Monoclonal antibodies directed to the blood group A associated structure, galactosyl-A: specificity and relation to the Thomsen-Friedenreich antigen

Akkermansia muciniphila exoglycosidases target extended blood group antigens to generate ABO-universal blood

Matching donor and recipient blood groups based on red blood cell (RBC) surface ABO glycans and antibodies in plasma is crucial to avoid potentially fatal reactions during transfusions. Enzymatic conversion of RBC glycans to the universal group O is an attractive solution to simplify blood logistics and prevent ABO-mismatched transfusions. The gut symbiont Akkermansia muciniphila can degrade mucin O-glycans including ABO epitopes. Here we biochemically evaluated 23 Akkermansia glycosyl hydrolases and identified exoglycosidase combinations which efficiently transformed both A and B antigens and four of their carbohydrate extensions. Enzymatic removal of canonical and extended ABO antigens on RBCs significantly improved compatibility with group O plasmas, compared to conversion of A or B antigens alone. Finally, structural analyses of two B-converting enzymes identified a previously unknown putative carbohydrate-binding module. This study demonstrates the potential utility of mucin-degrading gut bacteria as valuable sources of enzymes for production of universal blood for transfusions.

Effect of temperature and pH on the structure and stability of tumor-specific lectin jacalin and insights into the location of its tryptophan residues: CD, DSC and fluorescence studies

Jacalin, the jackfruit seed lectin, exhibits high specificity for the tumor-specific T-antigen and is used in various biomedical and biotechnological applications. Here, we report biophysical studies on the thermal unfolding of jacalin and the effect of pH and temperature on its secondary structure. Differential scanning calorimetric (DSC) studies revealed that native jacalin unfolds at ∼60 °C and that carbohydrate binding stabilizes the protein structure. Circular dichroism spectroscopic studies indicated that the secondary structure of jacalin remains mostly unaffected over pH 2.0-9.0, whereas considerable changes were observed in the tertiary structure. DSC experiments demonstrated that jacalin exhibits two overlapping transitions between pH 2 and 5, which could be attributed to dissociation of the tetrameric protein into subunits and their unfolding. Interestingly, only one transition between pH 6 and 9 was observed, suggesting that the subunit dissociation and unfolding occur simultaneously. While quenching of the protein intrinsic fluorescence by acrylamide increased significantly upon carbohydrate binding, quenching by succinimide is essentially unaffected. We attribute this difference to increased exposure of Trp-123 in the α-chain as it is involved in carbohydrate binding. Both acrylamide and succinimide gave biphasic Stern-Volmer plots, consistent with differential accessibility of the two tryptophan residues of jacalin to them.

CRISPR-screen identifies ZIP9 and dysregulated Zn2+ homeostasis as a cause of cancer-associated changes in glycosylation

INTRODUCTION

In epithelial cancers, truncated O-glycans, such as the Thomson-nouveau antigen (Tn) and its sialylated form (STn), are upregulated on the cell surface and associated with poor prognosis and immunological escape. Recent studies have shown that these carbohydrate epitopes facilitate cancer development and can be targeted therapeutically; however, the mechanism underpinning their expression remains unclear.

METHODS

To identify genes directly influencing the expression of cancer-associated O-glycans, we conducted an unbiased, positive-selection, whole-genome CRISPR knockout-screen using monoclonal antibodies against Tn and STn.

RESULTS AND CONCLUSIONS

We show that knockout of the Zn2+-transporter SLC39A9 (ZIP9), alongside the well-described targets C1GALT1 (C1GalT1) and its molecular chaperone, C1GALT1C1 (COSMC), results in surface-expression of cancer-associated O-glycans. No other gene perturbations were found to reliably induce O-glycan truncation. We furthermore show that ZIP9 knockout affects N-linked glycosylation, resulting in upregulation of oligo-mannose, hybrid-type, and α2,6-sialylated structures as well as downregulation of tri- and tetra-antennary structures. Finally, we demonstrate that accumulation of Zn2+ in the secretory pathway coincides with cell-surface presentation of truncated O-glycans in cancer tissue, and that over-expression of COSMC mitigates such changes. Collectively, the findings show that dysregulation of ZIP9 and Zn2+ induces cancer-like glycosylation on the cell surface by affecting the glycosylation machinery.

Installation of O-glycan sulfation capacities in human HEK293 cells for display of sulfated mucins

The human genome contains at least 35 genes that encode Golgi sulfotransferases that function in the secretory pathway, where they are involved in decorating glycosaminoglycans, glycolipids, and glycoproteins with sulfate groups. Although a number of important interactions by proteins such as selectins, galectins, and sialic acid–binding immunoglobulin-like lectins are thought to mainly rely on sulfated O-glycans, our insight into the sulfotransferases that modify these glycoproteins, and in particular GalNAc-type O-glycoproteins, is limited. Moreover, sulfated mucins appear to accumulate in respiratory diseases, arthritis, and cancer. To explore further the genetic and biosynthetic regulation of sulfated O-glycans, here we expanded a cell-based glycan array in the human embryonic kidney 293 (HEK293) cell line with sulfation capacities. We stably engineered O-glycan sulfation capacities in HEK293 cells by site-directed knockin of sulfotransferase genes in combination with knockout of genes to eliminate endogenous O-glycan branching (core2 synthase gene GCNT1) and/or sialylation capacities in order to provide simplified substrates (core1 Galβ1–3GalNAcα1–O-Ser/Thr) for the introduced sulfotransferases. Expression of the galactose 3-O-sulfotransferase 2 in HEK293 cells resulted in sulfation of core1 and core2 O-glycans, whereas expression of galactose 3-O-sulfotransferase 4 resulted in sulfation of core1 only. We used the engineered cell library to dissect the binding specificity of galectin-4 and confirmed binding to the 3-O-sulfo-core1 O-glycan. This is a first step toward expanding the emerging cell-based glycan arrays with the important sulfation modification for display and production of glycoconjugates with sulfated O-glycans.

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.

Impact of Truncated O-glycans in Gastric-Cancer-Associated CD44v9 Detection

CD44 variant isoforms are often upregulated in cancer and associated with increased aggressive tumor phenotypes. The CD44v9 is one of the major protein splice variant isoforms expressed in human gastrointestinal cancer cells. Immunodetection of CD44 isoforms like CD44v9 in tumor tissue is almost exclusively performed by using specific monoclonal antibodies. However, the structural variability conferred by both the alternative splicing and CD44 protein glycosylation is disregarded. In the present work, we have evaluated the role of O-glycosylation using glycoengineered gastric cancer models in the detection of CD44v9 by monoclonal antibodies. We demonstrated, using different technical approaches, that the presence of immature O-glycan structures, such as Tn and STn, enhance CD44v9 protein detection. These findings can have significant implications in clinical applications mainly at the detection and targeting of this cancer-related CD44v9 isoform and highlight the utmost importance of considering glycan structures in cancer biomarker detection and in therapy targeting.

A validated collection of mouse monoclonal antibodies to human glycosyltransferases functioning in mucin-type O-glycosylation

Complex carbohydrates serve a wide range of biological functions in cells and tissues, and their biosynthesis involves more than 200 distinct glycosyltransferases (GTfs) in human cells. The kinetic properties, cellular expression patterns and subcellular topology of the GTfs direct the glycosylation capacity of a cell. Most GTfs are ER or Golgi resident enzymes, and their specific subcellular localization is believed to be distributed in the secretory pathway according to their sequential role in the glycosylation process, although detailed knowledge for individual enzymes is still highly fragmented. Progress in quantitative transcriptome and proteome analyses has greatly advanced our understanding of the cellular expression of this class of enzymes, but availability of appropriate antibodies for in situ monitoring of expression and subcellular topology have generally been limited. We have previously used catalytically active GTfs produced as recombinant truncated secreted proteins in insect cells for generation of mouse monoclonal antibodies (mAbs) to human enzymes primarily involved in mucin-type O-glycosylation. These mAbs can be used to probe subcellular topology of active GTfs in cells and tissues as well as their presence in body fluids. Here, we present several new mAbs to human GTfs and provide a summary of our entire collection of mAbs, available to the community. Moreover, we present validation of specificity for many of our mAbs using human cell lines with CRISPR/Cas9 or zinc finger nuclease (ZFN) knockout and knockin of relevant GTfs.

