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.
