What Is Vi Capsular Polysaccharide (CPS)?

In poor areas of developing countries, where sanitation is lacking, the problem of typhoid fever caused by Salmonella typhi continues to be a major concern for public health. The Vi CPS synthesized by S. typhi displays its remarkable capacity as a protective antigen against this debilitating disease. The Vi CPS is comprised of a linear homopolymer of α1,4-N-acetylgalactosaminouronic acid. And it is acetylated at the C-3 position to varying extents (60-90% O-acetylated). Vi antigen expression is modulated by two distinct loci, viaA, and viaB that are located at 43 and 92 min on the S. typhi chromosome, respectively. Functional viaA genes are identified not only in Vi-expressing strains of Salmonella and Citrobacter but also in Escherichia coli. Vi CPS is a crucial antigen that plays a pivotal role in the ongoing study of vaccines targeting typhoid fever.

Fig.1 The role of the Vi CPS in directing S. typhi. (Jiang, et al., 2023)

Salmonella CPS Production Services at CD BioGlyco

CD BioGlyco uses Citrobacter to produce Vi CPS. Because it is structurally similar and immunologically indistinguishable to Vi CPS from S. typhi. By utilizing Citrobacter as a safer alternative for producing Vi CPS, we develop an improved method for purifying PS. To purify Vi PS, we first precipitate it from the culture supernatant using cetyltrimethylammonium bromide (CTAB). Then, we dissolve the CTAB-PS complex in ethanol and replace the CTAB⁺ ion with the Na⁺ ion. Our purified Vi PS displays full O-acetylation and remarkable purity. We accurately assess the molecular size of purified Vi PS by high-performance liquid chromatography-size exclusion chromatography (HPLC-SEC). That also serves to scrutinize the absence of by-products derived from PS de-polymerization or aggregation.

We have developed a conjugate vaccine targeting Salmonella by linking Vi CPS to the non-toxic mutant diphtheria toxin Cross-reacting Material 197 (CRM197). We utilize an adipic dihydrazide spacer and N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide coupling chemistry for the conjugation. The resulting conjugates are meticulously characterized through a battery of analytical techniques, including sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), HPLC-SEC, proton nuclear magnetic resonance (¹H NMR), and mass spectrometry (MS).

Fig.2 The characterization of Vi CPS. (CD BioGlyco)

Advantages of Us

• Our method preserves the O-acetylation level of Vi PS and does not alter the original structure of Vi PS.
• Our process maintains the molecular weight distribution of Vi PS.
• Our process requires less complex apparatus.

CD BioGlyco is an esteemed biotechnology that is renowned for cutting-edge advancements in vaccine development. At CD BioGlyco, we proudly use the Glyco™ Vaccine Development Platform to innovate in the field of PS antigen production. Our foremost expertise lies in the realm of Carbohydrate-based Vaccine Development. If our services resonate with your needs, please feel free to contact us for more detailed information.

Reference:

1. Jiang, L.; et al. Nitric oxide is a host cue for Salmonella typhimurium systemic infection in mice. Communications Biology. 2023, 6(1): 1-13.