Effect of antigen binding affinity and effector function on the pharmacokinetics and pharmacodynamics of anti-IgE monoclonal antibodies

Modulating the binding affinities to IgE or changing the FcγR binding properties of anti-IgE antibodies offers an opportunity to enhance the therapeutic potential of anti-IgE antibodies, but the influence of increased affinity to IgE or reduced Fc effector function on the pharmacological properties of anti-IgE therapies remains unclear. Our studies were designed to characterize the pharmacokinetics, pharmacodynamics and immune-complex distribution of two high-affinity anti-IgE monoclonal antibodies, high-affinity anti-IgE antibody (HAE) 1 and 2, in mice and monkeys. HAE1, also known as PRO98498, is structurally similar to omalizumab (Xolair®), a humanized anti-IgE IgG1 marketed for the treatment of asthma, but differs by 9 amino acid changes in the complementarity-determining region resulting in a 23-fold improvement in affinity. HAE2 is similar to HAE1, but its Fc region was altered to reduce binding to Fcγ receptors. As expected given the decreased binding to Fcγ receptors, systemic exposure to pre-formed HAE2:IgE complexes in mice was greater (six-fold) and distribution to the liver lower (four-fold) compared with HAE1:IgE complexes. In monkeys, systemic exposure to HAE1 was similar to that previously observed for omalizumab in this species, but required comparatively lower serum drug concentrations to suppress free IgE levels. HAE2 treatment resulted in greater exposure and greater increase of total IgE, relative to HAE1, because of decreased clearance of HAE2:IgE complexes. Overall, these data suggest that increased binding affinity to IgE may provide a more effective therapeutic for asthma patients, and that retaining FcγR binding of the anti-IgE antibody is important for elimination of anti-IgE:IgE complexes.     

The presence of non-isotype-specific antibodies in polyclonal anti-IgE reagents: demonstration of their binding to specifically selected Epstein-Barr virus-transformed cell lines

Polyclonal anti-human IgE reagents were earlier shown to contain variable amounts of nonisotype-specific antibodies depending on the strategy used for their preparation. The presence of these antibodies in two commercial anti-IgE reagents was demonstrated in this work by (a) their binding to human Ig-surface-positive lymphoblastoid cells specifically selected by one of the polyclonal anti-human IgE reagents and (b) their binding to the non-IgE immunoglobulins secreted by those lymphoblastoid cells. Peripheral blood B lymphocytes from two normal and two atopic patients were immortalized with Epstein-Barr virus (EBV) and then selected for cells that rosette with anti-IgE-coated erythrocytes. Selection was repeated four times and cells were then cloned. The cloned cells formed rosettes and their supernatants agglutinated erythrocytes coated with rabbit anti-IgE. The immunoglobulins of these clones were positive in an ELISA for IgE, using two different polyclonal anti-human IgE reagents. They were shown, however, to be 19 S IgMs. This discrepancy was due apparently to substantial contamination of anti-non-IgE-isotype-specific antibodies in the polyclonal anti-IgE reagents used both in the selection of cells and in the ELISA. The human monoclonal B-cell lines which were applied here as targets amplified the non-IgE-isotype specific antibody contamination present in the polyclonal anti-human IgE reagents. Because of the normally very low frequency of IgE-positive cells, the use of polyclonal anti-IgE reagents to detect these cells has to be carefully evaluated.     

Effect of antigen binding affinity and effector function on the pharmacokinetics and pharmacodynamics of anti-IgE monoclonal antibodies

