Abstract Body (Do not enter title and authors here): Background: We previously reported that anti-CD47 therapy reduces atherosclerosis development in a preclinical Apoe null mouse model. After 12 weeks of treatment (10mg/kg), significant reductions in plaque burden and vascular inflammation were observed, with reductions in cathepsin B activity highlighting macrophage activity as a key mediator in this process.

Hypothesis: Blocking CD47 with a recombinant, high affinity SIRPA-Fc fusion protein, attenuates the progression of atherosclerosis by enhancing phagocytosis and promoting an inflammation-resolution phenotype in vascular macrophage populations. In this study we explored whether treatment induces such changes in macrophage phenotype early in disease development.

Methods: A total of 10 seven week old C57Bl/6 Apoe null mice on high fat diet were randomized to subcutaneous treatment with 10mg/kg of SIRPA-Fc fusion protein or IgG control administered 3x weekly for a total of 4 weeks. At study conclusion, the animal’s circulatory system was perfused with 10% formalin, the proximal 2cm of thoracic aorta was harvested, formalin-fixed, and stored in 70% EtOH until embedding and sectioning. In total, 40 axial sections from the 10 mice (4 sections per animal) were mounted on 2 slides and underwent spatial transcriptomic analysis (10X Xenium In Situ). After quality control, Xenium output underwent clustering, differential expression and pathway analysis to compare transcriptomic changes between mice treated with a SIRPA-Fc fusion protein or IgG control.

Results: A total of 30,810 cells were available for downstream analysis. We identified 16 total clusters, with canonical markers identifying populations of endothelial cells, smooth muscle cells, macrophages, and fibroblasts. Differential expression analysis demonstrated that the expression of several genes, including Lifr (pro-resolving), and C1qa (canonical efferocytosis) were significantly upregulated in the macrophages exposed to CD47 blockade (P < 0.05 after multiple testing correction). Macrophage-specific pathway analysis (GSEA) revealed “Fc gamma R-mediated phagocytosis” as the most significantly upregulated pathway associated with anti-CD47 therapy (P =0.009).

Conclusion: Four weeks of CD47 blockade with a SIRPA-Fc fusion protein is associated with transcriptomic changes leading to enhanced efferocytosis and an inflammation-resolution phenotype within vascular macrophages.