Identification and verification of hybridoma-derived monoclonal antibody variable region sequences using recombinant DNA technology and mass spectrometry

Characterization of Two Highly Specific Monoclonal Antibodies Targeting the Glycan Loop of the Zika Virus Envelope Protein

Zika virus (ZIKV) is an emerging flavivirus associated with several neurological diseases such as Guillain-Barré syndrome in adults and microcephaly in newborn children. Its distribution and mode of transmission (via Aedes aegypti and Aedes albopictus mosquitoes) collectively cause ZIKV to be a serious concern for global health. High genetic homology of flaviviruses and shared ecology is a hurdle for accurate detection. Distinguishing infections caused by different viruses based on serological recognition can be misleading as many anti-flavivirus monoclonal antibodies (mAbs) discovered to date are highly cross-reactive, especially those against the envelope (E) protein. To provide more specific research tools, we produced ZIKV E directed hybridoma cell lines and characterized two highly ZIKV-specific mAb clones (mAbs A11 and A42) against several members of the Flavivirus genus. Epitope mapping of mAb A11 revealed glycan loop specificity in Domain I of the ZIKV E protein. The development of two highly specific mAbs targeting the surface fusion protein of ZIKV presents a significant advancement in research capabilities as these can be employed as essential tools to enhance our understanding of ZIKV identification on infected cells ex vivo or in culture.

Analytical Techniques for the Characterization and Quantification of Monoclonal Antibodies

Monoclonal antibodies (mAbs) are a fast-growing class of biopharmaceuticals. They are widely used in the identification and detection of cell makers, serum analytes, and pathogenic agents, and are remarkably used for the cure of autoimmune diseases, infectious diseases, or malignancies. The successful application of therapeutic mAbs is based on their ability to precisely interact with their appropriate target sites. The precision of mAbs rely on the isolation techniques delivering pure, consistent, stable, and safe lots that can be used for analytical, diagnostic, or therapeutic applications. During the creation of a biologic, the key quality features of a particular mAb, such as structure, post-translational modifications, and activities at the biomolecular and cellular levels, must be characterized and profiled in great detail. This implies the requirement of powerful state of the art analytical techniques for quality control and characterization of mAbs. Until now, various analytical techniques have been developed to characterize and quantify the mAbs according to the regulatory guidelines. The present review summarizes the major techniques used for the analyses of mAbs which include chromatographic, electrophoretic, spectroscopic, and electrochemical methods in addition to the modifications in these methods for improving the quality of mAbs. This compilation of major analytical techniques will help students and researchers to have an overview of the methodologies employed by the biopharmaceutical industry for structural characterization of mAbs for eventual release of therapeutics in the drug market.

Afucosylation of HLA-specific IgG1 as a potential predictor of antibody pathogenicity in kidney transplantation

Antibody-mediated rejection (AMR) is the leading cause of graft failure. While donor-specific antibodies (DSAs) are associated with a higher risk of AMR, not all patients with DSAs develop rejection, suggesting that the characteristics of alloantibodies determining their pathogenicity remain undefined. Using human leukocyte antigen (HLA)-A2-specific antibodies as a model, we apply systems serology tools to investigate qualitative features of immunoglobulin G (IgG) alloantibodies including Fc-glycosylation patterns and FcγR-binding properties. Levels of afucosylated anti-A2 antibodies are elevated in seropositive patients, especially those with AMR, suggesting potential cytotoxicity via FcγRIII-mediated mechanisms. Afucosylation of both glycoengineered monoclonal and naturally glycovariant polyclonal serum IgG specific to HLA-A2 drives potentiated binding to, slower dissociation from, and enhanced signaling through FcγRIII, a receptor widely expressed on innate effector cells, and greater cytotoxicity against HLA-A2+ cells mediated by natural killer (NK) cells. Collectively, these results suggest that afucosylated DSA may be a biomarker of AMR and contribute to pathogenesis.

