Depth Filters Containing Diatomite Achieve More Efficient Particle Retention than Filters Solely Containing Cellulose Fibers

Membrane-based inverse-transition purification facilitates a rapid isolation of various spider-silk elastin-like polypeptide fusion proteins from extracts of transgenic tobacco

Plants can produce complex pharmaceutical and technical proteins. Spider silk proteins are one example of the latter and can be used, for example, as compounds for high-performance textiles or wound dressings. If genetically fused to elastin-like polypeptides (ELPs), the silk proteins can be reversibly precipitated from clarified plant extracts at moderate temperatures of ~ 30 °C together with salt concentrations > 1.5 M, which simplifies purification and thus reduces costs. However, the technologies developed around this mechanism rely on a repeated cycling between soluble and aggregated state to remove plant host cell impurities, which increase process time and buffer consumption. Additionally, ELPs are difficult to detect using conventional staining methods, which hinders the analysis of unit operation performance and process development. Here, we have first developed a surface plasmon resonance (SPR) spectroscopy-based assay to quantity ELP fusion proteins. Then we tested different filters to prepare clarified plant extract with > 50% recovery of spider silk ELP fusion proteins. Finally, we established a membrane-based purification method that does not require cycling between soluble and aggregated ELP state but operates similar to an ultrafiltration/diafiltration device. Using a data-driven design of experiments (DoE) approach to characterize the system of reversible ELP precipitation we found that membranes with pore sizes up to 1.2 µm and concentrations of 2-3 M sodium chloride facilitate step a recovery close to 100% and purities of > 90%. The system can thus be useful for the purification of ELP-tagged proteins produced in plants and other hosts.

Design, optimization, production and activity testing of recombinant immunotoxins expressed in plants and plant cells for the treatment of monocytic leukemia

Antibody-drug conjugates (ADCs) can improve therapeutic indices compared to plain monoclonal antibodies (mAbs). However, ADC synthesis is complex because the components are produced separately in CHO cells (mAb) and often by chemical synthesis (drug). They are individually purified, coupled, and then the ADC is purified, increasing production costs compared to regular mAbs. In contrast, it is easier to produce recombinant fusion proteins consisting of an antibody derivative, linker and proteinaceous toxin, i.e. a recombinant immunotoxin (RIT). Plants are capable of the post-translational modifications needed for functional antibodies and can also express active protein toxins such as the recombinant mistletoe lectin viscumin, which is not possible in prokaryotes and mammalian cells respectively. Here, we used Nicotiana benthamiana and N. tabacum plants as well as tobacco BY-2 cell-based plant cell packs (PCPs) to produce effective RITs targeting CD64 as required for the treatment of myelomonocytic leukemia. We compared RITs with different subcellular targeting signals, linkers, and proteinaceous toxins. The accumulation of selected candidates was improved to ~ 40 mg kg-1 wet biomass using a design of experiments approach, and corresponding proteins were isolated with a purity of ~ 80% using an optimized affinity chromatography method with an overall yield of ~ 84%. One anti-CD64 targeted viscumin-based drug candidate was characterized in terms of storage stability and cytotoxicity test in vitro using human myelomonocytic leukemia cell lines. We identified bottlenecks in the plant-based expression platform that require further improvement and assessed critical process parameters that should be considered during process development for plant-made RITs.

Killer to cure: Expression and production costs calculation of tobacco plant-made cancer-immune checkpoint inhibitors

Immune checkpoint inhibitors (ICIs) have achieved huge clinical success. However, many still have limited response rates, and are prohibitively costly. There is a need for effective and affordable ICIs, as well as local manufacturing capacity to improve accessibility, especially to low-to-middle income countries (LMICs). Here, we have successfully expressed three key ICIs (anti-PD-1 Nivolumab, anti-NKG2A Monalizumab, and anti-LAG-3 Relatimab) transiently in Nicotiana benthamiana and Nicotiana tabacum plants. The ICIs were expressed with a combination of different Fc regions and glycosylation profiles. They were characterized in terms of protein accumulation levels, target cell binding, binding to human neonatal Fc receptors (hFcRn), human complement component C1q (hC1q) and various Fcγ receptors, as well as protein recovery during purification at 100 mg- and kg-scale. It was found that all ICIs bound to the expected target cells. Furthermore, the recovery during purification, as well as Fcγ receptor binding, can be altered depending on the Fc region used and the glycosylation profiles. This opens the possibility of using these two parameters to fine-tune the ICIs for desired effector functions. A scenario-based production cost model was also generated based on two production scenarios in hypothetical high- and low-income countries. We have shown that the product accumulation and recovery of plant production platforms were as competitive as mammalian cell-based platforms. This highlights the potential of plants to deliver ICIs that are more affordable and accessible to a widespread market, including LMICs.

