BIOTECHNOLOGY production via The moss has a number of unique properties which make it superior to other cell systems – animal cells, higher plants, bacteria, fungi – in the production of .

Dr Sabrina Wagner, greenovation

urrent production of complex biopharmaceuti- time (for example, several months of cultivation) Ccals relies mainly on animal cell systems such as and is highly homogeneous since it is composed the CHO-cell. Plant systems show major safety and of only two cell types. The moss bioreactor has cost advantages over processes based on animal cells, further unique properties: but differences in glycosylation as well as environmen- tal release are factors that may give rise to concerns. • The moss tolerates humanisation of the glycosyla- Moss tissue can be cultivated in liquid culture and, as tion pattern through homologous recombination, Time-to-market such, cultivation is achieved in a contained system. • Time-to-market is comparable with traditional is comparable Glycosylation patterns on proteins produced in systems. A transient expression system allows with traditional can be engineered to be ‘human-like’. Thus, feasibility studies to be undertaken, and stable systems. A transient the moss bioreactor as a contained plant tissue-based production strain development takes only four expression system cultivation system combines the best of two worlds. to six months, allows feasibility greenovation’s moss bioreactor is based on the • Cultivation in suspension allows for the scale-up of studies to be fermentation of moss protonema (Figure 1). This moss photobioreactors up to several 1000 L, and undertaken, and fully differentiated tissue is extremely stable over • Through phototrophic cultivation, a simple stable production medium can be utilised which is non-hazard- Figure 1 Moss protonema. strain development ous. This, in combination with secretion of takes only four to six the heterologous protein of interest, greatly months... facilitates downstream processing.

Proof of concept The moss, , has been a for physiological and genetic research for more than 30 years. Much EST (expressed sequence tag) data are available on the internet and in various publications. Physcomitrella patens hhasas a ccomparativelyomparatively small genome (511 mbp) and it is a haploid organism. For proof of concept purposes, Physcomitrella was transformed to express human VEGF (vascular endothelial growth factor); production and secretion

56 Innovations in Pharmaceutical Technology BIOTECHNOLOGY

Figure 2 WesternWestern blot analysis under non-reducing fucosyl-1,6-residue in plants. No pharmacokinetic conditionsconditions ofof mossderivedmossderived transientlytransiently expressedexpressed effects are related to this sugar residue, so no aller- rhVEGF with different leader peptides: 1) Control 5ng, 2) 10ng, 3, 4) Different leader peptide. genic potential is expected as a result of this missing sugar residue. In addition, a decrease in the amount of this sugar residue signifi cantly increases antibody- dependent cellular cytotoxicity (ADCC) of recom- binant antibodies. It is concluded that this missing sugar in plants may prove to be an advantage. Terminal galactose residues are not usually asso- ciated with protein activity, but they may have a pharmacokinetic effect – and so the lack of these residues needs to be engineered. Should the galac- tose residue be relevant for the fi nal product, the of the functional protein was shown. VEGF is a gly- appropriate galactosyltransferase should be inserted. cosylated protein which is a homo-dimer linked by Galactose is available in the organism, so that this disulfi de bridges. The protein is correctly and com- single insertion is suffi cient to ensure galactosyla- pletely assembled in Physcomitrella (Figure(Figure 2).2). tion. Data from higher plants have shown that this modifi cation has no infl uence on plant viability. Humanisation of the glycosylation pattern By carrying out these steps – that is, knock-out Compared with bacteria, mosses are far more com- of two plant-specifi c transferases and insertion of plex organisms and display more sophisticated post- one new transferase – the engineered moss tissue translational modifi cation capabilities. Because of is able to attach a glycosylation pattern to the anti- the inherent limitations of bacterial and mycotic body protein of interest typical for the production systems, many proteins cannot be expressed in such of monoclonal antibodies. organisms in a functional form. Glycosylation patterns in mosses are the same Time-to-market as for the higher plants. This means that the core Time-to-market for biopharmaceuticals produced structure of N-glycosylation is identical to the typical via the moss bioreactor is comparable with tradi- bi-antennary structure found in animal cell fermen- tional systems. A transient expression system allows tation systems. The differences are two additional feasibility studies to be undertaken, and stable pro- plant-specifi c residues and the lack of terminal galac- duction strain development does not require cross- tose residues. The additional beta 1-2 linked xylosyl- ing steps or the regeneration of whole plants. and alpha 1-3 linked fucosyl-residues found in plants The transient system is based on transformation of are generally associated with an allergenic potential. moss protoplasts (Figure 3); the system enables pro- Removal of these residues is therefore relevant, espe- duction of milligram quantities for feasibility studies cially for parentally administered drugs. within several weeks. Protoplasts are obtained from Moss is the only Moss is the only known plant system which protonema cultures and cultured in 96-well-plates for known plant system shows a high frequency of homologous recombina- 96 hours producing signifi cant amounts of the protein which shows a tion. This attribute allows for targeted gene insertion of interest. Cultivation in 96-well-plates also allows high frequency leading to the stable integration of foreign gene(s). for automation of major elements of the process. of homologous Another important aspect of the moss system is that Production of a stable expression strain takes recombination. This it can be manipulated to make targeted gene knock- four to six months. This process also leads to strains attribute allows outs. Homologous recombination is therefore a containing multiple copies of the heterologous gene, for targeted gene highly attractive tool for production strain design. so that the optimal production strain can be directly insertion leading The xylosyl- and fucosyl-transferases can be selected from a fi rst pool of transformants. to the stable knocked out resulting in removal of these sugar integration of residues, as confi rmed by Maldi-TOF analysis. Figure 3 Moss protoplasts. foreign gene(s) Through this, the plant-specifi c glycosylation pat- tern is manipulated while retaining glycosylation pat- terns that are highly similar to those found in animal cells. Major parts of this work have been performed in cooperation with Professor Reski at the University of Freiburg (Germany). These knock-out mutants have been analysed at the physiological level and also for the secretion of heterologous proteins. No dif- ferences could be found relative to moss strains with a wild-type glycosylation pattern. Another difference in plant glycosylation patterns, as compared with animal structures, is the lack of a

