The cover image illustrates murine aortic leukocyte heterogeneity in 20-week-old Apoe−/− mice. Using a 35-marker pan-leukocyte mass cytometry (CyTOF) antibody panel, and a tSNE-based cluster detection algorithm, 23 leukocyte clusters were identified above a detection threshold. Most of these leukocyte populations, including T cells, B cells, and myeloid cells, show dynamic regulation between mice fed chow diet or a Western diet. The article within shows the unexpected complexity of the immune cell landscape in atherosclerosis using multiple omics approaches, demonstrates the association of individual murine aortic leukocyte population gene signatures with risk of developing secondary ischemic event in patients, and describes the existence of several novel leukocyte subsets as a launching point for future research. See related article, page 1675.