Theranostics 2019; 9(12):3565-3579. doi:10.7150/thno.33046

Research Paper

Regulated Delayed Shigella flexneri 2a O-antigen Synthesis in Live Recombinant Salmonella enterica Serovar Typhimurium Induces Comparable Levels of Protective Immune Responses with Constitutive Antigen Synthesis System

Huali Su1, Qing Liu2, Shifeng Wang1, Roy Curtiss III1, Qingke Kong1✉

1. Department of Infectious Diseases and Immunology, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA
2. College of Animal Science and Technology, Southwest University, Chongqing, China

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Citation:
Su H, Liu Q, Wang S, Curtiss R III, Kong Q. Regulated Delayed Shigella flexneri 2a O-antigen Synthesis in Live Recombinant Salmonella enterica Serovar Typhimurium Induces Comparable Levels of Protective Immune Responses with Constitutive Antigen Synthesis System. Theranostics 2019; 9(12):3565-3579. doi:10.7150/thno.33046. Available from http://www.thno.org/v09p3565.htm

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Abstract

Shigella flexneri (S. flexneri), a leading cause of bacillary dysentery, is a major public health concern particularly affecting children in developing nations. We have constructed a novel attenuated Salmonella vaccine system based on the regulated delayed antigen synthesis (RDAS) and regulated delayed expression of attenuating phenotype (RDEAP) systems for delivering the S. flexneri 2a (Sf2a) O-antigen.

Methods: The new Salmonella vaccine platform was constructed through chromosomal integration of the araC PBAD lacI and araC PBAD wbaP cassettes, resulting in a gradual depletion of WbaP enzyme. An expression vector, encoding Sf2a O-antigen biosynthesis under the control of the LacI-repressible Ptrc promoter, was maintained in the Salmonella vaccine strain through antibiotic-independent selection. Mice immunized with the vaccine candidates were evaluated for cell-mediate and humoral immune responses.

Results: In the presence of exogenous arabinose, the Salmonella vaccine strain synthesized native Salmonella LPS as a consequence of WbaP expression. Moreover, arabinose supported LacI expression, thereby repressing Sf2a O-antigen production. In the absence of arabinose in vivo, native Salmonella LPS synthesis is repressed whilst the synthesis of the Sf2a O-antigen is induced. Murine immunization with the Salmonella vaccine strain elicited robust Sf2a-specific protective immune responses together with long term immunity.

Conclusion: These findings demonstrate the protective efficacy of recombinant Sf2a O-antigen delivered by a Salmonella vaccine platform.

Keywords: Shigella flexneri 2a, regulated delayed antigen synthesis, O-antigen, attenuated Salmonella vaccine.