Gordana Wozniak Knopp

Introduction Allergen‐specific IgE‐blocking IgG antibodies contribute to successful allergen immunotherapy (AIT), however, not much is known about their affinity. Since affinity measurements of polyclonal antibodies in serum are technically challenging we evaluated the applicability of acidic disruption of antibody‐allergen complexes by a modified ELISA protocol with monoclonal antibodies (mAbs) specific for the relevant major allergens Betv1 and Mald1. Then, AIT‐induced blocking and non‐blocking Mald1‐specific antibodies in sera from individuals with or without reduced apple allergy were compared. Methods After testing their pH stability coated recombinant allergens were incubated with (i) mAbs diluted in PBS or human serum and (ii) sera from individuals after sublingual administration of Mald1 or Betv1 for 16 weeks. Immune complexes were exposed to buffers in the pH range of 6.4–3.4 and residual antibodies were measured. Avidity indexes (AI), defined as the pH removing 50% of antibodies, were compared to the dissociation constants ( K D ) of mAbs determined by surface plasmon resonance. Results The selected pH range was applicable to disrupt allergen complexes with highly affine mAbs without compromising allergen integrity. AIs of mAbs accorded with K D values and were unaffected by epitope specificity or the presence of serum proteins. The inter‐assay variability was <4% CV. Protective Mald1‐specific IgG antibodies from individuals with reduced apple allergy showed a higher collective binding strength than that of the non‐protective antibodies of individuals without reduced apple allergy. Conclusion Acidic disruption of allergen‐antibody complexes may be used to estimate the net‐binding force of polyclonal serum antibodies and eases the investigation of affinity‐related research questions in AIT.

High numbers of membrane immunoglobulin E (IgE)-positive cells are characteristic of allergic conditions, atopic dermatitis, or IgE myeloma. Antibodies targeting the extracellular membrane-proximal domain of the membranous IgE-B-cell receptor (BCR) fragment can be used for specific depletion of IgE-BCR-positive cells. In this study, we derivatized such an antibody with a toxin and developed an antibody–drug conjugate (ADC) that showed strong cytotoxicity for an IgE-positive target cell line. Site-specific conjugation with maleimidocaproyl-valine-citrulline-p-aminobenzoyloxycarbonyl-monomethyl-auristatin E via a newly introduced single cysteine residue was used to prepare a compound with a drug–antibody ratio of 2 and favorable biophysical properties. The antibody was rapidly taken up by the target cells, showing almost complete internalization after 4 h of treatment. Its cytotoxic effect was potentiated upon cross-linking mediated by an anti-human IgG F(ab’)2 fragment. Because of its fast internalization and strict target specificity, this antibody–drug conjugate presents a valuable starting point for the further development of an anti-IgE cell-depleting agent, operating by the combined action of receptor cross-linking and toxin-mediated cytotoxicity.