Chemoenzymatically synthesized multimeric Tn/STn MUC1 glycopeptides elicit cancer-specific anti-MUC1 antibody responses and override tolerance

Chimeric antigen receptor dendritic cells targeted delivery of a single tumoricidal factor for cancer immunotherapy

BACKGROUND

Chimeric antigen receptor (CAR)-T cells have been used to treat blood cancers by producing a wide variety of cytokines. However, they are not effective in treating solid cancers and can cause severe side-effects, including cytokine release syndrome. TNFα is a tumoricidal cytokine, but it markedly increases the protein levels of cIAP1 and cIAP2, the members of inhibitor of apoptosis protein (IAP) family of E3 ubiquitin ligase that limits caspase-induced apoptosis. Degradation of IAP proteins by an IAP antagonist does not effectively kill cancer cells but enables TNFα to strongly induce cancer cell apoptosis. It would be a promising approach to treat cancers by targeted delivery of TNFα through an inactive adoptive cell in combination with an IAP antagonist.

METHODS

Human dendritic cells (DCs) were engineered to express a single tumoricidal factor, TNFα, and a membrane-anchored Mucin1 antibody scFv, named Mucin 1 directed DCs expressing TNFα (M-DCsTNF). The efficacy of M-DCsTNF in recognizing and treating breast cancer was tested in vitro and in vivo.

RESULTS

Mucin1 was highly expressed on the surface of a wide range of human breast cancer cell lines. M-DCsTNF directly associated with MDA-MB-231 cells in the bone of NSG mice. M-DCsTNF plus an IAP antagonist, SM-164, but neither alone, markedly induce MDA-MB-231 breast cancer cell apoptosis, which was blocked by TNF antibody. Importantly, M-DCsTNF combined with SM-164, but not SM-164 alone, inhibited the growth of patient-derived breast cancer in NSG mice.

CONCLUSION

An adoptive cell targeting delivery of TNFα combined with an IAP antagonist is a novel effective approach to treat breast cancer and could be expanded to treat other solid cancers. Unlike CAR-T cell, this novel adoptive cell is not activated to produce a wide variety of cytokines, except for additional overexpressed TNF, and thus could avoid the severe side effects such as cytokine release syndrome.

Immunomodulatory Peptides for Tumor Treatment

Peptides exhibit various biological activities, including biorecognition, cell targeting, and tumor penetration, and can stimulate immune cells to elicit immune responses for tumor immunotherapy. Peptide self-assemblies and peptide-functionalized nanocarriers can reduce the effect of various biological barriers and the degradation by peptidases, enhancing the efficiency of peptide delivery and improving antitumor immune responses. To date, the design and development of peptides with various functionalities have been extensively reviewed for enhanced chemotherapy; however, peptide-mediated tumor immunotherapy using peptides acting on different immune cells, to the knowledge, has not yet been summarized. Thus, this work provides a review of this emerging subject of research, focusing on immunomodulatory anticancer peptides. This review introduces the role of peptides in the immunomodulation of innate and adaptive immune cells, followed by a link between peptides in the innate and adaptive immune systems. The peptides are discussed in detail, following a classification according to their effects on different innate and adaptive immune cells, as well as immune checkpoints. Subsequently, two delivery strategies for peptides as drugs are presented: peptide self-assemblies and peptide-functionalized nanocarriers. The concluding remarks regarding the challenges and potential solutions of peptides for tumor immunotherapy are presented.

Serum antibody screening using glycan arrays

Humans and other animals produce a diverse collection of antibodies, many of which bind to carbohydrate chains, referred to as glycans. These anti-glycan antibodies are a critical part of our immune systems' defenses. Whether induced by vaccination or natural exposure to a pathogen, anti-glycan antibodies can provide protection against infections and cancers. Alternatively, when an immune response goes awry, antibodies that recognize self-glycans can mediate autoimmune diseases. In any case, serum anti-glycan antibodies provide a rich source of information about a patient's overall health, vaccination history, and disease status. Glycan microarrays provide a high-throughput platform to rapidly interrogate serum anti-glycan antibodies and identify new biomarkers for a variety of conditions. In addition, glycan microarrays enable detailed analysis of the immune system's response to vaccines and other treatments. Herein we review applications of glycan microarray technology for serum anti-glycan antibody profiling.

A multivalent CD44 glycoconjugate vaccine candidate for cancer immunotherapy

Cancer presents a high mortality rate due to ineffective treatments and tumour relapse with progression. Cancer vaccines hold tremendous potential due to their capability to eradicate tumour and prevent relapse. In this study, we present a novel glycovaccine for precise targeting and immunotherapy of aggressive solid tumours that overexpress CD44 standard isoform (CD44s) carrying immature Tn and sialyl-Tn (sTn) O-glycans. We describe an enzymatic method and an enrichment strategy to generate libraries of well-characterized cancer-specific CD44s-Tn and/or sTn glycoproteoforms, which mimic the heterogeneity found in tumours. We conjugated CD44-Tn-derived glycopeptides with carrier proteins making them more immunogenic, with further demonstration of the importance of this conjugation to overcome the glycopeptides' intrinsic toxicity. We have optimized the glycopeptide-protein maleimide-thiol conjugation chemistry to avoid undesirable cross-linking between carrier proteins and CD44s glycopeptides. The resulting glycovaccines candidates were well-tolerated in vivo, inducing both humoral and cellular immunity, including immunological memory. The generated antibodies exhibited specific reactivity against synthetic CD44s-Tn glycopeptides, CD44s-Tn glycoengineered cells, and human tumours. In summary, we present a promising prototype of a cancer glycovaccine for future therapeutical pre-clinical efficacy validation.

Glycosyltransferases as versatile tools to study the biology of glycans

All cells are decorated with complex carbohydrate structures called glycans that serve as ligands for glycan-binding proteins (GBPs) to mediate a wide range of biological processes. Understanding the specific functions of glycans is key to advancing an understanding of human health and disease. However, the lack of convenient and accessible tools to study glycan-based interactions has been a defining challenge in glycobiology. Thus, the development of chemical and biochemical strategies to address these limitations has been a rapidly growing area of research. In this review, we describe the use of glycosyltransferases (GTs) as versatile tools to facilitate a greater understanding of the biological roles of glycans. We highlight key examples of how GTs have streamlined the preparation of well-defined complex glycan structures through chemoenzymatic synthesis, with an emphasis on synthetic strategies allowing for site- and branch-specific display of glyco-epitopes. We also describe how GTs have facilitated expansion of glyco-engineering strategies, on both glycoproteins and cell surfaces. Coupled with advancements in bioorthogonal chemistry, GTs have enabled selective glyco-epitope editing of glycoproteins and cells, selective glycan subclass labeling, and the introduction of novel biomolecule functionalities onto cells, including defined oligosaccharides, antibodies, and other proteins. Collectively, these approaches have contributed great insight into the fundamental biological roles of glycans and are enabling their application in drug development and cellular therapies, leaving the field poised for rapid expansion.

