Oral immunization: turning fantasy into reality

The application of oral immunization as the primary means to deliver multivalent vaccines to large populations has many theoretical advantages. However, widespread success in achieving protective immunity against these diseases through oral immunization requires additional understanding of the basic mechanisms of host resistance in the mucosal tissues. Fundamental issues, such as the lineage and repertoire or regulatory pathway of mucosal effector cells, are only now just beginning to be understood. A more comprehensive understanding of these issues could greatly enhance our success at designing and applying successful oral immunization programs.