Recombinant mAb Research Articles

In Vivo Delivery of Synthetic Human DNA-Encoded Monoclonal Antibodies Protect against Ebolavirus Infection in a Mouse Model

SUMMARYSynthetically engineered DNA-encoded monoclonal antibodies (DMAbs) are an in vivo platform for evaluation and delivery of human mAb to control against infectious disease. Here, we engineer DMAbs encoding potent anti-Zaire ebolavirus (EBOV) glycoprotein (GP) mAbs isolated from Ebola virus disease survivors. We demonstrate the development of a human IgG1 DMAb platform for in vivo EBOV-GP mAb delivery and evaluation in a mouse model. Using this approach, we show that DMAb-11 and DMAb-34 exhibit functional and molecular profiles comparable to recombinant mAb, have a wide window of expression, and provide rapid protection against lethal mouse-adapted EBOV challenge. The DMAb platform represents a simple, rapid, and reproducible approach for evaluating the activity of mAb during clinical development. DMAbs have the potential to be a mAb delivery system, which may be advantageous for protection against highly pathogenic infectious diseases, like EBOV, in resource-limited and other challenging settings.

208 - Resurrecting an antibody against an alternative conformation of cytochrome c: the recombinant mAb 1D3

Cytochrome c can undergo reversible conformational changes under biologically-relevant conditions including oxidative post-translational modifications, interactions with phospholipids and electric fields. Revealing the existence and relevance of these alternative cytochrome c proteoforms at the cell and tissue level is challenging and has benefitted from immunochemical approaches. Indeed, a monoclonal antibody that recognizes a major alternative conformation of cytochrome c, 1D3, was previously developed and characterized. The alternative conformation involves the destabilization of the Ω-loops encompassing residues 70 to 85 and 40 to 57 and the displacement of the Met80 heme ligand. However, the 1D3 producing hybridoma was lost and several attempts to reproduce it failed. Thus, with the remaining amounts of mAb 1D3 we aimed to “resurrect” 1D3 by the generation of a recombinant version of it. We employed the Valens algorithm for proteomic sequencing of 1D3. Briefly, the antibody was digested with multiple proteases and analyzed via LC-MS/MS using multiple fragmentation modes. By combining de novo peptide sequencing and homology mapping, we were able to obtain full-length sequences for the heavy and light chains of 1D3. Gene fragments representing the predicted heavy and light chain variable domains were synthesized using gBLOCK technology (IDT Inc., http://www.idtdna.com/). These were cloned into the heavy and light chain frameworks, respectively, using standard molecular biology techniques. Expression of light and heavy chains of 1D3 and its molecular assembly in HEK293 and CHO cells resulted in a functional antibody as tested by competitive ELISA with, for example, nitrotyrosine-containing cytochrome c species (NO274Tyr-Cyt c), known to adopt an alternative conformation. The recombinant 1D3 has the same specificity and affinity as the “original” 1D3 and is being successfully applied to various cellular models; enhanced levels of the 1D3-detectable alternative conformation of cytochrome c and their nuclear translocation are observed under conditions of altered cell homeostasis.

Pathogenic Citrulline-Multispecific B Cell Receptor Clades in Rheumatoid Arthritis.

