Designing of a conserved subunit multiepitope vaccine candidate against Francisella tularensis Schu S4 using immunoinformatics.

Francisella tularensis Schu S4 is the most virulent strain responsible for tularemia, a highly infectious zoonotic disease. Despite its potential as a pathogen of concern, no effective vaccine has been developed for this pathogen. In this study, two multi-epitope subunit vaccine candidates were designed targeting the virulence factors DacD and DsbA to reduce disease severity caused by F. tularensis Schu S4. Using a comprehensive immunoinformatics approach, the most efficient B- and T-cell epitopes were identified from conserved sequences and linked with adjuvants and linkers to generate two vaccine constructs. These constructs were modeled, refined, and validated through molecular docking against Toll-Like Receptors (TLRs) and MHC alleles, followed by 200 ns molecular dynamics simulations. Their immunogenic potential and expression efficiency were further evaluated through immune simulations and computational cloning into the pET30a( +) vector. Both the constructed vaccine candidates, TulaVac1 and TulaVac2, showed high antigenicity, immunogenicity, stability, and solubility. The epitope conservancy was nearly 100%, with global population coverage rates of 73.19% and 99.74% for MHC class I and II epitopes, respectively. Docking analyses revealed six CTL epitopes with binding energies of ≤ -9.0 kcal/mol, while vaccine-TLR and MHC docking suggested superior performance of TulaVac1. MM/GBSA analysis yielded favorable binding energies ranging from - 87.22 to - 161.30 kcal/mol, MD simulations confirmed the stable interaction for 200 ns, and immune simulations showed robust immune responses with satisfactory codon adaptation. These findings position TulaVac1 and TulaVac2 as promising candidates for effective prophylaxis against tularemia.