Production of antibody fragments in Escherichia coli

Recombinant Protein Production in E. coli Using the phoA Expression System

Auto-inducible promoter systems have been reported to increase soluble product formation in the periplasm of E. coli compared to inducer-dependent systems. In this study, we investigated the phosphate (PO4)-sensitive phoA expression system (pAT) for the production of a recombinant model antigen-binding fragment (Fab) in the periplasm of E. coli in detail. We explored the impact of non-limiting and limiting PO4 conditions on strain physiology as well as Fab productivity. We compared different methods for extracellular PO4 detection, identifying automated colorimetric measurement to be most suitable for at-line PO4 monitoring. We showed that PO4 limitation boosts phoA-based gene expression, however, the product was already formed at non-limiting PO4 conditions, indicating leaky expression. Furthermore, cultivation under PO4 limitation caused physiological changes ultimately resulting in a metabolic breakdown at PO4 starvation. Finally, we give recommendations for process optimization with the phoA expression system. In summary, our study provides very detailed information on the E. coli phoA expression system, thus extending the existing knowledge of this system, and underlines its high potential for the successful production of periplasmic products in E. coli.

NMR mapping of the highly flexible regions of 13C/15N-labeled antibody TTAC-0001-Fab

Monoclonal antibody (mAb) drugs are clinically important for the treatment of various diseases. TTAC-0001 is under development as a new anti-cancer antibody drug targeting VEGFR-2. As the less severe toxicity of TTAC-0001 compared to Bevacizumab, likely due to the decreased in vivo half-life, seems to be related to its structural flexibility, it is important to map the exact flexible regions. Although the ¹³C/¹⁵N-labeled protein is required for NMR analyses, it is difficult to obtain antibody fragments (Fab and scFv) containing disulfide bonds through general cytosolic expression in Escherichia coli (E. coli). Here, we notably increased the periplasmic expression of the ¹³C/¹⁵N-labeled TTAC-0001-Fab (¹³C/¹⁵N-TTAC-Fab) through simple isopropyl β-D-1-thiogalactopyranoside (IPTG)-induction at an increased optical density (1.5 OD_600nm). Through NMR triple resonance experiments, two loop insertions (LI-1 between the V_H and C_H1; LI-2 between the V_L and C_L) were confirmed to be highly flexible. The additional LIs could be another way to engineer the antibody by changing the pharmacokinetic properties.

Development of an Immunoassay for Chloramphenicol Based on the Preparation of a Specific Single-Chain Variable Fragment Antibody

Specific antibodies are essential for the immune detection of small molecule contaminants. In the present study, the heavy and light variable regions (V(H )and V(L)) of the immunoglobulin genes from a hybridoma secreting a chloramphenicol (CAP)-specific monoclonal antibody (mAb) were cloned and sequenced. In addition, the light and heavy chains obtained from the monoclonal antibody were separated using SDS-PAGE and analyzed using Orbitrap mass spectrometry. The results of DNA sequencing and mass spectrometry analysis were compared, and the V(H) and V(L) chains specific for CAP were determined and used to construct a single-chain variable fragment (scFv). This fragment was recombinantly expressed as a soluble scFv-alkaline phosphatase fusion protein and used to develop a direct competitive ELISA. Compared with the parent mAb, scFv exhibits lower sensitivity but better food matrix resistance. This work highlights the application of engineered antibodies for CAP detection.

Process development of periplasmatically produced single chain fragment variable against epidermal growth factor receptor in Escherichia coli

Prokaryotic production systems have been widely used to manufacture recombinant therapeutic proteins. Economically, the prokaryotic production – especially of small therapeutic molecules – is advantageous compared to eukaryotic production strategies. However, due to the potential endotoxin and host cell protein contamination, the requirements for the purification process are disproportionately higher and therefore more expensive and elaborate to circumvent. For this reason, the goal of this work was to develop and establish a rapid, simple, inexpensive and ‘up-scalable’ production and purification process, using the therapeutic relevant protein anti-EGFR scFv hu225 as model molecule. Configuring high cell density cultivation of Escherichia coli – using the rha-BAD expression system as production platform – a specific product concentration up to 20 mgscFv/gCDW was obtained. By combining freeze-and-thaw, osmotic shock and pH induced host cell protein precipitation, almost 70% of the product was extracted from the biomass. In a novel approach a mixed mode chromatography was implemented as a capturing and desalting step, which allowed the direct application of further ion exchange chromatography steps for purification up to pharmaceutical grade. Thereby, 50% of the produced scFv could be purified within 10 h while maintaining the biological activity.

