Combinations of gene deletions for live attenuated Shigella vaccine strains
Inventors
Venkatesan, Malabi M. • Ranallo, Ryan T. • Barnoy, Shoshana
Assignees
Walter Reed Army Institute of Research • United States Department of the Army
Publication Number
US-8986708-B2
Publication Date
2015-03-24
Expiration Date
2028-04-25
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Abstract
Shigella vaccine strains whose primary attenuating feature is deletion of the virG(icsA) gene and additional two or more deletions in setAB(shET1), senA(shET2), senB(shET2-2), stxAB, and msbB2 genes. Thus, the vaccine strain will have three or more deletions in the identified genes, will be safer, and will reduce or eliminate symptoms of fever and diarrhea in humans. The following specific vaccine strains have been constructed: WRSS3 (ΔsenA, ΔsenB, ΔvirG, ΔmsbB2), WRSf2G15 (ΔvirG, ΔsetAB, ΔsenA, ΔsenB, ΔmsbB2), and WRSd5 (ΔvirG, ΔstxAB, ΔsenA, ΔsenB, ΔmsbB2).
Core Innovation
The invention relates to live attenuated Shigella vaccine strains characterized primarily by deletion of the virG(icsA) gene along with two or more additional deletions in the genes setAB(shET1), senA(shET2), senB(shET2-2), stxAB, and msbB2. This combination of three or more deletions aims to create vaccine strains that are safer and reduce or eliminate symptoms of fever and diarrhea in humans following vaccination.
The problem addressed by the invention arises from prior live attenuated Shigella vaccine strains with only the virG(icsA) gene deletion, which, although safe at certain doses, caused unacceptable reactogenic symptoms such as mild diarrhea and fever in 15-25% of volunteers. Additional enterotoxic and lipid A-modifying genes contribute to these symptoms, necessitating further attenuation through combined gene deletions to reduce reactogenicity without compromising immunogenicity or protective efficacy.
The invention details specific vaccine strains, including WRSS3, WRSf2G15, and WRSd5, each containing a combination of gene deletions targeting virG(icsA) plus enterotoxin and lipid A-related genes. These strains have been shown to be invasive in epithelial cells but lack plaque formation, do not induce keratoconjunctivitis in guinea pigs, elicit protective immunity, and are efficiently excreted in monkeys. They can be formulated singly or in multivalent mixtures covering major Shigella serogroups, administered at low doses, and have potential as carriers for antigens or immune modulators from other pathogens.
Claims Coverage
The patent includes fourteen claims, comprising one independent apparatus claim directed to live attenuated Shigella vaccine strains with specific gene deletions and one independent method claim directed to their administration. The main inventive features identified from the claims focus on the combination of gene deletions defining the vaccine strains and their use as vaccines.
Live attenuated Shigella vaccine strain with specified combinations of gene deletions
A live attenuated gut-colonizing Shigella vaccine strain characterized by deletions or inactivations of virG(icsA), senA(shET2), and senB(shET2-2), combined with one or more deletions or inactivations selected from setAB(shET1), stxAB, and msbB2 genes.
Serogroup and strain specificity of the vaccine strain
The vaccine strain is a virulent strain selected from four major Shigella serogroups: S. flexneri, S. sonnei, S. dysenteriae, and S. boydii, including specific embodiments such as S. flexneri 2a and S. dysenteriae 1.
Phenotypic characteristics of the vaccine strain
The strain displays one or more traits such as invasiveness in epithelial cells, absence of plaque formation in epithelial cell monolayers, or lack of keratoconjunctivitis induction in guinea pig eyes.
Specific constructed vaccine strains
Vaccine strains exemplified include WRSS3 (ΔsenA, ΔsenB, ΔvirG, ΔmsbB2), WRSf2G15 (ΔvirG, ΔsetAB, ΔsenA, ΔsenB, ΔmsbB2), and WRSd5 (ΔvirG, ΔstxAB, ΔsenA, ΔsenB, ΔmsbB2), among others.
Formulation of immunogenic compositions and vaccine kits
Compositions comprising one or more of the defined Shigella vaccine strains with a pharmaceutically acceptable carrier are encompassed, as well as kits containing one or more containers with the vaccine strains, optionally with written instructions.
Method of administration for inducing protective immune response
A method comprising administering an effective oral dose of 10^4 to 10^6 CFU of one or more of the defined vaccine strains to a subject in need thereof to induce protective immunity against Shigella spp.
The claims cover mutant Shigella strains combining virG(icsA) deletion with multiple deletions of enterotoxin and lipid A-related genes, their phenotypic and serogroup characteristics, formulations as vaccines and kits, and methods of administration to achieve protection against Shigella infections.
Stated Advantages
The vaccine strains are safer with reduced or eliminated reactogenic symptoms such as fever and diarrhea in human volunteers.
The genetic modifications do not compromise invasiveness, immunogenicity, or protective efficacy of the vaccine strains.
The strains can be administered orally at low doses (10^4 to 10^6 CFU) with a protective immune response achieved often in a single dose.
The strains maintain gut colonization and viability, essential for inducing immune responses.
The strains can be used in multivalent vaccines covering multiple Shigella serogroups and combined with live vaccines against enterotoxigenic E. coli (ETEC).
The vaccine strains can serve as carriers for antigens or immune modulators from other diarrheal pathogens, enhancing their versatility.
Documented Applications
Prevention and treatment of dysentery and diarrhea caused by Shigella flexneri, Shigella sonnei, Shigella dysenteriae, and Shigella boydii.
Use in multivalent live attenuated vaccines combining two or more Shigella serotypes.
Combination with live attenuated vaccines against enterotoxigenic E. coli (ETEC) to provide protection against multiple diarrheal pathogens.
Prime-boost vaccination strategies where live vaccines are followed by subunit vaccines to enhance protection against Shigella.
Use as carriers of antigens from other diarrheal pathogens such as Campylobacter, or as mucosal delivery vectors for other prokaryotic and eukaryotic antigens and carriers for immune modulators like cytokines.
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