Generation of Recombinant Monoclonal Antibodies from Immunised Mice and Rabbits via Flow Cytometry and Sorting of Antigen-Specific IgG+ Memory B Cells

High-throughput strategies for monoclonal antibody screening: advances and challenges

Antibodies characterized by high affinity and specificity, developed through high-throughput screening and rapid preparation, are crucial to contemporary biomedical industry. Traditional antibody preparation via the hybridoma strategy faces challenges like low efficiency, long manufacturing cycles, batch variability and labor intensity. Advances in molecular biology and gene editing technologies offer revolutionary improvements in antibody production. New high-throughput technologies like antibody library display, single B cell antibody technologies, and single-cell sequencing have significantly cut costs and boosted the efficiency of antibody development. These innovations accelerate commercial applications of antibodies, meeting the biopharmaceutical industry's evolving demands. This review explores recent advancements in high-throughput development of antibody, highlighting their potential advantages over traditional methods and their promising future.

Development and Validation of a High Sensitivity Rapid Xylazine Dipstick for Clinical Urine Testing

Background

Xylazine has been increasingly linked to human overdose deaths. No antidote has been identified and naloxone cannot reverse the effect of xylazine. Xylazine withdrawal is not alleviated by opioids. It is imperative to detect xylazine when treating overdoses. No screening method for xylazine has been approved by FDA. We aim to develop a rapid and high sensitivity xylazine test for clinical urine testing.

Methods

Monoclonal antibodies with high sensitivity and specificity against xylazine were developed. The leading clone was used to develop a competitive lateral flow immunoassay. The analytical cutoff, specificity and clinical performance of this test was characterized using standards in drug-free urine and clinical urine samples.

Results

The rapid xylazine dipstick test has a test time of 5 minutes, and a cutoff of 10 ng/mL xylazine in drug-free urine. No cross reactivity with other commonly used drugs or endogenous metabolites were observed, except for 3% cross reactivity with clonidine. In 181 mass spectrometry confirmed clinical urine samples with xylazine concentrations > 10 ng/mL and 120 urine samples with xylazine concentrations <10 ng/mL, the dipstick demonstrated a clinical sensitivity of 100% and a clinical specificity of 97%. All 4 false positives had combined xylazine and 4-hydroxy-xylazine concentrations in the 5-10 ng/mL range, with additional xylazine metabolites detected by mass spectrometry.

Conclusions

When used with 10 ng/mL cutoff, the rapid xylazine dipstick demonstrates high clinical sensitivity and clinical specificity in urine samples, compared to gold standard mass spectrometry methods. This novel test has the potential to enable informed clinical decisions in suspected xylazine overdoses.

Heterologous expression, purification and generation of specific antibodies for Annexin A8

Annexin A8 (ANXA8) is a member of the Annexin gene family, with high levels of its mRNA and protein observed in various tumor tissues, making it a potential tumor biomarker. In this study, we developed an enzyme-linked immunosorbent assay (ELISA) to specifically detect the presence and accurately determine the concentration of ANXA8. To this end, we expressed a series of proteins using both Pichia pastoris and Escherichia coli expression systems. Particularly, human ANXA8 expressed in Pichia pastoris was used as the antigen and for antibody screening, while human ANXA2 and ANXA5 expressed in Pichia pastoris and murine ANXA8 expressed in E. coli BL21 (DE3) were used as counter screens to eliminate cross-reactive antibodies and to select antibodies that show specificity to ANXA8 from both human and mouse. Through research efforts with production and purification of recombinant proteins, immunization, specificity screening and selection of epitope pairing, two specific monoclonal antibodies, E9 and B7, apparently targeting different epitopes of ANXA8, were obtained. The specificity of the antibody pair was checked against recombinant human ANXA2 and ANXA5 with ANXA8 as the positive control. Western Blot and Sandwich ELISA demonstrate superb sensitivity and specificity with a detection limit of about 0.065 ng/mL for the latter. In summary, this study provides an experimental tool for the quantitative determination of ANXA8 concentration and a potential tumor biomarker to monitor disease progression.

Optimizing the method for expressing human monoclonal antibodies from a single peripheral blood cell from vaccinated donors

Human monoclonal antibodies are essential diagnostic and research tools and one of the most promising therapeutics. In the past years, single B cell technologies have evolved and over-come conventional methods' limitations, enabling the isolation of scarce B cell populations with desirable characteristics. In this study, we describe a simple and efficient method to isolate anti-gen-specific plasmablasts and memory B cells from hepatitis B virus vaccinated donors' peripheral blood and consequently amplification of immunoglobulin variable region genes. Amplified immunoglobulin variable region genes were cloned into expression vectors and transfected into a human cell line to produce human recombinant monoclonal antibodies. Major challenges in this protocol were isolation of antigen-specific B cells based on surface markers, recovering mRNA from a single cell for efficient amplification, and cloning the correct insert into a desired expression vector. The essential feature of our protocol was the separation of B cells from peripheral blood mononuclear cells before sorting. We identified antigen-specific binding B cells based on the expression of surface markers CD19, CD27, IgG, and binding to hepatitis B surface antigen. Efficient single-cell reverse transcription and polymerase chain reaction (RT-PCR) were achieved using a random primer mix and Kapa Hifi Hot Start Polymerase. Amplification efficiency differed among heavy and light chain variable regions (highest at heavy chain (68 %) and lowest at lambda light chain (22 %)). After co-transfection of HEK293T/17 with successfully cloned heavy and light chain vectors, 70 % of transfected cells produced recombinant monoclonal antibodies at a concentration ∼ 4 μg/ml and 7 % of them showed binding to HBsAg. Human monoclonal antibodies from peripheral blood have advantages over antibodies of mouse origin or phage display libraries, because of their high specificity and self-tolerance. Using the described protocol, we can generate fully human monoclonal antibodies to any other antigen for application in immunotherapy or basic research.

Screening of Neutralizing Antibodies against FaeG Protein of Enterotoxigenic Escherichia coli

The misuse of antibiotics in veterinary medicine presents significant challenges, highlighting the need for alternative therapeutic approaches such as antibody drugs. Therefore, it is necessary to explore the application of antibody drugs in veterinary settings to reduce economic losses and health risks. This study focused on targeting the F4ac subtype of the FaeG protein, a key adhesion factor in enterotoxigenic Escherichia coli (ETEC) infections in piglets. By utilizing formaldehyde-inactivated ETEC and a soluble recombinant FaeG (rFaeG) protein, an antibody library against the FaeG protein was established. The integration of fluorescence-activated cell sorting (FACS) and a eukaryotic expression vector containing murine IgG Fc fragments facilitated the screening of anti-rFaeG IgG monoclonal antibodies (mAbs). The results demonstrate that the variable regions of the screened antibodies could inhibit K88-type ETEC adhesion to IPEC-J2 cells. Furthermore, in vivo neutralization assays in mice showed a significant increase in survival rates and a reduction in intestinal inflammation. This research underscores the potential of antibody-based interventions in veterinary medicine, emphasizing the importance of further exploration in this field to address antibiotic resistance and improve animal health outcomes.

Isolation of anti-tumor monoclonal antibodies targeting on MICA/B α3 domain by single B cell technology for colon cancer therapy

Colon cancer (CC) is one of the most common gastrointestinal malignancies. Effectiveness of the existing therapies is limited. Immunotherapy is a promising complementary treatment approach for CC. Major histocompatibility complex class I-related protein A and B (MICA/B) are ligands for NK cells. Shedding of MICA/B from the surface of tumor cells by cleavage of MICA/B at the membrane proxial region in MICA/B α3 structural domain is one of immune evasion strategies leading to escape of cancer cells from immunosurveillance. In this study, we generated a panel of MICA/B monoclonal antibodies (mAbs) and identified one of mAbs, mAb RDM028, that had high binding affinity to MICA/B and recognized a site on MICA/B α3 structural domain that is critically important for cleavage of MICA/B. Our study has further demonstrated that RDM028 augmented the surface expression of MICA/B on HCT-116 human CC cells by inhibiting the MICA/B shedding resulting in the enhanced cyotoxicity of NK cells against HCT-116 human CC cells and mediated anti-tumor activity in nude mouse model of colon cancer. These results indicate that mAb RDM028 could be explored for developing as an effective immuno therapy against CC by targeting the MICA/B α3 domain to promot immunosurveillance mediated by MICA/B-NKG2D interaction.

