Monoclonal antibodies defining epitopes on human IgE

The role of omalizumab in the treatment of chronic rhinosinusitits with nasal polyposis

Introduction: Chronic rhinosinusitis with nasal polyposis (CRSwNP) poses a significant healthcare challenge, with diminished quality of life for patients and high costs and resource utilization for disease management. The understanding of CRSwNP pathophysiology has progressed with identification of various inflammatory biomarkers and subsequent development of monoclonal antibodies that target the underlying mechanisms of inflammation.Areas covered: Omalizumab is a biologic agent for CRSwNP treatment that targets immunoglobulin (Ig)-E. The US FDA has approved the use of omalizumab as an add-on biologic therapy for nasal polyposis in December 2020. Two Phase III clinical trials, POLYP 1 and POLYP 2, have shown that omalizumab improves both subjective patient-reported outcomes and objective physician-evaluated metrics for CRSwNP. Ongoing studies are still exploring the efficacy, safety, and cost-effectiveness of biologics for CRSwNP.Expert opinion: Biologics will continue develop as a viable management option for CRSwNP. Omalizumab is regarded as a promising addition to current treatment strategies for refractory disease.

Chronic Rhinosinusitis with Nasal Polyps: Targeting IgE with Anti-IgE Omalizumab Therapy

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a complex, clinically heterogeneous and persistent inflammatory disorder of the upper airway. Detailed mechanistic insights into disease pathogenesis are lacking, but it is now accepted that local tissue IgE driven T2-high inflammatory pathways are critical to disease. The recent CRSwNP Phase 3 POLYP1 and POLYP2 replicate studies of blocking IgE with omalizumab confirmed rapid improvements in all clinical parameters of sinonasal disease, confirming a pivotal role for IgE driven inflammatory pathways in CRSwNP. This review summarises the biology of IgE in relation to CRSwNP. Insight into how IgE may drive CRSwNP is evaluated in the context of clinical improvements seen with omalizumab. The need for further studies using a broader patient and biomarker specific groups to aid more precise drug-patient selection alongside more detailed mechanistic studies of omalizumab in CRSwNP is highlighted.

Anti-IgE treatment in allergic rhinitis

OBJECTIVES

To review the efficacy of anti-IgE therapy in allergic rhinitis (AR).

METHODS

Literature search was performed using the PubMed and Proquest Central databases at Kırıkkale University Library.

RESULTS

Although the skin prick testing in patients suffering from AR is positive (indicating that antigen-specific Immunoglobulin E has been produced), there is no association with overall circulating IgE levels. Correlation was lacking between circulating IgE level and either skin prick tests or laboratory testing for specific IgE. Omalizumab binds to uncomplexed IgE in man more avidly than does Fc-epsilon. The effect of omalizumab is to lower the level of IgE and downgrade production of FceRI receptors (which bind IgE) in mast cells and basophils, causing less mast cell recruitment and responsivity and thus diminishing eosinophilic infiltration and activation. Anti-IgE therapy through omalizumab may shorten the lifetime of mast cells and causes dendritic cells to downgrade their production of FcεRI. There are reports indicating benefit from omalizumab in managing food allergies, nasal polyp formation, essential anaphylaxis, AR, venom allergy and eczema. Omalizumab acts to lessen circulating IgE levels, whilst reducing production of FceRI by mast cells and basophils. The fact that omalizumab influences how eosinophils respond may be down to disruption of the antigen-IgE-mast cell interactions, with mast cells being recruited at lower levels and thus chemotactic eosinophilic recruitment via cytokines being greatly reduced. Omalizumab has the effect in cases of perennial AR of blocking the increased eosinophilic recruitment and tissue infiltration initiated by seasonal antigens. Likewise, in omalizumab-treated cases, circulating unbound IgE levels showed significant decreases. For patients with perennial AR, the average daily nasal severity score was significantly reduced where omalizumab was administered, compared to placebo.

CONCLUSION

Omalizumab has efficacy in ameliorating symptoms and reduces the necessity for additional medication in both seasonal and perennial allergic rhinitis.

Reduction of total IgE by targeted coengagement of IgE B-cell receptor and FcγRIIb with Fc-engineered antibody

BACKGROUND

Sequestration of IgE to prevent its binding to high-affinity IgE receptor FcεRI on basophils and mast cells is an effective therapy for allergic asthma. IgE production requires differentiation of activated IgE(+) B cells into plasma cells upon allergen sensitization. B-cell receptor signaling is suppressed by the inhibitory IgG Fc receptor FcγRIIb; therefore, we reasoned that a therapeutic antibody that coengages FcγRIIb and IgE B-cell receptor would not only sequester IgE but also suppress its production by blocking IgE(+) B-cell activation and differentiation to IgE-secreting plasma cells.

