An Investigation into the Use of a Plant-Expressed Virus-Like Particle as an Oral Vaccine Candidate

Abstract Plant-expressed virus-like particles (VLPs) could offer an alternative method for the oral delivery of vaccines. VLPs' robustness, combined with their compartmentalisation within the plant cells, should favour their stability in the harsh gastro-intestinal (GI) environment. In the small intestine, intact VLPs should be available for absorption by the Follicle-associated epithelium (FAE), considered the main portal of entry for antigens in the gut. In this work, Hepatitis B core antigen (HBcAg) VLPs, expressed transiently in Nicotiana benthamiana leaves, were extracted, purified and characterised. The stability of purified HBcAg VLPs in simulated human gastric and intestinal media was investigated. The results suggested that the antigen was unstable when subjected to various simulated gastric fluids. Upon incubation in simulated human and ex vivo pig intestinal fluids, HBcAg maintained higher stability. Leaves expressing HBcAg VLPs could be dried, retaining good antigen stability, but the natural encapsulation in the leaves failed to protect the antigen from degradation in the simulated GI fluids. However, enteric-coated “green” tablets containing dried leaves expressing HBcAg could be produced and were shown to confer protection in simulated gastric fluids but allowed the release of intact antigen in simulated intestinal fluids. Purified HBcAg VLPs could be formulated into spray-dried and spray freeze-dried microparticles using a pH-responsive polymer. However, such formulations showed poor gastro-resistance, negating their use for targeted intestinal delivery. HBcAg VLPs could be also freeze-dried, suggesting the potential use of freeze-drying for further processing of the antigen into an oral formulation. A human cell culture model of the small intestinal epithelium indicated selective absorption of HBcAg VLPs by the FAE but limited overall absorption. In vivo ligated loop studies in mice suggested poor intestinal absorption, mainly relegated to the FAE. This research represents an original investigation into the possible applications of plant-expressed HBcAg VLPs for oral drug delivery.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2013

Author dc:creator

• Berardi, Alberto

Language dc:language

en