Modulating the binding affinities to IgE or changing the FcγR binding properties of anti-IgE antibodies offers an opportunity to enhance the therapeutic potential of anti-IgE antibodies, but the influence of increased affinity to IgE or reduced Fc effector function on the pharmacological properties of anti-IgE therapies remains unclear. Our studies were designed to characterize the pharmacokinetics, pharmacodynamics and immune-complex distribution of two high-affinity anti-IgE monoclonal antibodies, high-affinity anti-IgE antibody (HAE) 1 and 2, in mice and monkeys. HAE1, also known as {"type":"entrez-protein","attrs":{"text":"PRO98498","term_id":"1357788844","term_text":"PRO98498"}}PRO98498, is structurally similar to omalizumab (Xolair®), a humanized anti-IgE IgG1 marketed for the treatment of asthma, but differs by 9 amino acid changes in the complementarity-determining region resulting in a 23-fold improvement in affinity. HAE2 is similar to HAE1, but its Fc region was altered to reduce binding to Fcγ receptors. As expected given the decreased binding to Fcγ receptors, systemic exposure to pre-formed HAE2:IgE complexes in mice was greater (six-fold) and distribution to the liver lower (four-fold) compared with HAE1:IgE complexes. In monkeys, systemic exposure to HAE1 was similar to that previously observed for omalizumab in this species, but required comparatively lower serum drug concentrations to suppress free IgE levels. HAE2 treatment resulted in greater exposure and greater increase of total IgE, relative to HAE1, because of decreased clearance of HAE2:IgE complexes. Overall, these data suggest that increased binding affinity to IgE may provide a more effective therapeutic for asthma patients, and that retaining FcγR binding of the anti-IgE antibody is important for elimination of anti-IgE:IgE complexes.     

Monoclonal antibody specific for T cell-derived human IgE binding factors

A B cell hybridoma secreting monoclonal antibody against human IgE binding factors was obtained by immunization of BALB/c mice with partially purified IgE binding factors, and fusion of their spleen cells with SP-2/0-AG14 cells. The monoclonal antibody bound all of the 60,000, 30,000, and 15,000 dalton IgE binding factors from two T cell hybridomas and those from activated T cells of a normal individual. The antibody bound both IgE-potentiating factors, which had affinity for lentil lectin, and IgE-suppressive factors, which had affinity for peanut agglutinin. However, the monoclonal anti-IgE-binding factor bound neither Fc epsilon R on RPMI 8866 cells nor IgE binding factors from the B lymphoblastoid cells. A monoclonal antibody against Fc epsilon R on B cells (H107) bound the 60,000 and 30,000 dalton IgE binding factors from both T cell hybridomas and RPMI 8866 cells but did not bind the 15,000 dalton IgE binding factors from either T cells or B cells. The results indicate that T cell-derived IgE binding factors have a unique antigenic determinant that is lacking in both Fc epsilon R on B cells and B cell-derived IgE binding factors. The anti-IgE binding factor and anti-Fc epsilon R monoclonal antibodies both failed to stain cell surface components of IgE binding factor-producing T cell hybridomas. However, both antibodies induced the T cell hybridoma to form IgE binding factors. The results suggest that the T cell hybridomas bear low numbers of Fc epsilon R that share antigenic determinants with IgE binding factors secreted from the cells.     

Relationships between epitopes on IgE recognized by defined monoclonal antibodies and by the FC epsilon receptor on basophils

The present study investigated whether the sites on the FC region of the IgE molecule, recognized by different anti-IgE monoclonal antibodies (mAb), are identical to those recognized by the Fc receptor (Fc epsilon R). The anti-IgE mAb recognize different clusters of epitopes on the Fc region of IgE and could interfere to different degrees with the binding of IgE to mast cells and basophils, but still recognized cell-bound IgE. Analysis of the stoichiometry and affinity binding of 125I anti-IgE mAb Fab' to free IgE have revealed that anti-IgE mAb of one group (51.3) recognized three repetitive determinants on the IgE Fc portion, and another group (95.3) recognized only one determinant. When these stoichiometric studies were performed with cell-bound IgE, it was found that only one of the sites recognized by 51.3 mAb was involved in the Fc epsilon R binding site. On the other hand, the site recognized by 95.3 mAb was not the Fc epsilon R binding site. Such findings establish mAb 51.3 as a useful tool for isolating the IgE peptides involved in the binding site to the receptor.     