58 Innovations in Pharmaceutical Technology BIOTECHNOLOGY

corresponds to the yield of a typical fed-batch culture system over 20 days of 600 mg per litre. The typical process for the moss bioreactor will be a perfusion sys- tem, since the moss system is stable for long periods of time (>180 days). The risk of contamination with the moss system is extremely low. Further increases in yield will be achieved by the optimisation of production strains for specifi c proteins. As downstream processing involves few purifi cation steps, yield loss downstream is reduced compared with animal cell systems.

Safety profi le Moss is photo-autotrophic and therefore only requires a very simple compared with the complex media needed for animal cell systems. Costs are thus reduced and media contamination risks are minimised. There are no moss viruses known and there are no known plant viruses that could be pathogenic to humans. Antibiotics are not needed for the cultivation of transgenic moss. Transgenes are integrated into the genome and contamination of the medium is highly Figure 4 Pilot reactor. improbable. Thus, the risk of having trace amounts of antibiotic residues present in the fi nal product is avoided. Scale-up Furthermore, in this contained system, there is no need to The moss bioreactor is based on cultivation of the address environmental issues that may be connected with moss, Physcomitrella patens, in a fermenter. The moss the release of transgenic plants into the environment. protonema is grown under photo-autotrophic condi- tions in a medium which consists essentially of water Dr Sabrina Wagner is and minerals. Light and carbon dioxide serve as the co-founder and CEO only energy and carbon sources. of greenovation. After Cultivation in suspension allows scale-up of the her biological studies, photo-bioreactors up to several 1000 L. Development she started working of the bioreactor is based on the adaptation of existing in the pharmaceutical technology for large-scale cultivation of algae, which industry in various is established in volumes of up to 30,000 L. A pilot marketing and sales reactor of 30 L volume (Figure 4) has been developed positions with the in cooperation with Professor Posten at the Technical companies Lederle University of Karlsruhe, (Germany). GmbH, Asche AG and medac GmbH. Downstream processing As Head of Export and Business Development for The moss secretes heterologous proteins into the Apogepha GmbH in Dresden, she was responsible medium. Transit peptides, that target the heterologous for international marketing and sales of Apogepha proteins for secretion, can be either of human origin or products, as well as for all in- and out-licensing agree- The yield of from other sources. During the processing in the ER ments for national and international marketing. In heterologous the transit peptides are cleaved from the protein. this position, she developed Apogepha’s national protein – using Downstream processing then involves purifi cation portfolio and international marketing strategies. She the model protein, of the protein from the low-salt medium, and therefore then worked independently in Dresden (Germany) as human VEGF – was involves only a few purifi cation steps. Ion exchange a consultant in business development and worldwide expected to reach chromatography will be a suitable fi rst purifi cation step marketing and sales for fi ne chemicals in PET diag- 30 mg per litre per for most proteins. The moss also tolerates a pH of the nostics produced by ABX GmbH (Dresden). day by the fourth culture medium within the range of 4 to 8; this allows quarter of 2003; this adaptation of the conditions to be optimal for the stabil- Note: greenovation Biotech GmbH is a privately-held corresponds to the ity and purifi cation of the specifi c biopharmaceutical. biotechnology company based in Freiburg, Germany. yield of a typical fed- Venture capital investors are Mediport Venture, Berlin, batch culture system Yield and the L-EA and Seed, Karlsruhe. Incorporated in 1999, over 20 days of 600 The yield of heterologous protein – using the model greenovation now has 22 employees. The company’s mg per litre protein, human VEGF – was expected to reach 30 mg business model is dependent on production strain devel- per litre per day by the fourth quarter of 2003; this opment in cooperation with pharmaceutical companies.

60 Innovations in Pharmaceutical Technology