Rapid and Sensitive Detection of Fentanyl and Its Analogs by a Novel Chemiluminescence Immunoassay

BACKGROUND

Abuse of fentanyl and its analogs is a major contributor to the opioid overdose epidemic in the United States, but detecting and quantifying trace amounts of such drugs remains a challenge without resorting to sophisticated mass spectrometry-based methods.

METHODS

A sensitive immunoassay with a sub-picogram limit of detection for fentanyl and a wide range of fentanyl analogs has been developed, using a novel high-affinity antibody fused with NanoLuc, a small-size luciferase that can emit strong and stable luminescence. When used with human urine samples, the assay has a sub-picogram limit of detection for fentanyl, with results fully concordant with LC-MS.

RESULTS

When applied to clinical samples, the novel chemiluminescence immunoassay can detect low positive fentanyl missed by routine screening immunoassays, with a limit of detection of 0.8 pg/mL in human urine. When applied to environmental samples, the assay can detect levels as low as 0.25 pg fentanyl per inch2 of environment surface. Assay turnaround time is less than 1 h, with inexpensive equipment and the potential for high-throughput automation or in-field screening.

CONCLUSIONS

We have established a novel assay that may have broad applications in clinical, environmental, occupational, and forensic scenarios for detection of trace amounts of fentanyl and its analogs.

The Development of Robust Antibodies to Sarcospan, a Dystrophin- and Integrin-Associated Protein, for Basic and Translational Research

Sarcospan (SSPN) is a 25-kDa transmembrane protein that is broadly expressed at the cell surface of many tissues, including, but not limited to, the myofibers from skeletal and smooth muscles, cardiomyocytes, adipocytes, kidney epithelial cells, and neurons. SSPN is a core component of the dystrophin-glycoprotein complex (DGC) that links the intracellular actin cytoskeleton with the extracellular matrix. It is also associated with integrin α7β1, the predominant integrin expressed in skeletal muscle. As a tetraspanin-like protein with four transmembrane spanning domains, SSPN functions as a scaffold to facilitate protein-protein interactions at the cell membrane. Duchenne muscular dystrophy, Becker muscular dystrophy, and X-linked dilated cardiomyopathy are caused by the loss of dystrophin at the muscle cell surface and a concomitant loss of the entire DGC, including SSPN. SSPN overexpression ameliorates Duchenne muscular dystrophy in the mdx murine model, which supports SSPN being a viable therapeutic target. Other rescue studies support SSPN as a biomarker for the proper assembly and membrane expression of the DGC. Highly specific and robust antibodies to SSPN are needed for basic research on the molecular mechanisms of SSPN rescue, pre-clinical studies, and biomarker evaluations in human samples. The development of SSPN antibodies is challenged by the presence of its four transmembrane domains and limited antigenic epitopes. To address the significant barrier presented by limited commercially available antibodies, we aimed to generate a panel of robust SSPN-specific antibodies that can serve as a resource for the research community. We created antibodies to three SSPN protein epitopes, including the intracellular N- and C-termini as well as the large extracellular loop (LEL) between transmembrane domains 3 and 4. We developed a panel of rabbit antibodies (poly- and monoclonal) against an N-terminal peptide fragment of SSPN. We used several assays to show that the rabbit antibodies recognize mouse SSPN with a high functional affinity and specificity. We developed mouse monoclonal antibodies against the C-terminal peptide and the large extracellular loop of human SSPN. These antibodies are superior to commercially available antibodies and outperform them in various applications, including immunoblotting, indirect immunofluorescence analysis, immunoprecipitation, and an ELISA. These newly developed antibodies will significantly improve the quality and ease of SSPN detection for basic and translational research.

A Microfluidic Strategy to Capture Antigen‐Specific High‐Affinity B Cells

Assessing B cell affinity to pathogen‐specific antigens prior to or following exposure could facilitate the assessment of immune status. Current standard tools to assess antigen‐specific B cell responses focus on equilibrium binding of the secreted antibody in serum. These methods are costly, time‐consuming, and assess antibody affinity under zero force. Recent findings indicate that force may influence BCR‐antigen binding interactions and thus immune status. Herein, a simple laminar flow microfluidic chamber in which the antigen (hemagglutinin of influenza A) is bound to the chamber surface to assess antigen‐specific BCR binding affinity of five hemagglutinin‐specific hybridomas from 65 to 650 pN force range is designed. The results demonstrate that both increasing shear force and bound lifetime can be used to enrich antigen‐specific high‐affinity B cells. The affinity of the membrane‐bound BCR in the flow chamber correlates well with the affinity of the matched antibodies measured in solution. These findings demonstrate that a microfluidic strategy can rapidly assess BCR‐antigen‐binding properties and identify antigen‐specific high‐affinity B cells. This strategy has the potential to both assess functional immune status from peripheral B cells and be a cost‐effective way of identifying individual B cells as antibody sources for a range of clinical applications.

A nanowell platform to identify, sort and expand high antibody-producing cells

Increased use of therapeutic monoclonal antibodies and the relatively high manufacturing costs fuel the need for more efficient production methods. Here we introduce a novel, fast, robust, and safe isolation platform for screening and isolating antibody-producing cell lines using a nanowell chip and an innovative single-cell isolation method. An anti-Her2 antibody producing CHO cell pool was used as a model. The platform; (1) Assures the single-cell origin of the production clone, (2) Detects the antibody production of individual cells and (3) Isolates and expands the individual cells based on their antibody production. Using the nanowell platform we demonstrated an 1.8-4.5 increase in anti-Her2 production by CHO cells that were screened and isolated with the nanowell platform compared to CHO cells that were not screened. This increase was also shown in Fed-Batch cultures where selected high production clones showed titers of 19-100 mg/L on harvest day, while the low producer cells did not show any detectable anti-Her2 IgG production. The screening of thousands of single cells is performed under sterile conditions and the individual cells were cultured in buffers and reagents without animal components. The time required from seeding a single cell and measuring the antibody production to fully expanded clones with increased Her-2 production was 4-6 weeks.

Antibody-mediated degradation of 4R-tau restores mitochondrial membrane polarization in human induced pluripotent stem cell-derived neurons with the MAPT 10+16 mutation

Microtubule-associated protein tau is inextricably linked to a group of clinically diverse neurodegenerative diseases termed tauopathies. The ratio balance of the major tau splicing isoform groups (3 R- and 4 R-tau) is critical in maintaining healthy neurons. An imbalance causing excess 4 R tau is associated with diseases such as progressive supranuclear palsy and frontotemporal dementia. The mechanisms by which increased 4 R results in neuronal dysfunction and neurodegeneration are not fully understood, and progress has been limited partly by a lack of suitable tools to investigate tau isoform imbalance. This work generated novel 3 R- and 4 R-specific antibody tools and 4 R-tau degrading intracellular antibody fragment "degrabodies". These were used to probe the molecular mechanisms of excess 4 R-tau in disease-mutant induced pluripotent stem cell-derived neurons. For the first time, we demonstrate a causative link between excess 4 R-tau and mitochondrial membrane hyperpolarization with wide-ranging potential for elucidating novel therapeutic approaches to treat neurodegenerative disease.

