Generating Informative Sequence Tags from Antigen-Binding Regions of Heavily Glycosylated IgA1 Antibodies by Native Top-Down Electron Capture Dissociation

Immunoglobulins A (IgA) include some of the most abundant human antibodies and play an important role in defending mucosal surfaces against pathogens. The unique structural features of the heavy chain of IgA subclasses (called IgA1 and IgA2) enable them to polymerize via the joining J-chain, resulting in IgA dimers but also higher oligomers. While secretory sIgA oligomers are dominant in milk and saliva, IgAs exist primarily as monomers in serum. No method currently allows disentangling the millions of unique IgAs potentially present in the human antibody repertoire. Obtaining unambiguous sequence reads of their hypervariable antigen-binding regions is a prerequisite for IgA identification. We here report a mass spectrometric method that uses electron capture dissociation (ECD) to produce straightforward-to-read sequence ladders of the variable parts of both the light and heavy chains of IgA1s, in particular, of the functionally critical CDR3 regions. We directly compare the native top-down ECD spectra of a heavily and heterogeneously N- and O-glycosylated anti-CD20 IgA1, the corresponding N-glycosylated anti-CD20 IgG1, and their Fab parts. We show that while featuring very different MS1 spectra, the native top-down ECD MS2 spectra of all four species are nearly identical, with cleavages occurring specifically within the CDR3 and FR4 regions of both the heavy and light chain. From the sequence-informative ECD data of an intact glycosylated IgA1, we foresee that native top-down ECD will become a valuable complementary tool for the de novo sequencing of IgA1s from milk, saliva, or serum.

Preparation and properties of recombinant Clostridium ramosum IgA proteinase. Isolation of Fc-SC and Fab fragments of human secretory IgA

Immunoglobulin A (IgA) proteinase from Clostridium ramosum is the enzyme which cleaves IgA of both subclasses; in contrast, the other bacterial proteinases cleave only IgA1 proteins. Previous reports characterized the activity of proteinase naturally secreted by C. ramosum specific for the normal human serum IgA of IgA1 and IgA2m(1) subclasses and also for secretory IgA (SIgA). Its amino acid sequence was determined, and the recombinant proteinase which cleaved IgA of both subclasses was prepared. Here we report the optimized expression, purification, storage conditions and activity testing against purified human milk SIgA. The recombinant C. ramosum IgA proteinase isolated in the high degree of purity exhibited almost complete cleavage of SIgA of both subclasses. The proteinase remained active upon storage for more than 10 month at -20 °C without substantial loss of enzymatic activity. Purified SIgA fragments are suitable for studies of all antigen-binding and Fc-dependent functions of SIgA involved in the protection against infections with mucosal pathogens.

QSAR Implementation for HIC Retention Time Prediction of mAbs Using Fab Structure: A Comparison between Structural Representations

Monoclonal antibodies (mAbs) constitute a rapidly growing biopharmaceutical sector. However, their growth is impeded by high failure rates originating from failed clinical trials and developability issues in process development. There is, therefore, a growing need for better in silico tools to aid in risk assessment of mAb candidates to promote early-stage screening of potentially problematic mAb candidates. In this study, a quantitative structure–activity relationship (QSAR) modelling workflow was designed for the prediction of hydrophobic interaction chromatography (HIC) retention times of mAbs. Three novel descriptor sets derived from primary sequence, homology modelling, and atomistic molecular dynamics (MD) simulations were developed and assessed to determine the necessary level of structural resolution needed to accurately capture the relationship between mAb structures and HIC retention times. The results showed that descriptors derived from 3D structures obtained after MD simulations were the most suitable for HIC retention time prediction with a R² = 0.63 in an external test set. It was found that when using homology modelling, the resulting 3D structures became biased towards the used structural template. Performing an MD simulation therefore proved to be a necessary post-processing step for the mAb structures in order to relax the structures and allow them to attain a more natural conformation. Based on the results, the proposed workflow in this paper could therefore potentially contribute to aid in risk assessment of mAb candidates in early development.

Structures of Human Antibodies Bound to SARS-CoV-2 Spike Reveal Common Epitopes and Recurrent Features of Antibodies

Neutralizing antibody responses to coronaviruses mainly target the receptor-binding domain (RBD) of the trimeric spike. Here, we characterized polyclonal immunoglobulin Gs (IgGs) and Fabs from COVID-19 convalescent individuals for recognition of coronavirus spikes. Plasma IgGs differed in their focus on RBD epitopes, recognition of alpha- and beta-coronaviruses, and contributions of avidity to increased binding/neutralization of IgGs over Fabs. Using electron microscopy, we examined specificities of polyclonal plasma Fabs, revealing recognition of both S1A and RBD epitopes on SARS-CoV-2 spike. Moreover, a 3.4 Å cryo-electron microscopy (cryo-EM) structure of a neutralizing monoclonal Fab-spike complex revealed an epitope that blocks ACE2 receptor binding. Modeling based on these structures suggested different potentials for inter-spike crosslinking by IgGs on viruses, and characterized IgGs would not be affected by identified SARS-CoV-2 spike mutations. Overall, our studies structurally define a recurrent anti-SARS-CoV-2 antibody class derived from VH3-53/VH3-66 and similarity to a SARS-CoV VH3-30 antibody, providing criteria for evaluating vaccine-elicited antibodies.

Development of a hyperimmune equine serum therapy for COVID-19 in Argentina

The disease named COVID-19, caused by the SARS-CoV-2 coronavirus, is currently generating a global pandemic. Vaccine development is no doubt the best long-term immunological approach, but in the current epidemiologic and health emergency there is a need for rapid and effective solutions. Convalescent plasma is the only antibody-based therapy available for COVID-19 patients to date. Equine polyclonal antibodies (EpAbs) put forward a sound alternative. The new generation of processed and purified EpAbs containing highly purified F(ab')2 fragments demonstrated to be safe and well tolerated. EpAbs are easy to manufacture allowing a fast development and scaling up for a treatment. Based on these ideas, we present a new therapeutic product obtained after immunization of horses with the receptor-binding domain of the viral Spike glycoprotein. Our product shows around 50 times more potency in in vitro seroneutralization assays than the average of convalescent plasma. This result may allow us to test the safety and efficacy of this product in a phase 2/3 clinical trial to be conducted in July 2020 in the metropolitan area of Buenos Aires, Argentina.

Refinement strategy for antivenom preparation of high yield and quality

Antivenoms from hyperimmune animal plasma are the only specific pharmaceuticals against snakebites. The improvement of downstream processing strategies is of great interest, not only in terms of purity profile, but also from yield-to-cost perspective and rational use of plasma of animal origin. We report on development of an efficient refinement strategy for F(ab')2-based antivenom preparation. Process design was driven by the imperative to keep the active principle constantly in solution as a precautionary measure to preserve stability of its conformation (precipitation of active principle or its adsorption to chromatographic stationary phase has been completely avoided). IgG was extracted from hyperimmune horse plasma by 2% (V/V) caprylic acid, depleted from traces of precipitating agent and digested by pepsin. Balance between incomplete IgG fraction breakdown, F(ab')2 over-digestion and loss of the active principle's protective efficacy was achieved by adjusting pepsin to substrate ratio at the value of 4:300 (w/w), setting pH to 3.2 and incubation period to 1.5 h. Final polishing was accomplished by a combination of diafiltration and flow-through chromatography. Developed manufacturing strategy gave 100% pure and aggregate-free F(ab')2 preparation, as shown by size-exclusion HPLC and confirmed by MS/MS. The overall yield of 75% or higher compares favorably to others so far reported. This optimised procedure looks also promising for large-scale production of therapeutic antivenoms, since high yield of the active drug and fulfillment of the regulatory demand considering purity was achieved. The recovery of the active substance was precisely determined in each purification step enabling accurate estimation of the process cost-effectiveness.