Anti-citrullinated protein antibodies (ACPAs) have proven highly useful as biomarkers for rheumatoid arthritis (RA). However, composition and functionality of the associated autoreactive B cell repertoire have not been directly assessed. We aimed to selectively investigate citrullinated autoantigen-specific B cell receptors (BCRs) involved in RA and initiate studies on their pathogenicity. Blood samples were obtained from patients in a University of Minnesota cohort with ACPA-positive RA (n = 89). Tetramer sets bearing citrullinated filaggrin peptide cfc1 or citrullinated α-enolase peptide were constructed to specifically capture autoreactive B cells from the unaltered, polyclonal repertoire in RA patients. Citrullinated peptide tetramer-bound B cells were subjected to flow cytometric cell sorting and single-cell IGH, IGK, and IGL gene sequencing for B cell lineage determinations. BCR gene sequences were also expressed as recombinant monoclonal antibodies (mAb) for direct evaluation of citrullinated autoantigen binding and effector functionality. Using citrullinated peptide tetramer enrichment to investigate single autoreactive blood B cells, we identified biased V-region gene usage and conserved junction arrangements in BCRs from RA patients. Parsimonious clustering of related immunoglobulin gene nucleotide sequences revealed clonal expansions of rare individual B cell clades, in parallel with divergent sequence mutations. Correspondingly, recombinant mAb generated from such BCR lineages demonstrated citrulline-dependent cross-reactivity extending beyond the citrullinated peptides used for B cell capture. A pair of citrullinated autoantigen-specific mAb with cross-reactive binding profiles also promoted arthritis in mice. Our findings suggest that broad ACPA specificities in RA arise from a restricted repertoire of evolving citrulline-multispecific B cell clades with pathogenic potential.

An Effective Way of Producing Fully Assembled Antibody in Transgenic Tobacco Plants by Linking Heavy and Light Chains via a Self-Cleaving 2A Peptide.

Therapeutic monoclonal antibodies (mAbs) have evolved into an important class of effective medicine in treatment of various diseases. Since the antibody molecule consists of two identical heavy chains (HC) and two light chains (LC), each chain encoded by two different genes, their expressions at similar levels are critical for efficient assembly of functional recombinant mAbs. Although the plant-based expression system has been tested to produce fully assembled recombinant mAbs, coordinately expressing HC and LC at similar levels in a transgenic plant remains a challenge. A sequence coding for a foot-and-mouth disease virus (FMDV) 2A peptide has been successfully used to link two or more genes, which enable the translated polyprotein to be “self-cleaved” into individual protein in various genetically modified organisms. In the present study, we exploited the usage of F2A in Ebola virus monoclonal antibody (EBOV mAb) production. We found that transgenic tobacco plants carrying a transcription unit containing HC and LC linked by 2A not only produced similar levels of HC and LC but also rendered a higher yield of fully assembled EBOV mAb compared to those expressing HC and LC in two independent transcription units. Purified EBOV mAb bound to an Ebola epitope peptide with apparent Kd-values of 90.13–149.2 nM, indicating its proper assembly and high affinity binding to Ebola epitope peptide. To our knowledge, this is the first report showing mAb production by overexpressing a single transcription unit consisting of HC, LC and 2A in stable transformed tobacco plants.

Construction strategies for developing expression vectors for recombinant monoclonal antibody production in CHO cells.

Recent years have seen the use of recombinant proteins in the treatment of different diseases. Among them, monoclonal antibodies (mAbs) are currently the fastest growing class of bio-therapeutic recombinant proteins. Chinese hamster ovary (CHO) cells are the most commonly used host cells for production of these recombinant mAbs. Expression vectors determine the expression level and quality of recombinant mAbs. Currently, few construction strategies for recombinant mAbs expression vectors in CHO cells have been developed, including monocistronic vector, multiple-promoter expression vector, and tricistronic vector mediated by internal ribosome entry site (IRES) or Furin-2A element. Among them, Furin-2A-mediated vector is an effective approach due to advantages of high "self-cleavage" efficiency, and equal expression of light and heavy chains from a single open reading frame. Here, we have reviewed the progress in development of different strategies for constructing recombinant mAb expression vectors in CHO cells and its potential advantages and disadvantages.

A novel glycosylated anti-CD20 monoclonal antibody from transgenic cattle

The monoclonal antibody (mAb) against CD20 known as Rituxan is widely used to treat autoimmune diseases and lymphomas. However, further application of Rituxan faces challenges of high production cost, which limits its availability in developing countries. Here, we report a new approach for large production of a recombinant anti-CD20 mAb in the milk of transgenic cattle (at a yield of up to ~6.8 mg/mL), with ~80% recovery rate and >99% purity. Crystallography study showed that our recombinant mAb is structurally nearly identical to Rituxan with only minor differences in N-linked glycosylation pattern. Functional study showed that, while our mAb shared similar target-cell binding capacities and complement-dependent cytotoxicity with Rituxan, our product exhibited a higher binding affinity for FcγRIIIα and a greater antibody-dependent cellular cytotoxicity. Accordingly, our recombinant mAb demonstrated a superior efficacy over Rituxan against B-cell lymphomas in severe combined immunodeficiency mice. Taken together, our data supports transgenic cattle as a novel model for cost-competitive, large-scale production of therapeutic antibodies.