Patient-Specific Targeting of the T-Cell Receptor Variable Region as a Therapeutic Strategy in Clonal T-Cell Diseases

PURPOSE

Targeted therapeutics are a goal of medicine. Methods for targeting T-cell lymphoma lack specificity for the malignant cell, leading to elimination of healthy cells. The T-cell receptor (TCR) is designed for antigen recognition. T-cell malignancies expand from a single clone that expresses one of 48 TCR variable beta (Vβ) genes, providing a distinct therapeutic target. We hypothesized that a mAb that is exclusive to a specific Vβ would eliminate the malignant clone while having minimal effects on healthy T cells.

EXPERIMENTAL DESIGN

We identified a patient with large granular T-cell leukemia and sequenced his circulating T-cell population, 95% of which expressed Vβ13.3. We developed a panel of anti-Vβ13.3 antibodies to test for binding and elimination of the malignant T-cell clone.

RESULTS

Therapeutic antibody candidates bound the malignant clone with high affinity. Antibodies killed engineered cell lines expressing the patient TCR Vβ13.3 by antibody-dependent cellular cytotoxicity and TCR-mediated activation-induced cell death, and exhibited specific killing of patient malignant T cells in combination with exogenous natural killer cells. EL4 cells expressing the patient's TCR Vβ13.3 were also killed by antibody administration in an in vivo murine model.

CONCLUSIONS

This approach serves as an outline for development of therapeutics that can treat clonal T-cell-based malignancies and potentially other T-cell-mediated diseases. See related commentary by Varma and Diefenbach, p. 4024.

A microfluidic strategy to capture antigen-specific high affinity B cells

Assessing B cell affinity to pathogen-specific antigens prior to or following exposure could facilitate the assessment of immune status. Current standard tools to assess antigen-specific B cell responses focus on equilibrium binding of the secreted antibody in serum. These methods are costly, time-consuming, and assess antibody affinity under zero-force. Recent findings indicate that force may influence BCR-antigen binding interactions and thus immune status. Here, we designed a simple laminar flow microfluidic chamber in which the antigen (hemagglutinin of influenza A) is bound to the chamber surface to assess antigen-specific BCR binding affinity of five hemagglutinin-specific hybridomas under 65- to 650-pN force range. Our results demonstrate that both increasing shear force and bound lifetime can be used to enrich antigen-specific high affinity B cells. The affinity of the membrane-bound BCR in the flow chamber correlates well with the affinity of the matched antibodies measured in solution. These findings demonstrate that a microfluidic strategy can rapidly assess BCR-antigen binding properties and identify antigen-specific high affinity B cells. This strategy has the potential to both assess functional immune status from peripheral B cells and be a cost-effective way of identifying individual B cells as antibody sources for a range of clinical applications.

Development of Porcine Monoclonal Antibodies with In Vitro Neutralizing Activity against Classical Swine Fever Virus from C-Strain E2-Specific Single B Cells

Neutralizing antibodies (nAbs) can be used before or after infection to prevent or treat viral diseases. However, there are few efficacious nAbs against classical swine fever virus (CSFV) that have been produced, especially the porcine-originated nAbs. In this study, we generated three porcine monoclonal antibodies (mAbs) with in vitro neutralizing activity against CSFV, aiming to facilitate the development of passive antibody vaccines or antiviral drugs against CSFV that offer the advantages of stability and low immunogenicity. Pigs were immunized with the C-strain E2 (CE2) subunit vaccine, KNB-E2. At 42 days post vaccination (DPV), CE2-specific single B cells were isolated via fluorescent-activated cell sorting (FACS) baited by Alexa Fluor™ 647-labeled CE2 (positive), goat anti-porcine IgG (H + L)-FITC antibody (positive), PE mouse anti-pig CD3ε (negative) and PE mouse anti-pig CD8a (negative). The full coding region of IgG heavy (H) chains and light (L) chains was amplified by reverse transcription-polymerase chain reaction (RT-PCR). Overall, we obtained 3 IgG H chains, 9 kappa L chains and 36 lambda L chains, which include three paired chains (two H + κ and one H + λ). CE2-specific mAbs were successfully expressed in 293T cells with the three paired chains. The mAbs exhibit potent neutralizing activity against CSFVs. They can protect ST cells from infections in vitro with potent IC50 values from 14.43 µg/mL to 25.98 µg/mL for the CSFV C-strain, and 27.66 µg/mL to 42.61 µg/mL for the CSFV Alfort strain. This study is the first report to describe the amplification of whole-porcine IgG genes from single B cells of KNB-E2-vaccinated pig. The method is versatile, sensitive, and reliable. The generated natural porcine nAbs can be used to develop long-acting and low-immunogenicity passive antibody vaccine or anti-CSFV agents for CSF control and prevention.

Development of a Novel Recombinant Full-Length IgY Monoclonal Antibody against Human Thymidine Kinase 1 for Automatic Chemiluminescence Analysis on a Sandwich Biotin-Streptavidin Platform for Early Tumour Discovery

Serum thymidine kinase 1 protein (STK1p) concentration has been used successfully as a reliable proliferating serum biomarker in early tumour discovery and clinical settings. It is detected by an enhanced chemiluminescence (ECL) dot blot assay with the biotin-streptavidin (BSA) platform (a gold standard) based on chicken anti-human thymidine kinase 1 IgY polyclonal antibody (hTK1-IgY-pAb). However, ECL dot blotting is a semiautomatic method that has been limited to large-scale applications due to the differences among batches of antibodies from individual hens, and the skill level of operation technicians sometimes results in unstable STK1p values. Therefore, a highly stable recombinant chicken full-length IgY monoclonal antibody in combination with a fully automated sandwich biotin-streptavidin (sandwich-BSA) platform was developed. Hens were immunized with 31-peptide, a key sequence of human TK1 (hTK1), before constructing an immune phage display scFv library. Finally, a recombinant full-length IgY monoclonal antibody (hTK1-IgY-rmAb#5) with high-affinity binding with human recombinant TK1 (rhTK1) ( $3.95\times {10}^{-10}$  mol/L), high sensitivity with hTK1 calibrators (slope of linear curve: 89.98), and high specificity with low/elevated STK1p ( $r\approx 0.92$ -0.963) was identified. hTK1-IgY-rmAb#5 showed a specific immune response with thymidine kinase 1 (TK1) in TK1-positive/negative cell lysates by Western blotting and immunohistochemistry (IHC) in normal and cancer tissues. In particular, the detection of TK1 serum samples from health centres showed a high coincidence rate ( $r=0.988,n=90$ ) between hTK1-IgY-rmAb#5 and hTK1-IgY-pAb and between the semiautomatic ECL dot blot BSA platform and the novel automatic chemiluminescence sandwich-BSA platform ( $r=0.857,n=292$ ). hTK1-IgY-rmAb#5 is stable and highly sensitive for detecting the lowest STK1p value at 0.01 pmol/L (pM). The accuracy is high ( $\text{SD}<2.5\%$ ) between different batches. It is easy to use the novel hTK1-IgY-rmAb#5 on a new automatic chemiluminescence sandwich-BSA platform. It will be beneficial for large-scale health screenings.

