Mouse monoclonal antibodies in biological research: strategies for high-throughput production

An efficient approach for SARS-CoV-2 monoclonal antibody production via modified mRNA-LNP immunization

Throughout the COVID-19 pandemic, many prophylactic and therapeutic drugs have been evaluated and introduced. Among these treatments, monoclonal antibodies (mAbs) that bind to and neutralize SARS-CoV-2 virus have been applied as complementary and alternative treatments to vaccines. Although different methodologies have been utilized to produce mAbs, traditional hybridoma fusion technology is still commonly used for this purpose due to its unmatched performance record. In this study, we coupled the hybridoma fusion strategy with mRNA-lipid nanoparticle (LNP) immunization. This time-saving approach can circumvent biological and technical hurdles, such as difficult-to-express membrane proteins, antigen instability, and the lack of posttranslational modifications on recombinant antigens. We used mRNA-LNP immunization and hybridoma fusion technology to generate mAbs against the receptor binding domain (RBD) of SARS-CoV-2 spike (S) protein. Compared with traditional protein-based immunization approaches, inoculation of mice with RBD mRNA-LNP induced higher titers of serum antibodies and markedly increased serum neutralizing activity. The mAbs we obtained can bind to SARS-CoV-2 RBDs from several variants. Notably, RBD-mAb-3 displayed particularly high binding affinities and neutralizing potencies against both Alpha and Delta variants. In addition to introducing specific mAbs against SARS-CoV-2, our data generally demonstrate that mRNA-LNP immunization may be useful to quickly generate highly functional mAbs against emerging infectious diseases.

Monoclonal Antibody Discovery Based on Precise Selection of Single Transgenic Hybridomas with an On-Cell-Surface and Antigen-Specific Anchor

Hybridoma technology is widely used for monoclonal antibody (mAb) discovery, whereas the generation and identification of single hybridomas by the limiting dilution method (LDM) are tedious, inefficient, and time- and cost-consuming, especially for hapten molecules. Here, we describe a single transgenic hybridoma selection method (STHSM) that employs a transgenic Sp2/0 with an artificial and stable on-cell-surface anchor. The anchor was designed by combining the truncated variant transmembrane domain of EGFR with a biotin acceptor peptide AVI-tag, which was stably integrated into the genome of Sp2/0 via a piggyBac transposon. To ensure the subsequent precise selection of the hybridoma, the number of on-cell-surface anchors of the transfected Sp2/0 for fusion with immunized splenocytes was further normalized by flow cytometry at the single cell level. Then the single antigen-specific transgenic hybridomas were precisely identified and automatically selected using a CellenONE platform based on the fluorescence assay of the on-cell-surface anchor with the corresponding secreted antigen-specific mAb. The STHSM produced 579 single chloramphenicol (CAP)-specific transgenic hybridomas with a positive rate of 62.7% in 10 plates within 2 h by one-step selection, while only 12 single CAP-specific hybridomas with a positive rate of 6.3% in 40 plates required at least 32 days using the LDM with multiple subcloning steps. The best affinity of mAbs from the STHSM was more than 2-fold higher than that of those from the LDM, and this was mainly due to the preaffinity selection based on the on-cell-surface anchors and more interactions between the mAb and CAP. Then the mAbs from the STHSM and LDM were used to develop an immunoassay for CAP in spiked and natural biological samples. The method displayed satisfactory sensitivity, accuracy, and precision, demonstrating that the STHSM we developed is a versatile, practical, and efficient method for mAb discovery.

Single B cell technologies for monoclonal antibody discovery

Monoclonal antibodies (mAbs) are often selected from antigen-specific single B cells derived from different hosts, which are notably short-lived in ex vivo culture conditions and hence, arduous to interrogate. The development of several new techniques and protocols has facilitated the isolation and retrieval of antibody-coding sequences of antigen-specific B cells by also leveraging miniaturization of reaction volumes. Alternatively, mAbs can be generated independently of antigen-specific B cells, comprising display technologies and, more recently, artificial intelligence-driven algorithms. Consequently, a considerable variety of techniques are used, raising the demand for better consolidation. In this review, we present and discuss the major techniques available to interrogate antigen-specific single B cells to isolate antigen-specific mAbs, including their main advantages and disadvantages.

