Daniel F. Carr

Decreased epidermal high‐mobility group box 1 (HMGB1) expression is an early marker of epidermal injury in Stevens–Johnson syndrome/toxic epidermal necrolysis (SJS/TEN). Etanercept, an anti‐tumor necrosis factor therapeutic, is effective in the treatment of SJS/TEN. The objective was to characterize antitumor necrosis factor‐alpha (TNF‐α)‐mediated HMGB1 keratinocyte/epidermal release and etanercept modulation. HMGB1 release from TNF‐α treated (± etanercept), or doxycycline‐inducible RIPK3 or Bak‐expressing human keratinocyte cells (HaCaTs) was determined by western blot/ELISA. Healthy skin explants were treated with TNF‐α or serum (1:10 dilution) from immune checkpoint inhibitor‐tolerant, lichenoid dermatitis or SJS/TEN patients ± etanercept. Histological and immunohistochemical analysis of HMGB1 was undertaken. TNF‐α induced HMGB1 release in vitro via both necroptosis and apoptosis. Exposure of skin explants to TNF‐α or SJS/TEN serum resulted in significant epidermal toxicity/detachment with substantial HMGB1 release which was attenuated by etanercept. Whole‐slide image analysis of biopsies demonstrated significantly lower epidermal HMGB1 in pre‐blistered SJS/TEN versus control ( P < 0.05). Keratinocyte HMGB1 release, predominantly caused by necroptosis, can be attenuated by etanercept. Although TNF‐α is a key mediator of epidermal HMGB1 release, other cytokines/cytotoxic proteins also contribute. Skin explant models represent a potential model of SJS/TEN that could be utilized for further mechanistic studies and targeted therapy screening.