Cross-protective efficacy of a conserved Leishmania braziliensis recombinant protein as a candidate vaccine against visceral leishmaniasis

Abstract

Background: Leishmaniasis represents a disease complex in the world ranging from self-limiting cutaneous leishmaniasis (CL) to the fatal visceral leishmaniasis (VL). The development of new vaccines to prevent VL is a desirable measure to control the disease. An important challenge for the development of an effective antileishmanial vaccine is the low efficacy of the tested antigens to protect against distinct Leishmania spp., since candidates usually offer a species-specific protection, although there significant protein homology between species. Aiming to solve this issue, in the present study, the L. braziliensis enolase protein, was evaluated as a protective antigen, associated with saponin, to offers heterologous protection against L. infantum infection. Methods & Materials: The DNA sequence was cloned and the recombinant protein (rEnolase) was evaluated as a vaccine, associated with saponin, as an immune adjuvant. The protective efficacy of the vaccine was investigated in BALB/c mice (n = 16 per group) against experimental visceral leishmaniasis. Three doses were administered at two-week intervals in all animals. Thirty days after the last immunization, mice (n = 8, in each group) were euthanized and their sera samples and spleen were collected to analyze the immune response. At the same time, remaining animals were subcutaneously infected with 1 × 107 stationary-phase promastigotes of L. infantum. Ten weeks after challenge these animals were euthanized to analyze the immune response and parasite burden. Results: The results revealed that the vaccine induced higher levels of IFN-γ, IL-12, and GM-CSF when a capture ELISA and flow cytometry were performed, as well as an antileishmanial nitrite production after using in vitro stimulation with rEnolase and an antigenic Leishmania preparation. The vaccinated animals, when compared to the control groups, showed a lower parasite burden in the liver, spleen, bone marrow, and paws’ draining lymph nodes when both a limiting dilution technique and RT-PCR assay were performed. In addition, these mice showed low levels of antileishmanial IL-4, IL-10, and anti-Leishmania IgG1 isotype antibodies. Partial protection was associated with IFN-γ production, which was mainly mediated by CD4+ T cells. Conclusion: In conclusion, the present study's data showed that the L. braziliensis enolase protein could be considered a vaccine candidate that offers heterologous protection against VL.