Abstact

BACKGROUND Neuromuscular blocking agents (NMBA) are muscle relaxants used to assist mechanical ventilation but lead in 1/10,000 anesthesia to severe acute hypersensitivity reactions i.e., anaphylaxis. Incidences vary between types of NMBAs. Rocuronium, a widely used non-depolarizing aminosteroid NMBA, induces among the highest anaphylaxis rates. Rocuronium-induced anaphylaxis is proposed to rely on pre-existing rocuronium-binding antibodies, but no such antibodies have ever been identified. OBJECTIVES Identify rocuronium-specific antibody repertoires from plasma cells or plasmablasts of rocuronium-immunized mice, and determine the affinities, structures and anaphylactogenic potential of these antibodies for rocuronium. METHODS Herein, we engrafted rocuronium onto carrier proteins allowing immunization of mice against rocuronium, screening for rocuronium-specific antibody responses, and sorting of rocuronium-specific plasma cells using droplet microfluidics coupled to single-cell antibody gene (VH and VL) sequencing. RESULTS The two different repertoires of >500 VH-VL pairs were oligoclonal, comprised of three major clonal families, and displayed convergence. Expressed as human IgG1, these antibodies demonstrated subnanomolar affinities for rocuronium with families either monospecific for rocuronium or cross-reactive only for closely-related NMBAs. Expressed as human IgE, they triggered human mast cell and basophil activation, and severe passive systemic anaphylaxis in mice humanized for the IgE receptor FcεRI. Co-crystal structures between rocuronium and antibody representatives of three different VH-VL families revealed distinct interaction modes with, however, the ammonium group involved systematically in the binding interface. CONCLUSIONS This work identifies the epitopes of antibody reactivity to rocuronium, demonstrates anaphylactogenic potential of anti-rocuronium IgE and establishes the first mouse model of NMBA anaphylaxis.