Madhwal Aashwina, Vakamalla Sai Simha Reddy, Li Siqi, Zhang Weiping
Department of Pathobiology, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA.
Appl Environ Microbiol. 2025 Sep 17;91(9):e0117525. doi: 10.1128/aem.01175-25. Epub 2025 Aug 22.
There are no licensed vaccines against , a leading cause of children's diarrhea and travelers' diarrhea. To develop a cross-protective vaccine against heterogeneous 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 virulence determinants. With invasion plasmid antigens B and D functional epitopes identified in recent studies, in this study, we focused on 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 predicted continuous B-cell immunodominant epitopes from the IcsA functional passenger domain, and we fused each epitope to a non-homologous carrier protein, adhesin CS4 subunit CsaB, for epitope fusions. We then immunized mice with each epitope fusion and examined antibody functions against 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 or 2a bacterial invasion or adherence , particularly from the fusion with epitope #2 (GDNNDGNSCGGNG), #3 (GGSGADHNGDGGE), #7 (YIISGKEDDGTQNV), #9 (WNDTDGDSHG), or #10 (TILADNLSHHNIN). These IcsA epitopes are more effective in inducing functional antibodies, suggesting their antigenic utility in constructing an optimal polyvalent immunogen and developing a cross-protective vaccine, and perhaps in better understanding their role in IcsA biogenesis.IMPORTANCEAn effective vaccine is urgently needed to reduce -associated diarrhea and dysentery. IcsA (or VirG) plays a crucial role in bacterial pathogenesis and is conserved across species and serotypes, thus making IcsA an excellent antigen target in 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 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 species and serotypes, effectively preventing shigellosis and dysentery. Data from this study may also provide insightful information for a better understanding of IcsA biogenesis.
志贺氏菌是儿童腹泻和旅行者腹泻的主要病因，目前尚无针对它的许可疫苗。为研发一种针对志贺氏菌不同菌株和血清型的交叉保护疫苗，我们尝试应用基于表位和结构的疫苗学平台——多表位融合抗原，构建一种具有关键志贺氏菌毒力决定因素功能性表位的最佳多价嵌合免疫原。鉴于近期研究已鉴定出侵袭质粒抗原B和D的功能性表位，在本研究中，我们聚焦于细胞内扩散蛋白A（IcsA；也称为毒力基因G，VirG），这是一种多功能毒力因子，在细菌黏附、侵袭，特别是细胞内和细胞间扩散中发挥作用。我们从IcsA功能性乘客结构域预测连续的B细胞免疫显性表位，并将每个表位与非同源载体蛋白——黏附素CS4亚基CsaB融合，以进行表位融合。然后，我们用每个表位融合物免疫小鼠，并检测其针对志贺氏菌细菌侵袭和黏附的抗体功能。我们鉴定出11个IcsA B细胞表位并将其与CsaB融合。用每个表位融合物进行肌肉注射免疫的小鼠产生了IgG反应。小鼠血清抗体显著降低了福氏志贺氏菌或宋内氏志贺氏菌2a的细菌侵袭或黏附，特别是来自与表位#2（GDNNDGNSCGGNG）、#3（GGSGADHNGDGGE）、#7（YIISGKEDDGTQNV）、#9（WNDTDGDSHG）或#10（TILADNLSHHNIN）融合的抗体。这些IcsA表位在诱导功能性抗体方面更有效，表明它们在构建最佳多价志贺氏菌免疫原和研发交叉保护疫苗中具有抗原效用，或许还能更好地理解它们在IcsA生物合成中的作用。
迫切需要一种有效的志贺氏菌疫苗来减少与志贺氏菌相关的腹泻和痢疾。IcsA（或VirG）在志贺氏菌发病机制中起关键作用，并且在志贺氏菌不同菌株和血清型中保守，因此使IcsA成为志贺氏菌疫苗研发中的一个优秀抗原靶点。本研究中对IcsA乘客结构域功能性表位的鉴定，使我们能够构建一种基于表位和结构的最佳多价免疫原，用于交叉保护的多价志贺氏菌疫苗。与基于脂多糖的全细胞或亚单位疫苗候选物不同，后者是血清型特异性的，携带保守毒力决定因素功能性表位的多价疫苗将对志贺氏菌不同菌株和血清型具有交叉保护作用，有效预防志贺氏菌病和痢疾。本研究的数据也可能为更好地理解IcsA生物合成提供有见地的信息。