In vitro binding of an IgE protein to human platelets

Bronchoconstriction in extrinsic asthma is initiated by mediators released from IgE-sensitized leukocytes after contact with polyvalent antigen. Because platelets also contain soluble mediators that can cause bronchoconstriction, platelet activation and release of the contents of platelet granules may play a role in IgE-mediated responses under some circumstances. We therefore sought to determine if platelets are capable of binding IgE and if cross-linking this cell-bound IgE initiates secretion of platelet granule contents. Platelets from 10 normal donors were studied by using automated fluorescence analysis and fluorescence microscopy. We detected binding of a purified myeloma IgE protein to 24.1 +/- 9.6% (mean +/- 2 SD) of the gel-filtered platelets from these normal individuals. Although we could detect the binding of IgE and anti-IgE to a minority of cells, every normal individual had a population of platelets that bound IgE. The amount of IgE that bound to normal platelets appeared to be distributed heterogeneously among the IgE-positive platelet population. Platelets from two individuals with type II Glanzmann's thrombasthenia bound normal amounts of heat-aggregated IgG, but less than 3% of the platelets bound detectable IgE. Moreover, a combination of monoclonal antibodies to glycoproteins IIb and IIIa inhibited the binding of the IgE protein to normal platelets but did not affect the binding of aggregated IgG. Thus, the binding of IgE to human platelets appeared to require the presence of the glycoprotein IIb-IIIa complex. Binding of monomeric IgE to platelets, by itself, did not initiate either platelet aggregation or release of 14C-serotonin. However, both aggregation and secretion of serotonin followed the addition of anti-IgE to IgE-sensitized platelets. These studies indicate that human platelets can bind an IgE myeloma protein in vitro and that cross-linking of surface-bound IgE with anti-IgE initiates aggregation and secretion. If platelets have a similar capacity to bind normal IgE in vivo, it is possible that platelets may participate directly in several atopic or inflammatory disorders in man mediated by this class of antibody.     

Transfectomas expressing both secreted and membrane-bound forms of chimeric IgE with anti-viral specificity.

Because of the lack of a cell line expressing on surface and secreting human IgE of known Ag specificity, the construction of a transfectoma line possessing such properties would be useful for studying the roles of surface IgE and the effects of anti-IgE antibodies on IgE-producing B cells. Toward this goal, the human genomic DNA segment encompassing the two exons encoding the membrane anchor peptide of epsilon-chain and their flanking regions was sequenced. Hybrid epsilon and kappa genomic DNA comprising the C regions of human epsilon- and kappa-chains and the H and L chain V regions of the murine mAb BAT123, which reacts with the gp120 envelope protein of HIV-1, were constructed. Mammalian expression vectors containing these fusion genes were used to transfect murine myeloma Sp2/0 cells, and transfectants stably expressing on surface and secreting into culture medium chimeric IgE were obtained. The chimeric IgE showed identical Ag-binding properties as the murine mAb BAT123. Acting in concert with the specific peptide Ag polyvalently coupled to a protein carrier, the chimeric antibody could induce histamine release from human blood basophils. These results demonstrate the potential utility of the transfectoma cells and the chimeric IgE in studying the roles of membrane-bound IgE and effects of anti-IgE antibodies on IgE-producing B cells.     

Interleukin 12: still a promising candidate for tumor immunotherapy?

Interleukin 12 (IL-12) seemed to represent the ideal candidate for tumor immunotherapy, due to its ability to activate both innate (NK cells) and adaptive (cytotoxic T lymphocytes) immunities. However, despite encouraging results in animal models, very modest antitumor effects of IL-12 in early clinical trials, often accompanied by unacceptable levels of adverse events, markedly dampened  hopes of the successful use of this cytokine in cancer patients. Recently, several clinical studies have been initiated in which IL-12 is applied as an adjuvant in cancer vaccines, in gene therapy including locoregional injections of IL-12 plasmid and in the form of tumor-targeting immunocytokines (IL-12 fused to monoclonal antibodies). The near future will show whether this renewed interest in the use of IL-12 in oncology will result in meaningful therapeutic effects in a select group of cancer patients.     

Development and characterization of a novel anti-IgE monoclonal antibody

IgE is the central macromolecular mediator responsible for the progression of allergic reactions. Omalizumab (Xolair) is a humanized monoclonal anti-IgE antibody directed at the FcεRI-binding domain of human IgE, which represents a novel therapeutic approach in the management of asthma. In this study, we developed a monoclonal antibody (7A5) against human IgE via hybridoma technique. Our data showed that 7A5 could inhibit free IgE molecules to bind to receptors without affecting IgE already bound to cellular receptors. Importantly, 7A5 was able to inhibit IgE-induced histamine release of basophilic leukemia cells. Next, the phage display peptide library technology was employed to select peptides binding to 7A5 and a striking peptide sequence motif was recovered, which is homologous to the sequence ³⁹¹KQR³⁹³ within the Cε3 domain of IgE-Fc, Our results further indicated that 7A5 specifically bound to the synthesized peptide “³⁸⁸KEEKQRN³⁹⁴” containing the ³⁹¹KQR³⁹³ motif in IgE-Fc. The epitope of 7A5 was found to be spatially close to the FcεRI-binding site, suggesting that 7A5 binding to IgE might block IgE binding to receptors via steric hindrance. The anti-IgE monoclonal antibody 7A5 may have the potential to be developed as a therapeutic agent for the treatment of allergic diseases.     

