Transfected Babesia bovis Expressing a Tick GST as a Live Vector Vaccine

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-1α (elongation factor 1 alpha) promoter of B. bovis controlling expression of two independent genes, the selectable marker GFP-BSD (green fluorescent protein–blasticidin deaminase), 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-1α locus. A B. bovis clonal line termed HlGST-Cln expressing intracellular GFP and HlGST in the surface of merozoites 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-1α 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. 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 B. bovis parasite to induce detectable anti-glutathione-S-transferase antibodies and a reduction in tick size and fecundity of R. microplus feeding in experimentally inoculated animals.

Stable transformation of Babesia bigemina and Babesia bovis using a single transfection plasmid

“…bovis using B . bigemina insertion and promoter sequences also has important implications for improving the design of Babesia sp.-based vectored vaccines 6 . On one hand, a vaccine delivery platform based on B .…”

“…The development of stable transfection systems for B . bovis 2 , 3 , have already facilitated several new avenues of research, including functional gene characterization 4 and novel vaccine development 5 , 6 , but such methods are not available for B . bigemina .…”

“…The development of genetic manipulation tools for B . bigemina will advance our understanding of parasite biology, gene function and improved control of bovine babesiosis 6 – 9 . A recent study described an effective B .…”

In Silico Characterization and Structural Modeling of Dermacentor andersoni p36 Immunosuppressive Protein

“…Existing antitick vaccines work by eliciting humoral and cellular responses against tick cell membrane antigens [ 5 , 6 ]. Vaccines capable of quelling both the arthropod vector and disease-causing pathogens are also under development [ 7 ]. Despite clear advantages of controlling ticks through vaccination, this strategy is presently hampered by antigenic sequence variations between geographically isolated tick populations and species causing vaccine resistance in some regions [ 8 ] and lack of efficacy in others [ 9 ].…”

Metazoan Parasite Vaccines: Present Status and Future Prospects

“…More studies are, however, needed using different encapsulation techniques for both endo- and ectoparasites, including protection parameters (such as vaccine efficacies) to assess whether microencapsulation will play a beneficial role in future commercial metazoan vaccine development. An interesting development in the field is the transformation of a vector-borne pathogen to produce vector-associated antigens to act as a dual live vector vaccine (e.g., B. bovis producing a Haemaphysalis longicornis glutathione-S-transferase) (Oldiges et al, 2016 ). Though this approach is still in its infancy, it could provide a new paradigm in vector-borne disease transmission management.…”