Simple plant-based production and purification of the assembled human ferritin heavy chain as a nanocarrier for tumor-targeted drug delivery and bioimaging in cancer therapy

Nanoparticles are used as carriers for the delivery of drugs and imaging agents. Proteins are safer than synthetic nanocarriers due to their greater biocompatibility and the absence of toxic degradation products. In this context, ferritin has the additional benefit of inherently targeting the membrane receptor transferrin 1, which is overexpressed by most cancer cells. Furthermore, this self-assembling multimeric protein can be loaded with more than 2000 iron atoms, as well as drugs, contrast agents, and other cargos. However, recombinant ferritin currently costs ~3.5 million € g^-1 , presumably because the limited number of producers cannot meet demand, making it generally unaffordable as a nanocarrier. Because plants can produce proteins at very-large-scale, we developed a simple, proof-of-concept process for the production of the human ferritin heavy chain by transient expression in Nicotiana benthamiana. We optimized the protein yields by screening different compartments and 5'-untranslated regions in PCPs, and selected the best-performing construct for production in differentiated plants. We then established a rapid and scalable purification protocol by combining pH and heat treatment before extraction, followed by an ultrafiltration/diafiltration size-based separation process. The optimized process achieved ferritin levels of ~40 mg kg^-1 fresh biomass although depth filtration limited product recovery to ~7%. The purity of the recombinant product was >90% at costs ~3% of the current sales price. Our method therefore allows the production of affordable ferritin heavy chain as a carrier for therapeutic and diagnostic agents, which is suitable for further stability and functionality testing in vitro and in vivo.

Seed- and leaf-based expression of FGF21-transferrin fusion proteins for oral delivery and treatment of non-alcoholic steatohepatitis

Non-alcoholic steatohepatitis (NASH) is a global disease with no effective medication. The fibroblast growth factor 21 (FGF21) can reverse this liver dysfunction, but requires targeted delivery to the liver, which can be achieved via oral administration. Therefore, we fused FGF21 to transferrin (Tf) via a furin cleavage site (F), to promote uptake from the intestine into the portal vein, yielding FGF21-F-Tf, and established its production in both seeds and leaves of commercial Nicotiana tabacum cultivars, compared their expression profile and tested the bioavailability and bioactivity in feeding studies. Since biopharmaceuticals need to be produced in a contained environment, e.g., greenhouses in case of plants, the seed production was increased in this setting from 239 to 380 g m^-2 a^-1 seed mass with costs of 1.64 € g^-1 by side branch induction, whereas leaves yielded 8,193 g m^-2 a^-1 leave mass at 0.19 € g^-1. FGF21-F-Tf expression in transgenic seeds and leaves yielded 6.7 and 5.6 mg kg^-1 intact fusion protein, but also 4.5 and 2.3 mg kg^-1 additional Tf degradation products. Removing the furin site and introducing the liver-targeting peptide PLUS doubled accumulation of intact FGF21-transferrin fusion protein when transiently expressed in Nicotiana benthamiana from 0.8 to 1.6 mg kg^-1, whereas truncation of transferrin (nTf338) and reversing the order of FGF21 and nTf338 increased the accumulation to 2.1 mg kg^-1 and decreased the degradation products to 7% for nTf338-FGF21-PLUS. Application of partially purified nTf338-FGF21-PLUS to FGF21^-/- mice by oral gavage proved its transfer from the intestine into the blood circulation and acutely affected hepatic mRNA expression. Hence, the medication of NASH via oral delivery of nTf338-FGF21-PLUS containing plants seems possible.

Strategies for Efficient and Sustainable Protein Extraction and Purification from Plant Tissues

Recombinant proteins produced in whole plants are usually extracted and purified from leaf or seed tissues. Here we describe a workflow that is suitable for most soluble pharmaceutical proteins produced in leafy biomass. We highlight options to streamline the process, reducing the total process time and costs, and eliminating certain unit operations if the product allows. The overall process is a combination of batch-wise or continuous extraction followed by a series of solid-liquid separation steps, which can be supported by chemically defined additives, and concludes with a sequence of optional membrane-based and regular chromatographic purification operations.

Comparison of microbial and transient expression (tobacco plants and plant-cell packs) for the production and purification of the anticancer mistletoe lectin viscumin

Cancer is the leading cause of death in industrialized countries. Cancer therapy often involves monoclonal antibodies or small-molecule drugs, but carbohydrate-binding lectins such as mistletoe (Viscum album) viscumin offer a potential alternative treatment strategy. Viscumin is toxic in mammalian cells, ruling them out as an efficient production system, and it forms inclusion bodies in Escherichia coli such that purification requires complex and lengthy refolding steps. We therefore investigated the transient expression of viscumin in intact Nicotiana benthamiana plants and Nicotiana tabacum Bright Yellow 2 plant-cell packs (PCPs), comparing a full-length viscumin gene construct to separate constructs for the A and B chains. As determined by capillary electrophoresis the maximum yield of purified heterodimeric viscumin in N. benthamiana was ~7 mg/kg fresh biomass with the full-length construct. The yield was about 50% higher in PCPs but reduced 10-fold when coexpressing A and B chains as individual polypeptides. Using a single-step lactosyl-Sepharose affinity resin, we purified viscumin to ~54%. The absence of refolding steps resulted in estimated cost savings of more than 80% when transient expression in tobacco was compared with E. coli. Furthermore, the plant-derived product was ~3-fold more toxic than the bacterially produced counterpart. We conclude that plants offer a suitable alternative for the production of complex biopharmaceutical proteins that are toxic to mammalian cells and that form inclusion bodies in bacteria.

