Engineered plant viruses are popularly employed for the production of vaccines in plants. Efficacy of plant virus to deliver vaccine gene into the plants are rapid and efficient expression of recombinant protein have been realised. The main strategy involves engineering of viral coat protein (CP) in fusion with antigenic protein or peptide.
The formation of infectious particle display antigen on their surface. Widely used virus reactor is tobacco mosaic virus (TMO). Because of its rapidity of infection, 50% of the plant dry weight comes from TMV. Several companies, including Biosource technology has successfully implemented novel method of producing therapeutic protein.
Currently, utilization of 15-acre tobacco plant has been shown to produce therapeutic proteins of 75-80-kD expressed by viral vector. Vectors derived from TMV shown to produce oral antihypertensive peptide (angiotensive-converting enzyme inhibition) in tomato and tobacco and inhibition of HIV replication (N-trichosanthin) in tobacco. Expression of malarial epitope in tobacco mosaic viruses has been established.
Roger Beachy at scripps Research Institute (USA) have engineered TMV to produce mouse zonna pellucida ZP3 protein, which is immunocontraceptive. In future, their efforts to produce plant that may serve as cheap source of oral contraceptive. Researchers at John Innus Institute have also engineered cow pea mosaic virus to contain a surface protein of human immunodeficiency virus (HIV) chimeric coat protein.
The epitope of VP2 capsid protein of mink enteric virus was chimerically expressed in Vigna unguiculata resulting in the accumulation of 1-1.2 mg/g plant. Apart from TMV and cow pea virus, tomato bushy stunt virus (TBSV) was modified to display 13 amino acid V3 peptide from HIV, SP120. The foreign peptide was attached to the coat protein (CP).
Purification from the infected tobacco plant shows that the structure of virus particle resulted in display of 180 copies of antigen per virus. Main constraints with engineering of CP are the size restriction on the antigenic insert. The coat protein of alfa alfa mosaic virus (A1MV) can be exploited to accommodate larger the size of the genome.