Design and structural characterization of a chimeric protein displayed on virus-like particles for targeted immune activation against Salmonella Typhi.

This study explores the design of a recombinant chimeric protein integrating key immunogenic epitopes from Salmonella Typhi into a macromolecular framework using the innovative SpyCatcher/SpyTag dual conjugation system. S. typhi remains a significant global health challenge, emphasizing the need for novel therapeutic approaches. The engineered chimeric protein, incorporating epitopes from three major S. typhi virulence factors OmpC, OmpF, and flagellin was displayed on AP205 virus-like particles (VLPs), creating a stable and immunogenic complex. Analytical techniques confirmed the successful conjugation and structural integrity of the chimeric protein on VLPs. Molecular dynamics simulations revealed robust interactions between the chimeric protein, incorporating the FliC sequence, and TLR5, highlighting its potential to stimulate both Th1 and Th2 immune responses. The chimeric protein antigen, administered via both subcutaneous and oral routes in different formulations (alone, with adjuvant, or conjugated to VLPs), elicited significant immune responses in BALB/c mice, assessed through antibody assays, cytokine profiling, and challenge tests. Although the chimeric protein alone did not confer full protection, formulations such as the chimeric protein displayed on VLPs (hereafter referred to as NanosalVAX) provided 100% survival against a lethal bacterial challenge. The primary objective is to design a macromolecular VLP platform displaying a S. typhi chimeric antigen (OFFS-ST) to elicit synergistic humoral-cellular immunity against typhoid. This study underscores the potential of engineered macromolecules, such as chimeric proteins and VLPs, in advancing therapeutic applications and highlights their potential in combating infectious diseases.