Single-Cell Multi-Omics Identifies Specialized Cytotoxic and Migratory CD8⁺ Effector T Cells in Acute Myocarditis

Acute myocarditis (AM), particularly fulminant myocarditis (FM), is an infrequent but life-threatening cardiac inflammation, with limited effective precision-targeted treatments available. This urgent clinical challenge has prompted further investigations into the mechanisms underlying this pathology to develop novel therapeutic approaches.

We enrolled 40 patients diagnosed with AM (24 mild, 16 fulminant) between December 2022 and November 2023. Using a multi-omics approach, we analyzed peripheral blood mononuclear cells and plasma, integrating single-cell RNA sequencing, single-cell T-cell receptor sequencing, cytometry by time of flight, and Olink proteomics to identify specific pathogenic immune subsets and molecular alterations. In vitro experiments validated the function and inducing signals of identified pathogenic subsets. In coxsackievirus B3-induced FM mice, cytometry by time of flight analysis was performed on peripheral blood mononuclear cells and cardiac infiltrating immune cells. Pharmacological blockade of key molecules was tested to assess potential therapeutic efficacy.

We identified that a specialized type of CD8⁺ effector T cells, CD57⁺CD8⁺ T cells with high cytotoxicity and migration potential, were substantially enriched and exhibited large clonal expansion in AM. Differential expression analysis revealed upregulation of natural killer-like receptor genes in CD57⁺CD8⁺ effector T cells from FM compared with mild cases, which was positively associated with enhanced cytotoxicity and migration potential. In vitro experiments confirmed the existence of circulating CD57⁺CD8⁺ effector T cells with high cytotoxic degranulation and migration potential inducing cardiomyocyte apoptosis, supporting their cardiac migration and cardiomyocyte cytotoxicity in pathogenesis. Elevated circulating interleukin (IL)-18 levels in patients with AM induced the functional differentiation of CD57⁺CD8⁺ effector T cells. In addition, increased proinflammatory CXCL8⁺CD14⁺ monocytes potentially contributed to increasing IL-18 levels and crosstalk with CD57⁺CD8⁺ effector T cells. In FM mice, we observed the analogous expansions of CD57⁺CD8⁺ effector T cells and CXCL2⁺LY6C⁺ monocytes in both blood and hearts, accompanied by elevated plasma IL-18 levels. Disrupting the pathogenic axis involving proinflammatory monocytes, IL-18 signaling, and CCR5-mediated cardiac recruitment significantly alleviated FM in mice.

Our study provides a comprehensive immune landscape for understanding the pathogenesis of AM, especially in FM, highlighting clonal CD57⁺CD8⁺ effector T cells with high cytotoxicity and migration potential, along with their upstream inflammatory signals, as potential therapeutic targets for mitigating immune-related cardiac damage in AM management, especially in FM.