Effect of three elution buffers on the recovery and structure of monoclonal antibodies

Purification of antibody fragments via interaction with detergent micellar aggregates

The research described in this report seeks to present proof-of-concept for a novel and robust platform for purification of antibody fragments and to define and optimize the controlling parameters. Purification of antigen-binding F(ab')₂ fragments is achieved in the absence of chromatographic media or specific ligands, rather by using clusters of non-ionic detergent (e.g. Tween-60, Brij-O20) micelles chelated via Fe²⁺ ions and the hydrophobic chelator, bathophenanthroline (batho). These aggregates, quantitatively capture the F(ab')₂ fragment in the absence or presence of E. coli lysate and allow extraction of only the F(ab')₂ domain at pH 3.8 without concomitant aggregate dissolution or coextraction of bacterial impurities. Process yields range from 70 to 87% by densitometry. Recovered F(ab')₂ fragments are monomeric (by dynamic light scattering), preserve their secondary structure (by circular dichroism) and are as pure as those obtained via Protein A chromatography (from a mixture of F(ab')₂ and Fc fragments). The effect of process parameters on Ab binding and Ab extraction (e.g. temperature, pH, ionic strength, incubation time, composition of extraction buffer) are reported, using a monoclonal antibody (mAb) and polyclonal human IgG's as test samples.

Mass Cytometry, Imaging Mass Cytometry, and Multiplexed Ion Beam Imaging Use in a Clinical Setting

Mass cytometry (MC), imaging mass cytometry (IMC), and multiplexed ion beam imaging (MIBI) represent a new generation of tools to understand increasingly complex systems. Although these technologies differ in their intended applications, with MC being most similar to flow cytometry, and IMC/MIBI being similar to immunohistochemistry, they all share a time of flight mass spectrometry (TOF MS) platform. These TOF MS platforms use metal conjugated antibodies as opposed to fluorophores, increasing the measurable parameters up to approximately 50 with a theoretic limit approximately 100 parameters. These tools are being adapted to understand highly complex systems in basic and clinical research.

A manual multiplex immunofluorescence method for investigating neurodegenerative diseases

BACKGROUND

Neurodegenerative diseases feature stereotypical deposits of protein aggregates that selectively accumulate in vulnerable cells. The ability to simultaneously localize multiple targets in situ is critical to facilitate discovery and validation of pathogenic molecular pathways. Immunostaining methods enable in situ detection of specific targets. Effective stripping of antibodies, allowing successive rounds of staining while maintaining tissue adhesion and antigen integrity, is the main roadblock for enabling multiplex immunostaining in standard labs. Furthermore, stripping techniques require antibody-specific optimization, validation, and quality control steps.

NEW METHOD

Aiming to create protocols for multiplex localization of neurodegenerative-related processes, without the need for specialized equipment, we evaluated several antibody stripping techniques. We also recommend quality control steps to validate stripping efficacy and ameliorate concerns of cross-reactivity and false positives based on extensive testing.

RESULTS

A protocol using β-mercaptoethanol and SDS consistently enables reliable antibody stripping across multiple rounds of staining and minimizes the odds of cross-reactivity while preserving tissue adhesion and antigen integrity in human postmortem tissue.

COMPARISON WITH EXISTING METHODS

Our proposed method is optimal for standard lab settings and shows consistent efficacy despite the intricacies of suboptimal human postmortem tissue and the need to strip markers bound to highly aggregated proteins. Additionally, it incorporates quality control steps to validate antibody stripping.

CONCLUSIONS

Multiplex immunofluorescence methods for studying neurodegenerative diseases in human postmortem tissue are feasible even in standard laboratories. Nevertheless, evaluation of stripping parameters during optimization and validation phases of experiments is prudent.

