Rational monoclonal antibody development to emerging pathogens, biothreat agents and agents of foreign animal disease: The antigen scale

In-line buffer exchange in the coupling of Protein A chromatography with weak cation exchange chromatography for the determination of charge variants of immunoglobulin G derived from chinese hamster ovary cell cultures

Immunoglobulin G (IgG) is the most common monoclonal antibody (mAb) grown for therapeutic applications. While IgG is often selectively isolated from cell lines using protein A (ProA) chromatography, this is only a stepping stone for complete characterization. Further classification can be obtained from weak cation exchange chromatography (WCX) to determine IgG charge variant distributions. The charge variants of monoclonal antibodies can influence the stability and efficacy in vivo, and deviations in charge heterogeneity are often cell-specific and sensitive to upstream process variability. Current methods to characterize IgG charge variants are often performed off-line, meaning that the IgG eluate from the ProA separation is collected, diluted to adjust the pH, and then transferred to the WCX separation, adding time, complexity, and potential contamination to the sample analysis process. More recently, reports have appeared to streamline this separation using in-line two-dimensional liquid chromatography (2D-LC). Presented here is a novel, 2D-LC coupling of ProA in the first dimension (1D) and WCX in the second dimension (2D) chromatography. As anticipated, the initial direct column coupling proved to be challenging due to the pH incompatibility between the mobile phases for the two stages. To solve the solvent compatibility issue, a size exclusion column was placed in the switching valve loop of the 2D-LC instrument to act as a means for the on-line solvent exchange. The efficacy of the methodology presented was confirmed through a charge variant determination using the NIST monoclonal antibody standard (NIST mAb), yielding correct acidic, main, and basic variant compositions. The methodology was employed to determine the charge variant profile of IgG from an in-house cultured Chinese hamster ovary (CHO) cell supernatant. It is believed that this methodology can be easily implemented to provide higher-throughput assessment of IgG charge variants for process monitoring and cell line development.

Introduction to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) are innovative biopharmaceutical products in which a monoclonal antibody is linked to a small molecule drug with a stable linker. Most of the ADCs developed so far are for treating cancer, but there is enormous potential for using ADCs to treat other diseases. Currently, ten ADCs have been approved by the United States Food and Drug Administration (FDA), and more than 90 ADCs are under worldwide clinical development. Monoclonal antibodies have evolved from research tools to powerful therapeutics in the past 30 years. Tremendous strides have been made in antibody discovery, protein bioengineering, formulation, and delivery devices. This manuscript provides an overview of the biology, chemistry, and biophysical properties of each component of ADC design. This review summarizes the advances and challenges in the field to date, with an emphasis on antibody conjugation, linker-payload chemistry, novel payload classes, drug-antibody ratio (DAR), and product development. The review emphasizes the lessons learned in the development of oncology antibody conjugates and look towards future innovations enabling other therapeutic indications. The review discusses resistance mechanisms to ADCs, and give an opinion on future perspectives.

Approaches and advances in the development of potential therapeutic targets and antiviral agents for the management of SARS-CoV-2 infection

Virus onslaughts continue to spread fear and cause rampage across the world every now and then. The twenty first century is yet again witnessing a gross global pandemic, Coronavirus Disease 2019 (COVID-19) caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Globally no vaccines or drug specific to COVID-19 is available. Corona viruses have been in mutual relationship with humans and other hosts over many decades though aggressive zoonotic strains have caused havoc. Zoonotic emergent corona viruses prior to SARS-COV-2 included severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), with the former leading to aggressive infectious spread and the later with high mortality rate. Although they emerged in the early period of the twenty first century, resilient biomedical and expertise in pharmaceutical domain could not appropriate any proprietary therapeutics. Studies envisaged towards curtailing their spread employed different stages of the virus life cycle with all zoonotic coronaviruses (CoVs) sharing genomic and structural similarities. Hence the strategies against SARS-CoV and MERS-CoV could prove effective against the recent outbreak of SAR-CoV-2. The review unravels key events involved in the lifecycle of SARS-CoV-2 while highlighting the possible avenues of therapy. The review also holds the scope in better understanding a broad-spectrum antivirals, monoclonal antibodies and small molecule inhibitors against viral glycoproteins, host cell receptor, viral mRNA synthesis, RNA-dependent RNA polymerase (RdRp) and viral proteases in order to design and develop antiviral drugs for SARS-CoV-2.