With or without sugar? (A)glycosylation of therapeutic antibodies

Antibodies and antibody-based drugs are currently the fastest-growing class of therapeutics. Over the last three decades, more than 30 therapeutic monoclonal antibodies and derivatives thereof have been approved for and successfully applied in diverse indication areas including cancer, organ transplants, autoimmune/inflammatory disorders, and cardiovascular disease. The isotype of choice for antibody therapeutics is human IgG, whose Fc region contains a ubiquitous asparagine residue (N297) that acts as an acceptor site for N-linked glycans. The nature of these glycans can decisively influence the therapeutic performance of a recombinant antibody, and their absence or modification can lead to the loss of Fc effector functions, greater immunogenicity, and unfavorable pharmacokinetic profiles. However, recent studies have shown that aglycosylated antibodies can be genetically engineered to display novel or enhanced effector functions and that favorable pharmacokinetic properties can be preserved. Furthermore, the ability to produce aglycosylated antibodies in lower eukaryotes and bacteria offers the potential to broaden and simplify the production platforms and avoid the problem of antibody heterogeneity, which occurs when mammalian cells are used for production. In this review, we discuss the importance of Fc glycosylation focusing on the use of aglycosylated and glyco-engineered antibodies as therapeutic proteins.

High-yield export of a native heterologous protein to the periplasm by the tat translocation pathway in Escherichia coli

Numerous high-value recombinant proteins that are produced in bacteria are exported to the periplasm as this approach offers relatively easy downstream processing and purification. Most recombinant proteins are exported by the Sec pathway, which transports them across the plasma membrane in an unfolded state. The twin-arginine translocation (Tat) system operates in parallel with the Sec pathway but transports substrate proteins in a folded state; it therefore has potential to export proteins that are difficult to produce using the Sec pathway. In this study, we have produced a heterologous protein (green fluorescent protein; GFP) in Escherichia coli and have used batch and fed-batch fermentation systems to test the ability of the newly engineered Tat system to export this protein into the periplasm under industrial-type production conditions. GFP cannot be exported by the Sec pathway in an active form. We first tested the ability of five different Tat signal peptides to export GFP, and showed that the TorA signal peptide directed most efficient export. Under batch fermentation conditions, it was found that TorA-GFP was exported efficiently in wild type cells, but a twofold increase in periplasmic GFP was obtained when the TatABC components were co-expressed. In both cases, periplasmic GFP peaked at about the 12 h point during fermentation but decreased thereafter, suggesting that proteolysis was occurring. Typical yields were 60 mg periplasmic GFP per liter culture. The cells over-expressed the tat operon throughout the fermentation process and the Tat system was shown to be highly active over a 48 h induction period. Fed-batch fermentation generated much greater yields: using glycerol feed rates of 0.4, 0.8, and 1.2 mL h(-1), the cultures reached OD(600) values of 180 and periplasmic GFP levels of 0.4, 0.85, and 1.1 g L(-1) culture, respectively. Most or all of the periplasmic GFP was shown to be active. These export values are in line with those obtained in industrial production processes using Sec-dependent export approaches.

