Carbohydrate vaccines as immunotherapy for cancer

Increasing the antigenicity of synthetic tumor-associated carbohydrate antigens by targeting Toll-like receptors

SYNTHETIC CANCER VACCINES: A number of fully synthetic vaccine candidates have been designed, chemically synthesized, and immunologically evaluated to establish a strategy to overcome the poor immunogenicity of tumor-associated carbohydrates and glycopeptides and to determine the importance of Toll-like receptor (TLR) engagement for antigenic responses against these compounds.Epithelial cancer cells often overexpress mucins that are aberrantly glycosylated. Although it has been realized that these compounds offer exciting opportunities for the development of immunotherapy for cancer, their use is hampered by the low antigenicity of classical immunogens composed of a glycopeptide derived from a mucin conjugated to a foreign carrier protein. We have designed, chemically synthesized, and immunologically evaluated a number of fully synthetic vaccine candidates to establish a strategy to overcome the poor immunogenicity of tumor-associated carbohydrates and glycopeptides. The compounds were also designed to allow study of the importance of Toll-like receptor (TLR) engagement for these antigenic responses in detail. We have found that covalent attachment of a TLR2 agonist, a promiscuous peptide T-helper epitope, and a tumor-associated glycopeptide gives a compound (1) that elicits in mice exceptionally high titers of IgG antibodies that recognize MCF7 cancer cells expressing the tumor-associated carbohydrate. Immunizations with glycolipopeptide 2, which contains lipidated amino acids instead of a TLR2 ligand, gave significantly lower titers of IgG antibodies; this demonstrates that TLR engagement is critical for optimum antigenic responses. Although mixtures of compound 2 with Pam(3)CysSK(4) (3) or monophosphoryl lipid A (4) elicited titers of IgG antibodies similar to those seen with 1, the resulting antisera had impaired ability to recognize cancer cells. It was also found that covalent linkage of the helper T-epitope to the B-epitope is essential, probably because internalization of the helper T-epitope by B-cells requires assistance of the B-epitope. The results presented here show that synthetic vaccine development is amenable to structure-activity relationship studies for successful optimization of carbohydrate-based cancer vaccines.

Enhanced immune recognition of cryptic glycan markers in human tumors

Abnormal glycosylation is one of the hallmarks of the cancer cell and is associated with tumor invasion and metastasis. The development of tumor-associated carbohydrate antigen (TACA) vaccines has been problematic due to poor immunogenicity. However, when appropriate targets can be identified, passive immunization with monoclonal antibodies (mAbs) directed against TACAs has been shown to have antitumor activity. Fas ligand (FasL) is a transmembrane protein that induces apoptosis in cells expressing its receptor, Fas. When grafted into mice, FasL-expressing tumor cells break immunologic tolerance to self-antigens and induce antibody-mediated tumor immunity. Here, five IgM mAbs were produced from mice vaccinated with FasL-expressing B16F10 mouse melanoma cells. They recognize various syngeneic and allogeneic murine tumor cell lines. One mAb, TM10, recognizes a range of human tumor cell lines, including melanoma, prostate, and ovarian cancer. It does not bind to untransformed cells. The epitopes recognized by all the mAbs were carbohydrates expressed on proteins. Using carbohydrate microarrays, the antigenic targets of TM10 were found to be high-mannose core structures of N-linked glycans. In normal cells, high-mannose clusters are hidden by extensive saccharide branching but they become exposed in cancer cells as a result of abnormal glycosylation pathways. Vaccination with FasL-expressing tumors therefore enables the immune system to break tolerance to self-antigens, allowing identification of novel TACAs that can form the basis of future humoral anticancer therapy.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.

