Cyclic peptide ligand with high binding capacity for affinity purification of immunoglobulin G

Biomimetic affinity chromatography for antibody purification: Host cell protein binding and impurity removal

Peptide affinity chromatography has received increasing attention as an alternative to protein A chromatography in antibody purification. However, its lower selectivity than protein A chromatography has impeded its success in practical applications. In particular, efficient removal of contaminants, including host cell proteins (HCPs) and DNA, is a great challenge for peptide affinity chromatography in monoclonal antibody (mAb) manufacturing. In this work, a biomimetic peptide ligand (bPL), FYWHCLDE, was coupled onto Sepharose 6 Fast Flow (SepFF) to synthesize a peptide affinity gel, SepFF-bPL, for the investigation of the binding mechanism of HCP as well as the feasibility of antibody capture. The results showed that the SepFF-bPL column exhibited effective removal of mAb aggregates as well as mAb capture from feedstocks of various origins, whereas poor removal of HCP and DNA was found. Mechanistic studies of HCP binding indicated that electrostatic interactions dominated HCP binding on the SepFF-bPL gel and that ionic conductivity had a significant influence on HCP binding at low salt concentrations. Thus, combined chromatin extraction and anion exchange adsorption were introduced prior to SepFF-bPL chromatography for initial contaminant removal to reduce mAb aggregation induced by HCP and the loading burden of contaminants in SepFF-bPL chromatography. A proof-of-concept study of the purification train demonstrated a high recovery of mAb (68.7%) and low levels of HCP (23 ppm) and DNA (below the limit of detection) in the final product, which were acceptable for the mandatory requirements in clinical applications. This research provided a deep understanding of HCP binding on the peptide affinity column and led to the development of an effective purification train.

Matrices and Affinity Ligands for Antibody Purification and Corresponding Applications in Radiotherapy

Antibodies have become an important class of biological products in cancer treatments such as radiotherapy. The growing therapeutic applications have driven a demand for high-purity antibodies. Affinity chromatography with a high affinity and specificity has always been utilized to separate antibodies from complex mixtures. Quality chromatographic components (matrices and affinity ligands) have either been found or generated to increase the purity and yield of antibodies. More importantly, some matrices (mainly particles) and affinity ligands (including design protocols) for antibody purification can act as radiosensitizers or carriers for therapeutic radionuclides (or for radiosensitizers) either directly or indirectly to improve the therapeutic efficiency of radiotherapy. This paper provides a brief overview on the matrices and ligands used in affinity chromatography that are involved in antibody purification and emphasizes their applications in radiotherapy to enrich potential approaches for improving the efficacy of radiotherapy.

Engineering a Minimal Leucine-rich Repeat IgG-binding Module

Sea lamprey immunization can yield leucine-rich repeat (LRR) protein binders analogous to globular antibodies developed from mammals. A novel minimal LRR was discovered through lamprey immunization with human immunoglobulin G Fc domain (IgG Fc). Initial attempts to solubly express this LRR protein, VLRB.IgGFc, in Escherichia coli proved challenging, so it was analyzed using the cell-free method ribosome display. In ribosome display, VLRB.IgGFc was found to bind specifically to the Fc domain of IgG, with little observed cross-reactivity to IgA or IgM. The minimal repeat protein architecture of VLRB.IgGFc may facilitate modular LRR extensions to incorporate additional or augmented functionality within a continuous, structurally defined scaffold. We exploited this modularity to design a chimera of a well-characterized, soluble LRR repebody and the initially insoluble VLRB.IgGFc to produce soluble Repe-VLRB.IgGFc. The minimal IgG Fc-binding module, Repe-VLRB.IgGFc, and future-engineered variants thereof should be useful additions to the biotechnological toolbox for detecting, purifying, or targeting IgGs. More generally, this two-step approach of minimal LRR binder discovery via sea lamprey immunization followed by modular augmentation of functionality may be of general utility in protein engineering.

Peptide Affinity Chromatography Applied to Therapeutic Antibodies Purification

The interest in therapeutic monoclonal antibodies (mAbs) has significantly grown in the pharmaceutical industry, exceeding 100 FDA mAbs approved. Although the upstream processing of their industrial production has been significantly improved in the last years, the downstream processing still depends on immobilized protein A affinity chromatography. The high cost, low capacity and short half-life of immobilized protein A chromatography matrices, encouraged the design of alternative short-peptide ligands for mAb purification. Most of these peptides have been obtained by screening combinatorial peptide libraries. These low-cost ligands can be easily produced by solid-phase peptide synthesis and can be immobilized on chromatographic supports, thus obtaining matrices with high capacity and selectivity. Furthermore, matrices with immobilized peptide ligands have longer half-life than those with protein A due to the higher stability of the peptides. In this review the design and synthesis of peptide ligands, their immobilization on chromatographic supports and the evaluation of the affinity supports for their application in mAb purification is described.