Magnetic Nanoparticles with Surface Nanopockets for Highly Selective Antibody Isolation

Monoclonal antibodies (mAbs) are key components of revolutionary disease immunotherapies and are also essential for medical diagnostics and imaging. The impact of cost is illustrated by a price >$200,000 per year per patient for mAb-based cancer therapy. Purification represents a major issue in the final cost of these immunotherapy drugs. Protein A (PrA) resins are widely used to purify antibodies, but resin cost, separation efficiency, reuse, and stability are major issues. This paper explores a synthesis strategy for low-cost, reusable, stable PrA-like nanopockets on core-shell silica-coated magnetic nanoparticles (NPs) for IgG antibody isolation. Mouse IgG_2a, a strong PrA binder, was used as a template protein, first attaching it stem-down onto the NP surface. The stem-down orientation of IgG_2a on the NP surface before polymerization is critical for designing the films to bind IgGs. Following this, 1-tetraethoxysilane and four organosilane monomers with functional groups capable of mimicking binding interactions of proteins with IgG antibody stems were reacted to form a thin polymer coating on the NPs. After blocking nonspecific binding sites, removal of the mouse IgG_2a provided nanopockets on the core-shell NPs that showed binding characteristics for antibodies remarkably similar to PrA. Both smooth and rough core-shell NPs were used, with the latter providing much larger binding capacities for IgGs, with an excellent selectivity slightly better than that of commercial PrA magnetic beads. This paper is the first report of IgG-binding NPs that mimic PrA selectivity. These nanopocket NPs can be used for at least 15 regeneration cycles, and cost/use was 57-fold less than a high-quality commercial PrA resin.

A microfluidic chip for screening high-producing hybridomas at single cell level

Hybridomas are a commonly used, or even the only option, for laboratory study and pilot production of monoclonal antibodies (mAbs), which are crucial for both targeted therapy and biomedical study. A long-term culture of hybridomas will inevitably induce a heterogenization of the whole hybridoma population, resulting in a continuous growth of non-producing hybridomas. To overcome the limits of existing methods of screening heterogeneous hybridomas, in which the whole multi-round screening process is performed in multi-well plates or other discrete modules, this study presents a novel method in which all processing steps of a multi-round hybridoma screening are finished in a single microfluidic chip. This microfluidic chip comprehensively performs hybridoma trapping/proliferating/transferring and fluorescent identification of protein-antibody binding at single cell level. By performing a two-round screening of anti-CD45 mAb secreting hybridomas, the novel microfluidic chip was proved capable of screening several single high-producing hybridomas with minimum cell loss/human labor/time cost, and more importantly, enhanced accuracy and definite monoclonality, which is one of the most important properties of mAb production.

Immunotoxin Screening System: A Rapid and Direct Approach to Obtain Functional Antibodies with Internalization Capacities

Toxins, while harmful and potentially lethal, have been engineered to develop potent therapeutics including cytotoxins and immunotoxins (ITs), which are modalities with highly selective targeting capabilities. Currently, three cytotoxins and IT are FDA-approved for treatment of multiple forms of hematological cancer, and additional ITs are tested in the clinical trials or at the preclinical level. For next generation of ITs, as well as antibody-mediated drug delivery systems, specific targeting by monoclonal antibodies is critical to enhance efficacies and reduce side effects, and this methodological field remains open to discover potent therapeutic monoclonal antibodies. Here, we describe our application of engineered toxin termed a cell-based IT screening system. This unique screening strategy offers the following advantages: (1) identification of monoclonal antibodies that recognize cell-surface molecules, (2) selection of the antibodies that are internalized into the cells, (3) selection of the antibodies that induce cytotoxicity since they are linked with toxins, and (4) determination of state-specific activities of the antibodies by differential screening under multiple experimental conditions. Since the functional monoclonal antibodies with internalization capacities have been identified successfully, we have pursued their subsequent modifications beyond antibody drug conjugates, resulting in development of immunoliposomes. Collectively, this screening system by using engineered toxin is a versatile platform, which enables straight-forward and rapid selection for discovery of novel functional antibodies.

Antibody Screening by Microarray Technology-Direct Identification of Selective High-Affinity Clones

The primary screening of hybridoma cells is a time-critical and laborious step during the development of monoclonal antibodies. Often, critical errors occur in this phase, which supports the notion that the generation of monoclonal antibodies with hybridoma technology is difficult to control and hence, a risky venture. We think that it is crucial to improve the screening process to eliminate most of the critical deficits of the conventional approach. With this new microarray-based procedure, several advances could be achieved: Selectivity for excellent binders, high-throughput, reproducible signals, avoidance of misleading avidity (multivalency) effects, and performance of simultaneous competition experiments. The latter can also be used to select clones of desired cross-reactivity properties. In this paper, a model system with two excellent clones against carbamazepine, two weak clones, and blank supernatant containing fetal bovine serum was designed to examine the effectiveness of the new system. The excellent clones could be detected largely independent of the immunoglobulin G (IgG) concentration, which is usually unknown during the clone screening since the determination and subsequent adjustment of the antibody concentration are not feasible in most cases. Furthermore, in this approach, the enrichment, isolation, and purification of IgG for characterization is not necessary. Raw cell culture supernatant can be used directly, even when fetal calf serum (FCS) or other complex media is used. In addition, an improved method for the oriented antibody-immobilization on epoxy-silanized slides is presented. Based on the results of this model system with simulated hybridoma supernatants, we conclude that this approach should be preferable to most other protocols leading to many false positives, causing expensive and lengthy elimination steps to weed out the poor clones.