Multivalent lectin-carbohydrate interactions: Energetics and mechanisms of binding

The biological signaling properties of lectins, which are carbohydrate-binding proteins, are due to their ability to bind and cross-link multivalent glycoprotein receptors on the surface of normal and transformed cells. While the cross-linking properties of lectins with multivalent carbohydrates and glycoproteins are relatively well understood, the mechanisms of binding of lectins to multivalent glycoconjugates are less well understood. Recently, the thermodynamics of binding of lectins to synthetic clustered glycosides, a multivalent globular glycoprotein, and to linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules. Importantly, the mechanism of binding of lectins to mucins is similar to that for a variety of protein ligands binding to DNA. Recent analysis also shows that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects which facilitate binding and subsequent complex formation including enzymology.

Mucin Glycans: A Target for Cancer Therapy

Mucin glycans are an important component of the mucus barrier and a vital defence against physical and chemical damage as well as pathogens. There are 20 mucins in the human body, which can be classified into secreted mucins and transmembrane mucins according to their distributions. The major difference between them is that secreted mucins do not have transmembrane structural domains, and the expression of each mucin is organ and cell-specific. Under physiological conditions, mucin glycans are involved in the composition of the mucus barrier and thus protect the body from infection and injury. However, abnormal expression of mucin glycans can lead to the occurrence of diseases, especially cancer, through various mechanisms. Therefore, targeting mucin glycans for the diagnosis and treatment of cancer has always been a promising research direction. Here, we first summarize the main types of glycosylation (O-GalNAc glycosylation and N-glycosylation) on mucins and the mechanisms by which abnormal mucin glycans occur. Next, how abnormal mucin glycans contribute to cancer development is described. Finally, we summarize MUC1-based antibodies, vaccines, radio-pharmaceuticals, and CAR-T therapies using the best characterized MUC1 as an example. In this section, we specifically elaborate on the recent new cancer therapy CAR-M, which may bring new hope to cancer patients.

Targeting Solid Cancers with a Cancer-Specific Monoclonal Antibody to Surface Expressed Aberrantly O-glycosylated Proteins

The lack of antibodies with sufficient cancer selectivity is currently limiting the treatment of solid tumors by immunotherapies. Most current immunotherapeutic targets are tumor-associated antigens that are also found in healthy tissues and often do not display sufficient cancer selectivity to be used as targets for potent antibody-based immunotherapeutic treatments, such as chimeric antigen receptor (CAR) T cells. Many solid tumors, however, display aberrant glycosylation that results in expression of tumor-associated carbohydrate antigens that are distinct from healthy tissues. Targeting aberrantly glycosylated glycopeptide epitopes within existing or novel glycoprotein targets may provide the cancer selectivity needed for immunotherapy of solid tumors. However, to date only a few such glycopeptide epitopes have been targeted. Here, we used O-glycoproteomics data from multiple cell lines to identify a glycopeptide epitope in CD44v6, a cancer-associated CD44 isoform, and developed a cancer-specific mAb, 4C8, through a glycopeptide immunization strategy. 4C8 selectively binds to Tn-glycosylated CD44v6 in a site-specific manner with low nanomolar affinity. 4C8 was shown to be highly cancer specific by IHC of sections from multiple healthy and cancerous tissues. 4C8 CAR T cells demonstrated target-specific cytotoxicity in vitro and significant tumor regression and increased survival in vivo. Importantly, 4C8 CAR T cells were able to selectively kill target cells in a mixed organotypic skin cancer model having abundant CD44v6 expression without affecting healthy keratinocytes, indicating tolerability and safety.

Chemoenzymatic Tagging of Tn/TF/STF Antigens in Living Systems

Truncated mucin-type O-glycans, such as Tn-associated antigens, are aberrantly expressed biomarkers of cancer, but remain challenging to target. Reactive antibodies to these antigens either lack high-affinity or are prone to antigen escape. Here, we have developed a robust chemoenzymatic strategy for the global labeling of Tn-associated antigens, i.e. Tn (GalNAcα-O-Ser/Thr), Thomsen-Friedenreich (Galβ1-3GalNAcα-O-Ser/Thr, TF) and STF (Neu5Acα2-3Galβ1-3GalNAcα-O-Ser/Thr, STF) antigens, in human whole blood with high efficiency and selectivity. This method relies on the use of the O-glycan sialyltransferase ST6GalNAc1 to transfer a sialic acid-functionalized adaptor to the GalNAc residue of these antigens. By tagging, the adaptor functionalized antigens can be easily targeted by customized strategies such as, but not limited to, chimeric antigen receptor T-Cells (CAR-T). We expect this tagging system to find broad applications in cancer diagnostics and targeting in combination with established strategies.

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.

Single CAR-T cell treatment controls disseminated ovarian cancer in a syngeneic mouse model

BACKGROUND

Treatment of some blood cancers with T cells that express a chimeric antigen receptor (CAR) against CD19 have shown remarkable results. In contrast, CAR-T cell efficacy against solid tumors has been difficult to achieve.

METHODS

To examine the potential of CAR-T cell treatments against ovarian cancers, we used the mouse ovarian cancer cell line ID8 in an intraperitoneal model that exhibits disseminated solid tumors in female C57BL/6J mice. The CAR contained a single-chain Fv from antibody 237 which recognizes a Tn-glycopeptide-antigen expressed by ID8 due to aberrant O-linked glycosylation in the absence of the transferase-dependent chaperone Cosmc. The efficacy of four Tn-dependent CARs with varying affinity to Tn antigen, and each containing CD28/CD3ζ cytoplasmic domains, were compared in vitro and in vivo in this study.

RESULTS

In line with many observations about the impact of aberrant O-linked glycosylation, the ID8Cosmc knock-out (ID8Cosmc-KO) exhibited more rapid tumor progression compared with wild-type ID8. Despite the enhanced tumor growth in vivo, 237 CAR and a mutant with 30-fold higher affinity, but not CARs with lower affinity, controlled advanced ID8Cosmc-KO tumors. Tumor regression could be achieved with a single intravenous dose of the CARs, but intraperitoneal administration was even more effective. The CAR-T cells persisted over a period of months, allowing CAR-treated mice to delay tumor growth in a re-challenge setting. The most effective CARs exhibited the highest affinity for antigen. Antitumor effects observed in vivo were associated with increased numbers of T cells and macrophages, and higher levels of cleaved caspase-3, in the tumor microenvironment. Notably, the least therapeutically effective CAR mediated tonic signaling leading to antigen-independent cytokine expression and it had higher levels of the immunosuppressive cytokine interleukin10.

