Bystander suppression to unrelated allergen sensitization through intranasal administration of tolerogenic exosomes in mouse.

Exosomes represent a new family of bioactive nanovesicles (30-100 nm in diameter) secreted by different cell types whose appealing features can be exploited for designing vaccines in the context of several human diseases. We previously reported the potential of bronchoalveolar lavage fluid (BALF)-derived tolerogenic exosomes (Exo(Tol)) to be used as a nasal allergy vaccine in a mouse model of sensitization to Ole e 1, the main allergen of olive pollen. The aim of the study was to investigate whether such nanovesicles specific to Ole e 1 can also prevent the sensitization to other unrelated allergen, as Bet v 1 from birch pollen. Exo(Tol) were isolated from BALF of mice tolerized against Ole e 1 and used in a prophylactic approach. BALB/c mice were intranasally pretreated with Exo(Tol) one week before sensitization/challenge with Bet v 1, and the magnitude of allergen-specific response was analyzed. Intranasal pretreatment with Exo(Tol) resulted in significant inhibition of both specific IgE and IgG1 antibodies levels. Moreover, T cells from mice pretreated with Exo(Tol) showed a reduction in IL-5 and IL-13 (Th2 cytokines) production. Lung inflammatory response triggered by unrelated allergen-challenge was also significantly reduced after pretreatment: perivascular/peribronchial inflammatory cell infiltration, eosinophilia and mucus secretion. In conclusion, Exo(Tol) specific to Ole e 1, in addition to inhibit specific immune response to this allergen, blocked the allergic response to a second unrelated allergen such as Bet v 1. The in vivo "bystander suppression" that we herein describe for Exo(Tol) may have implications for the treatment of allergy based on mucosal tolerance induction.