Selecting and screening recombinant antibody libraries

Development of a new affinity maturation protocol for the construction of an internalizing anti-nucleolin antibody library

Over the last decades, monoclonal antibodies have substantially improved the treatment of several conditions. The continuous search for novel therapeutic targets and improvements in antibody's structure, demands for a constant optimization of their development. In this regard, modulation of an antibody's affinity to its target has been largely explored and culminated in the discovery and optimization of a variety of molecules. It involves the creation of antibody libraries and selection against the target of interest. In this work, we aimed at developing a novel protocol to be used for the affinity maturation of an antibody previously developed by our group. An antibody library was constructed using an in vivo random mutagenesis approach that, to our knowledge, has not been used before for antibody development. Then, a cell-based phage display selection protocol was designed to allow the fast and simple screening of antibody clones capable of being internalized by target cells. Next generation sequencing coupled with computer analysis provided an extensive characterization of the created library and post-selection pool, that can be used as a guide for future antibody development. With a single selection step, an enrichment in the mutated antibody library, given by a decrease in almost 50% in sequence diversity, was achieved, and structural information useful in the study of the antibody-target interaction in the future was obtained.

Screening and construction of nanobodies against human CD93 using phage libraries and study of their antiangiogenic effects

Background

Cluster of Differentiation 93 (CD93) plays an important role in angiogenesis and is considered an important target for inhibiting tumor angiogenesis, but there are currently no therapeutic antibodies against CD93 in the clinic. Thus, we describe the screening of novel nanobodies (Nbs) targeting human CD93 from a phage library of shark-derived Nbs.

Methods

Screening and enrichment of phage libraries by enzyme-linked immunosorbent assay (ELISA). Anti-CD93 Nbs were purified by expression in E. coli. The binding affinity of anti-CD93 Nbs NC81/NC89 for CD93 was examined by flow cytometry (FC) and ELISA. The thermal stability of NC81/NC89 was examined by ELISA and CD spectroscopy. Afterward, the anti-angiogenic ability of NC81/NC89 was examined by MTT, wound healing assay, and tube formation assay. The expression level of VE-cadherin (VE-Ca) and CD93 was detected by Western Blot (WB). The binding sites and binding forms of NC81/NC89 to CD93 were analyzed by molecular docking.

Results

The anti-CD93 Nbs were screened in a phage library, expressed in E. coli, and purified to >95% purity. The results of FC and ELISA showed that NC81/NC89 have binding ability to human umbilical vein endothelial cells (HUVECs). The results of ELISA and CD spectroscopy showed that NC81/NC89 retained the ability to bind CD93 at 80°C and that the secondary structure remained stable. In vitro, the results showed that NC81 and NC89 significantly inhibited the proliferation and migration of human umbilical vein endothelial cells (HUVECs) as well as tube formation on Matrigel. Western Blot showed that NC81 and NC89 also inhibited the expression of VE-Ca thereby increasing vascular permeability. It was found during molecular docking that the CDR regions of NC81 and NC89 could be attached to CD93 by strong hydrogen bonds and salt bridges, and the binding sites were different.

Conclusion

We have successfully isolated NC81 and NC89, which bind CD93, and both Nbs significantly inhibit angiogenesis and increase vascular permeability. These results suggest that NC81 and NC89 have potential clinical applications in angiogenesis-related therapies.

A systemic approach to identifying sequence frameworks that decrease mAb production in a transient Chinese hamster ovary cell expression system

Monoclonal antibodies (mAbs) are often engineered at the sequence level for improved clinical performance yet are rarely evaluated prior to candidate selection for their "developability" characteristics, namely expression, which can necessitate additional resource investments to improve the manufacturing processes for problematic mAbs. A strong relationship between primary sequence and expression has emerged, with slight differences in amino acid sequence resulting in titers differing by up to an order of magnitude. Previous work on these "difficult-to-express" (DTE) mAbs has shown that these phenotypes are driven by post-translational bottlenecks in antibody folding, assembly, and secretion processes. However, it has been difficult to translate these findings across cell lines and products. This work presents a systematic approach to study the impact of sequence variation on mAb expression at a larger scale and under more industrially relevant conditions. The analysis found 91 mutations that decreased transient expression of an IgG1κ in Chinese hamster ovary (CHO) cells and revealed that mutations at inaccessible residues, especially those leading to decreases in residue hydrophobicity, are not favorable for high expression. This workflow can be used to better understand sequence determinants of mAb expression to improve candidate selection procedures and reduce process development timelines.

In vivo affinity maturation of mouse B cells reprogrammed to express human antibodies

Mice adoptively transferred with mouse B cells edited via CRISPR to express human antibody variable chains could help evaluate candidate vaccines and develop better antibody therapies. However, current editing strategies disrupt the heavy-chain locus, resulting in inefficient somatic hypermutation without functional affinity maturation. Here we show that these key B-cell functions can be preserved by directly and simultaneously replacing recombined mouse heavy and kappa chains with those of human antibodies, using a single Cas12a-mediated cut at each locus and 5' homology arms complementary to distal V segments. Cells edited in this way to express the human immunodeficiency virus type 1 (HIV-1) broadly neutralizing antibody 10-1074 or VRC26.25-y robustly hypermutated and generated potent neutralizing plasma in vaccinated mice. The 10-1074 variants isolated from the mice neutralized a global panel of HIV-1 isolates more efficiently than wild-type 10-1074 while maintaining its low polyreactivity and long half-life. We also used the approach to improve the potency of anti-SARS-CoV-2 antibodies against recent Omicron strains. In vivo affinity maturation of B cells edited at their native loci may facilitate the development of broad, potent and bioavailable antibodies.

A Detailed Protocol for Constructing a Human Single-Chain Variable Fragment (scFv) Library and Downstream Screening via Phage Display

The development of monoclonal antibodies (mAbs) represents a significant milestone in both basic research and clinical applications due to their target specificity and versatility in therapeutic and diagnostic applications. The innovative strategy of mAb screening, utilizing phage display, facilitates the in vitro screening of antibodies with high affinity to target antigens. The single-chain variable fragment (scFv) is a subset of mAb derivatives, known for its high binding affinity and smaller size-just one-third of that of human IgG. This report outlines a detailed and comprehensive procedure for constructing a scFv phagemid library derived from human patients, followed by screening via phage display affinity selection. The protocol utilizes 348 primer combinations spanning the entire human antibody repertoire to minimize sequence bias and maintain library diversity during polymerase chain reaction (PCR) for scFv generation, resulting in a library size greater than 1 × 108. Furthermore, we describe a high-throughput phage display screening protocol using enzyme-linked immunosorbent assay (ELISA) to evaluate more than 1200 scFv candidates. The generation of a highly diverse scFv library, coupled with the implementation of a phage display screening methodology, is expected to provide a valuable resource for researchers in pursuit of scFvs with high affinity for target antigens, thus advancing both research and clinical endeavors.