A general platform for antibody purification utilizing engineered-micelles

We introduce a new concept and potentially general platform for antibody (Ab) purification that does not rely on chromatography or specific ligands (e.g., Protein A); rather, it makes use of detergent aggregates capable of efficiently capturing Ab while rejecting hydrophilic impurities. Captured Ab are then extracted from the aggregates in pure form without co-extraction of hydrophobic impurities or aggregate dissolution. The aggregates studied consist of conjugated "Engineered-micelles" built from the nonionic detergent, Tween-20; bathophenanthroline, a hydrophobic metal chelator, and Fe²⁺ions. When tested in serum-free media with or without bovine serum albumin as additive, human or mouse IgGs were recovered with good overall yields (70-80%, by densitometry). Extraction of IgGs with 7 different buffers at pH 3.8 sheds light on possible interactions between captured Ab and their surrounding detergent matrix that lead to purity very similar to that obtained via Protein A or Protein G resins. Extracted Ab preserve their secondary structure, specificity and monomeric character as determined by circular dichroism, enzyme-linked immunosorbent assay and dynamic light scattering, respectively.

Multiplex Staining by Sequential Immunostaining and Antibody Removal on Routine Tissue Sections

Multiplexing, labeling for multiple immunostains in the very same cell or tissue section in situ, has raised considerable interest. The methods proposed include the use of labeled primary antibodies, spectral separation of fluorochromes, bleaching of the fluorophores or chromogens, blocking of previous antibody layers, all in various combinations. The major obstacles to the diffusion of this technique are high costs in custom antibodies and instruments, low throughput, and scarcity of specialized skills or facilities. We have validated a method based on common primary and secondary antibodies and diffusely available fluorescent image scanners. It entails rounds of four-color indirect immunofluorescence, image acquisition, and removal (stripping) of the antibodies, before another stain is applied. The images are digitally registered and the autofluorescence is subtracted. Removal of antibodies is accomplished by disulfide cleavage and a detergent or by a chaotropic salt treatment, this latter followed by antigen refolding. More than 30 different antibody stains can be applied to one single section from routinely fixed and embedded tissue. This method requires a modest investment in hardware and materials and uses freeware image analysis software. Multiplexing on routine tissue sections is a high throughput tool for in situ characterization of neoplastic, reactive, inflammatory, and normal cells.

Immunoaffinity Chromatography: Concepts and Applications

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. Immunoaffinity chromatography is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimization of critical experimental parameters such as (a) the biological affinity pair, (b) the matrix support, (c) the immobilization coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in immunoaffinity chromatography and also provides specific examples of their potential applications.

Immunoaffinity chromatography

Antibody-based separation methods, such as immunoaffinity chromatography (IAC), are powerful purification and isolation techniques. Antibodies isolated using these techniques have proven highly efficient in applications ranging from clinical diagnostics to environmental monitoring. IAC is an efficient antibody separation method which exploits the binding efficiency of a ligand to an antibody. Essential to the successful design of any IAC platform is the optimisation of critical experimental parameters such as: (a) the biological affinity pair, (b) the matrix support, (c) the immobilisation coupling chemistry, and (d) the effective elution conditions. These elements and the practicalities of their use are discussed in detail in this review. At the core of all IAC platforms is the high-affinity interactions between antibodies and their related ligands; hence, this review entails a brief introduction to the generation of antibodies for use in IAC and also provides specific examples of their potential applications.

Nanoparticle technology: Addressing the fundamental roadblocks to protein biomarker discovery

The incorporation of affinity baits into N-isopropylacrylamide-hydrogel-based nanoparticles offers a novel technology that addresses the major analytical challenges of disease biomarker discovery. In solution in complex biologic fluids (e.g. blood or urine), core-shell bait-containing nanoparticles can perform three functions in one step: (a) sieve molecules according to size, (b) sequestrate and concentrate target analytes, and (c) protect analytes from degradation.

