Production technologies for monoclonal antibodies and their fragments

Monoclonal antibodies - A repertoire of therapeutics

Antibodies are a class of biomolecules armed with extraordinary diversity, unmatched in the biological world by any other class of molecules. This characteristic feature equips antibodies to recognize, bind, and eliminate an infinite number of pathogens/antigens facilitated by their effector functions. The repertoire of natural binding specificities of antibodies (Abs) is greater than the calculated estimate of ∼1012 in humans, as a naive, single antigen-binding site may bind more than one antigen employing the plasticity in antigen-antibody interactions, potentiating Abs to fight infinite pathogenic insults and restrict the development of cancers. Additionally, advanced technological interventions, by allowing manipulation of the germline and acquired specificities of human/animal immunoglobulins (Ig) have contributed immensely to broaden their existing repertoire and scope of clinical applications. The available natural repertoire of Ig and Ig-like molecules in other animals, e.g., mice, horses, cows, pigs, rabbits, camels, llamas, etc., further diversified the source of unique antigen-binding specificities. The recombinant DNA technology, in association with hybridoma , transgenic, and phage display technologies, has helped create a parallel repertoire of unique antibody molecules [animal Abs, camelid heavy chain Abs (hcAbs), chimeric Abs, chimeric hcAbs, humanized Abs, humanized nanobody (Nb)-hcAbs, human Abs, etc.], monoclonal Ab (mAb) derived fragments [antigen-binding-fragment (Fab), single-chain-variable-fragment (scFv), variable-fragement (Fv), single-variable-domain of hcAbs (VHH), bispecific scFv, diabodies, triabodies, intrabodies, bispecific Fabs, tri-specific Fabs, etc.), and immunoconjugates generated by fusing/conjugating mAb fragments with enzyme, toxin, prodrug etc., molecules. The current chapter provides a detailed description of the natural and engineered antibody repertoires and discusses various strategies using which these molecules are being inducted as novel immunotherapeutics for treating a significant number of human diseases.

A single-domain antibody library based on a stability-engineered human VH3 scaffold

Using conventional immunoglobulin G (IgG) molecules as therapeutic agents presents several well-known disadvantages owing to their large size and structural complexity, negatively impacting development and production efficiency. Single-domain antibodies (sdAbs) are the smallest functional antibody format (~ 15 kDa) and represent a viable alternative to IgG in many applications. However, unlike natural single-domain antibodies, such as camelid VHH, the variable domains of conventional antibodies show poor physicochemical properties when expressed as sdAbs. This report identified stable sdAb variants of human VH3-23 from a framework region 2-randomized human VH library by phage display selection under thermal challenge. Synthetic complementarity determining region diversity was introduced to one of the selected variants with high thermal stability, expression level, and monomeric content to construct a human VH sdAb library. The library was validated by panning against a panel of antigens, and target-specific binders were identified and characterized for their affinity and biophysical properties. The results of this study suggest that a synthetic sdAb library based on a stability-engineered human VH scaffold could be a facile source of high-quality sdAb for many practical applications.

Development of a latex agglutination test based on VH antibody fragment for detection of Streptococcus suis serotype 2

Streptococcus suis serotype 2 (SS2) is an important porcine pathogen that causes diseases in both swine and human. For rapid SS2 identification, a novel latex agglutination test (LAT) based on heavy-chain variable domain antibody (VH) was developed. Firstly, the soluble 47B3 VH antibody fragment from a phage display library, in which cysteine residues were engineered at the C-terminus, was expressed in Escherichia coli. The purified protein was then gently reduced to form monomeric soluble 47B3 VH subsequently used to coat with latex beads by means of site-specific conjugation. The resulting VH-coated beads gave a good agglutination reaction with SS2. The LAT was able to distinguish S. suis serotype 2 from serotype 1/2, which shares some common sugar residues, and showed no cross-reaction with other serotypes of S. suis or other related bacteria. The detection sensitivity was found to be as high as 1.85x106 cells. The LAT was stable at 4°C for at least six months without loss of activity. To the best of our knowledge, this is the first LAT based on a VH antibody fragment that can be considered as an alternative for conventional antibody-based LAT where VHs are the most favored recombinant antibody.

Expressing antigen binding fragments with high titers in a targeted integration CHO host by optimizing expression vector gene copy numbers and position: A case study

Antigen binding fragments (Fab) are a promising class of therapeutics as they maintain high potency while having significantly smaller size relative to full-length antibodies. Because Fab molecules are aglycosylated, many expression platforms, including prokaryotic, yeast, and mammalian cells, have been developed for their expression, with Escherichia coli being the most commonly used Fab expression system. In this study, we have examined production of a difficult to express Fab molecule in a targeted integration (TI) Chinese Hamster Ovary (CHO) host. Without a need for extensive host or process optimization, as is usually required for E. coli, by simply using different vector configurations, clones with very high Fab expression titers were obtained. In this case, by increasing heavy chain (HC) gene copy numbers, clones with titers of up to 7.4 g/L in the standard fed-batch production culture were obtained. Our findings suggest that having a predetermined transgene integration site, as well as the option to optimize gene copy number/dosage, makes CHO TI hosts an effective system for expression of Fab molecules, allowing Fab expression using platform process and without significant process development efforts.