OBJECTIVE

To explore the effects of IgE sequestration versus IgE suppression by comparing omalizumab to FcγRIIb-optimized anti-IgE antibodies in humanized mouse models of immunoglobulin production.

METHODS

By using a murine anti-IgE antibody as a template, we humanized, increased IgE binding, and modified its Fc domain to increase affinity for FcγRIIb. We next compared effects of this antibody (XmAb7195) versus omalizumab on the secretion of IgE and other isotypes in human PBMC cultures and in PBMC-engrafted severe combined immunodeficiency mice.

RESULTS

Relative to omalizumab, XmAb7195 has a 5-fold higher affinity for human IgE and more than 400-fold higher affinity for FcγRIIb. In addition to sequestering soluble IgE, XmAb7195 inhibited plasma cell differentiation and consequent human IgE production through coengagement of IgE B-cell receptor with FcγRIIb. In PBMC-engrafted mice, XmAb7195 reduced total human IgE (but not IgG or IgM) levels by up to 40-fold relative to omalizumab.

CONCLUSION

XmAb7195 acts by IgE sequestration coupled with an FcγRIIb-mediated inhibitory mechanism to suppress the formation of IgE-secreting plasma cells and reduce both free and total IgE levels.

Omalizumab in the management of patients with allergic (IgE-mediated) asthma

Immunoglobulin E (IgE) is central to the pathophysiology of allergic asthma. Omalizumab, an anti-IgE monoclonal antibody, binds to the FcɛRI binding site on free IgE. As a result, circulating free IgE is reduced, IgE is prevented from attaching to mast cells and basophils, and FcɛRI receptor expression is down-regulated. The inflammatory response to allergens and the acute and chronic effector phases of allergic inflammation are thereby attenuated. In clinical trials in adults and adolescents, omalizumab reduced asthma exacerbations, severe asthma exacerbations, inhaled corticosteroid requirements, and emergency visits, as well as significantly improving asthma-related quality of life, morning peak expiratory flow and asthma symptom scores in patients with severe allergic (IgE-mediated) asthma. Results from clinical trials in children (<12 years) are consistent with those in the adult population. It is difficult to predict which patients will respond to omalizumab. Responders to omalizumab should be identified after a 16-week trial of therapy using the physician's overall assessment. When treatment is targeted to these responders, omalizumab provides a cost-effective therapy for inadequately controlled severe allergic (IgE-mediated) asthma. Long-term therapy with omalizumab shows the potential for disease-modification in asthma. Ongoing studies are also evaluating the use of omalizumab in other non-asthma IgE-mediated conditions.

Molecular and cellular targets of anti-IgE antibodies

Immunoglobulin E (IgE) was the last of the immunoglobulins discovered. It is present in very low amounts (nano- to micro-gram per ml range) in the serum of normal healthy individuals and normal laboratory mouse strains and has a very short half-life. This contrasts with the other immunoglobulin classes, which are present in much higher concentrations (micro- to milligram per ml range) and form a substantial component of serum proteins. Immunoglobulins play a role in homeostatic mechanisms and they represent the humoral arm of defence against pathogenic organisms. Since IgE antibodies play a key role in allergic disorders, a number of approaches to inhibit IgE antibody production are currently being explored. In the recent past the use of nonanaphylactic, humanized anti-IgE antibodies became a new therapeutic strategy for allergic diseases. The therapeutic rational beyond the idea derives from the ability of the anti-IgE antibodies to bind to the same domains on the IgE molecule that interact with the high-affinity IgE receptor, thereby interfering with the binding of IgE to this receptor without cross-linking the IgE on the receptor (nonanaphylactic anti-IgE antibodies). Treatment with anti-IgE antibodies leads primarily to a decrease in serum IgE levels. As a consequence thereof, the number of high-affinity IgE receptors on mast cells and basophils decreases, leading to a lower excitability of the effector cells reducing the release of inflammatory mediator such as histamine, prostaglandins and leukotrienes. Experimental studies in mice indicate that injection of some monoclonal anti-IgE antibodies also inhibited IgE production in vivo. The biological mechanism behind this reduction remains speculative. A possible explanation may be that these antibodies can also interact with membrane bound IgE on B cells, which could interfere the IgE production.

