Scaleup of monoclonal antibody purification using radial streaming ion exchange chromatography

Hapten-Branched Polyethylenimine as a New Antigen Affinity Ligand to Purify Antibodies with High Efficiency and Specificity

Purification of antibodies has become a critical factor in antibody production. A high-purity specific antibody against antigens, especially small molecules, seems to be difficult to obtain, even with the help of a protein A affinity column, which is a conventional and broadly used ligand for the separation of antibody and non-antibody proteins. Therefore, it is urgent to develop a cheap, simple, efficient, and stable method to separate the specific antibody from other antibodies. In this study, to improve the sensitivity and accuracy of immunoassay results, enrofloxacin (ENR) was grafted onto polyethylenimine (PEI) by the abundant amino groups and then the whole ligand (ENR-PEI) was conjugated to CNBr-Sepharose 4B to prepare the affinity column for the purification of the specific antibody against ENR from polyclonal antibodies. Scanning electron microscopy and Fourier transform infrared spectroscopy verification showed that Sepharose 4B was successfully modified by ENR-PEI with excellent uniformity. The capacity of the prepared column could reach to 6.15 mg of specific antibody with high purity per milliliter resin due to the high coupling ratio (49.3:1) of ENR on PEI, and the IC₅₀ value of the antibody after purification was 47.58 ng/mL with a lowest limit of detection (IC₁₀) of 1.099 ng/mL-18 times lower than those of the antibody purified through the protein A column. All the results showed that this new kind of resin could be used as the potential ligand in the purification of the trace-specific antibody against antigens in complex mixtures with high efficiency and specificity.

Heterogeneity of Monoclonal Antibodies

Heterogeneity of monoclonal antibodies is common due to the various modifications introduced over the lifespan of the molecules from the point of synthesis to the point of complete clearance from the subjects. The vast number of modifications presents great challenge to the thorough characterization of the molecules. This article reviews the current knowledge of enzymatic and nonenzymatic modifications of monoclonal antibodies including the common ones such as incomplete disulfide bond formation, glycosylation, N-terminal pyroglutamine cyclization, C-terminal lysine processing, deamidation, isomerization, and oxidation, and less common ones such as modification of the N-terminal amino acids by maleuric acid and amidation of the C-terminal amino acid. In addition, noncovalent associations with other molecules, conformational diversity and aggregation of monoclonal antibodies are also discussed. Through a complete understanding of the heterogeneity of monoclonal antibodies, strategies can be employed to better identify the potential modifications and thoroughly characterize the molecules.

Short monolithic columns as stationary phases for biochromatography

Monolithic supports represent a novel type of stationary phases for liquid and gas chromatography, for capillary electrochromatography, and as supports for bioconversion and solid phase synthesis. As opposed to individual particles packed into chromatographic columns, monolithic supports are cast as continuous homogeneous phases. They represent an approach that provides high rates of mass transfer at lower pressure drops as well as high efficiencies even at elevated flow rates. Therefore, much faster separations are possible and the productivity of chromatographic processes can be increased by at least one order of magnitude as compared to traditional chromatographic columns packed with porous particles. Besides the speed, the nature of the pores allows easy access even in the case of large molecules, which make monolithic supports a method of choice for the separation of nanoparticles like pDNA and viruses. Finally, for the optimal purification of larger biomolecules, the chromatographic column needs to be short. This enhances the speed of the separation process and reduces backpressure, unspecific binding, product degradation and minor changes in the structure of the biomolecule, without sacrificing resolution. Short Monolithic Columns (SMC) were engineered to combine both features and have the potential of becoming the method of choice for the purification of larger biomolecules and nanopartides on the semi-preparative scale.

Large-scale purification of antisense oligonucleotides by high-performance membrane adsorber chromatography

Very high flux ion-exchange membranes were utilized for a novel purification of antisense oligonucleotides (20-mer). Strong anion-exchange membranes were produced by attaching polymeric ligands onto a microporous cellulosic matrix. The oligonucleotides purified were therapeutic single-stranded phosphorothioates deoxyribonucleotides. Although small-scale membrane devices (15 cm2) had similar resolution to traditional chromatographic columns; their throughputs were superior. Greater than a 1300-fold scale-up produced very similar purity and yields of the phosphorothionate product. Scale-up experiments were conducted with a 2 m2 surface area membrane module. These modules were easily capable of very high throughputs of 0.5 to 2 l/min. High purity and yields were achieved by both step and linear gradient elution.

