Strategies to systemically block IgE-synthesis

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 non-anaphylactic, humanized anti-IgE antibodies became a systemic therapeutic strategy for allergic diseases. The principle of the idea is that these antibodies bind to the same site on the IgE molecule that interacts with the high-affinity IgE receptor, thereby interfering with the binding of IgE to this receptor without cross-linking the IgE on the receptor. Treatment with anti-IgE antibodies leads primarily to a decrease in serum IgE levels. As a consequence, the number of high- affinity IgE receptors on mast cells and basophils decreases, leading to a lower excitability of the effector cells. As a consequence, inflammatory mediator such as histamine, prostaglandins and leukotrienes will not be triggered. Recently we suggested an alternative systemic approach, based on targeting the IgE antigen receptor itself. In a prophylactic study anti-membrane-IgE antibody mAbA9 was passively administrated to mice in parallel with Bet v1a as sensitizing allergen. Compared with the control group only treated with Bet v1a we observed a drastic reduction in the production of Bet v1a-specific IgE antibodies with a long lasting effect on the development of a Bet v1a-specific IgE-memory cell population. However, IgE-secreting plasma cells do not express mIgE and presumably are not affected by anti-IgE. These cells reside in the bone marrow and have a life span of several weeks to several months. Since new IgE-secreting plasma cells go through mIgE-expressing B cell stages during differentiation, if their generation is abrogated by anti-IgE treatment, the existing plasma cells will die off in several weeks to several months, and thus the production of IgE will also gradually abate in similar periods. Thus, memory B cells are the main targets and may possibly be affected by anti-mIgE. If this occurs, anti-mIgE may have long-term effects on the fundamental disease process. The molecular mechanisms, leading to the depletion of these cells might be explained by apoptosis and reached by the immunological process of tolerance and/or anergy induction. In the present project proposal, on the one hand, we want to pursue the idea of systemic interference of the IgE response and, in continuation to the already published passive immunization strategy, investigate an animal model based on a possible "therapeutic capacity" of mAbA9 but also develop an active anti-mIgE immunization approach in the mouse. On the other hand, the mouse studies should be the basis for the development of a homologous human anti-mIgE application. Both main scientific questions will be investigated with four related, but independent experimental approaches. First, special focus will be set on the investigation of the detailed molecular mechanism, leading to the clonal B cell deletion in answer to anti-mIgE treatment Second, we want to establish a combinatorial "passive mAbA9/active DNA-allergen" based therapeutic immunization protocol, to demonstrate an additional benefit, to the already described parallel application during SIT, of an anti-mIgE antibody. Third, as alternative to the passive immunization we further plan, in the murine system, to establish and investigate the benefit of an active anti-vaccination strategy based on mimotope peptides and thereof deduced DNA based vaccines. Fourth, as performed for the generation of the murine anti-mIgE antibody, we now want to use the human EMPD region as target for the selection of anti-human mIgE monoclonal antibodies.

Today, almost 30% of the western population suffer from undesirable allergic reactions. With increasing rate all over the world from year to year, allergy has turned out to be a severe threat in a biological sense and displays a tremendous socio-economic challenge. IgE, the key player in allergic disorders, has been studied extensively, and anti-IgE therapy has become the standard tool of medical treatment. In this project, we have tried to establish a modified anti-IgE therapy. Instead of targeting free IgE molecules in the serum of an individual, we laid our focus on B cells carrying IgE on their membrane surface. In previous experiments, we could demonstrate that passive immunization with an antibody directed against membrane-bound IgE molecules during antigen sensitization led to strongly reduced IgE serum levels. In a next step, we further pursued our idea of systemic anti-IgE treatment combined with an active immunization approach, i.e. allowing an organism to actively produce anti-membrane IgE antibodies. Passive immunization is a very expensive and time-consuming method, and whenever possible, active immunization would be favoured from both sociological as well as economical point of view. For active generation of anti-membrane IgE antibodies, we used a technique that allowed us to screen for peptides that were mimicking a short sequence of membrane-bound IgE molecules.Immunization with these peptides should then trigger the immune system to start an immune reaction and to produce anti-membrane bound IgE antibodies. All experimental approaches were performed in the mouse model. First, we could successfully show that after immunization with these peptides anti-membrane IgE antibodies were generated. Moreover, subsequent immunization with a sensitizing antigen that usually induces the production of IgE in an allergic individual demonstrated the biological capability of peptide-induced anti-membrane IgE antibodies to successfully interfere with IgE production, as IgE titers were markedly reduced. Mice, which were pre-immunized with the peptides, showed much lower IgE serum levels than the control group. These results clearly demonstrated that anti-membrane IgE antibodies, which were generated actively by peptide immunization, were targeting newly emerging allergen-induced IgE B cells. In terms of a possible medical treatment in the future, DNA vaccines were designed too and successfully tested. One therapeutic potential of such anti-membrane IgE antibodies lies within the suppression of newly developing IgE antibodies during specific immunotherapy, leaving established immunity untouched.