Single-cell landscape of peripheral immune response in patients with anti-melanoma differentiation–associated gene 5 dermatomyositis

Abstract Objective Anti-melanoma differentiation–associated gene 5 (Anti-MDA5)–positive DM is a rare but life-threatening autoimmune disorder that is associated with a high risk of developing rapidly progressive interstitial lung disease. Current empirical therapies offer limited benefit in terms of patient survival, as little is known about the aetiology of anti-MDA5 DM. To best understand its immune landscape, we applied single-cell RNA sequencing (scRNA-seq) to peripheral blood samples from DM patients and healthy controls. Methods Peripheral blood mononuclear cells (PBMCs) from eight DM patients (including three distinct subtypes of DM) and two healthy donors were sequenced using the 10X Genomics platform. Additional scRNA-seq data for four healthy donors were incorporated for further bioinformatic analysis. Results Aberrantly increased proportions of CD14+ monocytes and plasma cells were observed in anti-MDA5 DM PBMC samples. Moreover, we found an overactivated type I IFN response and antiviral immunity in both innate and adaptive immune cells derived from anti-MDA5 DM patients that was positively correlated with disease severity. Importantly, a unique subset of CD14+ monocytes that highly expressed IFN alpha–inducible protein 27 (IFI27), a biomarker for viral infection, and IFN induced with helicase C domain 1 (IFIH1, which encodes MDA5) was specifically identified in anti-MDA5 DM samples for the first time. Conclusion Our study has illustrated the peripheral immune cell atlas of a number of DM subtypes, has provided compelling evidence for a viral infection–derived origin for anti-MDA5 DM, and has indicated potential targets for innovative therapeutic interventions.