Drugs against SARS-CoV-2: What do we know about their mode of action?

The health emergency caused by the recent Covid-19 pandemic highlights the need to identify effective treatments against the virus causing this disease (SARS-CoV-2). The first clinical trials have been testing repurposed drugs that show promising anti-SARS-CoV-2 effects in cultured cells. Although more than 2400 clinical trials are already under way, the actual number of tested compounds is still limited to approximately 20, alone or in combination. In addition, knowledge on their mode of action (MoA) is currently insufficient. Their first results reveal some inconsistencies and contradictory results and suggest that cohort size and quality of the control arm are two key issues for obtaining rigorous and conclusive results. Moreover, the observed discrepancies might also result from differences in the clinical inclusion criteria, including the possibility of early treatment that may be essential for therapy efficacy in patients with Covid-19. Importantly, efforts should also be made to test new compounds with a documented MoA against SARS-CoV-2 in clinical trials. Successful treatment will probably be based on multitherapies with antiviral compounds that target different steps of the virus life cycle. Moreover, a multidisciplinary approach that combines artificial intelligence, compound docking, and robust in vitro and in vivo assays will accelerate the development of new antiviral molecules. Finally, large retrospective studies on hospitalized patients are needed to evaluate the different treatments with robust statistical tools and to identify the best treatment for each Covid-19 stage. This review describes different candidate antiviral strategies for Covid-19, by focusing on their mechanism of action.

Use of a Branched Linker for Enhanced Biosensing Properties in IgG Detection from Mixed Chinese Hamster Ovary Cell Cultures

Tris(2-aminoethyl)-amine (TREN), a branched amine, was coupled to planar surfaces of alkanethiol self-assembled monolayers (SAMs) to increase the grafting density of IgG-binding peptide (HWRGWV or HWRGWVG) on gold surfaces. One of the three primary amine pendant groups of TREN anchors onto the SAM, while the other two are available for grafting with the C-termini of the peptide. The ellipsometric peptide density on the SAM-branched amine was 1.24 molecules nm^-2. The surfaces carrying the peptides were investigated via surface plasmon resonance (SPR) to quantify the adsorption of IgG and showed maximum binding capacity, Q_m of 4.45 mg m^-2, and dissociation constant, K_d of 8.7 × 10^-7 M. Real-time dynamic adsorption data was used to determine adsorption rate constants, k_a values, and the values were dependent on IgG concentration. IgG binding from complex mixtures of Chinese hamster ovary supernatant (CHO) was investigated and regeneration studies were carried out. Compared to the unbranched amine-based surfaces, the branched amines increased the overall sensitivity and selectivity for IgG adsorption from complex mixtures. Regeneration of the branched amine-based surfaces was achieved with 0.1 M NaOH, with less than 10% decline in peptide activity after 12 cycles of regeneration-binding.

Peptide specific monoclonal antibodies of Leptospiral LigA for acute diagnosis of leptospirosis

Leptospirosis is underdiagnosed due to low sensitivity, need of specialised equipment, and expensive reagents for serological and molecular diagnosis respectively. Considering the sensitivity, rapidity, inexpensive reagents and collection of clinical samples, the monoclonal antibody based antigen detection method from urine samples has been developed and evaluated. LigA (LK90) based B-cell specific epitopes were predicted and synthesised as peptides for the production of monoclonal antibody. LK90₅₄₃: SNAQKNQGNA (amino acids: 543 to 552), and LK90₁₁₁₀: DHHTQSSYTP (amino acids: 1110 to 1119) with VaxiJen score of 1.3719 and 1.2215, respectively were used. Thirty two and 28 urine samples from confirmed and seronegative healthy human subjects, respectively were included for the evaluation of MAb-based dot blot ELISA. The specificity of the evaluated MAbs, P1B1 and P4W2 were found to be in the range of ~93–96%. Moreover, the MAbs did not show cross-reactivity with other bacterial antigens as confirmed by IgG ELISA, further validating its specificity for leptospiral antigens. These findings suggest that the developed MAb based dot blot ELISA is a simple, rapid performed in less than 8 h, inexpensive with a ICER of $8.7/QALY, and affordable in developing countries and area where laboratory facilities are limited.