Glycan-directed CAR-T cells

Cancer immunotherapy is rapidly advancing in the treatment of a variety of hematopoietic cancers, including pediatric acute lymphoblastic leukemia and diffuse large B cell lymphoma, with chimeric antigen receptor (CAR)-T cells. CARs are genetically encoded artificial T cell receptors that combine the antigen specificity of an antibody with the machinery of T cell activation. However, implementation of CAR technology in the treatment of solid tumors has been progressing much slower. Solid tumors are characterized by a number of challenges that need to be overcome, including cellular heterogeneity, immunosuppressive tumor microenvironment (TME), and, in particular, few known cancer-specific targets. Post-translational modifications that differentially occur in malignant cells generate valid cell surface, cancer-specific targets for CAR-T cells. We previously demonstrated that CAR-T cells targeting an aberrant O-glycosylation of MUC1, a common cancer marker associated with changes in cell adhesion, tumor growth and poor prognosis, could control malignant growth in mouse models. Here, we discuss the field of glycan-directed CAR-T cells and review the different classes of antibodies specific for glycan-targeting, including the generation of high affinity O-glycopeptide antibodies. Finally, we discuss historic and recently investigated glycan targets for CAR-T cells and provide our perspective on how targeting the tumor glycoproteome and/or glycome will improve CAR-T immunotherapy.

The Thomsen-Friedenreich Antigen: A Highly Sensitive and Specific Predictor of Microsatellite Instability in Gastric Cancer

Microsatellite instability (MSI) is a distinct molecular subtype of gastric cancer. In recent years, the clinical consequences of MSI and the therapeutic opportunities to target this peculiar cancer subtype became evident. However, despite the importance of MSI for the stratification of patients, the time and resources required for diagnosis still present an obstacle. In an attempt to identify a new marker for MSI in gastric cancer, we evaluated the expression of five cancer-associated glycan epitopes in a cohort of 13 MSI and 17 microsatellite stable (MSS) cases. Our analysis revealed a highly significant (p < 0.001) association between the expression of the Thomsen-Friedenreich (TF) antigen and MSI status. Hence, we present here the identification of the first single marker for MSI in gastric cancer, excelling with a specificity of 94% (16/17), sensitivity of 69.2% (9/13), negative predictive value of 80% (16/20), and positive predictive value of 90% (9/10). The TF antigen, detected by simple antibody-based assays, is highly specific for carcinoma being undetectable in gastric healthy and premalignant epithelia. This finding lays the basis for new studies and holds promise in improving the rapid identification of MSI in the clinical setting.

Preclinical Analysis of JAA-F11, a Specific Anti-Thomsen-Friedenreich Antibody via Immunohistochemistry and In Vivo Imaging

The tumor specificity of JAA-F11, a novel monoclonal antibody specific for the Thomsen-Friedenreich cancer antigen (TF-Ag-alpha linked), has been comprehensively studied by in vitro immunohistochemical (IHC) staining of human tumor and normal tissue microarrays and in vivo biodistribution and imaging by micro-positron emission tomography imaging in breast and lung tumor models in mice. The IHC analysis detailed herein is the comprehensive biological analysis of the tumor specificity of JAA-F11 antibody performed as JAA-F11 is progressing towards preclinical safety testing and clinical trials. Wide tumor reactivity of JAA-F11, relative to the matched mouse IgG3 (control), was observed in 85% of 1269 cases of breast, lung, prostate, colon, bladder, and ovarian cancer. Staining on tissues from breast cancer cases was similar regardless of hormonal or Her2 status, and this is particularly important in finding a target on the currently untargetable triple-negative breast cancer subtype. Humanization of JAA-F11 was recently carried out as explained in a companion paper "Humanization of JAA-F11, a Highly Specific Anti-Thomsen-Friedenreich Pancarcinoma Antibody and In Vitro Efficacy Analysis" (Neoplasia 19: 716-733, 2017), and it was confirmed that humanization did not affect chemical specificity. IHC studies with humanized JAA-F11 showed similar binding to human breast tumor tissues. In vivo imaging and biodistribution studies in a mouse syngeneic breast cancer model and in a mouse-human xenograft lung cancer model with humanized 124I- JAA-F11 construct confirmed in vitro tumor reactivity and specificity. In conclusion, the tumor reactivity of JAA-F11 supports the continued development of JAA-F11 as a targeted cancer therapeutic for multiple cancers, including those with unmet need.

Targeted O-glycoproteomics explored increased sialylation and identified MUC16 as a poor prognosis biomarker in advanced-stage bladder tumours

Bladder carcinogenesis and tumour progression is accompanied by profound alterations in protein glycosylation on the cell surface, which may be explored for improving disease management. In a search for prognosis biomarkers and novel therapeutic targets we have screened, using immunohistochemistry, a series of bladder tumours with differing clinicopathology for short-chain O-glycans commonly found in glycoproteins of human solid tumours. These included the Tn and T antigens and their sialylated counterparts sialyl-Tn(STn) and sialyl-T(ST), which are generally associated with poor prognosis. We have also explored the nature of T antigen sialylation, namely the sialyl-3-T(S3T) and sialyl-6-T(S6T) sialoforms, based on combinations of enzymatic treatments. We observed a predominance of sialoglycans over neutral glycoforms (Tn and T antigens) in bladder tumours. In particular, the STn antigen was associated with high-grade disease and muscle invasion, in accordance with our previous observations. The S3T and S6T antigens were detected for the first time in bladder tumours, but not in healthy urothelia, highlighting their cancer-specific nature. These glycans were also overexpressed in advanced lesions, especially in cases showing muscle invasion. Glycoproteomic analyses of advanced bladder tumours based on enzymatic treatments, Vicia villosa lectin-affinity chromatography enrichment and nanoLC-ESI-MS/MS analysis resulted in the identification of several key cancer-associated glycoproteins (MUC16, CD44, integrins) carrying altered glycosylation. Of particular interest were MUC16 STn⁺ -glycoforms, characteristic of ovarian cancers, which were found in a subset of advanced-stage bladder tumours facing the worst prognosis. In summary, significant alterations in the O-glycome and O-glycoproteome of bladder tumours hold promise for the development of novel noninvasive diagnostic tools and targeted therapeutics. Furthermore, abnormal MUC16 glycoforms hold potential as surrogate biomarkers of poor prognosis and unique molecular signatures for designing highly specific targeted therapeutics.

Innate immune defense in the inner ear - mucines are expressed by the human endolymphatic sac

The human endolymphatic sac has been shown recently to have immunological capacities and has thus been proposed as the main entity protecting the inner ear from pathogen invasion, equivalent to mucosa-associated lymphoid tissue (MALT). Although the sac expresses molecules of the innate immune system, the potential expression of members of the important mucin family has not been detailed. Thus, this paper explores endolymphatic sac expression of a number of mucins and mucin precursors. Twelve fresh tissue samples from the human endolymphatic sac were obtained during translabyrinthine surgery. The expression of Mucin 1, 2, 5B/AC and 16, as well as the core structure elements (mucin precursors) T-antigen, Tn-antigen and Sialyl-Tn-antigen was investigated by immunohistochemistry. The endolymphatic sac epithelium expressed MUC1 (both apically towards the endolymphatic sac (ES) lumen and basally towards the capillary network), MUC 16 and Tn-antigen. There was no labeling after incubation with antibodies against T-antigen, sialyl-Tn-antigen, MUC2 and MUC5B/AC. We conclude that the human endolymphatic sac epithelium expresses a number of mucin molecules, which supports the hypothesis of the sac as the primary immunological tissue structure of the inner ear, equivalent to MALT in other organs. The mucins may also play a role in the formation and continuous homeostasis of the inner ear fluids, as well as the pathogenesis of Meniere's disease.

