A Case of Local Relapse of Pemphigus Vegetans Detected IL-17A⁺ Tissue-Resident Memory T Cells in Lesional Skin

A 49-year-old man with pemphigus vegetans (PVeg) relapsed several times due to cessation of therapy. At the age of 66, vegetative plaques developed at the left oral commissure following mechanical plucking of approximately 500 beard hairs. Treatment with prednisolone (20 mg/day) was continued but yielded no clinical improvement. Subsequently, rituximab (1000 mg twice, 2 weeks apart) led to a rapid decline of anti-desmoglein 3 (Dsg3) autoantibody and clinical improvement. The lesion resolved after 18 months, and prednisolone was tapered without recurrence. Based on the site-specific recurrence and chronicity, we hypothesized that tissue-resident memory T (T_RM) cells and high endothelial venules (HEV)-like vessels contributed to disease persistence. Immunohistochemical analysis revealed a substantial presence of IL-17A-producing CD69 +⁺ CD103 +⁺ T_RM cells in the dermis. In addition, PNAd+⁺ HEV-like vessels were increased, accompanied by infiltrates of B cells and plasma cells. Notably, Dsg3-specific B cells were also detected, indicating that rituximab-mediated B cell depletion likely contributed to lesion resolution in this case.