The pharmacological basis of anti-IgE therapy

The treatment of asthma and allergic rhinitis using unique, humanized anti-IgE monoclonal antibodies with very particular binding specificities is now supported by the results of multiple phase II and III human clinical studies. The therapeutic efficacy of this approach is attributable to several pharmacological mechanisms. In addition to the expected effects of these monoclonal antibodies in neutralizing free IgE and inhibiting IgE production by B cells, several indirect biochemical and cellular effects have been uncovered during the course of the clinical trials. These include the accumulation of potentially beneficial IgE-anti-IgE immune complexes and the downregulation of the high-affinity IgE Fc receptors (FcvarepsilonRI) on basophils and mast cells. This article analyzes the structural basis of the specificity of the anti-IgE antibodies and pertinent results from in vitro experiments, animal model studies, and human clinical trials in an attempt to provide a cogent pharmacological interpretation of the therapeutic effects of anti-IgE therapy in both the near- and long term. The development of anti-IgE therapy over the past 10 years provides an interesting example of the emergence of a conceptually new, biotechnology-produced pharmaceutical.

Efficient production of syngeneic anti-IgE monoclonal antibodies with high affinity and diverse specificity

Syngeneic monoclonal anti-IgE antibodies are of value in studies of the suppression of IgE synthesis. Procedures are described here for the production of high titers of murine anti-IgE antibodies by initiating immunization in the perinatal period, before mice develop tolerance to their autologous IgE. This in turn facilitates the production of monoclonal anti-IgE antibodies. Properties of some of these mAbs are reported, including affinity, fine specificity and ability to bind to IgE on B lymphoma cells or mast cells.

Production and characterization of murine monoclonal antibodies specific for baboon IgG heavy and light chain epitopes

We have generated a panel of murine monoclonal antibodies (MAbs) that recognize baboon IgG epitopes. The reactivity of the MAbs with IgG from other primate species was also examined. Specificity for IgG heavy (H) or light (L) chain epitopes was determined by Western blot analysis. The H chain-specific MAbs were analyzed for IgG subclass specificity and the L chain-specific MAbs for reactivity with baboon IgM and polymeric sIgA. Finally, an ELISA was developed to demonstrate the utility of the MAbs in analysis of humoral immune responses in baboons.

Anti-human IgE monoclonal antibodies recognizing epitopes related to the binding sites of high and low affinity IgE receptors

Anti-human IgE monoclonal antibodies (mAbs) were produced and eight clones recognizing epitopes on native IgE were selected. Epitopes were mapped by a competitive inhibition enzyme-linked immunosorbent assay, Western blotting and a multi-pin peptide technology. Four sites (one each in the C epsilon 1, C epsilon 2, C epsilon 2/C epsilon 3 junction and C epsilon 3) were recognized by the mAbs. The relationship between the four epitopes and the binding sites of high and low affinity IgE receptors (Fc epsilon RI and Fc epsilon RII, respectively) was studied using a monovalent Fab fragment of each mAb as a binding inhibitor. The IgE-Fc epsilon RII binding was clearly inhibited by the mAb recognizing the C epsilon 2/C epsilon 3 junction, suggesting that Fc epsilon RII binds to a rather limited area around the C epsilon 2/C epsilon 3 junction. The IgE-Fc epsilon RI binding, on the other hand, was scarcely inhibited by any single mAb. However, the binding was inhibited when the epitope in C epsilon 2 was blocked simultaneously with that at the C epsilon 2/C epsilon 3 junction or with that in C epsilon 3, indicating that these three distinct epitopes are related to the Fc epsilon RI binding sites. When these three epitopes were shown in the stereograph of human IgE, the Fc epsilon RI binding area was spread largely on the groove side between C epsilon 2 and C epsilon 3 domains. These results suggest that Fc epsilon RI acquires the high affinity through multiple bindings.

Monoclonal antibodies against heavy and light chains of domestic mink IgG

A panel of 26 monoclonal antibodies (MAbs) specific to mink IgG was produced and analyzed by ELISA, immunodiffusion assay (IDA) and immunoblotting assay. All the raised MAbs were directed against the isotypic IgG epitopes. Immunoblotting assay demonstrated that 11 MAbs reacted only with the Fc-fragments of IgG and 7 only with the light chains. Four antibodies bound to the Fab-containing fragments and failed to react with the Fc-fragments or isolated L-chains. Three MAbs did not react with IgG in IDA. Based on the results of IDA and cross-blocking assays, the MAbs were divided into 10 groups, with the MAbs of each group recognizing the same epitope. In IDA some MAbs were able to react with the epitopes which are common to the IgGs of some other representatives of Mustelidae family and also to some mammalian species remote from mink (dog, horse, pig, fox and rabbit).