Production of different glycosylation variants of the tumour-targeting mAb H10 in Nicotiana benthamiana: influence on expression yield and antibody degradation

Heterologous expression of fungal L-asparaginase: a systematic review

Aim: To review the available literature about heterologous expression of fungal L-asparaginase (L-ASNase). Materials & methods: A search was conducted across PubMed, Science Direct, Scopus and Web of Science databases; 4172 citations were identified and seven articles were selected. Results: The results showed that heterologous expression of fungal L-ASNase was performed mostly in bacterial expression systems, except for a study that expressed L-ASNase in a yeast system. Only three publications reported the purification and characterization of the enzyme. Conclusion: The information reported in this systematic review can contribute significantly to the recognition of the importance of biotechnological techniques for L-ASNase production.

Recombinant N-glycosylation isoforms of Legume lectins: Production and purification from Nicotiana benthamiana leaves following RuBisCO depletion

An efficient purification of recombinant proteins often requires a high ratio of recombinant to host proteins. In plants, Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is the most abundant leaf protein, thus strongly impacting purification yield. Here, we describe a simple and robust purification procedure for recombinant proteins based on a differential precipitation of RuBisCO. In this context, four Legume lectin domains of Arabidopsis thaliana which belong to receptor-like kinases and cell wall proteins were produced from Nicotiana benthamiana leaves. The recombinant proteins exhibit a unique lectin domain consisting of around 250 amino acid residues with several predicted N-glycosylation sites and a six His-tag at the N-terminus. After ammonium sulphate precipitation of total soluble proteins, depletion of RuBisCO was obtained using citrate and succinate buffers during the salting-in step: this depletion was pH-dependent and the presence of di- or tri-carboxylic acids was required. The depleted protein extracts were then subjected to two chromatographic steps which were used in the negative mode to submit a protein fraction enriched as much as possible in recombinant lectin domains to a third chromatographic step (immobilized metal-ion chromatography). Three of the Legume lectin domains were purified near to homogeneity and revealed multiple N-glycosylation isoforms, particularly those from receptor-like kinases, which were characterised using specific lectins and deglycosylation enzymes. The production and purification of recombinant lectin domains will facilitate their biochemical characterisation in the context of cell-to-cell signalling and cell wall organisation.

The papain-like cysteine proteinases NbCysP6 and NbCysP7 are highly processive enzymes with substrate specificities complementary to Nicotiana benthamiana cathepsin B

The tobacco-related plant Nicotiana benthamiana is gaining interest as a versatile host for the production of monoclonal antibodies and other protein therapeutics. However, the susceptibility of plant-derived recombinant proteins to endogenous proteolytic enzymes limits their use as biopharmaceuticals. We have now identified two previously uncharacterized N. benthamiana proteases with high antibody-degrading activity, the papain-like cysteine proteinases NbCysP6 and NbCysP7. Both enzymes are capable of hydrolysing a wide range of synthetic substrates, although only NbCysP6 tolerates basic amino acids in its specificity-determining S2 subsite. The overlapping substrate specificities of NbCysP6 and NbCysP7 are also documented by the closely related properties of their other subsites as deduced from the action of the enzymes on proteome-derived peptide libraries. Notable differences were observed to the substrate preferences of N. benthamiana cathepsin B, another antibody-degrading papain-like cysteine proteinase. The complementary activities of NbCysP6, NbCysP7 and N. benthamiana cathepsin B indicate synergistic roles of these proteases in the turnover of recombinant and endogenous proteins in planta, thus representing a paradigm for the shaping of plant proteomes by the combined action of papain-like cysteine proteinases.

