Protective vaccination against experimental canine visceral leishmaniasis using a combination of DNA and protein immunization with cysteine proteinases type I and II of L. infantum.

Leishmania infantum is known to be associated with visceral leishmaniasis in Iran and canids are natural reservoirs. Control of disease in dogs appears to be one of the most effective approaches for interrupting the domestic cycle of the disease. In search for successful vaccine strategies, we evaluated the cysteine proteinases (CPs) type I and II using a heterologous prime-boost regime for vaccination against experimental visceral leishmaniasis in dogs. Following vaccination and challenge, dogs were followed for 12 months. Ten dogs vaccinated by prime/boost with DNA/recombinant CPs (in combination with CpG ODN and Montanide 720) remained free of infection in their bone morrow. In contrast, three out of four dogs in the control groups had infection in their bone marrow. The peripheral lymphocytes from protected animals had generally higher proliferation responses to F/T antigen, recombinant CPA (rCPA) and recombinant CPB (rCPB) than controls. During post-challenge period, the difference in stimulation index is significant (p<0.05) on months 11 and 12 to F/T antigens, all months for rCPA and 5, 7, 9, 11 and 12 months for rCPB. Analysis of cytokine mRNA level suggested that vaccinated dogs had elevated IFN-gamma mRNA in peripheral blood mononuclear cells (PBMC), whereas there was a consistent increase in the level of IL-10 in the control groups and some vaccinated dogs. The level of total IgG and IgG2, but not IgG1, to rCPA and rCPB was significantly higher in the vaccinated group (p<0.05) than the control groups. We also showed that with the exception of one dog, all dogs in the vaccinated group in comparison to control dogs had strong DTH responses. We propose that the combination of DNA and recombinant protein vaccination using CPs could be instrumental to control (VL) in dogs.