Viability characterization of Taxus chinensis plant cell suspension cultures by rapid colorimetric- and image analysis-based techniques.

For the commercially established process of paclitaxel production with Taxus chinensis plant cell culture, the size of plant cell aggregates and phenotypic changes in coloration during cultivation have long been acknowledged as intangible parameters. So far, the variability of aggregates and coloration of cells are challenging parameters for any viability assay. The aim of this study was to investigate simple and non-toxic methods for viability determination of Taxus cultures in order to provide a practicable, rapid, robust and reproducible way to sample large amounts of material. A further goal was to examine whether Taxus aggregate cell coloration is related to general cell viability and might be exploited by microscopy and image analysis to gain easy access to general cell viability. The Alamar Blue assay was found to be exceptionally eligible for viability estimation. Moreover, aggregate coloration, as a morphologic attribute, was quantified by image analysis and found to be a good and traceable indicator of T. chinensis viability.

Chemical and biological characterization of vaccine adjuvant QS-21 produced via plant cell culture.

Many vaccines, including those using recombinant antigen subunits, rely on adjuvant(s) to enhance the efficacy of the host immune responses. Among the few adjuvants clinically approved, QS-21, a saponin-based immunomodulatory molecule isolated from the tree bark of Quillaja saponaria (QS) is used in complex formulations in approved effective vaccines. High demand of the QS raw material as well as manufacturing scalability limitation has been barriers here. We report for the first-time successful plant cell culture production of QS-21 having structural, chemical, and biologic, properties similar to the bark extracted product. These data ensure QS-21 and related saponins are broadly available and accessible to drug developers.

Moss-based production of asialo-erythropoietin devoid of Lewis A and other plant-typical carbohydrate determinants.

Protein therapeutics represent one of the most increasing areas in the pharmaceutical industry. Plants gain acceptance as attractive alternatives for high-quality and economical protein production. However, as the majority of biopharmaceuticals are glycoproteins, plant-specific N-glycosylation has to be taken into consideration. In Physcomitrella patens (moss), glyco-engineering is an applicable tool, and the removal of immunogenic core xylose and fucose residues was realized before. Here, we present the identification of the enzymes that are responsible for terminal glycosylation (α1,4 fucosylation and ß1,3 galactosylation) on complex-type N-glycans in moss. The terminal trisaccharide consisting of α1,4 fucose and ß1,3 galactose linked to N-acetylglucosamine forms the so-called Lewis A epitope. This epitope is rare on moss wild-type proteins, but was shown to be enriched on complex-type N-glycans of moss-produced recombinant human erythropoietin, while unknown from the native human protein. Via gene targeting of moss galactosyltransferase and fucosyltransferase genes, we identified the gene responsible for terminal glycosylation and were able to completely abolish the formation of Lewis A residues on the recombinant biopharmaceutical.

Chromosomal high mobility group (HMG) proteins of the HMGB-type occurring in the moss Physcomitrella patens.

High mobility group (HMG) proteins of the HMGB family are chromatin-associated proteins that act as architectural factors in nucleoprotein structures, which regulate DNA-dependent processes including transcription. Members of the HMGB family have been characterised from various mono-and dicot plants, but not from lower plant species. Here, we have identified three candidate HMGB proteins encoded in the genome of the moss Physcomitrella patens. The structurally similar HMGB2 and HMGB3 proteins display the typical overall structure of higher plant HMGB proteins consisting of a central HMG-box DNA-binding domain that is flanked by a basic N-terminal and an acidic C-terminal domain. The HMGB1 protein differs from higher plant HMGB proteins by having a very extensive N-terminal domain and by lacking the acidic C-terminal domain. Like higher plant HMGB proteins, HMGB3 localises to the cell nucleus, but HMGB1 is targeted to plastids. Analysis of the HMG-box domains of HMGB1 and HMGB3 by CD revealed that HMGB1box and the HMGB3box have an alpha-helical structure. While the HMGB3box interacts with DNA comparable to typical higher plant counterparts, the HMGB1box has only a low affinity for DNA. Cotransformation assays in Physcomitrella protoplasts demonstrated that expression of HMGB3 resulted in repression of reporter gene expression. In summary, our data show that functional HMGB-type proteins occur in Physcomitrella and most likely in other lower plant species.

Physcomitrella HMGA-type proteins display structural differences compared to their higher plant counterparts.