Production and purification of Clostridium perfringens type C beta-toxin and IgG and IgY antitoxins

OBJECTIVES

This study aimed to produce and purify Clostridium perfringens type C beta-toxin, sheep anti-beta toxin immunoglobulin G (IgG) and chicken immunoglobulin Y (IgY).

METHODS

Two methods were used for beta-toxin purification: single-step metal affinity chromatography (MAC) using zinc as a chelator and ion exchange chromatography (IEX). The purified and inactivated beta-toxoids were then administered to sheep and chickens in order to produce IgG and IgY.

RESULTS

All assays using the IEX failed. In contrast, MAC purified more than 21 mg of toxin per run in a single-step protocol. The purified and inactivated beta-toxoids were then administered to sheep and chickens, and IgG and IgY were purified with a high yield, medium antibody titer of 50 IU/mL, and high avidity (73.2 %).

CONCLUSIONS

C. perfringens type C beta-toxin and sheep or chicken anti-beta toxin IgG and IgY antibodies were successfully produced and purified using a simple protocol. This protocol can be used for the production of components used in the diagnosis and research of necrotic enteritis caused by C. perfringens type C, as well as for the evaluation of existing vaccines and the development of new preventive methods against this disease.

Development of Recombinant Antibody by Yeast Surface Display Technology

Recombinant antibodies have emerged as powerful tools in various fields, including therapeutics, diagnostics, and research applications. The selection of high-affinity antibodies with desired specificity is a crucial step in the development of recombinant antibody-based products. In recent years, yeast surface display technology has gained significant attention as a robust and versatile platform for antibody selection. This graphical review provides an overview of the yeast surface display technology and its applications in recombinant antibody selection. We discuss the key components involved in the construction of yeast surface display libraries, including the antibody gene libraries, yeast host strains, and display vectors. Furthermore, we highlight the strategies employed for affinity maturation and optimization of recombinant antibodies using yeast surface display. Finally, we discuss the advantages and limitations of this technology compared to other antibody selection methods. Overall, yeast surface display technology offers a powerful and efficient approach for the selection of recombinant antibodies, enabling the rapid generation of high-affinity antibodies for various applications.

The dengue-specific immune response and antibody identification with machine learning

Dengue virus poses a serious threat to global health and there is no specific therapeutic for it. Broadly neutralizing antibodies recognizing all serotypes may be an effective treatment. High-throughput adaptive immune receptor repertoire sequencing (AIRR-seq) and bioinformatic analysis enable in-depth understanding of the B-cell immune response. Here, we investigate the dengue antibody response with these technologies and apply machine learning to identify rare and underrepresented broadly neutralizing antibody sequences. Dengue immunization elicited the following signatures on the antibody repertoire: (i) an increase of CDR3 and germline gene diversity; (ii) a change in the antibody repertoire architecture by eliciting power-law network distributions and CDR3 enrichment in polar amino acids; (iii) an increase in the expression of JNK/Fos transcription factors and ribosomal proteins. Furthermore, we demonstrate the applicability of computational methods and machine learning to AIRR-seq datasets for neutralizing antibody candidate sequence identification. Antibody expression and functional assays have validated the obtained results.

Advancing Antibody Engineering through Synthetic Evolution and Machine Learning

Abs are versatile molecules with the potential to achieve exceptional binding to target Ags, while also possessing biophysical properties suitable for therapeutic drug development. Protein display and directed evolution systems have transformed synthetic Ab discovery, engineering, and optimization, vastly expanding the number of Ab clones able to be experimentally screened for binding. Moreover, the burgeoning integration of high-throughput screening, deep sequencing, and machine learning has further augmented in vitro Ab optimization, promising to accelerate the design process and massively expand the Ab sequence space interrogated. In this Brief Review, we discuss the experimental and computational tools employed in synthetic Ab engineering and optimization. We also explore the therapeutic challenges posed by developing Abs for infectious diseases, and the prospects for leveraging machine learning-guided protein engineering to prospectively design Abs resistant to viral escape.

A Directed Evolution Protocol for Engineering Minimal Transcription Factors, Based on CIS Display

Directed evolution is an efficient strategy for obtaining desired biomolecules. Since the 1990s, the emergence of display techniques has enabled high-throughput screening of functional proteins. However, classical methods require library construction by plasmid cloning and are limited by transformation efficiencies, typically limiting library sizes to ~106-107 variants. More recently, in vitro techniques have emerged that avoid cloning, allowing library sizes of >1012 members. One of these, CIS display, is a DNA-based display technique which allows high-throughput selection of biomolecules in vitro. CIS display creates the genotype-phenotype link required for selection by a DNA replication initiator protein, RepA, that binds exclusively to the template from which it has been expressed. This method has been successfully used to evolve new protein-protein interactions but has not been used before to select DNA-binding proteins, which are major components in mammalian synthetic biology. In this chapter, we describe a directed evolution method using CIS display to efficiently select functional DNA-binding proteins from pools of nonbinding proteins. The method is illustrated by enriching the minimal transcription factor Cro from a low starting frequency (1 in 109). This protocol is also applicable to engineering other DNA-binding proteins or transcription factors from combinatorial libraries.

Recent Advances in the Development of Monoclonal Antibodies and Next-Generation Antibodies

mAbs are highly indispensable tools for diagnostic, prophylactic, and therapeutic applications. The first technique, hybridoma technology, was based on fusion of B lymphocytes with myeloma cells, which resulted in generation of single mAbs against a specific Ag. Along with hybridoma technology, several novel and alternative methods have been developed to improve mAb generation, ranging from electrofusion to the discovery of completely novel technologies such as B cell immortalization; phage, yeast, bacterial, ribosome, and mammalian display systems; DNA/RNA encoded Abs; single B cell technology; transgenic animals; and artificial intelligence/machine learning. This commentary outlines the evolution, methodology, advantages, and limitations of various mAb production techniques. Furthermore, with the advent of next-generation Ab technologies such as single-chain variable fragments, nanobodies, bispecific Abs, Fc-engineered Abs, Ab biosimilars, Ab mimetics, and Ab-drug conjugates, the healthcare and pharmaceutical sectors have become resourceful to develop highly specific mAb treatments against various diseases such as cancer and autoimmune and infectious diseases.

High throughput purification of monoclonal recombinant antibodies using a Protein-A coated membrane plate system

The therapeutic use of monoclonal antibodies (mAbs) ranges from cancer treatment to immune-mediated conditions, covering infectious and cardiovascular disorders, among others. The development of improved methods for therapeutic antibody discovery has accelerated the identification of numerous mAbs: a discovery campaign can be deeply mined, resulting in hundreds, even thousands, of potential antibody leads for a given target of interest. High throughput mAb expression and purification methods are required for the rapid validation of those leads. In this work, we describe the implementation of a Protein-A coated membrane plate system, the Purexa™ AHT membrane plate, for robust preparative purification of hundreds of recombinant mAbs, without the need for automation. The high efficiency (>80%) recovery generated sufficient mAb for downstream screening analyses such as ELISA and surface plasmon resonance (SPR). This new system allows the functional validation of hundreds of lead antibodies from discovery campaigns in a timely manner regardless of operational size.