Hybridoma technology for the generation of rodent mAbs via classical fusion

Monoclonal antibodies (mAbs) have proven to be instrumental in the advancement of research, diagnostic, industrial vaccine, and therapeutic applications. The use of mAbs in laboratory protocols has been growing in an exponential fashion for the last four decades. Described herein are methods for the development of highly specific mAbs through traditional hybridoma fusion. For ultimate success, a series of simultaneously initiated protocols are to be undertaken with careful attention to cell health of both the myeloma fusion partner and immune splenocytes. Coordination and attention to detail will enable a researcher with basic tissue culture skills to generate mAbs from immunized rodents to a variety of antigens (including proteins, carbohydrates, DNA, and haptens) (see Note 1). Furthermore, in vivo and in vitro methods used for antigen sensitization of splenocytes prior to somatic fusion are described herein.

Epitope characterization of sero-specific monoclonal antibody to Clostridium botulinum neurotoxin type A

Botulinum neurotoxins (BoNTs) are extremely potent toxins that can contaminate foods and are a public health concern. Anti-BoNT antibodies have been described that are capable of detecting BoNTs; however there still exists a need for accurate and sensitive detection capabilities for BoNTs. Herein, we describe the characterization of a panel of eight monoclonal antibodies (MAbs) generated to the non-toxic receptor-binding domain of BoNT/A (H(C)50/A) developed using a high-throughput screening approach. In two independent hybridoma fusions, two groups of four IgG MAbs were developed against recombinant H(C)50/A. Of these eight, only a single MAb, F90G5-3, bound to the whole BoNT/A protein and was characterized further. The F90G5-3 MAb slightly prolonged time to death in an in vivo mouse bioassay and was mapped by pepscan to a peptide epitope in the N-terminal subdomain of H(C)50/A (H(CN)25/A) comprising amino acid residues (985)WTLQDTQEIKQRVVF(999), an epitope that is highly immunoreactive in humans. Furthermore, we demonstrate that F90G5-3 binds BoNT/A with nanomolar efficiency. Together, our results indicate that F90G5-3 is of potential value as a diagnostic immunoreagent for BoNT/A capture assay development and bio-forensic analysis.

Llama-derived single domain antibodies specific for Abrus agglutinin

Llama derived single domain antibodies (sdAb), the recombinantly expressed variable heavy domains from the unique heavy-chain only antibodies of camelids, were isolated from a library derived from llamas immunized with a commercial abrin toxoid preparation. Abrin is a potent toxin similar to ricin in structure, sequence and mechanism of action. The selected sdAb were evaluated for their ability to bind to commercial abrin as well as abrax (a recombinant abrin A-chain), purified abrin fractions, Abrus agglutinin (a protein related to abrin but with lower toxicity), ricin, and unrelated proteins. Isolated sdAb were also evaluated for their ability to refold after heat denaturation and ability to be used in sandwich assays as both capture and reporter elements. The best binders were specific for the Abrus agglutinin, showing minimal binding to purified abrin fractions or unrelated proteins. These binders had sub nM affinities and regained most of their secondary structure after heating to 95 °C. They functioned well in sandwich assays. Through gel analysis and the behavior of anti-abrin monoclonal antibodies, we determined that the commercial toxoid preparation used for the original immunizations contained a high percentage of Abrus agglutinin, explaining the selection of Abrus agglutinin binders. Used in conjunction with anti-abrin monoclonal and polyclonal antibodies, these reagents can fill a role to discriminate between the highly toxic abrin and the related, but much less toxic, Abrus agglutinin and distinguish between different crude preparations.

