Protection against leptospirosis conferred by Mycobacterium bovis BCG expressing antigens from Leptospira interrogans

Leptospirosis is a zoonotic disease worldwide and caused by the pathogenic spirochetes of the genus Leptospira. Bacterins make up the vaccines used against leptospirosis, but they only succeed in providing short-term and serovar-specific protection. The use of Mycobacterium bovis BCG as a live vaccine vector expressing leptospiral antigens is a promising alternative, particularly due to its adjuvant properties. Four distinct portions P₁ (lipL32), P₂ (ligAni), P₃ (lemA:ligAni) and P₄ (lipL32:lemA) of a recombinant chimera composed of the lipL32, lemA and ligANI genes from Leptospira interrogans were cloned individually according to the BioBricks® strategy in the plasmid pUP500/P_pAN. These constructs were individually transformed into a BCG Pasteur strain, and protein expression was detected by Western blot. For vaccination, 5 groups of 10 Golden Syrian hamsters were used, aged 4-6 weeks - group 1, rBCG (LipL32); group 2, rBCG (LigAni); group 3, rBCG (LemA:LigAni); group 4, (LipL32:LemA); group 5, wild-type BCG Pasteur (negative control). Two doses containing 10⁶ CFU of rBCG were administered subcutaneously, the challenge was performed with 5 × LD₅₀ of Leptospira interrogans serovar Copenhageni L1-130, and the animals were observed for a 30-day period until the endpoint was reached. Humoral immunity was assessed via indirect ELISA, while renal colonisation was assessed by culture and quantitative real-time PCR. All vaccinated groups were protected against lethal challenge and renal colonisation, in comparison with negative control group (P < 0.05). Recombinant vaccines were not effective at inducing significant humoral immunity, which suggests the induction of cellular immunity - a characteristic of M. bovis BCG. In conclusion, all formulations provide 100% significant protection against leptospirosis in hamsters with no renal colonisation. The use of rBCG as a vaccine vector represents a promising alternative for the control of animal leptospirosis, allowing for protection against clinical signs of leptospirosis and renal colonisation.