Development of an oral mimotope vaccine against Her-2/neu overexpressing tumors

The project application presented is based on two major scientific achievements of our group in the allergy and tumor immunology field during the recent years: 1.) Epitope mimics, socalled mimotopes, can be generated from phage display libraries and applied for active immunizations and the induction of epitope-specific humoral immune responses. This is an important progress in allergy as well as in tumor immunology, where allergen- blocking antibodies or growth inhibitory antibodies, respectively, can be generated in an epitope-specific fashion. 2.) Protein feedings in oral immunizations of Balb/c mice result in IgE antibody production when feedings are done under hypoacidic conditions using anti-acids like Sucralfate, H2 receptor blockers or proton pump inhibitiors. This results in IgE-mediated food allergy when normally harmless proteins are gavaged. We aim to exploit these findings by feeding tumor antigens in combination with anti-acids, which should lead to a beneficial, tumor- inhibitory type of IgE antibodies. The development of an oral mimotope vaccine would substantially increase the quality of life of cancer patients. Epitope-specific immunizations with mimotopes are feasible, at least in murine models. Mimotopes can be selected from phage display peptide libraries using an antibody of interest. When allergen-specific IgE antibodies were used for selections, mimotopes could be derived that induced blocking antibodies of the IgG isotype upon immunizations. When the clinically approved antibody Trastuzumab (directed against Her-2/neu of the epidermal growth factor receptor family) was used, mimotopes were generated which induced trastuzumab-type IgG antibodies in mice upon parenteral immunization. Interestingly, these actively induced antibodies showed similar biological features as the original antibody itself. These mimotopes may thus in the future be used in active immunotherapy for the treatment of breast cancer patients. Preliminary results demonstrated that feeding Her-2/neu mimotopes under anti-acidic conditions induce high levels of specific IgE and IgG1 in Balb/c mice. We expect that the IgE response takes advantage of an attractive subset of cells which could actively combat a Her-2/neu overexpressing tumor: mast cells, eosinophils and basophils. The aims of this project are to analyse the biological effects of an oral mimotope immunization by in vitro assays (histamine release tests, skin tests in mice), as well as to monitor the anti-tumor effects in a transgenic in vivo murine model. The results of this project will be directly translatable into clinical studies.

Mimotopes are peptides that mimic three-dimensional surface structures of antigens and can be used for immunizations. Generally, the advantage of a vaccine is that induced antibodies are available continuously in the patient and also complete self molecules. Our previously generated HER-2 mimotopes imitate exactly the binding site of the IgG antibody trastuzumab (Herceptin ) which is today in clinical use for treating breast cancer patients. When applied orally, these mimotopes induced in mice antibodies with the same tumoricidic activity as the clinically approved trastuzumab antibody (Riemer et al, Cancer Research 2007), but of the IgE isotype. IgE antibodies are well known from allergy where they are responsible for hypersensitivity towards innocuous allergens. They interact with a number of inflammatory effector cells which possess IgE receptors. The cognition from our study that IgE could play a role against cancer opened new avenues for our research. In consequence, two international symposia, being the first allergooncology meetings worldwide, were arranged in Vienna, rendering the birth of an international network focusing on the subject. The consortium co-authored a review (Jensen-Jarolim et al, Allergy 2008), and a book will be published in 2009 (Eds. M. Penichet & E. Jensen-Jarolim, Springer, 2009). On the research level, a recombinant IgE antibody of exactly the same specificity as trastuzumab was constructed for passive immunotherapy in a fruitful collaboration with Prof. Hannah Gould, King`s College, London (Karagiannis et al, Cancer Immunol. Immunother. 2008). We succeeded to show its in vitro efficacy by a newly established 3-color FACS assay. Clearly, trastuzumab-like IgE had a higher cytotoxic and lower phagocytic capacity than the original antibody, showing thus complementary features. Similarly, the findings could be repeated for an IgE variant of cetuximab antibody against the colon cancer antigen EGFR Consequently, in presently ongoing studies we investigate the occurrence of natural IgE (versus IgG) in diverse tumor tissues by array technology in several collaborations. Taken together, the results from this project confirmed our original working hypothesis that IgE could be an effective means for tumor surveillance and therapy, and rendered, besides public awareness of the subject, several novel IgE-based strategies for the therapy of cancer.