Expression platform

Careful empirical selection of the expression platform for carotenogenesis has included selection of the best strains for stability and degree of accumulation and the selection of compatible drug-resistance combinations and low copy number polycistronic plasmids to enhance product accumulation by decrease of metabolic burden." 5 Matthews and Wurtzel discussed culture and induction conditions - that have been explored in most studies. Most efforts to engineer carotenoid biosynthesis in E. coli focused on the genes and enzymes of the pathway and had a modest effect on improved accumulation. For example, substitution and over-expression of a GGPPS that uses IPP directly (discussed in... 

PI. polymorpha [80] is generally referred to as safe and was widely used for pharma-protein production (cytokines, vaccines, coagulation factors) [80]. The genome sequence is known and DNA chip technologies have been established. Hansenula was developed to an expression platform which was implemented for the production of recombinant vaccines. 

Gellissen, G., Kunze, G., Gaillardin, C. et al. (2005) New yeast expression platforms based on methylotrophic Hansenula polymorpha and Pichia pastoris and on dimorphic Arxula adeninivorans and Yarrowia lipolytica - a comparison. FEMS Yeast Research, 5 (11), 1079-1096. 

In this chapter, we have looked at the properties of different expression hosts and expression systems, and considered some of the available strategies to control transgene expression and protein accumulation. When all these variations are combined, there exists a very diverse range of potential expression platforms that can be used to produce recombinant proteins. The choice depends on many factors, some intrinsic to the plant species or expression system, some dependent on the recombinant pro-... 

The amount of vaccine or therapeutic protein produced in a plant can reach industrial-scale levels. The typical yield of biopharmaceuticals produced in a plant-based system is 0.1%-1.0% of total soluble protein (Twyman et al., 2003). This value is competitive with other expression systems therefore, a plant expression platform for biopharmaceuticals is economically viable. As an example, one bushel of maize can produce as much avidin as one ton of chicken eggs but at 0.5% the cost. 

Many of the new companies have leveraged novelty of an expression platform (e.g., containment) as the competitiveness of the protein production platform. Epicyte, Inc. appears to have been an exception that developed proprietary expertise in antibody expression in plants without a discernable novel patent position (whether Epicyte obtained a license to operate from Monsanto is not clear Epicyte was acquired by another startup, BioLex, Inc. in 2004). Because expression of... 

This chapter reviews progress and challenges in the area of production of recombinant proteins, in particular biopharmaceuticals, in plants. Different expression platforms are summarized, including those based on the use of transgenic, transplastomic or transfected plants as production hosts. The quality and yield of recombinant proteins produced in and purified from plants, as well as progress in clinical trials with plant-made pharmaceutical proteins are described. The advantages, limitations and biological safety aspects of plant-based production of biopharmaceuticals are discussed. 

A relatively small number of biotechnology companies operate in the field of recombinant proteins production in plants (Table 6.4). This small number represents roughly one-third of approximately 60 dedicated plant biotechnology companies - an unfavorable comparison to the several hundred small and medium-sized businesses that use bacterial, yeast or animal-based expression platforms and operate in the sector of red biotechnology. The number of plant-made recombinant proteins that have reached the market is also very limited, but has a healthy tendency to grow. 

Kentucky). The company uses a TMV-based transient expression platform that is fast and easy to apply. The platform is built on viral vectors capable of systemic movement. 

This brief account of currently available products and under development (see Table 6.4) provides evidence that, despite several drawbacks, the production of recombinant proteins in plants is steadily progressing. However, it is also evident that all expression platforms in use have certain... 

Fig. 6.3 magnICON expression platform versatility Coomas-sie blue-stained SDS-PAGE of total soluble protein extracted from transfected Nicotiana leaves. The recombinant protein bands are circled. 

Plant ceU cultures combine the merits of plant-based systems with those of microbial and animal ceU cultures, particularly in terms of downstream processing. In their chapter they discuss the benefits of plant cell cultures compared to other systems, the technological requirements for producing biopharmaceutical proteins in plant cells and the unique aspects of downstream processing which are applied to this expression platform. 

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