Carbohydrate Microarrays Identify Blood Group Precursor Cryptic Epitopes as Potential Immunological Targets of Breast Cancer

Using carbohydrate microarrays, we explored potential natural ligands of antitumor monoclonal antibody HAE3. This antibody was raised against a murine mammary tumor antigen but was found to cross-react with a number of human epithelial tumors in tissues. Our carbohydrate microarray analysis reveals that HAE3 is specific for an O-glycan cryptic epitope that is normally hidden in the cores of blood group substances. Using HAE3 to screen tumor cell surface markers by flow cytometry, we found that the HAE3 glycoepitope, gp(HAE3), was highly expressed by a number of human breast cancer cell lines, including some triple-negative cancers that lack the estrogen, progesterone, and Her2/neu receptors. Taken together, we demonstrate that HAE3 recognizes a conserved cryptic glycoepitope of blood group precursors, which is nevertheless selectively expressed and surface-exposed in certain breast tumor cells. The potential of this class of O-glycan cryptic antigens in breast cancer subtyping and targeted immunotherapy warrants further investigation.

Glycoengineering of human cell lines using zinc finger nuclease gene targeting: SimpleCells with homogeneous GalNAc O-glycosylation allow isolation of the O-glycoproteome by one-step lectin affinity chromatography

Lectin affinity chromatography is a powerful technique for isolation of glycoproteins carrying a specific glycan structure of interest. However, the enormous diversity of glycans present on the cell surface, as well as on individual proteins, makes it difficult to isolate an entire glycoproteome with one or even a series of lectins. Here we present a technique to generate cell lines with homogenous truncated O-glycans using zinc finger nuclease gene targeting. Because of their simplified O-glycoproteome, the cells have been named SimpleCells. Glycoproteins from SimpleCells can be isolated in a single purification step by lectin chromatography performed on a long lectin column. This protocol describes Zinc finger nuclease gene targeting of human cells to simplify the glycoproteome, as well as lectin chromatography and isolation of glycopeptides from total cell lysates of SimpleCells.

What makes cancer stem cell markers different?

Since the cancer stem cell concept has been widely accepted, several strategies have been proposed to attack cancer stem cells (CSC). Accordingly, stem cell markers are now preferred therapeutic targets. However, the problem of tumor specificity has not disappeared but shifted to another question: how can cancer stem cells be distinguished from normal stem cells, or more specifically, how do CSC markers differ from normal stem cell markers? A hypothesis is proposed which might help to solve this problem in at least a subgroup of stem cell markers. Glycosylation may provide the key.

Microarray Glycoprofiling of CA125 improves differential diagnosis of ovarian cancer

The CA125 biomarker assay plays an important role in the diagnosis and management of primary invasive epithelial ovarian/tubal cancer (iEOC). However, a fundamental problem with CA125 is that it is not cancer-specific and may be elevated in benign gynecological conditions such as benign ovarian neoplasms and endometriosis. Aberrant O-glycosylation is an inherent and specific property of cancer cells and could potentially aid in differentiating cancer from these benign conditions, thereby improving specificity of the assay. We report on the development of a novel microarray-based platform for profiling specific aberrant glycoforms, such as Neu5Acα2,6GalNAc (STn) and GalNAc (Tn), present on CA125 (MUC16) and CA15-3 (MUC1). In a blinded cohort study of patients with an elevated CA125 levels (30-500 kU/L) and a pelvic mass from the UK Ovarian Cancer Population Study (UKOPS), we measured STn-CA125, ST-CA125 and STn-CA15-3. The combined glycoform profile was able to distinguish benign ovarian neoplasms from invasive epithelial ovarian/tubule cancer (iEOCs) with a specificity of 61.1% at 90% sensitivity. The findings suggest that microarray glycoprofiling could improve differential diagnosis and significantly reduce the number of patients elected for further testing. The approach warrants further investigation in other cancers.

Cancer vaccines and carbohydrate epitopes

Tumor-associated carbohydrate antigens (TACA) result from the aberrant glycosylation that is seen with transformation to a tumor cell. The carbohydrate antigens that have been found to be tumor-associated include the mucin related Tn, Sialyl Tn, and Thomsen-Friedenreich antigens, the blood group Lewis related Lewis(Y), Sialyl Lewis(X) and Sialyl Lewis(A), and Lewis(X) (also known as stage-specific embryonic antigen-1, SSEA-1), the glycosphingolipids Globo H and stage-specific embryonic antigen-3 (SSEA-3), the sialic acid containing glycosphingolipids, the gangliosides GD2, GD3, GM2, fucosyl GM1, and Neu5GcGM3, and polysialic acid. Recent developments have furthered our understanding of the T-independent type II response that is seen in response to carbohydrate antigens. The selection of a vaccine target antigen is based on not only the presence of the antigen in a variety of tumor tissues but also on the role this antigen plays in tumor growth and metastasis. These roles for TACAs are being elucidated. Newly acquired knowledge in understanding the T-independent immune response and in understanding the key roles that carbohydrates play in metastasis are being applied in attempts to develop an effective vaccine response to TACAs. The role of each of the above mentioned carbohydrate antigens in cancer growth and metastasis and vaccine attempts using these antigens will be described.

Role of sialic acid for platelet life span: exposure of beta-galactose results in the rapid clearance of platelets from the circulation by asialoglycoprotein receptor-expressing liver macrophages and hepatocytes

Although surface sialic acid is considered a key determinant for the survival of circulating blood cells and glycoproteins, its role in platelet circulation lifetime is not fully clarified. We show that thrombocytopenia in mice deficient in the St3gal4 sialyltransferase gene (St3Gal-IV(-/-) mice) is caused by the recognition of terminal galactose residues exposed on the platelet surface in the absence of sialylation. This results in accelerated platelet clearance by asialoglycoprotein receptor-expressing scavenger cells, a mechanism that was recently shown to induce thrombocytopenia during Streptococcus pneumoniae sepsis. We now identify platelet GPIbalpha as a major counterreceptor on ST3Gal-IV(-/-) platelets for asialoglycoprotein receptors. Moreover, we report data that establish the importance of sialylation of the von Willebrand factor in its function.

Distribution of the alphaGal- and the non-alphaGal T-antigens in the pig kidney: potential targets for rejection in pig-to-man xenotransplantation

Carbohydrate antigens, present on pig vascular endothelial cells, seem to be the prime agents responsible for graft rejection, and although genetically modified animals that express less amounts of carbohydrate antigen are available, it is still useful to decide the localization of the reactive xenoantigens in organs contemplated for xenotransplantation. Here we compare the distribution in pig kidney of antigens important in xenograft destruction, namely the Galalpha1-3Gal (alphaGal) glycans, with the localization of the T-antigen (Galbeta1-3GalNAc). The alpha-galactose-specific lectin Griffonia simplicifolia isolectin 1B4 was used to detect the Galalpha1-3Gal glycans, whereas Arachis hypogaea (PNA) lectin and a monoclonal antibody (3C9) detected T-antigen. In addition, two vascular markers (anti-caveolin-1 and anti-von Willebrand factor) served to identify vascular structures of the kidney. Both conventional fluorescence and confocal microscopy were used to distinguish lectin and immunohistochemical staining. On the basis of fluorescence signals, the results indicate that the carbohydrate antigens are heterogeneously distributed in the pig kidney. alphaGal epitopes were sparse in the capillary loops forming the glomeruli and in the capillaries surrounding the convoluted tubules, but showed stronger staining in capillaries surrounding the limbs of Henle. In addition, the brush border and basement membranes of the convoluted tubules strongly reacted with the GS1-B4-lectin. Finally, the Galalpha1-3Gal glycans were also present on epithelial cells of the large collecting tubules. Regarding the T-antigen, PNA and 3C9 reacted with different glomerular cells, whereas both reacted strongly with the endothelial cells lining the large kidney vessels. Human serum incubation of pig kidney sections, in which the alphaGal epitopes were blocked by unconjugated GS1-B4, showed staining of the same vascular structures as were obtained after incubation with the T-antigen-detecting agents. The study thus proves a complex spatial distribution of carbohydrate antigens relevant for xenotransplantation of pig kidney.