Functional and proteomic comparison of different techniques to produce equine anti-tetanus immunoglobulin F(ab')2 fragments

Tetanus is still a major cause of human deaths in several developing countries. In particular, the neonatal form remains a significant public health problem. According to the World Health Organization, administration of tetanus toxoid is recommended for neonatal tetanus patients. Furthermore, tetanus antitoxin or anti-tetanus immunoglobulin (Ig) are used for mild case or intensive care. This paper discusses a novel purification technique for improving equine anti-tetanus Ig production. First, equine plasma dealt with two steps salting out with ammonium sulfate; second, ultrafiltration concentration liquid purified by one successive protein G based affinity chromatography steps; finally, the purified F(ab')2 fragments was characterized using biochemical and proteomic methods and shown to be pure and homogeneous. Compared with the original technique product, specific activity increased by 80% (about 90,000 IU/g) and recovery of F(ab')2 is approximately equal 75%. Furthermore, Proteomic profiling of total technique process is demonstrated by nano-HPLC-MS and bioinformatics analysis. New technique to produce equine anti-tetanus immunoglobulin F(ab')2 fragments from crude plasma in high quality and yield. And it also could be used for industrial amplification.

Vaccine-elicited receptor-binding site antibodies neutralize two New World hemorrhagic fever arenaviruses

While five arenaviruses cause human hemorrhagic fevers in the Western Hemisphere, only Junin virus (JUNV) has a vaccine. The GP1 subunit of their envelope glycoprotein binds transferrin receptor 1 (TfR1) using a surface that substantially varies in sequence among the viruses. As such, receptor-mimicking antibodies described to date are type-specific and lack the usual breadth associated with this mode of neutralization. Here we isolate, from the blood of a recipient of the live attenuated JUNV vaccine, two antibodies that cross-neutralize Machupo virus with varying efficiency. Structures of GP1-Fab complexes explain the basis for efficient cross-neutralization, which involves avoiding receptor mimicry and targeting a conserved epitope within the receptor-binding site (RBS). The viral RBS, despite its extensive sequence diversity, is therefore a target for cross-reactive antibodies with activity against New World arenaviruses of public health concern.

A novel one-step approach for the construction of yeast surface display Fab antibody libraries

BACKGROUND

Yeast surface display (YSD) has proven to be a versatile platform technology for antibody discovery. However, the construction of antibody Fab libraries typically is a tedious three-step process that involves the generation of heavy chain as well as light chain display plasmids in different haploid yeast strains followed by yeast mating.

RESULTS

Within this study, we aimed at implementing a focused Golden Gate Cloning approach for the generation of YSD libraries. For this, antibodies heavy and light chains were encoded on one single plasmid. Fab display on yeast cells was either mediated by a two-directional promoter system (2dir) or by ribosomal skipping (bicis). The general applicability of this methodology was proven by the functional display of a therapeutic antibody. Subsequently, we constructed large antibody libraries with heavy chain diversities derived from CEACAM5 immunized animals in combination with a common light chain. Target-specific antibodies from both display systems were readily obtained after three rounds of fluorescence activated cell sorting. Isolated variants exhibited high affinities in the nanomolar and subnanomolar range as well as appropriate biophysical properties.

CONCLUSION

We demonstrated that Golden Gate Cloning appears to be a valid tool for the generation of large yeast surface display antibody Fab libraries. This procedure simplifies the hit discovery process of antibodies from immune repertoires.

Generating and Purifying Fab Fragments from Human and Mouse IgG Using the Bacterial Enzymes IdeS, SpeB and Kgp

Fab fragments are valuable research tools in various areas of science including applications in imaging, binding studies, removal of Fc-mediated effector functions, mass spectrometry, infection biology, and many others. The enzymatic tools for the generation of Fab fragments have been discovered through basic research within the field of molecular bacterial pathogenesis. Today, these enzymes are widely applied as research tools and in this chapter, we describe methodologies based on bacterial enzymes to generate Fab fragments from both human and mouse IgG. For all human IgG subclasses, the IdeS enzyme from Streptococcus pyogenes has been applied to generate F(ab')2 fragments that subsequently can be reduced under mild conditions to generate a homogenous pool of Fab' fragments. The enzyme Kgp from Porphyromonas gingivalis has been applied to generate intact Fab fragments from human IgG1 and the Fab fragments can be purified using a CH1-specific affinity resin. The SpeB protease, also from S. pyogenes, is able to digest mouse IgGs and has been applied to digest antibodies and Fab fragments can be purified on light chain affinity resins. In this chapter, we describe methodologies that can be used to obtain Fab fragments from human and mouse IgG using bacterial proteases.

The Biochemical Properties of Antibodies and Their Fragments

Immunoglobulins (Ig) or antibodies are powerful molecular recognition tools that can be used to identify minute quantities of a given target analyte. Their antigen-binding properties define both the sensitivity and selectivity of an immunoassay. Understanding the biochemical properties of this class of protein will provide users with the knowledge necessary to select the appropriate antibody composition to maximize immunoassay results. Here we define the general biochemical properties of antibodies and their similarities and differences, explain how these properties influence their functional relationship to an antigen target, and describe a method for the enzymatic fragmentation of antibodies into smaller functional parts.

Evaluation of chemical fluorescent dyes as a protein conjugation partner for live cell imaging

To optimize live cell fluorescence imaging, the choice of fluorescent substrate is a critical factor. Although genetically encoded fluorescent proteins have been used widely, chemical fluorescent dyes are still useful when conjugated to proteins or ligands. However, little information is available for the suitability of different fluorescent dyes for live imaging. We here systematically analyzed the property of a number of commercial fluorescent dyes when conjugated with antigen-binding (Fab) fragments directed against specific histone modifications, in particular, phosphorylated H3S28 (H3S28ph) and acetylated H3K9 (H3K9ac). These Fab fragments were conjugated with a fluorescent dye and loaded into living HeLa cells. H3S28ph-specific Fab fragments were expected to be enriched in condensed chromosomes, as H3S28 is phosphorylated during mitosis. However, the degree of Fab fragment enrichment on mitotic chromosomes varied depending on the conjugated dye. In general, green fluorescent dyes showed higher enrichment, compared to red and far-red fluorescent dyes, even when dye∶protein conjugation ratios were similar. These differences are partly explained by an altered affinity of Fab fragment after dye-conjugation; some dyes have less effect on the affinity, while others can affect it more. Moreover, red and far-red fluorescent dyes tended to form aggregates in the cytoplasm. Similar results were observed when H3K9ac-specific Fab fragments were used, suggesting that the properties of each dye affect different Fab fragments similarly. According to our analysis, conjugation with green fluorescent dyes, like Alexa Fluor 488 and Dylight 488, has the least effect on Fab affinity and is the best for live cell imaging, although these dyes are less photostable than red fluorescent dyes. When multicolor imaging is required, we recommend the following dye combinations for optimal results: Alexa Fluor 488 (green), Cy3 (red), and Cy5 or CF640 (far-red).

