Isolation and characterization of antibodies against three consecutive Tn-antigen clusters from a phage library displaying human single-chain variable fragments

Targeting altered glycosylation in secreted tumor glycoproteins for broad cancer detection

There is an urgent need to develop new tumor biomarkers for early cancer detection, but the variability of tumor-derived antigens has been a limitation. Here we demonstrate a novel anti-Tn antibody microarray platform to detect Tn+ glycoproteins, a near universal antigen in carcinoma-derived glycoproteins, for broad detection of cancer. The platform uses a specific recombinant IgG1 to the Tn antigen (CD175) as a capture reagent and a recombinant IgM to the Tn antigen as a detecting reagent. These reagents were validated by immunohistochemistry in recognizing the Tn antigen using hundreds of human tumor specimens. Using this approach, we could detect Tn+ glycoproteins at subnanogram levels using cell lines and culture media, serum, and stool samples from mice engineered to express the Tn antigen in intestinal epithelial cells. The development of a general cancer detection platform using recombinant antibodies for detection of altered tumor glycoproteins expressing a unique antigen could have a significant impact on cancer detection and monitoring.

Inhibition of galectins in cancer: Biological challenges for their clinical application

Galectins play relevant roles in tumor development, progression and metastasis. Accordingly, galectins are certainly enticing targets for medical intervention in cancer. To date, however, clinical trials based on galectin inhibitors reported inconclusive results. This review summarizes the galectin inhibitors currently being evaluated and discusses some of the biological challenges that need to be addressed to improve these strategies for the benefit of cancer patients.

Recent advances and future perspectives on carbohydrate-based cancer vaccines and therapeutics

Carbohydrates are abundantly expressed on the surface of both eukaryotic and prokaryotic cells, often as post translational modifications of proteins. Glycoproteins are recognized by the immune system and can trigger both innate and humoral responses. This feature has been harnessed to generate vaccines against polysaccharide-encapsulated bacteria such as Streptococcus pneumoniae, Hemophilus influenzae type b and Neisseria meningitidis. In cancer, glycosylation plays a pivotal role in malignancy development and progression. Since glycans are specifically expressed on the surface of tumor cells, they have been targeted for the discovery of anticancer preventive and therapeutic treatments, such as vaccines and monoclonal antibodies. Despite the various efforts made over the last years, resulting in a series of clinical studies, attempts of vaccination with carbohydrate-based candidates have proven unsuccessful, primarily due to the immune tolerance often associated with these glycans. New strategies are thus deployed to enhance carbohydrate-based cancer vaccines. Moreover, lessons learned from glycan immunobiology paved the way to the development of new monoclonal antibodies specifically designed to recognize cancer-bound carbohydrates and induce tumor cell killing. Herein we provide an overview of the immunological principles behind the immune response towards glycans and glycoconjugates and the approaches exploited at both preclinical and clinical level to target cancer-associated glycans for the development of vaccines and therapeutic monoclonal antibodies. We also discuss gaps and opportunities to successfully advance glycan-directed cancer therapies, which could provide patients with innovative and effective treatments.

C1GALT1 in health and disease

O-linked glycosylation (O-glycosylation) and N-linked glycosylation (N-glycosylation) are the two most important forms of protein glycosylation, which is an important post-translational modification. The regulation of protein function involves numerous mechanisms, among which protein glycosylation is one of the most important. Core 1 synthase glycoprotein-N-acetylgalactosamine 3-β-galactosyltransferase 1 (C1GALT1) serves an important role in the regulation of O-glycosylation and is an essential enzyme for synthesizing the core 1 structure of mucin-type O-glycans. Furthermore, C1GALT1 serves a vital role in a number of biological functions, such as angiogenesis, platelet production and kidney development. Impaired C1GALT1 expression activity has been associated with different types of human diseases, including inflammatory or immune-mediated diseases, and cancer. O-glycosylation exists in normal tissues, as well as in tumor tissues. Previous studies have revealed that changes in the level of glycosyltransferase in different types of cancer may be used as potential therapeutic targets. Currently, numerous studies have reported the dual role of C1GALT1 in tumors (carcinogenesis and cancer suppression). The present review reports the role of C1GALT1 in normal development and human diseases. Since the mechanism and regulation of C1GALT1 and O-glycosylation remain elusive, further studies are required to elucidate their effects on development and disease.

