultant glycopeptide epitopes can bind cell surface major histocompatibility complex (MHC) molecules and are susceptible to recognition by cytotoxic T lymphocytes (CTLs), whereas aberrantly glycosylated MUC1 protein on the tumor cell surface can be bound by antibodies to mediate antibody-dependent cell-mediated cytotoxicity (ADCC). Efforts to elicit CTLs and IgG antibodies against cancer-expressed MUC1 have not been successful when nonglycosylated MUC1 sequences were used for vaccination, probably due to conformational dissimilarities. Immunizations with densely glycosylated MUC1 peptides have also been ineffective due to impaired susceptibility to antigen processing. Given the challenges to immuno-target tumor-associated MUC1, we have identified the minimum requirements to consistently induce CTLs and ADCC-mediating antibodies specific for the tumor form of MUC1 resulting in a therapeutic response in a mouse model of mammary cancer. The vaccine is composed of the immunoadjuvant Pam(3)CysSK(4), a peptide T(helper) epitope and an aberrantly glycosylated MUC1 peptide. Covalent linkage of the three components was essential for maximum efficacy. The vaccine produced CTLs, which recognized both glycosylated and nonglycosylated peptides, whereas a similar nonglycosylated vaccine gave CTLs which recognized only nonglycosylated peptide. Antibodies elicited by the glycosylated tripartite vaccine were significantly more lytic compared with the unglycosylated control. As a result, immunization with the glycosylated tripartite vaccine was superior in tumor prevention. Besides its own aptness as a clinical target, these studies of MUC1 are likely predictive of a covalent linking strategy applicable to many additional tumor-associated antigens.

Natural and Induced Humoral Responses to MUC1

MUC1 is a membrane-tethered mucin expressed on the ductal cell surface of glandular epithelial cells. Loss of polarization, overexpression and aberrant glycosylation of MUC1 in mucosal inflammation and in adenocarcinomas induces humoral immune responses to the mucin. MUC1 IgG responses have been associated with a benefit in survival in patients with breast, lung, pancreatic, ovarian and gastric carcinomas. Antibodies bound to the mucin may curb tumor progression by restoring cell-cell interactions altered by tumor-associated MUC1, thus preventing metastatic dissemination, as well as counteracting the immune suppression exerted by the molecule. Furthermore, anti-MUC1 antibodies are capable of effecting tumor cell killing by antibody-dependent cell-mediated cytotoxicity. Although cytotoxic T cells are indispensable to achieve anti-tumor responses in advanced disease, abs to tumor-associated antigens are ideally suited to address minimal residual disease and may be sufficient to exert adequate immune surveillance in an adjuvant setting, destroying tumor cells as they arise or maintaining occult disease in an equilibrium state. Initial evaluation of MUC1 peptide/glycopeptide mono and polyvalent vaccines has shown them to be immunogenic and safe; anti-tumor responses are scarce. Progress in carbohydrate synthesis has yielded a number of sophisticated substrates that include MUC1 glycopeptide epitopes that are at present in preclinical testing. Adjuvant vaccination with MUC1 glycopeptide polyvalent vaccines that induce strong humoral responses may prevent recurrence of disease in patients with early stage carcinomas. Furthermore, prophylactic immunotherapy targeting MUC1 may be a strategy to strengthen immune surveillance and prevent disease in subjects at hereditary high risk of breast, ovarian and colon cancer.

Tn glycosylation of the MUC6 protein modulates its immunogenicity and promotes the induction of Th17-biased T cell responses

The Tn antigen (α-GalNAc-O-Ser/Thr) is one of the most specific human cancer-associated structures. This antigen, together with mucins, the major carriers of O-glycosylated tumor antigens in adenocarcinomas, are being evaluated as anti-cancer immunotherapeutic targets. In particular, the MUC6 protein, which is normally expressed only in gastric tissues, has been detected in intestinal, pulmonary, colorectal, and breast carcinomas. To develop anti-cancer vaccines based on the Tn antigen, we produced MUC6 proteins with different Tn density by using mixtures of recombinant ppGalNAc-T1, -T2, and -T7. The obtained glycoproteins were characterized and analyzed for their immunological properties, as compared with the non-glycosylated MUC6. We show that these various MUC6:Tn glycoproteins were well recognized by both MUC6 and Tn-specific antibodies. However, Tn glycosylation of the MUC6 protein strongly affected their immunogenicity by partially abrogating Th1 cell responses, and promoting IL-17 responses. Moreover, the non-glycosylated MUC6 was more efficiently presented than MUC6:Tn glycoproteins to specific T CD4(+) hybridomas, suggesting that Tn glycosylation may affect MUC6 processing or MHC binding of the processed peptides. In conclusion, our results indicate that Tn glycosylation of the MUC6 protein strongly affects its B and T cell immunogenicity, and might favor immune escape of tumor cells.

