Application of liposomes for development of oral vaccines: Stability of liposomes in vitro, and the serum and intestinal humoral immune responses of mice to orally administered antigen in liposomes.

To evaluate the usefulness of liposomes as oral vaccines, the stability of liposomes, and the serum and intestinal IgA antibody responses to antigen associated with liposomes after oral administration were examined. In the liposomes tested, liposomes composed of dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS), and cholesterol (Chol) (1 : 1 : 2, molar ratio), distearoylphosphatidylcholine (DSPC) and Chol (7 : 2, molar ratio), and DSPC, DPPS, and Chol (7 : 3 : 2 or 1 : 1 : 2, molar ratio) were stable in acidic solution (pH 2.0), bile, and pancreatin solution. After the oral immunization of antigen (ganglioside GM1)-containing liposomes composed of DPPC, DPPS, and Choi (1 : 1 : 2, molar ratio) to mice, the serum and intestinal IgA antibody responses against ganglioside GM1 were found. Furthermore, when monophosphoryl lipid A was incorporated into liposomes containing ganglioside GM1, further augmentation of serum IgA responses to ganglioside GM1 was observed. On the other hand, the oral administration with liposomes composed of DPPC, Chol, and ganglioside GM1 (unstable liposomes), ganglioside GM1 mixed with liposomes composed of DPPC, DPPS and Chol, and ganglioside GM1 alone was unable to induce any detectable anti-ganglioside GM1 IgA antibody responses. These results suggest that liposomes which showed the stability to acidic solution, bile, and pancreatin solution would serve effectively as an oral delivery vehicle for inducing mucosal immune responses.