Resumo

Leptospirosis is an emergent disease with a worldwide distribution that threatens mainly developing countries in tropical regions. The disease is caused by bacteria of the Leptospira genus, and is estimated that about of 500,000 cases of severe human leptospirosis occur annually. Vaccines represent a cost-effective approach to preventing neglected tropical diseases. Among current vaccines, whole cell bacterins have been used, but it´s side effects and serovar specific protection requires that new approaches be explored. DNA vaccines have been developed for leptospirosis but none of them have demonstrated significant protection in tested models. In this work, we propose a vaccination strategy using surface antigen LipL32, a protein that is recognized by host immune system and participates in the pathogenesis process. For this, LipL32 was expressed in Escherichia coli, and the gene cloned in pVax vector. After this, the transfection assay was carried out in HEK293 cells. For vaccine protection experiment, groups of six male hamsters were inoculated with the preparations on day 0 (first dose) and day 21 (second dose) and challenged on day 42 with an intraperitonial administration of 10³ leptospires. The four groups were as follow: (G1) pVaxLipL32 (day 0/21); (G2) pVaxLipL32 (day 0) and rLipL32+Al(OH)₃ (day 21); (G3) pVax (day 0/21); and (G4) pVax (day 0) and Al(OH)₃ (day 21). All hamsters suffered lethal challenge with 10³ leptospiras on day 42. The Fisher Exact test and log-rank sum test were used to determine significant differences for mortality and survival. As results, we found that LipL32 protein was successfully expressed and transfected in HEK293 cells. The challenge assay revealed that groups 1 and 2 were capable of generating significant (p<0.05) protection (G1 protected 100 % of the hamsters and G2 protected 50%) when compared to the PBS control and Al(OH)₃ group (0%). These results indicate that the DNA/DNA approach is more promising than DNA/protein. Other authors have demonstrated some protection with DNA vaccines against lethal leptospiral challenge, but this work is the first that demonstrate a 100% protection, and tested in the recommended model of leptospirosis vaccine trials. These results show that LipL32 DNA vaccine can protect against homologous challenge when used to immunize hamsters, but the prime-boost strategy needs further studies.