Preparation of transparent anti-pollution cellulose carbamate regenerated cellulose membrane with high separation ability

In this study, cellulose pulp and urea were used to synthesize cellulose carbamate (nitrogen content reaches 4.5%) by low-cost and environmentally friendly solid-liquid phase method. Cellulose carbamate fluid was prepared by using sodium hydroxide aqueous solution as solvent. The fluid was regenerated and formed in a coagulation bath, and finally a regenerated cellulose membrane with high transparency and separation ability was obtained. The simple chemical treatment of cellulose not only greatly increased the mass fraction of cellulose dissolution (It has reached 15%) and retains the original crystal form and thermal stability of cellulose. The surface of the membrane was relatively dense, and the inside has regular microchannel. The factors affect the transparency and water flux of regenerated cellulose membranes were discussed by orthogonal experimental range analysis. The ability of the regenerated cellulose membrane to reject dyes was tested. The results showed that the rejection of methyl blue and congo red reached 100%, and the rejection rate of methyl orange reached 60%. The oil/water separation ability and the anti-pollution ability of the regenerated cellulose membrane were tested. The oil/water separation effect reached 100%. This membrane may have application prospect in water treatment, biotechnology.

Plant Molecular Farming - Integration and Exploitation of Side Streams to Achieve Sustainable Biomanufacturing

Plants have unique advantages over other systems such as mammalian cells for the production of valuable small molecules and proteins. The benefits cited most often include safety due to the absence of replicating human pathogens, simplicity because sterility is not required during production, scalability due to the potential for open-field cultivation with transgenic plants, and the speed of transient expression potentially providing gram quantities of product in less than 4 weeks. Initially there were also significant drawbacks, such as the need to clarify feed streams with a high particle burden and the large quantities of host cell proteins, but efficient clarification is now readily achieved. Several additional advantages have also emerged reflecting the fact that plants are essentially biodegradable, single-use bioreactors. This article will focus on the exploitation of this concept for the production of biopharmaceutical proteins, thus improving overall process economics. Specifically, we will discuss the single-use properties of plants, the sustainability of the production platform, and the commercial potential of different biomass side streams. We find that incorporating these side streams through rational process integration has the potential to more than double the revenue that can currently be achieved using plant-based production systems.

Downstream processing of a plant-derived malaria transmission-blocking vaccine candidate

Plants as a platform for recombinant protein expression are now economically comparable to well-established systems, such as microbes and mammalian cells, thanks to advantages such as scalability and product safety. However, downstream processing accounts for the majority of the final product costs because plant extracts contain large quantities of host cell proteins (HCPs) that must be removed using elaborate purification strategies. Heat precipitation in planta (blanching) can remove ∼80% of HCPs and thus simplify further purification steps, but this is only possible if the target protein is thermostable. Here we describe a combination of blanching and chromatography to purify the thermostable transmission-blocking malaria vaccine candidate FQS, which was transiently expressed in Nicotiana benthamiana leaves. If the blanching temperature exceeded a critical threshold of ∼75 °C, FQS was no longer recognized by the malaria transmission-blocking monoclonal antibody 4B7. A design-of-experiments approach revealed that reducing the blanching temperature from 80 °C to 70 °C restored antibody binding while still precipitating most HCPs. We also found that blanching inhibited the degradation of FQS in plant extracts, probably due to the thermal inactivation of proteases. We screened hydrophobic interaction chromatography materials using miniature columns and a liquid-handling station. Octyl Sepharose achieved the highest FQS purity during the primary capture step and led to a final purity of ∼72% with 60% recovery via step elution. We found that 30-75% FQS was lost during ultrafiltration/diafiltration, giving a final yield of 9 mg kg-1 plant material after purification based on an initial yield of ∼49 mg kg-1 biomass after blanching.

Production of Functional Anti-Ebola Antibodies in Pichia pastoris

The 2013-2016 Ebola outbreak highlighted the limited treatment options and lack of rapid response strategies for emerging pathogen outbreaks. Here, we propose an efficient development cycle using glycoengineered Pichia pastoris to produce monoclonal antibody cocktails against pathogens. To enable rapid genetic engineering of P. pastoris, we introduced a genomic landing pad for reliable recombinase-mediated DNA integration. We then created strains expressing each of the three monoclonal antibodies that comprise the ZMapp cocktail, and demonstrated that the secreted antibodies bind to the Ebola virus glycoprotein by immunofluorescence assay. We anticipate that this approach could accelerate the production of therapeutics against future pathogen outbreaks.