Outer Membrane Vesicles Derived from Salmonella enterica Serotype Typhimurium Can Deliver Shigella flexneri 2a O-Polysaccharide Antigen To Prevent Shigella flexneri 2a Infection in Mice

Abstract

Shigellosis has become a serious threat to health in many developing countries due to the severe diarrhea it causes. Shigella flexneri 2a ( S. flexneri 2a) is the principal species responsible for this endemic disease. Despite multiple attempts to design a vaccine against shigellosis, no effective vaccine has not yet been developed. Lipopolysaccharide (LPS) is both an essential virulence factor and an antigen protective against Shigella , due to its outer domain, termed O-polysaccharide antigen. In the present study, S. flexneri 2a O-polysaccharide antigen was innovatively bio-synthesized in Salmonella and attached to core-lipid A via the ligase WaaL, with purified outer membrane vesicles (OMVs) utilized as vaccine vectors. Here, we identified the expression of the heterologous O-antigen and have described the isolation, characterization, and immune protection efficiency of the OMV vaccine. Furthermore, the results of animal experiments indicated that immunization of mice with the OMV vaccine both intranasally and intraperitoneally induced significant specific anti-Shigella LPS antibodies in the serum, with a similar trend IgA levels from vaginal secretions and fluid from bronchopulmonary lavage. The OMV vaccine derived from both routes of administration provided significant protection against virulent S. flexneri 2a infection, as judged by a serum bactericidal assay (SBA), opsonization assay, and challenge test. This vaccination strategy represents a novel and improved approach to control shigellosis by the combination of Salmonella glycosyl carrier lipid bioconjugation with OMVs. Importance: Shigella , the cause of shigellosis or bacillary dysentery, is a major public health concern, especially for children in developing countries. An effective vaccine would control the spread of the disease to some extent. However, no licensed vaccine against Shigella infection in humans has so far been developed. The Shigella O-antigen polysaccharide is effective in stimulating the production of protective antibodies and so could represent a vaccine antigen candidate. Additionally, bacterial outer membrane vesicles (OMVs) have been used as antigen delivery platforms due to their nanoscale properties and ease of antigen delivery to trigger an immune response. Therefore, the present study provides a new strategy for vaccine design, combining a glycoconjugated vaccine with OMVs. The design concept of this strategy is the expression of Shigella O-antigen via the LPS synthesis pathway in recombinant Salmonella , from which the OMV vaccine is then isolated. Based on these findings, we believe that the novel vaccine design strategy in which polysaccharide antigens are delivered via bacterial OMVs will be effective for the development and clinical application of an effective Shigella vaccine.

The Diversity of Escherichia coli Pathotypes and Vaccination Strategies against This Versatile Bacterial Pathogen

“…However, these approaches are not feasible in many low-income countries. Therefore, there is an increased demand for vaccine development, and strategies include the utilization of a live-attenuated strain, glycoconjugate-based candidates, novel antigen candidates such as Shigella outer membrane vesicles (OMV) encapsulated in nanoparticles, and protein subunit candidates [ 224 , 225 , 226 , 227 , 228 , 229 ]. There are several animal and human studies that have described the potential for vaccination using invasion plasmid antigens (IPAs), virG or Shigella O antibodies that cross-react with EIEC O antigens [ 230 , 231 ].…”

Bacterial outer membrane vesicles and their functionalization as vehicles for bioimaging, diagnosis and therapy

“…sonnei O-antigen polysaccharide is effective in stimulating the production of protective antibodies, Tian et al have developed the O-antigen based OMV vaccine by expressing the O-antigen in recombinant Salmonella via the LPS synthesis pathway. 107 Inspired by this work, vaccines basing on polysaccharide antigen-loaded bacterial OMVs have received increasing attention. In addition, OMVs can also be encapsulated in polyanhydride nanoparticles by a solvent displacement method using a copolymer of poly (methyl vinyl ether- co -maleic anhydride).…”

Outer Membrane Vesicle Vaccine Platforms

“…Tian et al biosynthesized S. flexneri 2a O-polysaccharide in Salmonella OMVs, showing that immunization of mice, both intranasally and intraperitoneally, with the OMV vaccine induced significant specific anti- Shigella LPS antibodies in the serum and IgA in vaginal secretions and fluid from bronchopulmonary lavage, and provided significant protection against virulent S. flexneri 2a infection [ 116 ].…”