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.

Specificity of human natural antibodies referred to as anti-Tn

To understand the role of human natural IgM known as antibodies against the carbohydrate epitope Tn, the antibodies were isolated using GalNAcα-Sepharose affinity chromatography, and their specificity was profiled using microarrays (a glycan array printed with oligosaccharides and bacterial polysaccharides, as well as a glycopeptide array), flow cytometry, and inhibition ELISA. The antibodies bound a restricted number of GalNAcα-terminated oligosaccharides better than the parent monosaccharide, e.g., 6-O-Su-GalNAcα and GalNAcα1-3Galβ1-3(4)GlcNAcβ. The binding with several bacterial polysaccharides that have no structural resemblance to the affinity ligand GalNAcα was quite unexpected. Given that GalNAcα is considered the key fragment of the Tn antigen, it is surprising that these antibodies bind weakly GalNAcα-OSer and do not bind a wide variety of GalNAcα-OSer/Thr-containing mucin glycopeptides. At the same time, we have observed specific binding to cells having Tn-positive glycoproteins containing similar glycopeptide motifs in a conformationally rigid macromolecule. Thus, specific recognition of the Tn antigen apparently requires that the naturally occurring "anti-Tn" IgM recognize a complex epitope comprising the GalNAcα as an essential component and a fairly long amino acid sequence where the amino acids adjacent to GalNAcα do not contact the antibody paratope; i.e., the antibodies recognize a spatial epitope or a molecular pattern rather than a classical continuous sequence. In addition, we have not found any increase in the binding of natural antibodies when GalNAcα residues were clustered. These results may help in further development of anticancer vaccines based on synthetic Tn constructs.

Phage display antibody libraries: A robust approach for generation of recombinant human monoclonal antibodies

Monoclonal antibodies (mAbs) and their derivatives have achieved remarkable success as medicine, targeting both diagnostic and therapeutic applications associated with communicable and non-communicable diseases. In the last 3 to 4 decades, tremendous success has been manifested in the field of cancer therapy, autoimmune diseases, cardiovascular and infectious diseases. MAbs are the fastest growing class of biopharmaceuticals, with more than 25 derivatives are in clinical use and 7 of these have been isolated through phage display technology. Phage display technology has gained impetus in the field of medical and health sciences, as a large repertoire of diverse recombinant antibodies, targeting various antigens have been generated in a short span of time. A prominent number of phage display derived antibodies are already approved for therapy and significant numbers are currently in clinical trials. In this review we have discussed the various strategies employed for generation of monoclonal antibodies; their advantages, limitations and potential therapeutic applications. We also discuss the potential of phage display antibody libraries in isolation of monoclonal antibodies.

T-Synthase Deficiency Enhances Oncogenic Features in Human Colorectal Cancer Cells via Activation of Epithelial-Mesenchymal Transition

Background

Immature truncated O-glycans such as Tn antigen are frequently detected in human colorectal cancer (CRC); however, the precise pathological consequences of Tn antigen expression on CRC are unknown. T-synthase is the key enzyme required for biosynthesis of mature O-glycans. Here we investigated the functional roles of Tn antigen expression mediated by T-synthase deficiency in CRC cells.

Methods

To knock out T-synthase, we used CRISPR-Cas9 technology to target C1GALT1, the gene encoding T-synthase, in a CRC cell line (HCT116). Deletion of T-synthase was confirmed by western blotting, and expression of Tn antigen was determined by flow cytometry in HCT116 cells. We then assessed the biological effects of T-synthase deficiency on oncogenic behaviors in HCT116 cells. Furthermore, we analyzed the mechanistic role of T-synthase deficiency in cancer cells by determining the epithelial-mesenchymal transition (EMT) pathway.

