IgE-neutralizing UB-221 mAb, distinct from omalizumab and ligelizumab, exhibits CD23-mediated IgE downregulation and relieves urticaria symptoms.

Over the last 2 decades, omalizumab is the only anti-IgE antibody that has been approved for asthma and chronic spontaneous urticaria (CSU). Ligelizumab, a higher-affinity anti-IgE mAb and the only rival viable candidate in late-stage clinical trials, showed anti-CSU efficacy superior to that of omalizumab in phase IIb but not in phase III. This report features the antigenic-functional characteristics of UB-221, an anti-IgE mAb of a newer class that is distinct from omalizumab and ligelizumab. UB-221, in free form, bound abundantly to CD23-occupied IgE and, in oligomeric mAb-IgE complex forms, freely engaged CD23, while ligelizumab reacted limitedly and omalizumab stayed inert toward CD23; these observations are consistent with UB-221 outperforming ligelizumab and omalizumab in CD23-mediated downregulation of IgE production. UB-221 bound IgE with a strong affinity to prevent FcԑRI-mediated basophil activation and degranulation, exhibiting superior IgE-neutralizing activity to that of omalizumab. UB-221 and ligelizumab bound cellular IgE and effectively neutralized IgE in sera of patients with atopic dermatitis with equal strength, while omalizumab lagged behind. A single UB-221 dose administered to cynomolgus macaques and human IgE (ε, κ)-knockin mice could induce rapid, pronounced serum-IgE reduction. A single UB-221 dose administered to patients with CSU in a first-in-human trial exhibited durable disease symptom relief in parallel with a rapid reduction in serum free-IgE level.

CɛmX peptide-carrying HBcAg virus-like particles induced antibodies that down-regulate mIgE-B lymphocytes.

Type-I hypersensitivity reactions play a critical role in the pathogenesis of various allergic diseases. The successful development of the anti-IgE antibody, omalizumab, has validated IgE as an effective therapeutic target for the treatment of various IgE-mediated allergic diseases. Two research groups have reported that mAbs specific for certain parts of CɛmX, a domain of 52 aa residues in human membrane-bound IgE (mIgE), can cause the lysis of mIgE-B cells by apoptosis and antibody-dependent cellular cytotoxicity (ADCC). Herein, we explore virus-like particles formed by hepatitis B virus core antigen (HBcAg) that harbors the entire CɛmX peptide or its fragments as immunogens for inducing anti-CɛmX antibodies. The results showed that mice immunized subcutaneously with these immunogens produced antibodies that bind to recombinant CɛmX-containing human IgE.Fc in ELISA and Western blot analyses, and to genetically engineered human mIgE-expressing Ramos B cell line in fluorescence flow cytometric assays. The IgG antibodies purified from the sera of immunized mice were able to cause the apoptosis of mIgE-expressing Ramos cells through a BCR-dependent caspase pathway. Furthermore, the IgG could mediate ADCC in human mIgE-expressing A20 murine B-cell lymphoma. These studies suggest that HBcAg-CɛmX peptide immunogens warrant further investigation as a therapeutic modality for modulating IgE in patients with IgE-mediated allergic diseases.

An anti-IgE monoclonal antibody that binds to IgE on CD23 but not on high-affinity IgE.Fc receptors.