Pre-clinical characterization of GMP grade CCL21-gene modified dendritic cells for application in a phase I trial in non-small cell lung cancer

Background

Our previous studies have demonstrated that transduction of human dendritic cells (DC) with adenovirus encoding secondary lymphoid chemokine, CCL21, led to secretion of biologically active CCL21 without altering DC phenotype or viability. In addition, intratumoral injections of CCL21-transduced DC into established murine lung tumors resulted in complete regression and protective anti-tumor immunity. These results have provided the rationale to generate a clinical grade adenoviral vector encoding CCL-21 for ex vivo transduction of human DC in order to assess intratumoral administration in late stage human lung cancer.

Methods

In the current study, human monocyte-derived DC were differentiated by exposure to GM-CSF and IL-4 from cryopreserved mononuclear cells obtained from healthy volunteers. Transduction with clinical grade adenoviral vector encoding CCL21 (1167 viral particles per cell) resulted in secretion of CCL21 protein.

Results

CCL21 protein production from transduced DC was detected in supernatants (24–72 hours, 3.5–6.7 ng/4–5 × 10⁶ cells). DC transduced with the clinical grade adenoviral vector were > 88% viable (n = 16), conserved their phenotype and maintained integral biological activities including dextran uptake, production of immunostimulatory cytokines/chemokines and antigen presentation. Furthermore, supernatant from CCL21-DC induced the chemotaxis of T2 cells in vitro.

Conclusion

Viable and biologically active clinical grade CCL21 gene-modified DC can be generated from cryopreserved PBMC.

Human tumor antigens Tn and sialyl Tn arise from mutations in Cosmc

Neoplastic lesions typically express specific carbohydrate antigens on glycolipids, mucins, and other glycoproteins. Such antigens are often under epigenetic control and are subject to reversion and loss upon therapeutic selective pressure. We report here that two of the most common tumor-associated carbohydrate antigens, Tn and sialyl Tn (STn), result from somatic mutations in the gene Cosmc that encodes a molecular chaperone required for formation of the active T-synthase. Diverse neoplastic lesions, including colon cancer and melanoma-derived cells lines, expressed both Tn and STn antigen due to loss-of-function mutations in Cosmc. In addition, two human cervical cancer specimens that showed expression of the Tn/STn antigens were also found to have mutations in Cosmc and loss of heterozygosity for the cross-linked Cosmc locus. This is the first example of somatic mutations in multiple types of cancers that cause global alterations in cell surface carbohydrate antigen expression.

Generation of tumour-rejecting anti-carbohydrate monoclonal antibodies using melanoma modified with Fas ligand

Carbohydrate antigens such as glycolipids and glycoproteins are over-expressed in a variety of cancers and have therefore been identified as ideal candidates for tumour vaccines. Detection of anti-carbohydrate antibodies is associated with a good prognosis in cancer patients. However, generation of an efficient adaptive immune response has been hampered by the low immunogenicity of carbohydrates due to tolerance. Here, we describe a method by which tumour-rejecting antibodies directed against carbohydrates can be elicited in two different melanoma mouse models. Thus, using the murine melanoma B16F10 over-expressing Fas ligand (FasL), we have generated mAbs against cancer carbohydrate antigens expressed by the melanoma. Importantly, passive transfer of mAbs resulted in rejection of melanoma in vivo. Their protective effect in vivo was dependent on FcR and in vitro antibody-dependent cellular phagocytosis. They were also able to delay tumour growth when injected after the tumour was established. FasL-expressing tumours as an adjuvant are a novel way to generate anti-carbohydrate antibodies able to reject tumours in vivo.

Glycopeptide analysis by mass spectrometry

Glycosylation is one of the most important post-translational modifications found in nature. Identifying and characterizing glycans is an important step in correlating glycosylation structure to the glycan's function, both in normal glycoproteins and those that are modified in a disease state. Glycans on a protein can be characterized by a variety of methods. This review focuses on the mass spectral analysis of glycopeptides, after subjecting the glycoprotein to proteolysis. This analytical approach is useful in characterizing glycan heterogeneity and correlating glycan compositions to their attachment sites on the protein. The information obtained from this approach can serve as the foundation for understanding how glycan compositions affect protein function, in both normal and aberrant glycoproteins.