Production of the first effective hyperimmune equine serum antivenom against Africanized bees

Victims of massive bee attacks become extremely ill, presenting symptoms ranging from dizziness and headache to acute renal failure and multiple organ failure that can lead to death. Previous attempts to develop specific antivenom to treat these victims have been unsuccessful. We herein report a F(ab)(´)(2)-based antivenom raised in horse as a potential new treatment for victims of multiple bee stings. The final product contains high specific IgG titers and is effective in neutralizing toxic effects, such as hemolysis, cytotoxicity and myotoxicity. The assessment of neutralization was revised and hemolysis, the primary toxic effect of these stings, was fully neutralized in vivo for the first time.

A novel human Fab antibody for Trop2 inhibits breast cancer growth in vitro and in vivo

Human trophoblastic cell surface antigen 2 (Trop2) has been suggested as an oncogene, which is associated with the different types of tumors. In this study, a human Fab antibody against Trop2 extracellular domain was isolated from phage library by phage display technology, and characterized by ELISA, FACS, fluorescence staining and Western blotting analysis. MTT, apoptosis assay and wound healing assay were employed to evaluate the inhibitory effects of Trop2 Fab on breast cancer cell growth in vitro, while tumor-xenograft model was employed to evaluate the inhibitory effects on breast cancer growth in vivo. The results showed that Trop2 Fab inhibited the proliferation, induced the apoptosis and suspended the migration of MDA-MB-231 cells in a dose dependent manner. The expression caspase-3 was activated, and the expression of Bcl-2 was reduced while that of Bax was elevated in MDA-MB-231 cells by treating with Trop2 Fab. In addition, Trop2 Fab inhibited the growth of breast cancer xenografts and the expression of Bcl-2 was reduced while that of Bax was elevated in xenografts. Trop2 Fab, which was isolated successfully in this research, is a promising therapeutic agent for the treatment of Trop2 expressing breast cancer.

Time-resolved FRET -based approach for antibody detection - a new serodiagnostic concept

Förster resonance energy transfer (FRET) is a phenomenon widely utilized in biomedical research of macromolecular interactions. In FRET energy is transferred between two fluorophores, the donor and the acceptor. Herein we describe a novel approach utilizing time-resolved FRET (TR-FRET) for the detection of antibodies not only in a solution-phase homogenous assay but also in single- and two-step solid-phase assays. Our method is based on the principle that the Y-shaped immunoglobulin G molecule is able to simultaneously bind two identical antigen molecules. Hence, if a specific IgG is mixed with donor- and acceptor-labeled antigens, the binding of antigens can be measured by TR-FRET. Using donor- and acceptor-labeled streptavidins (SAs) in conjunction with a polyclonal and a monoclonal anti-SA antibody we demonstrate that this approach is fully functional. In addition we characterize the immune complexes responsible for the TR-FRET signal using density gradient ultracentrifugation and solid-phase immunoassays. The homogenous TR-FRET assay described provides a rapid and robust tool for antibody detection, with a wide potential in medical diagnostics.

Separation of antigens and antibodies by immunoaffinity chromatography

CONTEXT

Affinity chromatography is an efficient antibody, antigen and protein separation method based on the interaction between specific immobilized ligands and target antibody, antigen, and so on. Populations of available ligands can be used to separate antibodies or their Fab fragments. Similarly, antigens can be isolated by immunoaffinity chromatography (IAC) on immobilized antibodies of low affinity.

OBJECTIVE

This review describes the advantages, the applications, as well as the drawbacks, of IAC in the separation and purification of antibodies and antigens.

METHODS

The present review discussed all types of purification and isolation of antibodies and antigens by IAC, including purification of antibodies using immobilized and synthetic mimic proteins A, G and L; isolation of Fab fragments of antibodies; separation of antibodies against different antigen forms; isolation of antigens by immobilized antibodies and so on. These methods come from over 60 references compiled from all major databases.

RESULTS

Purification of antigens with antibodies should choose low-affinity antibodies to avoid denaturation of most proteins. Concern for cost and safety, prompted research activities focused on novel synthetic ligands with improved properties such as lower cost, avoidance of the risk of contamination associated with natural ligands of human or animal origin to isolate antibodies and antigens.

CONCLUSION

It is anticipated that the improvements of IAC will have impact not only on large-scale production of antibodies but also on the generation of new affinity-based methods for the increasing number of proteins and antibody derivatives available by protein engineering and the proteomics revolution.

Immunological similarity of thyroid stimulating antibody (TSAb) and thyroid blocking antibody (TBAb) with animal IgG

Previously we reported neutralization and partial purification of TSAb and TBAb activity using heterophilic antibody (Ab) to animal IgG from Graves' disease. Thus, we examined immunological similarity of TSAb and TBAb with animal IgG using experimentally generated anti-animal IgG [dog (d), bovine (b), porcine (p) and rabbit (rb)] Abs. TBII activity of TSAb- and TBAb-positive serum was neutralized by these anti-animal IgG Abs. Applied TSAb- or TBAb-IgG protein (purified by Protein A) on these anti-animal IgG Abs-bound column was found mainly in the unbound fraction (UF) (>65%) and partially in the bound fraction(BF) (<35%). The TBII and TSAb activity of TSAb-IgG in the BF showed significantly higher than the UF. Thus, the ratio of TBII activity (U/L)/mg protein in the BF/UF was high. TBII activity of TBAb-IgG was similarly purified by this column. We examined immunological characteristics of TSAb-and TBAb-Fab or F(ab')₂ using rabbit anti-bF(ab')₂ Ab. TBII and TSAb activity of TSAb-Fab or- F(ab')₂ and TBII activity of TBAb-Fab or -F(ab')₂ were neutralized by anti-bF(ab')₂ Ab. Partial purification of TSAb- or TBAb-Fab and -F(ab')₂ by anti-bF(ab')₂ Ab-bound column was also possible. Immunological similarity of TSAb- and TBAb-IgG with animal IgG such as d, b, p, rb by anti-animal IgG Ab, and TSAb- or TBAb-Fab and -F(ab')₂ with bFab by anti-bF(ab')₂ Ab were demonstrated. These fact suggest that both Fab and Fc portion of TSAb- and TBAb-IgG molecule have immunological similarity with animal IgG.

Production of antibody fragments using the baculovirus-insect cell system

The baculovirus-insect cell system is effective in the production of large quantities of biologically active recombinant proteins. The secretory production of an antibody Fab fragment in lepidopteran insect cells infected with a recombinant baculovirus that contains both the heavy-chain (Hc; Fd fragment) and light-chain (Lc) genes of the Fab fragment is described in this chapter. The recombinant baculovirus can be generated rapidly and efficiently through site-specific transposon-mediated insertion of foreign genes into a baculovirus genome called a bacmid in Escherichia coli. Factors influencing the Fab fragment production are discussed.