Extracellular Loops of the Treponema pallidum FadL Orthologs TP0856 and TP0858 Elicit IgG Antibodies and IgG+-Specific B-Cells in the Rabbit Model of Experimental Syphilis

The resurgence of syphilis in the new millennium has called attention to the importance of a vaccine for global containment strategies. Studies with immune rabbit serum (IRS) indicate that a syphilis vaccine should elicit antibodies (Abs) that promote opsonophagocytosis of treponemes by activated macrophages. The availability of three-dimensional models for Treponema pallidum's (Tp) repertoire of outer membrane proteins (OMPs) provides an architectural framework for identification of candidate vaccinogens with extracellular loops (ECLs) as the targets for protective Abs. Herein, we used Pyrococcus furiosus thioredoxin (PfTrx) as a scaffold to display Tp OMP ECLs to interrogate sera and peripheral blood mononuclear cells (PBMCs) from immune rabbits for ECL-specific Abs and B cells. We validated this approach using a PfTrx scaffold presenting ECL4 from BamA, a known opsonic target. Using scaffolds displaying ECLs of the FadL orthologs TP0856 and TP0858, we determined that ECL2 and ECL4 of both proteins are strongly antigenic. Comparison of ELISA and immunoblot results suggested that the PfTrx scaffolds present conformational and linear epitopes. We then used the FadL ECL2 and ECL4 PfTrx constructs as "hooks" to confirm the presence of ECL-specific B cells in PBMCs from immune rabbits. Our results pinpoint immunogenic ECLs of two newly discovered OMPs, while advancing the utility of the rabbit model for circumventing bottlenecks in vaccine development associated with large-scale production of folded OMPs. They also lay the groundwork for production of rabbit monoclonal Abs (MAbs) to characterize potentially protective ECL epitopes at the atomic level. IMPORTANCE Recent identification and structural modeling of Treponema pallidum's (Tp) repertoire of outer membrane proteins (OMPs) represent a critical breakthrough in the decades long quest for a syphilis vaccine. However, little is known about the antigenic nature of these β-barrel-forming OMPs and, more specifically, their surface exposed regions, the extracellular loops (ECLs). In this study, using Pyrococcus furiosus thioredoxin (PfTrx) as a scaffold to display Tp OMP ECLs, we interrogated immune rabbit sera and peripheral blood mononuclear cells for the presence of antibodies (Abs) and circulating rare antigen-specific B cells. Our results pinpoint immunogenic ECLs of two newly discovered OMPs, while advancing the utility of the rabbit model for surveying the entire Tp OMPeome for promising OMP vaccinogens. This work represents a major advancement toward characterizing potentially protective OMP ECLs and future vaccine studies. Additionally, this strategy could be applied to OMPs of nonspirochetal bacterial pathogens.

Application of Microfluidic Technology in Antibody Screening

Specific antibodies are widely used in the biomedical field. Current screening methods for specific antibodies mainly involve hybridoma technology and antibody engineering techniques. However, these technologies suffer from tedious screening processes, long preparation periods, high costs, low efficiency, and a degree of automation, which have become a bottleneck for the screening of specific antibodies. To overcome these difficulties, microfluidics has been developed as a promising technology for high-throughput screening and high purity of antibody. In this review, we provide an overview of the recent advances in microfluidic applications for specific antibody screening. In particular, hybridoma technology and four antibody engineering techniques (including phage display, single B cell antibody screening, antibody expression, and cell-free protein synthesis) based on microfluidics have been introduced, challenges, and the future outlook of these technologies are also discussed. This article is protected by copyright. All rights reserved.

Screening of monoclonal antibodies against specific phosphonylation sites and analysis of serum samples exposed to soman and VX using an indirect competitive enzyme-linked immunosorbent assay

Organophosphorus nerve agents (OPNAs) covalently bind to tyrosine 411 of human serum albumin (HSA) and the formed adducts are stable biomarkers of OPNA exposure. The detection of these adducts has been limited to mass spectrometry techniques combined with protein digestion. Here, we developed indirect competitive ELISA (icELISA) methods to verify OPNA exposure by the detection of OPNA-phosphonylated adducts at tyrosine 411 residue (OPNA-HSA adducts), in which monoclonal antibodies (mAbs) against phosphonylation sites at tyrosine 411 were introduced. The two mAbs were prepared by the fourth generation of rabbit mAb technology using the phosphonylated peptides of LVRY^{(GD or VX)}TKKVPQC as the haptens. These mAbs were screened using our developed competitive ELISA method and then selected based on their individual affinity and selectivity. As a result, we obtained two mAbs that recognized the HSA Tyr 411 adduct of GD (mAb-5G2) or VX (mAb-12B9), respectively. They shared the highest affinity exhibiting a Kd value of about 10^-6 mol/L of the OPNA exposure concentration. They also had remarkable selectivity, which could especially recognize their individual OPNA-HSA adducts in a native state but did not recognize other OPNA-HSAs and unadducted HSAs. Especially for mAb-12B9, it could clearly distinguish VX-HSA and GB-HSA between which there was only one alkyl difference in their phosphonyl portion of the adducted sites. The two mAbs were then used to build the icELISA method for analysis of the serum samples exposed to OPNA. It was found that the detectable lowest GD- and VX-exposed concentrations in serum samples were respectively 1.0 × 10^-6 mol/L and 10.0 × 10^-6 mol/L. This study provides one novel approach and strategy for the retrospective detection of OPNA exposure, and the two mAbs have great potential to be extended for point-of-care testing of OPNA intoxication.

CellCelector™ as a platform in isolating primary B cells for antibody discovery

The most robust strategy in antibody discovery is the use of immunized animals and the ability to isolate and immortalize immune B-cells to hybridoma for further interrogation. However, capturing the full repertoire of an immunized animal is labor intensive, time consuming and limited in throughput. Therefore, techniques to directly mine the antibody repertoire of primary B-cells are of great importance in antibody discovery. In the current study, we present a method to isolate individual antigen-specific primary B-cells using the CellCellector™ single-cell isolation platform from XenoMouse® (XM) immunized with a recombinant therapeutic protein, EGFR. We screened a subset of CD138+ B-cells and identified 238 potential EGFR-specific B-cells from 1189 antibody-secreting cells (ASCs) and isolated 94 by CellCellector. We identified a diverse set of heavy chain complementarity-determining region sequences and cloned and expressed 20 into a standard human immunoglobulin G1 antibody format. We further characterized and identified 13 recombinant antibodies that engage soluble and native forms of EGFR. By extrapolating the method to all 400 000 CD138+ B-cells extracted from one EGFR immunized XM, a potential 1196 unique EGFR-specific antibodies could be discovered. CellCelector allows for interrogating the B-cell pool directly and isolating B-cells specific to the therapeutic target of interest. Furthermore, antibody sequences recovered from isolated B-cells engage the native and recombinant target, demonstrating the CellCellector can serve as a platform in antibody discovery.

Potent RBD-specific neutralizing rabbit monoclonal antibodies recognize emerging SARS-CoV-2 variants elicited by DNA prime-protein boost vaccination

Global concerns arose as the emerged and rapidly spreading SARS-CoV-2 variants might escape host immunity induced by vaccination. In this study, a heterologous prime-boost immunization strategy for COVID-19 was designed to prime with a DNA vaccine encoding wild type (WT) spike protein receptor-binding domain (RBD) followed by S1 protein-based vaccine in rabbits. Four vaccine-elicited rabbit monoclonal antibodies (RmAbs), including 1H1, 9H1, 7G5, and 5E1, were isolated for biophysical property, neutralization potency and sequence analysis. All RmAbs recognized RBD or S1 protein with KD in the low nM or sub nM range. 1H1 and 9H1, but neither 7G5 nor 5E1, can bind to all RBD protein variants derived from B.1.351. All four RmAbs were able to neutralize wild type (WT) SARS-CoV-2 strain in pseudovirus assay, and 1H1 and 9H1 could neutralize the SARS-CoV-2 WT authentic virus with IC50 values of 0.136 and 0.026 μg/mL, respectively. Notably, 1H1 was able to neutralize all 6 emerging SARS-CoV-2 variants tested including D614G, B.1.1.7, B.1.429, P.1, B.1.526, and B.1.351 variants, and 5E1 could neutralize against the above 5 variants except P.1. Epitope binning analysis revealed that 9H1, 5E1 and 1H1 recognized distinct epitopes, while 9H1 and 7G5 may have overlapping but not identical epitope. In conclusion, DNA priming protein boost vaccination was an effective strategy to induce RmAbs with potent neutralization capability against not only SARS-CoV-2 WT strain but also emergent variants, which may provide a new avenue for effective therapeutics and point-of-care diagnostic measures.

