The development of new strategies for the delivery of vaccine antigens or i
mmune modulators to the mucosal tissue includes innovative approaches such
as the use of genetically modified food microorganisms and plants. Even tho
ugh the 'proof-of-concept' has recently been established for these two syst
ems, key questions mainly related to efficacy and risk of breaking oral tol
erance remain to be critically addressed in the immediate future.