Cowpea mosaic virus capsid: a promising carrier for the development of carbohydrate based antitumor vaccines

Immunotherapy targeting tumor cell surface carbohydrates is a promising approach for cancer treatment. However, the low immunogenecity of carbohydrates presents a formidable challenge. We describe here the enhancement of carbohydrate immunogenicity by an ordered display on the surface of the cowpea mosaic virus (CPMV) capsid. The Tn glycan, which is overexpressed on numerous cancer cell surfaces, was selected as the model antigen for our study. Previously it has been shown that it is difficult to induce a strong T cell-dependent immune response against the monomeric form of Tn presented in several ways on different carriers. In this study, we first synthesized Tn antigens derivatized with either a maleimide or a bromoacetamide moiety that was conjugated selectively to a cysteine mutant of CPMV. The glycoconjugate was then injected into mice and pre- and post-immune antibody levels in the mice sera were measured by enzyme-linked immunosorbant assays. High total antibody titers and, more importantly, high IgG titers specific for Tn were obtained in the post-immune day 35 serum, suggesting the induction of T cell-dependent antibody isotype switching by the glycoconjugate. The antibodies generated were able to recognize Tn antigens presented in their native conformations on the surfaces of both MCF-7 breast cancer cells and the multidrug resistant breast cancer cell line NCI-ADR RES. These results suggest that the CPMV capsid can greatly enhance the immunogenicity of weak antigens such as Tn and this can provide a promising tool for the development of carbohydrate based anti-cancer vaccines.

Tumors: too sweet to remember?

Immunity, based on a natural and an educated system, is responsible for recognition and elimination of infectious particles, cellular waste, modified self and transformed cells. This dual system guarantees that dangerous particles are removed immediately after appearance and that a memory with maturated weapons exists, if the organism is re-infected by the same particle. For malignant cells, however, the immune response seems to be restricted to innate immunity, because at least for the humoral response, all so far detected tumor-specific antibodies belong to the natural immunity. In this review we try to explain why malignant cells might be "too sweet" to induce a memory.

Carbohydrate-based experimental therapeutics for cancer, HIV/AIDS and other diseases

This review, primarily for general readers, briefly presents experimental approaches to therapeutics of cancer, HIV/AIDS and various other diseases based on advances in glycobiology and glycochemistry. Experimental cancer and HIV/AIDS vaccines are being developed in attempts to overcome weak immunological responses to carbohydrate-rich surface antigens using carriers, adjuvants and novel carbohydrate antigen constructs. Current carbohydrate-based vaccines are used for typhus, pneumonia, meningitis; vaccines for anthrax, malaria and leishmaniasis are under development. The link between O-linked beta-N-acetylglucosamine glycosylation and protein phosphorylation in diseases including diabetes and Alzheimer's disease is also explored. Carbohydrate-associated drugs that are in current use or under development, such as heparan sulfate binders, lectins, acarbose, aminoglycosides, tamiflu and heparin, and technologies using carbohydrate and lectin microarrays that offer improved diagnostic and drug development possibilities, are described. Advances in carbohydrate synthesis, analysis and manipulation through the emerging fields of glycochemistry and glycobiology are providing new approaches to disease therapeutics.

Robust immune responses elicited by a fully synthetic three-component vaccine

The overexpression of saccharides such as Globo-H, Lewis(Y) and Tn antigen is a common feature of oncogenic transformed cells. Endeavors to exploit this aberrant glycosylation for cancer vaccine development have been complicated by difficulties in eliciting high titers of IgG antibodies against classical conjugates of tumor-associated carbohydrates to carrier proteins. We have designed, chemically synthesized and immunologically evaluated a number of fully synthetic vaccine candidates to establish strategies to overcome the poor immunogenicity of tumor-associated carbohydrates and glycopeptides. We have found that a three-component vaccine composed of a TLR2 agonist, a promiscuous peptide T-helper epitope and a tumor-associated glycopeptide can elicit in mice exceptionally high titers of IgG antibodies that can recognize cancer cells expressing the tumor-associated carbohydrate. The superior properties of the vaccine candidate are attributed to the local production of cytokines, upregulation of co-stimulatory proteins, enhanced uptake by macrophages and dendritic cells and avoidance of epitope suppression.