Preparation and application of a specific single-chain variable fragment against artemether

Artemether, an artemisinin derivative, is a component of the commonly used artemisinin-based combination therapy, artemether-lumefantrine. In this study, we cloned the VH and VL genes of a cell line (mAb 2G12E1) producing a monoclonal antibody specific to artemether, and used to construct a recombinant DNA of single-chain variable fragment (scFv). The scFv was constructed into prokaryotic expression vectors pET32a (+), pET22b (+), pGEX-2T, and pMAL-p5x, respectively. However, only the pMAL-p5x/scFv could be induced to express soluble scFv with comparable sensitivity and specificity to that of mAb 2G12E1. Based on the anti-artemether scFv, an indirect competitive enzyme-linked immunosorbent assay (icELISA) was developed. The 50% of inhibition concentration (IC₅₀) value and the working range based on IC₂₀ to IC₈₀ were 4.33 ng mL^-1 and 1.05-22.65 ng mL^-1, respectively. The artemether content in different drugs were determined by the developed icELISA, and the results were consistent to those determined by ultra performance liquid chromatography (UPLC). The anti-artemether scFv prepared in the current study could be a valuable genetically engineered antibody applied for artemether monitoring and specific binding mechanism studying.

Unusual substrate specificity in GH family 12: structure-function analysis of glucanases Bgh12A and Xgh12B from Aspergillus cervinus, and Egh12 from Thielavia terrestris

In this study, we compared the properties and structures of three fungal GH12 enzymes: the strict endoglucanase Bgh12A and the xyloglucanase Xgh12B from Aspergillus cervinus, and the endoglucanase Egh12 from Thielavia terrestris combining activity on linear β-glucan and branched xyloglucan. Egh12 from T. terrestris was produced in Pichia pastoris, purified, and characterized as a thermostable enzyme with maximal activity at 70 ºC and a half-life time of 138 min at 65 °C. We for the first time demonstrated that the GH12 endoglucanases Egh12 and Bgh12A, but not the strict xyloglucanase Xgh12B, hydrolyzed (1,3)-β-linkages in (1,3;1,4)-β-D-glucooligosaccharides and had transglycosylase activity on (1,3)-β-D-glucooligosaccharides. Phylogenetic analysis indicated that Egh12 from T. terrestris and Bgh12A from A. cervinus are more related than Bgh12A and Xgh12B isolated from one strain. The X-ray structure of Bgh12A was determined with 2.17 Å resolution and compared with 3D-homology models of Egh12 and Xgh12B. The enzymes have a β-jelly roll structure with a catalytic cleft running across the protein. Comparative analysis and a docking study demonstrated the importance of endoglucanase-specific loop 1 partly covering the catalytic cleft for correct placement of the linear substrates. Variability in substrate specificity between the GH12 endoglucanases is determined by non-conservative residues in structural loops framing the catalytic cleft. A residue responsible for the thermostability of Egh12 was predicted. The key structural elements and residues described in this study may serve as potential targets for modification aimed at the improvement of enzymatic properties. KEY POINTS: • Thermostable endoglucanase Egh12 from T. terrestris was produced in P. pastoris, purified, and characterized • The X-ray structure of GH12 endoglucanase Bgh12A from A. cervinus was resolved • GH12 endoglucanases, but not GH12 xyloglucanases, hydrolyze (1,3)-β-linkages in (1,3;1,4)-β-D-glucooligosaccharides.

Mini-review: The market growth of diagnostic and therapeutic monoclonal antibodies - SARS CoV-2 as an example

BACKGROUND

The emergence of novel viruses poses severe challenges to global public health highlighting the crucial necessity for new antivirals.

MAIN BODY

Monoclonal antibodies (mAbs) are immunoglobulins that bind to a single epitope. Mouse mAbs are generated by classic hybridoma technology and are mainly used for immunodiagnostics. For immunotherapy, it is critical to use monoclonal antibodies in their human form to minimize adverse reactions. They have been successfully used to treat numerous illnesses, accordingly, an increasing number of mAbs, with high potency against emerging viruses is the target of every biopharmaceutical company. The diagnostic and therapeutic mAbs market grows rapidly into a multi-billion-dollar business. Biopharmaceuticals are innovative resolutions which revolutionized the treatment of significant chronic diseases and malignancies. Currently, a variety of therapeutic options that include antiviral medications, monoclonal antibodies, and immunomodulatory agents are available for the management of COVID-19.

SHORT CONCLUSION

The invasion of mAbs in new medical sectors will increase the market magnitude as it is expected to generate revenue of about 300 billion $ by 2025. In the current mini-review, the applications of monoclonal antibodies in immune-diagnosis and immunotherapy will be demonstrated, particularly for COVID-19 infection and will focus mainly on monoclonal antibodies in the market.

Expression and purification of a novel single-chain diabody (scDb-hERG1/β1) from Pichia pastoris transformants

In the last decades, protein engineering has developed particularly in biotechnology and pharmaceutical field. In particular, the engineered antibody subclass has arisen. The single chain diabody format (scDb), conjugating small size with antigen specificity, offers versatility representing a gold standard for a variety of applications, spacing from research to diagnostics and therapy. Along with such advantages, comes the challenge of optimizing their production, improving expression systems, purification procedures and stability. All such parameters are detrimental for protein production in general and above all for recombinant antibody expression, which has to be fine-tuned, choosing a proper protein-expression host and adjusting expression protocols accordingly. In the present paper, we present data regarding the production and purification of a single chain diabody directed against the macromolecular complex hERG1/β1 integrin. We focus on the expression of clones deriving from the transformation of Pichia pastoris yeast cells. In particular, we compare two different clones arose from two separate transformation processes, demonstrating that both are suitable for proper protein expression. Moreover, we have set up an expression protocol and compared the yields obtained using two purification machines: Akta Pure and Akta Start, with a positive outcome.