Results

We showed that forced knockout of T-synthase in HCT116 cells significantly induced Tn antigen expression, which represented the occurrence of aberrant O-glycosylation. Loss of T-synthase significantly enhanced cell proliferation and adhesion, as well as migration and invasiveness in culture. More importantly, we demonstrated that T-synthase deficiency directly induced classical EMT characteristics in cancer cells. E-cadherin, a typical epithelial cell marker, was markedly decreased in T-synthase knockout HCT 116 cells, accompanied by an enhanced expression of mesenchymal markers including snail and fibronectin (FN).

Conclusions

These findings indicate that T-synthase deficiency in CRC cells not only is responsible for aberrant O-glycosylation, but also triggers the molecular process of EMT pathway, which may translate to increased invasiveness and metastasis in cancers.

Epitopes of MUC1 Tandem Repeats in Cancer as Revealed by Antibody Crystallography: Toward Glycopeptide Signature-Guided Therapy

Abnormally O-glycosylated MUC1 tandem repeat glycopeptide epitopes expressed by multiple types of cancer have long been attractive targets for therapy in the race against genetic mutations of tumor cells. Glycopeptide signature-guided therapy might be a more promising avenue than mutation signature-guided therapy. Three O-glycosylated peptide motifs, PDTR, GSTA, and GVTS, exist in a tandem repeat HGVTSAPDTRPAPGSTAPPA, containing five O-glycosylation sites. The exact peptide and sugar residues involved in antibody binding are poorly defined. Co-crystal structures of glycopeptides and respective monoclonal antibodies are very few. Here we review 3 groups of monoclonal antibodies: antibodies which only bind to peptide portion, antibodies which only bind to sugar portion, and antibodies which bind to both peptide and sugar portions. The antigenicity of peptide and sugar portions of glyco-MUC1 tandem repeat were analyzed according to available biochemical and structural data, especially the GSTA and GVTS motifs independent from the most studied PDTR. Tn is focused as a peptide-modifying residue in vaccine design, to induce glycopeptide-binding antibodies with cross reactivity to Tn-related tumor glycans, but not glycans of healthy cells. The unique requirement for the designs of antibody in antibody-drug conjugate, bi-specific antibodies, and chimeric antigen receptors are also discussed.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2009-2010

This review is the sixth update of the original article 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 2010. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, arrays and fragmentation are covered in the first part of the review and applications to various structural typed constitutes the remainder. The main groups of compound that are discussed in this section are oligo and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Many of these applications are presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis.

Affinity Chromatography of Native and Recombinant Proteins from Receptors for Insulin and IGF-I to Recombinant Single Chain Antibodies

Affinity chromatography is an efficient method to isolate proteins by taking advantage of their affinities for specific molecules such as substrates, inhibitors, antigens, ligands, antibodies, and other interacting molecules, including subunits. Nowadays, we take the effectiveness and excellence of this technology for granted. This essay will mainly cover the use of affinity chromatography based on my experience.

Purification and refolding of anti-T-antigen single chain antibodies (scFvs) expressed in Escherichia coli as inclusion bodies

T-antigen (Galβ1-3GalNAcα-1-Ser/Thr) is an oncofetal antigen that is commonly expressed as a carbohydrate determinant in many adenocarcinomas. Since it is associated with tumor progression and metastasis, production of recombinant antibodies specific for T-antigen could lead to the development of cancer diagnostics and therapeutics. Previously, we isolated and characterized 11 anti-T-antigen phage clones from a phage library displaying human single-chain antibodies (scFvs) and purified one scFv protein, 1G11. More recently, we purified and characterized 1E8 scFv protein using a Drosophila S2 expression system. In the current study, four anti-T-antigen scFv genes belonging to Groups 1-4 were purified from inclusion bodies expressed in Escherichia coli cells. Inclusion bodies isolated from E. coli cells were denatured in 3.5 M Gdn-HCl. Solubilized His-tagged scFv proteins were purified using Ni(2+)-Sepharose column chromatography in the presence of 3.5 M Gdn-HCl. Purified scFv proteins were refolded according to a previously published method of step-wise dialysis. Two anti-T-antigen scFv proteins, 1E6 and 1E8 that belong to Groups 1 and 2, respectively, were produced in sufficient amounts, thus allowing further characterization of their binding activity with T-antigen. Specificity and affinity constants determined using enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR), respectively, provided evidence that both 1E8 and 1E6 scFv proteins are T-antigen specific and suggested that 1E8 scFv protein has a higher affinity for T-antigen than 1E6 scFv protein.