Anti-Carbohydrate Antibodies Elicited by Polyvalent Display on a Viral Scaffold

Tetra- and hexasaccharides were arrayed on the exterior surface of cowpea mosaic virus by using a copper-catalyzed azide-alkyne cycloaddition reaction. Inoculation of chickens with these virus conjugates gave rise to large quantities of polyclonal anti-glycan IgY antibodies that displayed excellent avidity and specificity on analysis with printed glycan microarrays. Avian IgY antibodies are produced in significantly higher yield than is possible for mouse or rabbit IgG, and exhibit reduced cross reactivity with native mammalian proteins. For a tri-LacNAc antigen, affinity purification against immobilized mono-LacNAc was necessary to provide a set of antibodies with specific binding properties. Comparable performance was observed for the virus-based polyclonal versus a commercial monoclonal antibody raised against the globo-H tetrasaccharide; this highlights the utility of the glycan microarray for both quality control and rapid in-depth analysis. Virus-carbohydrate conjugates are promising candidates for development in diagnostic and immunotherapeutic applications.

Chemical glycosylation in the synthesis of glycoconjugate antitumour vaccines

Therapeutic vaccines derived from carbohydrate antigen-adjuvant combinations are a promising approach for cancer immunotherapy. One of the critical limitations in this area is access to sufficient quantities of tumour-associated carbohydrate antigens and glycoconjugate adjuvants. At present, availability of the complex oligosaccharide constructs that are needed for the systematic design and evaluation of novel vaccine formulations relies on de novo chemical synthesis. The use of both state-of-the-art and emerging glycosylation technologies has led to significant advances in this field, allowing the clinical exploration of carbohydrate-based antigens in the treatment of cancer.

Synthesis and medical applications of oligosaccharides

Our understanding of the different glycoconjugates present on cells, proteins and entire organisms is lagging far behind advances in genomics and proteomics. Carbohydrate sequencing and the synthesis of defined oligosaccharides are two key technologies that have contributed to progress in glycomics research. Synthetic tools and high-throughput experiments such as carbohydrate arrays are beginning to affect biological research. These techniques are now being applied to the development of carbohydrate-based diagnostics, vaccines and therapeutics.

High-throughput carbohydrate microarray profiling of 27 antibodies demonstrates widespread specificity problems

Progress toward understanding the biological roles of carbohydrates has been remarkably slow, and efforts to exploit this class of biopolymers as diagnostic and therapeutic targets have proven extremely challenging. Both basic and clinical research rely heavily on identifying and monitoring expression levels of carbohydrates. Over the last 30 years, the majority of expression information has been derived from antibody- and lectin-binding studies. Using a carbohydrate microarray containing 80 different glycans and glycoproteins, the specificities of 27 antiglycan antibodies were evaluated, including antibodies to histo-blood group A, B, and H antigens (81FR2.2, CLCP-19B, B389, 92FR-A2, B480, B460, B376, and B393), Lewis antigens (7LE, 15C02, 28, ZC-18C, 121SLE, CA199.02, PR.5C5, 2-25LE, BR55, T174, T218, F3, A70-C/C8, FR4A5, and K21), and other tumor-associated antigens (B389, 1A4, B1.1, and 5B5). In total, evaluation of over 2000 individual carbohydrate-protein interactions was carried out. More than half of the antibodies considered to be specific for their designated antigen were found to cross-react with other glycans. The cross-reactive glycans could be mistaken for the designated antigen in biopsy samples or other biological samples, leading to inaccurate conclusions.

