Advantageous features of plant-based systems for the development of HIV vaccines.

Plants have recently become an attractive option for the production of recombinant proteins. Plant-based systems can be used to produce many classes of foreign proteins including candidate vaccine antigens. The selected antigen can be purified from plant material prior to delivery by the preferred route, or alternatively delivered orally in edible plant material that has been processed to give a homogeneous and stable product. Several plant species have been used to express a wide range of vaccine candidates with tobacco, potato and corn being particularly favored. Corn seed is especially well suited to various food processing technologies that generate dry homogeneous material suitable for extended storage and refrigeration-free transport and distribution. Many antigens have been expressed in corn and assessed for efficacy in trials with generally positive results. Candidate HIV vaccines are particularly good targets for plant-based oral delivery since there is a great need for an easily distributed affordable vaccine that could be administered without injection and induce strong mucosal immune responses. As a first step in evaluating plant expression technology with a relevant antigen that might easily be tested in an animal system, we expressed the SIV major surface glycoprotein gp130 (analogous to HIV gp120) in corn seed. Expression levels were achieved that are compatible with conducting oral delivery trials in animals.