Human kappa light chain targeted Pseudomonas exotoxin A--identifying human antibodies and Fab fragments with favorable characteristics for antibody-drug conjugate development

Antibody-drug conjugates (ADC) represent promising agents for targeted cancer therapy. To allow rational selection of human antibodies with favorable characteristics for ADC development a screening tool was designed obviating the need of preparing individual covalently linked conjugates. Therefore, α-kappa-ETA' was designed as a fusion protein consisting of a human kappa light chain binding antibody fragment and a truncated version of Pseudomonas exotoxin A. α-kappa-ETA' specifically bound to human kappa light chains of human or human-mouse chimeric antibodies and Fab fragments. Antibody-redirected α-kappa-ETA' specifically inhibited proliferation of antigen-expressing cell lines at low toxin and antibody concentrations. Selected antibodies that efficiently delivered α-kappa-ETA' in the novel assay system were used to generate scFv-based covalently linked immunotoxins. These molecules efficiently triggered apoptosis of target cells, indicating that antibodies identified in our assay system can be converted to functional immunoconjugates. Finally, a panel of human epidermal growth factor receptor (EGFR) antibodies was screened--demonstrating favorable characteristics with antibody 2F8. These data suggest that antibodies with potential for Pseudomonas exotoxin A-based ADC development can be identified using the novel α-kappa-ETA' conjugate.

New method to produce equine antirabies immunoglobulin F(ab')₂ fragments from crude plasma in high quality and yield

Rabies is still a major cause of human deaths in several developing countries. According to the World Health Organization, administration of antirabies serum or antirabies immunoglobulin is recommended for patients who have experienced a category-III exposure to rabies. Improvement of antirabies immunoglobulin production is required to enhance safety and efficacy of the products. In this paper, a new method to produce equine antirabies immunoglobulin F(ab')(2) fragments from crude plasma is proposed. First, protein G affinity chromatography was used to purify IgG from equine plasma. Moreover, purification of IgG was shown to facilitate its digestion by pepsin. Compared to the direct digestion of crude plasma, a lower amount of pepsin and a shorter digestion time were required to completely digest the purified IgG to F(ab')(2). Complete digestion of purified IgG to F(ab')(2) was achieved at a pepsin/IgG (w/w) ratio of 5:45 with preservation of structure and potency. Finally, purification of F(ab')(2) was accomplished by a combination of protein A affinity chromatography and ultrafiltration with a 50-kDa nominal molecular weight cut-off membrane. The new process resulted in 68.9±0.6 (%) total recovery of F(ab')(2) and a F(ab')(2) product of high potency.

Production, purification, crystallization and preliminary X-ray diffraction analysis of the HIV-2-neutralizing V3 loop-specific Fab fragment 7C8

7C8 is a mouse monoclonal antibody that is specific for the third hypervariable loop (V3 loop) of the human immunodeficiency virus type 2 (HIV-2) associated protein gp125. Fab fragments of 7C8 effectively neutralize HIV-2. 7C8 was expressed and purified from a hybridoma cell line in order to establish the molecular basis underlying the specificity of the 7C8 antibody for the V3 loop as well as the specific role of the elongated third complementarity-determining region of the heavy chain (CDRH3). The antibody was digested with papain and Fab fragments were purified using size-exclusion chromatography. Hanging-drop vapour-diffusion crystallization techniques were employed and the protein was crystallized in 50 mM ammonium sulfate, 100 mM Tris-HCl pH 8.5, 25%(w/v) PEG 8000 and 2.5%(w/v) PEG 400 at 275 K. The analysed crystals belonged to the rhombohedral space group P3(2)21, with unit-cell parameters a = b = 100.1, c = 196.8 A, and diffracted to 2.7 A resolution.

Unique antigenic determinants (idiotypes) used as markers in a patient with macroglobulinemia and urticaria. Similar idiotypes demonstrated in the skin and on peripheral blood lymphocytes

An antiserum was raised against a monoclonal IgMk macroglobulin isolated from serum of a patient with recurrent urticaria. The antiserum was made idiotype-specific through adequate absorptions. The anti-idiotype antiserum reacted only with the immunizing protein and its Fab fragments and not with other monoclonal proteins of IgM and IgA class or pooled IgG as assayed in an enzyme-linked immunosorbent assay. IgM antibodies with the same idiotype as the monoclonal IgM protein were detected in the dermal/epidermal junction area of diseased skin. The similar idiotypic determinants could also be demonstrated on membrane-bound molecules of peripheral blood B and T lymphocytes using the immunofluorescence methods.

Guided selection methods through chain shuffling

We provide procedures for the panning of fully humanized Fab antibodies using guided selection. Human heavy and light chain genes are amplified. A parental light chain is cloned into a phage display vector and combined with the heavy chain library. After several rounds of panning, positive clones are identified and the heavy chain sequences that are recovered are combined with light chains for further selection by phage display. Human Fab antibodies are obtained that bind the same epitope as the parental antibody.

[Three-step purification of preparative-scale antiCD20 (Fab')2]

OBJECTIVE

To establish a three-step purification method of preparative-scale antiCD20 (Fab')2 using AKTA prime.

METHODS

AntiCD20 (Fab')2 was extracted by hyperosmotic solution and then purified by CM sepharose FF, phenyl sepharose FF, and protein G sepharose FF.

RESULTS

Around 8 mg anti-CD20 (Fab')2, whose purification was 96.678%, was purified. The antigen-binding activity of antiCD20 (Fab')2 was similar to that of antiCD20 (Fab')2 purified by protein G sepharose FF and S-100.

CONCLUSION

The three-step purification method can obtain high-purity preparative-scale antiCD20 (Fab')2 in a simple way.

A novel system to test for specificity of B cell receptors from tissue of Wegener's granulomatosis patients

OBJECTIVE

Wegener's granulomatosis (WG) is characterized by granulomatous inflammation of the respiratory tract and Anti Neutrophil Cytoplasmic Antibody (ANCA)-associated systemic vasculitis. The pathognomonic ANCA in WG is typically directed against proteinase 3 (PR3). Germinal centre-like clusters of lymphocytes were seen in granulomata of WG patients suggesting an antigen-driven maturation of B lymphocytes potentially leading to ANCA formation. The goal of this study was to develop a system to determine the specificity of B cells found in WG granulomata via the generation of fab fragments as antibody analogues. These fab fragments have the identical antigen binding site like the B-cell receptor from which the DNA was derived.

METHODS

Single B cells were isolated from B cell clusters within the granuloma of a WG patient by laser-assisted microdissection. Their immunoglobulin genes (VH/Vkappa, VH/Vlambda) were characterized by seminested single cell PCR and cloned into a phagemid vector in order to produce fab fragments. The fabs were characterized by protein gel electrophoresis and western blot.

RESULTS

The immunoglobulin genes from lymphocyte infiltrates of WG granulomata reveal antigen-driven selection. On the basis of two individual couples of mutated VH/Vlambda PCR products functional fabs were generated that represent the B cell receptors of WG tissue-derived single B cells.

CONCLUSION

This is the first in vitro model to test for specificity of B cell receptors from WG granulomata. With respect to ANCA origin in WG this system provides a tool to elucidate the structure-function relationship of apparently antigen-driven maturation of B cells within Wegener's granuloma.