Development of monoclonal antibodies to target the large surface protein of hepatitis B virus and their use in therapeutic and diagnostic applications

Over 250 million people are living with chronic infection caused by the hepatitis B virus (HBV). HBV has three surface proteins, namely small (SHBs), medium (MHBs) and large (LHBs), and they play different roles in the virus life cycle. The approved hepatitis B vaccine only contains the SHBs protein and many studies have focused on characterising the functional domains in SHBs. Although the LHBs protein is less studied, recent studies have shown that it plays important roles in mediating viral entry, replication and assembly. Over the years, there have been major advancements in monoclonal antibody (mAb) discovery tools and multiple mAbs have been developed to specifically target the preS1 domain in LHBs. We summarise the HBV infection systems and antibody discovery strategies that have been utilised by various research groups to assess the potential use of anti-preS1 mAbs as therapeutic antibodies against HBV or in the development of new diagnostic assays.

In vivo affinity maturation of murine B cells reprogrammed to express human antibodies

CRISPR-edited murine B cells engineered to express human antibody variable chains proliferate, class switch, and secrete these antibodies in vaccinated mice. However, current strategies disrupt the heavy-chain locus, resulting in inefficient somatic hypermutation without functional affinity maturation. Here we show that recombined murine heavy- and kappa-variable genes can be directly and simultaneously overwritten, using Cas12a-mediated cuts at their 3'-most J segments and 5' homology arms complementary to distal V segments. Cells edited in this way to express the HIV-1 broadly neutralizing antibodies 10-1074 or VRC26.25-y robustly hypermutated and generated potent neutralizing plasma in vaccinated recipient mice. 10-1074 variants isolated from these mice bound and neutralized HIV-1 envelope glycoprotein more efficiently than wild-type 10-1074 while maintaining or improving its already low polyreactivity and long in vivo half-life. We further validated this approach by generating substantially broader and more potent variants of the anti-SARS-CoV-2 antibodies ZCB11 and S309. Thus, B cells edited at their native loci affinity mature, facilitating development of broad, potent, and bioavailable antibodies and expanding the potential applications of engineered B cells.

Recent advances in the application of genetic and epigenetic modalities in the improvement of antibody-producing cell lines

There are numerous applications for recombinant antibodies (rAbs) in biological and toxicological research. Monoclonal antibodies are synthesized using genetic engineering and other related processes involved in the generation of rAbs. Because they can identify specific antigenic sites on practically any molecule, including medicines, hormones, microbial antigens, and cell receptors, rAbs are particularly useful in scientific research. The key benefits of rAbs are improved repeatability, control, and consistency, shorter manufacturing times than with hybridoma technology, an easier transition from one format of antibody to another, and an animal-free process. The engineering of the host cell has recently been developed method for enhancing the production efficiency and improving the quality of antibodies from mammalian cell lines. In this light, genetic engineering is mostly utilized to manage cellular chaperones, decrease cell death, increase cell viability, change the microRNAs (miRNAs) pattern in mammalian cells, and glycoengineered cell lines. Here, we shed light on how genetic engineering can be used therapeutically to produce antibodies at higher levels with greater potency and effectiveness.

Combinatorial mixtures of organic solutes for improved liquid/liquid extraction of ions

Biological systems routinely extract and organize ions in complex yet highly ordered and active systems. Much of this function is attributed to proteins, although recent evidence indicates aggregates of lipids are also capable of molecular recognition. Here we tested the hypothesis that combinatorial mixtures of organic solutes might lead to enhanced liquid/liquid extraction. We started with liquid oleic acid as an organic phase extracting copper ions from water and added a library of additives. By using Bayesian optimization to autonomously direct the combinatorial formulation, we discovered mixtures that enhanced the extraction performance. The main additive that improved the system was octylphosphonic acid. Interestingly, the optimal mixture has a significant improvement compared to this additive alone. This suggests that the combinations of organic solutes are better than using pure components in liquid/liquid extraction. Furthermore, we found that precipitation occurs in the samples showing better extraction efficiency, which has interesting material properties and potential for new types of supramolecular biosensors.

Exploring shark VNAR antibody against infectious diseases using phage display technology

Antibody with high affinity and specificity to antigen has widely used as a tool to combat various diseases. The variable domain of immunoglobulin new antigen receptor (VNAR) naturally found in shark contains autonomous function as single-domain antibody. Due to its excellent characteristics, the small, non-complex, and highly stable have made shark VNAR can acquires the antigen-binding capability that might not be reached by conventional antibody. Phage display technology enables shark VNAR to be presented on the surface of phage, allowing the exploration of shark VNAR as an alternative antibody format to target antigens from various infectious diseases. The application of phage-displayed shark VNAR in antibody library and biopanning eventually leads to the discovery and isolation of antigen-specific VNARs with diagnostic and therapeutic potential towards infectious diseases. This review provides an overview of the shark VNAR antibody, the types of phage display technology with comparison to the other types of display system, as well as the application and case studies of phage-displayed shark VNAR antibodies against infectious diseases.

Beyond canonical PROTAC: biological targeted protein degradation (bioTPD)

Targeted protein degradation (TPD) is an emerging therapeutic strategy with the potential to modulate disease-associated proteins that have previously been considered undruggable, by employing the host destruction machinery. The exploration and discovery of cellular degradation pathways, including but not limited to proteasomes and lysosome pathways as well as their degraders, is an area of active research. Since the concept of proteolysis-targeting chimeras (PROTACs) was introduced in 2001, the paradigm of TPD has been greatly expanded and moved from academia to industry for clinical translation, with small-molecule TPD being particularly represented. As an indispensable part of TPD, biological TPD (bioTPD) technologies including peptide-, fusion protein-, antibody-, nucleic acid-based bioTPD and others have also emerged and undergone significant advancement in recent years, demonstrating unique and promising activities beyond those of conventional small-molecule TPD. In this review, we provide an overview of recent advances in bioTPD technologies, summarize their compositional features and potential applications, and briefly discuss their drawbacks. Moreover, we present some strategies to improve the delivery efficacy of bioTPD, addressing their challenges in further clinical development.

