Inflammatory conversion of normal hematopoietic stem and progenitor cells by acute myeloid leukemia derived extracellular vesicles in vivo
Inflammation in the bone marrow (BM) microenvironment is a constitutive component of acute myeloid leukemia (AML) pathogenesis. Studies have demonstrated that leukemic blasts propagate acute inflammation in the AML niche. Our recent studies in a congenic AML model suggest residual healthy hematopoietic stem and progenitor cells (HSPCs) participate in the inflammatory crosstalk. However, the underlying mechanism that drives the inflammatory conversion of HSPCs remains unclear. Here, we ask whether AML-derived extracellular vesicles (EV-AML) can convert HSPCs into an inflammatory active state in vivo. Using EV-AML purified from inducible (i)MLL-AF9 AML blasts (AF9-EV-AML), we challenged healthy C57BL/6J mice with serial injections of AF9-EVAML and analyzed HSPCs transcriptome. We show that HSPC transcriptome corroborates the enrichment of inflammatory and innate immune responses in EVAML-challenged BM HSPCs compared to controls. Our findings suggest that AML converts HSPCs into an inflammatory hub via EVAML in the AML niche. Overall design: Healthy C57BL/6J mice (CD45.1; 8-12 weeks; female; Jacksons Laboratory) were challenged with either inducible(i)MLL-AF9 blasts-derived extracellular vesicles (AF9-EV), healthy peripheral blood extracellular vesicles (PB-EV), phosphat buffered saline (PBS), or lipopolysaccharides (LPS). AF9-EV (1-2E9 particles per injection), PB-EV (1-2E9 particles per injection), and PBS were administered every 24 hours for 3 days via intravenous (for the first two injections) and intraosseous (third injection). LPS (3mg/kg) were injected via single-dose (intraperitoneal) and serve as a positive control. Mice were sacrificed 24 hours the last injection and bone marrow HSPCs (Lin- cKit+ Sca1+)  were fluorescent-activated cell sorting (FACS)-sorted for gene expression assay.