Location: Animal Disease Research
Project Number: 2090-32000-039-045-I
Project Type: Interagency Reimbursable Agreement
Start Date: Jul 1, 2020
End Date: Jun 30, 2024
The immunodominant B. bovis rhoptry associated protein-1 (RAP-1) is a leading vaccine candidate that is expressed at least in B. bovis merozoites and sporozoites. The ability of the B. bovis RAP-1 to bind to the erythrocyte surface and the presence of RAP-1 neutralization sensitive epitopes leads to the hypothesis that RAP-1 is involved in erythrocyte invasion by the parasites. However, we previously demonstrated that strong humoral and cellular responses in vaccinated cattle with RAP-1 were unable to induce protection against challenge with virulent B. bovis. Expression of a recently identified subdominant and neutralization sensitive RAP-1 Related Antigen (RRA) in B. bovis merozoites that might function as a RAP-1 substitute is a potential explanation for the lack of protection using RAP-1 as an immunogen. Additionally, subdominant antigens like RRA may be reasonable candidates for developing vaccines which could potentially elicit a neutralizing antibody response in vivo. the goal of this project is to develop a subunit vaccine containing RAP-1 NT/RRA subdominant domains fused with the molecular adjuvant Flic to protect cattle against acute bovine babesiosis.
Our overall hypothesis is that a subunit vaccine targeting the NT immunosubdominant segment of RAP-1 and full-length RRA of B. bovis fused with the Flic flagellin molecular adjuvant protects cattle against acute bovine babesiosis. Two specific aims are proposed to test our hypothesis. In Specific Aim (SA) 1, we will express, purify, and test the antigenicity of RAP-1 NT and RRA fused with Flic. Recombinant proteins will be expressed in E. coli, purified using nickel columns, and their antigenicity will be evaluated using sera from B. bovis acutely infected and immune cattle. In SA2 we will evaluate whether a subunit vaccine containing B. bovis RAP-1 NT and full-length RRA fused with the molecular adjuvant Flic protects cattle against clinical signs of acute bovine babesiosis.