Industrial production of recombinant therapeutics in Escherichia coli and its recent advancements

Nearly 30% of currently approved recombinant therapeutic proteins are produced in Escherichia coli. Due to its well-characterized genetics, rapid growth and high-yield production, E. coli has been a preferred choice and a workhorse for expression of non-glycosylated proteins in the biotech industry. There is a wealth of knowledge and comprehensive tools for E. coli systems, such as expression vectors, production strains, protein folding and fermentation technologies, that are well tailored for industrial applications. Advancement of the systems continues to meet the current industry needs, which are best illustrated by the recent drug approval of E. coli produced antibody fragments and Fc-fusion proteins by the FDA. Even more, recent progress in expression of complex proteins such as full-length aglycosylated antibodies, novel strain engineering, bacterial N-glycosylation and cell-free systems further suggests that complex proteins and humanized glycoproteins may be produced in E. coli in large quantities. This review summarizes the current technology used for commercial production of recombinant therapeutics in E. coli and recent advances that can potentially expand the use of this system toward more sophisticated protein therapeutics.

Investigation of the impact of Tat export pathway enhancement on E. coli culture, protein production and early stage recovery

The twin arginine translocation (Tat) pathway occurs naturally in E. coli and has the distinct ability to translocate folded proteins across the inner membrane of the cell. It has the potential to export commercially useful proteins that cannot be exported by the ubiquitous Sec pathway. To better understand the bioprocess potential of the Tat pathway, this article addresses the fermentation and downstream processing performances of E. coli strains with a wild-type Tat system exporting the over-expressed substrate protein FhuD. These were compared to strains cell-engineered to over-express the Tat pathway, since the native export capacity of the Tat pathway is low. This low capacity makes the pathway susceptible to saturation by over-expressed substrate proteins, and can result in compromised cell integrity. However, there is concern in the literature that over-expression of membrane proteins, like those of the Tat pathway, can impact negatively upon membrane integrity itself. Under controlled fermentation conditions E. coli cells with a wild-type Tat pathway showed poor protein accumulation, reaching a periplasmic maximum of only 0.5 mg L⁻¹ of growth medium. Cells over-expressing the Tat pathway showed a 25% improvement in growth rate, avoided pathway saturation, and showed 40-fold higher periplasmic accumulation of FhuD. Moreover, this was achieved whilst conserving the integrity of cells for downstream processing: experimentation comparing the robustness of cells to increasing levels of shear showed no detrimental effect from pathway over-expression. Further experimentation on spheroplasts generated by the lysozyme/osmotic shock method--a scaleable way to release periplasmic protein--showed similar robustness between strains. A scale-down mimic of continuous disk-stack centrifugation predicted clarifications in excess of 90% for both intact cells and spheroplasts. Cells over-expressing the Tat pathway performed comparably to cells with the wild-type system. Overall, engineering E. coli cells to over-express the Tat pathway allowed for greater periplasmic yields of FhuD at the fermentation scale without compromising downstream processing performance.

Established bioprocesses for producing antibodies as a basis for future planning

In the early years of monoclonal antibody production for human therapy and diagnosis the methods used were arrived at by individual organisations. However, there is now an accumulating body of information on antibodies and fragments that have been produced by processes approved for human use. This information is becoming available at a time when the number of potential antibody-based medicines is growing sharply. The review addresses the reported production routes, their scale and the titres achieved. It identifies the performances of fed-batch and perfusion culture versus batch culture, and compares processes for the production of antibodies for diagnosis and for antibody fragments. The analysis defines the likely routes of future production in a sector where demanding regulations constrain new technology. It also indicates what levels of performance new approaches will need to meet to be competitive.

Construction, expression and in vitro biological behaviors of Ig scFv fragment in patients with chronic B cell leukemia

