Peripheral immune landscape of pediatric fulminant myocarditis revealed by single-cell sequencing

Abstract Fulminant myocarditis (FM) is one of the most feared diseases in children because of its fulminant nature and high mortality rate. However, the precise pathological immune subsets and molecular changes in FM are unknown. Here, we present the first comprehensive cellular and transcriptomic profiling of the peripheral blood mononuclear cells of children in FM acute and recovery phases using Single-cell RNA sequencing. 21 cell clusters are identified among 79542 cells. The proportion of T cells and NK cells increase, while myeloid cells and B cells reduce in acute phase, which were consistent with our flow cytometry data of 35 FM patients. Several unique cell types in peripheral blood are identified, including regulatory B cells, MAIT cells, adaptive NK cells and CD8+Tpex cells. The transcriptomic analysis exhibited elevated expression levels of chemokine receptor CXCR4 and S100A family genes almost in all cell types in FM acute phase, as well as MHC-II molecules in antigen-presenting cells. TCR and BCR exhibit remarkable amplification and obvious skewed usages of V genes in FM. Ligand receptor analysis show myeloid cells maintained active communication with other immune cells. Considering that CXCR4 may play an important role in myocarditis, we designed experiments to explore its function in mouse model. Vital myocarditis (VMC) mouse model was constructed using Coxsackie virus type3（CVB3）.We found that myocardial inflammation and myocardial injury of VMC mice were alleviated when treated with CXCR4 blocker. CXCR4 may be a potential therapeutic target for myocarditis. Our study will provide useful insights into key immune cell subsets and transcriptomic profiles implicated in pediatric fulminant myocarditis acute phase and recovery phase, thus providing several potential diagnostic and therapeutic targets for this disease.