Preclinical validation of a second generation leishmanization vaccine against vector transmitted fatal visceral leishmaniasis

Visceral Leishmaniasis (VL) is fatal if untreated. There is no licensed vaccine available against human leishmaniasis. We recently demonstrated protection in mice against L. major infection using a CRISPR genome edited attenuated Leishmania major strain ( LmCen −/− ). Here, as a pre-clinical step, we evaluated the protective efficacy of LmCen −/− against VL induced by sand fly transmitted Leishmania donovani in hamsters. Intradermal immunization of hamsters with LmCen −/− did not develop any lesion; while still priming a pro-inflammatory immune response. When challenged with L. donovani either by intradermal needle injection or by infected sand flies, LmCen −/− -immunized hamsters were protected, not showing spleen or liver pathology averting VL fatality compared to control animals. Spleen cells from LmCen −/− immunized and infected sand fly challenged hamsters produced significantly higher Th1-associated cytokines and chemokines including IFN-γ and TNF-α, and significantly reduced expression of the anti-inflammatory cytokines IL-10 and IL-21, compared to non-immunized challenged animals. We further developed a GLP-grade LmCen −/− which showed equal protection as laboratory-grade LmCen −/− parasites in hamsters. Importantly, GLP-grade LmCen −/− parasites also induced a proinflammatory immune response in the PBMCs isolated from healthy people living in non-endemic and endemic for VL as well as cured VL people living in endemic region. Together, this study demonstrates that the LmCen −/− parasites are safe and efficacious against VL and it is a strong candidate vaccine to be tested in a human clinical trial. ### Competing Interest Statement The authors have declared no competing interest.