Rapid, high-level production of hepatitis B core antigen in plant leaf and its immunogenicity in mice.

Hepatitis B core antigen (HBc or HBcAg) self-assembles into capsid particles and is extremely immunogenic. HBc has been extensively studied for its production in various expression systems and for the use of HBc particles for high-density, immunogenic presentation of foreign epitopes. Here we reported the high-level transient expression of HBc in plant leaf and its immunogenicity in mice. By using a novel plant viral expression system, HBc was produced in Nicotiana benthamiana leaves at levels up to 7.14% of total soluble protein (TSP) or 2.38 milligrams HBc per gram of fresh weight at 7 days post-infection (dpi). Plant-derived HBc (p-HBc) assembled into virus-like particles (VLPs) as revealed by sucrose gradients and electron microscopy. Partially purified p-HBc stimulated strong serum antibody responses in mice as Escherichia coli-derived HBc upon intraperitoneal (i.p.) injection. Furthermore, mice immunized mucosally (orally and intranasally) with p-HBc in the absence of adjuvants also developed HBc-specific serum IgG as well as intestinal IgA. Taken together, our results indicate the potential usefulness of p-HBc-VLP as a carrier for immunogenic presentation and mucosal delivery of foreign epitopes.