Glycoengineering of alphaGal xenoantigen on recombinant peptide bearing the J28 pancreatic oncofetal glycotope

In human pancreatic adenocarcinoma, alterations of glycosylation processes leads to the expression of tumor-associated carbohydrate antigens, representing potential targets for cancer immunotherapy. Among these pancreatic tumor-associated carbohydrate antigens, the J28 glycotope located within the O-glycosylated mucin-like C-terminal domain of the fetoacinar pancreatic protein (FAPP) and expressed at the surface of human tumoral tissues, can be a good target for anticancer therapeutic vaccines. However, the oncodevelopmental self character of the J28 glycotope associated with the low immunogenicity of tumor-associated carbohydrate antigens may be a major obstacle to effective anti-tumor vaccine therapy. In this study, we have investigated a method to increase the immunogenicity of the recombinant pancreatic oncofetal J28 glycotope by glycoengineering Galalpha1,3Galss1,4GlcNAc-R (alphaGal epitope) which may be recognized by natural anti-alphaGal antibody present in humans. For this purpose, we have developed a stable Chinese hamster ovary cell clone expressing the alphaGal epitope by transfecting the cDNA encoding the alpha1,3galactosyltransferase. These cells have been previously equipped to produce the recombinant O-glycosylated C-terminal domain of FAPP carrying the J28 glycotope. As a consequence, the C-terminal domain of FAPP produced by these cells carries the alphaGal epitope on oligosaccharide structures associated with the J28 glycotope. Furthermore, we show that this recombinant "alpha1,3galactosyl and J28 glycotope" may not only be targeted by human natural anti-alphaGal antibodies but also by the mAbJ28, suggesting that the J28 glycotope remains accessible to the immune system as vaccinating agent. This approach may be used for many identified tumor-associated carbohydrate antigens which can be glycoengineered to carry a alphaGal epitope to increase their immunogenicity and to develop therapeutic vaccines.

Preclinical studies of carbohydrate mimetic peptide vaccines for breast cancer and melanoma

Limited immune responses to tumor-associated carbohydrate antigens (TACA) are due in part to their being self-antigens. Immunization with xenoantigens of TACA provides an approach to break tolerance and augment responses to TACA. Carbohydrate mimetic peptides (CMPs) as xenoantigens can induce serum antibodies that target shared carbohydrate residues on differing carbohydrate structures. In preclinical studies, we observe that CMP immunization in mice induce immune responses that are effective in inhibiting the in vitro and in vivo growth of breast cancer and melanoma tumor cells expressing self-target antigens. CMPs of TACA can be further defined that induce IgM antibodies with broadened responses to both breast and melanoma cells. Consequently, CMPs are effective at generating a multifaceted carbohydrate-reactive immune response that should be clinically evaluated for their ability to amplify carbohydrate immune responses against circulating or disseminated tumor cells.

Sucres et vaccins : du polysaccharide purifié au glycoconjugué semi-synthétique

Over the last decades, capsular polysaccharides have been successfully used as antibacterial vaccines. Marketing several polysaccharide-protein conjugate vaccines filled the gap in many areas of children and infant vaccination. By facilitating access to structures of increasing complexity, recent progress in glycochemistry has enabled the design of more and more precisely defined glycoconjugate vaccines using synthetic saccharide components which mimic epitopes naturally implicated in protection. This strategy was recently validated in humans. It opens the way to new perspectives in vaccine research devoted to prophylactic and/or therapeutic applications against bacterial, fungal, parasitic or viral infections, and certain cancers.