Isolation of full-length IgG antibodies from combinatorial libraries expressed in the cytoplasm of Escherichia coli

Here we describe a facile and robust genetic selection for isolating full-length IgG antibodies from combinatorial libraries expressed in the cytoplasm of redox-engineered Escherichia coli cells. The method is based on the transport of a bifunctional substrate comprised of an antigen fused to chloramphenicol acetyltransferase, which allows positive selection of bacterial cells co-expressing cytoplasmic IgGs called cyclonals that specifically capture the chimeric antigen and sequester the antibiotic resistance marker in the cytoplasm. The utility of this approach is first demonstrated by isolating affinity-matured cyclonal variants that specifically bind their cognate antigen, the leucine zipper domain of a yeast transcriptional activator, with subnanomolar affinities, which represent a ~20-fold improvement over the parental IgG. We then use the genetic assay to discover antigen-specific cyclonals from a naïve human antibody repertoire, leading to the identification of lead IgG candidates with affinity and specificity for an influenza hemagglutinin-derived peptide antigen.

Noncovalent antibody catenation on a target surface greatly increases the antigen-binding avidity

Immunoglobulin G (IgG) antibodies are widely used for diagnosis and therapy. Given the unique dimeric structure of IgG, we hypothesized that, by genetically fusing a homodimeric protein (catenator) to the C-terminus of IgG, reversible catenation of antibody molecules could be induced on a surface where target antigen molecules are abundant, and that it could be an effective way to greatly enhance the antigen-binding avidity. A thermodynamic simulation showed that quite low homodimerization affinity of a catenator, e.g. dissociation constant of 100 μM, can enhance nanomolar antigen-binding avidity to a picomolar level, and that the fold enhancement sharply depends on the density of the antigen. In a proof-of-concept experiment where antigen molecules are immobilized on a biosensor tip, the C-terminal fusion of a pair of weakly homodimerizing proteins to three different antibodies enhanced the antigen-binding avidity by at least 110 or 304 folds from the intrinsic binding avidity. Compared with the mother antibody, Obinutuzumab(Y101L) which targets CD20, the same antibody with fused catenators exhibited significantly enhanced binding to SU-DHL5 cells. Together, the homodimerization-induced antibody catenation would be a new powerful approach to improve antibody applications, including the detection of scarce biomarkers and targeted anticancer therapies.

Accelerating therapeutic protein design with computational approaches toward the clinical stage

Therapeutic protein, represented by antibodies, is of increasing interest in human medicine. However, clinical translation of therapeutic protein is still largely hindered by different aspects of developability, including affinity and selectivity, stability and aggregation prevention, solubility and viscosity reduction, and deimmunization. Conventional optimization of the developability with widely used methods, like display technologies and library screening approaches, is a time and cost-intensive endeavor, and the efficiency in finding suitable solutions is still not enough to meet clinical needs. In recent years, the accelerated advancement of computational methodologies has ushered in a transformative era in the field of therapeutic protein design. Owing to their remarkable capabilities in feature extraction and modeling, the integration of cutting-edge computational strategies with conventional techniques presents a promising avenue to accelerate the progression of therapeutic protein design and optimization toward clinical implementation. Here, we compared the differences between therapeutic protein and small molecules in developability and provided an overview of the computational approaches applicable to the design or optimization of therapeutic protein in several developability issues.

Egg Yolk Antibody for Passive Immunization: Status, Challenges, and Prospects

The immunoglobulin Y (IgY) derived from hyperimmune egg yolk is a promising passive immune agent to combat microbial infections in humans and livestock. Numerous studies have been performed to develop specific egg yolk IgY for pathogen control, but with limited success. To date, the efficacy of commercial IgY products, which are all delivered through an oral route, has not been approved or endorsed by any regulatory authorities. Several challenging issues of the IgY-based passive immunization, which were not fully recognized and holistically discussed in previous publications, have impeded the development of effective egg yolk IgY products for humans and animals. This review summarizes major challenges of this technology, including in vivo stability, purification, heterologous immunogenicity, and repertoire diversity of egg yolk IgY. To tackle these challenges, potential solutions, such as encapsulation technologies to stabilize IgY, are discussed. Exploration of this technology to combat the COVID-19 pandemic is also updated in this review.

Generation and Next-Generation Sequencing-Based Characterization of a Large Human Combinatorial Antibody Library

Antibody phage display is a key technology for the discovery and development of target-specific monoclonal antibodies (mAbs) for use in research, diagnostics, and therapy. The construction of a high-quality antibody library, with larger and more diverse antibody repertoires, is essential for the successful development of phage display-derived mAbs. In this study, a large human combinatorial single-chain variable fragment library (1.5 × 10¹¹ colonies) was constructed from Epstein-Barr virus-infected human peripheral blood mononuclear cells stimulated with a combination of two of the activators of human B cells, the Toll-like receptor 7/8 agonist R848 and interleukin-2. Next-generation sequencing analysis with approximately 1.9 × 10⁶ and 2.7 × 10⁶ full-length sequences of heavy chain variable (VH) and κ light chain variable (Vκ) domains, respectively, revealed that the library consists of unique VH (approximately 94%) and Vκ (approximately 91%) sequences with greater diversity than germline sequences. Lastly, multiple unique mAbs with high affinity and broad cross-species reactivity could be isolated from the library against two therapeutically relevant target antigens, validating the library quality. These findings suggest that the novel antibody library we have developed may be useful for the rapid development of target-specific phage display-derived recombinant human mAbs for use in therapeutic and diagnostic applications.

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.

A fully human connective tissue growth factor blocking monoclonal antibody ameliorates experimental rheumatoid arthritis through inhibiting angiogenesis

BACKGROUND

Connective tissue growth factor (CTGF) plays a pivotal role in the pathogenesis of rheumatoid arthritis (RA) by facilitating angiogenesis and is a promising therapeutic target for RA treatment. Herein, we generated a fully human CTGF blocking monoclonal antibody (mAb) through phage display technology.

RESULTS

A single-chain fragment variable (scFv) with a high affinity to human CTGF was isolated through screening a fully human phage display library. We carried out affinity maturation to elevate its affinity for CTGF and reconstructed it into a full-length IgG1 format for further optimization. Surface plasmon resonance (SPR) data showed that full-length antibody IgG mut-B2 bound to CTGF with a dissociation constant (KD) as low as 0.782 nM. In the collagen-induced arthritis (CIA) mice, IgG mut-B2 alleviated arthritis and decreased the level of pro-inflammatory cytokines in a dose-dependent manner. Furthermore, we confirmed that the TSP-1 domain of CTGF is essential for the interaction. Additionally, the results of Transwell assays, tube formation experiments, and chorioallantoic membrane (CAM) assays showed that IgG mut-B2 could effectively inhibit angiogenesis.

CONCLUSION

The fully human mAb that antagonizes CTGF could effectively alleviate arthritis in CIA mice, and its mechanism is tightly associated with the TSP-1 domain of CTGF.