A serial lectin approach to the mucin-typeO-glycoproteome ofDrosophila melanogaster S2 cells

Identification of mucin-type O-glycosylated proteins with known functions in model organisms like Drosophila could provide keys to elucidate functions of the O-glycan moiety and proteomic analyses of O-glycoproteins in higher eukaryotes remain a challenge due to structural heterogeneity and a lack of efficient tools for their specific isolation. Here we report a strategy to evaluate the O-glycosylation potential of the embryonal hemocyte-like Drosophila Schneider 2 (S2) cell line by expression of recombinant glycosylation probes derived from tandem repeats of the human mucin MUC1 or of the Drosophila salivary gland protein Sgs1. We obtained evidence that mucin-type O-glycosylation in S2 cells grown under serum-free conditions is restricted to the Tn-antigen (GalNAcalpha-Ser/Thr) and the T-antigen (Galbeta1-3GalNAcalpha-Ser/Thr) and this structural homogeneity enables unique glycoproteomic strategies. We present a label-free strategy for the isolation, profiling and analysis of O-glycosylated proteins consisting of serial lectin affinity capture, 2-DE-based glycoprotein analysis by O-glycan specific mAbs and protein identification by MALDI-MS. Protein identity and O-glycosylation was confirmed by ESI-MS/MS with detection of diagnostic sugar oxonium-ion fragments. Using this strategy, we established 2-D reference maps and identified 21 secreted and intracellular mucin-type O-glycoproteins. Our results show that Drosophila S2 cells express O-glycoproteins involved in a wide range of biological functions including proteins of the extracellular matrix (Laminin gamma-chain, Peroxidasin and Glutactin), pathogen recognition proteins (Gnbp1), stress response proteins (Glycoprotein 93), secreted proteases (Matrix-metalloprotease 1 and various trypsin-like serine proteases), protease inhibitors (Serpin 27 A) and proteins of unknown function.

Biological significance of cancer-associated sialyl-Tn antigen: modulation of malignant phenotype in gastric carcinoma cells

The activation of an abnormal glycosylation pathway in cancer cells leads to the formation of the sialyl-Tn antigen, blocking regular carbohydrate chain elongation. Sialyl-Tn antigen is rarely expressed in normal tissues but is aberrantly expressed in a variety of carcinomas, where it constitutes a marker of poor prognosis. Although the clinical significance of sialyl-Tn is well characterized, a functional role for this glycan and its contribution to cancer progression remain to be elucidated. This study evaluates the capability of sialyl-Tn to modify processes like cell cycle, apoptosis, actin cytoskeleton dynamics, adhesion and motility on ECM components, cell-cell aggregation and invasion. De-novo expression of sialyl-Tn leads to major morphological and cell behavior alterations in gastric carcinoma cells which were reverted by specific antibody blockage. Sialyl-Tn antigen is able to modulate a malignant phenotype inducing a more aggressive cell behavior, such as decreased cell-cell aggregation and increased ECM adhesion, migration and invasion.

Expression of aberrantly glycosylated tumor mucin-1 on human DC after transduction with a fiber-modified adenoviral vector

BACKGROUND

DC-presenting tumor Ag are currently being developed to be used as a vaccine in human cancer immunotherapy. To increase chances for successful therapy it is important to deliver full-length tumor Ag instead of loading single peptides.

METHODS

In this study we used a fiber-modified adenoviral vector (rAd5F35) containing full-length tumor Ag cDNA to transduce human monocyte (Mo)-derived DC in vitro. Cells were efficiently transduced and survived for at least 3 days after adenoviral transduction. Phenotype and function after maturation of Mo-DC were not impaired by infection with adenovirus particles. Expression of the tumor-associated Ag mucin-1 (MUC1) was detected using MAb defining different MUC1 glycoforms.

RESULTS

Non-transduced mature Mo-DC express endogenous MUC1 with normal glycosylation. After transduction with the rAd5F35-MUC1 adenoviral vector, Mo-DC also expressed MUC1 with tumor-associated glycosylation (Tn and T glycoforms), although no changes in mRNA levels of relevant glycosyltransferases could be demonstrated.

DISCUSSION

The presence of aberrantly glycosylated MUC1 may influence Ag presentation of the tumor glycoforms of MUC1 to immune cells, affecting tumor cell killing. These findings could be highly relevant to developing strategies for cancer immunotherapy based on DC vaccines using MUC1 as tumor Ag.

Immune response to Thomsen-Friedenreich disaccharide and glycan engineering

Cancer-associated mucins show frequent alterations of their oligosaccharide chain profile, with a switch to unmask normally cryptic O-glycan backbone and core regions. Epithelial tumour cells typically show overexpression of the uncovered Gal(beta)1-3GalNAc(alpha)-O-Ser/Thr (Core 1) structure, known as the T antigen or the Thomsen-Friedenreich antigen, the oligosaccharide chain of which is called the Thomsen-Friedenreich disaccharide (TFD). T antigen expression has been associated with immunosuppression, metastasis dissemination, and the proliferation of cancer cells. Several different strategies have been used to trigger a specific immune response to TFD. Natural T antigen and synthetic TFD residues have low immunodominance. In the T antigen, flexibility of the glycosidic bond reduces the immunogenicity of the sugar residue. Enhanced rigidity should favour certain glycan conformations and thereby improve TFD immunotargeting. We propose the term 'glycan engineering' for this approach. Such engineering of TFD should reduce the flexibility of its glycan moiety and thereby enhance its stability, rigidity and immunogenicity.

Distribution of HPV infection and tumour markers in cervical intraepithelial neoplasia from cone biopsies of Mozambican women

AIMS

To evaluate human papillomavirus (HPV) infection in whole cervical cone specimens with cervical intraepithelial neoplasia (CIN). In addition, to evaluate the relation between the presence of CIN lesions and HPV infection and the expression of Ki-67, p53, cytokeratins, Gp230 glycoprotein, and simple mucin-type carbohydrates.

METHODS

Cervical cone specimens from five patients with CIN were studied. For each specimen, serial sections encompassing the whole cone were collected (52 samples). HPV infection and HPV types were detected by the polymerase chain reaction and enzyme immunoassay. The expression of Ki-67, p53, cytokeratins, Gp230, and simple mucin-type carbohydrates was examined immunohistochemically.

RESULTS

All cases showed high risk HPV types, namely types 16, 33, 35, and 58. Four of the five patients were infected by multiple viral types. HPV-58 was always seen in CIN III, whereas HPV-35 was more frequent in CIN I. The expression of Ki-67 and p53 was higher in CIN III lesions. The expression of cytokeratins 8 and 17 showed complete or almost complete overlap with CIN III. Altered expression of Gp230, Tn, and sialyl-T was often seen in all grades of CIN.

CONCLUSIONS

When whole cervical cone specimens are evaluated the rate of multiple HPV infection is very high. The expression of cytokeratins 8 and 17 is a useful marker of CIN III.

Thomsen-Friedenreich antigen expression in gastric carcinomas is associated with MUC1 mucin VNTR polymorphism

Aberrant glycosylation of mucins is a common phenomenon associated with oncogenic transformation. We investigated the association between expression of the tumor-associated antigens T, Tn, and sialyl-Tn and polymorphism in the length of the MUC1 mucin tandem repeat in a series of gastric carcinomas. We further evaluated the relevance of MUC1 tandem repeat length on the expression of these tumor-associated carbohydrate antigens (TACAs) using a gastric carcinoma cell line model expressing recombinant MUC1 constructs carrying 0, 3, 9, and 42 repeats. Gastric carcinomas showed a high prevalence of Tn and sialyl-Tn antigens, whereas T antigen was less frequently expressed. The expression of T antigen was significantly higher in gastric carcinomas from patients homozygous for MUC1 large tandem repeat alleles. No significant associations were found for Tn and sialyl-Tn antigens. This novel association was reinforced by the gastric carcinoma cell line model experiments, where de novo expression of T antigen was detected in clones transfected with larger VNTR regions. Our results indicate that polymorphism in the MUC1 tandem repeat influences the expression of TACAs in gastric cancer cells and may therefore allow the identification of subgroups of patients that develop more aggressive tumors expressing T antigen.

