Plant pathogens, such as Agrobacterium tumefaciens can transfer a segment of its DNA into the plant cell, resulting in the expression of the introduced genes. Development of these processes started so called molecular farming, after immunoglobulins and hepatitis B antigen were successfully expressed in tobacco 30 years ago.
Further studies on plant-Agrobacterium interactions resulted in a faster and more efficient transient expression system called agroinfiltration. When Agrobacterium transfers its DNA to plant cells a small proportion of this T-DNA is stably integrated into the plant genome. However, T-DNA can also be transiently introduced in the plant cell at a higher frequency, than stable integration, when using infiltration. These transient T-DNAs can express the gene of interest rapidly and to high volumes. The efficiency by which Agrobacterium can transiently transform some plant species, such as Nicotiana benthamiana, allows rapid gene expression with elevated levels of the desired target protein being produced after approximately 3-7 days following infiltration. This production time frame is comparable to bacterial expression systems. However, Agrobacterium plant-based transient expression has several advantages over other expression systems which include protein processing and secretion in eukaryotic cells along with the speed in evaluating the feasibility of the technique. Initial small-scale experiments can be completed very quickly in the laboratory to evaluate protein expression and allow success or failure to be understood within as little as two weeks.

Hypertrans® vector
All protein expression systems are reliant on the use of promoters which direct high-level expression of the gene of interest. A research group at the John Innes Centre (JIC), led by the world-renowned Professor George Lomonossoff, has developed the novel proprietary Hypertrans® system to allow high-level plant expression which is being further exploited at Leaf Expression Systems. Based on Cowpea mosaic virus (CPMV) the Hypertrans® system allows high-levels of expression and increased transcript stability, therefore enabling the efficient production of high levels of protein (up to 1.5 g per kg of leaf tissue). The Hypertrans® system has also been successfully used at Leaf Expression Systems to express several proteins, such as monoclonal antibodies for immunotherapy and virus-like particles (VLP) for vaccination.

Exciting developments in plant-based expression include the registration of plant expressed vaccines and have addressed previous scepticism regarding the ability to use plant-based technology where it can meet the regulatory requirements for pharmaceutical applications.
We work with companies and researchers as a contract development and manufacturing organisation. If you are interested in trying plant-based expression with your preferred protein or you would like to know more about the system used at Leaf Expression Systems, please get in touch with us.

References:
1. Hiatt A, Cafferkey R, Bowdish K. Production of antibodies in transgenic plants. Nature. 342(6245):76-8 (1989)
2. Mason HS, Lam DM, Arntzen CJ. Expression of hepatitis B surface antigen in transgenic plants. Proc Natl Acad Sci U S A. 89:11745-9 (1992)
3. Sainsbury F, Lavoie PO, D’Aoust MA, Vézina LP, Lomonossoff GP. Expression of multiple proteins using full-length and deleted versions of cowpea mosaic virus RNA-2. Plant Biotechnol J. 6:82-92 (2008)
4. Sparrow PA, Irwin JA, Dale PJ, Twyman RM, Ma JK. Pharma-Planta: road testing the developing regulatory guidelines for plant-made pharmaceuticals. Transgenic Res. 16:147-61 (2007)