Lipid-lowering approaches reduce atherosclerotic cardiovascular disease (ACVD), but significant residual risk remains. Macrophage (Mφ) accumulation and defective phagocytic clearance of apoptotic cells (ACs) by Mφs, i.e., defective efferocytosis, promote atherosclerotic plaque vulnerability and subsequent acute cardiovascular events. Enhancing efferocytosis represents a potential therapeutic strategy for residual risk reduction in ACVD. Discovering novel genes that can be harnessed to enhance efferocytosis addresses a major knowledge gap and provides opportunities for new ACVD therapeutics. As discovered in our genome-wide CRISPR screen of efferocytosis regulators, Pdcd6ip deficiency enhances Mφ efferocytosis, representing a novel therapeutic opportunity in atherosclerosis and management of CVD residual risk. Preliminary data show that transplantation of Pdcd6ip-/- mice bone marrow into atherosclerosis-prone Ldlr-/- mice increases features of plaque stability. This PPG project will test the central hypothesis that Pdcd6ip acts as a molecular break on Mφ efferocytosis and can be harnessed to ameliorate athero-progression or to promote athero-regression through effects on plaque stabilization, the central theme. Integrating with Drs. Tall and Tabas, the project will assess the therapeutic impact of Pdcd6ip inhibition on atherosclerosis with clonal hematopoiesis (CH) mutations, with implications for inflammation-related residual risk in CH patients. Aim 1 will determine how Pdcd6ip deficiency enhances efferocytosis in vitro in murine and human Mφs. Our data show that Pdcd6ip-/- induces cytokinesis arrest and increased formation of polyploid Mφ that demonstrate superior capability of continuing efferocytosis, suggesting a “super-eater” phenotype. Mononuclear Mφs with Pdcd6ip-/- also show enhanced primary efferocytosis, though not continuing efferocytosis. We will test the hypothesis that Pdcd6ip deficiency enhances efferocytosis via both polyploidy-dependent and -independent mechanisms. Aim 2 will determine if harnessing Pdcd6ip inhibition enhances efferocytosis to ameliorate athero-progression or to promote athero-regression in mice. We will determine: (A) whether Pdcd6ip deficiency ameliorates progression via converting proliferating Mφs to “super- eater” polyploid Mφs, including in JAK2-CH mice; and (B) whether Pdcd6ip deficiency promotes regression via enhancing efferocytosis-resolution cycle, including in DNMT3A-CH mice. Using fate-mapping and scRNA-seq, we will also address how Pdcd6ip deficiency promotes plaque stability via Mφ and stromal cell crosstalk (with Drs. Tall, Tabas, Reilly, Cores B&C). Aim 3 integrates the histological, clinical, transcriptomic, and spatial transcriptomics data of biobanked human plaques in the Munich Vascular Biobank (Dr. Maegdefessel, Core C) to prioritize potential efferocytosis regulators identified in our genome-wide CRISPR screen that are associated with human atheroma. The prioritized genes will accelerate mechanistic studies and support the translational promise of enhancing efferocytosis for residual risk reduction in ACVD, particularly in CH patients. In summary, our work will provide insights into new approaches to enhance Mφ efferocytosis and mitigate residual ACVD risk.