Reverse vaccinology approach to identify novel cattle tick protective antigens (#47)
A reverse vaccinology genomic approach was developed to identify novel antigens for the protection of cattle from the tick: Rhipicephalus (Boophilus) microplus. This ectoparasite causes extensive economic losses to cattle production in tropical and sub-tropical regions of the world through tick burdens, and the transmission of tick fever (babesiosis and anaplasmosis). Ticks rapidly develop resistance to acaricides and thus the development of a vaccine with long duration of immunity is an industry priority. Such a vaccine needs to be capable of producing an anamnestic (“remembered”) response following natural tick infestations. This research commenced with the analysis of available expressed sequence tags (ESTs) as the R. microplus genome is large (7.1Gb) and consists of ~80% repeat sequences. Subsequent steps included bioinformatics screening of existing (USDA database V.2 ~13,643 ESTs) and new targeted R. microplus sequences (subtraction library analysis, and cDNA microarray analysis of ticks collected from resistant vs susceptible cattle~300 ESTs). Identified candidates were further scrutinised using expression analysis (localisation to stages and organs), and further informatics (membrane and secretion predictions; domain analysis and B cell epitope analysis). B cell epitopes (748 representing 240 sequences from 95 candidate protein families and singletons) were screened against pools of sera collected from tick susceptible and resistant cattle following tick challenge. Eighty peptides representing those recognised by resistant cattle were used to prepare antibodies for in vitro adult female tick feeding experiments. Simultaneously, 6 polypeptide proteins were constructed from peptides shown to be recognised by resistant cattle. In vitro feeding % effectivity for each antibody treatment was determined by monitoring adult tick death, egg output (g), and % larval emergence in comparison to naive serum/blood fed tick controls. Successful cattle vaccinations with strong protection from tick challenge were observed using a mix of 6 peptides (selected from the strongest top 9 tick feeding effectivities), a polypeptide mixture (9 antigens with peptides recognised by tick resistant cattle) and a single recombinant (selected from the top 9 feeding effectivities). Current research is focussing on vaccine product development. This approach can be easily adapted for the identification of vaccine candidates for other parasites with large genomes.