Vaccine development reconsidered

LptD is a promising vaccine antigen and potential immunotherapeutic target for protection against Vibrio species infection

Outer membrane proteins (OMPs) are unique to Gram-negative bacteria. Several features, including surface exposure, conservation among strains and ability to induce immune responses, make OMPs attractive targets for using as vaccine antigens and immunotherapeutics. LptD is an essential OMP that mediates the final transport of lipopolysaccharide (LPS) to outer leaflet. The protein in Vibrio parahaemolyticus was identified to have immunogenicity in our previous report. In this study, broad distribution, high conservation and similar surface-epitopes of LptD were found among the major Vibrio species. LptD was further revealed to be associated with immune responses, and it has a strong ability to stimulate antibody response. More importantly, it conferred 100% immune protection against lethal challenge by V. parahaemolyticus in mice when the mice were vaccinated with LptD, and this finding was consistent with the observation of efficient clearance of bacteria in vaccination mice. Strikingly, targeting of bacteria by the LptD antibody caused significant decreases in both the growth and LPS level and an increase in susceptibility to hydrophobic antibiotics. These findings were consistent with those previously obtained in lptD-deletion bacteria. These data demonstrated LptD is a promising vaccine antigens and a potential target for antibody-based therapy to protect against Vibrio infections.

Conjugation of capsular polysaccharide to alpha-haemolysin from Staphylococcus aureus as a glycoprotein antigen

The capsular polysaccharides of two pathogenic strains of Staphylococcus aureus 8914 and 31 were isolated and purified. These polysaccharides were conjugated to alpha-haemolysin prepared from the same strains. Amongst the various coupling procedures which were tested the best results were obtained with sodium cyanoborohydride and glutaraldehyde. The conjugates were purified and their immunologic properties were tested. They gave a positive response against antisera from whole bacterial cells.