Intranasal Immunization of Mice with Multiepitope Chimeric Vaccine Candidate Based on Conserved Autotransporters SigA, Pic and Sap, Confers Protection against Shigella flexneri

Abstract

Shigellosis is a diarrheal disease and the World Health Organization prompts the development of a vaccine against Shigella flexneri. The autotransporters SigA, Pic and Sap are conserved among Shigella spp. We previously designed an in silico vaccine with immunodominat epitopes from those autotransporters, and the GroEL protein of S. typhi as an adjuvant. Here, we evaluated the immunogenicity and protective efficacy of the chimeric multiepitope protein, named rMESF, in mice against lethal infection with S. flexneri. rMESF was administered to mice alone through the intranasal (i.n.) route or accompanied with Complete Freund’s adjuvant (CFA) intradermically (i.d.), subcutaneously (s.c.), and intramuscular (i.m.), as well as with Imject alum (i.m.). All immunized mice increased IgG, IgG1, IgG2a, IgA and fecal IgA titers compared to PBS+CFA and PBS+alum control groups. Furthermore, i.n. immunization of mice with rMESF alone presented the highest titers of serum and fecal IgA. Cytokine levels (IFN-γ, TNF-α, IL-4, and IL-17) and lymphocyte proliferation increased in all experimental groups, with the highest lymphoproliferative response in i.n. mice immunized with rMESF alone, which presented 100% protection against S. flexneri. In summary, this vaccine vests protective immunity and highlights the importance of mucosal immunity activation for the elimination of S. flexneri.

Shigella flexneri vaccine development: Oral administration of peptides derived from the 49.8 kDa pili protein subunit activates the intestinal immune response in mice

“…A previous study reported a similar IL-4 production after administering a peptide derived from the EpiMix protein of S. flexneri [45]. Another study revealed that the recombinant chimeric protein rMESF of S. flexneri significantly increased IL-4 levels through all tested application routes; intranasal, intravenous, intramuscular, and subcutaneous [46].…”

“…The increase in sIgA levels in this study suggested that our vaccine candidates stimulated the mucosal immune responses. The vaccine using S. flexneri rMESF multiepitope protein increases sIgA-specific antibodies in the mucus layer and system wide [46]. EpiMix, S. flexneri protein fragment, produces a specific sIgA mucosal immune response from immunized animal fecal samples [45].…”

Recent Progress in Shigella and Burkholderia pseudomallei Vaccines

“…A multivalent vaccine, called rMESF, containing a chimeric protein derived from the immunodominant epitopes from SigA, Pic, and Sap bound to GroEL of S. Typhi as an adjuvant was used to I.n. immunize mice [48]. This vaccine elicited robust, rMESF-specific serum IgG and IgA and fecal IgA titers, and splenocytes from immunized mice elicited significant levels of TNFα, IL-17, and IFN-γ.…”

“…Chromosomally-encoded proteins have also been found to be immunogenic, including three autotransporters that are encoded on the pathogenicity island SHI-1: SigA, Pic, and Sap [48]. SigA and Pic are serine-protease autotransporters involved in virulence and immune recognition [49].…”

“…Lastly, immunization with rMESF provided 100% protection in mice against lethal I.n. challenge of S. flexneri [48].…”