Neutralizing human monoclonal antibodies to severe acute respiratory syndrome coronavirus: target, mechanism of action, and therapeutic potential

The emergence of Severe Acute Respiratory Syndrome Coronavirus (SARS‐CoV) led to a rapid response not only to contain the outbreak but also to identify possible therapeutic interventions, including the generation of human monoclonal antibodies (hmAbs). hmAbs may be used therapeutically without the drawbacks of chimeric or animal Abs. Several different methods have been used to generate SARS‐CoV specific neutralizing hmAbs including the immunization of transgenic mice, cloning of small chain variable regions from naïve and convalescent patients, and the immortalization of convalescent B cells. Irrespective of the techniques used, the majority of hmAbs specifically reacted with the receptor binding domain (RBD) of the spike (S) protein and likely prevented receptor binding. However, several hmAbs that can bind to epitopes either within the RBD, located N terminal of the RBD or in the S2 domain, and neutralize the virus with or without inhibiting receptor binding have been identified. Therapeutic utility of hmAbs has been further elucidated through the identification of potential combinations of hmAbs that could neutralize viral variants including escape mutants selected using hmAbs. These results suggest that a cocktail of hmAbs that can bind to unique epitopes and have different mechanisms of action might be of clinical utility against SARS‐CoV infection, and indicate that a similar approach may be applied to treat other viral infections. Copyright © 2011 John Wiley & Sons, Ltd.

Monoclonal antibodies against the leptospiral immunoglobulin-like proteins A and B conserved regions

Leptospirosis is an infectious disease caused by pathogenic spirochetes of the genus Leptospira that affects humans and a wide variety of animals. Recently the genomes of Leptospira interrogans, Leptospira borgpetersenii and Leptospira biflexa species were sequenced allowing the identification of new virulence factors involved in survival and pathogenesis of bacteria. LigA and LigB are surface-exposed bacterial adhesins whose expression is correlated with the virulence of Leptospira strains. In this study, we produced and characterized five monoclonal antibodies (MAbs) against a recombinant fragment of LigB (rLigBrep) with approximately 54kDa that comprise the portions of LigA and LigB (domains 2-7). The 5 MAbs obtained were of the IgG1 (2) and IgG2b (3) isotypes and their affinity constants for rLigBrep ranged from 7×10(7) M(-1) to 4×10(8) M(-1). The MAbs were able to react with the native antigen on the L. interrogans, L. borgpetersenii and Leptospira noguchii surfaces by indirect immunofluorescence, immunoblotting and immunoelectron microscopy. These results demonstrate that the MAbs anti-rLigBrep can be useful to complement genetic studies and to aid studies aiming understanding the role of Lig proteins in Leptospira pathogenesis and the development of Lig-based vaccines and improved diagnostic tests for leptospirosis.

Antibodies in infectious diseases: polyclonals, monoclonals and niche biotechnology

Antibody preparations have a long history of providing protection from infectious diseases. Although antibodies remain the only natural host-derived defense mechanism capable of completely preventing infection, as products, they compete against inexpensive therapeutics such as antibiotics, small molecule inhibitors and active vaccines. The continued discovery in the monoclonal antibody (mAb) field of leads with broadened cross neutralization of viruses and demonstrable synergy of antibody with antibiotics for bacterial diseases, clearly show that innovation remains. The commercial success of mAbs in chronic disease has not been paralleled in infectious diseases for several reasons. Infectious disease immunotherapeutics are limited in scope as endemic diseases necessitate active vaccine development. Also, the complexity of these small markets draws the interest of niche companies rather than big pharmaceutical corporations. Lastly, the cost of goods for mAb therapeutics is inherently high for infectious agents due to the need for antibody cocktails, which better mimic polyclonal immunoglobulin preparations and prevent antigenic escape. In cases where vaccine or convalescent populations are available, current polyclonal hyperimmune immunoglobulin preparations (pIgG), with modern and highly efficient purification technology and standardized assays for potency, can make economic sense. Recent innovations to broaden the potency of mAb therapies, while reducing cost of production, are discussed herein. On the basis of centuries of effective use of Ab treatments, and with growing immunocompromised populations, the question is not whether antibodies have a bright future for infectious agents, but rather what formats are cost effective and generate safe and efficacious treatments to satisfy regulatory approval.

