Abstract 350: Immune Profiling and Causal Antigen Discovery in Mouse and Human Models of Immune Checkpoint Inhibitor-induced Myocarditis

Introduction: Immune checkpoint inhibitors (ICIs) are novel drugs that activate T cell-mediated anti-tumor response by blocking immune checkpoints such as PD-1 or CTLA-4, leading to improved cancer patient survival. Despite these benefits, ICIs can result in autoimmune side effects including fulminant myocarditis and heart failure. While ICI-induced myocarditis is characterized by myocardial T cell infiltration, the causal mechanisms remain unknown. We hypothesize that ICI-induced myocarditis is caused by cardiac-specific auto-antigens triggering clonal expansion of myocardial CD8+ T-cells, leading to T-cell mediated myocardial damage.

Methods/Results: We have explored the ICI-induced inflammatory response in a mouse model of myocarditis induced by PD-1 knockout and in patients with ICI-induced myocarditis. PD-1 deficient-mice on a lupus-like autoimmune background (i.e. MRL/Pcd1-/- mice) develop spontaneous fatal myocarditis in 70% of animals by 5 weeks of age, with massive cardiac infiltration of CD8>CD4+ T-cells. Likewise, patients with ICI-induced myocarditis have CD8>CD4+ T-cell infiltrate in the heart. We have performed time-of-flight mass cytometry (CyTOF) to immunophenotype the T-cell subsets in the blood/myocardium of MRL/Pcd1-/- mice and in ICI-myocarditis patients. We have also conducted single cell sequencing of T-cell receptors (TCRs) from the blood +/- myocardial-derived T-cell samples of the mice and patients. Our preliminary results in ICI-myocarditis patients confirmed the previously reported CD8+ T-cell expansion in the blood and myocardium of myocarditis patients compared with healthy control. We are currently identifying candidate cardiac auto-antigen(s) responsible for this disease by performing Grouping Lymphocyte Interactions by Paratope Hotspots (GLIPH).

Conclusion: Myocarditis is a serious and life-threatening complication of ICI treatment. By understanding the unique immune response present during ICI-induced myocarditis and the responsible cardiac auto-antigen(s) involved, we will pave the way for the development of adjuvant therapies that target these antigens and mitigate their deleterious effects.