Isolation of atrazine nanobodies enhanced by depletion of anti-carrier protein phages and performance comparison between the nanobody and monoclonal antibody derived from the same immunogen

Nanobody, a single domain antibody, has been shown a great promise for immunoassay (IA) applications. To improve the panning efficiency so as to obtain a valuable nanobody, anti-carrier protein phages in a phage display library were depleted to enhance the selection of nanobodies against the herbicide atrazine by using immunomagnetic beads conjugated with bovine serum albumin (IMB-BSA). The depletion of anti-carrier protein phages from the atrazine phage display library tripled the number of atrazine positive phage clones after four rounds of panning. One of the most sensitive phage clones Nb3 selected from the IMB-BSA depleted library was used to compare the performance with the monoclonal antibody (mAb 5D9) developed from the same immunogen. The Nb3-based IA exhibited similar specificity with the mAb 5D9-based IA, but greater thermostability and organic solvent tolerance. The half-maximum inhibition concentration (IC₅₀) of the former was 3.5-fold greater than that of the latter (36.7 ng/mL versus 10.2 ng/mL). Because the Nb3-based IA was more robust than the mAb 5D9-based IA, the method detection limit of the two assays was 7.8 ng/mL of atrazine in river samples. The depletion strategy can increase the chance to acquire high quality nanobody and can be applicable for effective development of nanobodies against other small molecules.

Antibody engineering and its therapeutic applications

As a natural function, antibodies defend the host from infected cells and pathogens by recognizing their pathogenic determinants. Antibodies (Abs) gained wide acceptance with an enormous impact on human health and have predominantly captured the arena of bio-therapeutics and bio-diagnostics. The scope of Ab-based biologics is vast, and it is likely to solve many unmet clinical needs in future. The majority of attention is now devoted to developing innovative technologies for manufacturing and engineering Abs, better suited to satisfy human needs. The advent of Ab engineering technologies (AET) led to phenomenal developments leading to the generation of Abs-/Ab-derived molecules with desirable functional properties proportional to their expanding requirements. Evolution brought by AET, from the naturally occurring Ab forms to several advanced Ab formats and derivatives, was much needed as it is of great interest to the pharmaceutical industry. Thus, numerous advancements in AET have propelled success in therapeutic Ab development, along with the potential for ever-increasing improvements. Unique characteristics of Abs, such as its diversity, specificity, structural integrity and an array of possible applications, together inspire continuous innovation in the field. Overall, the AET could assist in conquer of several limitations of Abs in terms of their applicability in the field of therapeutics, diagnostics and research; AET has so far led to the production of next-generation Abs, which have revolutionized these arenas. Here in this review, we discuss the various distinguished engineering platforms for Ab development and the progress in modern therapeutics by the so-called "next-generation Abs."

Generation of a single-cell B cell atlas of antibody repertoires and transcriptomes to identify signatures associated with antigen specificity

Although new genomics-based pipelines have potential to augment antibody discovery, these methods remain in their infancy due to an incomplete understanding of the selection process that governs B cell clonal selection, expansion, and antigen specificity. Furthermore, it remains unknown how factors such as aging and reduction of tolerance influence B cell selection. Here we perform single-cell sequencing of antibody repertoires and transcriptomes of murine B cells following immunizations with a model therapeutic antigen target. We determine the relationship between antibody repertoires, gene expression signatures, and antigen specificity across 100,000 B cells. Recombinant expression and characterization of 227 monoclonal antibodies revealed the existence of clonally expanded and class-switched antigen-specific B cells that were more frequent in young mice. Although integrating multiple repertoire features such as germline gene usage and transcriptional signatures failed to distinguish antigen-specific from nonspecific B cells, other features such as immunoglobulin G (IgG) subtype and sequence composition correlated with antigen specificity.

A Two-Step Golden Gate Cloning Procedure for the Generation of Natively Paired YSD Fab Libraries

In vitro antibody display libraries have emerged as powerful tools for a streamlined discovery of novel antibody binders. While in vivo antibody repertoires are matured and selected as a specific pair of variable heavy and light chains (VH and VL) with optimal specificity and affinity, during the recombinant generation of in vitro libraries, the native sequence pairing is not maintained. Here we describe a cloning method that combines the flexibility and versatility of in vitro antibody display with the advantages of natively paired VH-VL antibodies. In this regard, VH-VL amplicons are cloned via a two-step Golden Gate cloning procedure, allowing the display of Fab fragments on yeast cells.

Antibody Isolation from Human Synthetic Libraries of Single-Chain Antibodies and Analysis Using NGS

Antibody libraries came into existence 30 years ago when the accumulating sequence data of immunoglobulin genes and the advent of PCR technology made it possible to clone antibody gene repertoires. Phage display (most common) and additional display and screening technologies were applied to pan out desired binding specificities from antibody libraries. As other antibody discovery tools, phage display is not an off-the-shelf technology and not offered as a kit but rather requires experience and expertise for making it indeed very useful.Next-generation sequencing (NGS) coupled with bioinformatics is a powerful tool for analyzing large amount of DNA sequence output of the panning. Here, we demonstrate how NGS analysis of phage biopanning (phage-Seq) of complex antibody libraries can facilitate the antibody discovery process and provide insights regarding the biopanning process (see Fig. 1).

In vivo Phage Display: A promising selection strategy for the improvement of antibody targeting and drug delivery properties

The discovery of hybridoma technology, described by Kohler and Milstein in 1975, and the resulting ability to generate monoclonal antibodies (mAbs) initiated a new era in antibody research and clinical development. However, limitations of the hybridoma technology as a routine antibody generation method in conjunction with high immunogenicity responses have led to the development of alternative approaches for the streamlined identification of most effective antibodies. Within this context, display selection technologies such as phage display, ribosome display, yeast display, bacterial display, and mammalian cell surface display have been widely promoted over the past three decades as ideal alternatives to traditional hybridoma methods. The display of antibodies on phages is probably the most widespread and powerful of these methods and, since its invention in late 1980s, significant technological advancements in the design, construction, and selection of antibody libraries have been made, and several fully human antibodies generated by phage display are currently approved or in various clinical development stages. With evolving novel disease targets and the emerging of a new generation of therapeutic antibodies, such as bispecific antibodies, antibody drug conjugates (ADCs), and chimeric antigen receptor T (CAR-T) cell therapies, it is clear that phage display is expected to continue to play a central role in antibody development. Nevertheless, for non-standard and more demanding cases aiming to generate best-in-class therapeutic antibodies against challenging targets and unmet medical needs, in vivo phage display selections by which phage libraries are directly injected into animals or humans for isolating and identifying the phages bound to specific tissues offer an advantage over conventional in vitro phage display screening procedures. Thus, in the present review, we will first summarize a general overview of the antibody therapeutic market, the different types of antibody fragments, and novel engineered variants that have already been explored. Then, we will discuss the state-of-the-art of in vivo phage display methodologies as a promising emerging selection strategy for improvement antibody targeting and drug delivery properties.

