Development of multi-epitope chimeric antigens for scrub typhus diagnostics and vaccines: An in-silico investigation

Scrub typhus is a zoonotic bacterial disease caused by Orientia tsutsugamushi and accounts for up to 20% of common febrile illnesses and hospitalizations. The main obstacle to vaccine development is the lack of identification of relevant immunodominant antigens that stimulate broad-spectrum immune responses, including antibody, CD4 + T cells, and CD8 + T cells production. We examined the 56-kDa type-specific cell membrane surface protein (TSA56) and ScaA as candidates for developing vaccine and diagnostic assays using an in-silico approach. We predicted 35 linear and 29 conformational immunogenic B-cell epitopes and 51 non-overlapping strong binders of MHC class I and 27 for MHC class II T-cell epitopes in the conserved and variable regions of TSA56. We used this information to design effective multi-epitope vaccine constructs that are predicted to stimulate cross-protective immunity. Furthermore, the epitope-based vaccine constructs showed antigenic, non-allergenic, and interferon gamma-inducing properties, as predicted by online servers. We cloned the chimeric gene into a pET-15b plasmid vector and successfully expressed the histidine-tagged recombinant antigen in an Escherichia coli expression system. The findings the present study provide a platform for validations of the predicted epitopes and chimeric antigens for designing effective epitope-based vaccine candidates and serological diagnostic assays against scrub typhus.