Role of the human ST6GalNAc-I and ST6GalNAc-II in the synthesis of the cancer-associated sialyl-Tn antigen

The Sialyl-Tn antigen (Neu5Acalpha2-6GalNAc-O-Ser/Thr) is highly expressed in several human carcinomas and is associated with carcinoma aggressiveness and poor prognosis. We characterized two human sialyltransferases, CMP-Neu5Ac:GalNAc-R alpha2,6-sialyltransferase (ST6GalNAc)-I and ST6GalNAc-II, that are candidate enzymes for Sialyl-Tn synthases. We expressed soluble recombinant hST6GalNAc-I and hST6GalNAc-II and characterized the substrate specificity of both enzymes toward a panel of glycopeptides, glycoproteins, and other synthetic glycoconjugates. The recombinant ST6GalNAc-I and ST6GalNAc-II showed similar substrate specificity toward glycoproteins and GalNAcalpha-O-Ser/Thr glycopeptides, such as glycopeptides derived from the MUC2 mucin and the HIVgp120. We also observed that the amino acid sequence of the acceptor glycopeptide contributes to the in vitro substrate specificity of both enzymes. We additionally established a gastric cell line, MKN45, stably transfected with the full length of either ST6GalNAc-I or ST6GalNAc-II and evaluated the carbohydrate antigens expression profile induced by each enzyme. MKN45 transfected with ST6GalNAc-I showed high expression of Sialyl-Tn, whereas MKN45 transfected with ST6GalNAc-II showed the biosynthesis of the Sialyl-6T structure [Galbeta1-3 (Neu5Acalpha2-6)GalNAc-O-Ser/Thr]. In conclusion, although both enzymes show similar in vitro activities when Tn antigen alone is available, whenever both Tn and T antigens are present, ST6GalNAc-I acts preferentially on Tn antigen, whereas the ST6GalNAc-II acts preferentially on T antigen. Our results show that ST6GalNAc-I is the major Sialyl-Tn synthase and strongly support the hypothesis that the expression of the Sialyl-Tn antigen in cancer cells is due to ST6GalNAc-I activity.

Multivalent scFv Display of Phagemid Repertoires for the Selection of Carbohydrate-specific Antibodies and its Application to the Thomsen–Friedenreich Antigen

The Thomsen-Friedenreich disaccharide (TF) is a promising target antigen for tumor immunotherapy, since it is almost exclusively expressed in carcinoma tissues. The TF-specific antibodies generated so far are IgMs of mouse origin with limited therapeutic potential. Phage-displayed scFv repertoires are an established source for recombinant antibodies; however, we were unable to identify scFvs binding to TF when applying libraries in the standard monovalent display format of phagemid systems. Here, we report on the successful selection of TF-specific antibody fragments using a multivalent scFv phagemid library format based on shortened linkers (one amino acid residue). The libraries were constructed from mice immunized with asialoglycophorin and selected using TF displayed on two different carrier molecules in combination with the proteolytically cleavable helper phage KM13. All isolated clones encoded the same framework genes and the same complementarity-determining regions. After affinity maturation only scFv with the founder sequence were selected from secondary repertoires. This indicates a very narrow sequence window for TF-specific antibodies. Investigating other linker-length formats revealed a clear inverse correlation between linker length and binding activity both as soluble proteins and displayed on phages. The highest affinity was obtained with the tetrameric format. The selected scFv was specific for TF on various carrier molecules and tumor cells and performed well in ELISA and immunohistochemistry. We postulate that scFv phagemid library formats with short linkers (i.e. multimeric scFvs) may, in general, be advantageous in selections for the generation of scFvs against carbohydrate epitopes or other epitopes associated with low intrinsic affinity per binding site), and expect that they will be superior in applications for diagnosis or therapy.

Polypeptide GalNAc-transferases, ST6GalNAc-transferase I, and ST3Gal-transferase I expression in gastric carcinoma cell lines

Mucin O-glycosylation in cancer is characterized by aberrant expression of immature carbohydrate structures leading to exposure of simple mucin-type carbohydrate antigens and peptide epitopes. Glycosyltransferases controlling the initial steps of mucin O-glycosylation are responsible for the altered glycosylation observed in cancer. We studied the expression in gastric cell lines of six UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GalNAc-T1, T2, T3, T4, T6, T11) that catalyze the initial key step in the regulation of mucin O-glycosylation, the transfer of GalNAc from UDP-GalNAc to serine and threonine residues. We also studied the expression of ST6GalNAc-I, the enzyme responsible for the synthesis of Sialyl-Tn antigen (NeuAcalpha2,6GalNAc) and the ST3Gal-I, the enzyme responsible for the synthesis of Sialyl-T antigen (NeuAcalpha2,3Galbeta1,3GalNAc). This study was done using specific monoclonal antibodies, enzymatic assays, and RT-PCR. Our results showed that GalNAc-T1, -T2, and -T3 have an ubiquitous expression in all gastric cell lines, whereas GalNAc-T4, -T6, and -T11 show a restricted expression pattern. The immunoreactivity with MAb VU-2-G7 suggests that, apart from GalNAc-T4, another GalNAc transferase is involved in the glycosylation of the Thr in the PDTR region of the MUC1 tandem repeat. The expression of ST3Gal-I correlates with the expression of the Sialyl-T antigen in gastric cell lines and in the control cell lines studied. The expression of ST6GalNAc-I is low in gastric cell lines, in accordance with the low/absent expression of the Sialyl-Tn antigen.

Influence of terminal residue on adjacent disaccharide immunogenicity

Aberrant O-glycosylation of cell surface mucin antigens is characteristic of epithelial cancer cells. For example, Thomsen-Friedenreich disaccharide (TFD) is a chemically well-defined carbohydrate antigen with a documented link to malignancy. There have been many attempts to improve immune response to carbohydrate antigens, for use in immunotherapy. As part of an alternative strategy to improve carbohydrate immunogenicity, we studied the influence of terminal benzyl (Bzl) or p-nitrophenyl (pNP) residue on immunogenicity of adjacent TFD. Mice immunized with keyhole limpets hemocyanin-TFD (KLH-TFD), KLH-TFD(alpha)Bzl, or KLH-TFD(alpha)pNP produced anti-KLH antibodies, which were analyzed by enzyme-linked immunosorbent assay (ELISA). KLH-TFD did not give significant anti-TFD antibody titer, confirming the poor immunogenicity of TFD. Immunization with KLH-TFD(alpha)Bzl and KLH-TFD(alpha)pNP raised antibody titers against TFD(alpha)Bzl and TFD(alpha)pNP, respectively. KLH-TFD(alpha)Bzl also gave higher anti-TFD antibody response, whereas KLH-TFD(alpha)pNP did not, indicating that terminal Bzl residue improves immune response to adjacent carbohydrate. Analysis of anti-TFD(alpha)Bzl or anti-TFD(alpha)pNP IgG antibodies by competitive ELISA, using carbohydrate-related antigens as inhibitors, demonstrated their high specificity to their respective antigens. Anti-TFD(alpha)pNP antibody was not inhibited by TFD, but was significantly inhibited by GalNAc(alpha)pNP. The fact that p-nitrophenol (pNPol) has more competitive ability that GalNAc indicates that terminal polar residue is the main target antigen. In contrast, anti-TFD(alpha)Bzl antibody was inhibited to a similar degree by GalNAc(alpha)Bzl and TFD, confirming the carbohydrate recognition by antibodies yielded by terminal non-polar modification of the immunogen.

Human platelets express gangliosides with LKE activity and ABH blood group activity

BACKGROUND

Platelets express several neutral glycosphingolipids with ABH and P blood group activity that may play a role in infectious, autoimmune, and alloimmune thrombocytopenia. In RBCs, sialylated glycosphingolipids or gangliosides with blood group activity have also been reported. To determine whether similar antigens are expressed by platelets, the total platelet ganglioside fraction was isolated and screened for blood-group-active glycosphingolipids.

STUDY DESIGN AND METHODS

Platelet gangliosides were isolated by organic extraction, base hydrolysis, anion exchange, silicic acid, and high-performance liquid chromatography. Gangliosides were identified and characterized by high-performance thin-layer chromatography-immunostaining with blood group-specific MoAbs and glycosidase digestion.

