Summary Genetically modified (or GM) plants have attracted a large amount of media attention in recent years and continue to do so. Despite this, the general public remains largely unaware of what a GM plant actually is or what advantages and disadvantages the technology has to offer, particularly with regard to the range of applications for which they can be used. From the first generation of GM crops, two main areas of concern have emerged, namely risk to the environment and risk to human health. As GM plants are gradually being introduced into the European Union there is likely to be increasing public concern regarding potential health issues. Although it is now commonplace for the press to adopt ‘health campaigns’, the information they publish is often unreliable and unrepresentative of the available scientific evidence. We consider it important that the medical profession should be aware of the state of the art, and, as they are often the first port of call for a concerned patient, be in a position to provide an informed opinion. This review will examine how GM plants may impact on human health both directly – through applications targeted at nutrition and enhancement of recombinant medicine production – but also indirectly, through potential effects on the environment. Finally, it will examine the most important opposition currently facing the worldwide adoption of this technology: public opinion.

In this study, we demonstrate that the folding and assembly of IgG in transgenic tobacco plants is orchestrated by BiP (binding protein), an endoplasmic reticulum resident chaperone. Expression of BiP and calreticulin was examined in transgenic tobacco plants that express immunoglobulin chains, either singly or in combination to form IgG antibody. BiP mRNA expression was lowest in wild‐type nontransformed plants and those that expressed immunoglobulin light chain alone. Higher mRNA levels were detected in plants expressing fully assembled immunoglobulin (light and heavy chains), and the most abundant levels of RNA transcript were found in those plants that expressed immunoglobulin heavy chain alone. Estimation of total BiP demonstrated a similar pattern, with the highest levels detected in plants expressing immunoglobulin heavy chain alone. Immunoprecipitation studies demonstrated that BiP was associated with immunoglobulin chains extracted from protoplast lysates, but not from secreted fluids. Again, most BiP was coprecipitated from plants expressing heavy chain only and those that produced full length IgG. The binding of BiP to Ig heavy chains was ATP‐sensitive. Co‐expression of heavy and light chain resulted in IgG assembly and displacement of BiP from the heavy chain as the amount of light chain increased. Although calreticulin mRNA and total protein levels varied in a similar manner to those of BiP in the transgenic plants, there was no evidence for association between calreticulin and Ig chains, by coimmunoprecipitation. The results indicate that BiP, but not calreticulin, takes part in immunoglobulin folding and assembly in transgenic plants.

Rhizosecretion is an attractive technology for the production of recombinant proteins from transgenic plants. However, to date, yields of plantderived recombinant pharmaceuticals by this method have been too low for commercial viability. Studies conducted focused on three transgenic plant lines grown in hydroponic culture medium, two expressing monoclonal antibodies Guy's 13 and 4E10 and one expressing a small microbicide polypeptide cyanovirin‐N. Rhizosecretion rates increased significantly by the addition of the plant growth regulator α‐naphthalene acetic acid. The maximum rhizosecretion rates achieved were 58 Hg/g root dry weight/24 h for Guy's 13, 10.43 μg/g root dry weight/24 h for 4E10, and 766 μg/g root dry weight/24 h for cyanovirin‐N, the highest figures so far reported for a full‐length antibody and a recombinant protein, respectively. The plant growth regulators indolebutyric acid, 6–benzylaminopurine, and kinetin were also demonstrated to increase rhizosecretion of Guy's 13. The effect of the growth regulators differed, as α‐naphthalene acetic acid and indole‐butyric acid increased the root dry weight of hydroponic plants, whereas the cytokinins benzylaminopurine and kinetin increased rhizosecretion without affecting root mass. A comparative glycosylation analysis between MAb Guy's 13 purified from either hydroponic culture medium or from leaf extracts demonstrated a similar pattern of glycosylation comprising high mannose to complex glycoforms. Analysis of the hydroponic culture medium at harvest revealed significantly lower and less complex levels of proteolytic enzymes, in comparison with leaf extracts, which translated to a higher proportion of intact Guy's 13 IgG in relation to other IgG products. Hydroponic medium could be added directly to a chromatography column for affinity purification, allowing simple and rapid production of high purity Guy's 13 antibody. In addition to the attractiveness of controlled cultivation within a contained environment for pharmaceutical‐producing plants, this study demonstrates advantages with respect to the quality and downstream purification of recombinant proteins.—Drake, P. M. W., Barbi, T., Sexton, A., McGowan, E., Stadlmann, J., Navarre, C., Paul, M. J., Ma, J. K.‐C. Development of rhizosecretion as a production system for recombinant proteins from hydroponic cultivated tobacco. FASEB J . 23, 3581–3589 (2009). www.fasebj.org