Antibody Binding Heterogeneity of Protein A Resins

Antibody-ligand interactions on a high-capacity staphylococcal protein A resin

Staphylococcal protein-A affinity chromatography has been optimized for antibody purification, achieving a current capacity of up to 90 mg/ml in packed bed. The morphology of the particles, the number of antibodies bound per ligand and the spatial arrangement of the ligands were assessed by in-situ Small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) combined with measurement of adsorption isotherms. We employed SAXS measurements to probe the nanoscale structure of the chromatographic resin. From scanning electron microcopy, the morphology and area of the beads were obtained. The adsorption isotherm revealed a bi-Langmuirian behavior where the association constant varied with the critical bulk concentration, indicating multilayer adsorption. Determining the antibody-ligand stoichiometry was crucial for understanding the adsorption mechanism, which was estimated to be 4 at lower concentrations and 4.5 at higher concentrations, suggestive of reversible protein-protein interactions. The same results were reached from the in-situ small angle X-ray scattering measurements. A stoichiometry of 6 cannot be achieved since the two protein A monomers are anchored to the stationary phase and thus sterically hindered. Normalization through ellipsoids facilitated SAXS analysis, enabling the determination of distances between ligands and antibody-ligand complexes. Density fluctuations were examined by subtracting the elliptical fit, providing insights into ligand density distribution. The dense ligand packing of TOYOPEARL® AF-rProtein A HC was confirmed, making further increases in ligand density impractical. Additionally, SAXS analysis revealed structural rearrangements of the antibody-ligand complex with increasing antibody surface load, suggesting reversible association of antibodies.

Quantification of human intravenous immunoglobulin from plasma and in process samples by affinity chromatography

Advances in affinity chromatography now make it possible to analyze immunoglobulin G from plasma and its fractions with a simple chromatographic method. Ligands derived from camelid antibodies have been developed which have affinity to all 4 subclasses of human IgG without a cross reactivity to other immunoglobulins. The commercially available Capture Select FcXL is the basis for a simple method for direct quantification of immunoglobulin G from plasma or from fractions from cold ethanol precipitation. After direct injection of the sample into the column the unbound proteins are washed out with equilibration buffer and eluted with a pH-step. The elution the peak is integrated, and quantity is derived form a standard curve. The limit of detection with 40 µg/mL, and a linearity up to 250 µg/mL allows an analysis of samples ranging from 0.04 to 50 mg/mL using varying injection volume without further dilution and the two-wavelength detection. A full cycle is completed within five minutes. This method can serve as orthogonal method for in-process control but also for process development.

Insights on Alanine and Arginine Binding to Silica with Atomic Resolution

Interactions of biomolecules with inorganic oxide surfaces such as silica in aqueous solutions are of profound interest in various research fields, including chemistry, biotechnology, and medicine. While there is a general understanding of the dominating electrostatic interactions, the binding mechanism is still not fully understood. Here, chromatographic zonal elution and flow microcalorimetry experiments were combined with molecular dynamic simulations to describe the interaction of different capped amino acids with the silica surface. We demonstrate that ion pairing is the dominant electrostatic interaction. Surprisingly, the interaction strength is more dependent on the repulsive carboxy group than on the attracting amino group. These findings are essential for conducting experimental and simulative studies on amino acids when transferring the results to biomolecule-surface interactions.

Influence of excipients in Protein A chromatography and virus inactivation

The purification of monoclonal antibodies and Fc fusion proteins consist of several unit operations operated commonly as a platform approach, starting with Protein A chromatography. The first capture step, the following low pH virus inactivation, and subsequent ion exchange chromatography steps are mostly able to remove any impurities, like host cell proteins, aggregates, and viruses. The changes in pH and conductivity during these steps can lead to additional unwanted product species like aggregates. In this study, excipients with stabilizing abilities, like polyols, were used as buffer system additives to study their impact on several aspects during Protein A chromatography, low pH virus inactivation, and cation exchange chromatography. The results show that excipients, like PEG4000, influence antibody elution behavior, as well as host-cell protein elution behavior in a pH-gradient setup. Sugar excipients, like Sucrose, stabilize the antibody during low pH virus inactivation. All excipients tested show no negative impact on virus inactivation and dynamic binding capacity in a subsequent cation exchange chromatography step. This study indicates that excipients and, possibly excipient combinations, can have a beneficial effect on purification without harming subsequent downstream processing steps.

