Shigella Mutant with Truncated O-Antigen as an Enteric Multi-Pathogen Vaccine Platform

<b>Background/Objectives</b>: Rising antibiotic resistance underscores the urgent need for effective vaccines against shigellosis. Our previous research identified the <i>Shigella flexneri</i> 2a truncated mutant (STM), a <i>wzy</i> gene knock-out strain cultivated in shake-flasks, as a promising broadly protective <i>Shigella</i> vaccine candidate. Expanding on this finding, our current study explores the feasibility of transitioning to a fermentor-grown STM as a vaccine candidate for further clinical development. <b>Methods</b>: The STM and STM-Cj, engineered to express the conserved <i>Campylobacter jejuni</i> N-glycan antigen, were grown in animal-free media, inactivated with formalin, and evaluated for key antigen retention and immunogenicity in mice. <b>Results</b>: The fermentor-grown STM exhibited significantly increased production yields and retained key antigens after inactivation. Immunization with the STM, particularly along with the double-mutant labile toxin (dmLT) adjuvant, induced robust immune responses to the conserved proteins IpaB, IpaC, and PSSP-1. Additionally, it provided protection against homologous and heterologous <i>Shigella</i> challenges in a mouse pulmonary model. The STM-Cj vaccine elicited antibody responses specific to the N-glycan while maintaining protective immune responses against <i>Shigella</i>. These findings underscore the potential of the fermentor-grown STM as a safe and immunogenic vaccine platform for combating shigellosis and possibly other gastrointestinal bacterial infections. <b>Conclusions</b>: Further process development to optimize growth and key antigen expression as well as expanded testing in additional animal models for the assessment of protection against <i>Shigella</i> and <i>Campylobacter</i> are needed to build on these encouraging initial results. Ultimately, clinical trials are essential to evaluate the efficacy and safety of STM-based vaccines in humans.