Pathogenic Keratinocyte States and Fibroblast Niches Define the Tissue Microenvironment in Severe Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease characterized by recurrent painful abscesses and tunnels in flexural sites. The mechanisms driving HS pathogenesis, particularly the roles of keratinocytes and fibroblasts in the HS inflammatory ecosystem, remain poorly understood. To characterise the cellular and molecular landscape of HS, we analyzed lesional skin from severe HS patients using single-cell RNA-sequencing and spatial transcriptomics to identify key keratinocyte states and cellular interactions, with a focus on fibroblast–keratinocyte crosstalk. Our study identifies a novel migratory S100+ pathogenic keratinocyte state and highlights critical interactions between COL6A5+ fibroblasts in HS lesion formation. We also detect tertiary lymphoid organ (TLO)-like structures enriched with activated B and plasma cells interacting with APOD+ fibroblasts, implicating their role in HS chronic inflammation. We show that fibroblast interactions with HS keratinocytes and specific immune cells, such as Langerhans cells, are key drivers of HS pathogenesis, and that two main fibroblast niches are present within the HS microenvironment. Targeting these cellular networks may offer new therapeutic strategies for HS management, and highlight the potential limitations of targeting individual pathways in isolation, when treating pathology present in HS tissue.