RESULTS

Group A, but not group O, platelets express five gangliosides with group A activity. Of five A MoAbs and lectins examined, only MoAbs Birma-1 and MHO4 recognized all five sialyl A bands. The sialyl A bands were sensitive to endoglycoceramidase and neuraminidase. One sialyl A band may represent a branched ganglioside with sialyl-I and group A activity. Platelets also express an LKE-active ganglioside consistent with sialyl-galactosylgloboside.

CONCLUSION

In addition to sialyl-iI and sialyl-Le(x) gangliosides, group A platelets express gangliosides with LKE activity and group A activity. Like RBCs, group A-active gangliosides may act as alloantigens and autoantigens to naturally occurring isohemagglutinins.

Analysis of IgA1 O-glycans in IgA nephropathy by fluorophore-assisted carbohydrate electrophoresis

Abnormal O-glycosylation of IgA1 may contribute to pathogenic mechanisms in IgA nephropathy (IgAN). Observations of altered lectin binding to IgA1 in IgAN suggest that the O-glycan chains may be undergalactosylated, but precise structural definition of the defect has proved technically difficult, and it remains unconfirmed. This is the first study using fluorophore-assisted carbohydrate electrophoresis (FACE) to analyze IgA1 O-glycans in IgAN and controls. IgA1 was purified from serum, and the intact O-glycans were released by hydrazinolysis at 60 degrees C. After re-N-acetylation, the glycans were fluorophore-labeled and separated by polyacrylamide gel electrophoresis. Sequential exoglycosidase digestions of IgA1 allowed identification of the different O-glycan bands on FACE gels, and their relative frequencies in IgA1 samples were measured by ultraviolet densitometry. Lectin binding of the IgA1 samples was also measured. In some patients with IgAN, FACE analysis demonstrated a significant increase in the percentage of IgA1 O-glycan chains consisting of single N-acetyl galactosamine (GalNAc) units rather than the more usual galactosylated and sialylated forms. This finding was confirmed using both desialylated IgA1 and enzymatically released O-glycans. Good correlation was also found between O-glycan agalactosylation on FACE analysis and IgA1 lectin binding in IgAN, supporting the value of lectins as tools for detection of this abnormality. This is the first study in which all of the predicted O-glycan forms of IgA1 have been analyzed simultaneously, and demonstrates that in IgAN, the IgA1 Oglycan chains are truncated, with increased terminal GalNAc. This abnormality has the potential to significantly affect IgA1 behavior and handling with pathogenic consequences in IgAN.

Blood-group-related carbohydrates are expressed in organotypic cultures of human skin and oral mucosa

Cellular maturation and migration are usually associated with changes in cell-surface carbohydrates, but the relationship between these changes and cell behaviour is at present largely unknown. To investigate whether an organotypic culture system can be used as an in vitro model to study the function of cell-surface carbohydrates, we established organotypic cultures of skin and buccal mucosa. In these cultures, keratinocytes are grown at the air-liquid interface on a supporting matrix consisting of homologous fibroblasts embedded in a collagen type I gel. We examined the expression of blood-group-related carbohydrate structures, including Lewis x, sialylated Lewis x, Lewis y, Lewis a, and Lewis b, on the surface of epithelial cells in the cultures. We compared the results with the expression of more well-established markers, including cytokeratins, integrins, bullous pemphigoid antigen and laminin, in the same cultures. The organotypic skin and oral mucosa cultures showed a histological differentiation pattern analogous to that of normal skin and buccal mucosa, and a tissue-specific expression of carbohydrate structures and cytokeratins. However, both types of organotypic cultures also expressed markers which are normally seen during wound healing, including Lewis y, cytokeratin 16, and cytokeratin 19. We conclude that the organotypic cultures of oral mucosa and skin are suitable models for future studies of the function of cell-surface carbohydrates, although the expression of wound healing markers has to be taken into consideration.

Altered expression of sialylated carbohydrate antigens in HT29 colonic carcinoma cells

To determine whether cell growth conditions impacted carbohydrate expression, HT29 cells were gradually transferred from a conventional glucose-containing media to a glucose-free galactose containing media. Indirect immunofluorescence on acetone fixed cells showed increased expression of sialyl Lewis A antigen (CA19-9), sialyl Lewis C (DUPAN2) and Tn/sialyl-Tn on the surface of HT29 cells grown in the glucose-free galactose containing media compared to those grown in the glucose containing media. Sialyltransferases responsible for the synthesis for these sialylated epitopes were Increased in the galactose-fed HT29 cells. Media overlying the cells was subjected to isopycnic ultracentrifugation in cesium chloride and the fractions derived from both glucose and galactose media with equivalent buoyant densities of 1.56 g/L, which are predicted to contain mucin glycoforms, were further separated by HPLC using a Mono-Q anion exchange column. The chromatograph of eluent from the sample derived from the cells growing in the galactose containing media showed an increased peak that reacted with the anti-sialyl Lewis A antibody, CA19-9. These results show that alteration of in vitro culture conditions may cause HT29 colonic carcinoma cells to alter the expression of sialylated carbohydrates.

Salivary gland carcinomas: prognostic significance of simple mucin-type carbohydrate antigens

The prognosis of salivary gland carcinomas is difficult to assess. Simple mucin-type carbohydrates (T and sialosyl-T antigens, Tn and sialosyl-Tn antigens) have been shown to be of value in predicting prognosis for carcinomas in other locations. We studied the prognostic significance of the expression of these structures in a retrospective study of 133 patients with salivary gland carcinomas, using immunohistochemistry and a panel of well-defined monoclonal antibodies (MAbs) on formalin-fixed paraffin-embedded tissues. Sialosyl-Tn, T and sialosyl-T antigens were not correlated with prognosis. Univariate analyses showed no overall difference in survival or locoregional control between patients with Tn-positive and patients with Tn-negative tumours, but indicated that expression of the Tn antigen was associated with early locoregional recurrences and deaths. Tn was, however, not an independent prognostic factor by multivariate regression analysis.

Development and characterization of an antibody directed to an alpha-N-acetyl-D-galactosamine glycosylated MUC2 peptide

In an attempt to raise anti-Tn antibodies, an alpha-N-acetyl-D-galactosamine glycosylated peptide based on the tandem repeat of the intestinal mucin MUC2 was used as an immunogen. The MUC2 peptide (PTTTPISTTTMVTPTPTPTC) was glycosylated in vitro using concentrated alpha-N-acetylgalactosaminyltransferases activity from porcine submaxillary glands which resulted in the incorporation of 8-9 mol of Ga/NAc. Rabbits and mice developed specific anti-MUC2-GalNAc glycopeptide antibodies and no detectable anti-Tn antibodies. Anti-glycopeptide antibodies did not show reactivity with the unglycosylated MUC2 peptide or with other GalNAc glycosylated peptides. A mouse monoclonal antibody (PMH1) representative of the observed immune response was generated and its immunohistological reactivity analysed in normal tissues. PMH1 reacted similarly to other anti-MUC2 peptide antibodies. However, in some cells the staining was not restricted to the supranuclear area but extended to the entire cytoplasm. In addition, PMH1 reacted with purified colonic mucin by Western blot analysis suggesting that PMH1 reacted with some glycoforms of MUC2. The present work presents a useful approach for development of anti-mucin antibodies directed to different glycoforms of individual mucins.

Expression of sialosyl-T and disialosyl-T antigens in erythroid cells

Expression of T, sialosyl-T and disialosyl-T antigens on normal blood and bone marrow cells as well as transformed cells was examined using specific monoclonal antibodies and multidimensional flow cytometry. Both anti-sialosyl-T (QSH1) and anti-disialosyl-T (QSH2) monoclonal antibodies aggregated erythrocytes. The anti-disialosyl-T antibody was specific for the erythroid lineage and did not react with neutrophils, monocytes or T-lymphocytes, while the anti-sialosyl-T antibody reacted with erythroid cells and a subset of T-lymphocytes. The developing erythroid cells in bone marrow showed coordinate expression of glycophorin A and the two carbohydrate chains, sialosyl-T and disialosyl-T. Analysis of neoplastic cells showed that the anti-disialosyl-T antibody only reacted with glycophorin A-positive blasts from erythroleukemia (FAB M6) patients (4/4) and one patient with chronic myeloid leukemia in erythroblastic transformation (CMLET). Leukemic blasts from these patients demonstrated coordinate quantitative expression of glycophorin A and disialosyl-T. The anti-sialosyl-T antibody reacted with glycophorin A-positive blasts from FAB M6 patients (4/4) and one CMLET patient; however, the antibody also reacted with glycophorin A-negative blasts from one FAB M6 and the one CMLET patients and transformed cells from other types of leukemia. The anti-T monoclonal antibody (HH8) did not react with any of the other cells tested. These results indicate that glycophorin A and disialosyl-T expression are tightly linked during normal erythroid development and erythroid leukemogenesis.