Differential gene expression of a feed-spiked super-producing CHO cell line

Feed supplements are concentrated cell culture media that contain a variety of nutrients, which can be added during a bioprocess. During fed-batch cultivation, feed media are typically added to a growing cell culture to maximize cell and product concentrations. In this study, only a single shot of feed medium was added on day 0 to a basal cell culture medium and compared to non-supplemented basal medium (feed-spiked at day 0 versus control experiments) by cultivation of a recombinant mAb expressing CHO cell line in batch mode under controlled conditions in a bioreactor. Since the feed-spike at day 0 was based on existing medium components without introducing additional supplements, a desirable process with decreased complexity was generated. Unlike cells in basal medium, feed-spiked cultures reached almost 2× higher peak cell concentrations (10 × 106 c/mL vs. 18 × 106 c/mL) and 3× higher antibody concentrations (0.8 g/L vs. 2.4 g/L). Batch process time and the integral over the viable cell count were similar for both process types. Constantly high cell-specific production rates in feed-spiked cultures (70 pg/cell/day) compared to continuously declining rates in basal medium (from 70 to 10 pg/cell/day) were responsible for an overall 70% higher cell-specific production rate and the higher product concentrations. To associate gene expression patterns to different process proceedings, transcriptome analysis was performed using microarrays. Several transcripts that are involved with glutamine de novo synthesis and citric acid cycle were significantly upregulated on several days in feed-spiked cultures. The top identified gene ontology (GO) terms related well to cell cycle and primary metabolism, cellular division as well as nucleobase formation or regulation, which indicated a more active proliferative state for feed-spiked cultures. KEGG biochemical pathway analysis and Gene set enrichment analysis (GSEA) further confirmed these findings from a complementary perspective. Moreover, several interesting gene targets, which have not yet been associated with recombinant protein expression, were identified that related to a higher proliferative state, growth, protein synthesis, cell-size control, metabolism, cell survival as well as genes that are associated with the control of the mammalian target of rapamycin (mTOR) in feed-spiked cultures. Analysis of critical product quality attributes (i.e. glycosylation, charge variants and size distribution) showed that feed-spiking did not change antibody quality.

Efficacy of Human Monoclonal Antibody Monotherapy Against Bundibugyo Virus Infection in Nonhuman Primates.

The 2013-2016 Ebola virus disease (EVD) epidemics in West Africa highlighted a need for effective therapeutics for treatment of the disease caused by filoviruses. Monoclonal antibodies (mAbs) are promising therapeutic candidates for prophylaxis or treatment of virus infections. Data about efficacy of human mAb monotherapy against filovirus infections in preclinical nonhuman primate models are limited. Previously, we described a large panel of human mAbs derived from the circulating memory B cells from Bundibugyo virus (BDBV) infection survivors that bind to the surface glycoprotein (GP) of the virus. We tested one of these neutralizing mAbs that recognized the glycan cap of the GP, designated mAb BDBV289, as monotherapy in rhesus macaques. We found that recombinant mAb BDBV289-N could confer up to 100% protection to BDBV-infected rhesus macaques when treatment was initiated as late as 8 days after virus challenge. Protection was associated with survival and decreased viremia levels in the blood of treated animals. These findings define the efficacy of monotherapy of lethal BDBV infection with a glycan cap-specific mAb and identify a candidate mAb therapeutic molecule that could be included in antibody cocktails for prevention or treatment of ebolavirus infections.

