MRGPRX2 and Adverse Drug Reactions

Many adverse reactions to therapeutic drugs appear to be allergic in nature, and are thought to be triggered by patient-specific Immunoglobulin E (IgE) antibodies that recognize the drug molecules and form complexes with them that activate mast cells. However, in recent years another mechanism has been proposed, in which some drugs closely associated with allergic-type events can bypass the antibody-mediated pathway and trigger mast cell degranulation directly by activating a mast cell-specific receptor called Mas-related G protein-coupled receptor X2 (MRGPRX2). This would result in symptoms similar to IgE-mediated events, but would not require immune priming. This review will cover the frequency, severity, and dose-responsiveness of allergic-type events for several drugs shown to have MRGPRX2 agonist activity. Surprisingly, the analysis shows that mild-to-moderate events are far more common than currently appreciated. A comparison with plasma drug levels suggests that MRGPRX2 mediates many of these mild-to-moderate events. For some of these drugs, then, MRGPRX2 activation may be considered a regular and predictable feature after administration of high doses.

A humanized mouse model to study mast cells mediated cutaneous adverse drug reactions

Recently a G‐protein‐coupled receptor, MAS Related GPR Family Member X2 (MRGPRX2), was identified as a specific receptor on human mast cells responsible for IgE independent adverse drug reactions (ADR). Although a murine homologue, Mrgprb2, has been identified for this receptor, its affinity for many ADR‐causing drugs is poor making it difficult to undertake in vivo studies to examine mechanisms of ADR and to develop therapeutic strategies. Here, we have created humanized mice capable of generating MRGPRX2‐expressing human MCs allowing for the study of MRGPRX2 MCs‐mediated ADR in vitro as well as in vivo. Humanized mice were generated by hydrodynamic‐injection of plasmids expressing human GM‐CSF and IL‐3 into NOD‐scid IL2R‐γ^−/− strain of mice that had been transplanted with human hematopoietic stem cells. These GM/IL‐3 humice expressed high numbers of tissue human MCs but the MRGPRX2 receptor expressed in MCs were limited to few body sites including the skin. Importantly, large numbers of MRGPRX2‐expressing human MCs could be cultured from the bone marrow of GM/IL‐3 humice revealing these mice to be an important source of human MCs for in vitro studies of MRGPRX2‐related MCs activities. When GM/IL‐3 humice were exposed to known ADR causing contrast agents (meglumine and gadobutrol), the humice were found to experience anaphylaxis analogous to the clinical situation. Thus, GM/IL‐3 humice represent a valuable model for investigating in vivo interactions of ADR‐causing drugs and human MCs and their sequelae, and these mice are also a source of human MRGPRX2‐expressing MCs for in vitro studies.

Self-Assembling Peptide Nanoscaffold That Activates Human Mast Cells

Engineering biomaterials to manipulate the immune response to elicit specific therapeutic outcomes is a burgeoning field of research. Mast cells play a distinct and central role in the innate immune response, and are characterized by their rapid release of a myriad of proinflammatory mediators in response to stimulation. These mediators are central to protective actions such as wound healing, angiogenesis, and host defense against pathogens and animal venoms. Considering that mast cells are widely distributed in tissues that interface with the external environment, and are loaded with large amounts of preformed protective compounds, they are ideal targets for novel immunotherapies. Here we report that, by using an engineered nanoscaffold, human mast cells can be contact activated in cell and primary human skin tissue culture using a specific receptor-ligand mechanism. The IgE independent PAMP-12 peptide activates human mast cells through the recently identified Mas-related G-protein coupled receptor member X2 (MRGPRX₂) receptor. The PAMP-12 motif was conjugated, via a glycine spacer, with the self-assembling peptide (RADA)₄ and mixed with unmodified (RADA)₄ to form a nanofiber matrix; mast cell activation was influenced directly by this ratio. Moreover, conjugating the PAMP-12 motif within the matrix was shown to only activate local, tissue-resident mast cells. The result of ex vivo human skin tissue tests confirmed that the engineered nanoscaffold successfully activated skin-resident mast cells by contact. Thus, this nanoscaffold design may provide a new platform to modulate localized mast cell functions thereby facilitating their protective role in the skin.