Mechanisms of Immediate Non-IgE-mediated Drug Hypersensitivity Reactions (MIND-HR) - PROJECT SUMMARY/ABSTRACT Although IgE-mediated HSRs are the most feared, most drug HSRs are non-IgE-mediated and often require only dosage and administration adjustments rather than complete drug avoidance. Clinical similarities between IgE- and non-IgE-mediated immediate HSRs lead to misclassification, unnecessary drug avoidance, less effective treatments, and increased costs. Recent research has emphasized the role of non-IgE receptors, such as MRGPRX2, in mast cell (MC) activation. MRGPRX2, expressed primarily on skin MCs, is a ligand for positively charged drugs like vancomycin, fluoroquinolones, and some neuromuscular blocking agents. MRGPRX2 activation requires sustained and high tissue drug concentrations, often surpassing therapeutic levels. This discrepancy may stem from differences in MRGPRX2 expression or functionality. It is unknown if individuals with an MRGPRX2 ligand-mediated HSR exhibit elevated MRGPRX2 expression levels in sera and skin MCs or heightened sensitivity to other MRGPRX2 ligands, suggesting a definable hyperreactive phenotype. Using vancomycin infusion reactions (VIR) as a prototypical MRGPRX2 ligand-induced HSR, this proposal aims to compare MRGPRX2 expression levels in sera and skin MCs and skin test dose responses to other MRGPRX2 ligands in subjects with VIR compared to vancomycin-tolerant controls. The research rationale is based on preliminary data suggesting that VIR subjects have a significantly lower vancomycin skin test dose threshold for a positive response than vancomycin-tolerant subjects, raising the possibility that these individuals may also exhibit lower thresholds and increased sensitivity to other MRGPRX2 ligands. A multiphase study will be conducted by three U.S. Allergy Centers. In the UG3 Phase, Aim 1 will validate a vancomycin skin test with an optimal vancomycin concentration to discriminate VIR subjects with an ROC ≥0.8. Aim 2 will optimize and validate an immunofluorescence (IF)-based assay for quantifying MRGPRX2 in skin MCs with a reproducibility coefficient of variation of <10% for MRGPRX2 staining intensity. Once the UG3 Milestones are accomplished, the project will move into the UH3 Phase. Aim 3 will compare MRGPRX2 expression levels in sera and skin MCs using the validated IF assay from Aim 2 and determine their correlation with vancomycin skin test dose responses in VIR and vancomycin-tolerant subjects using the validated skin test from Aim 1. Lastly, Aim 4 will determine if VIR subjects exhibit skin hyperreactivity to other MRGPRX2 ligands apart from vancomycin. The expected outcomes will significantly advance the understanding of the MRGPRX2-mediated drug HSR mechanism and provide a comprehensive methodology for studying other non-IgE-mediated HSRs. Ultimately, the long-term goal is to advance knowledge of immediate drug HSR mechanisms and develop diagnostic tools that can identify non-IgE-mediated HSRs, thus preventing misclassification and unnecessary drug avoidance.
