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Monoclonal Antibodies produced by Plants - an Update on Plantal Genepharming

The idea of using whole plants as drugs synthesis factories blossomed ever since researchers first succeeded in generating an antibody from an engineered tobacco plant. In theory, therapeutic proteins, antibodies and vaccines would be harvested cheaply from vast fields of engineered plants.
To make a plant produce a desired protein, the target gene is isolated and inserted into the plant infecting Agrobacterium. Through the infection the gene becomes a part of the plant’s genome and is therefore inherited by the following generation of plants. The foreign gene is now transcribed as much as if it were one of the plant’s own genes.
A shortcut for this method was invented by the company Large Scale Biology Corp. when they were producing a lymphoma vaccine. They simply sprayed tobacco plants with a tobacco mosaic virus carrying the desired gene. The vaccine was produced by the leaves within 14 days and worked in mice. The advantage of this technique is the rapid generation of products and that the tobacco plants carry the foreign gene just as long as they carry their leaves and are not permanently modified. Worries about pharma crops escaping from their experimental plots and getting into the food supply are the major concerns regarding plantal drug production. Yet the cost difference is immense. The monoclonal antibodies produced in tobacco cost about $100 per kilogram as compared to $3 million for the same amount of antibody produced by mammalian cells. Plus the antibodies would be simpler to process because they would not harbour animal pathogens.
Nevertheless no plant-made human drug has ever made it through clinical trials. Some proteins are on the market as supplements, but the flying visions have not been fulfilled yet.

Current efforts to finally getting to a plantal drug factory include a corn-grown gastric lipase and from transgenic safflowers, both entering clinical trials this year. A different approach abandons the idea of growing crops and instead works with just the cells, like the production of a Gaucher disease enzyme in carrot cell culture or interferon production in duckweed grown as a layer in plastic bags. Also, the EU-funded project of an anti-HIV microbicide grown in corn or tobacco could be ready for testing next year.

The most realistic future for plantal drugs, however, may reside in the high-volume biologics like microbicides and monoclonal antibodies or the production of large amounts of cheap vaccines for developing countries.

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