A novel approach for rapid high-throughput selection of recombinant functional rat monoclonal antibodies

Background

Most monoclonal antibodies against mouse antigens have been derived from rat spleen-mouse myeloma fusions, which are valuable tools for purposes ranging from general laboratory reagents to therapeutic drugs, and yet selecting and expressing them remains a time-consuming and inefficient process. Here, we report a novel approach for the rapid high-throughput selection and expression of recombinant functional rat monoclonal antibodies with different isotypes.

Results

We have developed a robust system for generating rat monoclonal antibodies through several processes involving simultaneously immunizing rats with three different antigens expressing in a mixed cell pools, preparing hybridoma cell pools, in vitro screening and subsequent cloning of the rearranged light and heavy chains into a single expression plasmid using a highly efficient assembly method, which can decrease the time and effort required by multiple immunizations and fusions, traditional clonal selection and expression methods. Using this system, we successfully selected several rat monoclonal antibodies with different IgG isotypes specifically targeting the mouse PD-1, LAG-3 or AFP protein from a single fusion. We applied these recombinant anti-PD-1 monoclonal antibodies (32D6) in immunotherapy for therapeutic purposes that produced the expected results.

Conclusions

This method can be used to facilitate an increased throughput of the entire process from multiplex immunization to acquisition of functional rat monoclonal antibodies and facilitate their expression and feasibility using a single plasmid.

Electronic supplementary material

The online version of this article (10.1186/s12865-018-0274-8) contains supplementary material, which is available to authorized users.

Discovery of functional monoclonal antibodies targeting G-protein-coupled receptors and ion channels

The development of recombinant antibody therapeutics is a significant area of growth in the pharmaceutical industry with almost 50 approved monoclonal antibodies on the market in the US and Europe. Despite this growth, however, certain classes of important molecular targets have remained intractable to therapeutic antibodies due to complexity of the target molecules. These complex target molecules include G-protein-coupled receptors and ion channels which represent a large potential target class for therapeutic intervention with monoclonal antibodies. Although these targets have typically been addressed by small molecule approaches, the exquisite specificity of antibodies provides a significant opportunity to provide selective modulation of these target proteins. Given this opportunity, substantial effort has been applied to address the technical challenges of targeting these complex membrane proteins with monoclonal antibodies. In this review recent progress made in the strategies for discovery of functional monoclonal antibodies for these challenging membrane protein targets is addressed.

Development of therapeutic antibodies to G protein-coupled receptors and ion channels: Opportunities, challenges and their therapeutic potential in respiratory diseases

The development of recombinant antibody therapeutics continues to be a significant area of growth in the pharmaceutical industry with almost 50 approved monoclonal antibodies on the market in the US and Europe. Therapeutic drug targets such as soluble cytokines, growth factors and single transmembrane spanning receptors have been successfully targeted by recombinant monoclonal antibodies and the development of new product candidates continues. Despite this growth, however, certain classes of important disease targets have remained intractable to therapeutic antibodies due to the complexity of the target molecules. These complex target molecules include G protein-coupled receptors and ion channels which represent a large target class for therapeutic intervention with monoclonal antibodies. Although these targets have typically been addressed by small molecule approaches, the exquisite specificity of antibodies provides a significant opportunity to provide selective modulation of these important regulators of cell function. Given this opportunity, a significant effort has been applied to address the challenges of targeting these complex molecules and a number of targets are linked to the pathophysiology of respiratory diseases. In this review, we provide a summary of the importance of GPCRs and ion channels involved in respiratory disease and discuss advantages offered by antibodies as therapeutics at these targets. We highlight some recent GPCRs and ion channels linked to respiratory disease mechanisms and describe in detail recent progress made in the strategies for discovery of functional antibodies against challenging membrane protein targets such as GPCRs and ion channels.