Anthrax spore detection by a luminex assay based on monoclonal antibodies that recognize anthrose-containing oligosaccharides

The similarity of endospore surface antigens between bacteria of the Bacillus cereus group complicates the development of selective antibody-based anthrax detection systems. The surface of B. anthracis endospores exposes a tetrasaccharide containing the monosaccharide anthrose. Anti-tetrasaccharide monoclonal antibodies (MAbs) and anti-anthrose-rhamnose disaccharide MAbs were produced and tested for their fine specificities in a direct spore enzyme-linked immunosorbent assay (ELISA) with inactivated spores of a broad spectrum of B. anthracis strains and related species of the Bacillus genus. Although the two sets of MAbs had different fine specificities, all of them recognized the tested B. anthracis strains and showed only a limited cross-reactivity with two B. cereus strains. The MAbs were further tested for their ability to be implemented in a highly sensitive and specific bead-based Luminex assay. This assay detected spores from different B. anthracis strains and two cross-reactive B. cereus strains, correlating with the results obtained in direct spore ELISA. The Luminex assay (detection limit 10(3) to 10(4) spores per ml) was much more sensitive than the corresponding sandwich ELISA. Although not strictly specific for B. anthracis spores, the developed Luminex assay represents a useful first-line screening tool for the detection of B. anthracis spores.

Neutralizing epitopes of the SARS-CoV S-protein cluster independent of repertoire, antigen structure or mAb technology

Neutralizing antibody responses to the surface glycoproteins of enveloped viruses play an important role in immunity. Many of these glycoproteins, including the severe acute respiratory syndrome-coronavirus (SARS-CoV) spike (S) protein form trimeric units in the membrane of the native virion. There is substantial experimental and pre-clinical evidence showing that the S protein is a promising lead for vaccines and therapeutics. Previously we generated a panel of monoclonal antibodies (mAbs) to whole inactivated SARS-CoV which neutralize the virus in vitro. Here, we define their specificity and affinity, map several of their epitopes and lastly characterise chimeric versions of them. Our data show that the neutralizing mAbs bind to the angiotensin-converting enzyme 2 (ACE2) receptor-binding domain (RBD) of the SARS S protein. Three of the chimeric mAbs retain their binding specificity while one conformational mAb, F26G19, lost its ability to bind the S protein despite high level expression. The affinity for recombinant S is maintained in all of the functional chimeric versions of the parental mAbs. Both parental mAb F26G18 and the chimeric version neutralize the TO R2 strain of SARS-CoV with essentially identical titres (2.07 and 2.47 nM, respectively). Lastly, a comparison with other neutralizing mAbs to SARS-CoV clearly shows that the dominance of a 33 amino acid residue loop of the SARS-CoV RBD is independent of repertoire, species, quaternary structure, and importantly, the technology used to derive the mAbs. In cases like this, the dominance of a compact RBD antigenic domain and the central role of the S protein in pathogenesis may inherently create immunoselection pressure on viruses to evolve more complex evasion strategies or die out of a host species. The apparent simplicity of the mechanism of SARS-CoV neutralization is in stark contrast to the complexity shown by other enveloped viruses.

Development and characterization of a monoclonal antibody against Taura syndrome virus

We produced a panel of monoclonal antibodies (MAbs) from the fusion of Taura syndrome virus variants from Belize (TSV-BZ) immunized BALB/cJ mouse spleen cells and non-immunoglobulin secreting SP2/0 mouse myeloma cells. One antibody, 2C4, showed strong specificity and sensitivity for TSV in dot-blot immunoassay and immunohistochemistry (IHC) analysis. The MAb reacted against native TSV-BZ, TSV variants from Sinaloa, Mexico (TSV-SI) and TSV variants from Hawaii (TSV-HI) in dot-blot immunoassay. By IHC, the antibody identified the virus in a pattern similar to the digoxigenin-labelled TSV-cDNA probe for the TSV-BZ, TSV-HI and TSV-SI variants, but not for the TSV variants from Venezuela (TSV-VE) and the TSV variants from Thailand (TSV-TH). MAb 2C4 did not react against other shrimp pathogens or with normal shrimp tissue. Western blot analysis showed a strong reaction against CP2, a region of high antigenic variability amongst TSV variants. This antibody has potential diagnostic application in detection and differentiation of certain TSV biotypes.

