Low-frequency parasitized cells in bone marrow alter myelopoiesis following immunization with the live attenuated Leishmania major Cen−/− vaccine

Leishmaniasis lacks an effective vaccine. We developed a live-attenuated Leishmania major Centrin-deficient strain ( LmCen −/− ) that is safe and protective in murine and canine models through IFN-γ-producing effector T cells. Because persistent low-level infection supports durable immunity, we investigated latent parasites and immune remodeling in the bone marrow. Dual single-cell RNA sequencing detected parasitized bone marrow cells 28 days after intradermal inoculation with either virulent LmWT or attenuated LmCen −/− . Flow cytometry showed increased myelopoiesis following LmCen −/− immunization compared with LmWT infection. Cell-cell communication analysis implicated enhanced granulin-Sort3 signaling as a potential driver of this response. Bone marrow monocytes from LmCen −/− -immunized mice efficiently cleared virulent LmWT parasites in co-culture, consistent with the induction of trained innate immunity. These findings identify the bone marrow as an active site of anti- Leishmania immune programming and suggest that LmCen −/− vaccination promotes durable protection through coordinated adaptive and innate mechanisms.