Bacterial expression and characterization of a novel human anti-IgE scFv fragment

Antibodies highly specific to human immunoglobulin (Ig) E are capable of selectively blocking the IgE interaction or eliminating IgE-producing cells, thus providing valuable agents for diagnostics and treatment of various allergic illness. An example is omalizumab, a humanized monoclonal anti-IgE antibody that is approved for the treatment of patients with moderate-to-severe allergic diseases in the US, European Union and other countries. Here, we describe the generation and characterization of a novel human anti-IgE as a single-chain antibody fragment (scFv). The bacterially-synthesized scFv showed high affinity (86 nM) and specificity to the Fc region of human IgE. To our knowledge, this is the first report of the production of a human anti-IgE scFv in E. coli. Its further development as a potential candidate for medical applications is discussed.Key words: anti-IgE, E. coli expression, scFv, antibody engineering, human antibodies, allergy diseases, antibody therapeutics     

IgE-mediated release of histamine from human cutaneous mast cells

We investigated the ability of antigen-IgE interactions to stimulate histamine release from human infant cutaneous mast cells. Skin obtained at circumcision contained numerous perivascular mast cells, as assessed by light and electron microscopy. The histamine content of this tissue averaged 17.7 ng (+/- 1.5 SEM)/mg wet weight. Challenge of 200-microns thick sections of unsensitized skin with varying concentrations of monoclonal murine antibodies to human IgE caused no net release of histamine. After skin sections were incubated in the presence of 5 micrograms/ml of human myeloma IgE (S) for 120 min at 37 degrees C, monoclonal anti-IgE challenge resulted in 40.1% (+/- 6.0 SEM) histamine release. Similar passive sensitization with 1/20 dilutions of serum from humans expressing IgE to purified Juniperus sabinoides (JS) antigen rendered the tissue responsive to specific antigen challenge. Dose-related histamine release occurred over 30 min with optimal release of 12.6% (+/- 2.4 SEM) after stimulation with 100 ng/ml of JS antigen. This reaction required sensitization with serum containing IgE to JS and was antigen-specific. Optimal reactions to antigen occurred at 3 mM added Ca++, 34 degrees C to 37 degrees C, pH 7.2. Antigen-induced release was markedly influenced by the added Ca++ concentration; no release occurred in the absence of Ca++, 54% of the optimal response was observed at 2 mM Ca++, and 28% of the optimal response occurred at 4 mM Ca++. The addition of Mg++ did not influence antigen-induced release. The results of this study provide functional evidence that 1) human infant cutaneous mast cells express Fc-epsilon receptors; 2) these receptors are largely unoccupied in vivo; and 3) stimulation of passively sensitized infant mast cells with anti-IgE or specific antigen leads to immediate histamine release. This new system should permit detailed in vitro studies of immediate hypersensitivity reactions in human skin.     

Animal models for IgE-meditated cancer immunotherapy

Although most monoclonal antibodies developed for cancer therapy are of the IgG class, antibodies of the IgE class have certain properties that make them attractive as cancer therapeutics. These properties include the superior affinity for the Fc epsilon receptors (FcεRs), the low serum level of IgE that minimizes competition of endogenous IgE for FcεR occupancy, and the ability to induce a broad and vigorous immune response through the interaction with multiple cells including mast cells, basophils, monocytes, macrophages, dendritic cells, and eosinophils. Tumor-targeted IgE antibodies are expected to harness the allergic response against tumors and activate a secondary, T-cell-mediated immune response. Importantly, the IgE antibody can be used for passive immunotherapy and as an adjuvant of cancer vaccines. However, there are important limitations in the use of animal models including the fact that human IgE does not interact with rodent FcεRs and that there is a different cellular distribution of FcεRs in humans and rodents. Despite these limitations, different murine models have been used with success to evaluate the in vivo anti-cancer activity of several IgE antibodies. These models include wild-type immunocompetent animals bearing syngeneic tumors, xenograft models using immunocompromised mice bearing human tumors and reconstituted with human effector cells, and human FcεRIα transgenic mice bearing syngeneic tumors. In addition, non-human primates such as cynomolgus monkeys can be potentially used for toxicological and pharmacokinetic studies. This article describes the advantages and disadvantages of these models and their use in evaluating the in vivo properties of IgE antibodies for cancer therapy.     