The role of phage display in therapeutic antibody discovery

Phage display involves the expression of selected proteins on the surface of filamentous phage through fusion with phage coat protein, with the genetic sequence packaged within, linking phenotype to genotype selection. When combined with antibody libraries, phage display allows for rapid in vitro selection of antigen-specific antibodies and recovery of their corresponding coding sequence. Large non-immune and synthetic human libraries have been constructed as well as smaller immune libraries based on capturing a single individual’s immune repertoire. This completely in vitro process allows for isolation of antibodies against poorly immunogenic targets as well as those that cannot be obtained by animal immunization, thus further expanding the utility of the approach. Phage antibody display represents the first developed methodology for high throughput screening for human therapeutic antibody candidates. Recently, other methods have been developed for generation of fully human therapeutic antibodies, such as single B-cell screening, next-generation genome sequencing and transgenic mice with human germline B-cell genes. While each of these have their particular advantages, phage display has remained a key methodology for human antibody discovery due its in vitro process. Here, we review the continuing role of this technique alongside other developing technologies for therapeutic antibody discovery.

Development of a functional antibody by using a green fluorescent protein frame as the template

Single-chain variable fragment (scFv) antibodies are widely used as diagnostic and therapeutic agents or biosensors for a majority of human disease. However, the limitations of the present scFv antibody in terms of stability, solubility, and affinity are challenging to produce by traditional antibody screening and expression formats. We describe here a feasible strategy for creating the green fluorescent protein (GFP)-based antibody. Complementarity-determining region 3 (CDR3), which retains the antigen binding activity, was introduced into the structural loops of superfolder GFP, and the result showed that CDR3-inserted GFP displayed almost the same fluorescence intensity as wild-type GFP, and the purified proteins of CDR3 insertion showed the similar binding activity to antigen as the corresponding scFv. Among of all of the CDRs, CDR3s are responsible for antigen recognition, and only the CDR3a insertion is the best format for producing GFP-based antibody binding to specific antigen. The wide versatility of this system was further verified by introducing CDR3 from other scFvs into loop 9 of GFP. We developed a feasible method for rapidly and effectively producing a high-affinity GFP-based antibody by inserting CDR3s into GFP loops. Further, the affinity can be enhanced by specific amino acids scanning and site-directed mutagenesis. Notably, this method had better versatility for creating antibodies to various antigens using GFP as the scaffold, suggesting that a GFP-based antibody with high affinity and specificity may be useful for disease diagnosis and therapy.

Engineering production of functional scFv antibody in E. coli by co-expressing the molecule chaperone Skp

Single-chain variable fragment (scFv) is a class of engineered antibodies generated by the fusion of the heavy (V_H) and light chains (V_L) of immunoglobulins through a short polypeptide linker. ScFv play a critical role in therapy and diagnosis of human diseases, and may in fact also be developed into a potential diagnostic and/or therapeutic agent. However, the fact that current scFv antibodies have poor stability, low solubility, and affinity, seriously limits their diagnostic and clinical implication. Here we have developed four different expression vectors, and evaluated their abilities to express a soluble scFv protein. The solubility and binding activity of the purified proteins were determined using both SDS-PAGE and ELISA. Amongst the four purified proteins, the Skp co-expressed scFv showed the highest solubility, and the binding activity to antigen TLH was 3-4 fold higher than the other three purified scFv. In fact, this scFv is specific for TLH and does not cross-react with other TLH-associated proteins and could be used to detect TLH directly in real samples. These results suggest that the pACYC-Duet-skp co-expression vector might be a useful tool for the production of soluble and functional scFv antibody.

