Mucosal immunisation and adjuvants: a brief overview of recent advances and challenges

Mucosal immunisation may be used both to prevent mucosal infections through the activation of anti-microbial immunity and to treat selected autoimmune, allergic or infectious-immunopathological disorders through the induction of antigen-specific tolerance. The development of mucosal vaccines, whether for prevention of infectious diseases or for immunotherapy, requires antigen delivery and adjuvant systems that can efficiently help to present vaccine or immunotherapy antigens to the mucosal immune system. Promising advances have recently been made in the design of more efficient mucosal adjuvants based on detoxified bacterial toxin derivatives or CpG motif-containing DNA, and perhaps even more striking progress has been done in the use of virus-like particles as mucosal delivery systems for vaccines and of cholera toxin B subunit as antigen vector for immunotherapeutic tolerance induction. However, it is a memento that two recently developed mucosal vaccines for human use against rotavirus diarrhoea and influenza were withdrawn after a short period in the market because of adverse reactions among the vaccinees, thus emphasising the difficult and challenging task also for mucosal immunisation of combining vaccine and adjuvant efficacy with safety and acceptability.