Human monoclonal antibodies specific for the tumour associated Thomsen-Friedenreich antigen

Five hybridomas producing human monoclonal antibodies (MAbs) of IgA and IgM isotypes reacting with the tumour associated TF antigen were generated after in vitro immunisation or antigen specific isolation of normal peripheral blood B cells using asialoglycophorin, a TF containing antigen. All 5 antibodies produced by the hybridomas bound strongly to asialoglycophorin and to synthetic glycoprotein containing the TF-epitope, with preference to the beta form (Galb1-3GalNAc-beta-O-CETE-BSA) as compared to the alpha form (Galbl-3GalNAc-alpha-O-APE-HSA) in ELISA. Flow cytometry analysis revealed binding to carcinoma cell lines of different origin such as breast, colon, pancreas, ovary, bladder, lung and, in addition, to some tumour cell lines of haematopoietic origin. Immunohistochemical analysis of tumour tissues revealed staining patterns typical for mucins, and the antibodies were found to bind to glycoproteins among the MUC-1 positive high m.w. fraction shed from a TF antigen positive ovarian carcinoma cell line.

Imparting exquisite specificity to peanut agglutinin for the tumor-associated Thomsen-Friedenreich antigen by redesign of its combining site

Lectins from legumes constitute one of the most thoroughly studied families of proteins, yet the absence of a rigorous framework to explain their carbohydrate binding specificities appears to have prevented a rational approach to alter their ligand binding activity. Studies reported here deal with the redesign of the recognition propensity of peanut agglutinin (PNA), an important member of the family. PNA is extensively used as a tool for recognition of the tumor-associated Thomsen-Friedenrich antigen (T-antigen; Galbeta1-3GalNAc) on the surfaces of malignant cells and immature thymocytes. PNA also recognizes N-acetyllactosamine (LacNAc; Galbeta1-4GlcNAc), which is present at the termini of several cell-surface glycoproteins. The crystal structure of the PNA-lactose complex revealed, in addition to the expected interactions with the residues constituting the binding site, the presence of leucine 212 at a position close enough to be in steric contact with the acetamido group on LacNAc. We report here two leucine mutants, one to asparagine (L212N) and the other to alanine (L212A), that exhibit distinct preference for T-antigen and N-acetyllactosamine, respectively. Carbohydrate binding studies reveal that mutant L212N does not recognize LacNAc at high concentrations, thus making it an exquisitely specific cell-surface marker compared with its wild-type counterpart.

Thomsen-Friedenreich-related carbohydrate antigens in normal adult human tissues: a systematic and comparative study

A broad variety of normal human tissues were examined for the expression of Thomsen-Friedenreich (TF)-related histo-blood group antigens, TF (Gal beta 1-3GalNAc alpha 1-R), Tn (TF precursor, GalNAc alpha 1-R), sialosyl-Tn (NeuAc alpha 2-6GalNAc alpha 1-R), considered to be useful in cancer diagnosis and immunotherapy, and sialosyl-TF, the cryptic form of TF. These antigens or, more correctly, glycotopes, were determined by immunohistochemistry with at least two monoclonal antibodies (mAbs) each (except sialosyl-TF) as well as by lectin histochemistry. For a better dissection of sialosyl-TF and TF glycotopes, tissue sections were pretreated with galactose oxidase or the galactose oxidase-Schiff sequence. Staining with mAbs appeared to be more restricted than with the lectins used. Distribution patterns among normal epithelia were different for all four antigens. These antigens were also detected in some non-epithelial tissues. They can be classified in the following sequence according to the frequency of their occurrence in normal tissues: sialosyl-TF > > sialosyl-Tn > Tn > TF. Most of the positively staining sites for TF, Tn, and sialosyl-Tn are located in immunologically privileged areas. The complex results obtained with anti-TF mAbs (after treatment of the tissue sections with sialidase from Vibrio cholerae) and the lectins amaranthin and jacalin revealed a differential distribution of the subtypes of sialosyl-TF [NeuAc alpha 2-3Gal beta 1-3GalNAc alpha 1-R and Gal beta 1-3 (NeuAc alpha 2-6)GalNAc alpha 1-R] in normal human tissues. From our data it can be inferred that TF, Tn, and sialosyl-Tn are promising targets for a cancer vaccine.

Constitutively hyposialylated human T-lymphocyte clones in the Tn-syndrome: binding characteristics of plant and animal lectins

Previously, beta 1,3-galactosyltransferase-deficient (Tn+) and normal (TF+) T-lymphocyte clones have been established from a patient suffering from Tn-syndrome [Thurnher et al. (1992) Eur J Immunol 22: 1835-42]. Tn+ T lymphocytes express only Tn antigen GalNAc alpha 1-O-R) while other O-glycan structures such as sialosyl-Tn (Neu5Ac alpha 2,6GalNAc alpha 1-O-R) or TF (Gal beta 1-3GalNAc alpha 1-O-R) antigens are absent from these cells as shown by flow cytometry using specific mABs for TF and sialosyl-Tn antigen, respectively. Normal T lymphocytes express the TF antigen and derivatives thereof. The surface glycans of Tn+ and TF+ cells were then analysed by flow cytometry using the following sialic acid-binding lectins: Amaranthus caudatus (ACA), Maackia amurensis (MAA), Limax flavus (LFA), Sambucus nigra (SNA) and Triticum vulgare (WGA). Equal and weak binding of MAA and SNA to both TF+ and Tn+ cells was found. WGA, LFA and ACA bound more strongly to TF+ cells than to Tn+ cells. Binding of ACA to TF+ cells was enhanced after sialidase treatment. To investigate the possible biological consequences of hyposialylation, binding of three sialic acid-dependent adhesion molecules to Tn+ and TF+ cells was estimated using radiolabelled Fc-chimeras of sialoadhesin (Sn), myelin-associated glycoprotein (MAG) and CD22. Equal and strong binding of human CD22 to both TF+ and Tn+ cells was found. Whereas binding of Sn and MAG to TF+ cells was strong (100%), binding to Tn+ cells amounted only to 33% (Sn) and 19% (MAG). These results indicate that the in vivo interactions of T lymphocytes in the Tn syndrome with CD22 are not likely to be affected, whereas adhesion mediated by Sn or MAG could be strongly reduced.

A novel mode of carbohydrate recognition in jacalin, a Moraceae plant lectin with a beta-prism fold

Jacalin, a tetrameric two-chain lectin (66,000 Mr) from jackfruit seeds, is highly specific for the tumour associated T-antigenic disaccharide. The crystal structure of jacalin with methyl-alpha-D-galactose reveals that each subunit has a three-fold symmetric beta-prism fold made up of three four-stranded beta-sheets. The lectin exhibits a novel carbohydrate-binding site involving the N terminus of the alpha-chain which is generated through a post-translational modification involving proteolysis, the first known instance where such a modification has been used to confer carbohydrate specificity. This new lectin fold may be characteristic of the Moraceae plant family. The structure provides an explanation for the relative affinities of the lectin for galactose derivatives and provides insights into the structural basis of its T-antigen specificity.