Production of a tumour-targeting antibody with a human-compatible glycosylation profile in N. benthamiana hairy root cultures

Hairy root (HR) cultures derived from Agrobacterium rhizogenes transformation of plant tissues are an advantageous biotechnological manufacturing platform due to the accumulation of recombinant proteins in an otherwise largely protein free culture medium. In this context, HRs descending from transgenic Nicotiana tabacum plants were successfully used for the production of several functional mAbs with plant-type glycans. Here, we expressed the tumor-targeting monoclonal antibody mAb H10 in HRs obtained either by infecting a transgenic N. tabacum line expressing H10 with A. rhizogenes or a glyco-engineered N. benthamiana line (ΔXTFT) with recombinant A. rhizogenes carrying mAb H10 heavy and light chain cDNAs. Selected HR clones derived from both plants accumulated mAb H10 in the culture medium with similar yields (2-3 mg/L). N-glycosylation profiles of antibodies purified from HR supernatant revealed the presence of plant-typical complex structures for N. tabacum-derived mAb H10 and of GnGn structures lacking xylose and fucose for the ΔXTFT-derived counterpart. Both antibody glyco-formats exhibited comparable antigen binding activities. Collectively, these data demonstrate that the co-infection of ΔXTFT Nicotiana benthamiana with recombinant A. rhizogenes is an efficient procedure for the generation of stable HR cultures expressing the tumor-targeting mAb H10 with a human-compatible glycosylation profile, thus representing an important step towards the exploitation of root cultures for the production of 'next generation' human therapeutic antibodies.

Site-specific proteolytic degradation of IgG monoclonal antibodies expressed in tobacco plants

Plants are promising hosts for the production of monoclonal antibodies (mAbs). However, proteolytic degradation of antibodies produced both in stable transgenic plants and using transient expression systems is still a major issue for efficient high-yield recombinant protein accumulation. In this work, we have performed a detailed study of the degradation profiles of two human IgG1 mAbs produced in plants: an anti-HIV mAb 2G12 and a tumour-targeting mAb H10. Even though they use different light chains (κ and λ, respectively), the fragmentation pattern of both antibodies was similar. The majority of Ig fragments result from proteolytic degradation, but there are only a limited number of plant proteolytic cleavage events in the immunoglobulin light and heavy chains. All of the cleavage sites identified were in the proximity of interdomain regions and occurred at each interdomain site, with the exception of the VL /CL interface in mAb H10 λ light chain. Cleavage site sequences were analysed, and residue patterns characteristic of proteolytic enzymes substrates were identified. The results of this work help to define common degradation events in plant-produced mAbs and raise the possibility of predicting antibody degradation patterns 'a priori' and designing novel stabilization strategies by site-specific mutagenesis.

Deletion of plant-specific sugar residues in plant N-glycans by repression of GDP-D-mannose 4,6-dehydratase and β-1,2-xylosyltransferase genes

Production of pharmaceutical glycoproteins, such as therapeutic antibodies and cytokines, in plants has many advantages in safety and reduced costs. However, plant-made glycoproteins have N-glycans with plant-specific sugar residues (core β-1,2-xylose and α-1,3-fucose) and a Lewis a (Le(a)) epitope, Galβ(1-3)[Fucα(1-4)]GlcNAc. Because it is likely that these sugar residues and glycan structures are immunogenic, many attempts have been made to delete them. Previously, we reported the simultaneous deletion of the plant-specific core α-1,3-fucose and α-1,4-fucose residues in Le(a) epitopes by repressing the GDP-D-mannose 4,6-dehydratase (GMD) gene, which is associated with GDP-L-fucose biosynthesis, in Nicotiana benthamiana plants (rGMD plants, renamed to ΔGMD plants) (Matsuo and Matsumura, Plant Biotechnol. J., 9, 264-281, 2011). In the present study, we generated a core β-1,2-xylose residue-repressed transgenic N. benthamiana plant by co-suppression of β-1,2-xylosyltransferase (ΔXylT plant). By crossing ΔGMD and ΔXylT plants, we successfully generated plants in which plant-specific sugar residues were repressed (ΔGMDΔXylT plants). The proportion of N-glycans with deleted plant-specific sugar residues found in total soluble protein from ΔGMDΔXylT plants increased by 82.41%. Recombinant mouse granulocyte/macrophage-colony stimulating factor (mGM-CSF) and human monoclonal immunoglobulin G (hIgG) harboring N-glycans with deleted plant-specific sugar residues were successfully produced in ΔGMDΔXylT plants. Simultaneous repression of the GMD and XylT genes in N. benthamiana is thus very useful for deleting plant-specific sugar residues.