A study of the performance characteristics of immunoaffinity solid phase microextraction probes for extraction of a range of benzodiazepines

Immunoaffinity solid phase microextraction (SPME) probes have been developed with antibodies specific for the benzodiazepine class of drugs, covalently immobilized to glass rods. This involved both purification of the polyclonal antibodies to isolate the drug-specific fraction, and optimization of the immobilization procedure. Such probes have been used previously for the extraction of 7-aminoflunitrazepam. This article presents a comprehensive study of their performance and characteristics beyond that described previously, and an evaluation of their application to additional benzodiazepines. The influence of non-specific drug binding (nsb) was determined, with the result that nsb was found to be insignificant for the probes when used in their dynamic range. Immobilized antibodies had specific affinities in the range of 10(9)-10(10)M(-1). Cross-reactivity was evaluated both for a range of benzodiazepines as well as a structurally unrelated molecule (erythromycin). For analysis of benzodiazepines individually or in the presence of erythromycin, limits of detection were 0.001-0.015 ng/mL depending on the antibody, and the dynamic range (based on 80-90% antigenic site occupancy) extended to 0.2-2 ng/mL.

Induced binding of proteins by ammonium sulfate in affinity and ion-exchange column chromatography

In general, proteins bind to affinity or ion-exchange columns at low salt concentrations, and the bound proteins are eluted by raising the salt concentration, changing the solvent pH, or adding competing ligands. Blue-Sepharose is often used to remove bovine serum albumin (BSA) from samples, but when we applied BSA to Blue-Sepharose in 20 mM phosphate, pH 7.0, 50%-60% of the protein flowed through the column; however, complete binding of BSA was achieved by the addition of 2 M ammonium sulfate (AS) to the column equilibration buffer and the sample. The bound protein was eluted by decreasing the AS concentration or by adding 1 M NaCl or arginine. AS at high concentrations resulted in binding of BSA even to an ion-exchange column, Q-Sepharose, at pH 7.0. Thus, although moderate salt concentrations elute proteins from Blue-Sepharose or ion-exchange columns, proteins can be bound to these columns under extreme salting-out conditions. Similar enhanced binding of proteins by AS was observed with an ATP-affinity column.

Biotechnology applications of amino acids in protein purification and formulations

Amino acids are widely used in biotechnology applications. Since amino acids are natural compounds, they can be safely used in pharmaceutical applications, e.g., as a solvent additive for protein purification and as an excipient for protein formulations. At high concentrations, certain amino acids are found to raise intra-cellular osmotic pressure and adjust to the high salt concentrations of the surrounding medium. They are called "compatible solutes", since they do not affect macromolecular function. Not only are they needed to increase the osmotic pressure, they are known to increase the stability of the proteins. Sucrose, glycerol and certain amino acids were used to enhance the stability of unstable proteins after isolation from natural environments. The mechanism of the action of these protein-stabilizing amino acids is relatively well understood. On the contrary, arginine was accidentally discovered as a useful reagent for assisting in the refolding of recombinant proteins. This effect of arginine was ascribed to its ability to suppress aggregation of the proteins during refolding, thereby increasing refolding efficiency. By the same mechanism, arginine now finds much wider applications than previously anticipated in the research and development of proteins, in particular in pharmaceutical applications. For example, arginine solubilizes proteins from loose inclusion bodies, resulting in efficient production of active proteins. Arginine suppresses protein-protein interactions in solution and also non-specific adsorption to gel permeation chromatography columns. Arginine facilitates elution of bound proteins from various column resins, including Protein-A or dye affinity columns and hydrophobic interaction columns. This review covers various biotechnology applications of amino acids, in particular arginine.

A highly sensitive immunoassay resistant to autoantibody interference for detection of the diabetes-associated autoantigen glutamic acid decarboxylase 65 in blood and other biological samples

BACKGROUND

Glutamic acid decarboxylase-65 (GAD65) is a major autoantigen in autoimmune diabetes and is discharged from injured islet beta cells. GAD65 may also be released by transplanted islets undergoing immunological rejection. To test hypotheses regarding the utility of GAD65 as a biomarker for transplant rejection or diabetes-associated islet damage and also regarding the timing and instigators of GAD65 release in humans or animal models, a sensitive assay capable of measuring GAD65 in serum or plasma will be necessary. Ideally, this assay would also be resistant to interference by anti-GAD65 autoantibodies.