Characterization and crystallization of a recombinant IgE Fab fragment in complex with the bovine beta-lactoglobulin allergen

A D1 Fab fragment containing the allergen-binding variable domains of the IgE antibody was characterized by ESI FT-ICR mass spectrometry and crystallized with bovine beta-lactoglobulin (BLG) using the hanging-drop vapour-diffusion method at 293 K. X-ray data suitable for structure determination were collected to 2.8 A resolution using synchrotron radiation. The crystal belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 67.0, b = 100.6, c = 168.1 A. The three-dimensional structure of the D1 Fab fragment-BLG complex will provide the first insight into IgE antibody-allergen interactions at the molecular level.

Production of a recombinant antibody fragment in whole insect larvae

Infection of insect cells with baculovirus expression constructs is commonly used to produce recombinant proteins that require post-translational modifications for their activity, such as mammalian proteins. However, technical restraints limit the capacity of insect cell-based culture systems to be scaled up to produce the large amounts of recombinant protein required for human pharmaceuticals. In this study, we designed an automated insect rearing system and whole insect baculovirus expression system (PERLXpress) for the expression and purification of recombinant proteins on a large scale. As a test model, we produced a recombinant mouse anti-botulinum antibody fragment (Fab) in Trichoplusia ni larvae. A recombinant baculovirus co-expressing the Fab heavy and light chains together with N-terminal sequences from the silkworm hormone bombyxin, to direct proteins into the secretory pathway, was constructed. Fifth instar larvae were reared and infected orally with recombinant (pre- occluded) baculovirus using the automated system and harvested approximately after 4 days. The total yield of recombinant Fab was 1.1 g/kg of larvae, resulting in 127 mg of pure Fab in one production run. The Fab was purified to homogeneity using immobilized metal affinity chromatography, gel filtration, and anion exchange chromatography. The identity of the purified protein was verified by Western blots and size-exclusion chromatography. Purified recombinant Fab was used to detect botulinum toxin in ELISA experiments, demonstrating that the heavy and light chains were properly assembled and folded into functional heterodimers. We believe that this is the first demonstration of the expression of a recombinant antibody in whole insect larvae. Our results demonstrate that a baculovirus-whole larvae expression system can be used to express functionally active recombinant Fab fragments. As the PERLXpress system is an automated and linearly scalable technology, it represents an attractive alternative to insect cell culture for the production of large amounts of human pharmaceuticals.

Construction of human Fab (gamma1/kappa) library and identification of human monoclonal Fab possessing neutralizing potency against Japanese encephalitis virus

A combinatorial human Fab library was constructed using RNAs from peripheral blood lymphocytes obtained from Japanese encephalitis virus hyper-immune volunteers on pComb3H phagemid vector. The size of the constructed Fab library was 3.3x10(8) Escherichia coli transformants. The library was panned 3 times on the purified Japanese encephalitis virus (JEV) virion, and phage clones displaying JEV antigen-specific Fab were enriched. The enriched phage pool was then screened for clones producing Fab molecule with JEV neutralizing activity by the focus reduction-neutralizing test. Among 188 randomly selected clones, 9 Fab preparations revealed neutralizing activities against JEV strain Nakayama. An E. coli transformed with TJE12B02 clone, which produced human monoclonal Fab with the highest neutralizing activity was cultured in a large scale, and the Fab molecule was purified using affinity chromatography. The purified FabTJE12B02 showed the 50% focus reduction endpoint at the concentration of 50.2 microg/ml (ca. 1,000 nM) when JEV strain Nakayama was used. The FabTJE12B02 recognized E protein of JEV strain Nakayama, and the dissociation equilibrium constant (Kd) of the FabTJE12B02 against purified JEV antigen was calculated as 1.21x10(-8) M. Sequence analysis demonstrated that TJE12B02 used a VH sequence homologous to the VH3 family showing 88.8% homology to germline VH3-23, and used a Vkappa sequence homologous to the VkappaII subgroup showing 92.8% homology to germline A17.

Evolution of endotoxin contamination during production of a therapeutic serum

A comparative bench-scale study of endotoxin contamination is presented for two common processes of immunoglobulin purification from equine plasma: ammonium sulphate fractionation of F(ab')2 fragments and caprylic acid precipitation of non-IgG proteins. To this end, both processes were carried out under normal sterile conditions, using sanitized material and equipment and optimal water quality in a clean but open environment. Stream samples, taken at different stages from each process, were analyzed for endotoxin content by the Limulus Amebocyte Lysate (LAL) test. It was found that exogenous contamination preferentially came from endotoxins already present in reagents and/or raw materials, whereas contamination from the environment was minimal. Endogenous endotoxin accumulation, concomitant with the concentration of proteins during processing, was found to be an important factor. With classic technology, blood extraction and sterilizing filtration are critical points for both processes. It is concluded that sterility is not a sufficient condition to obtain an endotoxin-free product. Only with proper sanitization of material, and by applying the caprylic acid purification process with a starting plasma below 4-5 EU/mL, would it be possible to achieve a final product within the norm.

Characterization of chimpanzee/human monoclonal antibodies to vaccinia virus A33 glycoprotein and its variola virus homolog in vitro and in a vaccinia virus mouse protection model

Three distinct chimpanzee Fabs against the A33 envelope glycoprotein of vaccinia virus were isolated and converted into complete monoclonal antibodies (MAbs) with human gamma 1 heavy-chain constant regions. The three MAbs (6C, 12C, and 12F) displayed high binding affinities to A33 (K(d) of 0.14 nM to 20 nM) and may recognize the same epitope, which was determined to be conformational and located within amino acid residues 99 to 185 at the C terminus of A33. One or more of the MAbs were shown to reduce the spread of vaccinia virus as well as variola virus (the causative agent of smallpox) in vitro and to more effectively protect mice when administered before or 2 days after intranasal challenge with virulent vaccinia virus than a previously isolated mouse anti-A33 MAb (1G10) or vaccinia virus immunoglobulin. The protective efficacy afforded by anti-A33 MAb was comparable to that of a previously isolated chimpanzee/human anti-B5 MAb. The combination of anti-A33 MAb and anti-B5 MAb did not synergize the protective efficacy. These chimpanzee/human anti-A33 MAbs may be useful in the prevention and treatment of vaccinia virus-induced complications of vaccination against smallpox and may also be effective in the immunoprophylaxis and immunotherapy of smallpox and other orthopoxvirus diseases.

Automated high-throughput purification of antibody fragments to facilitate evaluation in functional and kinetic based assays

Screening antibodies from phage displayed in vitro libraries and from affinity maturation of lead antibodies requires testing of antibody fragments (scFvs and Fabs) for function and binding affinities. Crude scFv or Fab periplasmic preparations from Escherichia coli are often not pure and/or concentrated enough for use in functional and affinity assays. We have developed an automated high-throughput approach for small and large-scale expression and purification of His-tagged scFvs and Fabs using the Qiagen BioRobot 3000 LS with optimized application software. This automated procedure enabled us to rapidly evaluate antibody fragments in functional and surface plasmon resonance (SPR) assays. We have used these procedures to make thousands of purified scFv/Fabs for several antibody maturation campaigns and significantly decreased the time needed to select the best candidates. The assay results from these purified samples were used to prioritize candidates before converting them to IgG. This protocol can process up to 300 small-scale and up to 72 large-scale scFvs or Fabs per week per full-time employee (FTE).

