Rationale for a five-grass pollen vaccine

Grass pollen allergic patients are naturally exposed and sensitized to multiple pollens from various Pooideae species. The question arises as to whether such patients should be desensitized with extracts based on a single pollen or a pollen mixture. Neither conventional diagnosis based on IgE reactivity nor pollen counts enable the identification of which grass species are involved in patient sensitization. Significant cross-immunogenicity is observed between allergens from Pooideae pollens due to their conserved amino acid sequences (e.g. >90% for group 1, 55–80% for group 5, 30–60% for other allergens, including minor allergens). Nevertheless, pollen allergens also contain species-specific T or B cell epitopes, and there is evidence that at least 50% of allergic patients are sensitized to such distinct epitopes. In addition, substantial quantitative differences exist in the allergen (e.g. group 1, 2/3, 4, 5, 6, 10, 13) content of pollens obtained from distinct grass species. In this context, we recommend a vaccine consisting of a combination of pollens from five common and well characterized Pooideae including Anthoxanthum odoratum, Dactylis glomerata, Lolium perenne, Phleum pratense and Poa pratensis for desensitization purposes. This 5-grass mixture is recommended because, (i) it has been validated, in terms of safety and efficacy, by established clinical practice; (ii) it better reflects natural exposure and sensitization conditions at the molecular level than a single pollen; and (iii) it provides a consistent and well-balanced composition of critical allergens, while extending the repertoire of T and B cell epitopes.