Identification and characterization of type VII collagen-targeting autoantibodies in experimental epidermolysis bullosa acquisita

Abstract

Autoantibodies (Aab) are a major cause of autoimmune diseases. Understanding the generation and molecular properties of Aab is pivotal to understanding Aab-mediated autoimmunity. Epidermolysis bullosa acquisita (EBA) is a severe Aab-mediated autoimmune blistering disease (AIBD) characterized by Aab targeting type VII collagen (COLVII) at the dermal-epidermal junction (DEJ) in the skin. In EBA, Aab deposition at the DEJ leads to subsequent inflammation through effector functions mediated by the Aab constant region. Despite significant advances in understanding downstream pathomechanisms after Aab binding, the etiology of Aab — their clonal origins, genetic constraints, and subclass contributions determining pathogenicity remain poorly characterized. Monoclonal Aabs capable of inducing disease in murine models have not been identified, limiting mechanistic insights into Aab-mediated tissue damage. This study employed phage display coupled with next-generation sequencing (NGS) to isolate and characterize monoclonal antibodies (mAbs) targeting murine COLVII (mCOLVII). This represents the first comprehensive genetic-level analysis of the murine B cell receptor repertoire in EBA research, revealing germinal center-driven affinity maturation of autoreactive clones. Using two immune-libraries from lymphoid tissues of an mCOLVII-immunized mouse, four dominant variable heavy chain (VH) clonotypes with restricted genetic diversity were identified, suggesting constraints in the autoreactive B cell response. B cell receptor repertoire sequencing (BCR-seq) revealed tissue-specific isotype distribution and expansion patterns, while tracking clonotypes to originating tissues. BCR-seq uncovered an unexpected predominance of IgG1 in highly mutated clones in the draining lymph nodes (dLN), potentially challenging the current understanding of subclass roles in EBA pathogenesis. Selected clones were expressed in the complement-activating IgG2b format, demonstrating antigen specificity and constant region functionality in vitro. Additional mCOLVII-targeting clones were acquired from fellow researchers and likewise expressed and characterized. In vivo validation of six phage display-derived clones and two acquired clones revealed DEJ binding of all and complement C3 deposition for the latter; however, these molecular events proved insufficient for clinical disease manifestation, indicating additional requirements for pathogenic Aab beyond target recognition and complement activation. These findings suggest that synergistic epitope targeting, enhanced Fc-mediated effector functions or multiple subclasses may be required for clinical disease induction. This study provides critical insights into anti-mCOLVII Aab genetics and functionality, establishing foundations for understanding Aab pathogenicity determinants in EBA while providing valuable tools for understanding tissue-specific Aab mechanisms.