The Salmonella Paratyphi A O-Antigen Glycoconjugate Vaccine Is Able to Induce Antibodies with Bactericidal Activity Against a Panel of Clinical Isolates.

Abstract

Background: Typhoid and paratyphoid fevers represent a global health burden, especially in Southern Asia, exacerbated by the increase in antimicrobial resistance. While vaccines against Salmonella Typhi have been successfully introduced, a vaccine against S. Paratyphi A is not available, yet. Efforts to develop an effective vaccine targeting both Salmonella serovars are currently ongoing. GVGH is developing a bivalent vaccine constituted by the Vi-CRM₁₉₇ typhoid conjugate vaccine (TCV), and the Salmonella Paratyphi A O-antigen (O:2), also conjugated to the CRM₁₉₇ carrier protein (O:2-CRM₁₉₇). In this work we have characterized a panel of S. Paratyphi A clinical isolates from endemic regions, differing in terms of their O:2 structural features.

Methods: Rabbits were immunized with the S. Paratyphi A component of the vaccine candidate and the resulting sera were tested for their ability to bind and kill the isolates using flow cytometry and luminescence-based serum bactericidal assay (L-SBA).

Results: The O:2-CRM₁₉₇ glycoconjugate induced a functional immune response in rabbits, effectively binding and killing a diverse panel of clinical isolates. The sera demonstrated bactericidal activity independent of the O:2 structural variations, including differences in O-acetylation and glucosylation levels. Additionally, the study found that the O:2-CRM₁₉₇ conjugate's adsorption to Alhydrogel did not significantly impact its immunogenicity or bactericidal efficacy.

Conclusions: The O:2-CRM₁₉₇ component of the bivalent vaccine candidate shows promise in providing broad protection against S. Paratyphi A isolates, regardless of their O-antigen structural variations. The ongoing clinical studies on human sera are expected to confirm these results.