Long-term hematopoietic stem cells trigger quiescence in Leishmania parasites

Quiescence and posttreatment relapse constitute an important therapeutic constraint across the microbiological spectrum. This study unveils that Leishmania infantum and L. donovani parasites rapidly enter quiescence after an estimated 4-6 divisions in both mouse and human stem cells of the bone marrow but not in macrophages as primary host cells. Quiescent amastigotes display a reduced size and evidence for a rapid evolutionary adaptation response with genetic alterations. We formally demonstrate that acquisition of a quiescent phenotype endows parasites with a capacity to survive antileishmanial treatment. Transition through quiescence also results in an increased cellular infectivity and high transmission capacity through the sand fly vector. Transcriptional profiling of quiescent and non-quiescent metabolic states identified a limited set of 26 upregulated genes that are of particular interest given their predicted involvement as regulators of cell cycle progression and of gene expression at various levels. The differential gene set constitutes a reliable source for the identification of novel markers and potential drivers of quiescence, a metabolic state bestowing parasites the capacity to escape drug treatment.