Tripartite split-GFP assay to identify selective intracellular nanobody that suppresses GTPase RHOA subfamily downstream signaling

Strategies based on intracellular expression of artificial binding domains present several advantages over manipulating nucleic acid expression or the use of small molecule inhibitors. Intracellularly-functional nanobodies can be considered as promising macrodrugs to study key signaling pathways by interfering with protein-protein interactions. With the aim of studying the RAS-related small GTPase RHOA family, we previously isolated, from a synthetic phage display library, nanobodies selective towards the GTP-bound conformation of RHOA subfamily proteins that lack selectivity between the highly conserved RHOA-like and RAC subfamilies of GTPases. To identify RHOA/ROCK pathway inhibitory intracellular nanobodies, we implemented a stringent, subtractive phage display selection towards RHOA-GTP followed by a phenotypic screen based on F-actin fiber loss. Intracellular interaction and intracellular selectivity between RHOA and RAC1 proteins was demonstrated by adapting the sensitive intracellular protein-protein interaction reporter based on the tripartite split-GFP method. This strategy led us to identify a functional intracellular nanobody, hereafter named RH28, that does not cross-react with the close RAC subfamily and blocks/disrupts the RHOA/ROCK signaling pathway in several cell lines without further engineering or functionalization. We confirmed these results by showing, using SPR assays, the high specificity of the RH28 nanobody towards the GTP-bound conformation of RHOA subfamily GTPases. In the metastatic melanoma cell line WM266-4, RH28 expression triggered an elongated cellular phenotype associated with a loss of cellular contraction properties, demonstrating the efficient intracellular blocking of RHOA/B/C proteins downstream interactions without the need of manipulating endogenous gene expression. This work paves the way for future therapeutic strategies based on protein-protein interaction disruption with intracellular antibodies.

Research progress and applications of nanobody in human infectious diseases

Infectious diseases, caused by pathogenic microorganisms, are capable of affecting crises. In addition to persistent infectious diseases such as malaria and dengue fever, the vicious outbreaks of infectious diseases such as Neocon, Ebola and SARS-CoV-2 in recent years have prompted the search for more efficient and convenient means for better diagnosis and treatment. Antibodies have attracted a lot of attention due to their good structural characteristics and applications. Nanobodies are the smallest functional single-domain antibodies known to be able to bind stably to antigens, with the advantages of high stability, high hydrophilicity, and easy expression and modification. They can directly target antigen epitopes or be constructed as multivalent nanobodies or nanobody fusion proteins to exert therapeutic effects. This paper focuses on the construction methods and potential functions of nanobodies, outlines the progress of their research, and highlights their various applications in human infectious diseases.

A scFv phage targeting the C. albicans cell wall screened from a bacteriophage-based library of induced immune protection in mice

C. albicans is the most prevalent opportunistic fungal and can cause life-threatening systemic infections under certain circumstances. The inefficiency and resistance of traditional therapy make the development of novel techniques indispensable. The main components, proteins and glycoproteins, of the C. albicans cell wall are highly immunogenic and very different from those of the host, making it an ideal source of targets for antifungal drug development. This study aimed to screen and identify specific peptides that bind to the C. albicans cell wall using a phage-display peptide library, and to develop a peptide-based therapy targeted to C. albicans. After four rounds of screening, JC-1 ScFv was found to bind to the C. albicans cell wall specifically, inhibit C. albicans growth and viability in vitro, and protect mice from C. albicans infection in vivo. Further study showed that JC-1 could provoke an immune response in C. albicans-infected mice. These results indicated that JC-1 ScFv screened from a phage-display peptide library had the potential to be developed as a vector for targeting C. albicans.

Monoclonal antibodies (mAbs) and single chain variable fragment (scFv) antibodies targeting envelope protein VP28 of white spot syndrome virus provide protection against viral infection

White spot syndrome virus (WSSV) is extremely pathogenic and causes huge economic losses in the shrimp farming industry. Neutralizing antibodies against WSSV is expected to be an effective means of preventing infection with the virus. In the present study, eight monoclonal antibodies (mAbs) against VP28 were developed by immunizing BALB/c mice with WSSV-VP28 recombinant protein. Among them, three mAbs named 3B7, 2G3 and 5D2 were determined to be able to delay the mortality of WSSV-infected shrimp in vivo neutralization assay, suggesting their neutralizing ability against WSSV infection. Immunoblotting results showed that the three mAbs reacted specifically with native VP28 of WSSV, and could also recognize the virions in the gills of WSSV-infected shrimp by IFA. Furthermore, the single chain variable fragment (scFv) genes specific for WSSV-VP28 were cloned from the three hybridoma cells and expressed in Escherichia coli. After purification and refolding, three biologically active scFv recombinant proteins were all capable of recognizing the native VP28 of WSSV and delayed the mortality of WSSV-infected shrimp, indicating their neutralizing capacity against WSSV. Subsequently, the eukaryotic expression plasmids of three scFv genes were constructed and the transcriptional properties of expression vectors in shrimp were analyzed. Animal experiments also proved that the scFv eukaryotic expression plasmids were able to partially neutralize WSSV infection. Thus, the production of neutralizing mAb and recombinant scFv antibodies against WSSV has a promising therapeutic potential in prevention and treatment of white spot disease of shrimp.

Antibody-receptor bioengineering and its implications in designing bioelectronic devices

Antibodies play a crucial role in the defense mechanism countering pathogens or foreign antigens in eukaryotes. Its potential as an analytical and diagnostic tool has been exploited for over a century. It forms immunocomplexes with a specific antigen, which is the basis of immunoassays and aids in developing potent biosensors. Antibody-based sensors allow for the quick and accurate detection of various analytes. Though classical antibodies have prolonged been used as bioreceptors in biosensors fabrication due to their increased fragility, they have been engineered into more stable fragments with increased exposure of their antigen-binding sites in the recent era. In biosensing, the formats constructed by antibody engineering can enhance the signal since the resistance offered by a conventional antibody is much more than these fragments. Hence, signal amplification can be observed when antibody fragments are utilized as bioreceptors instead of full-length antibodies. We present the first systematic review on engineered antibodies as bioreceptors with the description of their engineering methods. The detection of various target analytes, including small molecules, macromolecules, and cells using antibody-based biosensors, has been discussed. A comparison of the classical polyclonal, monoclonal, and engineered antibodies as bioreceptors to construct highly accurate, sensitive, and specific sensors is also discussed.

Insights into intercellular receptor-ligand binding kinetics in cell communication

Cell-cell communication is crucial for cells to sense, respond and adapt to environmental cues and stimuli. The intercellular communication process, which involves multiple length scales, is mediated by the specific binding of membrane-anchored receptors and ligands. Gaining insight into two-dimensional receptor-ligand binding kinetics is of great significance for understanding numerous physiological and pathological processes, and stimulating new strategies in drug design and discovery. To this end, extensive studies have been performed to illuminate the underlying mechanisms that control intercellular receptor-ligand binding kinetics via experiment, theoretical analysis and numerical simulation. It has been well established that the cellular microenvironment where the receptor-ligand interaction occurs plays a vital role. In this review, we focus on the advances regarding the regulatory effects of three factors including 1) protein-membrane interaction, 2) biomechanical force, and 3) bioelectric microenvironment to summarize the relevant experimental observations, underlying mechanisms, as well as their biomedical significances and applications. Meanwhile, we introduce modeling methods together with experiment technologies developed for dealing with issues at different scales. We also outline future directions to advance the field and highlight that building up systematic understandings for the coupling effects of these regulatory factors can greatly help pharmaceutical development.

