Affinity Membranes and Monoliths for Protein Purification

Application of mechanistic modelling in membrane and fiber chromatography for purification of biotherapeutics - A review

Mechanistic modelling is a simulation tool which has been effectively applied in downstream bioprocessing to model resin chromatography. Membrane and fiber chromatography are newer approaches that offer higher rates of mass transfer and consequently higher flow rates and reduced processing times. This review describes the key considerations in the development of mechanistic models for these unit operations. Mass transfer is less complex than in resin columns, but internal housing volumes can make modelling difficult, particularly for laboratory-scale devices. Flow paths are often non-linear and the dead volume is often a larger fraction of the overall volume, which may require more complex hydrodynamic models to capture residence time distributions accurately. In this respect, the combination of computational fluid dynamics with appropriate protein binding models is emerging as an ideal approach.

Mechanistic modeling of empty-full separation in recombinant adeno-associated virus production using anion-exchange membrane chromatography

Recombinant adeno-associated viral vectors (rAAVs) have become an industry-standard technology in the field of gene therapy, but there are still challenges to be addressed in their biomanufacturing. One of the biggest challenges is the removal of capsid species other than that which contains the gene of interest. In this work, we develop a mechanistic model for the removal of empty capsids-those that contain no genetic material-and enrichment of full rAAV using anion-exchange membrane chromatography. The mechanistic model was calibrated using linear gradient experiments, resulting in good agreement with the experimental data. The model was then applied to optimize the purification process through maximization of yield studying the impact of mobile phase salt concentration and pH, isocratic wash and elution length, flow rate, percent full (purity) requirement, loading density (challenge), and the use of single-step or two-step elution modes. A solution from the optimization with purity of 90% and recovery yield of 84% was selected and successfully validated, as the model could predict the recovery yield with remarkable fidelity and was able to find process conditions that led to significant enrichment. This is, to the best of our knowledge, the first case study of the application of de novo mechanistic modeling for the enrichment of full capsids in rAAV manufacturing, and it serves as demonstration of the potential of mechanistic modeling in rAAV process development.

Development of a New Affinity Gold Polymer Membrane with Immobilized Protein A

New and highly selective stationary phases for affinity membrane chromatography have the potential to significantly enhance the efficiency and specificity of therapeutic protein purification by reduced mass transfer limitations. This work developed and compared different immobilization strategies for recombinant Protein A ligands to a gold-sputtered polymer membrane for antibody separation in terms of functionalization and immobilization success, protein load, and stability. Successful, functionalization was validated via X-ray photoelectron spectroscopy (XPS). Here, a recombinant Protein A ligand was coupled by N-hydroxysuccinimide (NHS)/N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide (EDC) chemistry to carboxy-functionalized, gold-sputtered membranes. We achieved a binding capacity of up to 104 ± 17 mg of the protein ligand per gram of the gold-sputtered membrane. The developed membranes were able to successfully capture and release the monoclonal antibody (mAb) Trastuzumab, as well as antibodies from fresh frozen human blood plasma in both static and dynamic setups. Therefore, they demonstrated successful functionalization and immobilization strategies. The antibody load was tested using bicinchoninic acid (BCA), ultraviolet-visible spectroscopy (UV-vis) measurements, and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The outcome is a fully functional affinity membrane that can be implemented in a variety of different antibody purification processes, eliminating the need for creating individualized strategies for modifying the surface to suit different substrates or conditions.

Purification of phage for therapeutic applications using high throughput anion exchange membrane chromatography

As cases of multidrug resistant bacterial infections increase, scientists and clinicians around the world are increasingly turning to bacteriophages as alternatives to antibiotics. Even though our understanding of phage has increased significantly since the early days of its discovery, over a century ago, the currently used tools and technologies for phage purification for therapeutic applications are severely limited. Bacteriophages are produced by bacterial cultures, and impurities such as endotoxins must therefore be removed before clinical use. We present an anion exchange bind-and-elute membrane chromatographic method for purifying T7 bacteriophage from Escherichia coli culture supernatant that removes undesirable impurities, while ensuring a high viable phage count in the purified product. Our method does not involve the use of chemicals such as organic solvents and caesium chloride that could typically leave residual toxicity in the final product. It also does not require expensive equipment, such as an ultracentrifuge. Using our method, that is based on an in-house designed membrane module, 65% of viable T7 phage was recovered, and up to 94% endotoxins could be removed. The method, which took approximately 15 min, is rapid and scalable, and produces quite pure bacteriophage samples in a single step. It therefore potentially represents a major improvement over the status quo, and shows the way ahead for streamlining phage manufacturing for therapeutic use.

