Biopharming: Turning Plants into Factories
Since the early 1990s, biotech companies have proposed using food and feed crops as miniature factories for producing pharmaceutical proteins and industrial chemicals that they do not make naturally. This technology, called “biopharming,” involves the insertion into plant cells of foreign genes coding for medically important proteins, such as therapeutic proteins, monoclonal antibodies, and vaccines. To date, however, the FDA has yet to approve a single drug made by this method.
One approach to biopharming is to insert the gene for a desired protein into the DNA of chloroplasts, membrane-bound organelles containing chlorophyll. Chloroplasts have their own circular set of genes that is distinct from the main genome in the cell nucleus. In the leaves of higher plants, each cell has as many as 100 chloroplasts, each of which contains up to 100 copies of the genome. Thus, by inserting a transgene into the chloroplast genome, one can greatly amplify the gene and produce large amounts of the corresponding protein.
Production of biopharmaceuticals in transgenic plants may offer a cost-effective alternative to using engineered bacteria or mammalian cell culture. One advantage of biopharming is that plant cells possess the biochemical machinery needed to fold complex proteins and to perform the post-translational modifications (such as glycosylation, the addition of sugar molecules) required for full biological activity. Moreover, unlike mammalian cells, plants do not contain retroviruses and other infectious agents (such as prions) that cause disease in humans.4