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.

Discovery and characterization of high-affinity, potent SARS-CoV-2 neutralizing antibodies via single B cell screening

Monoclonal antibodies that target SARS-CoV-2 with high affinity are valuable for a wide range of biomedical applications involving novel coronavirus disease (COVID-19) diagnosis, treatment, and prophylactic intervention. Strategies for the rapid and reliable isolation of these antibodies, especially potent neutralizing antibodies, are critical toward improved COVID-19 response and informed future response to emergent infectious diseases. In this study, single B cell screening was used to interrogate antibody repertoires of immunized mice and isolate antigen-specific IgG1⁺ memory B cells. Using these methods, high-affinity, potent neutralizing antibodies were identified that target the receptor-binding domain of SARS-CoV-2. Further engineering of the identified molecules to increase valency resulted in enhanced neutralizing activity. Mechanistic investigation revealed that these antibodies compete with ACE2 for binding to the receptor-binding domain of SARS-CoV-2. These antibodies may warrant further development for urgent COVID-19 applications. Overall, these results highlight the potential of single B cell screening for the rapid and reliable identification of high-affinity, potent neutralizing antibodies for infectious disease applications.

Rabbit Antidiethoxyphosphotyrosine Antibody, Made by Single B Cell Cloning, Detects Chlorpyrifos Oxon-Modified Proteins in Cultured Cells and Immunopurifies Modified Peptides for Mass Spectrometry

Chronic low-dose exposure to organophosphorus pesticides is associated with the risk of neurodegenerative disease. The mechanism of neurotoxicity is independent of acetylcholinesterase inhibition. Adducts on tyrosine, lysine, threonine, and serine can occur after exposure to organophosphorus pesticides, the most stable being adducts on tyrosine. Rabbit monoclonal 1C6 to diethoxyphosphate-modified tyrosine (depY) was created by single B cell cloning. The amino acid sequence and binding constant (K_d 3.2 × 10^–8 M) were determined. Cultured human neuroblastoma SH-SY5Y and mouse neuroblastoma N2a cells incubated with a subcytotoxic dose of 10 μM chlorpyrifos oxon contained depY-modified proteins detected by monoclonal 1C6 on Western blots. depY-labeled peptides from tryptic digests of cell lysates were immunopurified by binding to immobilized 1C6. Peptides released with 50% acetonitrile and 1% formic acid were analyzed by liquid chromatography tandem mass spectrometry (LC-MS/MS) on an Orbitrap Fusion Lumos mass spectrometer. Protein Prospector database searches identified 51 peptides modified on tyrosine by diethoxyphosphate in SH-SY5Y cell lysate and 73 diethoxyphosphate-modified peptides in N2a cell lysate. Adducts appeared most frequently on the cytoskeleton proteins tubulin, actin, and vimentin. It was concluded that rabbit monoclonal 1C6 can be useful for studies that aim to understand the mechanism of neurotoxicity resulting from low-dose exposure to organophosphorus pesticides.

The Value of Flow Cytometry Clonality in Large Granular Lymphocyte Leukemia

Simple Summary

Large granular lymphocyte (LGL) leukemia, a lymphoproliferative disease, is characterized by an increased frequency of large-sized lymphocytes with typical expression of T-cell receptor (TCR) αβ, CD3, CD8, CD16, CD45RA, and CD57, and with the expansion of one to three subfamilies of the TCR variable β chain reflecting gene rearrangements. Molecular analysis remains the gold standard for confirmation of TCR clonality; however, flow cytometry is time and labor saving, and can be associated with simultaneous investigation of other surface markers. Moreover, Vβ usage by flow cytometry can be employed for monitoring clonal kinetics during treatment and follow-up of LGL leukemia patients.

Abstract

Large granular lymphocyte (LGL) leukemia is a lymphoproliferative disorder of mature T or NK cells frequently associated with autoimmune disorders and other hematological conditions, such as myelodysplastic syndromes. Immunophenotype of LGL cells is similar to that of effector memory CD8⁺ T cells with T-cell receptor (TCR) clonality defined by molecular and/or flow cytometric analysis. Vβ usage by flow cytometry can identify clonal TCR rearrangements at the protein level, and is fast, sensitive, and almost always available in every Hematology Center. Moreover, Vβ usage can be associated with immunophenotypic characterization of LGL clone in a multiparametric staining, and clonal kinetics can be easily monitored during treatment and follow-up. Finally, Vβ usage by flow cytometry might identify LGL clones silently underlying other hematological conditions, and routine characterization of Vβ skewing might identify recurrent TCR rearrangements that might trigger aberrant immune responses during hematological or autoimmune conditions.

Rabbit Monoclonal Antibody Specifically Recognizing a Linear Epitope in the RBD of SARS-CoV-2 Spike Protein

To date, SARS-CoV-2 pandemic has caused more than 188 million infections and 4.06 million deaths worldwide. The receptor-binding domain (RBD) of the SARS-CoV-2 spike protein has been regarded as an important target for vaccine and therapeutics development because it plays a key role in binding the human cell receptor ACE2 that is required for viral entry. However, it is not easy to detect RBD in Western blot using polyclonal antibody, suggesting that RBD may form a complicated conformation under native condition and bear rare linear epitope. So far, no linear epitope on RBD is reported. Thus, a monoclonal antibody (mAb) that recognizes linear epitope on RBD will become valuable. In the present study, an RBD-specific rabbit antibody named 9E1 was isolated from peripheral blood mononuclear cells (PBMC) of immunized rabbit by RBD-specific single B cell sorting and mapped to a highly conserved linear epitope within twelve amino acids ⁴⁸⁰CNGVEGFNCYFP⁴⁹¹ on RBD. 9E1 works well in Western blot on S protein and immunohistochemistry on the SARS-CoV-2 infected tissue sections. The results demonstrated that 9E1 can be used as a useful tool for pathological and functional studies of SARS-CoV-2.

Preparation of CD3 Antibody-Conjugated, Graphene Oxide Coated Iron Nitride Magnetic Beads and Its Preliminary Application in T Cell Separation

Immunomagnetic beads (IMBs) for cell sorting are universally used in medical and biological fields. At present, the IMBs on the market are ferrite coated with a silicon shell. Based on a new type of magnetic material, the graphene coated iron nitride magnetic particle (G@FeN-MP), which we previously reported, we prepared a novel IMB, a graphene oxide coated iron nitride immune magnetic bead (GO@FeN-IMBs), and explored its feasibility for cell sorting. First, the surface of the G@FeN-MP was oxidized to produce oxygen-containing groups as carboxyl, etc. by the optimized Hummers’ method, followed by a homogenization procedure to make the particles uniform in size and dispersive. The carboxy groups generated were then condensed and coupled with anti-CD3 antibodies by the carbodiimide method to produce an anti-CD3-GO@FeN-IMB after the coupling efficacy was proved by bovine serum albumin (BSA) and labeled antibodies. Finally, the anti-CD3-GO@FeN-IMBs were incubated with a cell mixture containing human T cells. With the aid of a magnetic stand, the T cells were successfully isolated from the cell mixture. The isolated T cells turned out to be intact and could proliferate with the activation of the IMBs. The results show that the G@FeN-MP can be modified for IMB preparation, and the anti-CD3-GO@FeN-IMBs we prepared can potentially separate T cells.