METHODS

A novel, magnetic bead-based assay was developed based on GAD65 capture by a monoclonal antibody directed to the only region of the protein known not to be significantly targeted by autoantibodies. A subsequent denaturation step allows sensitive immunodetection to proceed using anti-GAD65 polyclonal antibodies that would otherwise potentially be blocked by bound autoantibodies.

RESULTS

The GAD65 assay worked equally well with serum and plasma as with a solution of bovine serum albumin (BSA). The limit of blank was 31 pg/mL and did not differ significantly in the BSA solution (27 pg/mL). Mean recovery of GAD65 from the plasma of control subjects and GAD65 autoantibody-positive and -negative subjects with type 1 diabetes was 101 +/- 4.6%, 88 +/- 7.8%, and 99 +/- 7.0% (+/- SEM), respectively. The assay was used to quantify both recombinant GAD65 and the GAD65 content of human and rodent islets and other tissue extracts that were added to human plasma samples.

CONCLUSIONS

A sensitive, autoantibody-resistant GAD65 assay has been developed that is compatible with detection in serum and plasma and therefore will likely also work with a variety of other biologic fluids. This assay may enable the use of circulating GAD65 as a biomarker of islet damage or transplant rejection and will facilitate in vivo studies of the pathogenesis of anti-GAD65 autoreactivity.

Effective elution of antibodies by arginine and arginine derivatives in affinity column chromatography

It has been shown that the recovery of monomeric antibodies from protein A affinity chromatography is enhanced significantly by using arginine as an eluent. To extend the applications of arginine to antibody purification and obtain an insight into the mechanism of arginine elution, we compared arginine with citrate, guanidine hydrochloride (GdnHCl), arginine derivatives, and other amino acids in protein A chromatography. We also applied arginine to elution of polyclonal antibodies (pAbs) in antigen affinity chromatography. As described previously, arginine was effective in eluting monoclonal antibodies IgG1 and IgG4. Two arginine derivatives, acetyl-arginine and agmatine, resulted in efficient elution at pH 4.0 or higher, and this was comparable to arginine. On the other hand, other amino acids, such as glycine, proline, lysine, and histidine, are much less effective than arginine under identical pH conditions. Whereas elution increased with arginine concentration, elution with citrate was insignificant in excess of 1 M at pH 4.3. Arginine was also effective in fractionation of pAbs using antigen-conjugated affinity columns. Although GdnHCl was also effective under similar conditions, the eluted material showed more aggregation than did the protein eluted by arginine.

Specific detection of cytopathogenic Listeria monocytogenes using a two-step method of immunoseparation and cytotoxicity analysis

The development of rapid methods for detection of viable Listeria monocytogenes is crucial to prevent listeriosis and product recalls. While immunomagnetic separation has been used for isolating Listeria spp., lack of specificity and pathogenicity determination render this method unsatisfactory. A two-step method using Protein A agarose beads (Immunobeads) coated with a more specific antibody, monoclonal antibody (MAb)-C11E9 for L. monocytogenes was developed. Immunobeads were allowed to capture Listeria cells from a variety of samples and tested for cytopathogenic action on a murine hybridoma B-lymphocyte, Ped-2E9 cell line by Trypan blue staining, and by an alkaline phosphatase (AP)-based cytotoxicity assay. The two-step method was used to test uninoculated hotdogs, bologna, and raw beef, chicken, and pork samples, following selective enrichment in half-Fraser broth. Pure culture studies proved the assay to be specific for L. monocytogenes, while a similar assay with Dynal Anti-Listeria immunomagnetic beads was positive for L. monocytogenes, L. ivanovii, and L. seeligeri. Detection and confirmation of cytopathogenicity of Listeria cells from food samples after 24-h selective enrichment were completed in 2-4 h. Isolates were further analyzed by the CAMP test for hemolytic activity and RiboPrinter for genomic patterns. Using immunoseparation and cytotoxicity as a two-step rapid method, viable L. monocytogenes could be isolated, detected, and confirmed as cytopathogenic in 28 h or less.