Ion exchange chromatography of antibody fragments

Effects of pH and conductivity on the ion exchange chromatographic purification of an antigen-binding antibody fragment (Fab) of pI 8.0 were investigated. Normal sulfopropyl (SP) group modified agarose particles (SP Sepharosetrade mark Fast Flow) and dextran modified particles (SP Sepharose XL) were studied. Chromatographic measurements including adsorption isotherms and dynamic breakthrough binding capacities, were complemented with laser scanning confocal microscopy. As expected static equilibrium and dynamic binding capacities were generally reduced by increasing mobile phase conductivity (1-25 mS/cm). However at pH 4 on SP Sepharose XL, Fab dynamic binding capacity increased from 130 to 160 (mg/mL media) as mobile phase conductivity changed from 1 to 5 mS/cm. Decreasing protein net charge by increasing pH from 4 to 5 at 1.3 mS/cm caused dynamic binding capacity to increase from 130 to 180 mg/mL. Confocal scanning laser microscopy studies indicate such increases were due to faster intra-particle mass transport and hence greater utilization of the media's available binding capacity. Such results are in agreement with recent studies related to ion exchange of whole antibody molecules under similar conditions.

Characterisation of an industrial affinity process used in the manufacturing of digoxin-specific polyclonal Fab fragments

This paper describes the effect of several variables on the affinity process for the production of the FDA approved biotherapeutic product Digoxin Immune Fab (Ovine) (DigiFab, Protherics Inc., TN, USA). The study considers the effects of column re-use on matrix capacity and on the subsequent recovery of the antibody product, and the impact of varying column loading on matrix performance. The methodology used could be equally applied to assess the feasibility of using an affinity matrix for commercial scale purification of alternative antibody derived biotherapeutics. The capacity and specific Fab recovery were calculated through 24h equilibrium and mass balance studies. Results were assessed against data obtained through confocal scanning laser microscopy. Scale-down experiments produced specific Fab recoveries and purities that were comparable with those at production scale. The matrix capacity was found to be 45+/-15 mg of Fab/ml of matrix. Through the use of fluorescent DigiFab and confocal scanning techniques, Fab uptake onto single affinity bead was evaluated. Average intensity values calculated for each sample provided direct real-time, measure of Fab binding and matrix capacity. The results suggest that the affinity matrix had a limited reuse life as a drop in recovery is observed following the completion of a small number of process cycles (30% after three runs). The findings support that which is seen at the current manufacturing scale, where the affinity column is used for a limited number of runs. Results from this study can be used as a basis for future optimisation of this purification process.

Stable Supply of Large Amounts of Human Fab from the Inclusion Bodies in E. coli

Recombinant human Fab-H chain and L chain were separately expressed as inclusion body using Escherichia coli. After solubilization of Fab-H chain and L chain by the reduction and S-alkyldisulphidation in 8 M urea, about 100 mg of purified Fab-H chain and about 160 mg of L chain could be obtained from 1 l of each culture by ion-exchange chromatogram in the presence of 8 M urea. Combination of the lyophilized Fab-H chain and L chain could be efficiently folded to native human Fab by using the stepwise dialysis method and the human Fab was purified with cation-exchange chromatogram. In the folding procedure, it was found that cysteamine and cystamine with positive charge were effective to improve the folding yield of human Fab. Moreover, from comparison of folding yield in the presence of ten kinds of additives, it was suggested that taurine was effective to improve the folding of human Fab. Consequently, we could obtain about 60 mg of folded human Fab from 1 l of each culture under the optimum conditions.

High level expression of a promising anti-idiotypic antibody fragment vaccine against HIV-1 in Pichia pastoris

We have expressed the anti-idiotypic antibody 3H6 Fab directed against the HIV-1 broadly neutralising antibody 2F5 in methylotrophic yeast Pichia pastoris. The chimeric human/mouse Fab fragment was expressed under control of the inducible AOX1 promoter and secreted via the alpha mating factor leader of Saccharomyces cerevisiae. Bioreactor experiments showed the ability of the recombinant P. pastoris clone to secrete up to 260 mg/L Fab fragment in the culture supernatant during a five days cultivation time. Codon optimisation of the Fab expression cassette gave no further improvement of specific productivity when comparing 12 clones of each construct. The subsequent purification of Fab containing supernatants was done by anion exchange and size-exclusion chromatography with a recovery resulting in 70% of the recombinant protein. For verification of the suitability of the expression system we characterised the expressed protein with respect to both, its specificity and binding affinity and could not detect any significant difference between products from yeast derived and the hybridoma derived product. Finally we tested the implicit requirement of the carbohydrate moiety in the H2 loop of the original 3H6 antibody by introducing an asparagine to alanine replacement and, in a second experiment, inhibition of N-glycosylation by tunicamycin treatment. Biochemical analysis confirmed that the N-glycosylation does not contribute to the binding properties of 3H6.

[Anti-rabies immunoglobulin preparation based on F(ab')2 fragments]

Technology of manufacturing of new anti-rabies immunoglobulin preparation based on F(ab')2 fragments has been developed. This preparation is characterized by low reactogenicity, increased virus-neutralizing activity and stability.

Human neutralizing Fab molecules against severe acute respiratory syndrome coronavirus generated by phage display

Human recombinant Fab fragments specific for the spike protein of severe acute respiratory syndrome coronavirus (SARS-CoV) were screened from a human Fab library, which was generated from RNAs from peripheral lymphocytes of convalescent SARS patients. Among 50 randomly picked clones, 12 Fabs specially reacted with S protein by an enzyme-linked immunosorbent assay. The microneutralizing test showed that one clone, designated M1A, had neutralizing activity on Vero E6 cells against SARS-CoV. DNA sequence analysis indicated that the light- and heavy-chain genes of M1A Fab belong to the kappa2a and 4f families, respectively. A neutralizing test on purified M1A demonstrated that 0.5 mg/ml of M1A completely inhibited SARS-CoV activity, with an absence of cytopathic effect for 7 days. Real-time fluorescence reverse transcription-PCR also proved the neutralizing capacity of M1A. These data showed that the number of virus copies was significantly reduced in the M1A-treated group, suggesting an important role for M1A in passive immunoprophylaxis against the SARS virus.

Comparison Between Therapeutic Antitoxin F(ab)2Fractionated with Ammonium Sulfate and Caprylic Acid

To date, animal derived therapeutic antibodies represent the best and only choice source of antitoxins, especially in developing countries. Furthermore, this industry needs to develop a production protocol to achieve safer products. Recently, several laboratories changed their production protocol from ammonium sulfate (AS) protocol to caprylic acid (CA) fractionation. Our results showed that using the CA protocol leads to improvement in the product quality, as assessed by the albumin and protein content decrease (from 4.75 to 3.54 g/dL and 0.64 to 0.18 g/dL, respectively), which yielded a purer antitoxin product. The F(ab)2 protein aggregate formation and turbidity have been significantly reduced, 4.60 versus 2.55 and 0.046 versus 0.021 (p < 0.01), respectively. However, the anti-complementary activity was also reduced, from 42 to 33. The total IgG content was higher in CA fractionated products than AS materials. The endotoxin content was worrisome in some F(ab)2 products.