Solubility, Stability, and Avidity of Recombinant Antibody Fragments Expressed in Microorganisms

Solubility of recombinant proteins (i.e., the extent of soluble versus insoluble expression in heterogeneous hosts) is the first checkpoint criterion for determining recombinant protein quality. However, even soluble proteins often fail to represent functional activity because of the involvement of non-functional, misfolded, soluble aggregates, which compromise recombinant protein quality. Therefore, screening of solubility and folding competence is crucial for improving the quality of recombinant proteins, especially for therapeutic applications. The issue is often highlighted especially in bacterial recombinant hosts, since bacterial cytoplasm does not provide an optimal environment for the folding of target proteins of mammalian origin. Antibody fragments, such as single-chain variable fragment (scFv), single-chain antibody (scAb), and fragment antigen binding (Fab), have been utilized for numerous applications such as diagnostics, research reagents, or therapeutics. Antibody fragments can be efficiently expressed in microorganisms so that they offer several advantages for diagnostic applications such as low cost and high yield. However, scFv and scAb fragments have generally lower stability to thermal stress than full-length antibodies, necessitating a judicious combination of designer antibodies, and bacterial hosts harnessed with robust chaperone function. In this review, we discuss efforts on not only the production of antibodies or antibody fragments in microorganisms but also scFv stabilization via (i) directed evolution of variants with increased stability using display systems, (ii) stabilization of the interface between variable regions of heavy (V_H) and light (V_L) chains through the introduction of a non-native covalent bond between the two chains, (iii) rational engineering of V_H-V_L pair, based on the structure, and (iv) computational approaches. We also review recent advances in stability design, increase in avidity by multimerization, and maintaining the functional competence of chimeric proteins prompted by various types of chaperones.

The Intracellular Delivery Of Anti-HPV16 E7 scFvs Through Engineered Extracellular Vesicles Inhibits The Proliferation Of HPV-Infected Cells

Purpose

Single-chain variable fragments (scFvs) are one of the smallest antigen-binding units having the invaluable advantage to be expressed by a unique short open reading frame (ORF). Despite their reduced size, spontaneous cell entry of scFvs remains inefficient, hence precluding the possibility to target intracellular antigens. Here, we describe an original strategy to deliver scFvs inside target cells through engineered extracellular vesicles (EVs). This approach relies on the properties of a Human Immunodeficiency Virus (HIV)-1 Nef mutant protein referred to as Nef^mut. It is a previously characterized Nef allele lacking basically all functions of wt Nef, yet strongly accumulating in the EV lumen also when fused at its C-terminus with a foreign protein. To gain the proof-of-principle for the efficacy of the proposed strategy, the tumor-promoting Human Papilloma Virus (HPV)16-E7 protein was considered as a scFv-specific intracellular target. The oncogenic effect of HPV16-E7 relies on its binding to the tumor suppressor pRb protein leading to a dysregulated cell duplication. Interfering with this interaction means impairing the HPV16-E7-induced cell proliferation.

Methods

The Nef^mut gene was fused in frame at its 3ʹ-terminus with the ORF coding for a previously characterized anti-HPV16-E7 scFv. Interaction between the Nef^mut-fused anti-HPV16-E7 scFv and the HPV16-E7 protein was tested by both confocal microscope and co-immunoprecipitation analyses on co-transfected cells. The in cis anti-proliferative effect of the Nef^mut/anti-HPV16-E7 scFv was assayed by transfecting HPV16-infected cells. The anti-proliferative effect of EVs engineered with Nef^mut/anti-HPV16-E7 scFv on HPV16-E7-expressing cells was evaluated in two ways: i) through challenge with purified EVs by a Real-Time Cell Analysis system and ii) in transwell co-cultures by an MTS-based assay.

Results

The Nef^mut/anti-HPV16-E7 scFv chimeric product is efficiently uploaded in EVs, binds HPV16-E7, and inhibits the proliferation of HPV16-E7-expressing cells. Most important, challenge with cell-free EVs incorporating the Nef^mut/anti-HPV16-E7 scFv led to the inhibition of proliferation of HPV16-E7-expressing cells. The proliferation of these cells was hindered also when they were co-cultured in transwells with cells producing EVs uploading Nef^mut/anti-HPV16-E7 scFv.

Conclusion

Our data represent the proof-of-concept for the possibility to target intracellular antigens through EV-mediated delivery of scFvs. This finding could be relevant to design novel methods of intracellular therapeutic interventions.

Development of a novel human phage display-derived anti-LAG3 scFv antibody targeting CD8+ T lymphocyte exhaustion

BACKGROUND

Lymphocyte-activation gene (LAG)3 is a 498 aa transmembrane type I protein acting as an immune inhibitory receptor. It is expressed on activated lymphocytes, natural killer cells and plasmacytoid dendritic cells. In activated lymphocytes, LAG3 expression is involved in negative control of cell activation/proliferation to ensure modulation and control of immune responses. In view of its deregulated expression in tumor-infiltrating lymphocytes, LAG3, together with the additional immune checkpoint inhibitors CTLA4 and PD1, is considered a major target in order to reverse the immunosuppression typically mounting in oncologic diseases. Since many patients still fail to respond to current immune checkpoints-based therapies, the identification of new effective immune inhibitors is a priority in the ongoing fight against cancer.

RESULTS

We identified a novel human single-chain variable fragment (scFv) Ab against a conformational epitope of LAG3 by in vitro phage display technology using the recombinant antigen as a bait. This scFv (referred to as F7) was characterized in terms of binding specificity to both recombinant antigen and human LAG3-expressing cells. It was then rebuilt into an IgG format pre-optimized for clinical usage, and the resulting bivalent construct was shown to preserve its ability to bind LAG3 on human cells. Next, we analyzed the activity of the anti-LAG3 scFvF7 using two different antigen-specific CD8+ T lymphocyte clones as target cells. We proved that the reconstituted anti-LAG3 F7 Ab efficiently binds the cell membrane of both cell clones after peptide-activation. Still more significantly, we observed a striking increase in the peptide-dependent cell activation upon Ab treatment as measured in terms of IFN-γ release by both ELISA and ELISPOT assays.

CONCLUSIONS

Overall, the biotechnological strategy described herein represents a guiding development model for the search of novel useful immune checkpoint inhibitors. In addition, our functional data propose a novel candidate reagent for consideration as a cancer treatment.