Francisella tularensis infection-derived monoclonal antibodies provide detection, protection, and therapy

Francisella tularensis is the causative agent of tularemia and a potential agent of biowarfare. As an easily transmissible infectious agent, rapid detection and treatment are necessary to provide a positive clinical outcome. As an agent of biowarfare, there is an additional need to prevent infection. We made monoclonal antibodies to the F. tularensis subsp. holarctica live vaccine strain (F. tularensis LVS) by infecting mice with a sublethal dose of bacteria and, following recovery, by boosting the mice with sonicated organisms. The response to the initial and primary infection was restricted to immunoglobulin M antibody directed solely against lipopolysaccharide (LPS). After boosting with sonicated organisms, the specificity repertoire broadened against protein antigens, including DnaK, LpnA, FopA, bacterioferritin, the 50S ribosomal protein L7/L12, and metabolic enzymes. These monoclonal antibodies detect F. tularensis LVS by routine immunoassays, including enzyme-linked immunosorbent assay, Western blot analysis, and immunofluorescence. The ability of the antibodies to protect mice from intradermal infection, both prophylactically and therapeutically, was examined. An antibody to LPS which provides complete protection from infection with F. tularensis LVS and partial protection from infection with F. tularensis subsp. tularensis strain SchuS4 was identified. There was no bacteremia and reduced organ burden within the first 24 h when mice were protected from F. tularensis LVS infection with the anti-LPS antibody. No antibody that provided complete protection when administered therapeutically was identified; however, passive transfer of antibodies against LPS, FopA, and LpnA resulted in 40 to 50% survival of mice infected with F. tularensis LVS.

A protein chip approach for high-throughput antigen identification and characterization

Proteomics research in humans and other eukaryotes demands a large number of high-quality mAbs. Here, we report a new approach to produce high-quality mAbs against human liver proteins using a combined force of high-throughput mAb production and protein microarrays. After immunizing mice with live cells from human livers, we isolated 54 hybridomas with binding activities to human cells and identified the corresponding antigens for five mAbs via screening on a protein microarray of 1058 unique human liver proteins. Finally, we demonstrated that using the five mAbs we could characterize the expression profiles of their corresponding antigens by using tissue microarrays. Among them, we discovered that eIF1A expressed only in normal liver tissues, not in hepatocellular carcinoma in humans.

Advanced Techniques in the Diagnosis and Management of Infectious Pulmonary Diseases in Horses

Techniques for novel approaches to the diagnosis and management of equine pulmonary disease continue to be developed and used in clinical practice. Diagnostic techniques involving immunoassays and nucleic acid-based tests not only decrease the time in which results become available but increase the sensitivity and specificity of test results. These assays do not substitute for careful clinical evaluation but can shorten the time to a confirmed accurate diagnosis, and thus allow for early initiation of therapeutic strategies and prevention protocols. With further understanding of the molecular biology and immunology of equine pulmonary disease, diagnostic and management techniques should become further refined.

A simple and rapid protocol for the sequence determination of functional kappa light chain cDNAs from aberrant-chain-positive murine hybridomas

This protocol describes the application of a polymerase chain reaction to allow the cloning and sequencing of new functional kappa light chain cDNAs from murine hybridomas co-expressing aberrant endogenous kappa chain mRNAs. The presence of kappa light chain aberrant mRNAs can hinder or even prevent determination of the sequence of functional murine kappa light chain cDNAs amplified by PCR from hybridomas. The method described here employs a panel of kappa primers in the presence of molar excess of a primer complementary to the complementary determining region (CDR) 3 of the known aberrant chain sequence. Analysis of the PCR products reveals two bands for some reactions: one the functional, full-length kappa chain cDNA (approximately 400 bp) and another shorter (approximately 100 bp) band corresponding to short aberrant chain kappa CDR3-constant region. The full-length product is gel purified and cloned prior to sequencing and aligned with V-region germline sequences available in NCBI and GenBank databases. This method is used routinely in our laboratory and demonstrates consistency and reliability for sequence determination of kappa light chain V-gene cDNA of mAbs to diverse antigens. This protocol is a rapid and convenient method for determining the sequence of murine V kappa region genes from hybridomas expressing aberrant kappa chain mRNAs.