High mobility group (HMG) proteins of the HMGA family are chromatin-associated proteins that act as architectural factors in nucleoprotein structures involved in gene transcription. To date, HMGA-type proteins have been studied in various higher plant species, but not in lower plants. We have identified two HMGA-type proteins, HMGA1 and HMGA2, encoded in the genome of the moss model Physcomitrella patens. Compared to higher plant HMGA proteins, the two Physcomitrella proteins display some structural differences. Thus, the moss HMGA proteins have six (rather than four) AT-hook DNA-binding motifs and their N-terminal domain lacks similarity to linker histone H1. HMGA2 is expressed in moss protonema and it localises to the cell nucleus. Typical of HMGA proteins, HMGA2 interacts preferentially with A/T-rich DNA, when compared with G/C-rich DNA. In cotransformation assays in Physcomitrella protoplasts, HMGA2 stimulated reporter gene expression. In summary, our data show that functional HMGA-type proteins occur in Physcomitrella.

Compensation of endogenous IgG mediated inhibition of antibody-dependent cellular cytotoxicity by glyco-engineering of therapeutic antibodies.

A major limitation to the application of therapeutic IgG antibodies (Abs) is their reduced in vivo efficacy compared to their high efficacy as measured in vitro. Recently, Preithner et al. showed that the high amount of endogenous serum IgG impairs the antibody-dependent cellular cytotoxicity effector function (ADCC) of therapeutic Abs in vivo by competing for binding to Fcgamma-RIII on the effector cells. Modification of the glycosylation moieties attached to the Fc part of the Ab, e.g. de-fucosylation, has been shown to increase ADCC activity. We here show that the ADCC activity of a fucose-deficient, moss-produced therapeutic IgG is not impaired by normal human serum. The increased ADCC activity of the fucose-deficient Ab variant even in the presence of high endogenous IgG indicates that glyco-engineering of Abs may translate into improved clinical efficacy. Noteworthy, moss production of glyco-modified Abs should be applicable to a broad variety of therapeutic Abs currently in use indicative for the potential of this technology platform.

High-level expression of secreted complex glycosylated recombinant human erythropoietin in the Physcomitrella Delta-fuc-t Delta-xyl-t mutant.

The highly glycosylated peptide hormone erythropoietin (EPO) plays a key role in the regulation of erythrocyte maturation. Currently, marketed EPO is produced by recombinant technology in mammalian cell cultures. The complementary DNA (cDNA) for human EPO (hEPO) was transiently and stably expressed in the moss Physcomitrella patens wild-type and Delta-fuc-t Delta-xyl-t mutant, the latter containing N-glycans lacking the plant-specific, core-bound alpha1,3-fucose and beta1,2-xylose. New expression vectors were designed based on a Physcomitrella ubiquitin gene-derived promoter for the expression of hEPO cDNA. Transient expression in protoplasts was much stronger at 10 than at 20 degrees C. In Western blot analysis, the molecular size of moss-produced recombinant human EPO (rhEPO) was identified to be 30 kDa, and it accumulated in the medium of transiently transformed protoplasts to high levels around 0.5 microg/mL. Transgenic Physcomitrella Delta-fuc-t Delta-xyl-t mutant lines expressing EPO cDNA showed secretion of rhEPO through the cell wall to the culture medium. In 5- and 10-L photobioreactor cultures, secreted rhEPO accumulated to high levels above 250 microg/g dry weight of moss material after 6 days. Silver staining of rhEPO on sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) taken from the bioreactor culture demonstrated a high purity of the over-expressed secreted rhEPO, with a very low background of endogenous moss proteins. Peptide mapping of rhEPO produced by the Physcomitrella Delta-fuc-t Delta-xyl-t mutant indicated correct processing of the plant-derived signal peptide. All three N-glycosylation sites of rhEPO were occupied by complex-type N-glycans completely devoid of the plant-specific core sugar residues fucose and xylose.

Use of endogenous signal sequences for transient production and efficient secretion by moss (Physcomitrella patens) cells.