CONCLUSION

The findings support the development of affinity-optimized CAR-T cells as a potential treatment for established ovarian cancer, with the most effective CARs mediating a distinct pattern of inflammatory cytokine release in vitro. Importantly, the most potent Tn-dependent CAR-T cells showed no evidence of toxicity in tumor-bearing mice in a syngeneic, immunocompetent system.

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.

Development of Engineered CAR T Cells Targeting Tumor-Associated Glycoforms of MUC1 for the Treatment of Intrahepatic Cholangiocarcinoma

Intrahepatic cholangiocarcinoma (ICC) is a common malignancy arising from the liver with limited 5-year survival. Thus, there is an urgency to explore new treatment methods. Chimeric antigen receptor T (CAR T) cell therapy is a very promising cancer treatment. Though, several groups have investigated CAR T cells targeting MUC1 in solid cancer models, Tn-MUC1-targeted CAR T cells have not yet to be reported in ICC. In this study, we confirmed Tn-MUC1 as a potential therapeutic target for ICC and demonstrated that its expression level was positively correlated with the poor prognosis of ICC patients. More importantly, we successfully developed effective CAR T cells to target Tn-MUC1-positive ICC tumors and explored their antitumor activities. Our results suggest the CAR T cells could specifically eliminate Tn-MUC1-positive ICC cells, but not Tn-MUC1-negative ICC cells, in vitro and in vivo. Therefore, our study is expected to provide new therapeutic strategies and ideas for the treatment of ICC.

Identification of global inhibitors of cellular glycosylation

Small molecule inhibitors of glycosylation enzymes are valuable tools for dissecting glycan functions and potential drug candidates. Screening for inhibitors of glycosyltransferases are mainly performed by in vitro enzyme assays with difficulties moving candidates to cells and animals. Here, we circumvent this by employing a cell-based screening assay using glycoengineered cells expressing tailored reporter glycoproteins. We focused on GalNAc-type O-glycosylation and selected the GalNAc-T11 isoenzyme that selectively glycosylates endocytic low-density lipoprotein receptor (LDLR)-related proteins as targets. Our screen of a limited small molecule compound library did not identify selective inhibitors of GalNAc-T11, however, we identify two compounds that broadly inhibited Golgi-localized glycosylation processes. These compounds mediate the reversible fragmentation of the Golgi system without affecting secretion. We demonstrate how these inhibitors can be used to manipulate glycosylation in cells to induce expression of truncated O-glycans and augment binding of cancer-specific Tn-glycoprotein antibodies and to inhibit expression of heparan sulfate and binding and infection of SARS-CoV-2.

VT68.2: An Antibody to Chondroitin Sulfate Proteoglycan 4 (CSPG4) Displays Reactivity against a Tumor-Associated Carbohydrate Antigen

The anti-CSPG4 monoclonal antibodies (mAbs) have shown anti-tumor activity and therapeutic potential for treating breast cancer. In addition, CSPG4 is a dominant tumor-associated antigen that is also involved in normal-tissue development in humans. Therefore, the potential for off-tumor activity remains a serious concern when targeting CSPG4 therapeutically. Previous work suggested that glycans contribute to the binding of specific anti-CSPG4 antibodies to tumor cells, but the specificity and importance of this contribution are unknown. In this study, the reactivity of anti-CSPG4 mAbs was characterized with a peptide mimetic of carbohydrate antigens expressed in breast cancer. ELISA, flow cytometry, and microarray assays were used to screen mAbs for their ability to bind to carbohydrate-mimicking peptides (CMPs), cancer cells, and glycans. The mAb VT68.2 displayed a distinctly strong binding to a CMP (P10s) and bound to triple-negative breast cancer cells. In addition, VT68.2 showed a higher affinity for N-linked glycans that contain terminal fucose and fucosylated lactosamines. The functional assays demonstrated that VT68.2 inhibited cancer cell migration. These results define the glycoform reactivity of an anti-CSPG4 antibody and may lead to the development of less toxic therapeutic approaches that target tumor-specific glyco-peptides.

"Glyco-sulfo barcodes" regulate chemokine receptor function

Chemokine ligands and receptors regulate the directional migration of leukocytes. Post-translational modifications of chemokine receptors including O-glycosylation and tyrosine sulfation have been reported to regulate ligand binding and resulting signaling. Through in silico analyses, we determined potential conserved O-glycosylation and sulfation sites on human and murine CC chemokine receptors. Glyco-engineered CHO cell lines were used to measure the impact of O-glycosylation on CC chemokine receptor CCR5, while mutation of tyrosine residues and treatment with sodium chlorate were performed to determine the effect of tyrosine sulfation. Changing the glycosylation or tyrosine sulfation on CCR5 reduced the receptor signaling by the more positively charged CCL5 and CCL8 more profoundly compared to the less charged CCL3. The loss of negatively charged sialic acids resulted only in a minor effect on CCL3-induced signal transduction. The enzymes GalNAc-T1 and GalNAc-T11 were shown to be involved in the process of chemokine receptor O-glycosylation. These results indicate that O-glycosylation and tyrosine sulfation are involved in the fine-tuning and recognition of chemokine interactions with CCR5 and the resulting signaling.

Recent advances in the use of legume lectins for the diagnosis and treatment of breast cancer

Poor lifestyle choices and genetic predisposition are factors that increase the number of cancer cases, one example being breast cancer, the third most diagnosed type of malignancy. Currently, there is a demand for the development of new strategies to ensure early detection and treatment options that could contribute to the complete remission of breast tumors, which could lead to increased overall survival rates. In this context, the glycans observed at the surface of cancer cells are presented as efficient tumor cell markers. These carbohydrate structures can be recognized by lectins which can act as decoders of the glycocode. The application of plant lectins as tools for diagnosis/treatment of breast cancer encompasses the detection and sorting of glycans found in healthy and malignant cells. Here, we present an overview of the most recent studies in this field, demonstrating the potential of lectins as: mapping agents to detect differentially expressed glycans in breast cancer, as histochemistry/cytochemistry analysis agents, in lectin arrays, immobilized in chromatographic matrices, in drug delivery, and as biosensing agents. In addition, we describe lectins that present antiproliferative effects by themselves and/or in conjunction with other drugs in a synergistic effect.

Immunohistochemical analysis of Tn antigen expression in colorectal adenocarcinoma and precursor lesions

BACKGROUND

The Tn antigen (CD175) is an O-glycan expressed in various types of human adenocarcinomas, including colorectal cancer (CRC), though prior studies have relied heavily upon poorly characterized in-house generated antibodies and lectins. In this study, we explored Tn expression in CRC using ReBaGs6, a well-characterized recombinant murine antibody with high specificity for clustered Tn antigen.