Hysteretic Genetic Circuit for Detection of Proteasomal Degradation in Mammalian Cells

Synthetic hysteretic mammalian gene circuits generating sustained cellular responses to transient perturbations provide important tools to investigate complex cellular behaviors and reprogram cells for a variety of applications, ranging from protein production to cell fate decisions. The design rules of synthetic gene circuits with controlled hysteretic behaviors, however, remain uncharacterized. To identify the criteria for achieving predictable control of hysteresis, we built a genetic circuit for detection of proteasomal degradation (Hys-Deg). The Hys-Deg circuit is based on a tetracycline-controlled transactivator (tTA) variant engineered to interface with the ubiquitin proteasome system (UPS). The tTA variant activates its own expression, generating a positive feedback loop that is triggered by expression of another tTA gene that is constitutively regulated. Guided by predictive modeling, we characterized the hysteretic response of the Hys-Deg circuit. We demonstrated that control of the hysteretic response is achieved by modulating the ratio of expression of constitutive to inducible tTA. We also showed that the system can be finely tuned through dosage of the inducer tetracycline to calibrate the circuit for detection of the desired levels of UPS activation. This study establishes the design rules for building a hysteretic genetic circuit with an autoregulatory feedback loop and provides a synthetic memory module that could be easily integrated into regulatory gene networks to study and engineer complex cellular behaviors.

Intracellular human antibody fragments recognizing the VP35 protein of Zaire Ebola filovirus inhibit the protein activity

BACKGROUND

Ebola hemorrhagic fever is caused by the Ebola filovirus (EBOV), which is one of the most aggressive infectious agents known worldwide. The EBOV pathogenesis starts with uncontrolled viral replication and subversion of both the innate and adaptive host immune response. The multifunctional viral VP35 protein is involved in this process by exerting an antagonistic action against the early antiviral alpha/beta interferon (IFN-α/β) response, and represents a suitable target for the development of strategies to control EBOV infection. Phage display technology permits to select antibodies as single chain Fragment variable (scFv) from an artificial immune system, due to their ability to specifically recognize the antigen of interest. ScFv is ideal for genetic manipulation and to obtain antibody constructs useful for targeting either antigens expressed on cell surface or intracellular antigens if the scFv is expressed as intracellular antibody (intrabody) or delivered into the cells.

RESULTS

Monoclonal antibodies (mAb) in scFv format specific for the EBOV VP35 were isolated from the ETH-2 library of human recombinant antibodies by phage display technology. Five different clones were identified by sequencing, produced in E.coli and expressed in CHO mammalian cells to be characterized in vitro. All the selected scFvs were able to react with recombinant VP35 protein in ELISA, one of the scFvs being also able to react in Western Blot assay (WB). In addition, all scFvs were expressed in cell cytoplasm as intrabodies; a luciferase reporter gene inhibition assay performed in A549 cells showed that two of the scFvs can significantly hamper the inhibition of the IFN-β-induced RIG-I signaling cascade mediated by EBOV VP35.

CONCLUSION

Five antibodies in scFv format recognize an active form of EBOV VP35 in ELISA, while one antibody also recognizes VP35 in WB. Two of these scFvs were also able to interfere with the intracellular activity of VP35 in a cell system in vitro. These findings suggest that such antibodies in scFv format might be employed to develop therapeutic molecules able to hamper EBOV infections.

Effective and efficient characterization of Chinese hamster ovary production cell lines using automated intracellular staining and statistical modeling

Mammalian cell line development is critical to bioproduct manufacturing. Success requires selecting a line with desirable performance characteristics, including consistent expression throughout the proposed manufacturing window. Given the genetic and phenotypic flux inherent to immortalized lines such as Chinese hamster ovary cells, clonally-derived cell line characterization is vital. We describe here the development and implementation of a novel addition to our characterization approach to ensure production cell line suitability: automated intracellular staining with statistical modeling. Case studies are presented which highlight this method's sensitivity to epigenetic expression effects, closing a gap left by our historically-leveraged genetic suitability characterization. Additionally, we demonstrate how an orthogonal, complimentary assay can help identify opportunities for improvement in even a well-established methodology such as our genetic suitability assessment. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:570-583, 2018.

Sustained secretion of anti-tumor necrosis factor α monoclonal antibody from ex vivo genetically engineered dermal tissue demonstrates therapeutic activity in mouse model of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a symmetric inflammatory polyarthritis associated with high concentrations of pro-inflammatory, cytokines including tumor necrosis factor (TNF)-α. Adalimumab is a monoclonal antibody (mAb) that binds TNF-α, and is widely used to treat RA. Despite its proven clinical efficacy, adalimumab and other therapeutic mAbs have disadvantages, including the requirement for repeated bolus injections and the appearance of treatment limiting anti-drug antibodies. To address these issues, we have developed an innovative ex vivo gene therapy approach, termed transduced autologous restorative gene therapy (TARGT), to produce and secrete adalimumab for the treatment of RA.

METHODS

Helper-dependent (HD) adenovirus vector containing adalimumab light and heavy chain coding sequences was used to transduce microdermal tissues and cells of human and mouse origin ex vivo, rendering sustained secretion of active adalimumab. The genetically engineered tissues were subsequently implanted in a mouse model of RA.

RESULTS

Transduced human microdermal tissues implanted in SCID mice demonstrated 49 days of secretion of active adalimumab in the blood, at levels of tens of microgram per milliliter. In addition, transduced autologous dermal cells were implanted in the RA mouse model and demonstrated statistically significant amelioration in RA symptoms compared to naïve cell implantation and were similar to recombinant adalimumab bolus injections.

CONCLUSIONS

The results of the present study report microdermal tissues engineered to secrete active adalimumab as a proof of concept for sustained secretion of antibody from the novel ex vivo gene therapy TARGT platform. This technology may now be applied to a range of antibodies for the therapy of other diseases.