Affinity-Based Methods for Site-Specific Conjugation of Antibodies

Conjugation of various reagents to antibodies has long been an elegant way to combine the superior binding features of the antibody with other desired but non-natural functions. Applications range from labels for detection in different analytical assays to the creation of new drugs by conjugation to molecules which improves the pharmaceutical effect. In many of these applications, it has been proven advantageous to control both the site and the stoichiometry of the conjugation to achieve a homogeneous product with predictable, and often also improved, characteristics. For this purpose, many research groups have, during the latest decade, reported novel methods and techniques, based on small molecules, peptides, and proteins with inherent affinity for the antibody, for site-specific conjugation of antibodies. This review provides a comprehensive overview of these methods and their applications and also describes a historical perspective of the field.

Tandem nanobody: A feasible way to improve the capacity of affinity chromatography

Nanobodies, referred to the binding domain of the heavy-chain-only antibodies, are the smallest antigen recognition unit. The molecular weight of monomeric nanobodies is about one-tenth of the conventional antibodies. The small size of nanobodies facilitates genetic manipulation and recombinant expression. This study aimed to investigate the effects of nanobody multivalency on the binding capacity of affinity resin. The nanobody (namely AFV), which binds to the fragment crystallizable (Fc) region of immunoglobulin G (IgG), was fused to the N-terminal of HaloTag in the form of monomeric (H-AFV), dimer (H-diAFV), trimer (H-triAFV), and tetramer (H-tetAFV). The fusion proteins were solubly expressed in Escherichia coli yielding at least 9.9 mg L-1. The biolayer interferometry confirmed an increment of avidity as the increase of AFV valences. The four recombinant proteins in crude cell lysate were site-specifically immobilized onto the Halo ligand resin via the self-labeling HaloTag, respectively. The generated affinity resins were able to isolate high purity IgG from mouse plasma. The highest improvement of the static binding capacity was achieved 73.7% by the H-diAFV resin other than the H-triAFV or H-tetAFV, as compared to the H-AFV resin.

Development of histidine-tagged cyclic peptide functionalized monolithic material for the affinity purification of antibodies in biological matrices

The rapidly increasing applications of monoclonal antibodies (mAbs) in therapy have necessitated the development of mAb production and purification technologies for both academic and industrial usage. Herein, a histidine-tagged cyclic peptide (HHHHHHGSGSGSDC*AWHLGELVWC*T, the disulfide-bonded cysteines of which are indicated by asterisks, named HT25-cyclopeptide) functionalized monolithic material was developed by the metal ion chelation-based approach. The resulting material possessed suitable affinity and peptide ligand density (13.8 mg peptide ligand per mL of material), good porosity (67.1 %), acceptable specific surface area (52.95 m²/g), and lots of macropores (4.13 μm). Moreover, excellent antibody-specific selectivity, comparable or even better binding capacity (for dried material, maximum static binding capacity and dynamic binding capacity are about 119.3 mg/g and 17.05 mg/g, respectively) for antibody compared to previously developed affinity materials, acceptable resistance to trypsin digestion, and negligible nonspecific protein adsorption, were also achieved on this novel monolithic material. Compared with the corresponding cyclic peptide-based sepharose material, milder elution conditions were employed for the HT25-cyclopeptide-based monolithic material, which could effectively prevent the aggregation and denaturation of the enriched antibodies. This novel material was then successfully applied to the affinity enrichment and purification of mAbs (including infliximab and rituximab) in different cell culture media or IgG in human serum.

Peptides and pseudopeptide ligands: a powerful toolbox for the affinity purification of current and next-generation biotherapeutics

Following the consolidation of therapeutic proteins in the fight against cancer, autoimmune, and neurodegenerative diseases, recent advancements in biochemistry and biotechnology have introduced a host of next-generation biotherapeutics, such as CRISPR-Cas nucleases, stem and car-T cells, and viral vectors for gene therapy. With these drugs entering the clinical pipeline, a new challenge lies ahead: how to manufacture large quantities of high-purity biotherapeutics that meet the growing demand by clinics and biotech companies worldwide. The protein ligands employed by the industry are inadequate to confront this challenge: while featuring high binding affinity and selectivity, these ligands require laborious engineering and expensive manufacturing, are prone to biochemical degradation, and pose safety concerns related to their bacterial origin. Peptides and pseudopeptides make excellent candidates to form a new cohort of ligands for the purification of next-generation biotherapeutics. Peptide-based ligands feature excellent target biorecognition, low or no toxicity and immunogenicity, and can be manufactured affordably at large scale. This work presents a comprehensive and systematic review of the literature on peptide-based ligands and their use in the affinity purification of established and upcoming biological drugs. A comparative analysis is first presented on peptide engineering principles, the development of ligands targeting different biomolecular targets, and the promises and challenges connected to the industrial implementation of peptide ligands. The reviewed literature is organized in (i) conventional (α-)peptides targeting antibodies and other therapeutic proteins, gene therapy products, and therapeutic cells; (ii) cyclic peptides and pseudo-peptides for protein purification and capture of viral and bacterial pathogens; and (iii) the forefront of peptide mimetics, such as β-/γ-peptides, peptoids, foldamers, and stimuli-responsive peptides for advanced processing of biologics.