METHODS

Using well-defined monoclonal antibodies, expression patterns of Tn and sialylated Tn (STn) antigens were characterized by immunostaining in CRC, in matched peritumoral [transitional margin (TM)] mucosa, and in normal colonic mucosa distant from the tumor, as well as in adenomas. Vicia villosa agglutinin lectin was used to detect terminal GalNAc expression. Histo-scoring (H scoring) of staining was carried out, and pairwise comparisons of staining levels between tissue types were performed using paired samples Wilcoxon rank sum tests, with statistical significance set at 0.05.

RESULTS

While minimal intracellular Tn staining was seen in normal mucosa, significantly higher expression was observed in both TM mucosa (p < 0.001) and adenocarcinoma (p < 0.001). This pattern was reflected to a lesser degree by STn expression in these tissue types. Interestingly, TM mucosa demonstrates a Tn expression level even higher than that of the adenocarcinoma itself (p = 0.019). Colorectal adenomas demonstrated greater Tn and STn expression relative to normal mucosa (p < 0.001 and p = 0.012, respectively).

CONCLUSIONS

In summary, CRC is characterized by alterations in Tn/STn antigen expression in neoplastic epithelium as well as peritumoral benign mucosa. Tn/STn antigens are seldom expressed in normal mucosa. This suggests that TM mucosa, in addition to CRC itself, represents a source of glycoproteins rich in Tn that may offer future biomarker targets.

Synthesis and biomedical applications of mucin mimic materials

Mucin glycoproteins are the major component of mucus and coat epithelial cell surfaces forming the glycocalyx. The glycocalyx and mucus are involved in the transport of nutrients, drugs, gases, and pathogens toward the cell surface. Mucins are also involved in diverse diseases such as cystic fibrosis and cancer. Due to inherent heterogeneity in native mucin structure, many synthetic materials have been designed to probe mucin chemistry, biology, and physics. Such materials include various glycopolymers, low molecular weight glycopeptides, glycopolypeptides, polysaccharides, and polysaccharide-protein conjugates. This review highlights advances in the area of design and synthesis of mucin mimic materials, and their biomedical applications in glycan binding, epithelial models of infection, therapeutic delivery, vaccine formulation, and beyond.

Determination of monosaccharide composition in human serum by an improved HPLC method and its application as candidate biomarkers for endometrial cancer

Altered glycan levels in serum have been associated with increased risk of cancer. In this study, we have developed and validated a HPLC-based method to analyze monosaccharide composition (D-mannose, Glucosamine, Galactosamine, Glucuronic acid, D-glucose, D-galactose, D-xylose, L-fucose) in human serum, with L-rhamnose, being used as internal standard. Monosaccharides obtained from hydrolyzed serum samples were derivatized by 1-Phenyl-3-methyl-5-pyrazolone. A ZORBAX XDB-C18 column(150×4.6mm) was used for chromatographic separation with 100 mM ammonium acetate buffer (NH4Ac-HAc, PH=5.5, solvent A), acetonitrile (ACN, solvent B) as a mobile phase. The calibration standard curves for the eight monosaccharides showed good linearity over the range of 2.5-500μg/mL with R² > 0.995. The relative standard deviation values for intra-day and inter-day precision were ≤ 5.49%. Recovery was 69.01-108.96%. We observed that this column exhibited high specificity and selectivity to separate monosaccharides from serum. This method was then applied to quantitatively analyze the serum monosaccharide levels in 30 patients with endometrial cancer and 30 matched healthy controls. Statistical analysis indicated that the serum monosaccharide levels were significantly higher in patients compared with healthy controls (P value< 0.0001). Overall, we report here a simple, reliable, low-cost, and reproducible HPLC method for the separation and quantification monosaccharides in the human serum, which has potential value to serve as a screening marker for endometrial cancer.

Synthesis of glycopeptides and glycopeptide conjugates

Protein glycosylation is a key post-translational modification important to many facets of biology. Glycosylation can have critical effects on protein conformation, uptake and intracellular routing. In immunology, glycosylation of antigens has been shown to play a role in self/non-self distinction and the effective uptake of antigens. Improperly glycosylated proteins and peptide fragments, for instance those produced by cancerous cells, are also prime candidates for vaccine design. To study these processes, access to peptides bearing well-defined glycans is of critical importance. In this review, the key approaches towards synthetic, well-defined glycopeptides, are described, with a focus on peptides useful for and used in immunological studies. Special attention is given to the glycoconjugation approaches that have been developed in recent years, as these enable rapid synthesis of various (unnatural) glycopeptides, enabling powerful carbohydrate structure/activity studies. These techniques, combined with more traditional total synthesis and chemoenzymatic methods for the production of glycopeptides, should help unravel some of the complexities of glycobiology in the near future.

Antibody-Based Approaches to Target Pancreatic Tumours

Pancreatic cancer is an aggressive cancer with a dismal prognosis. This is due to the difficulty to detect the disease at an early and curable stage. In addition, only limited treatment options are available, and they are confronted by mechanisms of resistance. Monoclonal antibody (mAb) molecules are highly specific biologics that can be directly used as a blocking agent or modified to deliver a drug payload depending on the desired outcome. They are widely used to target extracellular proteins, but they can also be employed to inhibit intracellular proteins, such as oncoproteins. While mAbs are a class of therapeutics that have been successfully employed to treat many cancers, they have shown only limited efficacy in pancreatic cancer as a monotherapy so far. In this review, we will discuss the challenges, opportunities and hopes to use mAbs for pancreatic cancer treatment, diagnostics and imagery.

Advances in MUC1-Mediated Breast Cancer Immunotherapy

Breast cancer (BRCA) is the leading cause of death from malignant tumors among women. Fortunately, however, immunotherapy has recently become a prospective BRCA treatment with encouraging achievements and mild safety profiles. Since the overexpression and aberrant glycosylation of MUC1 (human mucin) are closely associated with BRCA, it has become an ideal target for BRCA immunotherapies. In this review, the structure and function of MUC1 are briefly introduced, and the main research achievements in different kinds of MUC1-mediated BRCA immunotherapy are highlighted, from the laboratory to the clinic. Afterward, the future directions of MUC1-mediated BRCA immunotherapy are predicted, addressing, for example, urgent issues in regard to how efficient immunotherapeutic strategies can be generated.

