Immunogenicity and protective efficacy of tuzin protein as a vaccine candidate in Leishmania donovani-infected BALB/c mice

Visceral leishmaniasis (VL) is referred to as the most severe and fatal type of leishmaniasis basically caused by Leishmania donovani and L. infantum. The most effective method for preventing the spread of the disease is vaccination. Till today, there is no promising licensed vaccination for human VL. Hence, investigation for vaccines is necessary to enrich the therapeutic repertoire against leishmaniasis. Tuzin is a rare trans-membrane protein that has been reported in Trypanosoma cruzi with unknown function. However, tuzin is not characterized in Leishmania parasites. In this study, we for the first time demonstrated that tuzin protein was expressed in both stages (promastigote and amastigote) of L. donovani parasites. In-silico studies revealed that tuzin has potent antigenic properties. Therefore, we analyzed the immunogenicity of tuzin protein and immune response in BALB/c mice challenged with the L. donovani parasite. We observed that tuzin-vaccinated mice have significantly reduced parasite burden in the spleen and liver compared with the control. The number of granulomas in the liver was also significantly decreased compared with the control groups. We further measured the IgG2a antibody level, a marker of Th1 immune response in VL, which was significantly higher in the serum of immunized mice when compared with the control. Splenocytes stimulated with soluble Leishmania antigen (SLA) displayed a significant increase in NO and ROS levels compared with the control groups. Tuzin-immunized and parasite-challenged mice exhibit a notable rise in the IFN-γ/IL-10 ratio by significantly suppressing IL-10 expression level, an immunosuppressive cytokine that inhibits leishmanicidal immune function and encourages disease progression. In conclusion, tuzin immunizations substantially increase the protective immune response in L. donovani-challenged mice groups compared with control.

Leishmania genome analysis and high-throughput immunological screening identifies tuzin as a novel vaccine candidate against visceral leishmaniasis

Leishmaniasis is a neglected tropical disease caused by Leishmania species. It is a major health concern affecting 88 countries and threatening 350 million people globally. Unfortunately, there are no vaccines and there are limitations associated with the current therapeutic regimens for leishmaniasis. The emerging cases of drug-resistance further aggravate the situation, demanding rapid drug and vaccine development. The genome sequence of Leishmania, provides access to novel genes that hold potential as chemotherapeutic targets or vaccine candidates. In this study, we selected 19 antigenic genes from about 8000 common Leishmania genes based on the Leishmania major and Leishmania infantum genome information available in the pathogen databases. Potential vaccine candidates thus identified were screened using an in vitro high throughput immunological platform developed in the laboratory. Four candidate genes coding for tuzin, flagellar glycoprotein-like protein (FGP), phospholipase A1-like protein (PLA1) and potassium voltage-gated channel protein (K VOLT) showed a predominant protective Th1 response over disease exacerbating Th2. We report the immunogenic properties and protective efficacy of one of the four antigens, tuzin, as a DNA vaccine against Leishmania donovani challenge. Our results show that administration of tuzin DNA protected BALB/c mice against L. donovani challenge and that protective immunity was associated with higher levels of IFN-γ and IL-12 production in comparison to IL-4 and IL-10. Our study presents a simple approach to rapidly identify potential vaccine candidates using the exhaustive information stored in the genome and an in vitro high-throughput immunological platform.