The outbreaks of West Nile Virus (WNV) in North America over the last decade indicate its establishment and continued spread throughout the Western hemisphere. At present, no therapeutic or vaccine is available for human use. The continued expanding WNV epidemic demands effective therapeutics and new production technologies that can rapidly transfer them into the clinical setting. The proposed research will advance the development of immunotherapeutics, with an emphasis on technology that allows cost-saving scale-up capability through the use of transgenic plants. The proposed research exploits the facile capability of plant cells to rapidly express and accumulate post-translationally modified proteins, and builds upon our ongoing research to use plant-derived monoclonal antibodies (MAbs) and MAb fusion proteins as therapeutics for viral infections. Recent research has shown that a humanized murine MAb (hu-E16) has promising therapeutic potential. A single dose of hu-E16 protected mice and hamsters against WNV-induced mortality even 5 days after infection. In addition to creating a plant-derived hu-E16 mAb with equivalent activity, this project intends to create a novel blood-brain barrier (BBB) permeable variant to enhance potency and prolong the window of opportunity for treatment. Prototype plant-derived proteins will be produced in quantities sufficient for preclinical trials. We will also develop scale-up and purification technology for subsequent production under cGMP conditions. Transgenic plants are ideal for MAb production since plant-derived MAb and MAb fusion proteins can be rapidly expanded in commercial production without high-capital cost investments for traditional MAb facilities. Thus, in addition to generating novel therapeutic reagents for WNV, this study will provide proof-of-principle for the rapid development and use of "plantibodies" against human infectious diseases. Such technology can then be readily applied in the future to other emerging infectious diseases or bioterrorist threats.