Antibody-like Biorecognition Sites for Proteins from Surface Imprinting on Nanoparticles

Natural antibodies are used widely for important applications such as biomedical analysis, cancer therapy, and directed drug delivery, but they are expensive and may have limited stability. This study describes synthesis of antibody-like binding sites by molecular imprinting on silica nanoparticles (SiNP) using a combination of four organosilane monomers with amino acid-like side chains providing hydrophobic, hydrophilic, and H-bonding interactions with target proteins. This approach provided artificial antibody (AA) nanoparticles with good selectivity and specificity to binding domains on target proteins in a relatively low-cost synthesis. The AAs were made by polymer grafting onto SiNPs for human serum albumin (HSA) and glucose oxidase (GOx). Binding affinity, selectivity, and specificity was compared to several other proteins using adsorption isotherms and surface plasmon resonance (SPR). The Langmuir-Freundlich adsorption model was used to obtain apparent binding constants (KLF) from binding isotherms of HSA (6.7 × 10(4)) and GOx (4.7 × 10(4)) to their respective AAs. These values were 4-300 fold larger compared to a series of nontemplate proteins. SPR binding studies of AAs with proteins attached to a gold surface confirmed good specificity and revealed faster binding for the target proteins compared to nontarget proteins. Target proteins retained their secondary structures upon binding. Binding capacity of AAHSA for HSA was 5.9 mg HSA/g compared to 1.4 mg/g for previously report imprinted silica beads imprinted with poly(aminophenyl)boronic acid. Also, 90% recovery for HSA spiked into 2% calf serum was found for AAHSA.

Monoclonal Antibody Combinations that Present Synergistic Neutralizing Activity: A Platform for Next-Generation Anti-Toxin Drugs

Monoclonal antibodies (MAbs) are among the fastest-growing therapeutics and are being developed for a broad range of indications, including the neutralization of toxins, bacteria and viruses. Nevertheless, MAbs potency is still relatively low when compared to conventional polyclonal Ab preparations. Moreover, the efficacy of an individual neutralizing MAb may significantly be hampered by the potential absence or modification of its target epitope in a mutant or subtype of the infectious agent. These limitations of individual neutralizing MAbs can be overcome by using oligoclonal combinations of several MAbs with different specificities to the target antigen. Studies conducted in our lab and by others show that such combined MAb preparation may present substantial synergy in its potency over the calculated additive potency of its individual MAb components. Moreover, oligoclonal preparation is expected to be better suited to compensating for reduced efficacy due to epitope variation. In this review, the synergistic neutralization properties of combined oligoclonal Ab preparations are described. The effect of Ab affinity, autologous Fc fraction, and targeting a critical number of epitopes, as well as the unexpected contribution of non-neutralizing clones to the synergistic neutralizing effect are presented and discussed.

A fully automated primary screening system for the discovery of therapeutic antibodies directly from B cells

For a therapeutic antibody to succeed, it must meet a range of potency, stability, and specificity criteria. Many of these characteristics are conferred by the amino acid sequence of the heavy and light chain variable regions and, for this reason, can be screened for during antibody selection. However, it is important to consider that antibodies satisfying all these criteria may be of low frequency in an immunized animal; for this reason, it is essential to have a mechanism that allows for efficient sampling of the immune repertoire. UCB's core antibody discovery platform combines high-throughput B cell culture screening and the identification and isolation of single, antigen-specific IgG-secreting B cells through a proprietary technique called the "fluorescent foci" method. Using state-of-the-art automation to facilitate primary screening, extremely efficient interrogation of the natural antibody repertoire is made possible; more than 1 billion immune B cells can now be screened to provide a useful starting point from which to identify the rare therapeutic antibody. This article will describe the design, construction, and commissioning of a bespoke automated screening platform and two examples of how it was used to screen for antibodies against two targets.

Discovery of Functional Antibodies Targeting Ion Channels

Ion channels play critical roles in physiology and disease by modulation of cellular functions such as electrical excitability, secretion, cell migration, and gene transcription. Ion channels represent an important target class for drug discovery that has been largely addressed, to date, using small-molecule approaches. A significant opportunity exists to target these channels with antibodies and alternative formats of biologics. Antibodies display high specificity and affinity for their target antigen, and they have the potential to target ion channels very selectively. Nevertheless, isolating antibodies to this target class is challenging due to the difficulties in expression and purification of ion channels in a format suitable for antibody drug discovery in addition to the complexity of screening for function.

In this article, we will review the current state of ion channel biologics discovery and the progress that has been made. We will also highlight the challenges in isolating functional antibodies to these targets and how these challenges may be addressed. Finally, we also illustrate successful approaches to isolating functional monoclonal antibodies targeting ion channels by way of a number of case studies drawn from recent publications.