Labelling of colloidal gold with IgE. A quantitative study using monoclonal IgE anti-beta-lactoglobulin and evaluation of the biological activity of the gold complex with RBL-1 cells

Immunocytochemical markers prepared by labelling colloidal gold with antibodies are gaining wide acceptance both in transmission and scanning electron microscopy. However, detailed information on the process and extent of adsorption of IgG and IgE in particular are still lacking. The adsorption isotherm of mouse monoclonal 125I-IgE antibovine milk beta-lactoglobulin was studied quantitatively with colloidal gold buffered at pH 6.1-8.8 (28 nm in particle diameter). At low coverage of the particles (less that or equal to 5 molecules per particle), the isotherm was independent of pH. In the presence of a large excess of IgE, the highest coverage was obtained at pH 6.1 near the pI of IgE (5.2-5.8). The binding constants were higher at low coverage (side-on adsorption) than at high coverage where desorption was observed. IgE-Au markers were unreactive towards the immobilized antigen and did not bind to receptors for IgE of rat basophilic leukemia cells (RBL-1). The reactivity of immobilized anti-IgE antibodies with IgE-Au markers increased as a function of particle coverage. Mapping of RBL-1 cell membrane IgE receptors was achieved by incubating successively IgE-sensitized RBL-1 cells with anti-IgE antibodies and a protein A-gold marker at 4 degrees C. Surface clusters developed when the cells were incubated at 37 degrees C.     

Quantitation of serum IgE by using chimeras of human IgE receptor and avian immunoglobulin domains

Anti-IgE therapeutics represent an efficient approach in the management of IgE-mediated allergic asthma. However, monitoring the reduction of IgE levels into a therapeutically efficient range requires the determination of residual serum IgE. We established an analytical approach to distinguish free and anti-IgE complexed serum IgE based on soluble derivatives of the human high-affinity IgE receptor. Soluble receptor derivatives represent an ideal means to analyze receptor antagonism by any ligand or blocking antibody. Therefore, the FcεRI ectodomain was fused with avian IgY constant domains that circumvent susceptibility to interference phenomena and improve assay performance. After production in HEK293 cells, subsequent characterization by enzyme-linked immunosorbent assay and immunoblotting confirmed the suitability of avian IgY constant domains for immobilization and detection purposes. To provide further insights into the different IgE reactivities, free allergen-specific IgE was also determined. Monitoring of sera from omalizumab-treated patients during the course of therapy revealed the applicability for assessment of omalizumab-complexed versus noncomplexed serum IgE. These parameters may allow correlation to clinical responses during anti-IgE therapy with the perspective of biomonitoring.     

Using the allergic immune system to target cancer: activity of IgE antibodies specific for human CD20 and MUC1

Monoclonal antibodies are widely used in the treatment of many B cell lymphomas and certain solid tumors. All currently approved therapeutic monoclonal antibodies are of the immunoglobulin G (IgG) isotype. We hypothesized that tumor-specific monoclonal antibodies of the IgE isotype may serve as effective cancer therapeutics. To test this hypothesis, we produced mouse?Chuman chimeric IgE antibodies specific for the human B cell antigen CD20 and the epithelial antigen MUC1. We demonstrate here that anti-hCD20 IgE antibodies have in vitro cytotoxic activity when used with purified allergic effector cells derived from umbilical cord blood. At an effector-tumor ratio of 2:1, mast cells and tumor-specific IgE induced a 2.5-fold increase in tumor cell death, as compared to control IgE. Similar results were observed when eosinophils were used as effector cells. In an in vivo murine model of breast carcinoma, administration of anti-hMUC1 IgE reduced the growth of MUC1⁺ tumors by 25?C30?% in hFc??RI transgenic mice. In contrast, local production of IgE and cytokines chemotactic for macrophages, eosinophils and mast cells led to complete tumor eradication. These results suggest that allergic effector cells activated by IgE and cell surface antigens have the capacity to induce tumor cell death in vitro and in vivo. The use of chimeric antibodies and hFc??RI transgenic mice will greatly enhance investigations in the nascent field of allergo-oncology.     

