Persistent myeloid cell reprogramming despite miltefosine treatment in leishmania-infected macaques.

Visceral leishmaniasis (VL) is a neglected tropical disease caused by protozoan parasites. An inflammatory immune response, associated with tissue injury, occurs shortly after infection. Using a rhesus macaque model of VL, we evaluated the impact of miltefosine therapy administered during the acute phase of infection. Despite therapy, parasites persist in multiple tissues, including the spleen, bone marrow, peripheral, and mesenteric lymph nodes. Parasite burden inversely correlates with cellular miltefosine levels. Notably, L. infantum remains detectable three months post-treatment. Single-cell transcriptomic analysis reveals cellular heterogeneity and reprogramming of splenic myeloid cells post-treatment, including inflammatory macrophages, immature plasmacytoid dendritic cells, and type 2 dendritic cells (DCs). Flow cytometric sorting of splenic neutrophils, macrophages, and DCs confirms the presence of L. infantum post-treatment, highlighting the challenge of parasite clearance. Our findings reveal a disrupted innate immune landscape post-infection that persists after treatment, indicating myeloid cell reprogramming may sustain chronic infection and parasite persistence.