Shigella Vaccine Vector Expressing ETEC Antigens
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Solution Overview
Problem
Current vaccines for Shigella and ETEC-induced diarrheal diseases are insufficient, with existing attenuated strains facing challenges in balancing attenuation with immunogenicity and maintaining invasiveness for effective immune response.
Innovation Solution
Development of Shigella flexneri 2a strain SC608 as a vector for expressing ETEC antigens, using asd-based plasmids to ensure expression of CFA/I and LTB proteins on the bacterial surface without antibiotic markers, maintaining invasiveness and immune recognition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If attenuated Shigella strains are used as vaccine vectors, then safety is improved, but immunogenicity and protective efficacy deteriorate
Solution Approach 1:
The patent applies parameter changes by modifying specific virulence genes (icsA, iucA, rfb, wzx) to different degrees of attenuation. The icsA mutation prevents intracellular spreading while maintaining invasion capability, and the rfb/wzx mutations affect LPS structure to reduce virulence. This graded attenuation approach optimizes the balance between safety and immunogenicity by adjusting the severity of genetic modifications.
Solution Approach 2:
The patent segments the virulence factors into distinct targetable components (icsA for invasion control, iucA for siderophore production, rfb/wzx for LPS synthesis). By separately attenuating each virulence pathway, the vaccine maintains multiple functions: invasion capability for immune stimulation, reduced intracellular spreading for safety, and controlled systemic distribution for efficacy.
2Object-affected harmful factors
If Shigella strain is attenuated to improve safety, then ability to invade and stimulate immune response deteriorates
Solution Approach 1:
The patent applies local quality by specifically targeting the icsA gene which controls intracellular spreading rather than invasion itself. The mutation creates a localized defect in the invasion process (inability to spread cell-to-cell) while preserving the initial invasion capability and LPS-mediated immune stimulation, thus maintaining local immune response functions while improving safety.
3Adaptability or versatility
If heterologous antigens are expressed in Shigella vector, then vaccine valency is improved, but invasiveness and immunogenicity of vector deteriorate
Solution Approach 1:
The patent merges multiple vaccine functions into a single attenuated Shigella vector by co-expressing heterologous antigens (CFA/I fimbriae from ETEC and cholera toxin B subunit) alongside Shigella virulence factors. The attenuated vector provides invasion and immune stimulation while the heterologous antigens provide cross-protection, creating a multivalent vaccine that addresses multiple pathogens simultaneously without compromising the vector's core functions.
Solution Approach 2:
The patent creates a universal vaccine platform where the attenuated Shigella vector serves multiple functions: (1) provides its own protective immunity against shigellosis, (2) delivers heterologous ETEC antigens for co-protection, (3) stimulates robust mucosal and systemic immune responses through LPS and invasion mechanisms, and (4) can be adapted to express additional antigens. This multi-functionality achieves high vaccine valency while maintaining vector invasiveness through controlled attenuation.
Data Source
AI summary
With the goal of creating a combination vaccine against Shigella and other diarrheal pathogens we have constructed a prototype vaccine strain of Shigella flexneri 2a (SC608) that can serve as a vector for the expression and delivery of heterologous antigens to the mucosal immune system. SC608 is an asd derivative of SC602, a well-characterized vaccine strain, which has recently undergone several phase 1 and 2 trials for safety and immunogenicity. Using non-antibiotic asd-based plasmids, we have created novel constructs for the expression of antigens from enterotoxigenic E. coli (ETEC), including CFA/I (CfaB and CfaE) and the B-subunit from heat-labile enterotoxin (LTB) in Shigella vaccine strain SC608. Heterologous protein expression levels and cellular localization are critical to immune recognition and have been verified by immunoblot analysis. Following intranasal immunization (SC608(CFAI) and SC608(CFAI/LTB) of guinea pigs, serum IgG and IgA immune responses to both the Shigella LPS and ETEC antigens can be detected by ELISA. In addition, ELISPOT analysis for ASCs from cervical lymph nodes and spleen showed similar responses. All vaccine strains conferred high levels of protection against challenge with wild-type S. flexneri 2a using the Sereny test. Furthermore, serum from guinea pigs immunized with SC608 expressing CfaB and LTB contained antibodies capable of neutralizing the cytological affects of heat-labile toxin (HLT) on Chinese Hamster Ovary (CHO) cells. These initial experiments demonstrate the validity of a multivalent invasive Shigella strain that can serve as a vector for the delivery of pathogen-derived antigens.