Sublingual vaccination and delivery systems

Most infectious agents use mucosal tissues as entry portals, thus, mucosae are frequently defined as a first line of defense against pathogens. Mucosal protection generally operates through antibody-mediated and cytotoxic T-cell responses which can be triggered by mucosal vaccines. Sublingual vaccination provides many advantages such as systemic and mucosal responses (both locally and at remote mucosal sites), besides being a needle-free administration route with high patient compliance and limited adverse effects. Buccal mucosa complexity nonetheless represents a challenge for vaccine administration, hence, many efforts were recently deployed to improve vaccine components, mucoadhesion and/or penetration. Several innovative approaches indeed confirmed that a robust and protective immunity can be achieved by sublingual vaccines. This review will then specify the most recent delivery systems and improvements developed to increase sublingual vaccines efficiency. We will focus our description on the immune mechanisms involved and the requirements for optimal sublingual immunization and mucosal protection.