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TonB-dependent receptor epitopes expressed in M. bovis BCG induced significant protection in the hamster model of leptospirosis

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Abstract

Leptospirosis is an emerging infectious disease caused by pathogenic Leptospira spp. A universal vaccine against leptospirosis is likely to require highly conserved epitopes from pathogenic leptospires that are exposed on the bacterial surface and that generate a protective and sterilizing immune response. Our group recently identified several genes predicted to encode TonB-dependent receptors (TBDR) in Leptospira interrogans using a reverse vaccinology approach. Three leptospiral TBDRs were previously described and partially characterized as ferric-citrate, hemin, and cobalamin transporters. In the current study, we designed a fusion protein composed of predicted surface-exposed epitopes from three conserved leptospiral TBDRs. Based on their three-dimensional structural models and the prediction of immunogenic regions, nine putative surface-exposed fragments were selected to compose a recombinant chimeric protein. A Mycobacterium bovis BCG strain expressing this chimeric antigen encoded in the pUP500/PpAN mycobacterial expression vector was used to immunize Syrian hamsters. All animals (20/20) vaccinated with recombinant BCG survived infection with an endpoint dose of L. interrogans (p < 0.001). No animal survived in the negative control group. Immunization with our recombinant BCG elicited a humoral immune response against leptospiral TBDRs, as demonstrated by ELISA and immunoblot. No leptospiral DNA was detected by lipL32 qPCR in the kidneys of vaccinated hamsters. Similarly, no growth was observed in macerated kidney cultures from the same animals, suggesting the induction of a sterilizing immune response. Design of new vaccine antigens based on the structure of outer membrane proteins is a promising approach to overcome the impact of leptospirosis by vaccination.

Key points

• Predicted surface-exposed epitopes were identified in three leptospiral TBDRs.

• An M. bovis BCG strain expressing a chimeric protein (rTBDRchi) was constructed.

• Hamsters vaccinated with rBCG:TBDRchi were protected from lethal leptospirosis.

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Data availability

Leptospira interrogans Fiocruz L1-130 strain is available as described in the Fiocruz/CLEP collection (WDCM 1012). Raw data from epitope mapping are available as Online Resource (ESM_3). Any additional data and materials used in this article are available upon request.

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Acknowledgements

We are grateful to our lab technician Michele dos Santos and the UFPel’s animal facility staff for the assistance provided during this study.

Funding

Execution of this work was possible thanks to the support of CAPES, CNPq, and FAPERGS through grants and scholarships. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001.

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Authors

Contributions

EB, JD, AG, AM, TO, and OD contributed to conceive and design the study. EB, JD, AH, and AM performed research throughout the work. JD, AH, AM, and ASN performed animal experimentations. EB, AH, and JD analyzed the data. EB, AG, and AM wrote the paper. All authors contributed for manuscript review.

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Ethics approval

All procedures involving manipulations of animals were approved by the Ethics Committee in Animal Experimentation (CEEA) of Universidade Federal de Pelotas (UFPel) under protocol number 4646–2015. CEEA-UFPel is accredited by the Brazilian National Council for Animal Experimentation Control (CONCEA).

Conflict of interest

The authors declare no competing interests.

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Bettin, E.B., Dorneles, J., Hecktheuer, A.S. et al. TonB-dependent receptor epitopes expressed in M. bovis BCG induced significant protection in the hamster model of leptospirosis. Appl Microbiol Biotechnol 106, 173–184 (2022). https://doi.org/10.1007/s00253-021-11726-9

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  • DOI: https://doi.org/10.1007/s00253-021-11726-9

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  1. André A. Grassmann