Background and Purpose: Pemphigus is caused by autoantibodies against desmoglein (Dsg) 1, Dsg3, and/or non-Dsg antigens. Pemphigus vulgaris (PV) is the most common manifestation of pemphigus, with painful erosions on mucous membranes. In most cases, blistering also occurs on the skin, leading to areas of extensive denudation. Despite improvements in pemphigus treatment, time to achieve remission is long, severe adverse events are frequent and 20% of patients do not respond adequately. Current clinical developments focus exclusively on modulating B cell function or autoantibody half-life. However, topical modulation of PV autoantibody-induced blistering is an attractive target because it could promptly relieve symptoms. Experimental Approach: To address this issue, we performed an unbiased screening in a complex biological system using 141 low MW inhibitors from a chemical library. Specifically, we evaluated PV IgG-induced Dsg3 internalization in HaCaT keratinocytes. Validation of the 20 identified compounds was performed using keratinocyte fragmentation assays, as well as a human skin organ culture (HSOC) model. key Results: Overall, this approach led to the identification of four molecules involved in PV IgG-induced skin pathology: MEK1, TrkA, PI3Kα, and VEGFR2. Conclusion and Implications: This unbiased screening revealed novel mechanisms by which PV autoantibodies induce blistering in keratinocytes and identified new treatment targets for this severe and potentially life-threatening skin disease.

The full human skin organ culture (HSOC) model is a standardized test system for evaluating pharmacological substances on human skin in vitro. The acantholysis associated with pemphigus vulgaris (PV), a severe and potentially life‐threatening autoimmune skin blistering disease, can be induced in HSOC by injecting a bi‐specific anti‐desmoglein (dsg) 1 and 3 single‐chain antibody variable fragment (scFv). Compared to cell culture experiments (e.g., induction of dsg3‐internalization or keratinocyte dissociation using HaCaT cells or normal human epidermal keratinocytes) the HSOC model is more sophisticated and physiologically relevant. In this model, all three layers of the human skin are present, all cells are sustained in their physiological niche and orientation, and the cell‐cell‐contacts remain intact. Here we describe a protocol for HSOC, an ex vivo model of human skin, that has proved to be well‐established and informative in our laboratory. © 2019 by John Wiley & Sons, Inc.