Capsular polysaccharide-protein conjugate vaccines

Importance of α- and β/α-linked mannooligosaccharides in antibody response against C. dubliniensis

A conjugate of C. dubliniensis cell-wall mannan and human serum albumin (HSA) induced significant level of anti-mannan IgGs in sera of immunized rabbits, whereas mannan alone was not immunogenic. Binding affinities of anti-mannan IgGs induced by the conjugate were evaluated by inhibition ELISA (iELISA) using mannooligosaccharides (dimer-octamer), derived from the side chains of C. dubliniensis mannan, as the inhibitors. Inhibition power of the mannooligosaccharides increased exponentially with their size, with dimer being the weakest (IC(50) = 4 mmol/L) and heptamer/octamer the strongest inhibitors (IC(50) = 0.01 mmol/L). In addition, the mannooligosaccharides proved effective as inhibitors against antiserum obtained from rabbits immunized with C. dubliniensis heat-killed cells, demonstrating a high correlation in the IC(50) values with anti-conjugate serum (Pearson's correlation coefficient r = 0.98; P < 0.01). These findings suggest that a) the mannooligosaccharides comprising the side chains of C. dubliniensis mannan may represent relevant points of interaction with host immune system during infection and b) anti-mannan antibodies induced by the two antigens (the mannan conjugate and the yeast) are of similar specificities.

Automated synthesis of oligosaccharides as a basis for drug discovery

Carbohydrates present both potential and problems - their biological relevance has been recognized, but problems in procuring sugars rendered them a difficult class of compounds to handle in drug discovery efforts. The development of the first automated solid-phase oligosaccharide synthesizer and other methods to assemble defined oligosaccharides rapidly has fundamentally altered this situation. This review describes how quick access to oligosaccharides has not only contributed to biological, biochemical and biophysical investigations, but also to drug discovery. Particular focus will be placed on the development of carbohydrate-based vaccines, defined heparin oligosaccharides and aminoglycosides that have recently begun to affect drug discovery.

Capsular polysaccharide-protein conjugate vaccines and intravenous immunoglobulins

Capsular polysaccharides (CPs), present on the surface of most pathogenic bacteria, have been recognised as virulence factors. Antibodies specific to these polysaccharides can mediate the killing of these bacteria by phagocytes in the presence of complement. The conjugation of polysaccharides to carrier proteins enhances their immunogenicity and renders the immune response T-cell dependent. The currently licensed capsular polysaccharide vaccines and polysaccharide-protein conjugate vaccines under development for the prevention of bacterial infections will be discussed in this review. Use of these vaccines for active vaccination and for the vaccination of healthy plasma donors to produce hyperimmune iv. immunoglobulins for the passive immunisation of appropriate patient populations is also discussed.

Solvent accessibility studies on polysaccharides

The solvent accessible surface area (ASA) of the polysaccharides, namely (i) carrageenan (1CAR); (ii) agarose (1AGA); (iii) guaran (GUR); (iv) capsular polysaccharide (1CAP); and (v) hyaluronan (1HUA), have been computed using the solvent accessibility technique of Lee and Richards. The results show that the average variation of ASA for the various atoms in the molecules lie in the range 1-30 A(2). Irrespective of position of sulfation, either at two or four in the sugar residues in 1CAR, the charged groups interact almost equally with the solvent. The ASA values for the chains A and B in 1AGA and 1CAR indicate that there are not much interchain interactions and the chains in both the molecules interact equally with the solvent. Residue-wise analysis indicates that the ASAs of residues vary alternately, high-low-high value pattern that is similar to that of the hydrophobic behaviour of beta-strands in proteins. The results also suggest that in these polysaccharides D-configuration residues have higher ASA than L-configuration residues.

Emerging themes in medicinal glycoscience

The recognition of complex carbohydrates and glycoconjugates as mediators of important biological processes has stimulated investigation into their therapeutic potential. New approaches for the simplification of glycoconjugate synthesis are overcoming the limitations of existing methods and providing a diverse array of these biomolecules. As the accessibility of glycoconjugates increases, carbohydrate-based constructs are becoming available for analysis as medicinal agents in a wide range of therapies.