Abstract 12876: Identification of Pathogenic Immune Cell Subsets in Immunotherapy-Induced Myocarditis

Abstract

Introduction: Immune checkpoint inhibitors (ICIs) are monoclonal antibodies used to activate the immune system against tumor cells. Despite therapeutic benefits, ICIs have the potential to cause immune related adverse events (irAE) such as myocarditis, a rare but serious side effect with up to 50% mortality in affected patients. Histologically, patients with ICI myocarditis have lymphocytic infiltrates in the heart, implicating T-cell-mediated mechanisms. However, the precise pathologic immune subsets and molecular changes in ICI myocarditis are unknown. Hypothesis: We hypothesize that ICI myocarditis is associated with significant quantitative and molecular changes in pathogenic immune cell subsets. Methods: To identify immune subset(s) associated with ICI myocarditis, we performed time-of-flight mass cytometry (CyTOF) on peripheral blood mononuclear cells from 40 patients and controls with autoimmune adverse events (irAE) on ICI including four patients with ICI myocarditis. We also profiled 15 patients/controls using single cell T-cell receptor (TCR) sequencing and RNA sequencing (scRNA-seq) with feature barcoding for surface marker expression confirmation. Results: With both methods, we found expansion of cytotoxic CD8+ T effector cells re-expressing CD45RA (Temra CD8+ cells) in ICI myocarditis patients compared to controls. Using TCR sequencing, these CD8+ Temra cells were clonally expanded in myocarditis patients. Transcriptomic analysis of these Temra CD8+ clones confirmed a highly activated and cytotoxic phenotype with expression of granzyme/perforin. Longitudinal study demonstrated progression of these Temra CD8+ cells into an exhausted phenotype two months after treatment with glucocorticoids. Differential expression of proinflammatory chemokines (CCL4/CCL4L2/CCL5) was uncovered in clonally expanded Temra CD8+ cells, and ligand-receptor analysis implicated their regulation of other inflammatory cells such as monocytes and NK cells. Conclusions: Clonal cytotoxic Temra CD8+ cells are significantly increased in patients with ICI myocarditis, and have unique transcriptional changes, including upregulation of chemokines CCL4/CCL4L2/CCL5, which may serve as attractive diagnostic/therapeutic targets.