Mixed-mode size-exclusion silica resin for polishing human antibodies in flow-through mode.

The polishing step in the downstream processing of therapeutic antibodies removes residual impurities from Protein A eluates. Among the various classes of impurities, antibody fragments are especially challenging to remove due to the broad biomolecular diversity generated by a multitude of fragmentation patterns. The current approach to fragment removal relies on ion exchange or mixed-mode adsorbents operated in bind-and-gradient-elution mode. However, fragments that bear strong similarity to the intact product or whose biophysical features deviate from the ensemble average can elude these adsorbents, and the lack of a chromatographic technology enabling robust antibody polishing is recognized as a major gap in downstream bioprocessing. Responding to this challenge, this study introduces size-exclusion mixed-mode (SEMM) silica resins as a novel chromatographic adsorbent for the capture of antibody fragments irrespective of their biomolecular features. The pore diameter of the silica beads features a narrow distribution and is selected to exclude monomeric antibodies, while allowing their fragments to access the pores where they are captured by the mixed-mode ligands. The static and dynamic binding capacity of the adsorbent ranged respectively between 30-45 and 25-33 gs of antibody fragments per liter of resin. Selected SEMM-silica resins also demonstrated the ability to capture antibody aggregates, which adsorb on the outer layer of the beads. Optimization of the SEMM-silica design and operation conditions - namely, pore size (10 nm) and ligand composition (quaternary amine and alkyl chain) as well as the linear velocity (100 cm/h), ionic strength (5.7 mS/cm), and pH (7) of the mobile phase - afforded a significant reduction of both fragments and aggregates, resulting into a final antibody yield up to 80% and monomeric purity above 97%.

Rational design and experimental evaluation of peptide ligands for the purification of adeno-associated viruses via affinity chromatography.

Adeno-associated viruses (AAVs) have acquired a central role in modern medicine as delivery agents for gene therapies targeting rare diseases. While new AAVs with improved tissue targeting, potency, and safety are being introduced, their biomanufacturing technology is lagging. In particular, the AAV purification pipeline hinges on protein ligands for the affinity-based capture step. While featuring excellent AAV binding capacity and selectivity, these ligands require strong acid (pH <3) elution conditions, which can compromise the product's activity and stability. Additionally, their high cost and limited lifetime has a significant impact on the price tag of AAV-based therapies. Seeking to introduce a more robust and affordable affinity technology, this study introduces a cohort of peptide ligands that (i) mimic the biorecognition activity of the AAV receptor (AAVR) and anti-AAV antibody A20, (ii) enable product elution under near-physiological conditions (pH 6.0), and (iii) grant extended reusability by withstanding multiple regenerations. A20-mimetic CYIHFSGYTNYNPSLKSC and AAVR-mimetic CVIDGSQSTDDDKIC demonstrated excellent capture of serotypes belonging to distinct clones/clades - namely, AAV1, AAV2, AAV5, AAV6, AAV8, and AAV9. This corroborates the in silico models documenting their ability to target regions of the viral capsid that are conserved across all serotypes. CVIDGSQSTDDDKIC-Toyopearl resin features binding capacity (≈1014 vp mL-1 ) and product yields (≈60%-80%) on par with commercial adsorbents, and purifies AAV2 from HEK293 and Sf9 cell lysates with high recovery (up to 78%), reduction of host cell proteins (up to 700-fold), and high transduction activity (up to 65%).

The downstream bioprocess toolbox for therapeutic viral vectors.

Viral vectors are poised to acquire a prominent position in modern medicine and biotechnology owing to their role as delivery agents for gene therapies, oncolytic agents, vaccine platforms, and a gateway to engineer cell therapies as well as plants and animals for sustainable agriculture. The success of viral vectors will critically depend on the availability of flexible and affordable biomanufacturing strategies that can meet the growing demand by clinics and biotech companies worldwide. In this context, a key role will be played by downstream process technology: while initially adapted from protein purification media, the purification toolbox for viral vectors is currently undergoing a rapid expansion to fit the unique biomolecular characteristics of these products. Innovation efforts are articulated on two fronts, namely (i) the discovery of affinity ligands that target adeno-associated virus, lentivirus, adenovirus, etc.; (ii) the development of adsorbents with innovative morphologies, such as membranes and 3D printed monoliths, that fit the size of viral vectors. Complementing these efforts are the design of novel process layouts that capitalize on novel ligands and adsorbents to ensure high yield and purity of the product while safeguarding its therapeutic efficacy and safety; and a growing panel of analytical methods that monitor the complex array of critical quality attributes of viral vectors and correlate them to the purification strategies. To help explore this complex and evolving environment, this study presents a comprehensive overview of the downstream bioprocess toolbox for viral vectors established in the last decade, and discusses present efforts and future directions contributing to the success of this promising class of biological medicines.