Delineating monoclonal antibody specificity by mass spectrometry

Generation of monoclonal antibody (mAb) libraries against antigens in complex matrices can prove a valuable analytical tool. However, delineating the specificity of newly generated antibodies is the limiting step of the procedure. Here, we propose a strategy for mAb production by injecting mice with complex biological fluid and mAb characterization by coupling immunoaffinity techniques with Mass spectrometry (immuno-MS). Mice were immunized against fractionated seminal plasma and mAbs were produced. Different immuno-MS protocols based on four types of solid support (i.e. polystyrene microtiter plates, NHS-activated agarose beads, tosyl-activated magnetic beads and MSIA™ pipette tips) were established. A well-characterized mouse monoclonal anti-KLK3 (PSA) Ab was used as a model to evaluate each protocol's robustness and reproducibility and to establish a set of criteria which would allow antigen characterization of newly developed Abs. Three of the newly generated Abs were analyzed using our optimized protocols. Analysis revealed that all assay configurations used were capable of antibody characterization. Furthermore, low-abundance antigens (e.g. ribonuclease T2) could be identified as efficiently as the high-abundance ones. Our data suggest that complex biological samples can be used for the production of mAbs, which will facilitate the analysis of their proteome, while the established immuno-MS protocols can offer efficient mAb characterization.

BIOLOGICAL SIGNIFICANCE

The inoculation of animals with complex biological samples is aiming at the discovery of novel disease biomarkers, present in the biological specimens, as well as the production of rare reagents that will facilitate the ultra-sensitive analysis of the biomolecules' native form. In the present study, we initially propose a general workflow concerning the handling of biological samples, as well as the monoclonal antibody production. Furthermore, we established protocols for the reliable and reproducible identification of antibody specificity using various immuno-affinity purification techniques coupled to mass spectrometry. Our data suggest that processed biological fluids can be used for the production of mAbs targeting proteins of varying abundance, and that various immuno-MS protocols can offer great capabilities for the mAb characterization procedure.

Evaluating the synergistic neutralizing effect of anti-botulinum oligoclonal antibody preparations

Botulinum neurotoxins (BoNT) are considered some of the most lethal known substances. There are seven botulinum serotypes, of which types A, B and E cause most human botulism cases. Anti-botulinum polyclonal antibodies (PAbs) are currently used for both detection and treatment of the disease. However, significant improvements in immunoassay specificity and treatment safety may be made using monoclonal antibodies (MAbs). In this study, we present an approach for the simultaneous generation of highly specific and neutralizing MAbs against botulinum serotypes A, B, and E in a single process. The approach relies on immunization of mice with a trivalent mixture of recombinant C-terminal fragment (Hc) of each of the three neurotoxins, followed by a parallel differential robotic hybridoma screening. This strategy enabled the cloning of seven to nine MAbs against each serotype. The majority of the MAbs possessed higher anti-botulinum ELISA titers than anti-botulinum PAbs and had up to five orders of magnitude greater specificity. When tested for their potency in mice, neutralizing MAbs were obtained for all three serotypes and protected against toxin doses of 10 MsLD50-500 MsLD50. A strong synergistic effect of up to 400-fold enhancement in the neutralizing activity was observed when serotype-specific MAbs were combined. Furthermore, the highly protective oligoclonal combinations were as potent as a horse-derived PAb pharmaceutical preparation. Interestingly, MAbs that failed to demonstrate individual neutralizing activity were observed to make a significant contribution to the synergistic effect in the oligoclonal preparation. Together, the trivalent immunization strategy and differential screening approach enabled us to generate highly specific MAbs against each of the A, B, and E BoNTs. These new MAbs may possess diagnostic and therapeutic potential.

High-affinity monoclonal antibodies to cell surface tumor antigen glypican-3 generated through a combination of peptide immunization and flow cytometry screening

Isolating high-affinity antibodies against native tumor antigens on the cell surface is not straightforward using standard hybridoma procedures. Here, we describe a combination method of synthetic peptide immunization and high-throughput flow cytometry screening to efficiently isolate hybridomas for cell binding. Using this method, we identified high-affinity monoclonal antibodies specific for the native form of glypcian-3 (GPC3), a target heterogeneously expressed in hepatocellular carcinoma (HCC) and other cancers. We isolated a panel of monoclonal antibodies (YP6, YP7, YP8, YP9 and YP9.1) for cell surface binding. The antibodies were used to characterize GPC3 protein expression in human liver cancer cell lines and tissues by flow cytometry, immunoblotting and immunohistochemistry. The best antibody (YP7) bound cell surface-associated GPC3 with equilibrium dissociation constant, KD = 0.3 nmol/L and was highly specific for HCC, not normal tissues or other forms of primary liver cancers (such as cholangiocarcinoma). Interestingly, the new antibody was highly sensitive in that it detected GPC3 in low expression ovarian clear cell carcinoma and melanoma cells. The YP7 antibody exhibited significant HCC xenograft tumor growth inhibition in nude mice. These results describe an improved method for producing high-affinity monoclonal antibodies to cell surface tumor antigens and represent a general approach to isolate therapeutic antibodies against cancer. The new high-affinity antibodies described here have significant potential for GPC3-expressing cancer diagnostics and therapy.

