SBIR-STTR Award

This project develops a conjugate vaccine against Shigella flexneri 2a utilizing cGMP-compatible manufacturing processes. The antigenic component of the vaccine is deacylated-polysaccharide from the bacterial LPS that has an average of one O-antigen repeat unit per polysaccharide molecule. The polysaccharide is deacylated by a biological process, and has a core structure with intact phophosphoryl groups. It is expected that phosphorylated core components will elicit antibodies that cross-react with LPS of other strains and species of Shigella that share these core epitopes. Phase I research studies will provide a cGMP-compatible method for producing the conjugate vaccine, and Phase I Option studies will evaluate the immunogenicity of the vaccine, and its potential to elicit cross-reactive antibodies against several serotypes of S. flexneri and against other Shigella species.

Benefits:
1) This research will provide insights into the dominant cross-reactive epitopes found in the core structure of Shigella LPS. 2) It will provide a conjugate vaccine for S. flexneri 2A, which may prove significantly better than existing vaccines. 3) This conjugate vaccine may well show significant cross-protection against many shigella species, and if so, the cost savings achieved by needing only one vaccine instead of several, will be considerable.

Keywords:
Shigella flexneri, shigellosis, conjugate vaccine, cross-reactivity, polysaccharide, LPS, endotoxin

There is need for a commercial vaccine against shigellosis because all groups of pathogenic Shigella have acquired resistance to antibiotics. Shigella conjugate vaccines have proven safe and protective in previous clinical trials, but obstacles associated with large-scale manufacturing of these subunit vaccines have apparently hindered commercial development. The present project uses a new and simpler technology for manufacturing shigella conjugate vaccine. The goals of the project are to develop cGMP-manufacturing conditions for the new technology and to use these conditions to produce a clinical lot of refined, conjugate vaccine against Shigella flexneri 2a. The vaccine will contain completely deacylated polysaccharide (PS) from S. flexneri 2a lipopolysaccharide (LPS) and a carrier protein called Proteinase 1. To produce the vaccine, whole cells of S. flexneri 2a are fed to a culture of Dictyostelium cells. During growth on the bacteria, Dictyostelium cells synthesize Proteinase 1 and excrete PS molecules. After bacteria have been depleted in the culture, PS is harvested and purified from the culture media, and Proteinase 1 is extracted and purified from the Dictyostelium cells. The conjugate vaccine is constructed by covalent linkage of purified PS molecules to sugar-phosphate linker groups that occur as natural post-translational groups in Proteinase 1.

Keywords:
SHIGELLA FLEXNERI, SHIGELLOSIS, CONJUGATE VACCINE, LIPOPOLYSACCHARIDE, LPS, ENDOTOXIN, DICTYOSTELIUM DISCOIDEUM, DEACYLATION