Developing a novel hepatitis B core – based antigen presentation system

Plant-produced proteins of pharmaceutical interest are beginning to reach the market, and the advantages of transient plant expression systems are gaining increasing recognition. In parallel, the use of virus-like particles (VLPs) has become standard in vaccine design. The pEAQ-HT vector derived from the cowpea mosaic virus – based CPMV-HT expression system has been shown to allow the production of large amounts of recombinant proteins, including VLPs, in Nicotiana benthamiana. Moreover, previous work demonstrated that a tandem fusion of the core antigen (HBcAg) of hepatitis B virus (HBV) could direct the formation of core-like particles (CLPs) in plants. The work presented here demonstrated that the tandem core system is better suited for the plant-based production of CLPs presenting foreign antigens than SplitCore technology. It was shown that tandem core technology allows the plant-based production of CLPs which are suitable for the presentation of antigens either via chemical coupling or through antibody-antigen interactions. Of particular significance was the successful display of single domain antibody fragments of camelid origin (nanobodies, or VHH). The resulting “tandibody” particles, as they are named here, can bind to their cognate antigen to yield CLPs covered in the antigen of interest. Furthermore, it was shown that target antigens can be attached to CLPs via a fusion partner, raising the possibility of the development of a universal generic antigen-display platform. In addition to the transient expression work on HBcAg, lines of stably transformed N. benthamiana were created which constitutively expressed human gastric lipase (hGL), an enzyme of medical importance. In the future, this approach could be used to create transgenic plants constitutively expressing a universal tandibody, thus obviating the need for infiltration.