A Sensitive Immunodetection Assay Using Antibodies Specific to Staphylococcal Enterotoxin B Produced by Baculovirus Expression

Staphylococcal enterotoxin B (SEB) is a potent bacterial toxin that causes inflammatory stimulation and toxic shock, thus it is necessary to detect SEB in food and environmental samples. Here, we developed a sensitive immunodetection system using monoclonal antibodies (mAbs). Our study is the first to employ a baculovirus expression vector system (BEVS) to produce recombinant wild-type SEB. BEVS facilitated high-quantity and pure SEB production from suspension-cultured insect cells, and the SEB produced was characterized by mass spectrometry analysis. The SEB was stable at 4 °C for at least 2 years, maintaining its purity, and was further utilized for mouse immunization to generate mAbs. An optimal pair of mAbs non-competitive to SEB was selected for sandwich enzyme-linked immunosorbent assay-based immunodetection. The limit of detection of the immunodetection method was 0.38 ng/mL. Moreover, it displayed higher sensitivity in detecting SEB than commercially available immunodetection kits and retained detectability in various matrices and S. aureus culture supernatants. Thus, the results indicate that BEVS is useful for producing pure recombinant SEB with its natural immunogenic property in high yield, and that the developed immunodetection assay is reliable and sensitive for routine identification of SEB in various samples, including foods.

Transient production of receptor-binding domain of SARS-CoV-2 in Nicotiana benthamiana plants induces specific antibodies in immunized mice

BACKGROUND

The COVID-19 pandemic caused by the SARS-CoV-2 coronavirus has currently affected millions of people around the world. To combat the rapid spread of COVID-19 there is an urgent need to implement technological platforms for the production of vaccines, drugs and diagnostic systems by the scientific community and pharmaceutical companies. The SARS-CoV-2 virus enters the cells by the interaction between the receptor-binding domain (RBD) present in the viral surface spike protein and its human receptor ACE2. The RBD protein is therefore considered as the target for potential subunit-based vaccines.

METHODS AND RESULTS

We evaluate the use of Nicotiana benthamiana plants as the host to transiently-producing recombinant RBD (RBDr) protein. The identity of the plant-produced RBDr was confirmed by immune assays and mass spectrometry. Immunogenicity was confirmed through the specific antibodies generated in all of the immunized mice compared to the PBS treated group.

CONCLUSIONS

In conclusions, the immunogenicity of the RBDr produced in N. benthamiana was confirmed. These findings support the use of plants as an antigen expression system for the rapid development of vaccine candidates.

Generation and characterisation of a semi-synthetic siderophore-immunogen conjugate and a derivative recombinant triacetylfusarinine C-specific monoclonal antibody with fungal diagnostic application

Invasive pulmonary aspergillosis (IPA) is a severe life-threatening condition. Diagnosis of fungal disease in general, and especially that caused by Aspergillus fumigatus is problematic. A. fumigatus secretes siderophores to acquire iron during infection, which are also essential for virulence. We describe the chemoacetylation of ferrated fusarinine C to diacetylated fusarinine C (DAFC), followed by protein conjugation, which facilitated triacetylfusarinine C (TAFC)-specific monoclonal antibody production with specific recognition of the ferrated form of TAFC. A single monoclonal antibody sequence was ultimately elucidated by a combinatorial strategy involving protein LC-MS/MS, cDNA sequencing and RNAseq. The resultant murine IgG2_a monoclonal antibody was secreted in, and purified from, mammalian cell culture (5 mg) and demonstrated to be highly specific for TAFC detection by competitive ELISA (detection limit: 15 nM) and in a lateral flow test system (detection limit: 3 ng), using gold nanoparticle conjugated- DAFC-bovine serum albumin for competition. Overall, this work reveals for the first time a recombinant TAFC-specific monoclonal antibody with diagnostic potential for IPA diagnosis in traditional and emerging patient groups (e.g., COVID-19) and presents a useful strategy for murine Ig sequence determination, and expression in HEK293 cells, to overcome unexpected limitations associated with aberrant or deficient murine monoclonal antibody production.