Generation of antibody-producing hybridomas following one single immunization with a targeted DNA vaccine

The standard protocol for generating antibody (Ab)-producing hybridomas is based on fusion of plasmacytoma cells with Ab-producing B cells harvested from immunized mice. To increase the yield of hybridomas, it is important to use immunization protocols that induce a high frequency of B cells producing specific Abs. Our laboratory has developed a vaccine format, denoted vaccibody that promotes the immune responses towards the delivered antigen. The vaccine format targets antigens in a bivalent form to surface receptors on antigen-presenting cells (APCs). Here, we used the fluorescent protein (FP) mCherry as antigen and targeted it to APCs by use of either the natural ligand CCL3/MIP-1α or single-chain variable fragment specific for major histocompatibility complex class II. The vaccine format was delivered to mouse muscle as DNA combined with electroporation. By this procedure, we developed two monoclonal Abs that can be utilized to detect the FC mCherry in various applications. The data suggest that the targeted DNA vaccine format can be utilized to enhance the number of Ab-producing hybridomas and thereby be a tool to improve the B cell hybridoma technology.

Antibody discovery ex vivo accelerated by the LacO/LacI regulatory network

Monoclonal antibodies (mAbs) can be potent and highly specific therapeutics, diagnostics and research reagents. Nonetheless, mAb discovery using current in vivo or in vitro approaches can be costly and time-consuming, with no guarantee of success. We have established a platform for rapid discovery and optimization of mAbs ex vivo. This DTLacO platform derives from a chicken B cell line that has been engineered to enable rapid selection and seamless maturation of high affinity mAbs. We have validated the DTLacO platform by generation of high affinity and specific mAbs to five cell surface targets, the receptor tyrosine kinases VEGFR2 and TIE2, the glycoprotein TROP2, the small TNF receptor family member FN14, and the G protein-coupled receptor FZD10. mAb discovery is rapid and humanization is straightforward, establishing the utility of the DTLacO platform for identification of mAbs for therapeutic and other applications.

Alternative affinity tools: more attractive than antibodies?

Antibodies are the most successful affinity tools used today, in both fundamental and applied research (diagnostics, purification and therapeutics). Nonetheless, antibodies do have their limitations, including high production costs and low stability. Alternative affinity tools based on nucleic acids (aptamers), polypeptides (engineered binding proteins) and inorganic matrices (molecular imprinted polymers) have received considerable attention. A major advantage of these alternatives concerns the efficient (microbial) production and in vitro selection procedures. The latter approach allows for the high-throughput optimization of aptamers and engineered binding proteins, e.g. aiming at enhanced chemical and physical stability. This has resulted in a rapid development of the fields of nucleic acid- and protein-based affinity tools and, although they are certainly not as widely used as antibodies, the number of their applications has steadily increased in recent years. In the present review, we compare the properties of the more conventional antibodies with these innovative affinity tools. Recent advances of affinity tool developments are described, both in a medical setting (e.g. diagnostics, therapeutics and drug delivery) and in several niche areas for which antibodies appear to be less attractive. Furthermore, an outlook is provided on anticipated future developments.

Ribosome display selection of a murine IgG₁ Fab binding affibody molecule allowing species selective recovery of monoclonal antibodies

Affinity reagents recognizing constant parts of antibody molecules are invaluable tools in immunotechnology applications, including purification, immobilization, and detection of immunoglobulins. In this article, murine IgG₁, the primary isotype of monoclonal antibodies (mAbs) was used as target for selection of novel binders from a combinatorial ribosome display (RD) library of 10¹¹ affibody molecules. Four rounds of selection using three different mouse IgG₁ mAbs as alternating targets resulted in the identification of binders with broad mIgG₁ recognition and dissociation constants (K_D) in the low nanomolar to low micromolar range. For one of the binders, denoted Z_mab25, competition in binding to full length mIgG₁ by a streptococcal protein G (SPG) fragment and selective affinity capture of mouse IgG₁ Fab fragments after papain cleavage of a full mAb suggest that an epitope functionally overlapping with the SPG-binding site in the CH₁ domain of mouse IgG₁ had been addressed. Interestingly, biosensor-based binding experiments showed that neither human IgG₁ nor bovine Ig, the latter present in fetal bovine serum (FBS) was recognized by Z_mab25. This selective binding profile towards murine IgG₁ was successfully exploited in species selective recovery of two different mouse mAbs from complex samples containing FBS, resembling a hybridoma culture supernatant.