Improvement of solubility and refolding of an anti-human epidermal growth factor receptor 2 single-chain antibody fragment inclusion bodies

Single chain variable fragment antibodies (scFvs) have attracted many attentions due to their small size, faster bio-distribution and better penetration in to the target tissues, and ease of expression in Escherichia coli. Although, scFv expression in E. coli usually leads to formation of inclusion bodies (IBs). The aim of this research was to improve solubilizing and refolding conditions for IBs of scFv version of pertuzumab (anti-human epidermal growth factor receptor 2 (HER2) antibody). After protein overexpression in E. coli BL21 (DE3), bacterial cells were lysed and IBs were extracted via repeated washing and centrifugation. The effect of different types, concentrations, pHs, and additive of denaturing agents on IBs solubility were evaluated. More than 40 refolding additives were screened and combinations of 10 of the best additives were check out using Plackett-Burman design to choose three refolding additives with the most positive effect on refolding of the scFv. Response surface methodology (RSM) was used to optimize the concentration of adopted additives. The most efficient buffer to solubilize IBs was a buffer containing 6 M urea with 6 mM beta mercaptoethanol, pH 11. The optimum concentration of three buffer additives for refolding of the scFv was 23 mM tricine, 0.55 mM arginine, and 14.3 mM imidazole. The bioactivity of the refolded scFv was confirmed by immunohistochemical staining of breast cancer tissue, a specific binding based method. The systematic optimization of refolding buffer developed in the present work will contribute to improve the refolding of other scFv fragments.

An efficient route to bispecific antibody production using single-reactor mammalian co-culture

Bispecific antibodies have shown promise in the clinic as medicines with novel mechanisms of action. Lack of efficient production of bispecific IgGs, however, has limited their rapid advancement. Here, we describe a single-reactor process using mammalian cell co-culture production to efficiently produce a bispecific IgG with 4 distinct polypeptide chains without the need for parallel processing of each half-antibody or additional framework mutations. This method resembles a conventional process, and the quality and yield of the monoclonal antibodies are equal to those produced using parallel processing methods. We demonstrate the application of the approach to diverse bispecific antibodies, and its suitability for production of a tissue specific molecule targeting fibroblast growth factor receptor 1 and klotho β that is being developed for type 2 diabetes and other obesity-linked disorders.

Evolving trends in mAb production processes

Monoclonal antibodies (mAbs) have established themselves as the leading biopharmaceutical therapeutic modality. The establishment of robust manufacturing platforms are key for antibody drug discovery efforts to seamlessly translate into clinical and commercial successes. Several drivers are influencing the design of mAb manufacturing processes. The advent of biosimilars is driving a desire to achieve lower cost of goods and globalize biologics manufacturing. High titers are now routinely achieved for mAbs in mammalian cell culture. These drivers have resulted in significant evolution in process platform approaches. Additionally, several new trends in bioprocessing have arisen in keeping with these needs. These include the consideration of alternative expression systems, continuous biomanufacturing and non-chromatographic separation formats. This paper discusses these drivers in the context of the kinds of changes they are driving in mAb production processes.

Cultivation of Pichia pastoris carrying the scFv anti LDL (-) antibody fragment. Effect of preculture carbon source

Antibodies and antibody fragments are nowadays among the most important biotechnological products, and Pichia pastoris is one of the most important vectors to produce them as well as other recombinant proteins. The conditions to effectively cultivate a P. pastoris strain previously genetically modified to produce the single-chain variable fragment anti low density lipoprotein (−) under the control of the alcohol oxidase promoter have been investigated in this study. In particular, it was evaluated if, and eventually how, the carbon source (glucose or glycerol) used in the preculture preceding cryopreservation in 20% glycerol influences both cell and antibody fragment productions either in flasks or in bioreactor. Although in flasks the volumetric productivity of the antibody fragment secreted by cells precultured, cryopreserved and reactivated in glycerol was 42.9% higher compared with cells precultured in glucose, the use of glycerol in bioreactor led to a remarkable shortening of the lag phase, thereby increasing it by no less than thrice compared to flasks. These results are quite promising in comparison with those reported in the literature for possible future industrial applications of this cultivation, taking into account that the overall process time was reduced by around 8 h.

Bacterial production and structure-functional validation of a recombinant antigen-binding fragment (Fab) of an anti-cancer therapeutic antibody targeting epidermal growth factor receptor

Fragment engineering of monoclonal antibodies (mAbs) has emerged as an excellent paradigm to develop highly efficient therapeutic and/or diagnostic agents. Engineered mAb fragments can be economically produced in bacterial systems using recombinant DNA technologies. In this work, we established recombinant production in Escherichia coli for monovalent antigen-binding fragment (Fab) adopted from a clinically used anticancer mAB drug cetuximab targeting epidermal growth factor receptor (EGFR). Recombinant DNA constructs were designed to express both polypeptide chains comprising Fab in a single vector and to secrete them to bacterial periplasmic space for efficient folding. Particularly, a C-terminal engineering to confer an interchain disulfide bond appeared to be able to enhance its heterodimeric integrity and EGFR-binding activity. Conformational relevance of the purified final product was validated by mass spectrometry and crystal structure at 1.9 Å resolution. Finally, our recombinant cetuximab-Fab was found to have strong binding affinity to EGFR overexpressed in human squamous carcinoma model (A431) cells. Its binding ability was comparable to that of cetuximab. Its EGFR-binding affinity was estimated at approximately 0.7 nM of Kd in vitro, which was quite stronger than the binding affinity of natural ligand EGF. Hence, the results validate that our construction could serve as an efficient platform to produce a recombinant cetuximab-Fab with a retained antigen-binding functionality.

