Synthesis of Ligands Related to the O‐Specific Polysaccharides of Shigella flexneri Serotype 2a and Shigella flexneri Serotype 5a. Part 10. Blockwise Approach to Fragments of the O‐Specific Polysaccharide of Shigella flexneri Serotype 2a: Convergent Synthesis of a Decasaccharide Representative of a Dimer of the Branched Repeating Unit.

The Journal of Immunology

Costachel

Grandjean

et al. 2006

Self Cite

104

Protection against reinfection with noncapsulated Gram-negative bacteria, such as Shigella, an enteroinvasive bacterium responsible for bacillary dysentery, is mainly achieved by Abs specific for the O-Ag, the polysaccharide part of the LPS, the major bacterial surface Ag. The use of chemically defined glycoconjugates encompassing oligosaccharides mimicking the protective determinants carried by the O-Ag, thus expected to induce an efficient anti-LPS Ab response, has been considered an alternative to detoxified LPS-protein conjugate vaccines. The aim of this study was to identify such functional oligosaccharide mimics of the S. flexneri serotype 2a O-Ag. Using protective murine mAbs specific for S. flexneri serotype 2a and synthetic oligosaccharides designed to analyze the contribution of each sugar residue of the branched pentasaccharide repeating unit of the O-Ag, we demonstrated that the O-Ag exhibited an immunodominant serotype-specific determinant. We also showed that elongating the oligosaccharide sequence improved Ab recognition. From these antigenicity data, selected synthetic oligosaccharides were assessed for their potential to mimic the O-Ag by analyzing their immunogenicity in mice when coupled to tetanus toxoid via single point attachment. Our results demonstrated that induction of an efficient serotype 2a-specific anti-O-Ag Ab response was dependent on the length of the oligosaccharide sequence. A pentadecasaccharide representing three biological repeating units was identified as a potential candidate for further development of a chemically defined glycoconjugate vaccine against S. flexneri 2a infection.

Section: Synthetic Oligosaccharides Representative Of S Flexneri 2a mentioning

confidence: 99%

Characterization of Functional Oligosaccharide Mimics of the Shigella flexneri Serotype 2a O-Antigen: Implications for the Development of a Chemically Defined Glycoconjugate Vaccine

The Journal of Immunology

Costachel

Grandjean

et al. 2006

Self Cite

104

“…Therefore, the crucial LPS detoxification step is avoided. Following the synthesis of a large panel of SF2a O-SP fragments (21)(22)(23)(24)(25)(26) and extensive investigation of their recognition by protective murine monoclonal IgG (mIgG) Abs, we showed that selected synthetic OSs induced an anti-O-SP Ab response in mice, when administered as tetanus toxoid (TT) conjugates. Increasing the length of the carbohydrate hapten from a penta-to a deca-and pentadecasaccharide representing one, two, and three biological RUs of SF2a O-SP (Fig.…”

mentioning

confidence: 99%

A Synthetic Carbohydrate-Protein Conjugate Vaccine Candidate against Shigella flexneri 2a Infection

The Journal of Immunology

Tanguy

Grandjean

et al. 2009

Self Cite

123

108

The protective Ag of Shigella, the Gram-negative enteroinvasive bacterium causing bacillary dysentery, or shigellosis, is its O-specific polysaccharide (O-SP) domain of the LPS, the major bacterial surface component. As an alternative to the development of detoxified LPS-based conjugate vaccines, recent effort was put into the investigation of neoglycoproteins encompassing synthetic oligosaccharides mimicking the protective Ags of the O-SP. We previously reported that when coupled to tetanus toxoid via single point attachment, a synthetic pentadecasaccharide representing three biological repeating units of the O-SP of Shigella flexneri 2a (SF2a), one of the most common Shigella serotypes, elicits a better serum anti-LPS 2a Ab response in mice than shorter synthetic O-SP sequences. In this study, we show that the pentadecasaccharide-induced anti-LPS 2a Abs protect passively administered naive mice from Shigella infection. Therefore, this three repeating units sequence, which is recognized by anti-SF2a sera from infected patients, acts as a functional mimic of the native polysaccharide Ag. Analyses of parameters influencing immunogenicity revealed that an investigational SF2a vaccine displaying a pentadecasaccharide:tetanus toxoid molar loading of 14:1 triggers a high and sustained anti-LPS Ab response, without inducing anti-linker Ab, when administered four times at a dose corresponding to 1 g of carbohydrate. In addition, the profile of the anti-LPS Ab response, dominated by IgG1 production (Th2-type response), mimics that observed in human upon natural SF2a infection. This synthetic carbohydrate-based conjugate may be a candidate for a SF2a vaccine.

