Evaluation of the use of sub-immunodominant antigens of Babesia bovis with flagellin c adjuvant in subunit vaccine development

Authors: ROJAS, MANUEL - Washington State University; Bastos, Reginaldo; NAVAS HOYOS, JINA - Washington State University; ALZAN, HEBA - Washington State University; Laughery, Jacob; Lacy, Paul; Ueti, Massaro; Suarez, Carlos

Submitted to: Vaccines
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/23/2024
Publication Date: 10/25/2024
Citation: Rojas, M.J., Bastos, R.G., Navas Hoyos, J.A., Alzan, H.F., Laughery, J.M., Lacy, P.A., Ueti, M.W., Suarez, C.E. 2024. Evaluation of the use of sub-immunodominant antigens of Babesia bovis with flagellin c adjuvant in subunit vaccine development. Vaccines. 12(11):1215. https://doi.org/10.3390/vaccines12111215.
DOI: https://doi.org/10.3390/vaccines12111215

Interpretive Summary: New vaccines are needed against Bovine babesiosis caused by the tick-borne apicomplexan parasite Babesia bovis, which remains a threat for cattle worldwide. It was previously proposed that immune-subdominant (ISD) antigens are better candidates for vaccine development, since they may represent more valuable targets for protective immune responses. In this study we first defined a set of two immune-subdominant (ISD) B. bovis antigens and then, tested a vaccine formulation consisting of 2 antigens in their recombinant form, combined with the novel adjuvant FliC-Emulsigen, capable to stimulate strong cellular and humoral immune responses on a group of 6 calves. Vaccinations resulted in strong antibody responses against both recombinant antigens in all but one animal. Challenge of this group and a similar control group of animals inoculated with the adjuvant alone, resulted in acute disease in both groups of animals, but we detected differences a slower and significant rate of decrease of the hematocrit (a sign of anemia produced by the parasite) in the vaccinated animals. This finding, together with additional evidence on the number of circulating monocytes in 4 out of the 6 vaccinated animals, suggested elicitation of protective immune responses in some of the vaccinated animals. In conclusion, we confirmed the immune-subdominance of two B. bovis antigens, the ability of FliC-based adjuvants to increase the immunogenicity of ISD antigens and generated useful information towards developing future subunit-vaccines against B. bovis

Technical Abstract: Bovine babesiosis caused by the tick-borne apicomplexan parasite Babesia bovis, remains a threat for cattle worldwide, and new vaccines are needed. We propose using immune-subdominant (ISD) antigens as alternative vaccine candidates. Herein we first defined the immune-sub dominance of RAP-1 NT and RRA recombinant antigens in B. bovis-protected cattle, using ELISAs. Protected animals demonstrated high antibody responses against the known immunodominant rRAP-1 CT antigen, but significantly lower levels against the rRAP-1 NT and rRRA antigens. Next, a group of cattle (n=6) were vaccinated with rRRA, rRAP-1 NT using FliC-Emulsigen mix as adjuvant, and a control group (n=6) with the adjuvant mix alone. The immunized animals demonstrated elicitation of strong humoral immune responses against the two ISD antigens in all but one. Acute babesiosis occurred in both groups of cattle upon challenge with virulent B. bovis, but a significant delay in the average rate of decrease of hematocrit in the vaccinated group, and an early monocyte response was found in half of the vaccinated animals. In conclusion we confirmed the immune-sub dominance of rRRA, rRAP-1 NT, and the ability of FliC to increase immunogenicity of ISD antigens generated useful information towards developing future subunit-vaccines against B. bovis.