A broadly immunogenic polyvalent <i>Shigella</i> multiepitope fusion antigen protein protects against <i>Shigella sonnei</i> and <i>Shigella flexneri</i> lethal pulmonary challenges in mice

Abstract

There are no licensed vaccines for <i>Shigella</i>, a leading cause of children's diarrhea and a common etiology of travelers' diarrhea. To develop a cross-protective <i>Shigella</i> vaccine, in this study, we constructed a polyvalent protein immunogen to present conserved immunodominant epitopes of <i>Shigella</i> invasion plasmid antigens B (IpaB) and D (IpaD), VirG, GuaB, and Shiga toxins on backbone protein IpaD, by applying an epitope- and structure-based multiepitope-fusion-antigen (MEFA) vaccinology platform, examined protein (<i>Shigella</i> MEFA) broad immunogenicity, and evaluated antibody function against <i>Shigella</i> invasion and Shiga toxin cytotoxicity but also protection against <i>Shigella</i> lethal challenge. Mice intramuscularly immunized with <i>Shigella</i> MEFA protein developed IgG responses to IpaB, IpaD, VirG, GuaB, and Shiga toxins 1 and 2; mouse sera significantly reduced invasion of <i>Shigella sonnei</i>, <i>Shigella flexneri</i> serotype 2a, 3a, or 6, <i>Shigella boydii,</i> and <i>Shigella dysenteriae</i> type 1 and neutralized cytotoxicity of Shiga toxins of <i>Shigella</i> and Shiga toxin-producing <i>Escherichia coli in vitro</i>. Moreover, mice intranasally immunized with <i>Shigella</i> MEFA protein (adjuvanted with dmLT) developed antigen-specific serum IgG, lung IgG and IgA, and fecal IgA antibodies, and survived from lethal pulmonary challenge with <i>S. sonnei</i> or <i>S. flexneri</i> serotype 2a, 3a, or 6. In contrast, the control mice died, became unresponsive, or lost 20% of body weight in 48 h. These results indicated that this <i>Shigella</i> MEFA protein is broadly immunogenic, induces broadly functional antibodies, and cross-protects against lethal pulmonary challenges with <i>S. sonnei</i> or <i>S. flexneri</i> serotypes, suggesting a potential application of this polyvalent MEFA protein in <i>Shigella</i> vaccine development.