Antibody purification methods

Antibodies (Abs) from the sera of patients with autoimmune diseases are reported to have different catalytic functions. Their recovery by efficient purification methods is, therefore, a crucial step. This article reviews different available methods for their recovery and emphasizes a new approach, namely adsorbents with immobilized histidine, which allows a good purification both in yield and purity of Abs, with the additional advantage of using gentle elution conditions. This, in turn, will ensure the recovery of intact (nondenatured) catalytically functional Abs, directly from the sera.

Effect of porous structure of macroporous polymer supports on resolution in high-performance membrane chromatography of proteins

The effect of porous structures of 2-mm thick diethylamine functionalized monolithic polymethacrylate discs on their chromatographic behavior in ion-exchange mode has been studied. Discs with small pores did not perform well because they exhibited high back pressure and substantial peak broadening. Discs characterized with pores larger than 1,000 nm did not provide good separations either because the time required for some protein molecules to traverse the length across the pore to reach the wall for adsorption/desorption process that is essential for the separation may be longer than their residence time within the matrix. Optimum pore size is centered at about 700 nm. Excellent separations have been achieved with these discs even at very steep gradients and high flow-rates which allow to shorten the separation times substantially.

Characterization and application of new macroporous membrane ion exchangers

A new ready-to-use unit for high-performance membrane chromatography has been characterized. Its dynamic capacity, resolving power and protein recovery were measured at different flow-rates. The binding capacity was 0.5-2 mg/cm2 with a 95% recovery at 10 ml/min irrespective of the protein concentration up to 10 mg/ml. For very-high flow-rates (50 and 100 ml/min) the recovery was 90% and 70%. At these flow-rates, the maximum back-pressure was about 0.1 MPa and was independent of the filtration area. By increasing the filtration area, a proportional capacity increase was obtained, indicating an easy scale-up. High flow-rates had only a slight effect on resolution. This new adsorber was able to purify IgM from supernatant of cell culture of a human hybridoma in less than 8 min with a high degree of purity (95%).

Chromatography in the downstream processing of biotechnological products

Chromatography techniques are essential for the isolation and purification of most of the high value products of modern biotechnology. The economically sensible and technically satisfactory downstream processing of a therapeutic protein, usually involves a number of chromatographic steps. Its development and optimization require considerable knowledge of the various physico-chemical and engineering aspects of biochemical chromatography. This review addresses the various modes of chromatography and the design of chromatographic separation processes from a biotechnologist's point of view. Strategies for optimizing the structure of the downstream process are outlined and scaling up consideration are discussed. The importance of the different chromatographic methods in research and development is estimated in an analysis of protein purification schemes recently published in the literature. Finally, examples of the application of chromatographic procedures for process scale product purification in the biotechnological industry are given.

Characterization and application of strong ion-exchange membrane adsorbers as stationary phases in high-performance liquid chromatography of proteins

Filtration membranes carrying strong cation- or anion-exchange groups on their surface were evaluated for their potential as membrane adsorber stationary phases in the high-performance liquid chromatography of proteins. The membranes are commercially available and can be obtained inserted into ready-to-use filter holders. Owing to their thinness (170-190 microns), the pressure drop of the membranes is extremely low. Flow-rates of up to 65 ml min-1 per unit became thus possible. The low pressure drop of a single membrane layer also permitted an effortless scaling up, as a stack of several membranes or filter units could be used, if necessary. Sample distribution, protein binding capacity, elution conditions, separation efficiency and recovery were investigated as a function of the flow-rate. The time required for the separation of certain protein mixtures could be reduced to less than 1 min. Appropriate conditions were defined for the separation of human serum and for the isolation of subtilisin Carlsberg and beta-galactosidase from cell culture supernatants.

Scale-up of recombinant protein purification by hydrophobic interaction chromatography

The scale-up of hydrophobic interaction chromatography is described. Human recombinant superoxide dismutase was used as a model. The scale-up was performed by keeping the height to diameter (H/D) ratio of the column constant. The success of scale-up was evaluated by reversed-phase high-performance liquid chromatography of the eluted material. The wrong H/D ratio causes decreased resolution.

