Vacina candidata contra leptospirose utilizando Salmonella Typhimurium como vetor

Abstract

Leptospirosis is a zoonotic disease caused by bacteria of the genus Leptospira, which affects domestic and wild animals on a global scale. Currently, there is no universal commercial vaccine available to prevent the disease, driving the development of recombinant vaccines as a promising alternative to combat leptospirosis more effectively. In this context, the present study aimed to develop and evaluate vaccine prototypes against leptospirosis. In the first phase, the immunogenicity and protective potential of bacterin vaccines derived from Escherichia coli expressing a chimeric protein composed of Leptospira antigens, LipL32, LemA, and LigAni (rQ1), were investigated. The efficacy of these formulations was tested in hamsters, divided into experimental groups that received different formulations: recombinant bacterin (with and without aluminum hydroxide adjuvant, Al (OH)₃), subunit vaccines, and negative controls. The vaccinations were administered intramuscularly on days 0 and 14. The results obtained via indirect ELISA demonstrated that the group receiving the subunit vaccine showed significantly elevated levels of immunoglobulins (P < 0.05), distinguishing it from all other groups. The subunit vaccine group showed a 50% survival rate, whereas groups vaccinated with recombinant bacterins exhibited only 0– 10% protection. No vaccine group provided significant protective immunity against the lethal challenge with the L. interrogans strain. Although the subunit formulation elicited moderate immune responses, its efficacy remains limited, highlighting the need for further optimizations to develop an effective leptospirosis vaccine. In the second phase of the study, the Leptospira chimeric antigen (rQ1), cloned into the pTECH2 vector, was used to express the antigen in Salmonella Typhimurium LVR01. Hamsters were vaccinated orally (OR) and intramuscularly (IM) with 2 × 10⁷ colony-forming units (CFU) of S. Typhimurium LVR01 carrying pTECH2/rQ1, pTECH2 alone, or PBS as a control. The vaccinations were administered in two doses, 14 days apart. Following vaccination, serum samples were collected, and IgG antibodies and serotypes against rQ1 were measured using indirect ELISA. The results showed that on day 28, IgG antibodies were detected only in hamsters vaccinated via IM with the attenuated recombinant Salmonella vaccine. After the second vaccination, antibody levels in hamsters vaccinated IM with pTECH2/rQ1 were significantly higher (P < 0.0001) compared to the control groups (PBS and pTECH2). Furthermore, IgG2/3 levels against the rQ1 antigen in the intramuscularly vaccinated group were also significantly elevated (P < 0.0001) compared to the controls. In contrast, antibody levels in the group vaccinated orally with pTECH2/rQ1 showed a statistically significant difference (P < 0.05) compared to the controls. In conclusion, the attenuated vaccine based on S. Typhimurium did not demonstrate protective efficacy against homologous challenge in hamsters vaccinated with pTECH2/rQ1. These findings suggest that, although promising, the Salmonella-based platform requires further studies to enhance immune response and provide effective protection.