Immune checkpoint inhibitor (ICI) therapies in cancer accelerate atherosclerosis progression. Here, we have charted the landscape of immune checkpoint gene expression and defined the network of disease-relevant interactions with single-cell resolution. We found that signaling through PD-1 and CTLA4 is driven by a population of dendritic cells enriched for FSCN1 that can be derived from peripheral blood cells following anti-PD-1 or -CTLA4 treatment ex vivo. Type 2 diabetes dampened plaque PD-1 and CTLA4 signaling, showing that cardiometabolic comorbidities elicit unique responses to ICIs. Lipid-lowering therapy equalized the intensity and direction of immune checkpoint interactions in human blood, while atherosclerotic mice subjected to a lipid-lowering diet displayed both increased co-inhibitory signaling and a downregulation of inflammatory transcriptional programs in plaques. Our findings underscore the potential of lipid-lowering therapies in stabilizing immune checkpoint interactions and reducing plaque inflammation, offering new insights on atherosclerosis and cardiovascular risks in cancer patients undergoing ICI treatments. Overall design: CD45+ Immune cells were isolated from human carotid plaque tissue from patients undergoing carotid endarterectomy. Cells were profiled using scRNAseq.