A platform-agnostic, function first-based antibody discovery strategy using plasmid-free mammalian expression of antibodies

Hybridoma technology has been valuable in the development of therapeutic antibodies. More recently, antigen-specific B-cell selection and display technologies are also gaining importance. A major limitation of these approaches used for antibody discovery is the extensive process of cloning and expression involved in transitioning from antibody identification to validating the function, which compromises the throughput of antibody discovery. In this study, we describe a process to identify and rapidly re-format and express antibodies for functional characterization. We used two different approaches to isolate antibodies to five different targets: 1) flow cytometry to identify antigen-specific single B cells from the spleen of immunized human immunoglobulin transgenic mice; and 2) panning of phage libraries. PCR amplification allowed recovery of paired V_H and V_L sequences from 79% to 96% of antigen-specific B cells. All cognate V_H and V_L transcripts were formatted into transcription and translation compatible linear DNA expression cassettes (LEC) encoding whole IgG or Fab. Between 92% and 100% of paired V_H and V_L transcripts could be converted to LECs, and nearly 100% of them expressed as antibodies when transfected into Expi293F cells. The concentration of IgG in the cell culture supernatants ranged from 0.05 µg/ml to 145.8 µg/ml (mean = 18.4 µg/ml). Antigen-specific binding was displayed by 78–100% of antibodies. High throughput functional screening allowed the rapid identification of several functional antibodies. In summary, we describe a plasmid-free system for cloning and expressing antibodies isolated by different approaches, in any format of choice for deep functional screening that can be applied in any research setting during antibody discovery.

Hybridoma technology: is it still useful?

The isolation of single monoclonal antibodies (mAbs) against a given antigen was only possible with the introduction of the hybridoma technology, which is based on the fusion of specific B lymphocytes with myeloma cells. Since then, several mAbs were described for therapeutic, diagnostic, and research purposes. Despite being an old technique with low complexity, hybridoma-based strategies have limitations that include the low efficiency on B lymphocyte-myeloma cell fusion step, and the need to use experimental animals. In face of that, several methods have been developed to improve mAb generation, ranging from changes in hybridoma technique to the advent of completely new technologies, such as the antibody phage display and the single B cell antibody ones. In this review, we discuss the hybridoma technology along with emerging mAb isolation approaches, taking into account their advantages and limitations. Finally, we explore the usefulness of the hybridoma technology nowadays.

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Hybridoma technology is the most popular technique to obtain monoclonal antibodies.

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Hybridoma technology variants include B cell and stereospecific targeting protocols.

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Phage display and single B cell methods are hybridoma technology alternatives.

Rapid identification of anti-idiotypic mAbs with high affinity and diverse epitopes by rabbit single B-cell sorting-culture and cloning technology

The proactive generation of anti-idiotypic antibodies (anti-IDs) against therapeutic antibodies with desirable properties is an important step in pre-clinical and clinical assay development supporting their bioanalytical programs. Here, we describe a robust platform to generate anti-IDs using rabbit single B cell sorting-culture and cloning technology by immunizing rabbits with therapeutic drug Fab fragment and sorting complementarity determining regions (CDRs) specific B cells using designed framework control as a negative gate to exclude non-CDRs-specific B cells. The supernatants of cultured B cells were subsequently screened for binding to drug-molecule by enzyme-linked immunosorbent assay and the positive hits of B cell lysates were selected for cloning of their immunoglobulin G (IgG) variable regions. The recombinant monoclonal anti-IDs generated with this method have high affinity and specificity with broad epitope coverage and different types. The recombinant anti-IDs were available for assay development to support pharmacokinetic (PK) and immunogenicity studies within 12 weeks from the start of rabbit immunization. Using this novel rapid and efficient in-house approach we have generated a large panel of anti-IDs against a series of 11 therapeutic antibody drugs and successfully applied them to the clinical assay development.

Monoclonal Antibodies Counteract Opioid-Induced Behavioral and Toxic Effects in Mice and Rats

Monoclonal antibodies (mAbs) and vaccines have been proposed as medical countermeasures to treat opioid use disorder (OUD) and prevent opioid overdose. In contrast to current pharmacotherapies (e.g., methadone, buprenorphine, naltrexone, and naloxone) for OUD and overdose, which target brain opioid receptors, mAbs and vaccine-generated polyclonal antibodies sequester the target opioid in the serum and reduce drug distribution to the brain. Furthermore, mAbs offer several potential clinical benefits over approved medications, such as longer serum half-life, higher selectivity, reduced side effects, and no abuse liability. Using magnetic enrichment to isolate opioid-specific B cell lymphocytes prior to fusion with myeloma partners, this study identified a series of murine hybridoma cell lines expressing mAbs with high affinity for opioids of clinical interest, including oxycodone, heroin and its active metabolites, and fentanyl. In mice, passive immunization with lead mAbs against oxycodone, heroin, and fentanyl reduced drug-induced antinociception and the distribution of the target opioid to the brain. In mice and rats, mAb pretreatment reduced fentanyl-induced respiratory depression and bradycardia, two risk factors for opioid-related overdose fatality. Overall, these results support use of mAbs to counteract toxic effects of opioids and other chemical threats. SIGNIFICANCE STATEMENT: The incidence of fatal overdoses due to the widespread access to heroin, prescription opioids, and fentanyl suggests that current Food and Drug Administration-approved countermeasures are not sufficient to mitigate the opioid epidemic. Monoclonal antibodies (mAbs) may provide acute protection from overdose by binding to circulating opioids in serum. Use of mAbs prophylactically, or after exposure in combination with naloxone, may reduce hospitalization and increase survival.

RNase H-dependent PCR enables highly specific amplification of antibody variable domains from single B-cells

Immunization-based antibody discovery platforms require robust and effective protocols for the amplification, cloning, expression, and screening of antibodies from large numbers of B-cells in order to effectively capture the diversity of an experienced Ig-repertoire. Multiplex PCR using a series of forward and reverse primers designed to recover antibodies from a range of different germline sequences is challenging because primer design requires the recovery of full length antibody sequences, low starting template concentrations, and the need for all the primers to function under the same PCR conditions. Here we demonstrate several advantages to incorporating RNase H2-dependent PCR (rh-PCR) into a high-throughput, antibody-discovery platform. Firstly, rh-PCR eliminated primer dimer synthesis to below detectable levels, thereby eliminating clones with a false positive antibody titer. Secondly, by increasing the specificity of PCR, the rh-PCR primers increased the recovery of cognate antibody variable regions from single B-cells, as well as downstream recombinant antibody titers. Finally, we demonstrate that rh-PCR primers provide a more homogeneous sample pool and greater sequence quality in a Next Generation Sequencing-based approach to obtaining DNA sequence information from large numbers of cloned antibody cognate pairs. Furthermore, the higher specificity of the rh-PCR primers allowed for a better match between native antibody germline sequences and the VL/VH fragments amplified from single B-cells.

Complementary epitopes and favorable developability of monoclonal anti-LAMP1 antibodies generated using two transgenic animal platforms

Monoclonal antibodies (mAbs) for therapeutic applications should be as similar to native human antibodies as possible to minimize their immunogenicity in patients. Several transgenic animal platforms are available for the generation of fully human mAbs. Attributes such as specificity, efficacy and Chemistry, Manufacturing and Controls (CMC) developability of antibodies against a specific target are typically established for antibodies obtained from one platform only. In this study, monoclonal antibodies (mAbs) cross-reactive against human and cynomolgus LAMP1 were derived from the human immunoglobulin transgenic TRIANNI mouse and OmniChicken® platforms and assessed for their specificity, sequence diversity, ability to bind to and internalize into tumor cells, expected immunogenicity and CMC developability. Our results show that the two platforms were complementary at providing a large diversity of mAbs with respect to epitope coverage and antibody sequence diversity. Furthermore, most antibodies originating from either platform exhibited good manufacturability characteristics.