Random glycopeptide bead libraries for seromic biomarker discovery

Identification of disease-specific biomarkers is important to address early diagnosis and management of disease. Aberrant post-translational modifications (PTM) of proteins such as O-glycosylations (O-PTMs) are emerging as triggers of autoantibodies that can serve as sensitive biomarkers. Here we have developed a random glycopeptide bead library screening platform for detection of autoantibodies and other binding proteins. Libraries were build on biocompatible PEGA beads including a safety-catch C-terminal amide linker (SCAL) that allowed mild cleavage conditions (I(2)/NaBH(4) and TFA) for release of glycopeptides and sequence determination by ESI-Orbitrap-MS(n). As proof-of-principle, tumor -specific glycopeptide reporter epitopes were built-in into the libraries and were detected by tumor-specific monoclonal antibodies and autoantibodies from cancer patients. Sequenced and identified glycopeptides were resynthesized at the preparative scale by automated parallel peptide synthesis and printed on microarrays for validation and broader analysis with larger sets of sera. We further showed that chemical synthesis of the monosaccharide O-glycopeptide library (Tn-glycoform) could be diversified to other tumor glycoforms by on-bead enzymatic glycosylation reactions with recombinant glycosyltransferases. Hence, we have developed a high-throughput flexible platform for rapid discovery of O-glycopeptide biomarkers and the method has applicability in other types of assays such as lectin/antibody/enzyme specificity studies as well as investigation of other PTMs.

MUC1 immunotherapy

The overexpression and aberrant glycosylation of MUC1 is associated with a wide variety of cancers, making it an ideal target for immunotherapeutic strategies. This review highlights the main avenues of research in this field, focusing on adenocarcinomas, from the preclinical to clinical; the problems and possible solutions associated with each approach; and speculates on the direction of MUC1 immunotherapeutic research over the next 5-10 years.

The Tat-conjugated N-terminal region of mucin antigen 1 (MUC1) induces protective immunity against MUC1-expressing tumours

Mucin antigen 1 (MUC1) is overexpressed on various human adenocarcinomas and haematological malignancies and has long been used as a target antigen for cancer immunotherapy. Most of the preclinical and clinical studies using MUC1 have used the tandem repeat region of MUC1, which could be presented by only a limited set of major histocompatibility complex haplotypes. Here, we evaluated N-terminal region (2-147 amino acids) of MUC1 (MUC1-N) for dendritic cell (DC)-based cancer immunotherapy. We used Esherichia coli-derived MUC1-N that was fused to the protein transduction domain of human immunodeficiency virus Tat protein for three reasons. First, mature DCs do not phagocytose soluble protein antigens. Secondly, tumour cells express underglycosylated MUC1, which can generate epitopes repertoire that differs from normal cells, which express hyperglycosylated MUC1. Finally, aberrantly glycosylated MUC1 has been known to impair DC function. In our study, Tat-MUC1-N-loaded DCs induced type 1 T cell responses as well as cytotoxic T lymphocytes efficiently. Furthermore, they could break tolerance in the transgenic breast tumour mouse model, where MUC1-positive breast cancers grow spontaneously. Compared with DCs pulsed with unconjugated MUC1-N, DCs loaded with Tat-conjugated MUC1-N could delay tumour growth more effectively in the transgenic tumour model as well as in the tumour injection model. These results suggest that the recombinant N-terminal part of MUC1, which may provide a diverse epitope repertoire, could be utilized as an effective tumour antigen for DC-based cancer immunotherapy.

Identification of O-glycosylated decapeptides within the MUC1 repeat domain as potential MHC class I (A2) binding epitopes

The MUC1 glycoprotein is considered a tumor antigen due to its over expression and aberrant glycosylation in cancer tissues. The latter results in appearance of new antigenic tumor specific glycopeptides not found on normal glycoforms of the mucin. MUC1 glycopeptides can be presented by APCs on MHC class II molecules to activate glycopeptide specific helper T-cells. No study has yet reported presentation of MUC1 glycopeptides on MHC class I molecules as stimulators of cytotoxic T-cells. In this study we show that human immunoproteasomes and cathepsin-L can generate octa to undecameric glycopeptides from the MUC1 repeat domain in vitro. We identified glycosylated fragments of which the decameric glycopeptide SAP10 [SAPDT(GalNAc)RPAPG] containing a single sugar binds with comparable strength to the MHC class I allele HLA A*0201 as predicted high-score binding epitopes of the tandem repeat. The same sequence glycosylated with the disaccharide Gal-GalNAc does not bind. The glycan on SAP10 is predicted by molecular modeling to either protrude out or point into the MHC groove. SAPDTRPAPG peptide and the respective glycopeptide stimulated cytotoxic T-cells in vitro. Our findings suggest that MUC1 tandem repeat glycopeptides are capable of activating both helper and cytotoxic T-cells and thus represent good candidates for further development as vaccines.

Impact of glycans on T-cell tolerance to glycosylated self-antigens

There is now substantial evidence that antigen post-translational modifications are recognized by T cells, and alterations in epitope modification has been linked to a number of autoimmune diseases. An estimated one third of the MHC ligands contain post-translational modification of epitopes. A common post-translational modification of proteins is glycosylation and it is predicted on theoretical grounds that approximately 1-5% of MHC ligands may bear a glycan. From numerous studies over the past 15 years it is clear that glycans can influence T cell responses either by contribution to the structure of the epitope or by influencing the profile of peptide epitopes presented by APCs. The influence of glycans on antigen processing and T cell recognition has particular relevance to the induction of tolerance to self-antigens. Here we discuss the potential impact of glycans on the profile of self-epitopes presented by APCs and the consequence of changes in glycosylation to generate neo self-epitopes resulting in the loss of tolerance and the development of autoimmune diseases. With the recent developments in profiling T cell epitopes, and with strategies for modulating glycosylation in vivo, it is now feasible to directly examine the global influence of glycans on self-tolerance and autoimmunity.