Expression of human butyrylcholinesterase with an engineered glycosylation profile resembling the plasma-derived orthologue

Human butyrylcholinesterase (BChE) is considered a candidate bioscavenger of nerve agents for use in pre- and post-exposure treatment. However, the presence and functional necessity of complex N-glycans (i.e. sialylated structures) is a challenging issue in respect to its recombinant expression. Here we transiently co-expressed BChE cDNA in the model plant Nicotiana benthamiana with vectors carrying the genes necessary for in planta protein sialylation. Site-specific sugar profiling of secreted recombinant BChE (rBChE) collected from the intercellular fluid revealed the presence of mono- and di-sialylated N-glycans, which largely resembles to the plasma-derived orthologue. Attempts to increase that sialylation content of rBChE by the over-expression of an additional glycosylation enzyme that generates branched N-glycans (i.e. β1,4-N-acetylglucosaminyl-transferase IV), allowed the production of rBChE decorated with tri-sialylated structures (up to 70%). Sialylated and non-sialylated plant-derived rBChE exhibited functional in vitro activity comparable to that of its commercially available equine-derived counterpart. These results demonstrate the ability of plants to generate valuable proteins with designed sialylated glycosylation profiles optimized for therapeutic efficacy. Moreover, the efficient synthesis of carbohydrates present only in minute amounts on the native protein (tri-sialylated N-glycans) facilitates the generation of a product with superior efficacies and/or new therapeutic functions.

The human anti-HIV antibodies 2F5, 2G12, and PG9 differ in their susceptibility to proteolytic degradation: down-regulation of endogenous serine and cysteine proteinase activities could improve antibody production in plant-based expression platforms

The tobacco-related species Nicotiana benthamiana has recently emerged as a promising host for the manufacturing of protein therapeutics. However, the production of recombinant proteins in N. benthamiana is frequently hampered by undesired proteolysis. Here, we show that the expression of the human anti-HIV antibodies 2F5, 2G12, and PG9 in N. benthamiana leaves leads to the accumulation of discrete heavy chain-derived degradation products of 30-40 kDa. Incubation of purified 2F5 with N. benthamiana intercellular fluid resulted in rapid conversion into the 40-kDa fragment, whereas 2G12 proved largely resistant to degradation. Such a differential susceptibility to proteolytic attack was also observed when these two antibodies were exposed to various types of proteinases in vitro. While serine and cysteine proteinases are both capable of generating the 40-kDa 2F5 fragment, the 30-kDa polypeptide is most readily obtained by treatment with the latter class of enzymes. The principal cleavage sites reside within the antigen-binding domain, the VH -CH 1 linker segment and the hinge region of the antibodies. Collectively, these results indicate that down-regulation of endogenous serine and cysteine proteinase activities could be used to improve the performance of plant-based expression platforms destined for the production of biopharmaceuticals.

Generation of biologically active multi-sialylated recombinant human EPOFc in plants

Hyperglycosylated proteins are more stable, show increased serum half-life and less sensitivity to proteolysis compared to non-sialylated forms. This applies particularly to recombinant human erythropoietin (rhEPO). Recent progress in N-glycoengineering of non-mammalian expression hosts resulted in in vivo protein sialylation at great homogeneity. However the synthesis of multi-sialylated N-glycans is so far restricted to mammalian cells. Here we used a plant based expression system to accomplish multi-antennary protein sialylation. A human erythropoietin fusion protein (EPOFc) was transiently expressed in Nicotiana benthamiana ΔXTFT, a glycosylation mutant that lacks plant specific N-glycan residues. cDNA of the hormone was co-delivered into plants with the necessary genes for (i) branching (ii) β1,4-galactosylation as well as for the (iii) synthesis, transport and transfer of sialic acid. This resulted in the production of recombinant EPOFc carrying bi- tri- and tetra-sialylated complex N-glycans. The formation of this highly complex oligosaccharide structure required the coordinated expression of 11 human proteins acting in different subcellular compartments at different stages of the glycosylation pathway. In vitro receptor binding assays demonstrate the generation of biologically active molecules. We demonstrate the in planta synthesis of one of the most complex mammalian glycoforms pointing to an outstanding high degree of tolerance to changes in the glycosylation pathway in plants.