Seeking Innovative Affinity Approaches: A Performance Comparison between Magnetic Nanoparticle Agglomerates and Chromatography Resins for Antibody Recovery

Monoclonal antibodies are key molecules in medicine and pharmaceuticals. A potentially crucial drawback for faster advances in research here is their high price due to the extremely expensive antibody purification process, particularly the affinity capture step. Affinity chromatography materials have to demonstrate the high binding capacity and recovery efficiency as well as superior chemical and mechanical stability. Low-cost materials and robust, faster processes would reduce costs and enhance industrial immunoglobulin purification. Therefore, exploring the use of alternative materials is necessary. In this context, we conduct the first comparison of the performance of magnetic nanoparticles with commercially available chromatography resins and magnetic microparticles with regard to immobilizing Protein G ligands and recovering immunoglobulin G (IgG). Simultaneously, we demonstrate the suitability of bare as well as silica-coated and epoxy-functionalized magnetite nanoparticles for this purpose. All materials applied have a similar specific surface area but differ in the nature of their matrix and surface accessibility. The nanoparticles are present as micrometer agglomerates in solution. The highest Protein G density can be observed on the nanoparticles. IgG adsorbs as a multilayer on all materials investigated. However, the recovery of IgG after washing indicates a remaining monolayer, which points to the specificity of the IgG binding to the immobilized Protein G. One important finding is the impact of the ligand-binding stoichiometry (Protein G surface coverage) on IgG recovery, reusability, and the ability to withstand long-term sanitization. Differences in the materials' performances are attributed to mass transfer limitations and steric hindrance. These results demonstrate that nanoparticles represent a promising material for the economical and efficient immobilization of proteins and the affinity purification of antibodies, promoting innovation in downstream processing.

Mobile-Phase Modulators as Salt Tolerance Enhancers in Phenylboronate Chromatography: Thermodynamic Evaluation of the Mechanisms Underlying the Adsorption of Monoclonal Antibodies

Phenylboronate chromatography has been employed for bioseparation applications though details concerning the mechanisms of interaction between the ligand and macromolecules remain widely unknown. Here, the phenomena underlying the adsorption of an anti-human interleukin-8 (anti-IL8) monoclonal antibody (mAb) onto an m-aminophenylboronic acid (m-APBA) ligand in the presence of different mobile-phase modulators (NaF/MgCl ₂ /(NH ₄ ) ₂ SO ₄ ) and under different pH values (7.5/8.5/9.0) is investigated. Flow microcalorimetry (FMC) is applied to measure instantaneous heat energy transfer, providing insights about the role of specific and nonspecific interactions involved in the adsorptive process. Results show that the adsorption of anti-IL8 mAb to m-APBA is enthalpically driven, corroborating the presence of the reversible esterification reaction between boronic acid or boronates and cis-diol-containing molecules. Nevertheless, for all mobile-phase modulators studied, changes in thermogram profiles are observed as well as reductions in the net heat of adsorption when increasing the pH. Overall, FMC and parallel chromatographic experiments data suggest that ligand salt tolerance could be enhanced using mobile-phase modulators, with all salts studied promoting the specific cis-diol interactions and reducing nonspecific interactions. The last feature is more noticeable at pH values above ligand's pK _a , mainly due to the ability of NaF and (NH ₄ ) ₂ SO ₄ to diminish electrostatic interactions when compared to the commonly used NaCl.