Molecular engineering of cyclic azobenzene-peptide hybrid ligands for the purification of human blood Factor VIII via photo-affinity chromatography.

The use of benign stimuli to control the binding and release of labile biologics for their isolation from complex feedstocks is a key goal of modern biopharmaceutical technology. This study introduces cyclic azobenzene-peptide (CAP) hybrid ligands for the rapid and discrete photo-responsive capture and release of blood coagulation Factor VIII (FVIII). A predictive method - based on amino acid sequence and molecular architecture of CAPs - was developed to correlate the conformation of cis/trans CAP photo-isomers to FVIII binding and release. The combined in silico and in vitro analysis of FVIII:peptide interactions guided the design of a rational approach to optimize isomerization kinetics and biorecognition of CAPs. A photoaffinity adsorbent, prepared by conjugating selected CAP G-cycloAZOB[Lys-YYKHLYN-Lys]-G on translucent chromatographic beads, featured high binding capacity (> 6 mg of FVIII per mL of resin) and rapid photo-isomerization kinetics (τ < 30s) when exposed to 420-450 nm light at the intensity of 0.1 W·cm-2. The adsorbent purified FVIII from a recombinant harvest using a single mobile phase, affording high product yield (>90%), purity (>95%), and blood clotting activity. The CAPs introduced in this report demonstrate a novel route integrating gentle operational conditions in a rapid and efficient bioprocess for the purification of life-saving biotherapeutics.

Peptide ligands for the affinity purification of adeno-associated viruses from HEK 293 cell lysates.

Adeno-associated viruses (AAVs) are the vector of choice for delivering gene therapies that can cure inherited and acquired diseases. Clinical research on various AAV serotypes significantly increased in recent years alongside regulatory approvals of AAV-based therapies. The current AAV purification platform hinges on the capture step, for which several affinity resins are commercially available. These adsorbents rely on protein ligands-typically camelid antibodies-that provide high binding capacity and selectivity, but suffer from low biochemical stability and high cost, and impose harsh elution conditions (pH < 3) that can harm the transduction activity of recovered AAVs. Addressing these challenges, this study introduces peptide ligands that selectively capture AAVs and release them under mild conditions (pH = 6.0). The peptide sequences were identified by screening a focused library and modeled in silico against AAV serotypes 2 and 9 (AAV2 and AAV9) to select candidate ligands that target homologous sites at the interface of the VP1-VP2 and VP2-VP3 virion proteins with mild binding strength (KD ~ 10-5 -10- 6 M). Selected peptides were conjugated to Toyopearl resin and evaluated via binding studies against AAV2 and AAV9, demonstrating the ability to target both serotypes with values of dynamic binding capacity (DBC10% > 1013 vp/mL of resin) and product yields (~50%-80%) on par with commercial adsorbents. The peptide-based adsorbents were finally utilized to purify AAV2 from a HEK 293 cell lysate, affording high recovery (50%-80%), 80- to 400-fold reduction of host cell proteins (HCPs), and high transduction activity (up to 80%) of the purified viruses.

Development of peptide affinity ligands for the purification of polyclonal and monoclonal Fabs from recombinant fluids.

Engineered multi-specific monoclonal antibodies (msAbs) and antibody fragments offer valuable therapeutic options against metabolic disorders, aggressive cancers, and viral infections. The advancement in molecular design and recombinant expression of these next-generation drugs, however, is not equaled by the progress in downstream bioprocess technology. The purification of msAbs and fragments requires affinity adsorbents with orthogonal biorecognition of different portions of the antibody structure, namely its Fc (fragment crystallizable) and Fab (fragment antigen-binding) regions or the CH1-3 and CL chains. Current adsorbents rely on protein ligands that, while featuring high binding capacity and selectivity, need harsh elution conditions and suffer from high cost, limited biochemical stability, and potential release of immunogenic fragments. Responding to these challenges, we undertook the de novo discovery of peptide ligands that target different regions of human Fab and enable product release under mild conditions. The ligands were discovered by screening a focused library of 12-mer peptides against a feedstock comprising human Fab and Chinese hamster ovary host cell proteins (CHO HCPs). The identified ligands were evaluated via binding studies as well as molecular docking simulations, returning excellent values of binding capacity (Qmax ∼ 20 mg of Fab per mL of resin) and dissociation constant (KD = 2.16·10-6 M). Selected ligand FRWNFHRNTFFP and commercial Protein L ligands were further characterized by measuring the dynamic binding capacity (DBC10%) at different residence times (RT) and performing the purification of polyclonal and monoclonal Fabs from CHO-K1 cell culture fluids. The peptide ligand featured DBC10% ∼ 6-16 mg/mL (RT of 2 min) and afforded values of yield (93-96%) and purity (89-96%) comparable to those provided by Protein L resins.