Comparison of techniques to screen and characterize bacteria-specific hybridomas for high-quality monoclonal antibodies selection

Antibodies are very important materials for diagnostics. A rapid and simple hybridoma screening method will help in delivering specific monoclonal antibodies. In this study, we systematically developed the first antibody array to screen for bacteria-specific monoclonal antibodies using Listeria monocytogenes as a bacteria model. The antibody array was developed to expedite the hybridoma screening process by printing hybridoma supernatants on a glass slide coated with an antigen of interest. This screening method is based on the binding ability of supernatants to the coated antigen. The bound supernatants were detected by a fluorescently labeled anti-mouse immunoglobulin. Conditions (slide types, coating, spotting, and blocking buffers) for antibody array construction were optimized. To demonstrate its usefulness, antibody array was used to screen a sample set of 96 hybridoma supernatants in comparison to ELISA. Most of the positive results identified by ELISA and antibody array methods were in agreement except for those with low signals that were undetectable by antibody array. Hybridoma supernatants were further characterized with surface plasmon resonance to obtain additional data on the characteristics of each selected clone. While the antibody array was slightly less sensitive than ELISA, a much faster and lower cost procedure to screen clones against multiple antigens has been demonstrated.

Multiplexed evaluation of capture agent binding kinetics using arrays of silicon photonic microring resonators

High affinity capture agents recognizing biomolecular targets are essential in the performance of many proteomic detection methods. Herein, we report the application of a label-free silicon photonic biomolecular analysis platform for simultaneously determining kinetic association and dissociation constants for two representative protein capture agents: a thrombin-binding DNA aptamer and an anti-thrombin monoclonal antibody. The scalability and inherent multiplexing capability of the technology make it an attractive platform for simultaneously evaluating the binding characteristics of multiple capture agents recognizing the same target antigen, and thus a tool complementary to emerging high-throughput capture agent generation strategies.

Axon repair: surgical application at a subcellular scale

Injury to the nervous system is a common occurrence after trauma. Severe cases of injury exact a tremendous personal cost and place a significant healthcare burden on society. Unlike some tissues in the body that exhibit self healing, nerve cells that are injured, particularly those in the brain and spinal cord, are incapable of regenerating circuits by themselves to restore neurological function. In recent years, researchers have begun to explore whether micro/nanoscale tools and materials can be used to address this major challenge in neuromedicine. Efforts in this area have proceeded along two lines. One is the development of new nanoscale tissue scaffold materials to act as conduits and stimulate axon regeneration. The other is the use of novel cellular-scale surgical micro/nanodevices designed to perform surgical microsplicing and the functional repair of severed axons. We discuss results generated by these two approaches and hurdles confronting both strategies.

A high-affinity human/mouse cross-reactive monoclonal antibody, specific for VEGFR-2 linear and conformational epitopes

Vascular endothelial growth factors receptor 2 (VEGFR-2) has been implicated in playing an important role in the formation of new blood vessels in tumors and other diseases. A high affinity human/mouse cross-reactive anti-VEGFR-2 monoclonal antibody (mAb) named A8H1 was established by hybridoma technology. Several immunological methods were used to characterize the A8H1, including ELISA, affinity and kinetics assay, MALDI-TOF MS, WB, IP, IF, FASC and IHC. The results suggested that A8H1 could bind with linear and conformational epitopes of the VEGFR-2 antigen. The mAb had good specific reactivity with three forms of VEGFR-2 in HUVEC, and two forms in NIH-3T3 mouse fibroblast cells, which are regarded as non-expressive for VEGFR-2. The A8H1 mAb associated with intracellular and plasma membranes in HUVEC and with the nuclei in NIH-3T3 cells. This mAb also effectively identified VEGFR-2 over-expressing cells in a number of archived human cancer tissues.

