Molecular Basis for Nonanaphylactogenicity of a Monoclonal Anti-IgE Antibody

Abstract

IgE Abs mediate allergic responses by binding to specific high affinity receptors (FcεRI) on mast cells and basophils. Therefore, the IgE/FcεRI interaction is a target for clinical intervention in allergic disease. An anti-IgE mAb, termed BSW17, is nonanaphylactogenic, although recognizing IgE bound to FcεRI, and interferes with binding of IgE to FcεRI. Thus, BSW17 represents a candidate Ab for treatment of IgE-mediated disorders. By panning BSW17 against random peptide libraries displayed on phages, we defined mimotopes that mimic the conformational epitope recognized on human IgE. Two types of mimotopes, one within the Cε3 and one within the Cε4 domain, were identified, indicating that this mAb may recognize either a large conformational epitope or eventually two distinct epitopes on IgE. On the basis of alignments of the two mimotopes with the human IgE sequence, we postulate that binding of BSW17 to the Cε3 region predominantly blocks binding of IgE to FcεRI, leading to neutralization of IgE. Moreover, binding of BSW17 to the Cε4 region may explain how BSW17 recognizes FcεRI-bound IgE, and binding to this region may also interfere with degranulation of IgE sensitized cells (basophils and mast cells). As a practical application of these findings, mimotope peptides coupled to a carrier protein may be used for the development of a peptide-based anti–allergy vaccine by induction of anti-IgE Abs similar to the current approach of using humanized nonanaphylactogenic anti-IgE Abs as a passive vaccine.

DARPins against a functional IgE epitope

“…Functional anti-IgE antibodies such as omalizumab have been previously shown to recognize identical or overlapping epitopes with those of FcRI␣ [53][54][55][56] in the C3 domain of IgE, thereby being able to prevent the interaction of IgE and FcRI␣ initiating mast cell and basophil triggering. Thus, the capacity of the selected DARPins to react with the functionally active C3 domain of IgE was tested in a competition experiment using SPR.…”

A novel, nonanaphylactogenic, bispecific IgE-CD3 antibody eliminates IgE+ B cells

“…7 The murine anti-human IgE mAb used for construction of the bsc-IgE/CD3 antibody derivative was itself nonanaphylactogenic and had been analyzed in detail by mapping the relevant epitopes to isolated Cε3 and Cε4 of the IgE molecule, a conformational epitope apparently inaccessible on IgE when bound to its Fc receptors. 8 Nevertheless, we carefully examined whether the bscIgE/CD3 antibody construct is indeed free of any anaphylactogenic properties and devoid of any bystander cytotoxic activity in the presence of preactivated human T cells. Accordingly, we demonstrated that cells that bound soluble IgE either through the high-affinity FcεRI or the low-affinity FcεRII (CD23) were not affected by prestimulated CD8 1 T cells, even at high concentrations (1 mg/mL) of the bsc-IgE/CD3 antibody (Fig 2, A and B, and see Fig E3 in this article's Online Repository at www.jacionline.org).…”

Synthetic IgE peptide vaccine for immunotherapy of allergy

“…The site on human IgE responsible for binding to FcεRI has been associated with the Cε2, Cε3, and Cε4 domains by binding inhibition studies involving recombinant IgE truncations [5,6], chimaeric IgE [7], site-directed mutagenized IgE [8,9], synthetic peptides corresponding to IgE Fc domains and antibodies induced by such peptides [10][11][12][13][14], and mimetope peptides [9,15]. These observations pointed to a highly conformational receptor binding site that has recently been solved by resolution of the crystal structure of a human IgE-FcεRI complex.…”

“…These do not cross-link FcεRI-bound IgE and so they do not trigger degranulation and anaphylaxis [15,17,18]. Two of these antibodies are in clinical trial, and passive immunizations have provided desensitisation for patients with allergic rhinitis and allergic asthma [19][20][21][22][23].…”