Cloning of idiotype immunoglobulin genes in B cell lymphomas by anchored PCR and production of individual recombinant idiotype vaccines in Escherichia coli

OBJECTIVES

Individual immunoglobulins expressed by B-cell lymphomas represent tumor-specific antigens ('idiotypes'). Immunization with idiotype in follicular lymphoma patients may induce specific immune responses, sustained progression-free survival, and disappearance of minimal residual disease. Manufacturing of idiotype vaccines has mostly relied on heterohybridomas established from viable lymphoma cells. This paper describes the feasibility of production of GMP-grade idiotype vaccines as recombinant Fab fragments in Escherichia coli.

METHODS

IgH and IgL transcripts were analyzed by anchored PCR from 106 lymphoma and nine control biopsies. Lymphoma-derived V segments were inserted into prokaryotic expression plasmids. Recombinant idiotype Fab fragments were expressed in E. coli in a fermentation system.

RESULTS

Idiotype IgH and IgL transcripts were identified in 95% of 106 lymphoma biopsies according to stringent clonality criteria. Large-scale idiotype expression was successful in 69 of 78 cases (89%) and yielded a median of 17 mg (range: 1.2-250 mg) recombinant Fab protein. After affinity chromatography, median vaccine purity was 99% heterodimeric Fab protein (range: 72-100%). Bacterial protein contamination was detectable in one vaccine only. Fab proteins with IgL lambda chains had a tendency for inferior yield and lesser purity than kappa-type Fabs. Among other structural idiotype features (isotype, V family usage, somatic hypermutation pattern, novel glycosylation sites, CDR III net charge), no consistent influences on Fab yield or purity were detected.

CONCLUSIONS

Anchored PCR cloning and subsequent protein expression in E. coli provides a reliable technological basis for clinical idiotype vaccination trials.

Identification of human scFvs targeting atherosclerotic lesions: selection by single round in vivo phage display

Our aim was to investigate by in vivo biopanning the lesions developed early in atherosclerosis and identify human antibodies that home to diseased regions. We have designed a two-step approach for a rapid isolation of human Monoclonal phage-display single-chain antibodies (MoPhabs) reactive with proteins found in lesions developed in an animal model of atherosclerosis. After a single round of in vivo biopanning, the MoPhabs were eluted from diseased sections of rabbit aorta identified by histology and NMR microscopy. MoPhabs expressed in situ were selected by subtractive colony filter screening for their capacity to recognize atherosclerotic but not normal aorta. MoPhabs selected by our method predominantly bind atherosclerotic lesions. Two of them, B3.3G and B3.GER, produced as scFv fragments, recognized an epitope present on the surface in early atherosclerotic lesions and within the intimal thickness in more complex plaques. These human MoPhabs homed to atherosclerotic lesions in ApoE(-/-) mice after in vivo injection. A protein of approximately 56 kDa recognized by B3.3G was affinity-purified and identified by mass spectrometry analysis as vitronectin. This is the first time that single round in vivo biopanning has been used to select human antibodies as candidates for diagnostic imaging and for obtaining insight into targets displayed in atherosclerotic plaques.

Growth inhibition of breast cancer cell lines overexpressing Her2/neu by a novel internalized fully human Fab antibody fragment

The Her2/neu oncogene is overexpressed in various human cancers of epithelial origin and is associated with increased metastatic potential and poor prognosis. Blocking the Her2/neu signalling has been the focus of most therapeutic approaches. In this paper, the Her2/neu extracellular domain expressed in soluble form in yeast Pichia pastoris was used in order to isolate a fully human Fab fragment from a combinatorial Fab phage display library, derived from invaded lymph nodes of a breast cancer patient. The isolated fully human Fab63 binds specifically the native Her2/neu receptor and competes with Herceptin for binding to soluble Her2/neu receptor. In Her2/neu overexpressing cancer cells, Fab63 is rapidly internalized and has significant antiproliferative effects, where ligand-independent mechanisms dominate signal induction. Moreover, in the presence of the ligand heregulin, growth inhibition was also detected by Fab63. The human Fab63 is a non-immunogenic agent with unique properties that can be applied in diagnosis and cancer therapy, with great potential for further manipulation towards the generation of an effective anticancer molecule.

Rapid isolation of single-chain antibodies for structural genomics

High throughput approaches to structural genomics requires expression, purification, and crystallization of proteins derived from predicted open reading frames cloned into a host organism, typically E. coli. Early results from this approach suggest that the success rate of obtaining well diffracting crystals from eukaryotic proteins is disappointingly low. A proven method of improving the odds of crystallization is formation of a complex with a conformation-stabilizing partner of known structure that is easily crystallized. Such complexes are also able to engage in different crystal contacts than the original protein by itself. Fab fragments derived from monoclonal antibodies have been successfully used for this purpose for a variety of proteins, however conventional methods for the isolation of monoclonal antibodies from hybridomas are time consuming and expensive. We are exploring the use of phage display to generate recombinant antibodies to target proteins that can be used to obtain co-complexes to facilitate crystallization and structural determination. We are using a large, human single-chain Fv (scFv) library to select for antibodies that bind to a panel of Leishmania major target proteins. Thirteen out of 16 target proteins yielded good binders after three rounds of enrichment. A total of 55 distinct scFvs were identified, with five targets each yielding at least five different scFvs. Individual clones were analyzed for binding specificity and soluble scFv can be readily produced and purified via the appended His(6) epitope tag. Using immunoaffinity chromatography, eight scFv target protein pairs were identified that exhibit stable complex formation and are suitable for co-crystallization trials.

Antibody variable region interactions with Protein A: implications for the development of generic purification processes

In this paper, a wide range of antibodies from various subclasses and subfamilies are employed to evaluate the creation of generic separation processes using Protein A chromatography. The reasons for elution pH differences amongst several IgG1s, IgG2s, antibody fragments, and Fc-fusion proteins during Protein A chromatography are investigated using several complimentary techniques. The results indicate that variable region interactions play a major role in determining elution pH for VH3 subfamily antibodies while using traditional protein A chromatographic materials. On the other hand, experiments with a resin which employs a ligand consisting solely of B domain of Protein A indicate that variable region interactions can be mitigated, enabling the use of a single elution pH for a range of antibodies. Finally, the moderation of elution conditions associated with this engineered ligand are shown to minimize problems associated with low pH induced aggregation. It is expected that the findings reported in this paper will facilitate faster process development cycle times for this important class of human therapeutics.

Transiently binding antibody fragments against Lewis x and sialyl-Lewis x

Biomolecular recognition is often characterised by low affinity where many weak interactions work either alone or in concert, resulting in an inherent dynamic situation. For example the well-studied weak binding of cell-cell interactions is predominantly based on a range of carbohydrates that interact with numerous (protein) ligands. Finding appropriate binders to these carbohydrate structures may pave the way for new analytical strategies based on low affinity, and recombinant antibody technology is a promising approach to the development of such reagents. We have in the present study characterised two low affinity human single chain antibody fragments (scFv) by surface plasmon resonance for use in such applications. The two clones, LeX1 and sLeX10, had been selected from a naive phage display library against Lewis x (Le(x)) and sialyl Le(x) (sLe(x)), respectively. Both LeX1 and sLeX10 showed low affinity, with K(D) values of 3.5+/-0.7 x 10(-5) M for Le(x) and 2.6+/-0.7 x 10(-5) M for sLe(x), respectively. Kinetic studies revealed the scFvs to be associated with fast dissociation rates, with Kd values higher than 0.1 s(-1) for both LeX1 and sLeX10. Apart from the Lewis structures Le(x) and sLe(x), we investigated the conformational isomers Lewis a and sialyl-Lewis a together with the monosaccharide units of the Lewis structures, and both scFvs showed high specificity for their respective carbohydrate. Taking these observations together we have demonstrated that scFv with fast reaction kinetics and low affinity have the necessary characteristics for further development as specific tools in analytical strategies, e.g. differentiation of cells based on the various configurations of carbohydrate epitopes.

