M2-polarized macrophages control LSC fate by enhancing stemness, homing, immune evasion and metabolic reprogramming

While it is increasingly becoming clear that cancers are a symbiosis of diverse cell types and tumor clones, the tumor microenvironment (TME) in acute myeloid leukemias (AML) remains poorly understood. Here, we uncover the functional and prognostic relevance of an M2-polarized macrophage compartment. Intra bone marrow co-injection of M2d-macrophages together with leukemic blasts that fail to engraft on their own now induce fatal leukemia in mice. Even a short-term two-day in vitro exposure to M2d macrophages can "train" leukemic blasts after which cells are protected against phagocytosis, display increased mitochondrial metabolism and improved in vivo homing, resulting in full-blown leukemia. Single-cell RNAseq analysis of AML associated macrophages revealed metabolic-related pathways such as Fatty Acid Oxidation and NAD+ generation as therapeutical targetable vulnerabilities. Our study provides insight into the mechanisms by which the immune landscape contributes to aggressive leukemia development and provides alternatives for effective targeting strategies.