Design of Glycoconjugate Vaccines against Invasive African Salmonella enterica Serovar Typhimurium

Abstract

dNontyphoidal salmonellae, particularly Salmonella enterica serovar Typhimurium, are a major cause of invasive disease in Africa, affecting mainly young children and HIV-infected individuals. Glycoconjugate vaccines provide a safe and reliable strategy against invasive polysaccharide-encapsulated pathogens, and lipopolysaccharide (LPS) is a target of protective immune responses. With the aim of designing an effective vaccine against S. Typhimurium, we have synthesized different glycoconjugates, by linking O-antigen and core sugars (OAg) of LPS to the nontoxic mutant of diphtheria toxin (CRM 197 ). The OAg-CRM 197 conjugates varied in (i) OAg source, with three S. Typhimurium strains used for OAg extraction, producing OAg with differences in structural specificities, (ii) OAg chain length, and (iii) OAg/CRM 197 ratio. All glycoconjugates were compared for immunogenicity and ability to induce serum bactericidal activity in mice. In vivo enhancement of bacterial clearance was assessed for a selected S. Typhimurium glycoconjugate by challenge with live Salmonella. We found that the largest anti-OAg antibody responses were elicited by (i) vaccines synthesized from OAg with the highest glucosylation levels, (ii) OAg composed of mixed-or medium-molecular-weight populations, and (iii) a lower OAg/CRM 197 ratio. In addition, we found that bactericidal activity can be influenced by S. Typhimurium OAg strain, most likely as a result of differences in OAg O-acetylation and glucosylation. Finally, we confirmed that mice immunized with the selected OAg-conjugate were protected against S. Typhimurium colonization of the spleen and liver. In conclusion, our findings indicate that differences in the design of OAg-based glycoconjugate vaccines against invasive African S. Typhimurium can have profound effects on immunogenicity and therefore optimal vaccine design requires careful consideration.

Salmonella enterica Serovar Typhi Lipopolysaccharide O-Antigen Modification Impact on Serum Resistance and Antibody Recognition

“…Typhimurium D23580 isolate (33), which can be attributed to the phage-borne family 2 gtr operon that is expressed in this specific strain (21). However, detailed analyses in the context of the host, disease, and serovars are needed to further clarify the impact of O-antigen acetylation and glucosylation (36, 37). …”

Bacteriophage-mediated Glucosylation Can Modify Lipopolysaccharide O-Antigens Synthesized by an ATP-binding Cassette (ABC) Transporter-dependent Assembly Mechanism

“…Given its effect on serotype, glucosylation is an important consideration in vaccine strategies (41,42). Molecular modeling studies have established that glucosylation alters the conformation of Shigella O-antigens.…”

Overexpression of O‐polysaccharide chain length regulators in Gram‐negative bacteria using the Wzx‐/Wzy‐dependent pathway enhances production of defined modal length O‐polysaccharide polymers for use as haptens in glycoconjugate vaccines

“…Typhimurium OPS is optimally immunogenic, however, the very long chain form was a poor vaccine hapten when end‐linked (Rondini et al . ). It has also been previously shown that the short‐chain COPS from S .…”