Single-cell spatial proteomics identifies the JAK/STAT pathway as an actionable therapeutic target in lethal cutaneous drug reactions

Toxic epidermal necrolysis (TEN) is a fatal drug-induced skin reaction and an emerging public health issue. Triggered by common medications, TEN patients undergo severe and sudden epidermal detachment caused by keratinocyte cell death. Although molecular mechanisms driving keratinocyte cell death have been proposed, the main drivers remain unknown and no effective therapy exists. To systematically map molecular changes that are associated with TEN and identify potential druggable targets, we employed the single- cell spatial proteomics technique Deep Visual Proteomics. We analyzed formalin-fixed paraffin-embedded archived skin-tissue biopsies of three types of cutaneous drug reactions with varying severity and quantified over 5,000 proteins in keratinocytes and skin-infiltrating immune cells. Most strikingly, this revealed a robust enrichment of Type-I and -II interferon signature in the immune cell and keratinocyte compartment of TEN patients, along with a drastic activation of pSTAT1. Targeted inhibition with pan- JAK inhibitor (JAKi) tofacitinib reduced keratinocyte-directed cytotoxicity in a novel live-cell imaging assay, using patient-derived keratinocytes and peripheral blood mononuclear cells (PBMCs). Furthermore, oral administration of pan-JAKi tofacitinib or baricitinib ameliorated clinical and histological disease severity in two distinct mouse models of TEN. Lastly, JAKi treatment was safe and associated with rapid cutaneous re- epithelialization and recovery in four patients with TEN. This study uncovers the JAK- STAT and interferon signaling pathways as key pathogenic drivers of TEN and demonstrates the potential of targeted JAK inhibition as a curative therapy.