Abstract 752: CovisoLinK: New bacterial transglutaminase Q-Tag substrate for the development of site specific antibody-drug conjugates

Abstract CovIsoLink™ (Covalently Isopeptide crosslinking) relates to methods for enzymatic covalently coupling drugs and other compounds through transglutaminase site specific generated in the targeted proteins including, polypeptides, proteins and immunoglobulins (patent pending1). Transglutaminases (TGases) catalyze covalent cross- linking of specific glutamine residues to the primary amine of peptide-bound lysine residues or primary amines of other compounds such as polyamines2. Using an in house peptide library and the transglutaminase colorometric assay3, we identified several amino acid sequences that were recognized as glutamine donor substrates. The optimum peptide sequences were selected and we further confirmed that these sequences have improved affinity compared with the conventional small peptides Z-QG. In different experiments we engineered Fc-containing polypeptide at the C-terminal domain and showed that mTG incorporates with high efficiency several types of amine donors to the engineered antibodies. CovIsoLink™ is now used to develop new antibody drug conjugates (ADCs) since the major advantage of this method is to obtain a homogenous immunoconjugate with uniform stoichiometry. We developed and characterized different recombinant anti Her2 IgG1 Mab carrying optimized enzymatic substrates (tag) by genetic insertion in the coding sequence of MAb. We then evaluated the best linkers and conformation to incorporate different compounds through bacterial Transglutaminase (mTG) enzymatic reaction. We set up experimental conditions, production, purification, HPLC/MS analysis and control of the immunoreactivity of CovIsoLink™ Her2-ADC. Using mTG, we obtained site specific conjugation of different modified drugs with optimized linker on the anti Her2 IgG1 antibody. By HIC analysis, we validated a specific and reproducible DAR reaching DAR2 depending on drugs and experimental conditions. In vitro and In vivo characterization and dose response studies of CovIsolink-ADC specificity and reactivity are currently performed in Her2 positive models demonstrating an improved efficacy by comparison with Kadcyla (T-DM1).1) PCT/EP2014/0792278, 2) El Alaoui S et al, Int J Cancer, 1991; 3) Perez AM et al, Anal Biochem, 2009. Citation Format: Eva Sivado, Vincent Thomas, Meddy El Alaoui, Anne-Catherine Jallas, Mike R. Dyson, John McCafferty, Said El Alaoui, Sandrine Valsesia-Wittmann. CovisoLinK: New bacterial transglutaminase Q-Tag substrate for the development of site specific antibody-drug conjugates [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 752.

Anti-CD40 Antibodies do not Cause Thromboembolism as Demonstrated by in Vitro and in Vivo Studies

Clinical trials with non-silenced anti-CD40L (anti-CD154) monoclonal antibodies (mAb) in patients with systemic lupus erythematosus (SLE) and idiopathic thrombocytopenic purpura (ITP) were halted after unexpected fatal thromboembolic events (TE). Previous results have shown that soluble CD40L/anti-CD40L mAb immune complexes (IC) can activate and induce pro-aggregatory effects on platelets in vitro via FcgRIIa. Pulmonary thrombi consisting of platelet aggregates and fibrin, and thrombocytopenia were found in humanized FcgRIIa transgenic mice after injection of pre-formed IC consisting of mouse soluble CD40L and anti-mouse CD40L mAb. To date, no such studies have been performed with IC of mouse sCD40 and anti-mouse CD40 mAbs. We therefore injected either single mouse proteins (soluble CD40L, soluble CD40) or antibodies (isotype controls, anti-mouse CD40L mAb, anti-mouse CD40 mAb), IC of soluble protein with the respective antibody into humanized FcgR transgenic mice. In addition, in vitro platelet aggregation was performed using blood from FcgR transgenic mice and human healthy donors. Whole blood samples from FcgR transgenic mice were treated with the same proteins and antibodies as in the in vivo study. For human whole blood, isotype controls, soluble CD40L, anti-CD40L mAb including IC in different ratios, soluble CD40, aCD40 mAbs (e.g. CFZ533) including IC in different ratios were used. We observed evidence of thromboembolism (thrombi formation in the lung shown by histopathology) and thrombocytopenia with the soluble CD40L/anti-CD40L mAb IC but not with the soluble proteins or antibodies alone, nor with the soluble CD40/anti-CD40 mAb IC. In vitro platelet aggregation assays performed using blood from FcgR transgenic mice and human healthy donors with recombinant proteins, mAbs and IC from respective species confirmed these findings. These data provide in vivo and in vitro evidence that all anti-CD40 mAbs, either alone or IC with soluble CD40 protein do not induce thromboembolism, indicating that the TE associated with anti-CD40L mAbs are target-related but not co-stimulation pathway specific. Combined with clinical evidence, these data further support the notion of minimal risk for patients developing life-threatening thromboembolic events following administration of a pathway blocking anti-CD40 mAb.