High-Throughput Screening for High Affinity Antibodies

UCB Selected Lymphocyte Antibody Method (SLAM) is a rapid and efficient process for the generation of high-quality monoclonal antibodies, in which variable region gene sequences are recovered directly from specific, single B cells. Monoclonal antibody generation has been limited in the past by the relatively low efficiency of the hybridoma process. UCB SLAM process is well suited to high-throughput screening and has been extensively automated at UCB. If necessary, in excess of 1 times 10 9 B cells can be screened in a campaign, to discover a rare therapeutic antibody candidate, which meets the stringent selection criteria. Primary screening for antigen binders, on purified or cell expressed antigen, is performed using a homogeneous fluorescence assay format. Supernatants from positive wells are consolidated to allow further secondary screening and selection of antibodies with desired characteristics. Individual, specific B cells are identified using a fluorescence based method and isolated using a micromanipulator. The antibody variable region genes are cloned from DNA extracted from the single B cell. The genes are sequenced then prepared for transient expression to confirm activity. Antibodies with affinities ( KD) in the sub 10 pM range against a range of therapeutic targets are routinely recovered using this process.

Generation of monoclonal antibodies against human recombinant interferon beta using genetic immunization with simultaneous expression of IgM and IgG isotypes

Monoclonal antibodies (MAbs) against human recombinant interferon beta (hrIFNbeta) were generated by genetic immunization (GI). In order to test two viral promoters frequently used in mammalian expression plasmid vectors, mice were inoculated four times by intramuscular injection, without adjuvant, with 100 microg of either pcDNA 3.1hrIFNbeta or pZeoSV2IFNbeta containing the entire human interferon beta gene and under the control of, respectively, human cytomegalovirus (HCMV) immediate-early promoter or early SV-40 enhancer/promoter. Only serum samples from mice immunized with pZeoSV2IFNbeta were positive to anti-hrIFNbeta. The spleens of the immunized mice were fused with myeloma Sp2/0 cells and the hybridoma clones generated screened by an in house enzyme-linked immunosorbent assay (ELISA). Fourteen MAbs were selected as reactive with hrIFNbeta. Western blot analysis was performed and only one recognized the 18 kDa isoform (non-glycosylated) of hrIFNbeta. All MAbs were subjected to antibody isotype characterization with a commercial ELISA and showed unusual profile with simultaneous expression of both IgM and IgG2a isotypes. This observation is further supported by RT-PCR amplification of the IgM CH4 domain using total RNA from hybridomas.

Three different immunogen preparation strategies for production of CD4 monoclonal antibodies

Monoclonal antibodies (MAb) specific to the protein of interest can be achieved following the classical hybridoma technique. However, obtaining a desired MAb is not always straightforward. The intrinsic quality of immunogen is one of the critical success factors. In this study, three sources of immunogens were compared for CD4 MAb production. CD4 proteins were isolated by immunoprecipitation and the CD4 immunoprecipitated (CD4-IP) beads were used as an immunogen. Recombinant CD4 protein-biotin carboxyl carrier protein (BCCP) fusion proteins (CD4-BCCP) were produced in Escherichia coli, isolated by streptavidin-coated beads, and the CD4-BCCP beads were used as an immunogen. CD4 expressing COS (CD4-COS) cells were generated, enriched by immunosorting, and used as an immunogen. After three immunizations, anti-CD4 antibodies could be observed in all immunized mice. The CD4 MAbs that were generated from CD4-IP bead and CD4-COS cell immunizations reacted with both CD4 expressed on transfected COS cells and lymphocytes. These MAbs could be used for immunoprecipitation of CD4 molecules from lymphocyte lysate and for enumerating CD4+ lymphocytes by flow cytometry. In contrast, the MAb generated from CD4-BCCP bead immunization reacted only with recombinant CD4-BCCP proteins but not with native CD4 expressed on CD4+ lymphocytes. Our results indicate that the proposed methods can facilitate the production of desired MAbs where the purified protein antigens are not available or difficult to prepare, but either the encoding cDNA or specific MAb is available.

Immunological cross-reactivity of mycobacterial topoisomerase I and divergence from other bacteria

Mycobacterium smegmatis topoisomerase I exhibits several distinctive characteristics among all topoisomerases. The enzyme is devoid of Zn2+ fingers found typically in other bacterial type I topoisomerases and binds DNA in a site-specific manner. Using polyclonal antibodies, we demonstrate the high degree of relatedness of the enzyme across mycobacteria but not other bacteria. This absence of cross-reactivity from other bacteria indicates that mycobacterial topoisomerase I has diverged from Escherichia coli and other bacteria. We have investigated further the immunological properties of the enzyme by raising a panel of monoclonal antibodies that recognises different antigenically active regions of the enzyme and binds it with widely varied affinity. Inhibition of a C-terminal domain-specific antibody binding by enzyme-specific and non-specific oligonucleotides suggests the possibility of using these monoclonal antibodies to probe the structure, function and in vivo role of the enzyme.