Epitope Mapping by HDX-MS Elucidates the Surface Coverage of Antigens Associated with High Blocking Efficiency of Antibodies to Birch Pollen Allergen.

Epitopes of a native pollen allergen protein, birch Bet v1, against four of the noncompeting anti-Bet v1 antibodies individually or in combination, were identified by solution-phase amide backbone H/D exchange (HDX) coupled with high-resolution Q-TOF or Orbitrap mass spectrometry. The HDX results indicates that the four anti-Bet v1 antibodies protected specific regions of Bet v1, explaining the difference in their blocking efficiency of each antibody against Bet v1 binding to polyclonal IgEs in Bet v1 allergic patients. An in-house HDX-MS system was further developed to explore the surface protection of Bet v1 in the presence of all four antibodies with 100% sequence coverage and high redundancy. The data demonstrated that four anti-Bet v1 antibodies were able to simultaneously bind to Bet v1 in solution to provide the most effective blocking for 9 of 10 tested IgE donors in an in vitro antibody-blocking assay. For the first time, we have applied HDX to elucidate the therapeutic advantage of combination antibodies compared with individual antibodies in treating Bet v1 induced allergy.