Attenuated Salmonella Typhimurium expressing chimeric antigen from Leptospira as a recombinant vaccine candidate against leptospirosis

Leptospirosis is a significant zoonotic disease caused by pathogenic spirochetes of the genus Leptospira. Attenuated Salmonella strains represent a promising vector for the development of safe and effective vaccines capable of eliciting a specific immune response. A chimeric Leptospira antigen (rQ1), previously described and based on the gene sequences of lipL32, lemA, and ligAni, was cloned into the pTECH2 vector for antigen expression in Salmonella Typhimurium LVR01. Hamsters were vaccinated orally (OR) and intramuscularly (IM) with 2 × 10^7 CFU of S. Typhimurium LVR01 carrying pTECH2/rQ1, pTECH2 alone, or PBS as a control. Vaccinations were administered twice, with a 14-day interval. Following OR and IM administration, serum samples were collected, and IgG antibodies against rQ1 were measured using indirect ELISA. The results showed that after the second immunization, IgG antibody levels in hamsters immunized IM with pTECH2/rQ1 were significantly higher (P < 0.0001) than in the control groups (PBS and pTECH2). Isotype analyses revealed significant levels of IgG2 (P < 0.05) in the group vaccinated IM with pTECH2/rQ1. However, the attenuated S. Typhimurium vaccine did not confer protective efficacy against homologous challenge in the hamsters immunized with pTECH2/rQ1. Further studies are necessary to explore this novel recombinant attenuated S. Typhimurium LVR01 vaccine and to further characterize the immune mechanisms involved.