BACKGROUND: Efficient targeting to appropriate cell organelles is one of the bottlenecks for the production of recombinant proteins in plant systems. A common practice is to use the native secretory signal peptide of the heterologous protein to be produced. Though general features of secretion signals are conserved between plants and animals, the broad sequence variability among signal peptides suggests differing efficiency of signal peptide recognition. RESULTS: Aiming to improve secretion in moss bioreactors, we quantitatively compared the efficiency of two human signal peptides and six signals from recently isolated moss (Physcomitrella patens) proteins. We therefore used fusions of the different signals to heterologous reporter sequences for transient transfection of moss cells and measured the extra- and intracellular accumulation of the recombinant proteins rhVEGF and GST, respectively. Our data demonstrates an up to fivefold higher secretion efficiency with endogenous moss signals compared to the two utilised human signal peptides. CONCLUSION: From the distribution of extra- and intracellular recombinant proteins, we suggest translational inhibition during the signal recognition particle-cycle (SRP-cycle) as the most probable of several possible explanations for the decreased extracellular accumulation with the human signals. In this work, we report on the supremacy of moss secretion signals over the utilised heterologous ones within the moss-bioreactor system. Though the molecular details of this effect remain to be elucidated, our results will contribute to the improvement of molecular farming systems.

Enhanced recovery of a secreted recombinant human growth factor using stabilizing additives and by co-expression of human serum albumin in the moss Physcomitrella patens.

The production of pharmaceutical proteins in plants provides a valuable alternative to other traditional eukaryotic expression systems from economic and safety perspectives. The moss Physcomitrella patens allows the expression and secretion of complex target proteins into a simple aqueous maintenance medium, which facilitates downstream processing by rendering it less complex. To address the question of whether the addition of protein-stabilizing substances enhances the recovery of a target protein secreted into the culture medium, several additives at different concentrations were tested in a small-scale screening system. Although polyvinylpyrrolidone (PVP) and human serum albumin (HSA) showed a significant impact on protein levels, supplementation of the medium with these substances was accompanied by certain limitations in upstream processes, such as foam formation (HSA), and in downstream processes, such as reduced binding efficiency on chromatography columns (PVP), respectively. In order to reap the benefit of the enhancing effect and to avoid the given negative aspects, we developed a new strategy based on the recombinant expression of HSA in plants that are already capable of expressing a target protein. First, we analysed the expression and secretion of recombinant HSA in transiently and stably transformed wild-type (WT) plants. HSA was then co-expressed in Physcomitrella plants transgenic for human vascular endothelial growth factor (VEGF). Even with high expression levels of recombinant human VEGF (rhVEGF), the co-expression of recombinant HSA (rHSA) resulted in 48%-102% higher recovery of the target protein without concomitant negative effects on the upstream process. This strategy enables the enhanced recovery of target protein and does not require the addition of foreign components directly to the culture medium.

A fast and flexible PEG-mediated transient expression system in plants for high level expression of secreted recombinant proteins.

Plant expression systems offer a valuable alternative to traditional systems for the production of recombinant biopharmaceuticals. A highly efficient polyethyleneglycol (PEG)-mediated transient expression system for secreted recombinant proteins in plants has been developed. The human vascular endothelial growth factor 121 (rhVEGF) has been successfully expressed and efficiently secreted into the culture medium by transiently transformed moss protoplasts. In order to obtain secretion efficiency data, different expressed signal peptides were analysed and time course studies were performed with expression constructs containing different promoters. The transformation procedure was optimised for high level expression (up to 10 microg/ml) and successfully performed even with a transgenic glyco-engineered strain lacking plant-specific immunogenic sugar residues in N-glycans. The amount of rhVEGF was produced in such quantity that it allowed for the analysis of biological activity, silver-staining and Western blotting, revealing the correct formation and processing of the homodimer. This fast and flexible transient expression system enables feasibility studies and construct optimisation to be concluded within a few days, thus avoiding the time consuming step of having to generate stably transformed lines.

A large plant beta-tubulin family with minimal C-terminal variation but differences in expression.

Tubulins, as the major structural component of microtubules (MT), are highly conserved throughout the entire eukaryotic kingdom. They consist of alpha/beta heterodimers. Both monomers, at least in multicellular organisms, are encoded by gene families. In higher plants up to eight beta-tubulin isotypes, mostly differing in their very C-termini, have been described. These variable beta-tubulin C-termini have been discussed in the context of functional microtubule diversity. However, in plants, in contrast to vertebrates, functional isotype specificity remains yet to be demonstrated. Unlike higher plants, unicellular green algae in general do not exhibit isotypic variations. The moss Physcomitrella patens is a phylogenetic intermediate between higher plants and green algae. We isolated six beta-tubulin genes from Physcomitrella, named PpTub1 to 6. We show that the exon/intron structure, with the exception of one additional intron in PpTub6, is identical with that of higher plants, and that some members of the family are differentially expressed. Moreover, we find that all Physcomitrella isotypes are highly conserved and, most strikingly, are almost identical within their C-terminal amino acids (aa). This evolutionary ancient and large beta-tubulin gene family without significant isotypic sequence variation points to a role of differential regulation in the evolution of plant tubulin isotypes.