Aptamers 101: aptamer discovery and in vitro applications in biosensors and separations

Aptamers are single-stranded nucleic acids that bind and recognize targets much like antibodies. Recently, aptamers have garnered increased interest due to their unique properties, including inexpensive production, simple chemical modification, and long-term stability. At the same time, aptamers possess similar binding affinity and specificity as their protein counterpart. In this review, we discuss the aptamer discovery process as well as aptamer applications to biosensors and separations. In the discovery section, we describe the major steps of the library selection process for aptamers, called systematic evolution of ligands by exponential enrichment (SELEX). We highlight common approaches and emerging strategies in SELEX, from starting library selection to aptamer-target binding characterization. In the applications section, we first evaluate recently developed aptamer biosensors for SARS-CoV-2 virus detection, including electrochemical aptamer-based sensors and lateral flow assays. Then we discuss aptamer-based separations for partitioning different molecules or cell types, especially for purifying T cell subsets for therapeutic applications. Overall, aptamers are promising biomolecular tools and the aptamer field is primed for expansion in biosensing and cell separation.

Efficient adeno-associated virus serotype 5 capture with affinity functionalized nanofiber adsorbents

Adeno-associated viruses (AAVs) are one of the most promising tools for gene therapy applications. These vectors are purified using affinity and ion exchange chromatography, typically using packed beds of resin adsorbents. This leads to diffusion and pressure drop limitations that affect process productivity. Due to their high surface area and porosity, electrospun nanofiber adsorbents offer mass transfer and flow rate advantages over conventional chromatographic media. The present work investigated the use of affinity cellulose-based nanofiber adsorbents for adeno-associated virus serotype 5 (AAV5) capture, evaluating dynamic binding capacity, pressure drop, and AAV5 recovery at residence times (RT) less than 5 s. The dynamic binding capacity was found to be residence time-dependent, but nevertheless higher than 1.0 × 10¹⁴ TP mL^-1 (RT = 1.6 s), with a pressure drop variation of 0.14 MPa obtained after loading more than 2,000 column volumes of clarified AAV5 feedstock. The single affinity chromatography purification step using these new affinity adsorbents resulted in 80% virus recovery, with the removal of impurities comparable to that of bead-based affinity adsorbents. The high binding capacity, virus recovery and reduced pressure drop observed at residence times in the sub-minute range can potentially eliminate the need for prior concentration steps, thereby reducing the overall number of unit operations, process time and costs.

Comparative Evaluation of Commercial Protein A Membranes for the Rapid Purification of Antibodies

Protein A chromatography is ubiquitous to antibody purification. The high specificity of Protein A for binding the Fc-region of antibodies and related products enables unmatched clearance of process impurities like host cell proteins, DNA, and virus particles. A recent development is the commercialization of research-scale Protein A membrane chromatography products that can perform capture step purification with short residence times (RT) on the order of seconds. This study investigates process-relevant performance and physical properties of four Protein A membranes: Purilogics Purexa™ PrA, Gore® Protein Capture Device, Cytiva HiTrap™ Fibro PrismA, and Sartorius Sartobind® Protein A. Performance metrics include dynamic binding capacity, equilibrium binding capacity, regeneration-reuse, impurity clearance, and elution volumes. Physical properties include permeability, pore diameter, specific surface area, and dead volume. Key results indicate that all membranes except the Gore® Protein Capture Device operate with flow rate-independent binding capacities; the Purilogics Purexa™ PrA and Cytiva HiTrap Fibro™ PrismA have binding capacities on par with resins, with orders of magnitude faster throughput; and dead volume and hydrodynamics play major roles in elution behavior. Results from this study will enable bioprocess scientists to understand the ways that Protein A membranes can fit into their antibody process development strategies.

Preparation of composite monoliths of quaternized chitosan and diatom earth for protein separation

In this study, composite monoliths with porous structures were prepared using quaternized chitosan and diatom earth for protein separation. Quaternized chitosan (N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride) dissolved in water was mixed with diatom earth and crosslinked with glutaraldehyde under low-temperature conditions to form a cryogel. Interconnected porous monoliths were obtained after removing ice crystals from the cryogel. The monoliths adsorbed bovine serum albumin selectively from the solution mixture of bovine serum albumin and bovine ɤ-globulin, and bovine ɤ-globulin was recovered in the flow-through fraction. The adsorption selectivity was enhanced by changing the solution pH from 6.8 to 5.5. The adsorption of bovine serum albumin by the monolith was replicated at least five times following its washing with a buffer containing 400 mM NaCl and subsequent regeneration with a 10 mM acetate buffer. The composited monolith is a promising adsorbent for the removal of acidic proteins, such as serum albumin contamination in neutral proteins, for example, ɤ-globulins, in bioproduction processes.

Protein Attachment Mechanism for Improved Functionalization of Affinity Monolith Chromatography (AMC)

This work aims at understanding the attachment mechanisms and stability of proteins on a chromatography medium to develop more efficient functionalization methodologies, which can be exploited in affinity chromatography. In particular, the study was focused on the understanding of the attachment mechanisms of bovine serum albumin (BSA), used as a ligand model, and protein G on novel amine-modified alumina monoliths as a stationary phase. Protein G was used to develop a column for antibody purification. The results showed that, at lower protein concentrations (i.e., 0.5 to 1.0 mg·mL⁻¹), protein attachment follows a 1st-order kinetics compatible with the presence of covalent binding between the monolith and the protein. At higher protein concentrations (i.e., up to 10 mg·mL⁻¹), the data preferably fit a 2nd-order kinetics. Such a change reflects a different mechanism in the protein attachment which, at higher concentrations, seems to be governed by physical adsorption resulting in a multilayered protein formation, due to the presence of ligand aggregates. The threshold condition for the prevalence of physical adsorption of BSA was found at a concentration higher than 1.0 mg·mL⁻¹. Based on this result, protein concentrations of 0.7 and 1.0 mg·mL⁻¹ were used for the functionalization of monoliths with protein G, allowing a maximum attachment of 1.43 mg of protein G/g of monolith. This column was then used for IgG binding–elution experiments, which resulted in an antibody attachment of 73.5% and, subsequently, elution of 86%, in acidic conditions. This proved the potential of the amine-functionalized monoliths for application in affinity chromatography.

