Reducing allergenicity by altering allergen fold: a mosaic protein of Phl p 1 for allergy vaccination

The major timothy grass pollen allergen, Phl p 1, resembles the allergenic epitopes of natural group I grass pollen allergens and is recognized by more than 95% of grass-pollen-allergic patients. Our objective was the construction, purification and immunologic characterization of a genetically modified derivative of the major timothy grass pollen allergen, Phl p 1 for immunotherapy of grass pollen allergy. A mosaic protein was generated by PCR-based re-assembly and expression of four cDNAs coding for Phl p 1 fragments and compared to the Phl p 1 wild-type by circular dichroism analysis, immunoglobulin E (IgE)-binding capacity, basophil activation assays and enzyme-linked immunosorbent assay competition assays. Immune responses to the derivative were studied in BALB/c mice. Grass-pollen-allergic patients exhibited greater than an 85% reduction in IgE reactivity to the mosaic as compared with the Phl p 1 allergen and basophil activation experiments confirmed the reduced allergenic activity of the mosaic. It also induced less Phl p 1-specific IgE antibodies than Phl p 1 upon immunization of mice. However, immunization of mice and rabbits with the mosaic induced IgG antibodies that inhibited patients' IgE-binding to the wild-type allergen and Phl p 1-induced degranulation of basophils. We have developed a strategy based on rational molecular reassembly to convert one of the clinically most relevant allergens into a hypoallergenic derivative for allergy vaccination.