Targeted knockouts of Physcomitrella lacking plant-specific immunogenic N-glycans.

Using plants as production factories for therapeutic proteins requires modification of their N-glycosylation pattern because of the immunogenicity of plant-specific sugar residues. In an attempt towards such humanization, we disrupted the genes for alpha1,3-fucosyltransferase and beta1,2-xylosyltransferase in Physcomitrella patens by homologous recombination. The single Deltafuc-t and Deltaxyl-t plants, as well as the double knockout, lacked transcripts of the corresponding genes, but did not differ from the wild-type moss in morphology, growth, development, and ability to secrete a recombinant protein, the human vascular endothelial growth factor VEGF(121), into the culture medium. N-Glycan analysis, however, revealed the absence of 1,3-fucosyl and/or 1,2-xylosyl residues, respectively. Therefore, the modifications described here represent the key step towards the generation of moss lines suitable for the production of plant-made glycosylated biopharmaceuticals with nonallergenic N-glycans.

Effects of the phosphodiesterase 4 inhibitors SB 207499 and AWD 12-281 on the inflammatory reaction in a model of allergic dermatitis.

The inhibitors of the phosphodiesterase 4, SB 207499 (cilomilast, c-4-cyano-4-(3-cyclopentyloxy-4-methoxy-phenyl)-r-L-cyclohexane carboxylic acid) and AWD 12-281 (N-(3,5-dichloropyrid-4-yl)-[1-(4-fluorobenzyl)-5-hydroxy-indole-3-yl]-glyoxylic acid amide) were tested in a model of allergic dermatitis in mice. To obtain an allergic dermatitis, BALB/c mice were sensitized to toluene-2,4-diisocyanate. The allergic reaction was challenged by topical administration of toluene-2,4-diisocyanate onto the mice ears. Before challenge, two groups of mice were treated topically (ear skin) with SB 207499 or AWD 12-281. There was a significant ear swelling in toluene-2,4-diisocyanate-challenged mice ears 4, 8, 16, 24 and 48 h after challenge. SB 207499 and AWD 12-281 inhibited this swelling significantly 8, 16, 24 and 48 h after the challenge. For biochemical parameters and histology, ears were sampled from mice sacrificed 4, 8 and 16 h after the challenge. In homogenized tissue, SB 207499 and AWD 12-281 inhibited significantly the secretion of interleukin 1beta induced by toluene-2,4-diisocyanate 4 and 8 h after challenge. The cell influx (granulocytes) observed in the toluene-2,4-diisocyanate-challenged mice 8 and 16 h after challenge was nearly abolished by AWD 12-281 and SB 204799.

AWD 12-281, a highly selective phosphodiesterase 4 inhibitor, is effective in the prevention and treatment of inflammatory reactions in a model of allergic dermatitis.

AWD 12-281 (N-(3,5-dichloro-4-pyridinyl)-2-[1-(4-fluorobenzyl)-5-hydroxy-1H-indol-3-yl]-2-oxoacetamide), a phosphodiesterase 4 inhibitor, which is optimized for topical administration, was tested in a model of allergic dermatitis in mice. To obtain an allergic dermatitis, BALB/c mice were sensitized to toluene-2,4-diisocyanate (TDI). The allergic reaction was challenged by topical administration of TDI onto the mice ears. AWD 12-281 was tested for its anti-inflammatory potential by oral, intraperitoneal and topical administration. The phosphodiesterase 4 inhibitor, cilomilast (SB 207499), and/or the corticosteroid, diflorasone diacetate, were used as reference compounds. Given orally and intraperitoneally 2 h before as well as 5 and 24 h after TDI challenge, AWD 12-281 showed no, or only a transient inhibition of the allergen-induced ear swelling, whereas cilomilast significantly inhibited this ear swelling. Applied topically onto the ears before TDI challenge, AWD 12-281, cilomilast and diflorasone diacetate caused total inhibition of ear swelling 24 h after challenge, confirmed by a decrease of the pro-inflammatory cytokines interleukin-4, interleukin-6 and macrophage inhibitory protein-2. Administered topically after TDI challenge as therapeutic intervention, AWD 12-281 and diflorasone diacetate caused significant inhibition of ear swelling; cilomilast failed to do so. These results indicate that topically administered AWD 12-281 may be potent in the prevention and treatment of allergic/inflammatory skin diseases.

