Immune Checkpoint Inhibitor Therapy Aggravates T Cell–Driven Plaque Inflammation in Atherosclerosis

Background Immunotherapy has revolutionized cancer treatment. However, immune checkpoint inhibitors (ICIs) that target PD-1 (programmed cell death protein-1) and/or CTLA-4 (cytotoxic T lymphocyte-associated antigen-4) are commonly associated with acute immune-related adverse events. Accumulating evidence also suggests that ICIs aggravate existing inflammatory diseases. Objectives As inflammation drives atherosclerotic cardiovascular disease, we studied the propensity of short-term ICI therapy to aggravate atherosclerosis. Methods We used 18F-FDG (2-deoxy-2-[fluorine-18]fluoro-D-glucose) positron emission tomography–computed tomography to detect macrophage-driven vascular and systemic inflammation in pembrolizumab and nivolumab/ipilimumab–treated melanoma patients. In parallel, atherosclerotic Ldlr–/– mice were treated with CTLA-4 and PD-1 inhibition to study the proinflammatory consequences of immune checkpoint inhibition. Results ICI treatment did not affect 18F-FDG uptake in the large arteries, spleen, and bone marrow of melanoma patients, nor myeloid cell activation in blood and lymphoid organs in hyperlipidemic mice. In contrast, we found marked changes in the adaptive immune response (i.e., increased CD4+ effector T cell and CD8+ cytotoxic T cell numbers in lymphoid organs and the arterial wall of our hyperlipidemic mice). Although plaque size was unaffected, plaques had progressed toward a lymphoid-based inflammatory phenotype, characterized by a 2.7-fold increase of CD8+ T cells and a 3.9-fold increase in necrotic core size. Increased endothelial activation was observed with a 2.2-fold and 1.6-fold increase in vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, respectively. Conclusions This study demonstrates that combination therapy with anti-CTLA-4 and anti-PD-1 antibodies does not affect myeloid-driven vascular and systemic inflammation in melanoma patients and hyperlipidemic mice. However, short-term ICI therapy in mice induces T cell–mediated plaque inflammation and drives plaque progression.

ICIs have revolutionized cancer immunotherapy and have shown efficacy in the treatment of many types of cancer, including melanoma and non-small cell lung cancer, and are considered standard of care for these and other malignancies (1,5,6). Combination strategies that target both CTLA-4 and PD-1 are increasingly applied in the clinic (7,8).
Unfortunately, immune-related adverse events are a common side effect of immune checkpoint inhibition and are caused by T cell-mediated cytotoxicity in various organs, with skin, intestine, lungs, liver, and endocrine organs being affected most frequently (2,7,9). Up to 59% of the patients who receive combination CTLA-4 and PD-1 inhibitors develop adverse events that are considered severe (2,10). Most of these events can be successfully overcome by corticosteroids treatment and (temporary) discontinuation of immune therapy (2,10). Recent evidence reveals that ICI therapy also aggravates pre-existing autoimmune and chronic inflammatory diseases in cancer patients: 27% to 75% of cancer patients with a history of rheumatoid arthritis, systemic lupus erythematosus, or inflammatory bowel disease experience an exacerbation upon ICI treatment (11,12).
A concern of ICI therapy is the potential adverse effects on the progression of cardiovascular disease (CVD) (13,14). Atherosclerosis, the underlying pathology of many cardiovascular events, is a chronic inflammatory disease of the larger arteries. Both lymphoid and myeloid immune cells drive atherosclerotic plaque formation and progression toward clinically unfavorable, unstable lesions that may cause myocardial infarction or ischemic stroke (15).
Whether immune checkpoint inhibition affects the inflammatory process that underlies atherosclerosis is currently unknown. However, ICI-related atherosclerotic CVD is increasingly reported in clinical studies and case reports (16)(17)(18).
In this study, we investigated the effects of short-term ICI therapy on vascular inflammation in a small group of patients with stage IV melanoma and in hyperlipidemic mice using a combination   (19,20).    The aortic root and aortic arch were isolated and fixed in 1% paraformaldehyde overnight. Longitudinal sections (4 mm) of the aortic arch and aortic root were stained with hematoxylin and eosin and analyzed for plaque extent, phenotype, and necrotic core size, as described previously (21). Intimal xanthoma, pathological intimal thickening, and fibrous cap atheroma (FCA) were identified (22). Expanded methods are available in the Supplemental Appendix.   Table 1). 18 F-FDG uptake in the thoracic aorta ( Figure 1B) and carotid arteries ( Figure 1C), as well as in spleen and bone marrow, was determined before and 6 weeks after the initiation of immune checkpoint inhibition. After 6 weeks of treatment, 18 F-FDG uptake had not increased in the thoracic aorta, carotid arteries, or spleen or bone marrow. In this small human cohort, these data suggest that short-term ICI therapy does not affect vascular or systemic inflammation ( Figure 1D).   Immune Checkpoint Inhibitor Therapy Aggravates Experimental Atherosclerosis    Figure 3L). The majority of the TUNEL þ cells was also   Figures 5D and 5E).

DISCUSSION
The key observation in our study is that short-term ICI treatment has profound effects on experimental atherosclerosis. We here show that antibody-