Development of peptide ligands for the purification of α-1 antitrypsin from cell culture fluids.

α-1 antitrypsin (AAT) deficiency, a major risk factor for chronic obstructive pulmonary disease, is one of the most prevalent and fatal hereditary diseases. The rising demand of AAT poses a defined need for new processes of AAT manufacturing from recombinant sources. Commercial affinity adsorbents for AAT purification present the intrinsic limitations of protein ligands - chiefly, the high cost and the lability towards the proteases in the feedstocks and the cleaning-in-place utilized in biomanufacturing - which limit their application despite their high capacity and selectivity. This work presents the development of small peptide affinity ligands for the purification of AAT from Chinese hamster ovary (CHO) cell culture harvests. An ensemble of ligand candidates identified via library screening were conjugated on Toyopearl resin and evaluated via experimental and in silico AAT-binding studies. Initial ranking based on equilibrium binding capacity indicated WHAKKSKFG- (12.9 mg of AAT per mL of resin), WHAKKSHFG- (16.3 mg/mL), and KWKHSHKWG- (15.8 mg/mL) Toyopearl resins as top performing adsorbents. Notably, the fitting of adsorption data to Langmuir isotherms concurred with molecular docking and dynamics in returning values of dissociation constant (KD) between 1 - 10 µM. These peptide-based adsorbents were thus selected for AAT purification from CHO fluids, affording values of AAT binding capacity up to 13 gram per liter of resin, and product yield and purity up to 77% and 97%. WHAKKSHFG-Toyopearl resin maintained its purification activity upon 20 consecutive uses, demonstrating its potential for AAT manufacturing from recombinant sources.

Towards continuous mAb purification: Clearance of host cell proteins from CHO cell culture harvests via "flow-through affinity chromatography" using peptide-based adsorbents.

The growth of advanced analytics in manufacturing monoclonal antibodies (mAbs) has highlighted the challenges associated with the clearance of host cell proteins (HCPs). Of special concern is the removal of "persistent" HCPs, including immunogenic and mAb-degrading proteins, that co-elute from the Protein A resin and can escape the polishing steps. Responding to this challenge, we introduced an ensemble of peptide ligands that target the HCPs in Chinese hamster ovary (CHO) cell culture fluids and enable mAb purification via flow-through affinity chromatography. This study describes their integration into LigaGuard™, an affinity adsorbent featuring an equilibrium binding capacity of ~30 mg of HCPs per mL of resin as well as dynamic capacities up to 16 and 22 mg/ml at 1- and 2-min residence times, respectively. When evaluated against cell culture harvests with different mAb and HCP titers and properties, LigaGuard™ afforded high HCP clearance, with logarithmic removal values (LRVs) up to 1.5, and mAb yield above 90%. Proteomic analysis of the effluents confirmed the removal of high-risk HCPs, including cathepsins, histones, glutathione-S transferase, and lipoprotein lipases. Finally, combining LigaGuard™ for HCP removal with affinity adsorbents for product capture afforded a global mAb yield of 85%, and HCP and DNA LRVs > 4.

De novo discovery of peptide-based affinity ligands for the fab fragment of human immunoglobulin G.

Antibody fragments and their engineered variants show true potential as next-generation therapeutics as they combine excellent targeting with superior biodistribution and blood clearance. Unlike full antibodies, however, antibody fragments do not yet have a standard platform purification process for large-scale production. Short peptide ligands are viable alternatives to protein ligands in affinity chromatography. In this work, an integrated computational and experimental scheme is described to de novo design 9-mer peptides that bind to Fab fragments. The first cohort of designed sequences was tested experimentally using human polyclonal Fab, and the top performing sequence was selected as a prototype for a subsequent round of ligand refinement in silico. The resulting peptides were conjugated to chromatographic resins and evaluated via equilibrium and dynamic binding studies using human Fab-κ and Fab-λ. The equilibrium studies returned values of binding capacities up to 32 mg of Fab per mL of resin with mild affinity (KD ∼ 10-5 M) that are conducive to high product capture and recovery. Dynamic studies returned values of product yield up to ∼90%. Preliminary purification studies provided purities of 83-93% and yields of 11-89%. These results lay the groundwork for future development of these ligands towards biomanufacturing translation.