Linkers Having a Crucial Role in Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) comprised of a desirable monoclonal antibody, an active cytotoxic drug and an appropriate linker are considered to be an innovative therapeutic approach for targeted treatment of various types of tumors and cancers, enhancing the therapeutic parameter of the cytotoxic drug and reducing the possibility of systemic cytotoxicity. An appropriate linker between the antibody and the cytotoxic drug provides a specific bridge, and thus helps the antibody to selectively deliver the cytotoxic drug to tumor cells and accurately releases the cytotoxic drug at tumor sites. In addition to conjugation, the linkers maintain ADCs' stability during the preparation and storage stages of the ADCs and during the systemic circulation period. The design of linkers for ADCs is a challenge in terms of extracellular stability and intracellular release, and intracellular circumstances, such as the acid environment, the reducing environment and cathepsin, are considered as the catalysts to activate the triggers for initiating the cleavage of ADCs. This review discusses the linkers used in the clinical and marketing stages for ADCs and details the fracture modes of the linkers for the further development of ADCs.

Enhancing full-length antibody production by signal peptide engineering

Background

Protein secretion to the periplasm of Escherichia coli offers an attractive route for producing heterologous proteins including antibodies. In this approach, a signal peptide is fused to the N-terminus of the heterologous protein. The signal peptide mediates translocation of the heterologous protein from the cytoplasm to the periplasm and is cleaved during the translocation process. It was previously shown that optimization of the translation initiation region (TIR) which overlaps with the nucleotide sequence of the signal sequence improves the production of heterologous proteins. Despite the progress, there is still room to improve yields using secretion as a means to produce protein complexes such as full-length monoclonal antibodies (mAbs).

Results

In this study we identified the inefficient secretion of heavy chain as the limitation for full-length mAb accumulation in the periplasm. To improve heavy chain secretion we investigated the effects of various signal peptides at controlled TIR strengths. The signal peptide of disulfide oxidoreductase (DsbA) mediated more efficient secretion of heavy chain than the other signal peptides tested. Mutagenesis studies demonstrated that at controlled translational levels, hydrophobicity of the hydrophobic core (H-region) of the signal peptide is a critical factor for heavy chain secretion and full-length mAb accumulation in the periplasm. Increasing the hydrophobicity of a signal peptide enhanced heavy chain secretion and periplasmic levels of assembled full-length mAbs, while decreasing the hydrophobicity had the opposite effect.

Conclusions

This study demonstrates that under similar translational strengths, the hydrophobicity of the signal peptide plays an important role in heavy chain secretion. Increasing the hydrophobicity of the H-region and controlling TIR strengths can serve as an approach to improve heavy chain secretion and full-length mAb production in E. coli.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0445-3) contains supplementary material, which is available to authorized users.

'Zipbody' leucine zipper-fused Fab in E. coli in vitro and in vivo expression systems

A small antibody fragment, fragment of antigen binding (Fab), is favorable for various immunological assays. However, production efficiency of active Fab in microorganisms depends considerably on the clones. In this study, leucine zipper-peptide pairs that dimerize in parallel (ACID-p1 (LZA)/BASE-p1 (LZB) or c-Jun/c-Fos) were fused to the C-terminus of heavy chain (Hc, VH-CH1) and light chain (Lc, VL-CL), respectively, to accelerate the association of Hc and Lc to form Fab in Escherichia coli in vivo and in vitro expression systems. The leucine zipper-fused Fab named 'Zipbody' was constructed using anti-E. coli O157 monoclonal antibody obtained from mouse hybridoma and produced in both in vitro and in vivo expression systems in an active form, whereas Fab without the leucine zipper fusion was not. Similarly, Zipbody of rabbit monoclonal antibody produced in in vitro expression showed significant activity. The purified, mouse Zipbody produced in the E. coli strain Shuffle T7 Express had specificity toward the antigen; in bio-layer interferometry analysis, the KD value was measured to be 1.5-2.0 × 10(-8) M. These results indicate that leucine zipper fusion to Fab C-termini markedly enhances active Fab formation in E. coli.

Methods to Design and Synthesize Antibody-Drug Conjugates (ADCs)

Antibody-drug conjugates (ADCs) have become a promising targeted therapy strategy that combines the specificity, favorable pharmacokinetics and biodistributions of antibodies with the destructive potential of highly potent drugs. One of the biggest challenges in the development of ADCs is the application of suitable linkers for conjugating drugs to antibodies. Recently, the design and synthesis of linkers are making great progress. In this review, we present the methods that are currently used to synthesize antibody-drug conjugates by using thiols, amines, alcohols, aldehydes and azides.

Current methods for the synthesis of homogeneous antibody-drug conjugates

Development of efficient and safe cancer therapy is one of the major challenges of the modern medicine. Over the last few years antibody-drug conjugates (ADCs) have become a powerful tool in cancer treatment with two of them, Adcetris® (brentuximab vedotin) and Kadcyla® (ado-trastuzumab emtansine), having recently been approved by the Food and Drug Administration (FDA). Essentially, an ADC is a bioconjugate that comprises a monoclonal antibody that specifically binds tumor surface antigen and a highly potent drug, which is attached to the antibody via either cleavable or stable linker. This approach ensures specificity and efficacy in fighting cancer cells, while healthy tissues remain largely unaffected. Conventional ADCs, that employ cysteine or lysine residues as conjugation sites, are highly heterogeneous. This means that the species contain various populations of the ADCs with different drug-to-antibody ratios (DARs) and different drug load distributions. DAR and drug-load distribution are essential parameters of ADCs as they determine their stability and efficacy. Therefore, various drug-loaded forms of ADCs (usually from zero to eight conjugated molecules per antibody) may have distinct pharmacokinetics (PK) in vivo and may differ in clinical performance. Recently, a significant progress has been made in the field of site-specific conjugation which resulted in a number of strategies for synthesis of the homogeneous ADCs. This review describes newly-developed methods that ensure homogeneity of the ADCs including use of engineered reactive cysteine residues (THIOMAB), unnatural amino acids, aldehyde tags, enzymatic transglutaminase- and glycotransferase-based approaches and novel chemical methods. Furthermore, we briefly discuss the limitation of these methods emphasizing the need for further improvement in the ADC design and development.