“…As an alternative to classical polysaccharide conjugate vaccines, we have developed a strategy based on synthetic carbohydrates that mimic the O-Ag of S. flexneri 2a, including a detailed analysis of the fine specificity of protective antibody/O-Ag recognition. Accordingly, a number of oligosaccharides representative of serotype 2a O-Ag fragments have been synthesized (9)(10)(11). Although several of these were immunogenic in mice when administered as tetanus toxoid conjugates, only certain sequences were able to induce IgG antibodies capable of recognizing the bacterial LPS (12,13).…”

mentioning

confidence: 99%

Structures of synthetic O-antigen fragments from serotype 2aShigella flexneriin complex with a protective monoclonal antibody

Normand

Saul

Proc. Natl. Acad. Sci. U.S.A.

et al. 2008

The anti-LPS IgG mAb F22-4, raised against Shigella flexneri serotype 2a bacteria, protects against homologous, but not heterologous, challenge in an experimental animal model. We report the crystal structures of complexes formed between Fab F22-4 and two synthetic oligosaccharides, a decasaccharide and a pentadecasaccharide that were previously shown to be both immunogenic and antigenic mimics of the S. flexneri serotype 2a O-antigen. F22-4 binds to an epitope contained within two consecutive 2a serotype pentasaccharide repeat units (RU). Six sugar residues from a contiguous nine-residue segment make direct contacts with the antibody, including the nonreducing rhamnose and both branching glucosyl residues from the two RUs. The glucosyl residue, whose position of attachment to the tetrasaccharide backbone of the RU defines the serotype 2a O-antigen, is critical for recognition by F22-4. Although the complete decasaccharide is visible in the electron density maps, the last four pentadecasaccharide residues from the reducing end, which do not contact the antibody, could not be traced. Although considerable mobility in the free oligosaccharides can thus be expected, the conformational similarity between the individual RUs, both within and between the two complexes, suggests that short-range transient ordering to a helical conformation might occur in solution. Although the observed epitope includes the terminal nonreducing residue, binding to internal epitopes within the polysaccharide chain is not precluded. Our results have implications for vaccine development because they suggest that a minimum of two RUs of synthetic serotype 2a oligosaccharide is required for optimal mimicry of O-Ag epitopes.antibody complex ͉ carbohydrate ͉ crystal structure ͉ polyliposaccharide ͉ shigellosis S higellosis (1), or bacillary dysentery, causes significant morbidity and mortality worldwide, particularly among young children (2). The disease arises from colonization and subsequent destruction of the colonic mucosa by the Gram-negative enteroinvasive bacteria Shigella. Immune protection induced by natural infection derives from antibodies directed against the bacterial surface antigen lipopolysaccharide (LPS) (3). Moreover, protection shows a serotype specificity that is determined by the repeat unit (RU) structure of the O-antigen (O-Ag), the polysaccharide moiety of LPS (4). In the species Shigella flexneri, which is responsible for endemic infections in developing countries, the serotype is defined by glucosyl and O-acetyl modifications added to the basic tri-rhamnose-N-acetyl-glucosamine tetrasaccharide (designated ABCD) of the O-Ag backbone (5). (Serotype 6 is an exception.) Of the 14 S. flexneri serotypes identified to date, the 2a serotype is the most prevalent in developing countries (2). The serotype 2a RU is characterized by a branching glucose (residue E) linked to the third rhamnose (residue C) to form the motif AB(E)CD (Fig. 1).The induction of protective immunity by natural infection with Shigella suggests that an effe...