Have Aliu,1–3 Carola Rask,1 Jens Brimnes,1 Thomas Lars Andresen2,3 1Immunology Department, In vivo Biology Team, ALK Abelló A/S, Hørsholm, 2Department of Micro- and Nanotechnology, Technical University of Denmark, 3Center for Nanomedicine and Theranostics, Technical University of Denmark, Kgs Lyngby, Denmark Abstract: Immunotherapy by sublingual administration of allergens provides high patient compliance and has emerged as an alternative to subcutaneous immunotherapy for the ­treatment of IgE-associated allergic diseases. However, sublingual immunotherapy (SLIT) can cause adverse events. Development of allergen delivery systems enabling more efficient delivery and hence lower allergen load might reduce the adverse events. In the present study, we have investigated neutral and cationic liposomes as delivery systems of ovalbumin (OVA), as a model allergen, in an OVA-induced allergic airway inflammation model. We investigated the liposome carriers’ ability to improve tolerance induction of antigens compared to the ­corresponding dose of free OVA. Mice were treated sublingually over 2 weeks with free or liposome encapsulated OVA followed by intraperitoneal injections and intranasal challenge. Mice sublingually treated with OVA-liposomes showed a significant reduction of airway eosinophilia and splenocyte proliferation in comparison to free OVA. A similar nonsignificant pattern was seen for OVA-specific IgE antibodies. In addition, reduced levels of interferon-γ and interleukin-5 were observed in spleen cell culture supernatants from OVA-liposome-treated mice compared to the sham-treated group. In conclusion, in vivo efficacy data showed that prophylactic SLIT with OVA-liposomes is significantly more effective in preventing allergic inflammation than the corresponding dose of free OVA. Keywords: sublingual immunotherapy, drug delivery, allergy, liposome