ABSTRACT There are no licensed vaccines against Shigella , a leading cause of children’s diarrhea and travelers’ diarrhea. To develop a cross-protective vaccine against heterogeneous Shigella species and serotypes, we attempted to apply an epitope- and structure-based vaccinology platform, multiepitope fusion antigen, to construct an optimal polyvalent chimeric immunogen with functional epitopes from the key Shigella virulence determinants. With Shigella invasion plasmid antigens B and D functional epitopes identified in recent studies, in this study, we focused on Shigella intracellular spread protein A (IcsA; also known as virulence gene G, VirG), a multifunctional virulence factor that plays roles in bacterial adherence, invasion, and particularly intracellular and intercellular spread. We in silico predicted continuous B-cell immunodominant epitopes from the IcsA functional passenger domain, and we fused each epitope to a non-homologous carrier protein, Escherichia coli adhesin CS4 subunit CsaB, for epitope fusions. We then immunized mice with each epitope fusion and examined antibody functions against Shigella bacterial invasion and adherence. Eleven IcsA B-cell epitopes were identified and fused to CsaB. Mice intramuscularly immunized with each epitope fusion developed IgG responses. Mouse serum antibodies significantly reduced Shigella sonnei or Shigella flexneri 2a bacterial invasion or adherence in vitro , particularly from the fusion with epitope #2 ( 122 GDNNDGNSCGGNG 134 ), #3 ( 156 GGSGADHNGDGGE 168 ), #7 ( 309 YIISGKEDDGTQNV 325 ), #9 ( 485 WNDTDGDSHG 494 ), or #10 ( 507 TILADNLSHHNIN 523 ). These IcsA epitopes are more effective in inducing functional antibodies, suggesting their antigenic utility in constructing an optimal polyvalent Shigella immunogen and developing a cross-protective vaccine, and perhaps in better understanding their role in IcsA biogenesis. IMPORTANCE An effective Shigella vaccine is urgently needed to reduce Shigella -associated diarrhea and dysentery. Shigella IcsA (or VirG) plays a crucial role in Shigella bacterial pathogenesis and is conserved across Shigella species and serotypes, thus making IcsA an excellent antigen target in Shigella vaccine development. Identification of the functional epitopes of the IcsA passenger domain from this study enables us to construct an optimal epitope- and structure-based polyvalent immunogen for a cross-protective multivalent Shigella vaccine. Unlike the lipopolysaccharide-based whole-cell or subunit vaccine candidates that are serotype-specific, a multivalent vaccine carrying functional epitopes of conserved virulence determinants would be cross-protective against the heterogeneous Shigella species and serotypes, effectively preventing shigellosis and dysentery. Data from this study may also provide insightful information for a better understanding of IcsA biogenesis.
Madhwal et al. (Fri,) studied this question.