Identification of anti-horn fly vaccine antigen candidates using a reverse vaccinology approach

Authors: DOMINGUES, LUISA - US Department Of Agriculture (USDA); Bendele, Kylie; HALOS, LENAIG - Boehringer Ingelheim; MORENO, YOVANY - Boehringer Ingelheim; EPE, CHRISTIAN - Boehringer Ingelheim; FIGUEIREDO, MONICA - Boehringer Ingelheim; LIEBSTEIN, MARTIN - Boehringer Ingelheim; GUERRERO, FELIX - Retired ARS Employee

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2021
Publication Date: 9/3/2021
Publication URL: https://handle.nal.usda.gov/10113/7497920
Citation: Domingues, L., Bendele, K.G., Halos, L., Moreno, Y., Epe, C., Figueiredo, M., Liebstein, M., Guerrero, F. 2021. Identification of anti-horn fly vaccine antigen candidates using a reverse vaccinology approach. Parasites & Vectors. 14. https://doi.org/10.1186/s13071-021-04938-5.
DOI: https://doi.org/10.1186/s13071-021-04938-5

Interpretive Summary: A reverse vaccinology approach using multiple vaccine prediction and annotation tools was taken to identify ten anti-horn fly vaccine candidates. Six candidates were successfully expressed in Pichia pastoris and were confirmed by real-time PCR to be found in adult horn fly RNA. One candidate antigen, BI-HS009, was used in immunogenicity and efficacy trials resulted in significantly higher IgG titers of vaccinated animals than control animals and produced significantly lower pupal and adult horn fly emergence compared to the control group.

Technical Abstract: Background: The horn fly, Haematobia irritans irritans, causes significant production losses to the cattle industry where it occurs. Horn fly control relies on insecticides; however, alternative control methods such as vaccines are needed due to the fly's capacity to quickly develop resistance to insecticides, and the pressure for eco-friendly options. Methods: We used a reverse vaccinology approach comprising three vaccine prediction and 11 annotation tools to evaluate and rank 79,542 translated open reading frames (ORFs) from the horn fly's transcriptome; and selected 10 transcript ORFs as vaccine candidates for expression in Pichia pastoris. The expression of the 10 selected transcripts and the proteins encoded by them were investigated in adult flies by reverse transcript-polymerase chain reaction (RT-PCR) and mass spectrometry, respectively. Then, we evaluated the immunogenicity of a vaccine candidate in an immunization trial and the antigen’s effects on horn fly mortality and fecundity in an in vitro feeding assay. Results: Six of the 10 vaccine candidate antigens could be successfully expressed in P. pastoris. RT-PCR confirmed the expression of all six ORFs in adult fly RNA. One of the vaccine candidate antigens, BI-HS009, was expressed in sufficient quantity for immunogenicity and efficacy trials. The IgG titers of animals vaccinated with BI-HS009 plus adjuvant were significantly higher than that of animals vaccinated with buffer plus adjuvant only from Days 21 - 112, with a peak on Day 56. Horn flies feeding upon blood from animals vaccinated with BI-HS009 plus adjuvant collected on Day 56 had significantly lower pupal and adult emergence compared with the control group. Conclusions: The reverse vaccinology approach streamlined the discovery process by prioritizing the large number of possible vaccine antigen candidates. Through a thoughtful process of selection and in vivo and in vitro evaluations, we were able to identify a promising component for an anti-horn fly vaccine.