Identifying the hematopoietic and leukemic stem cell niches

Acute myeloid leukemia (AML) is a devastating disease originating from immature hematopoietic cells in the bone marrow (BM) of patients. Leukemic stem cells (LSC) maintain the disease and likely cause relapse after treatment. Current treatment strategies in AML are mainly targeting actively dividing leukemic cells, but do not tackle quiescent and self-renewing LSCs, which likely explains its limited effectiveness. Therefore, to eradicate the disease, treatment must eliminate the LSC fraction. However, approaches to eradicate LSCs remain undeveloped. LSCs are sustained by unique interactions with the BM microenvironment (aka niche) defined by specific molecular/cellular determinants. Here, we propose a strategy to identify these determinants using a novel synthetic Notch reporter system (SynNotch). A synthetic Notch receptor contains the core of the Notch receptor but can be customized for their sensing and response behaviors by swapping the extracellular recognition domain and intracellular signaling domain to create a reporter of the receptor activity. Thereby one can monitor user-specified environmental clues such as direct cellular contact or specific extracellular ligand binding in cells expressing the SynNotch receptor. We will engineer our SynNotch system to identify BM niche cells that were in direct cellular contact with leukemic cells by the activation fluorescent reporter expression. The fluorescent cells will be isolated analyzed by single cells RNA sequencing to identify the molecular determinants specific to LSC niche interactions. Concluding, our proposal addresses the principal question whether it is possible to eradicate the LSC fraction of AML cells by targeting the LSC-niche.