Abstract
BackgroundVisceral leishmaniasis (VL) caused by an intracellular protozoan parasite Leishmania, is fatal in the absence of treatment. At present there are no effective vaccines against any form of leishmaniasis. Here, we evaluate the potency, efficacy and durability of DNA/DNA, DNA-prime/Protein-boost, and Protein/Protein based vaccination against VL in a susceptible murine model.Methods and FindingsTo compare the potency, efficacy, and durability of DNA, protein and heterologous prime-boost (HPB) vaccination against Leishmania donovani, major surface glycoprotein gp63 was cloned into mammalian expression vector pcDNA3.1 for DNA based vaccines. We demonstrated that gp63 DNA based vaccination induced immune responses and conferred protection against challenge infection. However, vaccination with HPB approach showed comparatively enhanced cellular and humoral responses than other regimens and elicited early mixed Th1/Th2 responses before infection. Moreover, challenge with parasites induced polarized Th1 responses with enhanced IFN-γ, IL-12, nitric oxide, IgG2a/IgG1 ratio and reduced IL-4 and IL-10 responses compared to other vaccination strategies. Although, vaccination with gp63 DNA either alone or mixed with CpG- ODN or heterologously prime-boosting with CpG- ODN showed comparable levels of protection at short-term protection study, DNA-prime/Protein-boost in presence of CpG significantly reduced hepatic and splenic parasite load by 107 fold and 1010 fold respectively, in long-term study. The extent of protection, obtained in this study has till now not been achieved in long-term protection through HPB approach in susceptible BALB/c model against VL. Interestingly, the HPB regimen also showed marked reduction in the footpad swelling of BALB/c mice against Leishmania major infection.Conclusion/SignificanceHPB approach based on gp63 in association with CpG, resulted in robust cellular and humoral responses correlating with durable protection against L. donovani challenge till twelve weeks post-vaccination. These results emphasize the potential of DNA-prime/Protein-boost vaccination over DNA/DNA and Protein/Protein based vaccination in maintaining long-term immunity against intracellular pathogen like Leishmania.
Highlights
Leishmaniasis comprise of several diseases caused by a unicellular, digenetic and most genetically diverse protozoan parasites belonging to the genus Leishmania
The clinical manifestations of human leishmaniasis depend on the infective parasite species as well as on the host immune response
The positive clones were selected by using PCR and restriction enzyme digestion analysis (Figure 1A), and the PCR product was further sent for sequence analysis
Summary
Leishmaniasis comprise of several diseases caused by a unicellular, digenetic and most genetically diverse protozoan parasites belonging to the genus Leishmania. The clinical manifestations range from the self-limiting cutaneous infections to overwhelming visceral disease. The clinical manifestations of human leishmaniasis depend on the infective parasite species as well as on the host immune response. The chemotherapeutic agents used presently are expensive, toxic and emerging drug resistance [3]. For these reasons, reinforced measures for leishmaniasis control, by the development of an affordable and effective vaccine is highly recommended. Visceral leishmaniasis (VL) caused by an intracellular protozoan parasite Leishmania, is fatal in the absence of treatment. At present there are no effective vaccines against any form of leishmaniasis. We evaluate the potency, efficacy and durability of DNA/DNA, DNA-prime/Protein-boost, and Protein/Protein based vaccination against VL in a susceptible murine model
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