Hematopoietic stem and progenitor cells in experimental remission model of acute myeloid leukemia in vivo [ATAC-seq]
Inflammation is a hallmark of cancer and is linked to patient prognosis in acute myeloid leukemia (AML). Our recent study revealed that hematopoietic stem and progenitor cells (HSPCs) exhibit an inflammatory active state and serve as a cellular source of inflammatory cytokine secretion in AML. Recent studies in infection and chronic inflammation related disease models have revealed that inflammation can reprogram HSPCs to fuel chronic inflammation related co-mobidities. Building on our report of AML-associated inflammation in HSPCs, here we ask whether AML-experienced normal HSPCs are reprogrammed in AML. To investigate this, we utilized a chimeric model of AML, carrying both doxycycline-inducible leukemic and healthy wildtype hematopoietic fractions, to generate an AML remission model. To test whether AML-experienced HSPCs harbor inflammatory memory, mice were challenged with heterogenous inflammatory activation. Our transcriptomic and epigenetic results show for the first time that phenotypically normal, AML-experienced HSPCs carry a durable inflammatory memory whereby primary exposure to AML secreted factors alters their response to secondary stimuli. Our finding suggests that AML-experienced HSPCs are innate immune reprogrammed in the AML niche. Overall design: AML remission model was generated by first co-transplanting non-induced whole bone marrow (WBM) from inducible MLL-AF9 (iMLL-AF9) mice (CD45.1; homozygous hMLL-AF9 and rtTA; 2E5 cells per recipient) together with WBM from healthy wildtype mice (double positive CD45.1+/2+; 8E5 cells per recipient), into lethally irradiated C57BL/6J recipients (CD45.2) and is termed "AF9+/+" mice. Control naive mice were generated by co-transplanting hMLL-AF9-null (CD45.1; hMLL-AF9-null, homozygous rtTA only; 2E5 cells per recipient) together with healthy wildtype mice (double positive CD45.1+/2+; 8E5 cells per recipient) and is termed "AF9-/-" mice. After 6-8 weeks after transplantation, AML remission state was generated by first subjecting mice to leukemogenesis (via doxycycline induction) for 5 weeks, followed by disease regression (via doxycycline withdraw) for 4 weeks. Mice were administered with either PBS or LPS to model baseline remission and inflammatory-challenged remission state. Mice were sacrificed 24 hours after the injection. Bone marrow hematopoietic stem and progenitor cells (HSPCs; CD45.1+/2+, Lin- cKit+ Sca1+) were fluorescent-activated cell sorting (FACS)-sorted for RNA-Seq and ATAC-Seq.