Immunoinformatics-driven design and in silico evaluation of a multi-epitope vaccine candidate against Orientia tsutsugamushi causing scrub typhus

Abstract

Despite decades of research, an effective vaccine against Orientia tsutsugamushi remains unavailable owing to the pathogen's high antigenic variability, intracellular persistence, and poor cross-protection between strains. This study was conducted to develop a conserved multi-epitope vaccine candidate against the 56kDa type specific antigen (TSA56) of O. tsutsugamushi through a reverse vaccinology and immunoinformatic strategy. Seven TSA56 protein sequences collected from the UniProtKB database were evaluated for their antigenicity, allergenicity, and toxicity. Chimeric vaccine candidates consisting of the conserved CTL, HTL, and B-cell epitopes, which showed immunogenic potential and good safety parameters, were constructed. Finalization of the construct exhibited good antigenic activity, no allergenicity, structural stability, and good physicochemical properties. The structural validation resulted in the finding that 95.5% of residues occupied the favoured Ramachandran regions, implying a stable tertiary structure. From molecular docking results, the molecule interacted stably with the Toll-like receptor 2 (TLR2) with the lowest docking energy of −1334.7. Normal mode analysis using iMODS validated the stability and coordinated molecular motions of the vaccine–TLR2 complex, further supporting its immunological potential. Prediction on immune system response indicated good humoral responses in terms of high levels of IgM and IgG antibodies with creation of immunological memory. Codon optimization and in silico cloning were done to confirm the applicability of the construct for expression in E. coli.