Unique Glycoform-Dependent Monoclonal Antibodies for Mouse Mucin 21

Mucin 21(Muc21)/epiglycanin is expressed on apical surfaces of squamous epithelia and has potentially protective roles, which are thought to be associated with its unique glycoforms, whereas its aberrant glycosylation is implicated in the malignant behaviors of some carcinomas. Despite the importance of glycoforms, we lack tools to detect specific glycoforms of mouse Muc21. In this study, we generated two monoclonal antibodies (mAbs) that recognize different glycoforms of Muc21. We used membrane lysates of Muc21-expressing TA3-Ha cells or Chinese hamster ovary (CHO)-K1 cells transfected with Muc21 as antigens. Specificity testing, utilizing Muc21 glycosylation variant cells, showed that mAb 1A4-1 recognized Muc21 carrying glycans terminated with galactose residues, whereas mAb 18A11 recognized Muc21 carrying sialylated glycans. mAb 1A4-1 stained a majority of mouse mammary carcinoma TA3-Ha cells in vitro and in engrafted tumors in mice, whereas mAb 18A11 recognized only a subpopulation of these. mAb 1A4-1 was useful in immunohistochemically detecting Muc21 in normal squamous epithelia. In conclusion, these mAbs recognize distinct Muc21 epitopes formed by combinations of peptide portions and O-glycans.

CAR T cells redirected against tumor-specific antigen glycoforms: can low-sugar antigens guarantee a sweet success?

Immune-based therapies have experienced a pronounced breakthrough in the past decades as they acquired multiple US Food and Drug Administration (FDA) approvals for various indications. To date, six chimeric antigen receptor T cell (CAR-T) therapies have been permitted for the treatment of certain patients with relapsed/refractory hematologic malignancies. However, several clinical trials of solid tumor CAR-T therapies were prematurely terminated, or they reported life-threatening treatment-related damages to healthy tissues. The simultaneous expression of target antigens by healthy organs and tumor cells is partly responsible for such toxicities. Alongside targeting tumor-specific antigens, targeting the aberrantly glycosylated glycoforms of tumor-associated antigens can also minimize the off-tumor effects of CAR-T therapies. Tn, T, and sialyl-Tn antigens have been reported to be involved in tumor progression and metastasis, and their expression results from the dysregulation of a series of glycosyltransferases and the endoplasmic reticulum protein chaperone, Cosmc. Moreover, these glycoforms have been associated with various types of cancers, including prostate, breast, colon, gastric, and lung cancers. Here, we discuss how underglycosylated antigens emerge and then detail the latest advances in the development of CAR-T-based immunotherapies that target some of such antigens.

CAR-Ts: new perspectives in cancer therapy

Chimeric antigen receptor (CAR)-T-cell therapy is a promising anticancer treatment that exploits the host's immune system to fight cancer. CAR-T cell therapy relies on immune cells being modified to express an artificial receptor targeting cancer-specific markers, and infused into the patients where they will recognize and eliminate the tumour. Although CAR-T cell therapy has produced encouraging outcomes in patients with haematologic malignancies, solid tumours remain challenging to treat, mainly due to the lack of cancer-specific molecular targets and the hostile, often immunosuppressive, tumour microenvironment. CAR-T cell therapy also depends on the quality of the injected product, which is closely connected to CAR design. Here, we explain the technology of CAR-Ts, focusing on the composition of CARs, their application, and limitations in cancer therapy, as well as on the current strategies to overcome the challenges encountered. We also address potential future targets to overcome the flaws of CAR-T cell technology in the treatment of cancer, emphasizing glycan antigens, the aberrant forms of which attain high tumour-specific expression, as promising targets for CAR-T cell therapy.

Mechanism of Mucin Recognition by Lectins: A Thermodynamic Study

Isothermal titration microcalorimetry (ITC) can directly determine the thermodynamic binding parameters of biological molecules including affinity constant, binding stoichiometry, heat of binding (enthalpy) and indirectly the entropy, and free energy of binding. ITC has been extensively used to study the binding of lectins to mono- and oligosaccharides, but limitedly in applications to lectin-glycoprotein interactions. Inherent experimental challenges to ITC include sample precipitation during the experiment and relative high amount of sample required, but careful design of experiments can minimize these problems and allow valuable information to be obtained. For example, the thermodynamics of binding of lectins to multivalent globular and linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules leading to increased affinity. Importantly, the mechanism of binding of lectins to mucins appears similar to that for a variety of protein ligands binding to DNA. Recent results also show that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects that facilitate binding interactions.

Mapping of truncated O-glycans in cancers of epithelial and non-epithelial origin

BACKGROUND

Novel immunotherapies targeting cancer-associated truncated O-glycans Tn (GalNAcα-Ser/Thr) and STn (Neu5Acα2-6GalNacα-Ser/Thr) are promising strategies for cancer treatment. However, no comprehensive, antibody-based mapping of truncated O-glycans in tumours exist to guide drug development.

METHODS

We used monoclonal antibodies to map the expression of truncated O-glycans in >700 tissue cores representing healthy and tumour tissues originating from breast, colon, lung, pancreas, skin, CNS and mesenchymal tissue. Patient-derived xenografts were used to evaluate Tn expression upon tumour engraftment.

RESULTS

The Tn-antigen was highly expressed in breast (57%, n = 64), colorectal (51%, n = 140) and pancreatic (53%, n = 108) tumours, while STn was mainly observed in colorectal (80%, n = 140) and pancreatic (56%, n = 108) tumours. We observed no truncated O-glycans in mesenchymal tumours (n = 32) and low expression of Tn (5%, n = 87) and STn (1%, n = 75) in CNS tumours. No Tn-antigen was found in normal tissue (n = 124) while STn was occasionally observed in healthy gastrointestinal tissue. Surface expression of Tn-antigen was identified across several cancers. Tn and STn expression decreased with tumour grade, but not with cancer stage. Numerous xenografts maintained Tn expression.

CONCLUSIONS

Surface expression of truncated O-glycans is limited to cancers of epithelial origin, making Tn and STn attractive immunological targets in the treatment of human carcinomas.

Global functions of O-glycosylation: promises and challenges in O-glycobiology

Mucin type O-glycosylation is one of the most diverse types of glycosylation, playing essential roles in tissue development and homeostasis. In complex organisms, O-GalNAc glycans comprise a substantial proportion of the glycocalyx, with defined functions in hemostatic, gastrointestinal, and respiratory systems. Furthermore, O-GalNAc glycans are important players in host-microbe interactions, and changes in O-glycan composition are associated with certain diseases and metabolic conditions, which in some instances can be used for diagnosis or therapeutic intervention. Breakthroughs in O-glycobiology have gone hand in hand with the development of new technologies, such as advancements in mass spectrometry, as well as facilitation of genetic engineering in mammalian cell lines. High-throughput O-glycoproteomics have enabled us to draw a comprehensive map of O-glycosylation, and mining this information has supported the definition and confirmation of functions related to site-specific O-glycans. This includes protection from proteolytic cleavage, as well as modulation of binding affinity or receptor function. Yet, there is still much to discover, and among the important next challenges will be to define the context-dependent functions of O-glycans in different stages of cellular differentiation, cellular metabolism, host-microbiome interactions, and in disease. In this review, we present the achievements and the promises in O-GalNAc glycobiology driven by technological advances in analytical methods, genetic engineering, and systems biology.