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 ß-/γ-peptides, peptoids, foldamers, and stimuli-responsive peptides for advanced processing of biologics.

Rational design of specific ligands for human serum albumin separation and applications.

Human serum albumin is widely used in clinical practice, and the development of new ligands with high affinity is beneficial to improve its separation efficiency. The Site II of human serum albumin is an active binding site of various molecules such as l-tryptophan, which was studied with molecular simulation to obtain insights for the design of new ligands. The results showed that the carboxyl and indolyl groups of l-tryptophan were critical for the binding on Site II. Seven ligands containing carboxyl groups and indolyl groups were designed, and molecular simulation showed that indole-3-pentanoic acid was the best ligand. A new ligand combined indole-3-acetic acid and cysteine was designed for easier resin preparation, and molecular simulation also indicated that the new ligand bound strongly to Site II. Resins with the new ligand designed was prepared and static adsorption experiments indicated that the new resin had high adsorption capacity of human serum albumin and strong salt tolerance. Finally, recombinant human serum albumin was separated from yeast broth with high purity of 90.4% and recovery of 94.2%, which indicated that the new resin had good adsorption selectivity and strong potential for applications.

Novel peptide ligands for antibody purification provide superior clearance of host cell protein impurities.

The quest for ligands alternative to Protein A for the purification of monoclonal antibodies (mAbs) has been pursued for almost three decades. Yet, the IgG-binding peptides known to date still fall short of the host cell protein (HCP) logarithmic removal value (LRV) set by Protein A media (2.5-3.1). In this study, we present an integrated computational-experimental approach leading to the discovery of peptide ligands that provide HCP LRVs on par with Protein A. First, the screening of 60,000 peptide variants was performed using a high-throughput search algorithm to identify sequences that ensure IgG affinity binding. Select sequences WQRHGI, MWRGWQ, RHLGWF, and GWLHQR were then negatively screened in silico against a panel of model HCPs to ensure the selection of peptides with high binding selectivity. Candidate ligands WQRHGI and MWRGWQ were conjugated to chromatographic resins and characterized by isothermal binding and breakthrough assays to quantify static and dynamic binding capacity (Qmax and DBC10%), respectively. The resulting Qmax were 52.6 mg of IgG per mL of adsorbent for WQRHGI and 57.48 mg/mL for MWRGWQ, while the DBC10% (2 minutes residence time) were 30.1 mg/mL for WQRHGI and 36.4 mg/mL for MWRGWQ. Evaluation of the peptides by isothermal titration calorimetry (ITC) confirmed the binding energy predicted in silico, and an amino acid scanning study corroborated the affinity-like binding activity of the peptides. WQRHGI-WorkBeads resin was finally characterized by purification of a monoclonal antibody from a Chinese Hamster Ovary (CHO) cell culture harvest, affording a remarkable HCP LRV of 2.7, and consistent product yield and purity over 100 chromatographic cycles. These results demonstrate the potential of WQRHGI as an effective alternative to Protein A for antibody purification.

Multimodal charge-induction chromatography for antibody purification.

Hydrophobic charge-induction chromatography (HCIC) has advantages of high capacity, salt-tolerance and convenient pH-controlled elution. However, the binding specificity might be improved with multimodal molecular interactions. New ligand W-ABI that combining tryptophan and 5-amino-benzimidazole was designed with the concept of mutimodal charge-induction chromatography (MCIC). The indole and benzimidazole groups of the ligand could provide orientated mutimodal binding to target IgG under neutral pH, while the imidazole groups could induce the electrostatic repulsion forces for efficient elution under acidic pH. W-ABI ligand was coupled successfully onto agarose gel, and IgG adsorption behaviors were investigated. High affinity to IgG was found with the saturated adsorption capacity of 70.4 mg/ml at pH 7, and the flow rate of mobile phase showed little impact on the dynamic binding capacity. In addition, efficient elution could be achieved at mild acidic pH with high recovery. Two separation cases (IgG separation from albumin containing feedstock and monoclonal antibody purification from cell culture supernatant) were verified with high purity and recovery. In general, MCIC with the specially-designed ligand is an expanding of HCIC with improved adsorption selectivity, which would be a potential alternative to Protein A-based capture for the cost-effective purification of antibodies.