Tobacco influenza virus

The tobacco mosaic virus (center right), a plant pathogen, has a structure similar to that of MB, but contains ssRNA instead of DNA. The poliovirus, which causes poliomyelitis, is also an RNA virus. In the influenza virus, the pathogen that causes viral flu, the nucleocapsid is additionally surrounded by a coat derived from the plasma membrane of the host cell (C). The coat carries viral proteins that are involved in the infection process. 

The first instance of a vaccine being made in plants was in 1990 when a patent was filed for a Streptococcus mutans protein (SpaA) expressed in tobacco. Since then, many other vaccines (e.g., cholera toxin B, Hepatitis virus surface antigen, Plasmodium surface protein) have been produced, and multiple different plant species (e.g., tomato, potato, banana, and rice) have been used, particularly as an edible host is needed for oral administration. An important sdentific milestone was when the E. coU heat labile enterotoxin (LT-B) was expressed in potatoes and was shown to be orally immunogenic when 5 g of transformed tuber was fed to mice over 18 days [70]. However how this might translate to an effective dose in humans is not yet established. Numerous other workers have since demonstrated for animal models that oral or injected immunization with plant-produced antigen would provide protection against diseases such as Yersinia pestis [71], or Avian Influenza Virus [72]. 

Fig.1. Viruses. Schematic representation of virus particles, all drawn to scale. The type of genome (RNA or DNA) is shown in brackets. Enveloped viruses 1 Pox virus (DNA). 2 Rabies virus (RNA). 3 Influenza virus (RNA). 4 Measles virus (RNA). 5 Chickenpox virus (ONA). Naked or unenveloped viruses 6 Yellow fever virus (RNA). 7 Adenovirus (DNA). 8 Reovirus (RNA). 9 Wart-papilloma virus (ONA). 10 Poliomyelitis virus (RNA). 11 Parvovirus (RNA). 12 Corona virus (RNA). 13 Tobacco mosaic virus (RNA). 14 Bacteriophage T2 (DNA).

The most widely studied therapeutic proteins produced in plants include monoclonal antibodies for passive immunotherapy and antigens for use as oral vaccines [40]. Antibodies against dental caries, rheumatoid arthritis, cholera, E. coli diarrhea, malaria, certain cancers, Norwalk virus, HIV, rhinovirus, influenza, hepatitis B virus and herpes simplex virus have been produced in transgenic plants. However, the anti-Streptococcus mutans secretory antibody for the prevention of dental caries is the only plant-derived antibody currently in Phase II clinical trials [40]. Until recently, most antibodies were expressed in tobacco, potato, alfalfa, soybean, rice and wheat [9], It has been estimated that for every 170 tons of harvested tobacco, 100 tons represents harvested leaves. A single hectare could thus yield 50 kg of secretory IgA [3, 41]. Furthermore, it has been estimated that the cost of antibody production in plants is half that in transgenic animals and 20 times lower than in mammalian cell cul-... 

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