Exploring PD-1+ and tissue resident memory T cells in atherosclerotic diseases

Abstract Funding Acknowledgements Type of funding sources: Other. Main funding source(s): Health Holland Visual Sonics Background Checkpoint inhibitor therapy (ICI), a potent oncologic treatment, has been associated with an enhanced risk for atherosclerotic cardiovascular events and increased plaque progression. Among the key players affected by ICI are tissue resident memory T cells (Trm), a subset residing in tissues and characterized by CD44, CD69, PD-1, and CD103. Although Trms have been associated with chronic inflammatory conditions, their role in atherosclerosis and accelerated atherosclerosis, as observed in postinterventional diseases such as vein graft disease, remains elusive Here, we present an investigation into the role of PD-1 positive cells and Trms in accelerated atherosclerosis as found in vein graft disease. Methods Human carotid atherosclerotic plaques were stained with a MOVAT stain and scored to determine plaque stability. 25 Stable and 25 unstable plaques were stained for CD3+ T cells and PD-1. Hypercholesterolemic ApoE3*Leiden mice underwent vein bypass surgery and were sacrificed at t7, t14, t28 (n=6 per time point). The vein grafts were processed for flow cytometry to quantify the Trms population, using markers including CD4+, CD8+, CD44+, CD25-, CD69+, CD103+ and PD-1+. Hypercholesterolemic ApoE3*Leiden mice underwent vein bypass surgery. Biweekly, mice received ICI (anti-PD-L1) or control antibody (n=7). After 28 days vein graft morphology was assed using MOVAT staining and vein graft inflammation by staining MAC3 and CXCL10. Results Within human atherosclerotic plaques, PD-1-expressing T cells were predominantly located in the shoulder regions of the necrotic core. Unstable lesions exhibited significantly higher levels of PD-1 expressing CD3+ T cells compared to stable lesions (p=0.001). Furthermore, the percentage of PD-1 expression positively correlated with immune cell infiltration scores (p=0.019). In murine vein grafts, Trms were identified through flow cytometry. A trend was observed indicating an increase in the number of CD4 and CD8 Trms at t14 compared to t7 Trms (CD8+, CD44+, CD69+/CD103+). At t28, the number of CD4 and CD8 Trms decreased compared to t14, with PD1+ expressing Trms showing a similar trend, peaking at t14. Vein grafts in mice receiving anti-PD-L1 mAb showed no morphological differences compared to the control group. However, a significant difference in inflammation was noted in the anti-PD-L1 treated group, characterized by a higher number of macrophages (p=0.02) and increased expression of CXCL10 (p=0.008). Conclusion Here we demonstrate the association of PD-1+ T cells with unstable lesions and reveals that Trms increase during the inflammatory phase and decrease during the stabilizing phase of accelerated atherosclerosis. Trms emerge as potential detrimental targets of ICI therapy, which is characterized by increased inflammation.