Defucosylation of Tumor-Specific Humanized Anti-MUC1 Monoclonal Antibody Enhances NK Cell-Mediated Anti-Tumor Cell Cytotoxicity

Simple Summary

Antibodies with their high specificity to antigens have been widely used in cancer immunotherapy. Natural killer (NK) cells are a group of innate immune cells which have strong cytotoxicity against cancerous cells, virus infected cells, or transformed cells. NK cells express abundant Fc receptors that can bind tumor-specific antibodies, thus allowing them to precisely redirect and eliminate cancer cells. In this study, we demonstrated that NK cells cytotoxicity toward MUC1-positive hematologic and solid tumor can be further enhanced by a humanized 5E5 anti-MUC1 antibody. Furthermore, Fc defucosylation of the antibodies further boosted the kill capacity of NK cells. We believe that our humanized anti-MUC1 antibody is a promising therapeutic candidate for clinical cancer treatment.

Abstract

Antibodies are commonly used in cancer immunotherapy because of their high specificity for tumor-associated antigens. The binding of antibodies can have direct effects on tumor cells but also engages natural killer (NK) cells via their Fc receptor. Mucin 1 (MUC1) is a highly glycosylated protein expressed in normal epithelial cells, while the under-glycosylated MUC1 epitope (MUC1-Tn/STn) is only expressed on malignant cells, making it an interesting diagnostic and therapeutic target. Several anti-MUC1 antibodies have been tested for therapeutic applications in solid tumors thus far without clinical success. Herein, we describe the generation of fully humanized antibodies based on the murine 5E5 antibody, targeting the tumor-specific MUC1-Tn/STn epitope. We confirmed that these antibodies specifically recognize tumor-associated MUC1 epitopes and can activate human NK cells in vitro. Defucosylation of these newly developed anti-MUC1 antibodies further enhanced antigen-dependent cellular cytotoxicity (ADCC) mediated by NK cells. We show that endocytosis inhibitors augment the availability of MUC1-Tn/STn epitopes on tumor cells but do not further enhance ADCC in NK cells. Collectively, this study describes novel fully humanized anti-MUC1 antibodies that, especially after defucosylation, are promising therapeutic candidates for cellular immunotherapy.

Probing the binding specificities of human Siglecs by cell-based glycan arrays

Siglecs are a family of sialic acid-binding receptors expressed by cells of the immune system and a few other cell types capable of modulating immune cell functions upon recognition of sialoglycan ligands. While human Siglecs primarily bind to sialic acid residues on diverse types of glycoproteins and glycolipids that constitute the sialome, their fine binding specificities for elaborated complex glycan structures and the contribution of the glycoconjugate and protein context for recognition of sialoglycans at the cell surface are not fully elucidated. Here, we generated a library of isogenic human HEK293 cells with combinatorial loss/gain of individual sialyltransferase genes and the introduction of sulfotransferases for display of the human sialome and to dissect Siglec interactions in the natural context of glycoconjugates at the cell surface. We found that Siglec-4/7/15 all have distinct binding preferences for sialylated GalNAc-type O-glycans but exhibit selectivity for patterns of O-glycans as presented on distinct protein sequences. We discovered that the sulfotransferase CHST1 drives sialoglycan binding of Siglec-3/8/7/15 and that sulfation can impact the preferences for binding to O-glycan patterns. In particular, the branched Neu5Acα2-3(6-O-sulfo)Galβ1-4GlcNAc (6'-Su-SLacNAc) epitope was discovered as the binding epitope for Siglec-3 (CD33) implicated in late-onset Alzheimer's disease. The cell-based display of the human sialome provides a versatile discovery platform that enables dissection of the genetic and biosynthetic basis for the Siglec glycan interactome and other sialic acid-binding proteins.

MUC1-Targeted Radiopharmaceuticals in Cancer Imaging and Therapy

Mucin 1 (MUC1) is a large, transmembrane mucin glycoprotein overexpressed in most adenocarcinomas and plays an important role in tumor progression. Regarding its cellular distribution, biochemical features, and function, tumor-related MUC1 varies from the MUC1 expressed in normal cells. Therefore, targeting MUC1 for cancer immunotherapy and imaging can exploit the difference between cancerous and normal cells. Radiopharmaceuticals have a potential use as carriers for the delivery of radionuclides to tumors for a diagnostic imaging and radiotherapy. Several radiolabeled targeting molecules like peptides, antibodies, and aptamers have been efficiently demonstrated in detecting and treating cancer by targeting MUC1. This review provides a brief overview of the current status of developments and applications of MUC1-targeted radiopharmaceuticals in cancer imaging and therapy.

Aberrant protein glycosylation in cancer: implications in targeted therapy

Aberrant cell surface glycosylation signatures are currently known to actively drive the neoplastic transformation of healthy cells. By disrupting the homeostatic functions of their protein carriers, cancer-associated glycans mechanistically underpin several molecular hallmarks of human malignancy. Furthermore, such aberrant glycan structures play key roles in the acquisition of molecular resistance to targeted therapeutic agents, which compromises their clinical efficacy, by modulating tumour cell aggressiveness and supporting the establishment of an immunosuppressive microenvironment. Recent advances in the study of the tumour cell glycoproteome have unravelled previously elusive molecular mechanisms of therapeutic resistance, guided the rational design of novel personalized therapeutic strategies, and may further improve the clinical performance of currently approved anti-cancer targeted agents. In this review, we highlight the impact of glycosylation in cancer targeted therapy, with particular focus on receptor tyrosine kinase-targeted therapy, immune checkpoints blockade therapy, and current developments on therapeutic strategies directed to glycan-binding proteins and other innovative glycan therapeutic strategies.

The clinical impact of glycobiology: targeting selectins, Siglecs and mammalian glycans

Carbohydrates - namely glycans - decorate every cell in the human body and most secreted proteins. Advances in genomics, glycoproteomics and tools from chemical biology have made glycobiology more tractable and understandable. Dysregulated glycosylation plays a major role in disease processes from immune evasion to cognition, sparking research that aims to target glycans for therapeutic benefit. The field is now poised for a boom in drug development. As a harbinger of this activity, glycobiology has already produced several drugs that have improved human health or are currently being translated to the clinic. Focusing on three areas - selectins, Siglecs and glycan-targeted antibodies - this Review aims to tell the stories behind therapies inspired by glycans and to outline how the lessons learned from these approaches are paving the way for future glycobiology-focused therapeutics.