A high cell density transient transfection system for therapeutic protein expression based on a CHO GS-knockout cell line: process development and product quality assessment

Transient gene expression (TGE) is a rapid method for the production of recombinant proteins in mammalian cells. While the volumetric productivity of TGE has improved significantly over the past decade, most methods involve extensive cell line engineering and plasmid vector optimization in addition to long fed batch cultures lasting up to 21 days. Our colleagues have recently reported the development of a CHO K1SV GS-KO host cell line. By creating a bi-allelic glutamine synthetase knock out of the original CHOK1SV host cell line, they were able to improve the efficiency of generating high producing stable CHO lines for drug product manufacturing. We developed a TGE method using the same CHO K1SV GS-KO host cell line without any further cell line engineering. We also refrained from performing plasmid vector engineering. Our objective was to setup a TGE process to mimic protein quality attributes obtained from stable CHO cell line. Polyethyleneimine (PEI)-mediated transfections were performed at high cell density (4 × 10(6) cells/mL) followed by immediate growth arrest at 32 °C for 7 days. Optimizing DNA and PEI concentrations proved to be important. Interestingly, found the direct transfection method (where DNA and PEI were added sequentially) to be superior to the more common indirect method (where DNA and PEI are first pre-complexed). Moreover, the addition of a single feed solution and a polar solvent (N,N dimethylacetamide) significantly increased product titers. The scalability of process from 2 mL to 2 L was demonstrated using multiple proteins and multiple expression volumes. Using this simple, short, 7-day TGE process, we were able to successfully produce 54 unique proteins in a fraction of the time that would have been required to produce the respective stable CHO cell lines. The list of 54 unique proteins includes mAbs, bispecific antibodies, and Fc-fusion proteins. Antibody titers of up to 350 mg/L were achieved with the simple 7-day process. Titers were increased to 1 g/L by extending the culture to 16 days. We also present two case studies comparing product quality of material generated by transient HEK293, transient CHO K1SV GS-KO, and stable CHO K1SV KO pool. Protein from transient CHO was more representative of stable CHO protein compared to protein produced from HEK293.

Efficient enrichment of high-producing recombinant Chinese hamster ovary cells for monoclonal antibody by flow cytometry

To screen a high-producing recombinant Chinese hamster ovary (CHO) cell from transfected cells is generally laborious and time-consuming. We developed an efficient enrichment strategy for high-producing cell screening using flow cytometry (FCM). A stable pool that had possibly shown a huge variety of monoclonal antibody (mAb) expression levels was prepared by transfection of an expression vector for mAb production to a CHO cell. To enrich high-producing cells derived from a stable pool stained with a fluorescent-labeled antibody that binds to mAb presented on the cell surface, we set the cell size and intracellular density gates based on forward scatter (FSC) and side scatter (SSC), and collected the brightest 5% of fluorescein isothiocyanate (FITC)-positive cells from each group by FCM. The final product concentration in a fed-batch culture of cells sorted without FSC and SSC gates was 1.2-1.3-times higher than that of unsorted cells, whereas that of cells gated by FSC and SSC was 3.4-4.7-fold higher than unsorted cells. Surprisingly, the fraction with the highest final product concentration indicated the smallest value of FSC and SSC, and the middle value of fluorescence intensity among all fractionated cells. Our results showed that our new screening strategy by FCM based on FSC and SSC gates could achieve an efficient enrichment of high-producing cells with the smallest value of FSC and SSC.

Strategies for Engineering Protein N-Glycosylation Pathways in Mammalian Cells

Complexity and heterogeneity of oligosaccharides present a considerable challenge to the biopharmaceutical industry to manufacture biotherapeutics with reproducible and consistent glycoform profiles. Mammalian cells, especially Chinese hamster ovary cells, are the most widely used platform for the production of biotherapeutics. The glycans produced are predominantly of the complex type, with some differences between human and nonhuman mammalian glycosylation existing. This review briefly summarizes metabolic glyco-engineering strategies used in mammalian cells in order to alter the glycosylation patterns attached to proteins applied for diverse biotechnology applications.

Generation of cell lines for monoclonal antibody production

Monoclonal antibodies (mAbs) represent the largest group of therapeutic proteins with 30 products approved in the USA and hundreds of therapies currently undergoing clinical trials. The complex nature of mAbs makes their development as therapeutic agents constrained by numerous criteria such as quality, safety, regulation, and quantity. Identification of a clonal cell line expressing high levels of mAb with adequate quality attributes and generated in compliance with regulatory standards is a necessary step prior to a program moving to large-scale production for clinical material. This chapter outlines the stable transfection technology that generates clonal cell lines for commercial manufacturing processes.

High efficient expression of a functional humanized single-chain variable fragment (scFv) antibody against CD22 in Pichia pastoris

Single-chain variable fragments (scFvs) have recently emerged as attractive candidates in targeted immunotherapy of various malignancies. The anti-CD22 scFv is able to target CD22, on B cell surface and is being considered as a promising molecule in targeted immunotherapy of B cell malignancies. The recombinant anti-CD22 scFv has been successfully expressed in Escherichia coli; however, the insufficient production yield has been a major bottleneck for its therapeutic application. The methylotrophic yeast Pichia pastoris has become a highly popular expression host for the production of a wide variety of recombinant proteins such as antibody fragments. In this study, we used the Pichia expression system to express a humanized scFv antibody against CD22. The full-length humanized scFv gene was codon optimized, cloned into the pPICZαA and expressed in GS115 strain. The maximum production level of the scFv (25 mg/L) were achieved at methanol concentration, 1 %; pH 6.0; inoculum density, OD600 = 3 and the induction time of 72 h. The correlation between scFv gene dosage and expression level was also investigated by real-time PCR, and the results confirmed the presence of such correlation up to five gene copies. Immunofluorescence and flow cytometry studies and Biacore analysis demonstrated binding to CD22 on the surface of human lymphoid cell line Raji and recombinant soluble CD22, respectively. Taken together, the presented data suggest that the Pichia pastoris can be considered as an efficient host for the large-scale production of anti-CD22 scFv as a promising carrier for targeted drug delivery in treatment of CD22(+) B cell malignancies.