Recognition of the Thomsen-Friedenreich pancarcinoma carbohydrate antigen by a lamprey variable lymphocyte receptor

Variable lymphocyte receptors (VLRs) are leucine-rich repeat proteins that mediate adaptive immunity in jawless vertebrates. VLRs were recently shown to recognize glycans, such as the tumor-associated Thomsen-Friedenreich antigen (TFα; Galβ1-3GalNAcα), with a selectivity rivaling or exceeding that of lectins and antibodies. To understand the basis for TFα recognition by one such VLR (VLRB.aGPA.23), we measured thermodynamic parameters for the binding interaction and determined the structure of the VLRB.aGPA.23-TFα complex to 2.2 Å resolution. In the structure, four tryptophan residues form a tight hydrophobic cage encasing the TFα disaccharide that completely excludes buried water molecules. This cage together with hydrogen bonding of sugar hydroxyls to polar side chains explains the exquisite selectivity of VLRB.aGPA.23. The topology of the glycan-binding site of VLRB.aGPA.23 differs markedly from those of lectins or antibodies, which typically consist of long, convex grooves for accommodating the oligosaccharide. Instead, the TFα disaccharide is sandwiched between a variable loop and the concave surface of the VLR formed by the β-strands of the leucine-rich repeat modules. Longer oligosaccharides are predicted to extend perpendicularly across the β-strands, requiring them to bend to match the concavity of the VLR solenoid.

Renewed interest in basic and applied research involving monoclonal antibodies against an oncofetal Tn-antigen

Tn-antigen (GalNAcα-Ser/Thr) is one of the most common aberrations associated with cancer progression and metastasis, and thus is an excellent target for development of cancer diagnostics and therapeutics. MLS128 monoclonal antibody (mAb), derived from a mouse immunized with human colon carcinoma cells, was reported to bind to two or three consecutive Tn-antigens (Tn2 or Tn3) with one-order higher affinity for Tn3 than for Tn2. Our recent studies demonstrated that MLS128 significantly inhibits breast and colon cancer cell growth. Molecular cloning of the variable regions of heavy (VH) and light (VL) chains revealed that the VH sequence of MLS128 shared 97% nucleotide sequence identity with the VH of 83D4 mAb, derived from breast cancer-immunized mice, which has a similar affinity for Tn2/Tn3. MLS128 single-chain antibodies (scFv) and scFv-Fc were constructed to confirm the affinity for synthetic Tn2/Tn3 peptides. Thermodynamic studies on MLS128 binding to Tn2/Tn3 revealed its unique nature of temperature-dependent binding.

Sugar-binding proteins from fish: selection of high affinity "lambodies" that recognize biomedically relevant glycans

Glycan-binding proteins are important for a wide variety of basic research and clinical applications, but proteins with high affinity and selectivity for carbohydrates are difficult to obtain. Here we describe a facile and cost-effective strategy to generate monoclonal lamprey antibodies, called lambodies, that target glycan determinants. We screened a library of yeast surface-displayed (YSD) lamprey variable lymphocyte receptors (VLR) for clones that can selectively bind various biomedically important glycotopes. These glycoconjugates included tumor-associated carbohydrate antigens (Tn and TFα), Lewis antigens (LeA and LeX), N-glycolylneuraminic acid, targets of broadly neutralizing HIV antibodies (poly-Man9 and the HIV gp120), and the glycoproteins asialo-ovine submaxillary mucin (aOSM) and asialo-human glycophorin A (aGPA). We isolated clones that bind each of these targets in a glycan-dependent manner and with very strong binding constants, for example, 6.2 nM for Man9 and 44.7 nM for gp120, determined by surface plasmon resonance (SPR). One particular lambody, VLRB.aGPA.23, was shown by glycan array analysis to be selective for the blood group H type 3 trisaccharide (BG-H3, Fucα1-2Galβ1-3GalNAcα), aGPA, and TFα (Galβ1-3GalNAcα), with affinity constants of 0.2, 1, and 8 nM, respectively. In human tissue microarrays this lambody selectively detected cancer-associated carbohydrate antigens in 14 different types of cancers. It stained 27% of non-small cell lung cancer (NSCLC) samples in a pattern that correlated with poor patient survival. Lambodies with exquisite affinity and selectivity for glycans may find myriad uses in glycobiology and biomedical research.