A new monoclonal antibody (mAb), specific for human IgE, the central mediator of immediate-type hypersensitivity reactions, has been shown to possess a unique set of binding specificities. The mAb, 8D6, binds to a conformational epitope on the CH3 domain of human e immunoglobulin and can compete with omalizumab for binding to IgE. Like omalizumab, it does not bind to IgE bound by the high-affinity IgE.Fc receptor (FcɛRI) on basophils and mast cells. It also does not cause activation and degranulation of IgE-pulsed, human FcɛRI-expressing rat basophilic leukemic cells (RBL SX-38). The mAb can inhibit IgE binding to recombinant α chain of human FcɛRI in ELISA and to human FcɛRI-expressing RBL SX38 cells in fluorescence flow cytometric analysis. However, unlike omalizumab, 8D6 can bind to IgE already bound by the low-affinity IgE.Fc receptors (FcɛRII, or CD23), as revealed in ELISA with recombinant CD23 and in flow cytometric analysis with human B cells. Since earlier investigators have shown that anti-CD23 mAbs can inhibit the synthesis of IgE in lymphocyte culture in vitro and can down-regulate IgE production in treated patients, 8D6 may offer pharmacological mechanisms in addition to those mediated by omalizumab, for controlling IgE in patients with allergic diseases.

Accumulated immune complexes of IgE and omalizumab trap allergens in an in vitro model.

The best understood mechanisms of omalizumab are that it neutralizes free IgE and down-regulates high-affinity IgE.Fc receptors (FcepsilonRI) on basophils and mast cells. It has been proposed that since complexes of IgE and omalizumab are accumulated to 5-10 times the basal levels of IgE, they may trap incoming allergens, contributing to omalizumab's effectiveness. In order to investigate the ability of IgE:omalizumab complexes in trapping allergens and inhibiting basophil activation in an in vitro reconstitution model, the ability of IgE:omalizumab complexes to tie up antigen and hence inhibit (a) antigen binding to IgE bound by FcepsilonRI, and (b) antigen-mediated activation of basophils, was examined. The free IgE was prepared by mixing different proportions of antigen-nonspecific IgE secreted by U266 cells and antigen-specific IgE, SE44 IgE, which recognizes a synthetic 15 a.a. peptide, R15K. The antigen was (R15K)(8)-ova, i.e. ovalbumin conjugated with an average of 8 copies of R15K per molecule. The solid-phase FcepsilonRI was a recombinant protein representing the extracellular portion of the alpha chain of the FcepsilonRI receptor complex. The model FcepsilonRI(+) basophilic cell line was RBL.SX-38, a rat basophilic leukemic line transfected with the genes for alpha, beta and gamma subunits of human FcepsilonRI. The results showed that the IgE:omalizumab complexes trapped increasing amounts of antigen with increasing (a) concentration of IgE, (b) proportion of antigen-specific IgE in total IgE, and (c) concentration of total immune complexes. Such trapping decreased the antigen-induced activation of FcepsilonRI(+) cells that had been pulsed with antigen-specific IgE, resulting in decreased mediator release. These results suggest that the rapidly accumulated IgE:omalizumab complexes in omalizumab-treated patients can capture allergens and consequently contribute to the pharmacological effects of omalizumab.

Anti-IgE as a mast cell-stabilizing therapeutic agent.

After nearly 20 years of development, humanized monoclonal anti-IgE antibodies have been shown in about 20 phase II and III clinical trials to be effective and safe in treating allergic asthma, perennial and seasonal allergic rhinitis, and allergic reactions to peanuts. Omalizumab has been approved in the United States, European Union, and several other countries for treating patients 12 years and older with moderate-to-severe allergic asthma. Although anti-IgE is often referred to as an IgE-neutralizing antibody and can block IgE's binding to high-affinity IgE Fc receptors (FcepsilonRI) on mast cells and basophils, it has multiple immunoregulatory effects. One such effect is that as the result of depleting free IgE, FcepsilonRI on mast cells and basophils is downregulated to less than 5% within a few weeks to a few months of anti-IgE treatment. This renders the mediator-packed inflammatory cells insensitive to allergen stimulation. Hence this therapeutic anti-IgE represents a new class of mast cell-stabilizing agents, reducing FcepsilonRI density on mast cells and basophils and causing them to be insensitive to allergens. This mechanism contrasts with that of cromones, mast cell-stabilizing agents that retard Ca++ mobilization and the degranulation process, thus deflating the intracellular activation signal triggered by IgE-FcepsilonRI aggregation.