Development of efficient on-bead protein elution process coupled to ultra-high performance liquid chromatography-tandem mass spectrometry to determine immunoglobulin G subclass and glycosylation for discovery of bio-signatures in pancreatic disease

Type 1 autoimmune pancreatitis (AIP) is a kind of IgG4-related disease in which higher IgG4 and total IgG levels have been found in patient serum. Due to the similar imaging features and laboratory parameters between AIP and pancreatic ductal adenocarcinoma (PDAC), a differential diagnosis is still challenging. Since IgG profiles can be potential bio-signatures for disease, we developed and validated a method which coupled on-bead enzymatic protein elution process to an efficient UHPLC-MS/MS method to determine IgG subclass and glycosylation. A stable-isotope labeled IgG was incorporated as internal standard to achieve accurate quantification. For calibration curves, the correlation coefficients for total IgG and the four IgG subclasses were higher than 0.995. Intraday (n = 5) and interday (n = 3) precisions of the peak area ratios of LLOQ, low, medium, and high QC samples were all less than 6.6% relative standard deviation (% RSD), and the accuracies were between 93.5 and 114.9%. Calibration curves, precision, and accuracy were also evaluated for 26 IgG glycopeptides. The method was applied to samples from healthy controls and patients with AIP and PDAC. Distinct IgG patterns were discovered among the groups, and 7 glycopeptides showed high potential in differentiating AIP and PDAC. The results demonstrated that the developed method is suitable for multi-feature analysis of human IgG, and the discovered IgG profiles can be used as bio-signatures for AIP and PDAC.

Peptide-Directed DNA-Templated Protein Labelling for The Assembly of a Pseudo-IgM

The development of methods for conjugation of DNA to proteins is of high relevance for the integration of protein function and DNA structures. Here, we demonstrate that protein-binding peptides can direct a DNA-templated reaction, selectively furnishing DNA-protein conjugates with one DNA label. Quantitative conversion of oligonucleotides is achieved at low stoichiometries and the reaction can be performed in complex biological matrixes, such as cell lysates. Further, we have used a star-like pentameric DNA nanostructure to assemble five DNA-Rituximab conjugates, made by our reported method, into a pseudo-IgM antibody structure that was subsequently characterized by negative-stain transmission electron microscopy (nsTEM) analysis.

Optimization of Sequence, Display, and Mode of Operation of IgG-Binding Peptide Ligands to Develop Robust, High-Capacity Affinity Adsorbents That Afford High IgG Product Quality

This work presents the use of peptide ligand HWRGWV and its cognate sequences to develop affinity adsorbents that compete with Protein A in terms of binding capacity and quality of the eluted product. First, the peptide ligand was conjugated to crosslinked agarose resins (WorkBeads) at different densities and using different spacer arms. The optimization of ligand density and display resulted in values of static and dynamic binding capacity of 85 mg/mL and 65 mg/mL, respectively. A selected peptide-WorkBeads adsorbent was utilized for purifying Mabs from Chinese Hamster Ovary (CHO) cell culture supernatants. The peptide-WorkBeads adsorbent was found able to withstand sanitization with strong alkaline solutions (0.5 M NaOH). The purity of the eluted product was consistently higher than 95%, with logarithmic removal value (LRV) of 1.5 for host cell proteins (HCPs) and 4.0 for DNA. HCP clearance was significantly improved by adding a post-load washing step with either 0.1 M Tris HCl pH 9 or 1 M NaCl. The cognate peptide of HWRGWV, constructed by replacing arginine (R) with citrulline, further increased the HCP LRV to 2.15. The peptide-based adsorbent also showed a remarkable performance in terms of removal of Mab aggregates; unlike Protein A, in fact, HWRGWV was found to bind only monomeric IgG. Collectively, these results demonstrate the potential of peptide-based adsorbents as alternative to Protein A for the purification of therapeutic antibodies.

Fc-Binding Ligands of Immunoglobulin G: An Overview of High Affinity Proteins and Peptides

The rapidly increasing application of antibodies has inspired the development of several novel methods to isolate and target antibodies using smart biomaterials that mimic the binding of Fc-receptors to antibodies. The Fc-binding domain of antibodies is the primary binding site for e.g., effector proteins and secondary antibodies, whereas antigens bind to the Fab region. Protein A, G, and L, surface proteins expressed by pathogenic bacteria, are well known to bind immunoglobulin and have been widely exploited in antibody purification strategies. Several difficulties are encountered when bacterial proteins are used in antibody research and application. One of the major obstacles hampering the use of bacterial proteins is sample contamination with trace amounts of these proteins, which can invoke an immune response in the host. Many research groups actively develop synthetic ligands that are able to selectively and strongly bind to antibodies. Among the reported ligands, peptides that bind to the Fc-domain of antibodies are attractive tools in antibody research. Besides their use as high affinity ligands in antibody purification chromatography, Fc-binding peptides are applied e.g., to localize antibodies on nanomaterials and to increase the half-life of proteins in serum. In this review, recent developments of Fc-binding peptides are presented and their binding characteristics and diverse applications are discussed.