Sequencing B cell receptors from ferrets (Mustela putorius furo)

The domestic ferret (Mustela putorius furo) provides a critical animal model to study human respiratory diseases. However immunological insights are restricted due to a lack of ferret-specific reagents and limited genetic information about ferret B and T cell receptors. Here, variable, diversity and joining genes within the ferret kappa, lambda and heavy chain immunoglobulin loci were annotated using available genomic information. A multiplex PCR approach was derived that facilitated the recovery of paired heavy and light chain immunoglobulin sequences from single sorted ferret B cells, allowing validation of predicted germline gene sequences and the identification of putative novel germlines. Eukaryotic expression vectors were developed that enabled the generation of recombinant ferret monoclonal antibodies. This work advances the ferret as an informative immunological model for viral diseases by allowing the in-depth interrogation of antibody-based immunity.

The PRRSV-Specific Memory B Cell Response Is Long-Lived in Blood and Is Boosted During Live Virus Re-exposure

Porcine reproductive and respiratory syndrome virus (PRRSV) is an important pathogen of swine health and well-being worldwide largely due to an insufficient understanding of the adaptive immune response to infection leading to ineffective PRRSV control. The memory and anamnestic response to infection are critical gaps in knowledge in PRRSV immunity. The lack of effective tools for the evaluation of the memory response previously hindered the ability to effectively characterize the porcine memory response to infection. However, the creation and validation of a PRRSV nsp7-specific B cell tetramer now facilitates the ability to detect very rare memory B cells and thus define the memory response of the pig. Here, we describe the PRRSV nsp7-specific B cell response following vaccination and challenge in six key secondary lymphoid organs including the identification of PBMCs as the tissue of interest for the memory immune response in pigs. Following live virus challenge of immune animals, an anamnestic response of nsp7-specific memory B cells and neutralizing antibodies was observed. This characterization of the functional humoral immune response to PRRSV answers key questions involved in regional specialization of the immune response following intramuscular inoculation of PRRSV MLV.

Cyto-Mine: An Integrated, Picodroplet System for High-Throughput Single-Cell Analysis, Sorting, Dispensing, and Monoclonality Assurance

The primary goal of bioprocess cell line development is to obtain high product yields from robustly growing and well-defined clonal cell lines in timelines measured in weeks rather than months. Likewise, high-throughput screening of B cells and hybridomas is required for most cell line engineering workflows. A substantial bottleneck in these processes is detecting and isolating rare clonal cells with the required characteristics. Traditionally, this was achieved by the resource-intensive method of limiting dilution cloning, and more recently aided by semiautomated technologies such as cell sorting (e.g., fluorescence-activated cell sorting) and colony picking. In this paper we report on our novel Cyto-Mine Single Cell Analysis and Monoclonality Assurance System, which overcomes the limitations of current technologies by screening hundreds of thousands of individual cells for secreted target proteins, and then isolating and dispensing the highest producers into microtiter plate wells (MTP). The Cyto-Mine system performs this workflow using a fully integrated, microfluidic Cyto-Cartridge. Critically, all reagents and Cyto-Cartridges used are animal component-free (ACF) and sterile, thus allowing fast, robust, and safe isolation of desired cells.

Single B Cell Cloning and Production of Rabbit Monoclonal Antibodies

Monoclonal antibodies are among the most significant biological tools used in medicine and biology that have revolutionized the field of diagnostics, therapeutics, and targeted drug delivery systems for many diseases. Among them, rabbit monoclonal antibodies have attracted significant attention for having high affinity and specificity. During the past few decades, different techniques have been developed to produce monoclonal antibodies. Single B cell cloning technology offers many advantages compared to other methods and has been used to generate monoclonal antibodies from different species including rabbits. This review briefly describes some of these methods, with main focus on single B cell cloning and production of rabbit monoclonal antibodies.

Development of Foot-and-Mouth Disease Virus-Neutralizing Monoclonal Antibodies Derived From Plasmablasts of Infected Cattle and Their Germline Gene Usage

Cattle are susceptible to foot-and-mouth disease virus (FMDV), and neutralizing antibodies are critical for protection against FMDV infection in this species. However, more information is needed on the host specific antigenic structure recognized by the FMDV-specific monoclonal antibodies (mAbs) and on the functional properties of the mAb that are produced in the natural host, cattle. Herein, we characterized 55 plasmablast-derived mAbs from three FMDV-infected cattle and obtained 28 FMDV-neutralizing antibodies by the single B cell antibody technique. The neutralizing mAbs (27/28) mainly recognized conformational epitopes that differ from the well-characterized immunodominant antigenic site 1 of FMDV as defined by murine mAbs. Of these FMDV-neutralizing mAbs, 13 mAbs showed intra-type broadly neutralizing activity against the three topotypes of FMDV serotype O (ME-SA, SEA, and Cathay topotypes). Moreover, all these intra-type broadly neutralizing antibodies competed with sera from FMDV infected or vaccinated cattle, which indicates their binding to native dominant epitopes, as revealed by a blocking ELISA. We further analyzed the germline V(D)J gene usage of the 55 FMDV-specific mAbs and found cattle IgG antibodies containing ultralong HCDR3 were exclusively restricted to usage of the germline gene segment V_H 1-7^*02. In addition, the restricted germline gene segments of V_H 1-7^*02 and V_L1-47^*01 or 1-52^*01 pairing were observed in all IgG antibodies with ultralong HCDR3. Furthermore, antibodies with longer HCDR3 were more inclined to display FMDV-neutralizing activity. This study presents a novel method for screening FMDV-specific cattle mAbs which then provide the most useful tools for studying FMDV antigenic structure and variation.

Rapid single B cell antibody discovery using nanopens and structured light

Accelerated development of monoclonal antibody (mAb) tool reagents is an essential requirement for the successful advancement of therapeutic antibodies in today’s fast-paced and competitive drug development marketplace. Here, we describe a direct, flexible, and rapid nanofluidic optoelectronic single B lymphocyte antibody screening technique (NanOBlast) applied to the generation of anti-idiotypic reagent antibodies. Selectively enriched, antigen-experienced murine antibody secreting cells (ASCs) were harvested from spleen and lymph nodes. Subsequently, secreted mAbs from individually isolated, single ASCs were screened directly using a novel, integrated, high-content culture, and assay platform capable of manipulating living cells within microfluidic chip nanopens using structured light. Single-cell polymerase chain reaction–based molecular recovery on select anti-idiotypic ASCs followed by recombinant IgG expression and enzyme-linked immunosorbent assay (ELISA) characterization resulted in the recovery and identification of a diverse and high-affinity panel of anti-idiotypic reagent mAbs. Combinatorial ELISA screening identified both capture and detection mAbs, and enabled the development of a sensitive and highly specific ligand binding assay capable of quantifying free therapeutic IgG molecules directly from human patient serum, thereby facilitating important drug development decision-making. The ASC import, screening, and export discovery workflow on the chip was completed within 5 h, while the overall discovery workflow from immunization to recombinantly expressed IgG was completed in under 60 days.

Antibodies and venom peptides: new modalities for ion channels

Ion channels play fundamental roles in both excitable and non-excitable tissues and therefore constitute attractive drug targets for myriad neurological, cardiovascular and metabolic diseases as well as for cancer and immunomodulation. However, achieving selectivity for specific ion channel subtypes with small-molecule drugs has been challenging, and there currently is a growing trend to target ion channels with biologics. One approach is to improve the pharmacokinetics of existing or novel venom-derived peptides. In parallel, after initial studies with polyclonal antibodies demonstrated the technical feasibility of inhibiting channel function with antibodies, multiple preclinical programmes are now using the full spectrum of available technologies to generate conventional monoclonal and engineered antibodies or nanobodies against extracellular loops of ion channels. After a summary of the current state of ion channel drug discovery, this Review discusses recent developments using the purinergic receptor channel P2X purinoceptor 7 (P2X7), the voltage-gated potassium channel KV1.3 and the voltage-gated sodium channel NaV1.7 as examples of targeting ion channels with biologics.