Correlation of ADCC activity with cytokine release induced by the stably expressed, glyco-engineered humanized Lewis Y-specific monoclonal antibody MB314.

A major limitation to the application of therapeutic monoclonal antibodies (mAbs) is their reduced in vivo efficacy compared with the high efficacy measured in vitro. Effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) are dramatically reduced in vivo by the presence of high amounts of endogenous IgG in the serum. Recent studies have shown that modification of the glycosylation moieties attached to the Fc part of the mAb can enhance binding affinity to FcγRIIIα receptors on natural killer cells and thus may counteract the reduced in vivo efficacy. In the present study, a humanized IgG1/κ monoclonal antibody recognizing the tumor-associated carbohydrate antigen Lewis Y was stably produced in a moss expression system that allows glyco-engineering. The glyco-modified mAb (designated MB314) showed a highly homogeneous N-glycosylation pattern lacking core-fucose. A side-by-side comparison to its parental counterpart produced in conventional mammalian cell-culture (MB311, formerly known as IGN311) by fluorescence-activated cell sorting analysis confirmed that the target specificity of MB314 is similar to that of MB311. In contrast, ADCC effector function of MB314 was increased up to 40-fold whereas complement dependent cytotoxicity activity was decreased 5-fold. Notably, a release of immunostimulatory cytokines, including interferon γ, monocyte chemotactic protein-1 (MCP-1), interleukin-6 and tumor necrosis factor (TNF) was particularly induced with the glyco-modified antibody. TNF release was associated with CD14 (+) cells, indicating activation of monocytes.

In vivo glyco-engineered antibody with improved lytic potential produced by an innovative non-mammalian expression system.

Recent studies have demonstrated that the reduction of the core fucosylation on N-glycans of human IgGs is responsible for a clearly enhanced antibody-dependent cellular cytotoxicity (ADCC). This finding might give access to improved active therapeutic antibodies. Here, the expression of the tumor antigen-specific antibody IGN311 was performed in a glyco-optimized strain of the moss Physcomitrella patens. Removal of plant specific N-glycan structures in this plant expression host was achieved by targeted knockout of corresponding genes and included quantitative elimination of core fucosylation. Antibodies transiently expressed and secreted by such genetically modified moss protoplasts assembled correctly, showed an unaltered antigen-binding affinity and, in extensive tests, revealed an up to 40-fold enhanced ADCC. Thus, the glyco-engineered moss-based transient expression platform combines a rapid technology with the subsequent analysis of glycooptimized therapeutics with regard to advanced properties.

Use of Physcomitrella patens actin 5' regions for high transgene expression: importance of 5' introns.

We have isolated four actin (Act) genes from Physcomitrella patens and used their corresponding 5' regions for recombinant expression of the human vascular endothelial growth factor (rhVEGF121) in transiently transformed Physcomitrella protoplasts and in stable transformed lines. In the transient system, we found up to 11-fold activity of the corresponding 5' regions as compared with that of the plant constitutive 35S promoter. Moreover, the use of an optimised expression vector in which the human VEGF signal peptide was exchanged with a plant signal peptide resulted in an additional 7-fold increase in secreted rhVEGF. We found that the 5' introns of PpAct1, PpAct5 and PpAct7 are essential for high expression. The enhancing mechanisms of the introns, however, seem to be different since in the case of PpAct1, the expression level is stimulated only in the presence of the endogenous promoter, whereas the 5' introns of PpAct5 and PpAct7 stimulate expression also in combination with the 35S promoter. Beyond this, the isolated 5' regions are shown to be useful for high expression levels in transgenic moss lines with values of secreted rhVEGF up to 96 microg g(-1) dry weight.

Isolation and characterisation of three moss-derived beta-tubulin promoters suitable for recombinant expression.

The moss Physcomitrella patens is an excellent tool to study plant gene-function relationships due to its high rate of homologous recombination (HR). It has also been shown to be very useful in the production of recombinant proteins which are secreted into a simple medium. Thus, there is a need for suitable promoters functional in this well established model organism. We isolated genomic flanking regions of the beta-tubulin gene family from Physcomitrella, concentrating on those family members showing high transcript abundance integrated over gametophytic tissues. Using a novel, fast and reliable quantification assay based on the transient expression and secretion of a recombinant human protein, three genomic upstream regions were characterised in serial deletion constructs. Expression rates were up to three times higher than those obtained with the 35S cauliflower mosaic virus (35S) promoter, which served as a reference.