Generation of recombinant antibodies by mammalian expression system for detecting S-metolachlor in environmental waters

Current immunoassays for herbicide detection are usually based on polyclonal or monoclonal antibodies (MAbs) raised in animals. The mammalian expression system allows the procurement of specific and highly sensitive antibodies, avoiding animal immunization. In this study, S-metolachlor-specific IgG vectors bearing either Thosea asigna virus 2A or internal ribosome entry site (S-T2A or S-IRES) and single-chain variable fragment (scFv) vectors were designed and expressed. The recombinant antibodies (RAbs) were characterized by indirect competitive enzyme-linked immunosorbent assays (icELISA). The results showed that full-length RAbs exhibited significantly better performance than scFv, and both bicistronic vectors expressed antibodies of correct size, while RAb S-T2A elicited a higher yield than RAb S-IRES. Further analyses showed that RAb S-T2A and RAb S-IRES exhibited comparable reactivities and specificities to the parental MAb, with IC₅₀ values of 3.44, 3.89 and 3.37 ng/mL, respectively. Finally, MAb- and RAb-based icELISAs were established for the determination of S-metolachlor in environmental waters. The recoveries were in the range of 73.0-128.1%, and the coefficients of variation were mostly below 10%. This article describes the production of RAbs for S-metolachlor from mammalian cells for the first time and paves the way to develop RAb-based immunoassays for monitoring herbicide residues in the environment.

Determination of variable region sequences from hybridoma immunoglobulins that target Mycobacterium tuberculosis virulence factors

Mycobacterium tuberculosis (Mtb) infects one-quarter of the world's population. Mtb and HIV coinfections enhance the comorbidity of tuberculosis (TB) and AIDS, accounting for one-third of all AIDS-associated mortalities. Humoral antibody to Mtb correlates with TB susceptibility, and engineering of Mtb antibodies may lead to new diagnostics and therapeutics. The characterization and validation of functional immunoglobulin (Ig) variable chain (IgV) sequences provide a necessary first step towards developing therapeutic antibodies against pathogens. The virulence-associated Mtb antigens SodA (Superoxide Dismutase), KatG (Catalase), PhoS1/PstS1 (regulatory factor), and GroES (heat shock protein) are potential therapeutic targets but lacked IgV sequence characterization. Putative IgV sequences were identified from the mRNA of hybridomas targeting these antigens and isotype-switched into a common immunoglobulin fragment crystallizable region (Fc region) backbone, subclass IgG2aκ. Antibodies were validated by demonstrating recombinant Ig assembly and secretion, followed by the determination of antigen-binding specificity using ELISA and immunoblot assay.

Characterization of Variable Region Genes and Discovery of Key Recognition Sites in the Complementarity Determining Regions of the Anti-Thiacloprid Monoclonal Antibody

Sequence-defined recombinant antibodies (rAbs) have emerged as alternatives to hybridoma-secreted monoclonal antibodies (mAbs) for performing immunoassays. However, the polyploidy nature of hybridomas often leads to the coexistence of aberrant or non-specific functional variable region (VR) gene transcripts, which complicates the identification of correct VR sequences. Herein, we introduced the use of LC-MS/MS combined with next-generation sequencing to characterize VR sequences in an anti-thiacloprid mAb, which was produced by a hybridoma with genetic antibody diversity. The certainty of VR sequences was verified by the functional analysis based on the recombinant antibody (rAb) expressed by HEK293 mammalian cells. The performance of the rAb was similar to that of the parental mAb, with IC50 values of 0.73 and 0.46 μg/L as measured by ELISAs. Moreover, molecular docking analysis revealed that Ser52 (H-CDR2), Trp98, and Trp93 (L-CDR3) residues in the complementarity determining regions (CDRs) of the identified VR sequences predominantly contributed to thiacloprid-specific recognition through hydrogen bonds and the CH-π interaction. Through single-site-directed alanine mutagenesis, we found that Trp98 and Trp93 (L-CDR3) showed high affinity to thiacloprid, while Ser52 (H-CDR2) had an auxiliary effect on the specific binding. This study presents an efficient and reliable way to determine the key recognition sites of hapten-specific mAbs, facilitating the improvement of antibody properties.