Camelid Single-Domain Antibodies: Promises and Challenges as Lifesaving Treatments

Since the discovery of camelid heavy-chain antibodies in 1993, there has been tremendous excitement for these antibody domains (VHHs/sdAbs/nanobodies) as research tools, diagnostics, and therapeutics. Commercially, several patents were granted to pioneering research groups in Belgium and the Netherlands between 1996–2001. Ablynx was established in 2001 with the aim of exploring the therapeutic applications and development of nanobody drugs. Extensive efforts over two decades at Ablynx led to the first approved nanobody drug, caplacizumab (Cablivi) by the EMA and FDA (2018–2019) for the treatment of rare blood clotting disorders in adults with acquired thrombotic thrombocytopenic purpura (TPP). The relatively long development time between camelid sdAb discovery and their entry into the market reflects the novelty of the approach, together with intellectual property restrictions and freedom-to-operate issues. The approval of the first sdAb drug, together with the expiration of key patents, may open a new horizon for the emergence of camelid sdAbs as mainstream biotherapeutics in the years to come. It remains to be seen if nanobody-based drugs will be cheaper than traditional antibodies. In this review, I provide critical perspectives on camelid sdAbs and present the promises and challenges to their widespread adoption as diagnostic and therapeutic agents.

Single-cell profiling of proteins and chromatin accessibility using PHAGE-ATAC

Multimodal measurements of single-cell profiles are proving increasingly useful for characterizing cell states and regulatory mechanisms. In the present study, we developed PHAGE-ATAC (Assay for Transposase-Accessible Chromatin), a massively parallel droplet-based method that uses phage displaying, engineered, camelid single-domain antibodies ('nanobodies') for simultaneous single-cell measurements of protein levels and chromatin accessibility profiles, and mitochondrial DNA-based clonal tracing. We use PHAGE-ATAC for multimodal analysis in primary human immune cells, sample multiplexing, intracellular protein analysis and the detection of SARS-CoV-2 spike protein in human cell populations. Finally, we construct a synthetic high-complexity phage library for selection of antigen-specific nanobodies that bind cells of particular molecular profiles, opening an avenue for protein detection, cell characterization and screening with single-cell genomics.

Biopharmaceutical Manufacturing: Historical Perspectives and Future Directions

This review describes key milestones related to the production of biopharmaceuticals-therapies manufactured using recombinant DNA technology. The market for biopharmaceuticals has grown significantly since the first biopharmaceutical approval in 1982, and the scientific maturity of the technologies used in their manufacturing processes has grown concomitantly. Early processes relied on established unit operations, with research focused on process scale-up and improved culture productivity. In the early 2000s, changes in regulatory frameworks and the introduction of Quality by Design emphasized the importance of developing manufacturing processes to deliver a desired product quality profile. As a result, companies adopted platform processes and focused on understanding the dynamic interplay between product quality and processing conditions. The consistent and reproducible manufacturing processes of today's biopharmaceutical industry have set high standards for product efficacy, quality, and safety, and as the industry continues to evolve in the coming decade, intensified processing capabilities for an expanded range of therapeutic modalities will likely become routine. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Antibody Purification Using Affinity Chromatography

Antibodies are an integral part of many biological assays and biotherapeutics. However, the sources from which antibodies are derived frequently contain other contaminants which may interfere with assays or cause adverse reactions if administered in vivo. Therefore, a means of isolating these antibodies from their source at high levels of purity is critical. Affinity chromatography is currently one of the most widely applied methods for the purification of antibodies. This method relies on specific and reversible, interactions between antibody structures, or recombinant tags fused to these structures, and ligands immobilized on solid support matrices, generally within a column. Herein, common chromatographic methods applied to antibody purification are described. These include the purification of IgG, and its recombinant forms, through protein A, protein G and immobilized metal affinity chromatography.

Improving antibody affinity through <i>in vitro</i> mutagenesis in complementarity determining regions

High-affinity antibodies are widely used in diagnostics and for the treatment of human diseases. However, most antibodies are isolated from semi-synthetic libraries by phage display and do not possess in vivo affinity maturation, which is triggered by antigen immunization. It is therefore necessary to engineer the affinity of these antibodies by way of in vitro assaying. In this study, we optimized the affinity of two human monoclonal antibodies which were isolated by phage display in a previous related study. For the 42A1 antibody, which targets the liver cancer antigen glypican-3, the variant T57H in the second complementarity-determining region of the heavy chain (CDR-H2) exhibited a 2.6-fold improvement in affinity, as well as enhanced cell-binding activity. For the I4A3 antibody to severe acute respiratory syndrome coronavirus 2, beneficial single mutations in CDR-H2 and CDR-H3 were randomly combined to select the best synergistic mutations. Among these, the mutation S53P-S98T improved binding affinity (about 3.7 fold) and the neutralizing activity (about 12 fold) compared to the parent antibody. Taken together, single mutations of key residues in antibody CDRs were enough to increase binding affinity with improved antibody functions. The mutagenic combination of key residues in different CDRs creates additive enhancements. Therefore, this study provides a safe and effective in vitro strategy for optimizing antibody affinity.

Generation and utility of a single-chain fragment variable monoclonal antibody platform against a baculovirus expressed recombinant receptor binding domain of SARS-CoV-2 spike protein

As the second wave of COVID-19 launched, various variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) have emerged with a dramatic global spread amongst millions of people causing unprecedented case fatalities and economic shut-downs. That initiated a necessity for developing specific diagnostics and therapeutics along with vaccines to control such a pandemic. This endeavor describes generation of murine derived recombinant single-chain fragment variable (scFv) as a monoclonal antibody (MAb) platform targeting the receptor binding domain (RBD) of Spike protein of SARS-CoV-2. A specific synthesized RBD coding sequence was cloned and expressed in Baculovirus expression system. The recombinant RBD (rRBD) was ascertained to be at the proper encoding size of ∼ 600bp and expressed protein of the molecular weight of ∼ 21KDa. Purified rRBD was proved genuinely antigenic and immunogenic, exhibiting specific reactivity to anti-SARS-CoV-2 antibody in an indirect enzyme-linked immunosorbent assay (ELISA), and inducing strong seroconversion in immunized mice. The scFv phage display library against rRBD was successfully constructed, revealing ∼ 90 % recombination frequency, and great enriching factor reaching 88 % and 25 % in polyclonal Ab-based and MAb-based ELISAs, respectively. Typically, three unique scFvs were generated, selected, purified and molecularly identified. That was manifested by their: accurate structure, close relation to the mouse immunoglobulin (Ig) superfamily, right anchored six complementarily-determining regions (CDRs) as three within variable heavy (vH) and variable light (vL) regions each, and proper configuration of the three-dimensional (3D) structure. Besides, their expression downstream in a non-suppressive amber codon of E. coli strain SS32 created a distinct protein band at an apparent molecular weight of ∼ 27KDa. Moreover, the purified scFvs showed authentic immunoreactivity and specificity to both rRBD and SARS-CoV-2 in western blot and ELISA. Accordingly, these developed scFvs platform might be a functional candidate for research, inexpensive diagnostics and therapeutics, mitigating spread of COVID-19.