Routine measurements of factor VIII activity and inhibitor titer in the presence of emicizumab utilizing anti‐idiotype monoclonal antibodies

Background Emicizumab is an anti-factor (F)IXa/X bispecific monoclonal antibody (mAb), mimicking the factor (F)VIIIa cofactor activity. Emicizumab does not require activation by thrombin and its shortening effect on the activated partial prothrombin time (APTT) is more pronounced than that of factor (F)VIII. APTT-based FVIII activity (FVIII:C) and FVIII inhibiter titer measurements are influenced by the presence of emicizumab. Aim To establish a reliable APTT-based assay to measure FVIII in the presence of emicizumab. Methods Plasmas from hemophilia A (HA) patients without or with inhibitors were studied using one-stage FVIII:C and Bethesda inhibitor assays. Two recombinant anti-idiotype mAbs to emicizumab (anti-emicizumab mAbs) were prepared, rcAQ8 to anti-FIXa-Fab and rcAJ540 to anti-FX-Fab. Results The combined anti-idiotype mAbs (2000 nm each) eliminated the effects of emicizumab on APTTs of HA plasmas without or with inhibitor by competitive inhibition of antibody binding to FIX(a)/FX(a). Measurements of FVIII coagulation activity in HA plasmas without inhibitor were overestimated in the presence of emicizumab (1 μm = ~150 μg mL-1 ) at all reference levels of FVIII. The addition of anti-emicizumab mAbs to the assay mixtures completely neutralized the emicizumab and facilitated accurate determination of FVIII:C. Anti-FVIII inhibitor titers were undetectable in the presence of emicizumab in HA plasmas with inhibitor or normal plasmas mixed with anti-FVIII neutralizing antibodies. These effects of emicizumab were completely counteracted by the addition of the anti-idiotype mAbs, allowing accurate assessment of inhibitor titers. Conclusion The in vitro inclusion of anti-emicizumab mAbs in the standard one-stage coagulation assays prevented interference by emicizumab and enabled accurate measurements of FVIII:C and inhibitor titers.

Investigation of Metal-Catalyzed Antibody Carbonylation With an Improved Protein Carbonylation Assay

Protein carbonylation is a posttranslational modification referring to the occurrence of aldehydes and ketones in proteins. The current understanding of how carbonylation, in particular, metal-catalyzed carbonylation, occurs in recombinant mAbs during production and storage is very limited. To facilitate investigations into mAb carbonylation, we developed a protein carbonylation assay with improved assay robustness and precision over the conventional assays. We applied this assay to investigate mAb carbonylation under production, storage, and stress conditions and showed that iron, hydrogen peroxide, and polysorbate 20 at pharmaceutically relevant levels critically influence the extent of mAb carbonylation. In addition, we found that while carbonylation correlates with mAb aggregation in several cases, carbonylation cannot be used as a general indicator for aggregation. Furthermore, we observed that mAb carbonylation level can decrease during storage, which indicates that carbonylation products may not be stable. Finally, we report for the first time a positive correlation between carbonylation and acidic charge heterogeneity of mAbs that underwent metal-catalyzed oxidation. This finding shows that the impact of protein carbonylation on product quality for mAbs is not limited to aggregation but also extends to charge heterogeneity.

