Probing the Rhipicephalus bursa Sialomes in Potential Anti-Tick Vaccine Candidates: A Reverse Vaccinology Approach

Abstract

In the wake of the ‘omics’ explosion of data, reverse vaccinology approaches are being applied more readily as an alternative for the discovery of candidates for next generation diagnostics and vaccines. Promising protective antigens for the control of ticks and tick-borne diseases can be discovered by mining available omics data for immunogenic epitopes. The present study aims to explore the previously obtained Rhipicephalus bursa sialotranscriptome during both feeding and Babesia infection, to select antigenic targets that are either membrane-associated or a secreted protein, as well as unique to the ectoparasite and not present in the mammalian host. Further, they should be capable of stimulating T and B cells for a potential robust immune response, and be non-allergenic or toxic to the host. From the R. bursa transcriptome, 5706 and 3025 proteins were identified as belonging to the surfaceome and secretome, respectively. Following a reverse genetics immunoinformatics pipeline, nine preferred candidates, consisting of one transmembrane-related and eight secreted proteins, were identified. These candidates showed a higher predicted antigenicity than the Bm86 antigen, with no homology to mammalian hosts and exposed regions. Only four were functionally annotated and selected for further in silico analysis, which examined their protein structure, surface accessibility, flexibility, hydrophobicity, and putative linear B and T-cell epitopes. Regions with overlapping coincident epitopes groups (CEGs) were evaluated to select peptides that were further analyzed for their physicochemical characteristics, potential allergenicity, toxicity, solubility, and potential propensity for crystallization. Following these procedures, a set of three peptides from the three R. bursa proteins were selected. In silico results indicate that the designed epitopes could stimulate a protective and long-lasting immune response against those tick proteins, reflecting its potential as anti-tick vaccines. The immunogenicity of these peptides was evaluated in a pilot immunization study followed by tick feeding to evaluate its impact on tick behavior and pathogen transmission. Combining in silico methods with in vivo immunogenicity evaluation enabled the screening of vaccine candidates prior to expensive infestation studies on the definitive ovine host animals.

From Bench to Field: A Guide to Formulating and Evaluating Anti-Tick Vaccines Delving beyond Efficacy to Effectiveness

“…For a deeper insight on the basics of immune responses, refer to Abbas et al [ 37 ] In regard to memory induction, highly immunogenic tick antigens such as Bm86 [ 38 ] and GSTs [ 39 ] are reported to have T- and B-cell epitopes. What this suggests is that after obtaining omics data, researchers should examine the immunogenic potential of the target protein(s) based on the presence of B- and T-cell epitopes [ 40 ]. Fortunately, this can easily be achieved using immunoinformatics tools.…”

Imunobioinformática para leigos

“…(B) Predição da topologia (com base na ferramenta Phobious) e localização da região CEG (amarelo) na estrutura da proteína. Fonte: Couto et al, 2021 [19].…”

Tick-borne Diseases, Transmission, Host Immune Responses, Diagnosis and Control

“…Best example is tick midgut antigen BM86 that was used to prepare highly effective and promising vaccine for cattle tick control [215] . This Bm86 vaccines was commercialized in the 1990s (GavacTM in Cuba and TickGARDPLUS™ in Australia), only Gavac™ is available [216] . TBEV vaccines molecules from tick saliva mainly toxins are used as antigens [217] .…”