Can plant-derived vaccines improve global human health?

Plants offer great advantages as production platforms for vaccines, antibodies and other biopharmaceutical proteins. Plant-derived vaccines provide an alternative to conventionally- made vaccines by enabling delivery to be safe and effective through the oral consumption of edible plant tissue. Since a large number of infectious diseases enter the body through mucosal surfaces including the gut, vaccines which can be expressed within edible plant tissue present a select advantage. Not only do the plant tissues act as the delivery vehicle, they protect the antigen as it passes through the harsh environment of the gastrointestinal tract. Another advantage lies in the fact that, in contrast to bacterial expression systems, plants are capable of producing recombinant antigens that undergo post-translational modifications which resemble their mammalian-derived counterparts. Moreover, the cost of producing proteins from plants is only a fraction of the cost of proteins produced from comparable mammalian cell culture systems. Proteins derived from plant expression platforms may subtly differ from analogous mammalian cell cultures in terms of their respective glycosylation profiles. It is important to note that many mammalian therapeutic proteins are in fact glycoproteins and possess glycosylation motifs which are absent from plants. In addition to this, differences in glycosylation profiles between plant and mammalian expression systems may lead to adverse effects such as increases in allergenicity.Plants can be glyco-engineered to more closely resemble their mammalian counterparts; this can be accomplished by altering glycosylation pathways which are found exclusively in plants and by incorporating in their place the necessary glycosylation pathways which prevail in humans. Therapeutic proteins targeted to accumulate in the endoplasmic reticulum of plant cells have also been produced; these proteins lack undesirable post-translational modifications that normally exist in a plant cellular environment. While plant transformation represents an original tactic to generate biopharmaceutical proteins, transient expression systems have also increased in popularity. Besides avoiding political controversy and lengthy time constraints involved in generating a transgenic plant, transient systems such as plant virus expression vectors are capable of producing high quantities of vaccine and other therapeutic proteins within a short time period (often within a week, depending on the virus/ host plant system involved). Plant viruses have been engineered which express either