Identification of galectin-3 as an autoantigen in patients with IgG4-related disease

The antigenic trigger that drives expansion of circulating plasmablasts and CD4+ cytotoxic T cells in patients with IgG4-related disease (IgG4-RD) is presently unknown. We sought to sequence immunoglobulin genes from single-cell clones of dominantly expanded plasmablasts and generate recombinant human mAbs to identify relevant antigens in patients with IgG4-RD by using mass spectrometry. Paired heavy and light chain cDNAs from dominant plasmablast clones were expressed as mAbs and used to purify antigens by using immunoaffinity chromatography. Affinity-purified antigens were identified by using mass spectrometry and validated by means of ELISA. Plasma levels of the antigen of interest were also determined by using ELISA. mAbs expressed from the 2 dominant plasmablast clones of a patient with multiorgan IgG4-RD stained human pancreatic tissue sections. Galectin-3 was identified as the antigen specifically recognized by both mAbs. Anti-galectin-3 autoantibody responses were predominantly of the IgG4 isotype (28% of the IgG4-RD cohort, P=.0001) and IgE isotype (11% of the IgG4-RD cohort, P=.009). No significant responses were seen from the IgG1, IgG2, or IgG3 isotypes. IgG4 anti-galectin-3 autoantibodies correlated with increased plasma galectin-3 levels (P=.001), lymphadenopathy (P=.04), total IgG level increase (P=.05), and IgG4 level increase (P=.03). Affinity chromatography using patient-derived mAbs identifies relevant autoantigens in patients with IgG4-RD. IgG4 galectin-3 autoantibodies are present in a subset of patients with IgG4-RD and correlate with galectin-3 plasma levels. The marked increases in levels of circulating IgG4 and IgE observed clinically are, at least in part, caused by the development of IgG4- and IgE-specific autoantibody responses.

Production of monoclonal antibodies in microfluidic devices

Herein, a microfluidic device with cistern design for cultivation of adherent eukaryotic cells for the production of recombinant proteins is presented. The geometric configuration of the microchannels in the device provided laminar flow with reduced velocity profiles in the cisterns, resulting in an adequate microenvironment for long-term adherent cell growth with passive pumping flow cycles of 24 hours. CHO-ahIFNα2b and HEK-ahIFNα2b adherent cell lines expressing a novel anti-hIFN-α2b recombinant monoclonal antibody (MAb) for the treatment of systemic lupus erythematosus were cultured on the surface of PDMS/glass microchannels coated with poly-d-lysine. A 24 day culture of CHO-ahIFNα2b cells resulted in MAb concentrations up to 166.4 μg mL-1 per day. The productivity of CHO-ahIFNα2b and HEK-ahIFNα2b cell lines was higher in the microdevice compared to that obtained using the adherent cell culture method (T-flask), with a 5.89- and 7.31-fold increase, respectively. Moreover, biological analysis of the MAbs produced in the microdevice showed no significant differences in the neutralizing antiproliferative activity of the hIFN-α2b or the cytokine cell signaling compared to the MAbs produced with cell adherent methods. These results suggest that this microfluidic device is suitable for long-term culture of mammalian cells and can improve the productivity of cells expressing recombinant MAbs with potential for therapeutic use without affecting the quality attributes of the product.

Improving the quality of a recombinant rabbit monoclonal antibody against PLXDC2 by optimizing transient expression conditions and purification method

