Gene expression profiling and multiplex immunofluorescence analysis of bullous pemphigoid immune-related adverse event reveal upregulation of toll-like receptor 4/complement-induced innate immune response and increased density of T_H1 T-cells

Background: Immune checkpoint inhibitor (ICI)-based cancer therapies cause a variety of cutaneous immune-related adverse events (irAEs) including immunobullous skin eruptions like bullous pemphigoid (BP). However, little is known about the underlying immunopathogenic drivers of these reactions, and understanding the unique gene expression profile and immune composition of BP-irAE remains a critical knowledge gap in the field of oncodermatology/oncodermatopathology. Methods: BP-irAE (n = 8) and de novo BP control (n = 8) biopsy samples were subjected to gene expression profiling using the NanoString® Technologies nCounter PanCancer Immune Profiling Panel. Multiplex immunofluorescence (mIF) studies using markers for T-cells (CD3 and CD8), T helper 1 (T_H1) cells (Tbet), T_H2 cells (Gata3), T_H17 cells (RORγT), and regulatory T-cells (Tregs; FoxP3) were further evaluated using InForm® image analysis. Results: Compared with de novo BP controls, BP-irAE samples exhibited upregulation of 30 mRNA transcripts (p < 0.025), including toll-like receptor 4 (TLR4) and genes associated with complement activation, and downregulation of 89 mRNA transcripts (p < 0.025), including genes associated with T_H2, T_H17, and B-cell immune response. BP-irAE demonstrated a greater density of Tbet⁺ (T_H1) cells in the dermis (p = 0.004) and fewer Tregs in the blister floor (p = 0.028) when compared with that of de novo control BP samples. Conclusions: BP-irAE exhibited activation of the TLR4/complement-driven classical innate immune response pathway, with dermal T_H1 immune cell polarization and decreased Tregs in the blister floor. TLR/complement signaling may underlie the immunopathogenesis of BP-irAE.