Preparation of double liposomes and their efficiency as an oral vaccine carrier

The usefulness of double liposomes (DL), liposomes containing liposomes inside, as an oral vaccine carrier was examined. Ovalbumin (OVA) encapsulating liposomes sized to 230 nm (small liposomes, SL) were prepared by the glass-beads (GB) method and sequential sonication and extrusion. For the purpose of stabilizing the model antigen, DL containing SL were prepared by the GB method and the reverse-phase evaporation (REV) method. They were named GB-DL and REV-DL, respectively. The morphological structure of DL was confirmed using confocal laser scanning microscopy and scanning electron microscopy by the freeze-fracture method. DL showed suppressed release of OVA and stabilized OVA in pepsin solution as compared with SL. BALB/c mice were immunized with OVA solution, SL and DL suspension by oral administration. Significantly higher levels of IgA in feces were observed in mice immunized with SL and REV-DL as compared with OVA solution, and REV-DL tended to show the higher level of IgA than SL. REV-DL elicited significantly higher anti-OVA IgG responses as compared with OVA solution. Furthermore, GB-DL tended to raise the IgG level as compared with SL. The results suggest that DL have the potential to be an effective carrier for oral immunization.