Rabbit monoclonal antibodies (mAbs) have many advantages over mouse antibodies in biological research and diagnostics applications because they exhibit high affinity and specificity. However, the methods of recombinant rabbit mAb production have not been optimized to the same extent as techniques used to produce mouse and human mAbs. In this study, we sought to optimize the production of a recombinant rabbit mAb against human plexin domain containing protein 2 (PLXDC2), a known cell surface antigen, by culturing HEK293-6E cells transfected with antibody-encoding genes at two different temperatures and by purifying the end-product by three different chromatography methods. The quality and function of purified antibody preparations were checked by electrophoresis and western blot analysis. The secreted rabbit mAb produced by a combination of culturing at 32 °C, purification by ammonium sulfate fractionation, and diethylaminoethyl resin (DEAE) ion exchange chromatography was of high quality. In contrast, the antibody produced by the cells grown at 37 °C for 6 days after transfection and purified by Protein A/G affinity method was low quality. Hypothermic conditions during production reduced protein heterogeneity probably by favorably affecting the levels of glycosylation and aggregation. In particular, according to western blotting data, CIMmultus DEAE chromatography that utilizes monolithic columns not only excluded inferior charge variants resulting from nonspecific reactions but also yielded rabbit mAb that was of better quality than commercially available rabbit polyclonal antibodies. The combination of techniques suggested by us may be a general approach to enhance product quality of rabbit mAbs produced by transient expression systems.

Generation of Recombinant Monoclonal Antibodies from Single B Cells Isolated from Synovial Tissue of Rheumatoid Arthritis Patients.

Ectopic lymphoid structure (ELS) can form in the target tissues of patients with chronic inflammatory autoimmune diseases such as rheumatoid arthritis (RA) and Sjögren's syndrome (SS). Although it is still not clear why ELS form only in a subset of patients, it is well known that these structures can acquire features of ectopic germinal centers and contribute actively to the production of autoantibodies. Here, we describe a method to generate recombinant monoclonal antibodies from single ELS+ synovial tissue B cells obtained from RA patients. This chapter gives a detailed description of the method beginning from the mononuclear cell preparation from RA synovial tissue, single-cell sort of B cells by flow cytometry, amplification of the immunoglobulin (Ig) genes (both heavy- and light-chain genes) by PCR, and subsequent Ig gene expression vector cloning for full recombinant IgG1 monoclonal antibody (rmAb) production in vitro. The recombinant mAbs generated can be then characterized for (1) analysis of the Ig gene repertoires for clonal studies, (2) immunoreactivity profile, and (3) functional studies both in vitro and in vivo.

Stability assessment of antibody-drug conjugate Trastuzumab emtansine in comparison to parent monoclonal antibody using orthogonal testing protocol

Antibody-drug conjugates (ADC) represent an emerging, novel class of biopharmaceuticals. The heterogeneity originating from the sophisticated structure requires orthogonal analytical techniques for quality and stability assessment of ADC to ensure safety and efficacy. In this study, the stability of Trastuzumab (recombinant humanized IgG1 mAb, targeting HER2 receptor) and its ADC with DM1 (anti-tubulin anticancer drug), Trastuzumab emtansine (T-DM1) were studied. SE-HPLC was used to monitor formation of aggregates and/or fragments of the monoclonal antibodies (mAb). Correlation with the results of reducing and non-reducing sodium dodecyl sulphate – polyacrylamide gel electrophoresis (SDS-PAGE) and dynamic light scattering (DLS) were performed to interpret the obtained results. RP-HPLC was used for assessment of the stability of DM1 in ADC while spectrophotometry was employed to determine drug antibody ratio (DAR) . The studied drugs were subjected to several stress conditions including pH, temperature, mechanical agitation and repeated freeze and thaw to generate possible degradation products and ensure suitability of the assay protocol. The degradation pattern and extent were demonstrated under the indicated stress conditions. The correlation between the results of SE-HPLC and those of SDS-PAGE and DLS ensured the validity of the orthogonal assay protocol and indicated aggregates that were not detected using SE-HPLC. Results showed clearly that T-DM1 is relatively less stable than its parent mAb. This was attributed to the presence of the drug-linker part that is attached to the mAb. RP-HPLC showed that the cytotoxic drug moiety is liable for degradation under the studied conditions resulting in alteration of DAR as well as formation of degradation products. This confirmed the need for more robust coupling chemistries for production of safe and effective ADC and highlighted the importance of orthogonal testing protocols for quality assessment. The assay protocol should be applicable for quality and stability assessment of various ADC.

