Putting the Spotlight Back on Plant Suspension Cultures

Abstract

Plant cell suspension cultures have several advantages that make them suitable for the production of recombinant proteins. They can be cultivated under aseptic conditions using classical fermentation technology, they are easy to scale-up for manufacturing, and the regulatory requirements are similar to those established for well-characterized production systems based on microbial and mammalian cells. It is therefore no surprise that taliglucerase alfa (Elelyso®)—the first licensed recombinant pharmaceutical protein derived from plants—is produced in plant cell suspension cultures. But despite this breakthrough, plant cells are still largely neglected compared to transgenic plants and the more recent plant-based transient expression systems. Here, we revisit plant cell suspension cultures and highlight recent developments in the field that show how the rise of plant cells parallels that of Chinese hamster ovary cells, currently the most widespread and successful manufacturing platform for biologics. These developments include medium optimization, process engineering, statistical experimental designs, scale-up/scale-down models, and process analytical technologies. Significant yield increases for diverse target proteins will encourage a gold rush to adopt plant cells as a platform technology, and the first indications of this breakthrough are already on the horizon.

CRISPR/Cas9‐mediated knockout of six glycosyltransferase genes in Nicotiana benthamiana for the production of recombinant proteins lacking β‐1,2‐xylose and core α‐1,3‐fucose

“…plant N‐glycans lack sialic acid and core α‐1,6‐fucose residues, but β‐1,2‐xylose and core α‐1,3‐fucose are present (Lerouge et al ., ). The potential immunogenicity of the plant‐specific N‐glycans has been discussed extensively in the context of molecular farming (Bardor et al ., ; Gomord et al ., ; Shaaltiel and Tekoah, ), and although there are no conclusive data questioning the safety of plant‐made pharmaceuticals (Gomord et al ., ; Rup et al ., ; Santos et al ., ; Tekoah et al ., ; Ward et al ., ), their elimination is desirable to produce glycoproteins lacking non‐human epitopes.…”

Inactivation of the β(1,2)-xylosyltransferase and the α(1,3)-fucosyltransferase genes in Nicotiana tabacum BY-2 Cells by a Multiplex CRISPR/Cas9 Strategy Results in Glycoproteins without Plant-Specific Glycans

“…Plant specific glycans, especially β(1,2)-xylose and α(1,3)-fucose, have been for years a real hurdle for the regulatory approval of recombinant proteins expressed in plants (Santos et al, 2016). Here, we provide an expression platform that possesses all of the conditions to produce recombinant proteins under GMP with no regulatory issues.…”

“…On the negative side, plant cells still have a lower production rate (e.g., 30–100 mg IgG/ml; Vasilev et al, 2013; Magy et al, 2014) while CHO cells can produce more than 1 g/L (Kunert and Reinhart, 2016). However, the production in plant cells has not yet benefited from the long research history that characterizes animal cells and yield improvement can be expected at different levels such as fed-batch strategies, elite line selection, gene amplification, inhibition of proteolytic activity, medium optimization (Santos et al, 2016). …”

“…Plant cell cultures require a simple and inexpensive growth medium and proteins such as antibodies can be secreted in the extracellular medium, facilitating the purification step. Moreover, plant cells are grown in a contained bioreactor avoiding the regulatory issues encountered by whole plant production (Santos et al, 2016). …”

Rapid production of therapeutic proteins using plant system

“…Several plant species are used for suspension cultures; the most commonly used ones are the domestic crops including tobacco, rice, alfalfa, tomato and soybean. Among this tobacco cultivar bright yellow (BY-2) and Nicotianatobacum 1 (NT-1) are used for recombinant protein production 26,27 . The increased production of recombinant proteins in the cell suspension culture can be achieved by the use of a suitable promoter, signal sequence and a terminator.…”