Nanobodies - Little helpers unravelling intracellular signaling

The identification of diagnostic and therapeutic targets requires a comprehensive understanding of cellular processes, for which advanced technologies in biomedical research are needed. The emergence of nanobodies (Nbs) derived from antibody fragments of camelid heavy chain-only antibodies as intracellular research tools offers new possibilities to study and modulate target antigens in living cells. Here we summarize this rapidly changing field, beginning with a brief introduction of Nbs, followed by an overview of how target-specific Nbs can be generated, and introduce the selection of intrabodies as research tools. Intrabodies, by definition, are intracellular functional Nbs that target ectopic or endogenous intracellular antigens within living cells. Such binders can be applied in various formats, e.g. as chromobodies for live cell microscopy or as biosensors to decipher complex intracellular signaling pathways. In addition, protein knockouts can be achieved by target-specific Nbs, while modulating Nbs have the potential as future therapeutics. The development of fine-tunable and switchable Nb-based systems that simultaneously provide spatial and temporal control has recently taken the application of these binders to the next level.

Fully human recombinant antibodies against EphA2 from a multi-tumor patient immune library suitable for tumor-targeted therapy

Enhanced EphA2 expression is observed in a variety of epithelial-derived malignancies and is an important target for anti-tumor therapy. Currently, Therapeutic monoclonal antibodies against immune checkpoints have shown good efficacy for tumor treatment. In this study, we constructed an immune single-chain fragment variable (scFv) library using peripheral blood mononuclear cells (PBMCs) from 200 patients with a variety of malignant tumors. High affinity scFvs against EphA2 can be easily screened from the immune library using phage display technology. Anti-EphA2 scFvs can be modified into any form of recombinant antibody, including scFv-Fc and full-length IgG1 antibodies, and the recombinant antibody affinity was improved following modification. Among the modified anti-EphA2 antibodies the affinity of 77-IgG1 was significantly increased, reaching a pmol affinity level (10⁻¹²). We further demonstrated the binding activity of recombinant antibodies to the EphA2 protein, tumor cells, and tumor tissues using macromolecular interaction techniques, flow cytometry and immunohistochemistry. Most importantly, both the constructed scFvs-Fc, as well as the IgG1 antibodies against EphA2 were able to inhibit the growth of tumor cells to some extent. These results suggest that the immune libraries from patients with malignant tumors are more likely to screen for antibodies with high affinity and therapeutic effect. The constructed fully human scFv immune library has broad application prospects for specific antibody screening. The screened scFv-Fc and IgG1 antibodies against EphA2 can be used for the further study of tumor immunotherapy.

Methods and cell-based strategies to produce antibody libraries: current state

Antibodies are critical components of the adaptive immune system, whose therapeutic applications have been growing exponentially in the last years. Discovery and development of therapeutic antibodies encompasses in vivo immunization, synthetic libraries, and surface display methodologies. To overcome some of their limitations, several platforms in higher eukaryotic cells have been developed. Moreover, these platforms aim to replicate in the bench both primary and secondary antibody diversification mechanisms that occur in vivo. Here, we describe the latest strategies that have been used to mirror both naïve and affinity-maturated antibody repertoire. KEY POINTS: • Therapeutic antibodies are one of the most promising classes of drugs to fight diseases. • Antibodies discovered through hybridoma or display technologies require further engineering. • Innovative antibody discovery platforms in higher eukaryotic cells have been developed.

A new antigen detection ELISA for the diagnosis of Strongyloides infection

Serodiagnosis is an essential component of the laboratory diagnosis of Strongyloides infection and is usually performed using an indirect IgG antibody test. A direct antigen detection method can complement the IgG assay, particularly for detecting early infection and post-treatment follow-up. In the present study, a recombinant scFv monoclonal antibody against NIE recombinant protein (rMAb23) that we had previously produced was used to develop a Strongyloides antigen detection ELISA (SsAg-ELISA). The assay is based on detecting immune complexes of circulating NIE antigens bound to Strongyloides-specific IgG antibodies. The optimized ELISA parameters were 10 µg/mL of rMAb23 coated on microtitre plate wells, 2% skim milk as blocking reagent, 1:100 serum dilution, and 1:1000 goat anti-human IgG F(ab')2 conjugated to horseradish peroxidase. Four groups of serum samples were used, i.e., Strongyloides-positive serum samples categorized into Groups IA and IB; the former were from probable chronic infections and the latter from probable early/acute infections. Strongyloides-negative samples comprising Groups II (healthy samples) and III (other infections); the latter were from eleven different types of other parasitic infections. The receiver operating characteristic (ROC) curve showed an area under the curve (AUC) of 1.00, cut-off optical density (OD₄₀₅) of 0.5002, and 100% diagnostic sensitivity and specificity. The results of the commercial IgG-ELISA and SsAg-ELISA from Group IA were found to be moderately correlated (r = 0.416; p < 0.05). Notably, ANOVA showed that the average ODs₄₀₅ of Group 1B were significantly higher (p < 0.05) than Group 1A, indicating that the assay may be useful to differentiate early and chronic infection. In conclusion, the developed SsAg-ELISA showed good diagnostic potential, and it merits further evaluation.

Potential of Phage Display Antibody Technology for Cardiovascular Disease Immunotherapy

Cardiovascular disease (CVD) is one of the leading causes of death worldwide. CVD includes coronary artery diseases such as angina, myocardial infarction, and stroke. "Lipid hypothesis" which is also known as the cholesterol hypothesis proposes the linkage of plasma cholesterol level with the risk of developing CVD. Conventional management involves the use of statins to reduce the serum cholesterol levels as means for CVD prevention or treatment. The regulation of serum cholesterol levels can potentially be regulated with biological interventions like monoclonal antibodies. Phage display is a powerful tool for the development of therapeutic antibodies with successes over the recent decade. Although mainly for oncology, the application of monoclonal antibodies as immunotherapeutic agents could potentially be expanded to CVD. This review focuses on the concept of phage display for antibody development and discusses the potential target antigens that could potentially be beneficial for serum cholesterol management.