The protection afforded to cattle immunized with Theileria annulata infected cell line is enhanced by subunit vaccine candidate TaSP

Mining gene expression data for rational identification of novel drug targets and vaccine candidates against the cattle tick, Rhipicephalus microplus

Control of complex parasites via vaccination remains challenging, with the current combination of vaccines and small drugs remaining the choice for an integrated control strategy. Studies conducted to date, are providing evidence that multicomponent vaccines will be needed for the development of protective vaccines against endo- and ectoparasites, though multicomponent vaccines require an in-depth understanding of parasite biology which remains insufficient for ticks. With the rapid development and spread of acaricide resistance in ticks, new targets for acaricide development also remains to be identified, along with novel targets that can be exploited for the design of lead compounds. In this study, we analysed the differential gene expression of Rhipicephalus microplus ticks that were fed on cattle vaccinated with a multi-component vaccine (Bm86 and 3 putative Bm86-binding proteins). The data was scrutinised for the identification of vaccine targets, small drug targets and novel pathways that can be evaluated in future studies. Limitations associated with targeting novel proteins for vaccine and/or drug design is also discussed and placed into the context of challenges arising when targeting large protein families and intracellular localised proteins. Lastly, this study provide insight into how Bm86-based vaccines may reduce successful uptake and digestion of the bloodmeal and overall tick fecundity.

Sequence polymorphisms in a Theileria annulata surface protein (TaSP) known to augment the immunity induced by live attenuated cell line vaccine

Theileria annulata is a tick-borne protozoan causing tropical theileriosis in cattle. The use of attenuated cell line vaccines in combination with subunit vaccines has been relatively successful as a control method, as exemplified by a recent study in which immunization with a local cell line followed by booster vaccinations with recombinant T. annulata surface protein (TaSP) resulted in 100% protection upon field challenge in Sudan. However, these findings cannot be directly extrapolated to other countries as culture-attenuated live vaccines are generated using local strains and no systematic evaluation of genotype differences between countries has been undertaken. In this study, we sequenced the TaSP gene from T. annulata cell lines and field isolates from Tunisia (n = 28) and compared them to genotypes from Sudan (n = 25) and Morocco (n = 1; AJ316259.1). Our analyses revealed 20 unique TaSP genotypes in the Tunisian samples, which were all novel but similar to genotypes found in Asia. The impact of these polymorphisms on the ability of the TaSP antigen to boost the immunity engendered by live cell line vaccines, especially in Tunisia where studies with TaSP have not been conducted, remains to be examined. Interestingly, phylogenetic analyses of publicly available TaSP sequences resolved the sequences into two clusters with no correlation to the geographical origin of the isolates. The availability of candidate vaccines that were recently attenuated using local strains from Sudan, Tunisia, Egypt and Morocco should be exploited to generate a comprehensive catalogue of genetic variation across this regional collection of attenuated live vaccines.