PLG microparticles stabilised using enteric coating polymers as oral vaccine delivery systems

Novel poly(dl-lactide-co-glycolide) microparticles for oral vaccine delivery were formulated using the enteric polymers Eudragit L100-55 and carboxymethylethylcellulose (CMEC) as stabilisers. To serve as a control, microparticles were also produced using the conventional PVA surfactant. In all three cases the antigen, ovalbumin (OVA)-loaded microparticles produced were less than 5 microm in diameter and had a spherical, smooth rounded appearance. The presence of surfactants at the microparticle surface was demonstrated by the surface analysis techniques, XPS and SSIMS. Incubation of microparticles with solutions of pepsin or trypsin led to the removal of a proportion of the antigen associated with all three systems. However, in three CMEC-stabilised microparticle formulations and one of three Eudragit formulations, a high percentage of the associated antigen was protected from removal by a solution of pepsin at pH 1.2 compared with the PVA-stabilised microparticles. In addition, with certain CMEC and Eudragit formulations a degree of protection was also afforded to the associated OVA against removal by trypsin at pH 7.4. Following the incubation of microparticles in simulated gastric fluid a higher percentage of intact antigenic OVA was detected in microparticles stabilised using CMEC than in the PVA- and Eudragit- stabilised formulations. Oral immunisation of mice with OVA-loaded microparticles stabilised using either of the three surfactants led to the induction of specific serum IgG and salivary IgA antibodies. Significantly higher levels of specific salivary IgA antibody to OVA were measured in mice immunised with the CMEC-stabilised microparticles than with the other two formulations. This novel approach in PLG microparticle formulation may have potential in increasing the efficacy of microparticulate systems for the oral administration of vaccines.