"Thus, the protein-polysaccharide conjugate vaccines against shigellosis S.sonnei have shown an insufficient immunogenicity in clinical trials on adults and children. It should be noted that the immunogenic properties of free, unconjugated O-polysaccharide from the LPS of the S. sonnei bacteria, phase I, as a vaccine immunogen is not known. Experimental data from Taylor et al show a practically full absence of immunogenic activity in mice against unconjugated polysaccharide from LPS of bacterial cells P. shigelloides, the structure of which is identical to that of S. sonnei, phase I O-antigen (
"Based on the aforementioned, the actuality of development of other approaches to the creation of O-antigen vaccines against S. sonnei infection is obvious. As alternative, perspective approach for development can be considered the creation of a unconjugated vaccine based on the O-antigen exopolysaccharide, produced by S. sonnei, phase I bacteria into the cultural medium. It is known, that many gram-positive and gram-negative bacteria produce not only polysaccharide components of cells, but also extracellular exopolysaccharides, which are secreted by the cell into the external medium and provide the protective function. Thus, the produced exopolysaccharides can be found both in a free state or form an extracellular capsule or microcapsule.
"Sometimes exopolysaccharides produced by cells into the external medium represent specific highly-immunogenic antigens--potent inducers of protective antibody synthesis. Thus, a variety of such polysaccharide antigens are used in the vaccine compositions for prevention of infections, caused by meningococcus groups A and C, typhoid bacteria (Lindberg A. A. Polyosides (encapsulated bacteria). C. R. Acad. Sci.
"Polysaccharide vaccine immunogenicity is determined by the primary structure of the polysaccharide antigen, its molecular mass, and ability to form aggregate structures (The vaccine book. Edited by
"However, neither the primary structure of the exopolysaccharide of bacteria S. sonnei, phase I, nor its physico-chemical, immunobiological, and protective properties, nor the method of its isolation, nor even the fact of its existence are described in the literature.
"The literature sources also do not describe the pharmaceutical compositions based on S. sonnei, phase I polysaccharides, the development of which can make significant contributions to clinical pharmacology. It only describes the usage of fragments of polysaccharides from LPS of S. sonnei, phase I cells, including from 1 to 5 disaccharide units, as nutrient supplement for oral administration, stimulating immune system development in infants between 1 and 6 months of age, determined by the increase of type1 T-helpers (Th1 response) to the type 2 T-helpers (Th2 response) ratio (US Pat. Appl. 2009/0317427 A1)."
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