The Journal Of Allergy And Clinical Immunology
To date no safe allergen-specific immunotherapy for peanut-allergic patients is available. Previous trials were associated with severe side effects. To determine the relative importance of conformational and linear IgE-binding epitopes of the major peanut allergen Ara h 2 and to produce a hypoallergenic variant with abolished anaphylactogenic activity. Wild-type Ara h 2 and a mutant lacking the loops containing linear IgE epitopes were produced in insect cells. Conformational IgE epitopes were removed by unfolding these proteins by reduction and alkylation. IgE binding was tested by ELISA with sera from 48 Ara h 2-sensitized, peanut-allergic patients. Basophil activation and T-cell proliferation were tested with blood samples from selected patients. Anaphylactogenic potency was tested by intraperitoneal challenge of mice sensitized intragastrically to peanut extract. Patients’ IgE recognized conformational and linear epitopes in a patient-specific manner. The unfolded mutant lacking both types of epitopes displayed a significantly lower IgE binding (median ELISA OD 0.03, interquartile range 0.01-0.06) than natural Ara h 2 (median 0.99, interquartile range 0.90-1.03; p<0.01). Basophil activation by unfolded mutant Ara h 2 was low (median area under the curve 72 versus 138 for native wild-type Ara h 2; p<0.05), but its ability to induce T-cell proliferation was retained. Unfolded mutants without conformational epitopes did not induce anaphylaxis in peanut-sensitized mice. By removing conformational and linear IgE epitopes, a hypoallergenic Ara h 2 mutant with abolished IgE binding and anaphylactogenic potency but retained T cell activation was generated. Copyright 2019. Published by Elsevier Inc.