Engineering stability into Escherichia coli secreted Fabs leads to increased functional expression

The recombinant expression of immunoglobulin domains, Fabs and scFvs in particular, in Escherichia coli can vary significantly from antibody to antibody. We hypothesized that poor Fab expression is often linked to poor intrinsic stability. To investigate this further, we applied a novel approach for stabilizing a poorly expressing anti-tetanus toxoid human Fab with a predisposition for being misfolded and non-functional. Forty-five residues within the Fab were chosen for saturation mutagenesis based on residue frequency analysis and positional entropy calculations. Using automated screening, we determined the approximate midpoint temperature of thermal denaturation (TM) for over 4000 library members with a maximum theoretical diversity of 855 unique mutations. This dataset led to the identification of 11 residue positions, primarily in the Fv region, which when mutated enhanced Fab stability. By combining these mutations, the TM of the Fab was increased to 92 degrees C. Increases in Fab stability correlated with higher expressed Fab yields and higher levels of properly folded and functional protein. The mutations were selected based on their ability to increase the apparent stability of the Fab and therefore the exact mechanism behind the enhanced expression in E.coli remains undefined. The wild-type and two optimized Fabs were converted to an IgG1 format and expressed in mammalian cells. The optimized IgG1 molecules demonstrated identical gains in thermostability compared to the Fabs; however, the expression levels were unaffected suggesting that the eukaryotic secretion system is capable of correcting potential folding issues prevalent in E.coli. Overall, the results have significant implications for the bacterial expression of functional antibody domains as well as for the production of stable, high affinity therapeutic antibodies in mammalian cells.

[Adsorption condition optimization for anti-HBsAg Fab fragment separation and purification from E. coli using Streamline SP]

OBJECTIVE

To optimize the adsorption condition of cation-exchange chromatographic media Streamline SP for separation and purification of anti-HBsAg Fab fragment from E. coli.

METHODS

The adsorption of the target protein for separation and purification by the cation-exchange chromatographic media Streamline SP was tested using test tube method in balanced buffer solution with different pH values and ion concentrations. The adsorption effect was then verified by cation-exchange chromatography using 1-ml Streamline SP prepacked column and 28-ml Streamline SP self-assembly column.

RESULTS

According to the experiment results of test tube method, the loading buffer with pH of 4.4 and ionic concentration of 100 to 600 mmol/L could achieve optimal target protein adsorption effect by cation-exchange chromatographic media Streamline SP, as verified by cation-exchange chromatography with 1-ml SP prepacked column and 28-ml Streamline SP self-assembly column.

CONCLUSION

The optimal condition of cation-exchange chromatography selected by test tube method can be applied for separation and purification of anti-HBsAg Fab fragment from E. coli.

Structural insights into AChE inhibition by monoclonal antibodies

The target sites of three inhibitory monoclonal antibodies, Elec403, 408 and 410, on eel AChE have been defined previously. Elec403 and 410 are directed toward distinct but overlapping epitopes at the enzyme peripheral site, while Elec408 binds to a distinct regulatory site on the enzyme surface, where the "back door" may be located. Elec410 also inhibits Bunganus fasciatus AChE. To investigate the molecular determinants for AChE inhibition by these antibodies, we have cloned and sequenced the IgGs, generated, purified, characterized the Fab molecules, and initiated crystallographic and theoretical modeling studies. Preliminary data are presented.

High-throughput affinity ranking of antibodies using surface plasmon resonance microarrays

A method was developed to rapidly identify high-affinity human antibodies from phage display library selection outputs. It combines high-throughput Fab fragment expression and purification with surface plasmon resonance (SPR) microarrays to determine kinetic constants (kon and koff) for 96 different Fab fragments in a single experiment. Fabs against human tissue kallikrein 1 (hK1, KLK1 gene product) were discovered by phage display, expressed in Escherichia coli in batches of 96, and purified using protein A PhyTip columns. Kinetic constants were obtained for 191 unique anti-hK1 Fabs using the Flexchip SPR microarray device. The highest affinity Fabs discovered had dissociation constants of less than 1 nM. The described SPR method was also used to categorize Fabs according to their ability to recognize an apparent active site epitope. The ability to rapidly determine the affinities of hundreds of antibodies significantly accelerates the discovery of high-affinity antibody leads.

Site-specific conjugation of bifunctional chelator BAT to mouse IgG1 Fab' fragment

AIM

To perform a site-specific conjugation of Fab' fragments of a mouse monoclonal antibody(MoAb) B43(of IgG1 subtype) to a bifunctional chelator 6-[p-(bromoacetamido)benzyl]-1,4,8,11-tetraazacyclotetradecane-N,N',N' 'N' ' '-tetraacetic acid (BAT) via the thiol groups in the hinge distal to the antigen-binding site of the Fab'.

METHODS

B43 was cleaved using a simple 2-step method. First, stable F(ab')(2) was produced by pepsin treatment. Fab' with free thiol in the hinge region was then obtained by cysteine reduction of F(ab')2. Second, a site-specific conjugation of Fab' to thiol-specific BAT was performed in a one-step reaction.

RESULTS

The Fab' fragment had approximately 1.8 free thiol groups per molecule after cysteine reduction. The conjugation efficiency and the chemical yield were approximately 1.28 moles chelator/Fab' and 74% of the initial concentration of Fab', respectively. The F(ab')2, Fab' and Fab'-BAT all maintained reasonable antigen-binding properties. (67)Cu labeling of the conjugate under standard conditions did not impair the immunoreactivity of Fab'-BAT.

CONCLUSION

This is a simple and efficient method for producing immunoreactive conjugates of Fab'-BAT, which can be used to make radiometal-labeled conjugates for further diagnostic and therapeutic applications.

Chimpanzee/human mAbs to vaccinia virus B5 protein neutralize vaccinia and smallpox viruses and protect mice against vaccinia virus

Chimpanzee Fabs against the B5 envelope glycoprotein of vaccinia virus were isolated and converted into complete mAbs with human gamma 1 heavy chain constant regions. The two mAbs (8AH8AL and 8AH7AL) displayed high binding affinities to B5 (Kd of 0.2 and 0.7 nM). The mAb 8AH8AL inhibited the spread of vaccinia virus as well as variola virus (the causative agent of smallpox) in vitro, protected mice from subsequent intranasal challenge with virulent vaccinia virus, protected mice when administered 2 days after challenge, and provided significantly greater protection than that afforded by a previously isolated rat anti-B5 mAb (19C2) or by vaccinia immune globulin. The mAb bound to a conformational epitope between amino acids 20 and 130 of B5. These chimpanzee/human anti-B5 mAbs may be useful in the prevention and treatment of vaccinia virus-induced complications of vaccination against smallpox and may also be effective in the immunoprophylaxis and immunotherapy of smallpox.