Recombinant IgE antibody engineering to target EGFR

Monoclonal antibodies have become a mainstay for the targeted treatment of cancer today. Some of the most successful targets of monoclonal antibodies are constituted by the epidermal growth factor receptor family spearheaded by the epidermal growth factor receptor (EGFR). Prompted by studies indicating that IgE compared to IgG may harness alternate effector functions to eradicate malignant cells, we addressed the establishment, engineering, and the potential tumoricidal effects of recombinant anti-EGFR IgE. Therefore, two different therapeutic EGFR-specific antibodies, 225 and 425, were chosen for re-cloning into different chimeric IgE and IgG formats and produced in human cells. Simultaneous antibody binding to the sEGFR demonstrated accessibility of both epitopes for recombinant IgE. Proliferation and cytotoxicity assays demonstrated signal blocking and effector mediating capability of IgE isotypes. Pronounced degranulation in the presence of sEGFR upon activation exclusively with two IgE antibodies verified the epitope proximity and provides evidence that tumor-targeting by anti-EGFR IgE is safe with regard to soluble target structures. Degranulation mediated by tumor cells expressing EGFR could be demonstrated for singular and combined IgE antibodies; however, use of two IgE specificities was not superior to use of one IgE alone. The data suggest that the surface distribution of EGFR is optimally suited to mount a robust effector cell trigger and corroborate the potential and specificity of the IgE/IgE receptor network to react to xenobiotic or pathogenic patterns for targeting malignancies.     

Molecular aspects of allergy

Atopic diseases such as asthma, rhinitis, eczema and food allergies have increased in most industrialised countries of the world during the last 20 years. The reasons for this increase are not known and different hypotheses have been assessed including increased exposure to sensitising allergens or decreased stimulation of the immune system during critical periods of development.

In allergic diseases there is a polarisation of the Th2 response and an increase in the production of type 2 cytokines which are involved in the production of immunoglobulin E and the development of mast cells, basophils and eosinophils leading to inflammation and disease. The effector phase of atopy is initiated by interaction with FcRI expressed on effector cells such as mast cells and basophils but also found on an ever increasing list of cells. Binding of a polyvalent allergen to the variable part of IgE leads to a cross-link of the receptor that triggers the cell to release histamine and pharmacological mediators of the symptomatic allergic response. Cross-linking of FcRI by autoantibodies against the -chain of the FcRI, causing subsequent histamine release is thought to be involved in the pathogenesis of other diseases such as chronic idiopathic urticaria (CIU).

To date, most therapeutic strategies are aimed at inhibiting and controlling components of the inflammatory response. Recently, new treatment strategies have emerged that focus on the development of preventive and even curative treatments. The most promising therapeutic approaches are aimed at inhibiting the IgE–FcRI interaction with the use of non-anaphylactogenic anti-IgE or anti-FcRI autoantibodies. Clinical trials in humans using an humanised anti-IgE antibody showed that this antibody was well tolerated and reduced both symptoms and use of medication in asthma and allergic rhinitis. Thus interruption of the atopic cascade at the level of the IgE–FcRI interaction with the use of non-anaphylactogenic antibodies is effective and represents an attractive therapy for the treatment of atopic disease.     

