Recombinant protein production by transient gene expression in plants provides an adaptable, robust and cost-effective alternative to some of the more traditional and established methods such as cell-based microbial and eukaryotic production platforms. Major advantages are that plant-based production is now easily scaled and time efficient1. Generating expression constructs is rapid and initial testing of new target pharmaceuticals, or related proteins, is particularly cost-effective as results can be obtained from a small number of plants within just a few weeks.
Once a pilot study has delivered the desired expression results, production can be readily scaled up to the required demand simply by increasing the number of plants grown within controlled conditions. This avoids the lengthy and cost intensive optimisation, common in fermenter-based cell systems. Nicotiana benthamiana, a relative of the tobacco plant, is well established as a bioreactor for transient expression of proteins. It is easy to cultivate and produces high yields of biomass in a short period of time; sowing to harvest typically takes just 6 weeks.
The use of controlled growth rooms or greenhouses offers further advantages to plant-based protein expression. What has been produced on a lab-scale can easily be adapted to accommodate larger scale requirements and production capacity can reach millions of plants yielding kg of the desired product. This has been demonstrated by several companies such as Medicago and Kentucky BioProcessing, and more recently with the setup of the Caliber facility in Texas, US1. The Caliber biotherapeutics-producing plant was set up in 2015 and is one of the largest worldwide plant-based production facilities capable of producing a weekly output of 3500kg plant biomass and foresees annual yields of over 150kg purified product.
Leaf Expression Systems: Plant Production and Quality Assurance
Parameters such as light2, nutrients3 and temperature4 are crucial factors for efficient growth and yield of product. Developmental work at Leaf Expression Systems is being carried out to further understand these impacts. All plant production at Leaf Expression Systems is contained under controlled environment conditions using state of the art technology consisting of four large walk-in controlled environment rooms (CERs) and eight smaller controlled environment chambers (CECs). All plant growth parameters can be monitored constantly ensuring optimal conditions and maintaining reproducible quality conditions. Humidity and temperature parameters can also be tightly controlled for reproducibility and special attention has also been paid to the right light installation for the ideal conditions.
All CECs and CERs are equipped with modern LED technology. LEDs, compared to conventional lighting systems such as fluorescent light, are far more energy efficient and environmentally friendly5 and also enable consistent growth conditions. In addition, day and night length can be controlled individually within each of the 12 units further enabling production demand. You can take a closer look at our CERs in this video.
Agroinfiltration-based gene delivery into plants and subsequent production of pharmaceutical, other proteins or high-value metabolites holds exciting potential6 as scalaeble technology. With the combination of large walk-in growth rooms and smaller plant growth chambers, Leaf Expression Systems has the unique opportunity to optimise the growing conditions for each product and maximise expression yield within the plants. This then enables rapid scale-up by growing more plants, whilst ensuring quality assurance around product segregation and that customers products are appropriately controlled at all times avoiding any risk of cross contamination.
- Holtz, B. R. et al. Commercial-scale biotherapeutics manufacturing facility for plant-made pharmaceuticals. Plant Biotechnol. J. 13, 1180–1190 (2015).
- Matsuda, R., Abe, T. & Fujiwara, K. Viral vector-based transient gene expression in Nicotiana benthamiana: effects of light source on leaf temperature and hemagglutinin content. Plant Cell Rep. 36, 1667–1669 (2017).
- Fujiuchi, N., Matsuda, R., Matoba, N. & Fujiwara, K. Effect of nitrate concentration in nutrient solution on hemagglutinin content of Nicotiana benthamiana leaves in a viral vector-mediated transient gene expression system. Plant Biotechnol. 31, 207–211 (2014).
- Matsuda, R., Abe, T., Fujiuchi, N., Matoba, N. & Fujiwara, K. Effect of temperature post viral vector inoculation on the amount of hemagglutinin transiently expressed in Nicotiana benthamiana leaves. J. Biosci. Bioeng. 124, 346–350 (2017).
- Zhang, H., Burr, J. & Zhao, F. A comparative life cycle assessment (LCA) of lighting technologies for greenhouse crop production. J. Clean. Prod. 140, 705–713 (2017).
- Huafang Lai, Q. C. & Jake Stahnke, J. H. Agroinfiltration as an Effective and Scalable Strategy of Gene Delivery for Production of Pharmaceutical Proteins. Adv. Tech. Biol. Med. 1, (2013).