Application of phase partitioning and thiophilic adsorption chromatography to the purification of monoclonal antibodies from cell culture fluid

A two-step method for the isolation of an IgG1 monoclonal antibody against horseradish peroxidase from hybridoma cell culture supernatant is described. Purification was achieved using an aqueous two-phase extraction procedure in conjunction with thiophilic adsorption chromatography. In an aqueous two-phase system composed of 5% PEG 1540 and 22% phosphate the monoclonal antibody preferentially associates with the PEG-rich top phase whereas proteins such as albumin and transferrin partition into the salt-rich bottom phase. Final purification of the monoclonal antibody was achieved by subjecting the PEG-rich top phase to thiophilic adsorption chromatography. The monoclonal antibody purified to homogeneity retained its specificity for horseradish peroxidase as revealed by polyacrylamide gel electrophoresis and an enzyme-linked immunosorbent assay. The potential of this purification protocol for large scale applications is discussed.

Surface-modified membranes as a matrix for protein purification

Recently introduced membrane-based chromatographic supports for protein separation are available either with a coupled ligand, e.g., protein A, protein G or ion-exchange groups, or as activated matrices for coupling a desired ligand. The coupling conditions for protein A and immunoglobulin G to an epoxy-activated membrane were determined. The performance of the prepared affinity membranes was investigated using pure rabbit immunoglobulin G and protein A as a model system. For practical application monoclonal antibodies from cell culture supernatant were purified with a prepared protein A membrane and for comparison with a sulphonic acid ion exchange membrane.

Affinity purification of plasminogen by radial-flow affinity chromatography

A method for the purification of plasminogen using immobilized L-lysine on a membrane, the whole system being constructed in a radial flow cartridge, is described. Human plasma was applied to the cartridge at 20 ml/min. The results showed that under the chromatographic conditions chosen, in a single pass, greater than 85% recovery of plasminogen was attained with a 110-fold increase in specific activity.

Isolation of isoproteins from monoclonal antibodies and recombinant proteins by chromatofocusing

A fast protein liquid chromatographic method for the preparative separation of the various isoproteins is described. Highly purified human monoclonal antibodies, recombinant human superoxide dismutase and human superoxide dismutase from erythrocytes were used as starting material. The isoproteins were separated by chromatofocusing on Mono P columns. A very narrow pH gradient was applied to achieve complete separation of the isoproteins. The prepurification steps and the pretreatment of the samples to achieve optimum resolution are described in detail. The method is also applicable to extremely basic monoclonal antibodies (pI = 9). The successful separation was checked by isoelectric focusing in immobilized pH gradients (Immobilines). The future of these methods is discussed, because for many different biochemical and biophysical investigations pure and homogeneous isoproteins are necessary.

Comparison of protein A, protein G and copolymerized hydroxyapatite for the purification of human monoclonal antibodies

Protein A Superose, protein G Sepharose fast flow and copolymerized hydroxyapatite were used for the purification of human monoclonal antibodies against HIV 1. Both desalted culture supernatant and a prepurified protein solution were used as starting materials. The different runs were compared with respect to yield and recovery of biological activity. The biological activity (specific reactivity) was checked by antigen enzyme-linked immunosorbent assay with recombinant antigen. The human monoclonal antibodies could not be selectively eluted from the hydroxyapatite but elution could be effected from the protein A Superose at pH 4.0 and from protein G at pH 3.0. The eluted immunoglobulin G was distributed over a broad pH range when protein G Superose was used. Biologically active material could be obtained from protein A Superose and protein G Sepharose fast flow.

Isolation of human monoclonal antibody isoproteins by preparative isoelectric focusing in immobilized pH gradients

A method for preparative isolation of human monoclonal antibody isoproteins is described in the present paper. A human monoclonal antibody directed against the transmembrane protein gp 41 from the human immunodeficiency virus (HIV-1) was used in this study. The antibody belongs to the IgG1 subtype and exhibits antibody dependent cellular cytotoxicity. The resolving power of conventional preparative protein separation techniques such as ion-exchange chromatography, chromatofocusing and lectin affinity chromatography is too poor for a complete separation of isoproteins. The more sophisticated technique of chromatofocusing on FPLC-based material (Mono P, Pharmacia) did not satisfy our expectation. With semipreparative IEF in immobilized pH gradients we were able to prepare the different isoproteins of a human monoclonal antibody in milligram amounts. No significant difference between the single isoproteins with respect to specificity and avidity to the recombinant antigen (rec gp 160) was detected. Therefore, we assume that the separation conditions did not influence the immunochemical nature of the antibody and significant denaturation and/or precipitation of the IgG did not occur. Furthermore the method affords preparative separation with resolution equivalent to analytical runs. Experiments for scale up and further characterization of isoproteins (carbohydrate composition, amino acid analysis, half life times etc.) are in progress.