Single-pot enzymatic synthesis of cancer-associated MUC16 O-glycopeptide libraries and multivalent protein glycoconjugates: a step towards cancer glycovaccines

Glycosyltransferases and nucleotide sugars are combined in single-pot settings to synthesize a library of cancer-associated MUC16 O-glycopeptides and multivalent protein glycoconjugates foreseeing future development of cancer glycovaccines.

Mucin-Type O-GalNAc Glycosylation in Health and Disease

Mucin-type GalNAc O-glycosylation is one of the most abundant and unique post-translational modifications. The combination of proteome-wide mapping of GalNAc O-glycosylation sites and genetic studies with knockout animals and genome-wide analyses in humans have been instrumental in our understanding of GalNAc O-glycosylation. Combined, such studies have revealed well-defined functions of O-glycans at single sites in proteins, including the regulation of pro-protein processing and proteolytic cleavage, as well as modulation of receptor functions and ligand binding. In addition to isolated O-glycans, multiple clustered O-glycans have an important function in mammalian biology by providing structural support and stability of mucins essential for protecting our inner epithelial surfaces, especially in the airways and gastrointestinal tract. Here the many O-glycans also provide binding sites for both endogenous and pathogen-derived carbohydrate-binding proteins regulating critical developmental programs and helping maintain epithelial homeostasis with commensal organisms. Finally, O-glycan changes have been identified in several diseases, most notably in cancer and inflammation, where the disease-specific changes can be used for glycan-targeted therapies. This chapter will review the biosynthesis, the biology, and the translational perspectives of GalNAc O-glycans.

Identification of Tn antigen O-GalNAc-expressing glycoproteins in human carcinomas using novel anti-Tn recombinant antibodies

The Tn antigen is a neoantigen abnormally expressed in many human carcinomas and expression correlates with metastasis and poor survival. To explore its biomarker potential, new antibodies are needed that specifically recognize this antigen in tumors. Here we generated two recombinant antibodies to the Tn antigen, Remab6 as a chimeric human IgG1 antibody and ReBaGs6 as a murine IgM antibody and characterized their specificities using multiple biochemical and biological approaches. Both Remab6 and ReBaGs6 recognize clustered Tn structures, but most importantly do not recognize glycoforms of human IgA1 that contain potential cross-reactive Tn antigen structures. In flow cytometry and immunofluorescence analyses, Remab6 recognizes human cancer cell lines expressing the Tn antigen, but not their Tn-negative counterparts. In immunohistochemistry (IHC), Remab6 stains many human cancers in tissue array format but rarely stains normal tissues and then mostly intracellularly. We used these antibodies to identify several unique Tn-containing glycoproteins in Tn-positive Colo205 cells, indicating their utility for glycoproteomics in future biomarker studies. Thus, recombinant Remab6 and ReBaGs6 are useful for biochemical characterization of cancer cells and IHC of tumors and represent promising tools for Tn biomarker discovery independently of recognition of IgA1.

Potential of Anti-MUC1 Antibodies as a Targeted Therapy for Gastrointestinal Cancers

Gastrointestinal cancers (GI) account for 26% of cancer incidences globally and 35% of all cancer-related deaths. The main challenge is to target cancer specific antigens. Mucins are heavily O-glycosylated proteins overexpressed in different cancers. The transmembrane glycoprotein MUC1 is the most likeable target for antibodies, owing to its specific overexpression and aberrant glycosylation in many types of cancers. For the past 30 years, MUC1 has remained a possible diagnostic marker and therapeutic target. Despite initiation of numerous clinical trials, a comprehensively effective therapy with clinical benefit is yet to be achieved. However, the interest in MUC1 as a therapeutic target remains unaltered. For all translational studies, it is important to incorporate updated relevant research findings into therapeutic strategies. In this review we present an overview of the antibodies targeting MUC1 in GI cancers, their potential role in immunotherapy (i.e., antibody-drug and radioimmunoconjugates, CAR-T cells), and other novel therapeutic strategies. We also present our perspectives on how the mechanisms of action of different anti-MUC1 antibodies can target specific hallmarks of cancer and therefore be utilized as a combination therapy for better clinical outcomes.

A review on development of MUC1-based cancer vaccine

Mucin 1 (MUC1) is a transmembrane mucin glycoprotein expressed on the surface of almost all epithelial cells. Aberrantly glycosylated MUC1 is associated with cellular transformation from a normal to malignant phenotype in human cancers. Therefore, MUC1 is the major target for the design and development of cancer vaccines. MUC1-based cancer vaccines are a promising strategy for preventing cancer progression and metastasis. This review summarizes the most significant milestones achieved to date in the development of different MUC-1-based vaccine approaches in clinical trials. Further, it provides perspectives for future research that may promote clinical advances in infection-associated cancers.

MUC1 antibody-based therapeutics: the promise of cancer immunotherapy

Antibody-based targeted therapies have been able to target cancers with enhanced specificity and high efficacy. In this regard, identifying cancer markers (antigens) that are only present (tumor-specific antigens) or have an increased expression (tumor-associated antigen) on the surface of cancer cells is a crucial step for targeted cancer treatment. Various cancer antigens have already been used for therapeutic and diagnostic purposes. MUC1 is one of the most important tumor markers with high levels of expression in various solid tumors which makes it as a potential target for antibody-based therapies. This review discusses preclinical and clinical results from various platforms based on monoclonal antibodies, nanobodies as well as bispecific antibodies against MUC1. We also highlight unmet challenges that must be overcome to generate more effective cancer immunotherapy strategies.

TF-containing MUC1 glycopeptides fail to entice Galectin-1 recognition of tumor-associated Thomsen-Freidenreich (TF) antigen (CD176) in solution

Aberrant Mucin-1 (MUC1) glycosylation with the Thomsen-Friedenreich (TF) tumor-associated antigen (CD176) is a hallmark of epithelial carcinoma progression and poor patient prognosis. Recognition of TF by glycan-binding proteins, such as galectins, enables the pathological repercussions of this glycan presentation, yet the underlying binding specificities of different members of the galectin family is a matter of continual investigation. While Galectin-3 (Gal-3) recognition of TF has been well-documented at both the cellular and molecular level, Galectin-1 (Gal-1) recognition of TF has only truly been alluded to in cell-based platforms. Immunohistochemical analyses have purported Gal-1 binding to TF on MUC1 at the cell surface, however binding at the molecular level was inconclusive. We hypothesize that glycan scaffold (MUC1's tandem repeat peptide sequence) and/or multivalency play a role in the binding recognition of TF antigen by Gal-1. In this study we have developed a method for large-scale expression of Gal-1 and its histidine-tagged analog for use in binding studies by isothermal titration calorimetry (ITC) and development of an analytical method based on AlphaScreen technology to screen for Gal-1 inhibitors. Surprisingly, neither glycan scaffold or multivalent presentation of TF antigen on the scaffold was able to entice Gal-1 recognition to the level of affinity expected for functional significance. Future evaluations of the Gal-1/TF binding interaction in order to draw connections between immunohistochemical data and analytical measurements are warranted.