Efficient elution of functional proteins in affinity chromatography

Many elution buffers are in use for the retrieval of proteins from affinity columns. While the aim of these buffers is to dissociate the various chemical bonds that make up protein-protein interactions and return the target protein to the mobile phase in active form, there is considerable difference of opinion as to which buffer is more suitable for particular applications. This review examines the chemical effect of various elution buffers on protein-protein interactions in the context of affinity chromatography and examines strategies that may be used for selection of an appropriate buffer.

Immunoaffinity solid-phase extraction for the trace-analysis of low-molecular-mass analytes in complex sample matrices

Immunoaffinity solid-phase extraction (SPE) sorbents, so-called immunosorbents (ISs), are based upon molecular recognition using antibodies. Thanks to the high affinity and high selectivity of the antigen-antibody interaction, they allow a high degree of molecular selectivity and have shown to be a unique tool in the sample preparation area these last few years. Extraction and clean-up of complex biological and environmental aqueous samples are achieved in the same step and from large volumes when required. Their application to extracts from solid matrixes is solvent-free and more simple than any other clean-up procedure. Single analytes can be targeted, but since an antibody can also bind one or more analytes having structure similar to the one used for its preparation, ISs have been developed for targeting a single analyte and its metabolites. The cross-reactivity was also exploited for developing ISs that could selectively extract a whole class of structurally related compounds. This review describes the current technology used for the synthesis of the ISs, their properties and their field of application. The different parameters governing the antigen-antibody interactions and the solid-phase extraction process are discussed. Emphasis is given to the optimisation of the SPE sequence, especially to the desorption and regeneration steps. The importance of the capacity and its relationship with the analytes recovery and breakthrough volumes is highlighted for class-specific ISs. Multi-class-selective ISs are also presented. Validation studies are reviewed using various certified reference materials. Relevant examples, involving combination with chromatography in both off-line and on-line mode, illustrate the high selectivity provided in various complex matrixes. Miniaturisation is also described, since it allows high throughput of samples.

Fractionation of polyclonal antibodies to fragments of a neuroreceptor using three increasingly chaotropic solvents

We have developed specific antibodies against fragments of anaplastic lymphoma kinase (ALK) in order to develop tools for characterizing the expression and biological function of this orphan receptor. The first fragment consisted of residues 280 to 480 of the murine extracellular domain, was expressed in Escherichia coli (E. coli), purified in the presence of urea from the pellet of mechanically lysed cells and injected into rabbits as an unfolded protein in urea. The second fragment consisted of residues 1519 to 1619 of the murine sequence, corresponding to the C-terminal side of the kinase domain. It was expressed in E. coli as a soluble glutathione-S-transferase fusion protein, purified from the supernatant of broken cells and injected into rabbits as a folded protein. Both antisera were purified using antigen affinity chromatography, with the polyclonal antibodies eluted stepwise using three different buffers, 0.1 M glycine, pH 2.9, followed by 7 M urea, pH 4, followed by 6 M guanidine-HCl (GdnHCl), pH 4. Antisera prepared against either antigen contained antibodies that eluted in each of the three pools, indicating that solvents more chaotropic than acid were required to elute antibody populations that were tightly bound to the antigen column. All three antibody pools were reactive towards their respective antigens upon Western blot analysis. Purified polyclonal antibodies (pAbs) to both fragments also recognized the full-length protein expressed in Chinese hamster ovary cells. In every case, the pAbs eluting in GdnHCl were the most sensitive for detecting full-length ALK.