The expression vector of SmIg scFv fragment was constructed in patient with B cell chronic lymphocyte leukemia (B-CLL) and expressed in E. coli to obtain scFv fragment, and the effect of the protein on the proliferation of stimulated peripheral blood mononuclear cells (PBMC) was investigated in vitro. Two pairs of primers were designed, and variable region genes of light chain and heavy chain were amplified by PCR respectively from the pGEM-T vectors previously constructed in our laboratory which containing light chain gene or Fd fragment of heavy chain gene. The PCR product was digested, purified and inserted into pHEN2 vector to construct the soluble expression vector pHEN2-scFv. After the induction by IPTG, the scFv protein was identified by SDS-PAGE electrophoresis and purified by Ni-NTA-Chromatography. MTT was used to determine the effect of purified protein on the proliferation of stimulated PBMC in vitro. Plasmid PCR and restriction enzyme digestion of pHEN2-scFv revealed the pHEN2-scFv vector was constructed successfully. Id-scFv protein was expressed in positive clone after induced by IPTG. SDS-PAGE analysis showed that the relative molecular weight of fusion protein was about 30 kD (1 kD= 0.9921 ku), which was consistent with the theoretically predicted value. Proliferation of PBMC could be induced by purified Id-scFv. It was suggested that the expression vector of SmIg scFv fragment was constructed successfully, and scFv protein was expressed and secreted from E. coli, which could induce proliferation of PBMC. This may lay an experimental foundation for further research of Id-HSP complex vaccine for B-CLL.

Contrasting secretory processing of simultaneously expressed heterologous proteins in Saccharomyces cerevisiae

In this study, secretory processing of cell-surface displayed Aga2p fusions to bovine pancreatic trypsin inhibitor (BPTI) and the single chain Fv (scFv) antibody fragment D1.3 are examined. BPTI is more efficiently processed than D1.3 both when secreted and surface-displayed, and D1.3 expression imparts a greater amount of secretory stress on the cell as assayed by a reporter of the unfolded protein response (UPR). Surprisingly, simultaneous expression of the two proteins in the same cell somewhat improves BPTI surface display while decreasing D1.3 surface display with minimal effect on UPR activation. Furthermore, co-expression leads to the accumulation of punctate vacuolar aggregates of D1.3 and increased secretion of the D1.3-Aga2p fusion into the supernatant. Overexpression of the folding chaperones protein disulfide isomerase (PDI) and BiP largely mitigates the D1.3 surface expression decrease, suggesting that changes in vacuolar and cell surface targeting may be due, in part, to folding inefficiency. Titration of constitutive UPR expression across a broad range progressively decreases surface display of both proteins as UPR increases. D1.3-Aga2p traffic through the late secretory pathway appears to be strongly affected by overall secretory load as well as folding conditions in the ER.

The production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi

In this review we will focus on the current status and views concerning the production of antibody fragments and antibody fusion proteins by yeasts and filamentous fungi. We will focus on single-chain antibody fragment production (scFv and VHH) by these lower eukaryotes and the possible applications of these proteins. Also the coupling of fragments to relevant enzymes or other components will be discussed. As an example of the fusion protein strategy, the 'magic bullet' approach for industrial applications, will be highlighted.

High-yield expression of the recombinant, atrazine-specific Fab fragment K411B by the methylotrophic yeast Pichia pastoris

In this report, we describe the high-yield secretory expression ( approximately 40 mg x l(-1)) of pure, atrazine-specific Fab fragments (K411B) from Pichia pastoris that was achieved by co-integration of the genes encoding the heavy and light chains (both under the control of the alcohol oxidase promoter) into the genome of the yeast cells. Antibody-expressing clones were selected by SDS-PAGE and ELISA and fed-batch fermentations were carried out in a 5-l scale. Both chains of the Fab were successfully expressed upon methanol induction and almost no other proteins were secreted into the media. Approximately 30% of the two chains formed the active Fab fragment containing the intermolecular disulphide bond, as determined by Western blot analysis under non-reducing conditions. Crude culture supernatant was used to study the binding properties of the Fab fragment toward different s-triazines by means of competitive ELISA: the IC50 value for the detection of atrazine was determined from the standard curve as 3 microg x l(-1), which is one magnitude higher than the value obtained with the parental mAb K4E7 but equals that obtained when the same Fab fragment was expressed in Escherichia coli cells. In addition, the cross-reactivity pattern of the Fab from Pichia is comparable to that of E. coli and to the parental mAb K4E7.