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.

Grant Number: 1UG3AI190386-01
NIH Institute/Center: NIH
Principal Investigator: Santiago Alvarez Arango