Preclinical validation of a live attenuated dermotropic Leishmania vaccine against vector transmitted fatal visceral leishmaniasis

Visceral Leishmaniasis (VL), a potentially fatal disease is caused by Leishmania donovani parasites with no vaccine available. Here we produced a dermotropic live attenuated centrin gene deleted Leishmania major (LmCen(−/−)) vaccine under Good Laboratory Practices and demonstrated that a single intradermal injection confers robust and durable protection against lethal VL transmitted naturally via bites of L. donovani-infected sand flies and prevents mortality. Surprisingly, immunogenicity characteristics of LmCen(−/−) parasites revealed activation of common immune pathways like L. major wild type parasites. Spleen cells from LmCen(−/−) immunized and L. donovani challenged hamsters produced significantly higher Th1-associated cytokines including IFN-γ, TNF-α, and reduced expression of the anti-inflammatory cytokines like IL-10, IL-21, compared to non-immunized challenged animals. PBMCs, isolated from healthy people from non-endemic region, upon LmCen(−/−) infection also induced more IFN-γ compared to IL-10, consistent with our immunogenicity data in LmCen(−/−) immunized hamsters. This study demonstrates that the LmCen(−/−) parasites are safe and efficacious against VL and is a strong candidate vaccine to be tested in a human clinical trial.