Development of a convenient competitive ELISA for the detection of the free and protein-bound nonhuman galactosyl-α-(1,3)-galactose epitope based on highly specific chicken single-chain antibody variable-region fragments

The presence of the nonhuman galactosyl-α-(1,3)-galactose (Gal-α-(1,3)-Gal) carbohydrate epitope on a number of recombinant therapeutic proteins has recently been reported, renewing interest in this immunogenic carbohydrate epitope. It is well-known that this motif is the primary contributing factor in hyperacute rejection of porcine organ xenograft, due to the existence of natural antibodies against this epitope in human serum. Though the number of epitopes on recombinant glycoproteins may be low when compared directly to whole tissue, circulating anti-Gal-α-R immunoglobulins can still induce anaphylaxis. Therefore, there is a need for rapid and convenient methods for detection and monitoring of this epitope in biopharmaceuticals produced in recombinant mammalian systems. To this end, we have generated immune-challenged chicken single-chain antibody variable-region fragment (scFv) libraries targeting the Gal-α-(1,3)-Gal motif and have selected a panel of scFv's that bind the target. We have used one of these antibodies to develop a competitive ELISA for both free and protein-bound Gal-α-(1,3)-Gal and have demonstrated that the ELISA is specific for the target and can be used to determine the loading of the target on glycoproteins. This competitive ELISA will provide a convenient method of detecting and quantifying Gal-α-(1,3)-Gal on therapeutic glycoproteins.

Screening for a single-chain variable-fragment antibody that can effectively neutralize the cytotoxicity of the Vibrio parahaemolyticus thermolabile hemolysin

Vibrio parahaemolyticus is a halophilic bacterium that is widely distributed in water resources. The bacterium causes lethal food-borne diseases and poses a serious threat to human and animal health all over the world. The major pathogenic factor of V. parahaemolyticus is thermolabile hemolysin (TLH), encoded by the tlh gene, but its toxicity mechanisms are unknown. A high-affinity antibody that can neutralize TLH activity effectively is not available. In this study, we successfully expressed and purified the TLH antigen and discovered a high-affinity antibody to TLH, named scFv-LA3, by phage display screening. Cytotoxicity analysis showed that scFv-LA3 has strong neutralization effects on TLH-induced cell toxicity.

Enhanced epimerization of glycosylated amino acids during solid-phase peptide synthesis

Glycopeptides are extremely useful for basic research and clinical applications, but access to structurally defined glycopeptides is limited by the difficulties in synthesizing this class of compounds. In this study, we demonstrate that many common peptide coupling conditions used to prepare O-linked glycopeptides result in substantial amounts of epimerization at the α position. In fact, epimerization resulted in up to 80% of the non-natural epimer, indicating that it can be the major product in some reactions. Through a series of mechanistic studies, we demonstrate that the enhanced epimerization relative to nonglycosylated amino acids is due to a combination of factors, including a faster rate of epimerization, an energetic preference for the unnatural epimer over the natural epimer, and a slower overall rate of peptide coupling. In addition, we demonstrate that use of 2,4,6-trimethylpyridine (TMP) as the base in peptide couplings produces glycopeptides with high efficiency and low epimerization. The information and improved reaction conditions will facilitate the preparation of glycopeptides as therapeutic compounds and vaccine antigens.

Analysis of Tn antigenicity with a panel of new IgM and IgG1 monoclonal antibodies raised against leukemic cells

CD175 or Tn antigen is a carbohydrate moiety of N-acetylgalactosamine (GalNAc)α1-O- linked to the residue of amino acid serine or threonine in a polypeptide chain. Despite the chemical simplicity of the Tn antigen, its antigenic structure is considered to be complex and the clear determinants of Tn antigenicity remain poorly understood. As a consequence, a broad variety of anti-Tn monoclonal antibodies (mAbs) have been generated. To further investigate the nature and complexity of the Tn antigen, we generated seven different anti-Tn mAbs of IgM and IgG classes raised against human Jurkat T cells, which are Tn-positive due to the low activity of T-synthase and mutation in specific chaperone Cosmc. The binding analysis of anti-Tn mAbs with the array of synthetic saccharides, glycopeptides and O-glycoproteins revealed unexpected differences in specificities of anti-Tn mAbs. IgM mAbs bound the terminal GalNAc residue of the Tn antigen irrespective of the peptide context or with low selectivity to the glycoproteins. In contrast, IgG mAbs recognized the Tn antigen in the context of a specific peptide motif. Particularly, JA3 mAb reacted to the GSPP or GSPAPP, and JA5 mAb recognized specifically the GSP motif (glycosylation sites are underlined). The major O-glycan carrier proteins CD43 and CD162 and isoforms of CD45 expressed on Jurkat cells were precipitated by anti-Tn mAbs with different affinities. In summary, our data suggest that Tn antigen-Ab binding capacity is determined by the peptide context of the Tn antigen, antigenic specificity of the Ab and class of the immunoglobulin. The newly generated anti-Tn IgG mAbs with the strong specificity to glycoprotein CD43 can be particularly interesting for the application in leukemia diagnostics and therapy.