Lack of pokeweed mitogen-induced IgE formation in vitro by human peripheral blood mononuclear cells: detection of cross-reacting idiotypic determinants on polyclonal Ig by antibodies to a single IgE myeloma protein

The ability of human peripheral blood mononuclear cells to synthesize IgE in vitro in response to pokeweed mitogen (PWM) is controversial. To determine whether the conflicting results obtained by different laboratories could be due to inherent qualitative differences in the anti-IgE antibodies used to measure low concentrations of IgE in culture supernatants, we compared the specificities of anti-IgE reagents prepared by various methods. Immunoadsorbent-purified antibodies were isolated from a goat antiserum to the lambda, IgE myeloma protein PS and a rabbit antiserum to the kappa, IgE protein Bed in three ways: 1) antibodies to IgE PS (anti-PS) were isolated from the goat antiserum by affinity chromatography with PS coupled to Sepharose 4B; these antibodies consisted of anti-epsilon chain-specific and anti-idiotypic antibodies to protein PS; 2) antibodies specific for the epsilon-chain (anti-epsilon) were purified by affinity chromatography with IgE myeloma proteins that were not used for immunization; and 3) antibodies to idiotypic determinants of proteins PS (anti-id PS) and Bed (anti-id Bed) were isolated on affinity columns with the respective myeloma proteins after absorption of the epsilon-chain-specific antibodies. These three types of antibodies were then used in a solid phase radioimmunosorbent test to quantitate the amount of "IgE" synthesized by peripheral blood mononuclear cells from nonatopic and atopic donors cultured for 7 days in the presence and absence of PWM. ANTI-PS antibodies detected a PWM-induced "IgE formation" in cell culture supernatants of both non-atopic and atopic donors. (ABSTRACT TRUNCATED AT 250 WORDS)     

A novel IgE-neutralizing antibody for the treatment of severe uncontrolled asthma

The critical role played by IgE in allergic asthma is well-documented and clinically precedented, but some patients in whom IgE neutralization may still offer clinical benefit are excluded from treatment with the existing anti-IgE therapy, omalizumab, due to high total IgE levels or body mass. In this study, we sought to generate a novel high affinity anti-IgE antibody (MEDI4212) with potential to treat a broad severe asthma patient population. Analysis of body mass, total and allergen-specific IgE levels in a cohort of severe asthmatics was used to support the rationale for development of a high affinity IgE-targeted antibody therapeutic. Phage display technology was used to generate a human IgG1 lead antibody, MEDI4212, which was characterized in vitro using binding, signaling and functional assay systems. Protein crystallography was used to determine the details of the interaction between MEDI4212 and IgE. MEDI4212 bound human IgE with an affinity of 1.95 pM and was shown to target critical residues in the IgE Cε3 domain critical for interaction with FcεRI. MEDI4212 potently inhibited responses through FcεRI and also prevented the binding of IgE to CD23. When used ex vivo at identical concentration, MEDI4212 depleted free-IgE from human sera to levels ~1 log lower than omalizumab. Our results thus indicate that MEDI4212 is a novel, high affinity antibody that binds specifically to IgE and prevents IgE binding to its receptors. MEDI4212 effectively depleted free-IgE from human sera ex vivo to a level (1 IU/mL) anticipated to provide optimal IgE suppression in severe asthma patients.     

Regulation of IgE activity in inhalational tolerance via formation of IgG anti-IgE/IgE immune complexes

Background

Allergic asthma is an inflammatory disorder of the airways that results from inappropriate production of IgE against harmless, environmental antigens. Sequestration of free IgE using humanized IgG anti-IgE is an effective therapy for asthma and other atopic disorders. However, the status of free IgE in subjects who have naturally developed immune tolerance to inhaled antigens has not been well studied.

Methods

C57BL/6 mice were sensitized and challenged with ovalbumin (OVA) for 7 days to induce allergic airway disease (AAD) or 6 weeks to induce a state of local inhalational tolerance (LIT). Serum from AAD or LIT mice, diluted to achieve equivalent levels of total OVA-specific IgE, was used to sensitize rat basophil leukemia cells for allergen-mediated degranulation. Levels of degranulation were measured in relation to serum concentrations of free IgE and IgG anti-IgE/IgE immune complexes.

Results

Serum from AAD animals induced a greater degree of basophil degranulation than serum from LIT animals. These results correlated with higher levels of free IgE in AAD animals, whereas LIT mice demonstrated a significant increase in IgG anti-IgE/IgE immune complexes relative to their diseased counterparts.

Conclusions

Sequestration of free IgE by naturally occurring IgG anti-IgE may aid in the development of immune tolerance against inhaled allergens. The decrease in bioavailability of free IgE may, in turn, contribute to the overall reduction of asthma symptoms via a mechanism that mimics the therapeutic effects of humanized IgG anti-IgE.