Centrin-deficient <i>Leishmania mexicana</i> confers protection against Old World visceral leishmaniasis

<jats:title>ABSTRACT</jats:title><jats:p>Leishmaniasis is one of the top neglected tropical diseases with significant morbidity and mortality in low and middle-income countries (LMIC). However, this disease is also spreading in the developed world. Currently, there is a lack of effective strategies to control this disease. Vaccination can be an effective measure to control leishmaniasis and has the potential to achieve disease elimination. Recently, we have generated <jats:italic>centrin</jats:italic> gene-deleted new world <jats:italic>L. mexicana</jats:italic> (<jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup>) parasites using CRISPR/Cas9 and showed that they protect mice against a homologous <jats:italic>L. mexicana</jats:italic> infection that causes cutaneous disease. In this study, we tested whether <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> parasites can also protect against visceral leishmaniasis caused by <jats:italic>L. donovani</jats:italic> in a hamster model. We show that immunization with <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> parasites is safe and does not cause lesions. Furthermore, such immunization conferred protection against visceral leishmaniasis caused by a needle-initiated <jats:italic>L. donovani</jats:italic> challenge, as indicated by a significant reduction in the parasite burdens in the spleen and liver and lack of mortality. Similar control of parasite burden was also observed against a sand fly mediated <jats:italic>L. donovani</jats:italic> challenge. Importantly, immunization with <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> down-regulated the Th2 response as indicated by a significant reduction in the anti-inflammatory cytokines such as IL-10 and IL-4 and increased pro-inflammatory cytokine IFN-γ resulting in higher IFN-γ/IL-10 and IFN-γ/IL4 ratios compared to non-immunized animals. This contrasts with our studies with <jats:italic>L. major centrin</jats:italic> deletion mutants that showed a dominant Th1 response compared to <jats:italic>L. major</jats:italic> wild-type infection suggesting the divergent mechanisms of protection in the two mutant parasites. <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> immunization resulted in long-lasting protection against <jats:italic>L. donovani</jats:italic> infection. Further, since the efficacy of <jats:italic>LmCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> has not been determined against <jats:italic>Leishmania</jats:italic> strains prevalent in the Americas, <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> may be a viable alternative. Taken together, our study demonstrates that immunization with <jats:italic>LmexCen</jats:italic><jats:sup><jats:italic>-/-</jats:italic></jats:sup> parasites is safe and efficacious against old world visceral leishmaniasis.</jats:p>