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risks and safety of transgenic plant systems (part ii)Protein isolation from plants is specific
The third reason why protein production in transgenic plants is safe is that the isolation process used to extract the protein product is very specific. For example, some rather ingenious advances in isolation techniques have been made in this area by Desai et al. They created in their study a rapid extraction technique that requires only mild conditions, which helps to preserve the function of the protein. Desai et al. created a tagged-protein system in which a model protein, τ-glucuronidase (GUS), was tagged with calmodulin. In the presence of calcium, the calmodulin binds specifically to a modified column affinity surface that they created and allows the isolation of GUS. Chelators can be added after isolation to dissociate the protein of interest from the column surface. The simplicity of this system allows the preservation of antibody function and is a marked improvement over other available techniques.
In addition to the preservation of function, it has also been demonstrated that the antibody isolation process from plants is specific. There has been considerable concern over the possibility of contamination from plant compounds, such as nicotine in transgenic tobacco systems, since compounds can generate unwanted immune responses in the patient, as the improper glycosylation of plantibodies has been shown to do, and exert unknown effects on the patient. With regard to transgenic tobacco plants, nicotine contamination is of concern since it is known to be addictive while its effect on the function of the protein produced is not understood. Ko et al. have demonstrated that the amount of nicotine extracted in protein samples from transgenic tobacco plants is of negligible level. The gas chromatography/mass spectroscopy system that they used to detect the nicotine is sensitive to concentrations above 5pg. The ideal next step, however, would be to validate this in all transgenic plant systems. In the meantime, it can be seen the isolation of antibodies from transgenic plants is quite safe, with little risk of contamination from plant compounds or effect on antibody structure.
In this article, current literature was examined to determine just how safe, how effective and how efficient transgenic plants are. Despite the many unknowns in this field, research thus far has shown that transgenic plants are safe: they do not transmit human pathogens and the isolation techniques used to extract proteins are specific. Potential undesired immune responses of mammalian systems against these plantibodies has been demonstrated and circumvented in many instances by the use of these antibodies orally. The latter route of antibody application is particularly useful in the treatment of immune diseases in which the presentation of self-antigens can help "train" the immune system to recognize self-antigens and reduce the severity the disease. Much remains to be resolved, however. The ideal next step for researchers would be to examine the function of these plantibodies in in vivo systems, rather than through the interaction of antibodies with antibodies. Answers to these types of questions need be found before transgenic plants can be used for the full-scale treatment of diseases, including autoimmune diseases. The possibilities, however, are bright.
references14) Desai UA, Sur G, Daunert S, Babbitt R, Li Q. Expression and affinity purification of recombinant proteins from plants. Protein Expr Purif 2002, 25: 195-202.
15) Ko K, Wei X, Crooks PA, Koprowski H. Elimination of alkaloids from plant-derived human monoclonal antibody. J Immunol Methods 2004, 286: 79-85.