Constructing conjugate vaccine against Salmonella Typhimurium using lipid-A free lipopolysaccharide
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RESEARCH
Open Access
Constructing conjugate vaccine against Salmonella Typhimurium using lipid-A free lipopolysaccharide Tzu-Wei Chiu1†, Chi-Jiun Peng1†, Ming-Cheng Chen1†, Mei-Hua Hsu2, Yi-Hua Liang2, Cheng-Hsun Chiu2,3,4*, Jim-Min Fang1,5* and Yuan Chuan Lee6
Abstract Background: Salmonella enterica serotype Typhimurium is a nontyphoidal and common foodborne pathogen that causes serious threat to humans. There is no licensed vaccine to prevent the nontyphoid bacterial infection caused by S. Typhimurium. Methods: To develop conjugate vaccines, the bacterial lipid-A free lipopolysaccharide (LFPS) is prepared as the immunogen and used to synthesize the LFPS–linker–protein conjugates 6a–9b. The designed bifunctional linkers 1–5 comprising either an o-phenylenediamine or amine moiety are specifically attached to the exposed 3-deoxy-Dmanno-octulosonic acid (Kdo), an α-ketoacid saccharide of LFPS, via condensation reaction or decarboxylative amidation. In addition to bovine serum albumin and ovalbumin, the S. Typhimurium flagellin (FliC) is also used as a self-adjuvanting protein carrier. Results: The synthesized conjugate vaccines are characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and fast performance liquid chromatography (FPLC), and their contents of polysaccharides and protein are determined by phenol–sulfuric acid assay and bicinchoninic acid assay, respectively. Enzyme-linked immunosorbent assay (ELISA) shows that immunization of mouse with the LFPS–linker–protein vaccines at a dosage of 2.5 μg is sufficient to elicit serum immunoglobulin G (IgG) specific to S. Typhimurium lipopolysaccharide (LPS). The straight-chain amide linkers in conjugates 7a–9b do not interfere with the desired immune response. Vaccines 7a and 7b derived from either unfractionated LFPS or the high-mass portion show equal efficacy in induction of IgG antibodies. The challenge experiments are performed by oral gavage of S. Typhimurium pathogen, and vaccine 7c having FliC as the self-adjuvanting protein carrier exhibits a high vaccine efficacy of 74% with 80% mice survival rate at day 28 post the pathogen challenge. (Continued on next page)
* Correspondence: [email protected]; [email protected] † Tzu-Wei Chiu, Chi-Jiun Peng and Ming-Cheng Chen contributed equally to this work. 2 Molecular Infectious Disease Research Center, Chang Gung Memorial Hospital, 5, Fuxing St., Guishan Dist, Taoyuan 33302, Taiwan 1 Department of Chemistry, National Taiwan University, 1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan Full list of author information is available at the end of the article © The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this ar
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