Ultra scale-down characterization of the impact of conditioning methods for harvested cell broths on clarification by continuous centrifugation-Recovery of domain antibodies from rec E. coli

The processing of harvested E. coli cell broths is examined where the expressed protein product has been released into the extracellular space. Pre-treatment methods such as freeze–thaw, flocculation, and homogenization are studied. The resultant suspensions are characterized in terms of the particle size distribution, sensitivity to shear stress, rheology and solids volume fraction, and, using ultra scale-down methods, the predicted ability to clarify the material using industrial scale continuous flow centrifugation. A key finding was the potential of flocculation methods both to aid the recovery of the particles and to cause the selective precipitation of soluble contaminants. While the flocculated material is severely affected by process shear stress, the impact on the very fine end of the size distribution is relatively minor and hence the predicted performance was only diminished to a small extent, for example, from 99.9% to 99.7% clarification compared with 95% for autolysate and 65% for homogenate at equivalent centrifugation conditions. The lumped properties as represented by ultra scale-down centrifugation results were correlated with the basic properties affecting sedimentation including particle size distribution, suspension viscosity, and solids volume fraction. Grade efficiency relationships were used to allow for the particle and flow dynamics affecting capture in the centrifuge. The size distribution below a critical diameter dependant on the broth pre-treatment type was shown to be the main determining factor affecting the clarification achieved. Biotechnol. Bioeng. 2014;111: 913–924. © 2013 The Authors. Biotechnology and Bioengineering Published by Wiley Periodicals, Inc.

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.

Gene expression in Mammalian cells and its applications

The production of proteins in appropriate quantity and quality is an essential requirement of the present time. There appears to be a progressive increase in the application of mammalian cells for proteins production. Expression systems utilizing mammalian cells for recombinant proteins are able to introduce proper protein folding, post-translational modifications, and product assembly, which are important for complete biological activity. This review article is totally based on literature survey. In this article much emphasis has been done on the mammalian expression system. The author focused on different mammalian cell lines that express the gene. The different vector systems that transfer the gene into mammalian cells like plasmid based expression vectors, adenovirus vectors, vaccinia vectors, retroviral vector and baculovirus as vectors were explored. The processes for the transfer of gene into mammalian cells were also reviewed. Application and limitations of mammalian expression system were also focused. The purpose of research in writing this article is to create awareness in researchers, starting their career in gene expression related to mammalian cells. The principal result and major conclusion of this article is to make available the molecular technologies, expression system and applications of gene expression in mammalian cell lines.

Efficient production of anti-fluorescein and anti-lysozyme as single-chain anti-body fragments (scFv) by Brevibacillus expression system

Expression of scFv in Brevibacillus choshinensis was tested using combinations of three different promoters and four different secretion signals. Two model scFv constructs, i.e., His-scFvFLU and His-scFvHEL, were successfully expressed with some of the combinations. Ni Sepharose column and size exclusion chromatography resulted in fairly pure preparations of these two proteins. The purified His-scFvFLU inhibited fluorescence from fluorescein, while the purified His-scFvHEL inhibited lysozyme activity. Relatively high yield of His-scFvFLU (∼40%) and His-scFvHEL (∼30%) was achieved with the expression and purification system described here.

Glycosylation: impact, control and improvement during therapeutic protein production

The emergence of the biopharmaceutical industry represented a major revolution for modern medicine, through the development of recombinant therapeutic proteins that brought new hope for many patients with previously untreatable diseases. There is a ever-growing demand for these therapeutics that forces a constant technological evolution to increase product yields while simultaneously reducing costs. However, the process changes made for this purpose may also affect the quality of the product, a factor that was initially overlooked but which is now a major focus of concern. Of the many properties determining product quality, glycosylation is regarded as one of the most important, influencing, for example, the biological activity, serum half-life and immunogenicity of the protein. Consequently, monitoring and control of glycosylation is now critical in biopharmaceutical manufacturing and a requirement of regulatory agencies. A rapid evolution is being observed in this context, concerning the influence of glycosylation in the efficacy of different therapeutic proteins, the impact on glycosylation of a diversity of parameters/processes involved in therapeutic protein production, the analytical methodologies employed for glycosylation monitoring and control, as well as strategies that are being explored to use this property to improve therapeutic protein efficacy (glycoengineering). This work reviews the main findings on these subjects, providing an up-to-date source of information to support further studies.

Expression of antibodies using single open reading frame (sORF) vector design: Demonstration of manufacturing feasibility

Efficient production of large quantities of therapeutic antibodies is becoming a major goal of the pharmaceutical industry. We developed a proprietary expression system using a polyprotein precursor-based approach to antibody expression in mammalian cells. In this approach, the coding regions for heavy and light chains are included within a single open reading frame (sORF) separated by an in-frame intein gene. A single mRNA and subsequent polypeptide are produced upon transient and stable transfection into HEK293 and CHO cells, respectively. Heavy and light chains are separated by the autocatalytic action of the intein and antibody processing proceeds to produce active, secreted antibody. Here, we report advances in sORF technology toward establishment of a viable manufacturing platform for therapeutic antibodies in CHO cells. Increasing expression levels and improving antibody processing by intein and signal peptide selection are discussed.