Monitoring activation sites on polysaccharides by GC–MS

A method has been developed to determine the location and order of activation for potential saccharide antigens used in conjugate vaccine development. Saccharides were monitored for activation by sodium periodate oxidation and subsequent analysis by gas chromatography-mass spectrometry (GC-MS). Pneumococcal serotype polysaccharides 7F and 18C were evaluated as polysaccharides containing multiple potential sites for activation. Sialyllactose was used as a model oligosaccharide compound to evaluate oxidation of terminally linked sialic acids and reducing sugar residues. Oxidized saccharides were analyzed by monosaccharide composition and/or linkage analysis to elucidate specific activation of cis versus trans diols, as well as diols containing primary versus secondary alcohols, at specified levels of periodate. Samples (100-500 microg) were sequentially oxidized, reduced, methanolyzed, and derivatized in a single reaction vial for routine analysis by GC-MS.

Fucosylation in prokaryotes and eukaryotes

Fucosylated carbohydrate structures are involved in a variety of biological and pathological processes in eukaryotic organisms including tissue development, angiogenesis, fertilization, cell adhesion, inflammation, and tumor metastasis. In contrast, fucosylation appears less common in prokaryotic organisms and has been suggested to be involved in molecular mimicry, adhesion, colonization, and modulating the host immune response. Fucosyltransferases (FucTs), present in both eukaryotic and prokaryotic organisms, are the enzymes responsible for the catalysis of fucose transfer from donor guanosine-diphosphate fucose to various acceptor molecules including oligosaccharides, glycoproteins, and glycolipids. To date, several subfamilies of mammalian FucTs have been well characterized; these enzymes are therefore delineated and used as models. Non-mammalian FucTs that possess different domain construction or display distinctive acceptor substrate specificity are highlighted. It is noteworthy that the glycoconjugates from plants and schistosomes contain some unusual fucose linkages, suggesting the presence of novel FucT subfamilies as yet to be characterized. Despite the very low sequence homology, striking functional similarity is exhibited between mammalian and Helicobacter pylori alpha1,3/4 FucTs, implying that these enzymes likely share a conserved mechanistic and structural basis for fucose transfer; such conserved functional features might also exist when comparing other FucT subfamilies from different origins. Fucosyltranferases are promising tools used in synthesis of fucosylated oligosaccharides and glycoconjugates, which show great potential in the treatment of infectious and inflammatory diseases and tumor metastasis.

Expression of MG7-Ag in patients with gastric cancer correlates with weaker T cell immune response and more proinflammatory cytokine secretion

MG7-Ag is a human gastric-carcinoma-associated antigen with a high specificity. So far it is remained unclear whether MG7-Ag is correlated with the in vivo cellular immune response of patients with gastric cancer. In this study, we detected the expression of the T cell receptor (TCR) repertoire of T cell subpopulations and cytokines in tumor-infiltrating lymphocytes (TIL), peripheral blood lymphocytes (PBL), and residue benign mucosal lymphocytes (NML) of patients with gastric cancer using semiquantitative RT-PCR. Our data showed that the expanded clones in CD8(+) NML and TIL and CD4+ NML and PBL in MG7-Ag-positive patients were significantly fewer than those of MG7-Ag-negative patients (p = 0.0360; p = 0.0026; p = 0.0065 p = 0.0109, respectively). The levels of IL-8 in CD8(+) TIL and TNF in CD4(+) TIL from the MG7-Ag-positive group were significantly higher than those from the MG7-Ag-negative group (p = 0.0302; p = 0.0177, respectively). Taken together, the results demonstrated a weaker T cell immune response and more proinflammatory cytokine secretion in MG7-Ag-positive patients with gastric cancer than in MG7-Ag-negative ones. This likely contributes to the poor prognosis in MG7-Ag-positive gastric-cancer patients.

Blood brothers: Carbohydrates in xenotransplantation and cancer immunotherapy

Carbohydrate antigens have a central role in the hyperacute rejection of animal-to-human organ grafts (xenotransplantation) and they are emerging in importance in the immunotherapy of cancer. This article traces the historical origins of the discovery of key carbohydrate antigens and explores the future impact of recent technological advances of the field of glycobiology as it relates to xenotransplantation and cancer.