Characterization of three different single chain antibodies recognizing non-reducing terminal mannose residues expressed in Escherichia coli by an inducible T7 expression system

We previously isolated phage antibodies from a phage library displaying human single chain antibodies (scFvs) by screening with a mannotriose (Man3)-bearing lipid. Of four independent scFv genes originally characterized, 5A3 gene products were purified as fusion proteins such as a scFv-human IgG1 Fc form, but stable clones secreting 1A4 and 1G4 scFv-Fc proteins had never been established. Thus, bacterial expression systems were used to purify 1A4 and 1G4 scFv gene products as soluble forms. Purification of 1A4 and 1G4 scFv proteins from inclusion bodies was also carried out together with purification of 5A3 scFv protein in order to compare their Man3-binding abilities. The present studies demonstrated that 1A4 and 1G4 scFv proteins have a higher affinity for Man3 than 5A3 scFv protein, which may determine whether scFv-Fc proteins expressed in mammalian cells are retained in the ER or secreted. Furthermore, the inhibitory effects of anti-Man3 1G4 scFv and anti-Tn antigen scFv proteins on MCF-7 cell growth were evaluated. Despite the fact that no obvious difference was detected in cell growth, microscopic observations revealed inhibition of foci formation in cells grown in the presence of the anti-carbohydrate scFv proteins. This finding provides a basis for the development of cancer therapeutics.

A new murine IgG1 anti-Tn monoclonal antibody with in vivo anti-tumor activity

The Tn antigen (GalNAc α-O-Ser/Thr) is heterogeneously synthesized by a variety of tumors and contains an epitope defined by lectins and antibodies as a cluster of αGalNAc carbohydrates synthesized within a peptide sequence, which is rich in serine and/or threonine. The Tn antigen has been utilized as a target in vaccine experiments and also used as a biomarker for prognosis of different cancer forms. In this paper, we present a new monoclonal antibody, GOD3-2C4, with the clear hallmarks of an anti-Tn antibody. It was generated through somatic cell hybridization after immunization of a mouse with a tumor cell line and a Tn carrying mucin. The antibody recognizes synthetic Tn antigen and binds breast, colon, lung, ovarian and pancreas cancer. The GOD3-2C4 antibody has antibody-dependent cellular cytotoxicity activity against Jurkat cells in vitro, and for the first time, it can be shown that an anti-Tn antibody has a significant in vivo effect on a human cancer cell line grown as a xenograft in severe combined immunodeficiency mice.

Glyco-biosensors: recent advances and applications for the detection of free and bound carbohydrates

The field of biosensor development now encompasses several areas specifically geared toward the rapid and sensitive detection, identification, and quantification of target analytes. In contrast to the more mature research and development of nucleic acid and protein biosensors, the development of 'glyco-biosensors' for detecting carbohydrates and conjugates of carbohydrates (glycoconjugates) is at a relatively nascent stage. The application of glyco-biosensors aims to open novel analytical and diagnostic avenues, encompassing industrial bioprocesses, biomedical and clinical applications. This area of research has been greatly aided by advancement brought by interdisciplinary mergers of engineering, biology, chemistry and physical sciences and enabling the miniaturization of detection platforms. In this review, we briefly introduce the need for glyco-biosensors, discuss current analytical technologies, and examine advances in glyco-biosensor approaches aimed at the detection and/or quantification of glycoconjugates or carbohydrates derived from glycoconjugates since 2005.