Efficacy of oral administration and oral intake of edible vaccines.

To evaluate whether vaccine administration via intragastric gavage is indicative for the outcome of edible vaccines, mice were orally immunised with ovalbumin (OVA) mixed with or without Vibrio cholerae toxin (CT) in various compositions via various routes: (1) OVA dissolved in saline and intragastrically (IG) administered ('IG'); (2) OVA mixed with food extract and administered IG ('food IG'); (3) food chow absorbed with OVA dissolved in saline and fed to the animals ('food'); and (4) OVA dissolved in saline and administered via drinking bottles ('drinking'). When given to naive mice, 'IG' and 'food IG' but not 'food' or 'drinking' induced anti-OVA IgG1 responses in serum, but oral boost immunisations were necessary. Serum IgA was not induced. Oral boosting of subcutaneously (SC) primed mice enhanced the IgG1 and IgA response in serum regardless of the route of immunisation or the vaccine composition. CT did not dramatically enhance the immune response. All immunisation routes except 'drinking' induced antigen-specific IgA antibody secreting cells (ASC) in the lamina propria of naive mice. But antigen-specific antibody responses in faeces were not observed. We concluded that oral (i.e. IG) administration is distinct from oral intake. The composition of the vaccine (food or saline) did not influence oral administration. We thus suggested that the route of administration greatly influenced the outcome of oral immunisation. Although oral administration is a well-accepted route to test the potentials of oral vaccines, our study demonstrated that it is merely indicative for the effectiveness of edible vaccines. Studies on the feasibility of edible vaccines should thus be performed by eating the vaccine.