Vaccination in cattle against Babesia bovis combining a modified vaccinia Ankara vector and protein ? adjuvant formulation based on a recombinant multi - antigen.

JARAMILLO ORTIZ J; GRAVISACO MJ; ECHAIDE I; PAOLETTA M; MONTENEGRO, VALERIA NOELY; DE LA FOURNIERE S; LOPEZ ARIAS L; VALENZANO M; GUILLEMI E; FARBER M; WILKOWSKY S. E

caba

Congreso; International Congress on Tropical Veterinary Medicine 2nd Joint AITVM-STVM Meeting; 2018

Society of Tropical Veterinary Medicina

The mechanisms of immunity to babesial parasites are hypothesized to require both innate and adaptive responses that include CD4+T cells and neutralizing antibodies. Therefore, tailored combinations of immunogens targeted at both arms of the immune system are strategies of choice to pursue sterilizing immunity. In previous work from our group, we have obtained a recombinant modified vaccinia virus Ankara (MVA) vector expressing a chimeric multi-antigen composed of B and T epitopes of three B. bovis immunodominant proteins: Merozoite Surface Antigen ? 2c (MSA-2c), Rhoptry Associated Protein ? 1 (RAP-1) and Heat Shock Protein 20 (HSP20). This novel immunogen was also expressed as a recombinant protein in E. coli and evaluated in mice as a candidate vaccine in heterologous immunizations using the multiantigenic protein as a prime and the recombinant MVA vector as boost. This scheme induced a mixed response in terms of high levels of specific IgG antibodies and secreted INFγ by CD4+ and CD8+ T cells. These results prompted us to evaluate these candidates in bovines, the natural hosts for B. bovis.In this study, 4 groups (G1 to G4) of 13 ? 15 month - old and highly susceptible male Holstein steers (n=5 per group) were immunized as follows: G1 received a subcutaneous dose (sc) of the multiantigen plus adjuvant as a prime and six weeks later they received an intramuscular dose (im) of the recombinant MVA as a boost. G2 received the currently live attenuated vaccine used in Argentina of the R1A strain at day 42 of the experiment. A prime of a heterologous recombinant protein and a boost of wild type MVA was used as control in G3 at the same time intervals as G1. Similarly, G4 received two shots of the vaccine vehicle as a control. Eleven weeks after the first immunization, all animals were challenged with a sc injection of 107 parasite-infected erythrocytes of the virulent B. bovis S2P strain. All along the experiment (150 days), all groups were monitored daily for fever and reduction of packed cell volume until the sacrifice of bovines. The results showed that both G1 and G2 groups developed a strong antigen - specific T cellular response characterized by an elevated proportion of antigen-specific multifunctional CD4 +IFN+/TNF+Tcells compared to the control groups. High antibody titres of total and subtype 2 IgG were also obtained. However, all bovines of the G1 group developed clinical symptoms of disease upon challenge characterized by fever and a 30% decrease in packed cell volume. As expected, both control groups G3 and G4 showed typical signs of acute babesiosis. Only one bovine from the G3 group required treatment. All together, these findings show that although the novel recombinant vaccine rMABbo ? rMVA exhibited a strong humoral and cellular response compared to the control groups, these markers did not correlate with protection, indicating that other antigens should be evaluated. Besides, there is a need of knowledge of different immunological surrogates of vaccine-induced protection in this parasite. A detailed immune characterization of the protective response obtained by the attenuated R1A strain would also be of great importance to understand the biological traits involved in the high level of efficacy of this vaccine.