Antigen-Specific Single B Cell Sorting and Monoclonal Antibody Cloning in Guinea Pigs

Here, we have established an antigen-specific single B cell sorting and monoclonal antibody (mAb) cloning platform for analyzing immunization- or viral infection-elicited antibody response at the clonal level in guinea pigs. We stained the peripheral blood mononuclear cells (PBMCs) from a guinea pig immunized with HIV-1 envelope glycoprotein trimer mimic (BG505 SOSIP), using anti-guinea pig IgG and IgM fluorochrome conjugates, along with fluorochrome-conjugated BG505 SOSIP trimer as antigen (Ag) probe to sort for Ag-specific IgG^hi IgM^lo B cells at single cell density. We then designed a set of guinea pig immunoglobulin (Ig) gene-specific primers to amplify cDNAs encoding B cell receptor variable regions [V(D)J segments] from the sorted Ag-specific B cells. B cell V(D)J sequences were verified by sequencing and annotated by IgBLAST, followed by cloning into Ig heavy- and light-chain expression vectors containing human IgG1 constant regions and co-transfection into 293F cells to reconstitute full-length antibodies in a guinea pig-human chimeric IgG1 format. Of 88 antigen-specific B cells isolated, we recovered 24 (27%) cells with native-paired heavy and light chains. Furthermore, 85% of the expressed recombinant mAbs bind positively to the antigen probe by enzyme-linked immunosorbent and/or BioLayer Interferometry assays, while five mAbs from four clonal lineages neutralize the HIV-1 tier 1 virus ZM109. In summary, by coupling Ag-specific single B cell sorting with gene-specific single cell RT-PCR, our method exhibits high efficiency and accuracy, which will facilitate future efforts in isolating mAbs and analyzing B cell responses to infections or immunizations in the guinea pig model.

Ion channels as therapeutic antibody targets

It is now well established that antibodies have numerous potential benefits when developed as therapeutics. Here, we evaluate the technical challenges of raising antibodies to membrane-spanning proteins together with enabling technologies that may facilitate the discovery of antibody therapeutics to ion channels. Additionally, we discuss the potential targeting opportunities in the anti-ion channel antibody landscape, along with a number of case studies where functional antibodies that target ion channels have been reported. Antibodies currently in development and progressing towards the clinic are highlighted.

Rapid Generation of Monoclonal Antibodies from Single B Cells by Ecobody Technology

Single B cell sampling following to direct gene amplification and transient expression in animal cells has been recognized as powerful monoclonal antibodies (mAbs) screening strategies. Here we report Ecobody technology which allows mAbs screening from single B cells in two days This technology uses Escherichia coli cell-free protein synthesis (CFPS) for mAb expression. In the CFPS step, we employed our original techniques: (1) ‘Zipbody’ as a modified Fab (fragment of antigen binding) format, in which the active Fab formation is facilitated by adhesive leucine zipper peptides fused at the C-termini of the light and heavy chains; and (2) an N-terminal SKIK peptide tag that can markedly increase protein production. By the Ecobody technology, we demonstrated rapid screening of antigen specific mAbs from immunized rabbits and Epstein-Barr Virus infected human B cells. We further obtained rabbit mAbs in E. coli expression system yielding to 8.5 mg of purified proteins from 1 L bacterial culture.

A multiplatform strategy for the discovery of conventional monoclonal antibodies that inhibit the voltage-gated potassium channel Kv1.3

Identifying monoclonal antibodies that block human voltage-gated ion channels (VGICs) is a challenging endeavor exacerbated by difficulties in producing recombinant ion channel proteins in amounts that support drug discovery programs. We have developed a general strategy to address this challenge by combining high-level expression of recombinant VGICs in Tetrahymena thermophila with immunization of phylogenetically diverse species and unique screening tools that allow deep-mining for antibodies that could potentially bind functionally important regions of the protein. Using this approach, we targeted human Kv1.3, a voltage-gated potassium channel widely recognized as a therapeutic target for the treatment of a variety of T-cell mediated autoimmune diseases. Recombinant Kv1.3 was used to generate and recover 69 full-length anti-Kv1.3 mAbs from immunized chickens and llamas, of which 10 were able to inhibit Kv1.3 current. Select antibodies were shown to be potent (IC₅₀<10 nM) and specific for Kv1.3 over related Kv1 family members, hERG and hNav1.5.

Strategies for Generating Diverse Antibody Repertoires Using Transgenic Animals Expressing Human Antibodies

Therapeutic molecules derived from antibodies have become a dominant class of drugs used to treat human disease. Increasingly, therapeutic antibodies are discovered using transgenic animal systems that have been engineered to express human antibodies. While the engineering details differ, these platforms share the ability to raise an immune response that is comprised of antibodies with fully human idiotypes. Although the predominant transgenic host species has been mouse, the genomes of rats, rabbits, chickens, and cows have also been modified to express human antibodies. The creation of transgenic animal platforms expressing human antibody repertoires has revolutionized therapeutic antibody drug discovery. The observation that the immune systems of these animals are able to recognize and respond to a wide range of therapeutically relevant human targets has led to a surge in antibody-derived drugs in current development. While the clinical success of fully human monoclonal antibodies derived from transgenic animals is well established, recent trends have seen increasingly stringent functional design goals and a shift in difficulty as the industry attempts to tackle the next generation of disease-associated targets. These challenges have been met with a number of novel approaches focused on the generation of large, high-quality, and diverse antibody repertoires. In this perspective, we describe some of the strategies and considerations we use for manipulating the immune systems of transgenic animal platforms (such as XenoMouse^®) with a focus on maximizing the diversity of the primary response and steering the ensuing antibody repertoire toward a desired outcome.

Ecobody technology: rapid monoclonal antibody screening method from single B cells using cell-free protein synthesis for antigen-binding fragment formation

We report a rapid and cost-effective monoclonal antibody screening method from single animal B cells using reverse transcription (RT)-PCR and Escherichia coli cell-free protein synthesis (CFPS), which allows evaluation of antibodies within 2 working days. This process is named "Ecobody technology". The method includes strategies to isolate B cells that specifically bind an antigen from the peripheral blood of immunised animals, and single-cell RT-PCR to generate DNA fragments of the V_H and V_L genes, followed by CFPS for production of fragments of antigen binding (Fab). In the CFPS step, we employed our techniques: 1) 'Zipbody' as a method for producing Fab, in which the association of heavy and light chains is facilitated by adhesive leucine zipper peptides fused at the C-termini of the Fab; and 2) an N-terminal SKIK peptide tag that can increase protein expression levels. Using Ecobody technology, we obtained highly-specific monoclonal antibodies for the antigens Vibrio parahaemolyticus and E. coli O26. The anti-V. parahaemolyticus Zipbody mAb was further produced in E. coli strain SHuffle T7 Express in inclusion bodies and refolded by a conventional method, resulting in significant antigen-binding activity (K _D = 469 pM) and productivity of 8.5 mg purified antibody/L-culture.

Advances in the Isolation of Specific Monoclonal Rabbit Antibodies

The rabbit monoclonal antibodies (mAbs) have advantages in pharmaceuticals and diagnostics with high affinity and specificity. During the past decade, many techniques have been developed for isolating rabbit mAbs, including single B cell antibody technologies. This review describes the basic characterization of rabbit antibody repertoire and summarizes methods of hybridoma technologies, phage display platform, and single B cell antibody technologies. With advances in antibody function and repertoire analysis, rabbit mAbs will be widely used in therapeutic applications in the coming years.

From rabbit antibody repertoires to rabbit monoclonal antibodies

In this review, we explain why and how rabbit monoclonal antibodies have become outstanding reagents for laboratory research and increasingly for diagnostic and therapeutic applications. Starting with the unique ontogeny of rabbit B cells that affords highly distinctive antibody repertoires rich in in vivo pruned binders of high diversity, affinity and specificity, we describe the generation of rabbit monoclonal antibodies by hybridoma technology, phage display and alternative methods, along with an account of successful humanization strategies.