Characterization of an anti-fetal AChR monoclonal antibody isolated from a myasthenia gravis patient

We report here the sequence and functional characterization of a recombinantly expressed autoantibody (mAb 131) previously isolated from a myasthenia gravis patient by immortalization of thymic B cells using Epstein-Barr virus and TLR9 activation. The antibody is characterized by a high degree of somatic mutations as well as a 6 amino acid insertion within the VHCDR2. The recombinant mAb 131 is specific for the γ-subunit of the fetal AChR to which it bound with sub-nanomolar apparent affinity, and detected the presence of fetal AChR on a number of rhabdomyosarcoma cell lines. Mab 131 blocked one of the two α-bungarotoxin binding sites on the fetal AChR, and partially blocked the binding of an antibody (mAb 637) to the α-subunit of the AChR, suggesting that both antibodies bind at or near one ACh binding site at the α/γ subunit interface. However, mAb 131 did not reduce fetal AChR ion channel currents in electrophysiological experiments. These results indicate that mAb 131, although generated from an MG patient, is unlikely to be pathogenic and may make it a potentially useful reagent for studies of myasthenia gravis, rhabdomyosarcoma and arthrogryposis multiplex congenita which can be caused by fetal-specific AChR-blocking autoantibodies.

Site-Specific Conjugation to Native and Engineered Lysines in Human Immunoglobulins by Microbial Transglutaminase.

The use of microbial transglutaminase (MTG) to produce site-specific antibody-drug conjugates (ADCs) has thus far focused on the transamidation of engineered acyl donor glutamine residues in an antibody based on the hypothesis that the lower specificity of MTG for acyl acceptor lysines may result in the transamidation of multiple native lysine residues, thereby yielding heterogeneous products. We investigated the utilization of native IgG lysines as acyl acceptor sites for glutamine-based acyl donor substrates. Of the approximately 80 lysines in multiple recombinant IgG monoclonal antibodies (mAbs), none were transamidated. Because recombinant mAbs lack the C-terminal Lys447 due to cleavage by carboxypeptidase B in the production cell host, we explored whether blocking the cleavage of Lys447 by the addition of a C-terminal amino acid could result in transamidation of Lys447 by a variety of acyl donor substrates. MTG efficiently transamidated Lys447 in the presence of any nonacidic, nonproline amino acid residue at position 448. Lysine scanning mutagenesis throughout the antibody further revealed several transamidation sites in both the heavy- and light-chain constant regions. Additionally, scanning mutagenesis of the hinge region in a Fab' fragment revealed sites of transamidation that were not reactive in the context of the full-length mAb. Here, we demonstrate the utility of single lysine substitutions and the C-terminal Lys447 for engineering efficient acyl acceptor sites suitable for site-specific conjugation to a range of glutamine-based acyl donor substrates.

Expression, Purification, and Refolding of Human Lipocalin 6 and Production of a Monoclonal Antibody Against This Protein.

Human lipocalin 6 (hLCN6) is a member of the lipocalin family, which is a group of structurally conserved hydrophobic ligand binding proteins, and widely distributed in animal, plant, and bacteria. Specific expression of hLCN6 in the epididymis and localization of this protein on the surface of spermatozoa suggest a role played by hLCN6, which may function as a transporter to carry ligands in the epididymal channel. However, the role of hLCN6 in sperm maturation has been largely unknown due to the lack of effective antibodies. In this study, we report the prokaryotic expression, purification, and refolding of recombinant hLCN6. Purified hLCN6 protein was used to generate monoclonal antibody (mAb) against this protein using conventional hybridoma techniques. The sensitivity and specificity of the anti-hLCN6 mAb were determined based on their activities in enzyme-linked immunosorbent assay and Western blotting analysis using various human tissues. The results showed that the antibody induced by recombinant hLCN6 protein had high sensitivity and specificity. Taken together, the recombinant hLCN6 protein and mAb against this protein obtained from our study provided useful tools for further exploration of the biological functions and molecular mechanism, as well as pathological significance of LCN6 in human.