Membrane Chromatography and Fractionation of Proteins from Whey—A Review

Membrane chromatography (MC) is an emerging bioseparation technology combining the principles of membrane filtration and chromatography. In this process, one type of molecule is adsorbed in the stationary phase, whereas the other type of molecule is passed through the membrane pores without affecting the adsorbed molecule. In subsequent the step, the adsorbed molecule is recovered by an elution buffer with a unique ionic strength and pH. Functionalized microfiltration membranes are usually used in radial flow, axial flow, and lateral flow membrane modules in MC systems. In the MC process, the transport of a solute to a stationary phase is mainly achieved through convection and minimum pore diffusion. Therefore, mass transfer resistance and pressure drop become insignificant. Other characteristics of MC systems are a minimum clogging tendency in the stationary phase, the capability of operating with a high mobile phase flow rate, and the disposable (short term) application of stationary phase. The development and application of MC systems for the fractionation of individual proteins from whey for investigation and industrial-scale production are promising. A significant income from individual whey proteins together with the marketing of dairy foods may provide a new commercial outlook in dairy industry. In this review, information about the development of a MC system and its applications for the fractionation of individual protein from whey are presented in comprehensive manner.

Affinity monolith chromatography: A review of general principles and recent developments

Affinity monolith chromatography (AMC) is a liquid chromatographic technique that utilizes a monolithic support with a biological ligand or related binding agent to isolate, enrich, or detect a target analyte in a complex matrix. The target-specific interaction exhibited by the binding agents makes AMC attractive for the separation or detection of a wide range of compounds. This article will review the basic principles of AMC and recent developments in this field. The supports used in AMC will be discussed, including organic, inorganic, hybrid, carbohydrate, and cryogel monoliths. Schemes for attaching binding agents to these monoliths will be examined as well, such as covalent immobilization, biospecific adsorption, entrapment, molecular imprinting, and coordination methods. An overview will then be given of binding agents that have recently been used in AMC, along with their applications. These applications will include bioaffinity chromatography, immunoaffinity chromatography, immobilized metal-ion affinity chromatography, and dye-ligand or biomimetic affinity chromatography. The use of AMC in chiral separations and biointeraction studies will also be discussed.

Rapid Purification of Immunoglobulin G Using a Protein A-​immobilized Monolithic Spin Column with Hydrophilic Polymers

A rapid purification method was developed for antibody production in Chinese hamster ovary (CHO) cells using a Protein A-immobilized monolithic silica spin column with hydrophilic polymers. Monolithic silica modified with copolymers of 2-hydroxyethylmethacrylate (HEMA) and glycidyl methacrylate (GMA) showed lower non-specific protein absorption than that modified with a silane reagent. The epoxy group of GMA was converted to an amino group, and Protein A was modified by the coupling reagent. The amount of immobilized Protein A was controlled by changing the ratio of GMA to HEMA and the mesopore size of monolith. A modified monolith disk was fixed to a spin column for rapid antibody purification. The linear curves (for the antibody concentrations over 10 - 300 μg/mL) had a correlation coefficient of >0.999. Our column had various analytical advantages over previously reported columns, including a shorter preparation time (<10 min) and smaller sample volumes for purification with Protein A-immobilized agarose.

Polymer Membrane with Glycosylated Surface by a Chemo-Enzymatic Strategy for Protein Affinity Adsorption

Membranes with glycosylated surfaces are naturally biomimetic and not only have excellent surface hydrophilicity and biocompatibility, but have a specific recognition to target biomacromolecules due to the unique chemo-biological properties of their surface carbohydrates; however, they cannot be easily chemically produced on large scales due to the complex preparation process. This manuscript describes the fabrication of a polypropylene membrane with a glycosylated surface by a chemo-enzymatic strategy. First, hydroxyl (OH) groups were introduced onto the surface of microporous polypropylene membrane (MPPM) by UV-induced grafting polymerization of oligo(ethylene glycol) methacrylate (OEGMA). Then, glycosylation of the OH groups with galactose moieties was achieved via an enzymatic transglycosylation by β-galactosidase (Gal) recombinanted from E. coli. The fabricated glycosylated membrane showed surprisingly specific affinity adsorption to lectin ricinus communis agglutinin (RCA120). The chemo-enzymatic route is easy and green, and it would be expected to have wide applications for large-scale preparation of polymer membranes with glycosylated surfaces.