Production of recombinant allergens in plants

The routine diagnostic set-up for atopic allergies includes detailed documentation of the clinical history, provocation tests in skin or other target organs, and serology (laboratory tests for total and allergen-specific IgE antibodies). Since decades, skin tests and other provocation tests, as well as allergen immunotherapy are performed with extracts from natural sources. Presently, these extracts are standardized for their content of certain major allergens, a prerequisite for the production of consistent preparations. However, products prepared from natural sources are very heterogeneous and contain many allergenic and non-allergenic proteins, and other substances. Thus, the replacement of extracts by selected recombinant allergens is an emerging strategy for improving allergy diagnosis and immunotherapy. In this respect, recombinant production based on plant systems offers a number of advantages such as appropriate post-translational modifications and enhanced safety due to absence of animal or human pathogens. So far, several approaches to express allergens using plant systems have been published. Immunologically active Der p 2, a major house dust mite (HDM) allergen, has been expressed in BY-2 tobacco suspension cell cultures. Mal d 2, a thaumatin-like allergenic protein from apple, and Bet v 1, the major birch pollen allergen, both have been overexpressed in Nicotiana benthamiana using a tobacco mosaic virus (TMV) vector. The major mugwort pollen allergen Art v 1 has been expressed in both TMV and Agrobacterium-transformed tobacco plants. Other approaches have explored the possibility of using seeds of cereal crops as vehicles for production of recombinant allergens and as direct delivery system without the need of allergen extraction and purification. Prototypes of such edible vaccines have been produced for a major HDM allergen Der f 1 in Lotus japonicus, and for T cell epitopes of Japanese cedar pollen allergens in rice seeds.