|OLDIGES, DP - Universidade Federal Do Rio Grande Do Norte|
|LAUGHERY, JM - Washington State University|
|TAGLIARI, NJ - Universidade Federal Do Rio Grande Do Norte|
|LEITE FILHO, RV - Universidade Federal Do Rio Grande Do Norte|
|DAVIS, WC - Washington State University|
|DA SILVA, VAZ JR. - Universidade Federal Do Rio Grande Do Norte|
|TERMIGNONI, C - Universidade Federal Do Rio Grande Do Norte|
|Knowles Jr, Donald|
Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2016
Publication Date: 12/2/2016
Citation: Oldiges, D., Laughery, J., Tagliari, N., Leite Filho, R., Davis, W., Da Silva, V.I., Termignoni, C., Knowles, D.P., Suarez, C.E. 2016. Transfected babesia bovis expressing a tick GST as a live vector vaccine. PLOS Neglected Tropical Diseases. doi:10.1371/journal.pntd.0005152.
Interpretive Summary: The cattle tick Rhipicephalus microplus is a hematophagous ectoparasite, responsible for the transmission of lethal parasites such as Babesia sp, limiting cattle production in tropical and subtropical regions of the world. There is an urgent emerging need for improved methods of control for these currently neglected tick and tick borne diseases. It is hypothesized that a dual attenuated-live vector vaccine containing a stably transfected tick antigen elicits protective immune responses against the parasite and the tick vector in vaccinated cattle. Live Babesia vaccines based on attenuated parasites are the only effective method available for preventing acute babesiosis. On the other hand, glutathione-S-transferase from Haemaphysalis longicornis (HlGST) is a known effective antigen against Rhipicephalus microplus, the most common vector for B. bovis. This study describes the development and testing of a transfected, attenuated B. bovis vaccine expressing HlGST against the tick R. microplus. A B. bovis clonal line designated HlGST-Cln expressing HlGST and GFP/BSD, and separately a control transfected B. bovis clonal line expressing only GFP/BSD was used to vaccinate calves in two independent experiments. All immunized calves developed mild babesiosis, and only calves immunized with the HlGST-Cln parasite line generated anti-HlGST antibodies. Tick egg fertility and fully engorged female tick weight were reduced significantly in R. microplus feeding on HlGST-Cln-vaccinated calves. Taken together, these data demonstrates the ability of transfected attenuated B. bovis to elicit antibodies against a heterologous tick antigen in cattle and to induce partial protection in the vaccinated animals against the cattle tick for the first time, representing a step toward the goal to produce a live vector anti-tick vaccine.
Technical Abstract: The Rhipicephalus microplus tick is a notorious blood-feeding ectoparasite of livestock, especially cattle, responsible for massive losses in animal production. It is the main vector for transmission of pathogenic bacteria and parasites, including Babesia bovis, an intraerythrocytic apicomplexan protozoan parasite responsible for bovine Babesiosis. This study describes the development and testing of a live B. bovis vaccine expressing the protective tick antigen glutathione-S-transferase from Haemaphysalis longicornis (HlGST). The B. bovis S74-T3B parasites were electroporated with a plasmid containing the bidirectional Ef-1 alpha promoter of B. bovis controlling expression of two independent genes, the selectable marker GFP-BSD, and HlGST fused to the MSA-1 (merozoite surface antigen-1) signal peptide from B. bovis. Electroporation followed by blasticidin selection resulted in the emergence of a mixed B. bovis transfected line (termed HlGST) in in vitro cultures, containing parasites with distinct patterns of insertion of both exogenous genes, either in or outside the Ef-1' locus. A B. bovis clonal line termed HlGST-Cln expressing HlGST and GFP was then derived from the mixed parasite line HlGST using a fluorescent activated cell sorter. Two independent calf immunization trials were performed via intravenous inoculation of the HlGST-Cln and a previously described control consisting of an irrelevant transfected clonal line of B. bovis designated GFP-Cln. The control GFP-Cln line contains a copy of the GFP-BSD gene inserted into the Ef-1 alpha locus of B. bovis in an identical fashion as the HIGST-Cln parasites. All animals inoculated with the HlGST-Cln and GFP-Cln transfected parasites developed mild babesiosis suggesting that both transfected cloned parasite lines are attenuated. Tick egg fertility and fully engorged female tick weight was reduced significantly in R. microplus feeding on HlGST-Cln-immunized calves. Collectively, these data show the efficacy of a transfected HlGST-Cln attenuated B. bovis parasite to induce a detectable anti-glutathione-S-transferase antibody and it was observed a reduction in tick size and fecundity of feeding R. microplus.