Evaluation of Live Recombinant Nonpathogenic Leishmania tarentolae Expressing Cysteine Proteinase and A2 Genes as a Candidate Vaccine against Experimental Canine Visceral Leishmaniasis.

Canine Visceral Leishmaniasis (CVL) is a major veterinary and public health problem caused by Leishmania infantum (L. infantum) in many endemic countries. It is a severe chronic disease with generalized parasite spread to the reticuloendothelial system, such as spleen, liver and bone marrow and is often fatal when left untreated. Control of VL in dogs would dramatically decrease infection pressure of L. infantum for humans, since dogs are the main domestic reservoir. In the past decade, various subunits and DNA antigens have been identified as potential vaccine candidates in experimental animal models, but none has been approved for human use so far. In this study, we vaccinated outbreed dogs with a prime-boost regimen based on recombinant L. tarentolae expressing the L. donovani A2 antigen along with cysteine proteinase genes (CPA and CPB without its unusual C-terminal extension (CPB-CTE) and evaluated its immunogenicity and protective immunity against L. infantum infectious challenge. We showed that vaccinated animals produced significantly higher levels of IgG2, but not IgG1, and also IFN-γ and TNF-α, but low IL-10 levels, before and after challenge as compared to control animals. Protection in dogs was also correlated with a strong DTH response and low parasite burden in the vaccinated group. Altogether, immunization with recombinant L. tarentolae A2-CPA-CPB-CTE was proven to be immunogenic and induced partial protection in dogs, hence representing a promising live vaccine candidate against CVL.

Immunological comparison of DNA vaccination using two delivery systems against canine leishmaniasis.

Visceral leishmaniasis (VL) is a fatal disease caused by the intracellular protozoan parasite Leishmania infantum. Dogs are the primary reservoirs of this parasite, and vaccination of dogs could be an effective method to reduce its transfer to humans. In order to develop a vaccine against VL (apart from the choice of immunogenic candidate antigens), it is necessary to use an appropriate delivery system to promote a proper antigen-specific immune response. In this study, we compared two vaccine delivery systems, namely electroporation and cationic solid-lipid nanoparticle (cSLN) formulation, to administer a DNA vaccine containing the Leishmania donovani A2 antigen, and L. infantum cysteine proteinases of type I (CPA) and II (CPB) without its unusual C-terminal extension. The protective potencies of these two vaccine delivery systems were evaluated against L. infantum challenge in outbred dogs. Our results show that the administration of pcDNA-A2-CPA-CPB(-CTE)GFP vaccine as a prime-boost by either electroporation or cSLN formulation protects the dogs against L. infantum infection. Partial protection in vaccinated dogs is associated with significantly (p<0.05) higher levels of IgG2, IFN-γ, and TNF-α and with low levels of IgG1 and IL-10 as compared to the control group. Protection was also correlated with a low parasite burden and a strong delayed-type hypersensitivity (DTH) response. This study demonstrates that both electroporation and cSLN formulation can be used as efficient vaccine delivery systems against visceral leishmaniasis.