Abstract Body: Atherosclerotic cardiovascular disease (ASCVD) is accompanied by systemic inflammation, including changes in circulating immune cells and their hematopoietic progenitors. Hypercholesterolemia and western diet (WD) have been shown to induce epigenetic and metabolic reprogramming of myeloid progenitors and monocytes in the bone marrow (BM) that elicit a hyperresponsive state. These changes, defined as trained immunity, result in amplified inflammatory responses upon subsequent immune challenges. We hypothesized that the immunomodulatory metabolite itaconate, which is produced by the immune-responsive gene 1 (Irg1/Acod1) enzyme, protects from atherosclerosis by reducing WD-induced trained immunity. To investigate the role of the Irg1-itaconate axis in innate immune memory in the context of atherosclerosis, Irg1-deficient mice (Irg1^–/–) were injected with a PCSK9-AAV to induce hypercholesterolemia and subjected to WD for 12 weeks. Compared to WT controls, Irg1^–/– mice presented with monocytosis and an increase in bone marrow leukocytes and granulocyte-monocyte progenitors (GMPs), suggestive of an increase in myelopoiesis. To understand how the Irg1-itaconate axis alters the epigenomic landscape of hematopoietic progenitors, we performed single cell (sc) multiomic gene expression and assay for transposase-accessible chromatin (ATAC) sequencing (scATAC-seq) in the BM. Transcription factor motif enrichment analysis revealed that Irg1-deficiency increased chromatin accessibility at loci regulated by the C/EBP superfamily and AP-1, a group of myeloid lineage-determining transcription factors, in a subset of common myeloid progenitors (CMPs), GMPs, and monocyte-dendritic cell progenitors (MDPs). Additionally, pathway analysis of genes associated with the differentially accessible (DA) peaks in these progenitors depicted an upregulation of biological processes involved in leukocyte activation and proliferation with Irg1-deficiency. Together, these data suggest that Irg1-itaconate helps to maintain the quiescence of progenitor cells with myeloid lineage commitment, and the loss of this protective pathway during hypercholesterolemia results in myeloid-biased expansion and monocytosis. Collectively, our findings reveal a role for the Irg1-itaconate axis in restraining myelopoiesis and systemic inflammation during hypercholesterolemia, highlighting the importance of this metabolic pathway in protecting from atherosclerosis.