Identification of Targets to Redirect CAR T Cells in Glioblastoma and Colorectal Cancer: An Arduous Venture

The chimeric antigen receptor (CAR) is an artificial molecule engineered to induce cytolytic T cell reactions in tumors. Generally, this molecule combines an extracellular single-chain variable fragment (scFv) able to recognize tumor-associated epitopes together with the intracellular signaling domains that are required for T cell activation. When expressed by T cells, the CAR enables the recognition and subsequent destruction of cancer cells expressing the complementary antigen on their surface. Although the clinical application for CAR T cells is currently limited to some hematological malignancies, researchers are trying to develop CAR T cell-based therapies for the treatment of solid tumors. However, while in the case of CD19, or other targets restricted to the hematopoietic compartment, the toxicity is limited and manageable, the scarcity of specific antigens expressed by solid tumors and not by healthy cells from vital organs makes the clinical development of CAR T cells in this context particularly challenging. Here we summarize relevant research and clinical trials conducted to redirect CAR T cells to surface antigens in solid tumors and cancer stem cells with a focus on colorectal cancer and glioblastoma. Finally, we will discuss current knowledge of altered glycosylation of CSCs and cancer cells and how these novel epitopes may help to target CAR T cell-based immunotherapy in the future.

Cell-Free Synthetic Glycobiology: Designing and Engineering Glycomolecules Outside of Living Cells

Glycans and glycosylated biomolecules are directly involved in almost every biological process as well as the etiology of most major diseases. Hence, glycoscience knowledge is essential to efforts aimed at addressing fundamental challenges in understanding and improving human health, protecting the environment and enhancing energy security, and developing renewable and sustainable resources that can serve as the source of next-generation materials. While much progress has been made, there remains an urgent need for new tools that can overexpress structurally uniform glycans and glycoconjugates in the quantities needed for characterization and that can be used to mechanistically dissect the enzymatic reactions and multi-enzyme assembly lines that promote their construction. To address this technology gap, cell-free synthetic glycobiology has emerged as a simplified and highly modular framework to investigate, prototype, and engineer pathways for glycan biosynthesis and biomolecule glycosylation outside the confines of living cells. From nucleotide sugars to complex glycoproteins, we summarize here recent efforts that harness the power of cell-free approaches to design, build, test, and utilize glyco-enzyme reaction networks that produce desired glycomolecules in a predictable and controllable manner. We also highlight novel cell-free methods for shedding light on poorly understood aspects of diverse glycosylation processes and engineering these processes toward desired outcomes. Taken together, cell-free synthetic glycobiology represents a promising set of tools and techniques for accelerating basic glycoscience research (e.g., deciphering the "glycan code") and its application (e.g., biomanufacturing high-value glycomolecules on demand).

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.

Structure-guided engineering of the affinity and specificity of CARs against Tn-glycopeptides

The potency of adoptive T cell therapies targeting the cell surface antigen CD19 has been demonstrated in hematopoietic cancers. It has been difficult to identify appropriate targets in nonhematopoietic tumors, but one class of antigens that have shown promise is aberrant O-glycoprotein epitopes. It has long been known that dysregulated synthesis of O-linked (threonine or serine) sugars occurs in many cancers, and that this can lead to the expression of cell surface proteins containing O-glycans comprised of a single N-acetylgalactosamine (GalNAc, known as Tn antigen) rather than the normally extended carbohydrate. Previously, we used the scFv fragment of antibody 237 as a chimeric antigen receptor (CAR) to mediate recognition of mouse tumor cells that bear its cognate Tn-glycopeptide epitope in podoplanin, also called OTS8. Guided by the structure of the 237 Fab:Tn-OTS8-glycopeptide complex, here we conducted a deep mutational scan showing that residues flanking the Tn-glycan contributed significant binding energy to the interaction. Design of 237-scFv libraries in the yeast display system allowed us to isolate scFv variants with higher affinity for Tn-OTS8. Selection with a noncognate human antigen, Tn-MUC1, yielded scFv variants that were broadly reactive with multiple Tn-glycoproteins. When configured as CARs, engineered T cells expressing these scFv variants showed improved activity against mouse and human cancer cell lines defective in O-linked glycosylation. This strategy provides CARs with Tn-peptide specificities, all based on a single scFv scaffold, that allows the same CAR to be tested for toxicity in mice and efficacy against mouse and human tumors.

Glycoconjugation: An approach to cancer therapeutics

Cancer constitutes the second leading cause of death globally and is considered to have been responsible for an estimated 9.6 million fatalities in 2018. Although treatments against gastrointestinal tumors have recently advanced, those interventions can only be applied to a minority of patients at the time of diagnosis. Therefore, new therapeutic options are necessary for advanced stages of the disease. Glycosylation of antitumor agents, has been found to improve pharmacokinetic parameters, reduce side effects, and expand drug half-life in comparison with the parent compounds. In addition, glycosylation of therapeutic agents has been proven to be an effective strategy for their targeting tumor tissue, thereby reducing the doses of the glycodrugs administered to patients. This review focusses on the effect of the targeting properties of glycosylated antitumor agents on gastrointestinal tumors.

Recent advances in tumor associated carbohydrate antigen based chimeric antigen receptor T cells and bispecific antibodies for anti-cancer immunotherapy

Tumor associated carbohydrate antigens (TACAs) are a class of attractive antigens for the development of anti-cancer immunotherapy. Besides monoclonal antibodies and vaccines, chimeric antigen receptor (CAR) T cells and bispecific antibodies (BsAbs) targeting TACA are exciting directions to harness the power of the immune system to fight cancer. In this review, we focus on two TACAs, i.e., the GD2 ganglioside and the mucin-1 (MUC1) protein. The latest advances in CAR T cells and bispecific antibodies targeting these two antigens are presented. The roles of co-stimulatory molecules, structures of the sequences for antigen binding, methods for CAR and antibody construction, as well as strategies to enhance solid tumor penetration and reduce T cell exhaustion and death are discussed. Furthermore, approaches to reduce "on target, off tumor" side effects are introduced. With further development, CAR T cells and BsAbs targeting GD2 and MUC1 can become powerful agents to effectively treat solid tumor.