A lysosomal cysteine proteinase from Dictyostelium discoideum contains N-acetylglucosamine-1-phosphate bound to serine but not mannose-6-phosphate on N-linked oligosaccharides

Previous studies showed that vegetative Dictyostelium discoideum cells make a lysosomal proteinase, proteinase-1, that contains multiple GlcNAc-alpha-1-P residues in phosphodiester linkage to serine. We extended these studies and, in contrast to earlier reports, found that proteinase-1 contains 7.5 mol of Fuc, 8 mol of Man, 2 mol of Xyl, and 30 mol of GlcNAc per calculated mol of protein but no Man-6-P residues. The protein binds to concanavalin A and wheat germ agglutinin lectin affinity columns, and PNGase-F digestion released most of the mannose and xylose but little of the GlcNAc. beta-Elimination under reducing conditions released only GlcNAc-alpha-1-P. There was no evidence for the release of disaccharides or of fucitol. A rabbit antiserum and monoclonal antibodies prepared against proteinase-1 recognize GlcNAc-alpha-1-P residues in immunoblots and are specifically competed by UDP-GlcNAc or GlcNAc-alpha-1-P. Use of other monoclonal antibodies showed the presence of mannose-6-sulfate on N-linked sugar chains, and alpha-fucose residues on the protein. Thus, proteinase-1 has at least two types of modifications: Glc NAc-alpha-1-P-Ser, which we call phosphoglycosylation, and N-linked oligosaccharides. This is the first purified lysosomal enzyme in Dictyostelium that does not contain Man-6-P residues. The GlcNAc-alpha-1-P-specific antibodies also recognize a group of developmentally regulated proteins, especially enriched in vegetative cells. Some of them are also lysosomal cysteine proteinases, and all bind to the GlcNAc-alpha-1-P-specific monoclonal antibody but not to the mammalian CI-Man-6-P receptor. Conversely, lysosomal enzymes that have Man-6-P do not bind to the GlcNAc-alpha-1-P-specific antibody. An exception to this is beta-N-acetylglucosaminidase, where 15% of the activity binds to this antibody. Thus, there appear to be two sets of lysosomal enzymes with distinct post-translational modifications.

Expression of Thomsen-Friedenreich-related antigens in primary and metastatic colorectal carcinomas. A reevaluation

BACKGROUND

Expression of the pancarcinoma Thomsen-Friedenreich (TF) carbohydrate antigen or, more correctly, hapten, in colorectal carcinomas is not generally agreed on. Furthermore, its suggested role in liver metastasis so far has not been substantiated by direct immunohistochemical evidence.

METHODS

Cryostat sections from 52 primary tumors (20 with adjacent transitional mucosa), 22 liver metastases of colorectal carcinomas, and 17 samples of normal mucosae were examined immunohistologically with a panel of at least two monoclonal antibodies (mAbs) each to TF, to its precursor, Tn, and to sialosyl-Tn, among them two newly developed anti-TF mAbs.

RESULTS

Of the primary colorectal carcinomas, 60% expressed TF. Staining was more intense with TF-alpha/beta-reactive than with exclusively TF-alpha- or TF-beta-reactive mAbs. Normal and transitional mucosae were negative. Liver metastases were positive for TF in a significantly higher percentage of cases (91%) than primary carcinomas. Patients with TF-positive primary tumors had a significantly higher risk to develop liver metastases compared with patients with TF-negative tumors (57% vs. 14%, respectively). Tn and sialosyl-Tn were expressed concomitantly in most primary (85%) and metastatic (95%) colorectal carcinomas. These antigens also were detected in transitional mucosae (Tn in 25%, sialosyl-Tn in 55% of cases). Normal mucosae were negative.

CONCLUSIONS

These results prove unequivocally the presence of exposed TF epitopes in a majority of colorectal carcinomas in which both anomers of TF are expressed. These data further suggest that TF favors liver metastasis and that its expression in primary colorectal carcinomas is a significant risk factor for the development of liver metastasis.

The Thomsen-Friedenreich (T) simple mucin-type carbohydrate antigen in salivary gland carcinomas

The simple mucin-type T (Thomsen-Friedenreich) antigen is a marker of carcinomas, and has been related to aggressiveness of malignant tumours. We studied the expression of T, sialosyl-T, A and H blood group antigens in salivary gland carcinomas. The aim was to study whether the tumours, based on the expression of these structures, could be divided into new diagnostic groups that may later show prognostic significance. Formalin fixed paraffin-embedded tissue sections from 77 salivary gland carcinomas of different histological types were studied using immunohistology and monoclonal antibodies (MAbs). Fresh frozen tissue was examined in 30 of the cases. Frozen sections were superior to paraffin sections in demonstrating T and H antigens. Aberrant glycosylation with accumulation of T (in cytoplasm) and sialosyl-T antigens (in cytoplasm, membrane and mucin) was found in all tumour types except acinic cell carcinomas. In carcinomas in pleomorphic adenomas (CinPA) the effect of fixation was minimal and T antigen location was different. In carcinomas with myoepithelial cell (MEC) participation, the MECs had retained a normal glycosylation pattern. H antigen was expressed in all tumour types, except acinic cell carcinomas and CinPA. A antigen was expressed in all tumour types from blood group A patients, except in CinPA. The expression of T, sialosyl-T, H and A antigens in relation to differentiation grade varied with tumour type in poorly differentiated areas. High and moderate differentiated areas were always stained, whereas poorly differentiated areas in some tumour types expressed T and sialosyl-T antigens and others did not. The accumulation versus lack of expression of the investigated structures in poorly differentiated areas of the tumours may be of prognostic significance.

Thomsen-Friedenreich (T) antigen as marker of myoepithelial and basal cells in the parotid gland, pleomorphic adenomas and adenoid cystic carcinomas. An immunohistological comparison between T and sialosyl-T antigens, alpha-smooth muscle actin and cytokeratin 14

Controversy centres on the role and identification of myoepithelial (MEC) and basal cells in salivary gland tumours, and recent studies suggest that both basal cells and myoepithelial cells participate in the formation of salivary gland tumours. We have correlated the expression of different well-known markers of normal MEC/basal cells (i.e. alpha-smooth muscle actin and cytokeratin 14) with T (Thomsen-Friedenreich) antigen and its sialylated derivative: sialosyl-T antigen,) in 17 normal parotid glands and in two tumour types with MEC participation (i.e pleomorphic adenomas (PA) and adenoid cystic carcinomas (ACC)) using immunohistology with well-defined monoclonal antibodies (MAbs). Paraffin-embedded/fresh frozen tissue sections were studied from 33/17 patients with PA and 15/7 patients with ACC. In normal parotid tissue coexpression of alpha-smooth muscle actin, cytokeratin 14, T and sialosyl-T antigens was found in all MEC and in some of the basal cells lining striated ducts. The remaining basal cells exclusively expressed cytokeratin 14, T and sialosyl-T antigens. In the tumours, cells believed to be modified myoepithelial cells showed two different staining patterns: 1) Coexpression of alpha-smooth muscle actin, cytokeratin 14, T and sialosyl-T antigens, and 2) Coexpression of cytokeratin 14, T and sialosyl-T antigens, but no alpha-smooth muscle actin. The epithelial ductular structures in the tumours showed aberrant expression of cytokeratin 14, T and sialosyl-T antigens, and cytokeratin 14 was the only marker of cells in solid undifferentiated areas of adenoid cystic carcinomas. Our study supports the view, that modified "myoepithelial" cells in the tumours consist of a mixture of basal cells and myoepithelial cells. None of the investigated structures was in itself an ideal marker in the identification of MEC/basal cells. The cells can be identified by a combination of markers (i.e. cytokeratin 14, alpha-smooth-muscle actin, T and sialosyl-T antigens).

A new monoclonal antibody (A78-G/A7) to the Thomsen-Friedenreich pan-tumor antigen

A new monoclonal antibody to the Thomsen-Friedenreich (TF) antigen (or, more precisely, epitope; Gal beta 1-3GalNAc-) has been developed that is specific for both anomeric forms of this disaccharide (TF alpha and TF beta, including related structures on glycolipids), and not assay restricted. We demonstrate that this avid antibody (A78-G/A7) is well suited for immunohistochemistry on paraffin-embedded and cryosectioned tissues, immunoblotting, ELISA techniques, and hemagglutination. Immunohistochemistry on paraffin sections does not require proteolytic or microwave pretreatment. The binding characteristics of this antibody are largely independent of variations in pH (6.0-8.2) and temperature (4-37 degrees C). Immunoblotting with KG-1 (human acute myelogenous leukemia) cells revealed a series of TF-active glycoproteins with a main band at about 155 kDa. Immunoprecipitation was performed using a new technique applicable to IgM-type antibodies.