# BECC-engineered live-attenuated Shigella vaccine candidates display reduced endotoxicity with robust immunogenicity in mice

## TL;DR

Scientists engineered safer Shigella vaccines that still trigger strong immune responses in mice.

## Contribution

BECC is used to modify Shigella vaccines to reduce endotoxicity while maintaining immunogenicity.

## Key findings

- BECC-modified Shigella strains showed reduced TLR4 signaling and endotoxic effects.
- Modified vaccines retained parental traits like cell invasion and mouse immunogenicity.
- The approach suggests a safe and effective Shigella vaccine strategy.

## Abstract

Shigella spp. infection contributes significantly to the global disease burden, primarily affecting young children in developing countries. Currently, there are no FDA-approved vaccines against Shigella, and the prevalence of antibiotic resistance is increasing, making therapeutic options limited. Live-attenuated vaccine strains WRSs2 (S. sonnei) and WRSf2G12 (S. flexneri 2a) are highly immunogenic, making them promising vaccine candidates, but possess an inflammatory lipid A structure on their lipopolysaccharide (LPS; also known as endotoxin). Here, we utilized bacterial enzymatic combinatorial chemistry (BECC) to ectopically express lipid A modifying enzymes in WRSs2 and WRSf2G12, as well as their respective wild-type strains, generating targeted lipid A modifications across the Shigella backgrounds. Dephosphorylation of lipid A, rather than deacylation, reduced LPS-induced TLR4 signaling in vitro and dampened endotoxic effects in vivo. These BECC-modified vaccine strains retained the phenotypic traits of their parental strains, such as invasion of epithelial cells and immunogenicity in mice without adverse endotoxicity. Overall, our observations suggest that BECC-engineered live attenuated vaccines are a promising approach to safe and effective Shigella vaccines.