Single particle cryo-EM of the complex between interphotoreceptor retinoid-binding protein and a monoclonal antibody

Interphotoreceptor retinoid‐binding protein (IRBP) is a highly expressed protein secreted by rod and cone photoreceptors that has major roles in photoreceptor homeostasis as well as retinoid and polyunsaturated fatty acid transport between the neural retina and retinal pigment epithelium. Despite two crystal structures reported on fragments of IRBP and decades of research, the overall structure of IRBP and function within the visual cycle remain unsolved. Here, we studied the structure of native bovine IRBP in complex with a monoclonal antibody (mAb5) by cryo‐electron microscopy, revealing the tertiary and quaternary structure at sufficient resolution to clearly identify the complex components. Complementary mass spectrometry experiments revealed the structure and locations of N‐linked carbohydrate post‐translational modifications. This work provides insight into the structure of IRBP, displaying an elongated, flexible three‐dimensional architecture not seen among other retinoid‐binding proteins. This work is the first step in elucidation of the function of this enigmatic protein.

A simplified workflow for monoclonal antibody sequencing

The diversity of antibody variable regions makes cDNA sequencing challenging, and conventional monoclonal antibody cDNA amplification requires the use of degenerate primers. Here, we describe a simplified workflow for amplification of IgG antibody variable regions from hybridoma RNA by a specialized RT-PCR followed by Sanger sequencing. We perform three separate reactions for each hybridoma: one each for kappa, lambda, and heavy chain transcripts. We prime reverse transcription with a primer specific to the respective constant region and use a template-switch oligonucleotide, which creates a custom sequence at the 5’ end of the antibody cDNA. This template-switching circumvents the issue of low sequence homology and the need for degenerate primers. Instead, subsequent PCR amplification of the antibody cDNA molecules requires only two primers: one primer specific for the template-switch oligonucleotide sequence and a nested primer to the respective constant region. We successfully sequenced the variable regions of five mouse monoclonal IgG antibodies using this method, which enabled us to design chimeric mouse/human antibody expression plasmids for recombinant antibody production in mammalian cell culture expression systems. All five recombinant antibodies bind their respective antigens with high affinity, confirming that the amino acid sequences determined by our method are correct and demonstrating the high success rate of our method. Furthermore, we also designed RT-PCR primers and amplified the variable regions from RNA of cells transfected with chimeric mouse/human antibody expression plasmids, showing that our approach is also applicable to IgG antibodies of human origin. Our monoclonal antibody sequencing method is highly accurate, user-friendly, and very cost-effective.

The path to VICTORy - a beginner's guide to success using commercial research antibodies

Commercial research antibodies are crucial tools in modern cell biology and biochemistry. In the USA some $2 billion a year are spent on them, but many are apparently not fit-for-purpose, and this may contribute to the 'reproducibility crisis' in biological sciences. Inadequate antibody validation and characterization, lack of user awareness, and occasional incompetence amongst suppliers have had immense scientific and personal costs. In this Opinion, I suggest some paths to make the use of these vital tools more successful. I have attempted to summarize and extend expert views from the literature to suggest that sustained routine efforts should made in: (1) the validation of antibodies, (2) their identification, (3) communication and controls, (4) the training of potential users, (5) the transparency of original equipment manufacturer (OEM) marketing agreements, and (5) in a more widespread use of recombinant antibodies (together denoted the 'VICTOR' approach).