Plant virus expression vectors

Much progress has been made in the development of plant virus expression vectors over the last decade and they can now be regarded as commercially viable systems... 

As it is imperative that the plant-derived hiopharmaceutical product must be obtained repeatedly and on a consistent basis, a master cell culture bank, seed bank for transgenic plants, or virus seed stock for transient expression systems must be constantly maintained. Storage conditions must therefore he optimized to prevent contamination and ensure viability. Both transgene stability (e.g., reversion to wild type or sequence drift of plant virus expression vectors) and protein expression levels must be monitored in a representative plant of a given bank or stock to minimize any possible variation in expression levels that may affect safety and consistency of the hnal product. A program that monitors lot-to-lot consistency of the hiochemical and biological properties by comparing the product with appropriate in-house reference standards could he implemented as a fundamental component of product development. 

Discusses the engineering of plant virus expression vectors for transient expression of vaccine proteins and other therapeutics in plant tissue... 

Selected Examples of Virus-Induced Gene Silencing Using Plant Viral Expression Vectors... 

Scholthof, H.B., Scholthof, K.-B.G., and Jackson, A.O. (1996). Plant virus gene vectors for transient expression of foreign proteins in plants. Anna. Rev. Phytopathol. 34 299-323. 

A detailed description of plant virus vectors for expression of biopharmaceuticals is found in Chapter 4. The development of application of plant viral expression vectors for large-scale field trials involves many important issues. In order for production to be scaled up, it is necessary to have... 

The lack of human pathogenicity of plant viruses rules out the risks of human infection by exposure in the field or in food products to a plant virus. However, biological containment of the virus expression vector remains a primary safety concern as it can be considered a risk to the environment. This includes the spread of recombinant viruses to weeds... 

Plant virus-based vectors have a number of advantages as heterologous gene expression tools (for general reviews see Porta and Lomonossoff, 1996 Scholthof et al, 1996). These include the ability to direct rapid and... 

The disadvantages of plant-virus-based vectors are that they typically lead to only transient expression of the foreign protein, only a limited number of virus vectors are available, the size of the foreign gene insert may be limited, and recombination within the plant may eliminate expression of the foreign viral protein. 

This chapter evaluates some of the approaches used to produce vaccines and heterologous proteins in plants using plant virus-based expression systems, and discusses novel strategies that are being considered for the development of better vectors. 

The majority of viruses that infect plants have single-stranded, positive-sense RNA genomes. It has therefore been necessary to use infectious cDNA clones for the in vitro manipulation of RNA viruses, allowing them to be developed as effective tools for the commercial production of target proteins in plants. This approach has also been used to study the genetic and metabolic profiles of both viruses and their host plants. Siegel [14] conceptualized the potential use of RNA viruses as expression vectors. Brome mosaic virus (BMV) and Tobacco mosaic vims (TMV) were the first two RNA viruses to be converted into expression vectors. These vectors have since been pro-... 

Tab. 6.1 Examples of plant viruses used in the development of expression vectors...

Excellent progress has been made in a relatively short period of time in demonstrating the potential of plant virus vectors not only as expression tools but also as elegant and efficient means for the administration of vaccine antigens by different routes. The targets seem to be unlimited. 

Recombinant plant viruses have been used as expression vectors because the infections are rapid and systemic, leading to high levels of recombinant protein produc-... 

FIGURE 4.3 Schematic representation comparing the full and deconstructed virus vector strategies, (a) TMV expression vector, (b) Provector system for rapid assembly of viral amplicons in planta. P promoter, TMV Pol TMV polymerase, MP movement protein, GOI gene of interest, CP capsid protein, T terminator, RS recombination site. (Adapted from Gleba et al. (2004). Curr. Opin. Plant Biol., 7, 182-188.)... 

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