Novel High-throughput Approach for Purification of Infectious Virions

Tutorial: design, production and testing of oncolytic viruses for cancer immunotherapy

Oncolytic viruses (OVs) represent a novel class of cancer immunotherapy agents that preferentially infect and kill cancer cells and promote protective antitumor immunity. Furthermore, OVs can be used in combination with established or upcoming immunotherapeutic agents, especially immune checkpoint inhibitors, to efficiently target a wide range of malignancies. The development of OV-based therapy involves three major steps before clinical evaluation: design, production and preclinical testing. OVs can be designed as natural or engineered strains and subsequently selected for their ability to kill a broad spectrum of cancer cells rather than normal, healthy cells. OV selection is further influenced by multiple factors, such as the availability of a specific viral platform, cancer cell permissivity, the need for genetic engineering to render the virus non-pathogenic and/or more effective and logistical considerations around the use of OVs within the laboratory or clinical setting. Selected OVs are then produced and tested for their anticancer potential by using syngeneic, xenograft or humanized preclinical models wherein immunocompromised and immunocompetent setups are used to elucidate their direct oncolytic ability as well as indirect immunotherapeutic potential in vivo. Finally, OVs demonstrating the desired anticancer potential progress toward translation in patients with cancer. This tutorial provides guidelines for the design, production and preclinical testing of OVs, emphasizing considerations specific to OV technology that determine their clinical utility as cancer immunotherapy agents.

Multimode chromatography-based techniques for high purity isolation of extracellular vesicles from human blood plasma

Extracellular vesicles (EVs) play a pivotal role in various biological pathways, such as immune responses and the progression of diseases, including cancer. However, it is challenging to isolate EVs at high purity from blood plasma and other biofluids due to their low abundance compared to more predominant biomolecular species such as lipoprotein particles and free protein complexes. Ultracentrifugation-based EV isolation, the current gold standard technique, cannot overcome this challenge due to the similar biophysical characteristics of such species. We developed several novel approaches to enrich EVs from plasma while depleting contaminating molecular species using multimode chromatography-based strategies. On average, we identified 716 ± 68 and 1054 ± 35 protein groups in EV isolates from 100 µL of plasma using multimode chromatography- and ultracentrifugation-based techniques, respectively. The developed methods resulted in similar EV isolates purity, providing significant advantages in simplicity, throughput, scalability, and applicability for various downstream analytical and potential clinical applications.

Scalable purification of extracellular vesicles with high yield and purity using multimodal flowthrough chromatography

Extracellular vesicles (EVs) are cell derived membranous nanoparticles. EVs are important mediators of cell-cell communication via the transfer of bioactive content and as such they are being investigated for disease diagnostics as biomarkers and for potential therapeutic cargo delivery to recipient cells. However, existing methods for isolating EVs from biological samples suffer from challenges related to co-isolation of unwanted materials such as proteins, nucleic acids, and lipoproteins. In the pursuit of improved EV isolation techniques, we introduce multimodal flowthrough chromatography (MFC) as a scalable alternative to size exclusion chromatography (SEC). The use of MFC offers significant advantages for purifying EVs, resulting in enhanced yields and increased purity with respect to protein and nucleic acid co-isolates from conditioned 3D cell culture media. Compared to SEC, significantly higher EV yields with similar purity and preserved functionality were also obtained with MFC in 2D cell cultures. Additionally, MFC yielded EVs from serum with comparable purity to SEC and similar apolipoprotein B content. Overall, MFC presents an advancement in EV purification yielding EVs with high recovery, purity, and functionality, and offers an accessible improvement to researchers currently employing SEC.

Purification of Epizootic Hemorrhagic Disease Virus (and Other Orbiviruses) Particles from Infected Mammalian or Insect Cells

Epizootic hemorrhagic disease virus (EHDV), like other orbiviruses, infects and replicates in mammalian and insect vector cells. Within its ruminant hosts EHDV, like bluetongue virus (BTV), it has mainly been associated with infection of endothelial cells of capillaries as well as leukocyte subsets. Furthermore, EHDV infects and replicates within its biological vector, Culicoides biting midges and Culicoides-derived cells. A wide range of common laboratory cell lines such as BHK, BSR, and Vero cells are susceptible to infection with certain EHDV strains. Cell culture supernatants of infected cells are commonly used for both in vivo and in vitro infection studies. For specific virological or immunological studies, using highly purified virus particles, however, might be beneficial or even required. Here we describe a purification method for EHDV particles, which had been originally developed for certain strains of BTV.

Quality by Digital Design for Developing Platform RNA Vaccine and Therapeutic Manufacturing Processes

Quality by digital design (QbDD) utilizes data-driven, mechanistic, or hybrid models to define and optimize a manufacturing design space. It improves upon the QbD approach used extensively in the pharmaceutical industry. The computational models developed in this approach identify and quantify the relationship between the product's critical quality attributes (CQAs) and the critical process parameters (CPPs) of unit operations within the manufacturing process. This chapter discusses the QbDD approach in developing and optimizing unit operations such as in vitro transcription, tangential flow filtration, affinity chromatography, and lipid nanoparticle (LNP) formulation in mRNA vaccine manufacturing. QbDD can be an efficient framework for developing a production process for a disease-agnostic product that requires extensive experimental and model-based process-product interaction characterization during the early process development phase.

Reovirus genomic diversity confers plasticity for protease utility during adaptation to intracellular uncoating

IMPORTANCE

Reoviruses infect many mammals and are widely studied as a model system for enteric viruses. However, most of our reovirus knowledge comes from laboratory strains maintained on immortalized L929 cells. Herein, we asked whether naturally circulating reoviruses possess the same genetic and phenotypic characteristics as laboratory strains. Naturally circulating reoviruses obtained from sewage were extremely diverse genetically. Moreover, sewage reoviruses exhibited poor fitness on L929 cells and relied heavily on gut proteases for viral uncoating and productive infection compared to laboratory strains. We then examined how naturally circulating reoviruses might adapt to cell culture conditions. Within three passages, virus isolates from the parental sewage population were selected, displaying improved fitness and intracellular uncoating in L929 cells. Remarkably, selected progeny clones were present at 0.01% of the parental population. Altogether, using reovirus as a model, our study demonstrates how the high genetic diversity of naturally circulating viruses results in rapid adaptation to new environments.

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.

Optimizing the Conditions for Whole-Genome Sequencing of Avian Reoviruses

Whole-genome sequencing (WGS) is becoming an essential tool to characterize the genomes of avian reovirus (ARV), a viral disease of economic significance to poultry producers. The current strategies and procedures used to obtain the complete genome sequences of ARV isolates are not cost-effective because most of the genetic material data resulting from next-generation sequencing belong to the host and cannot be used to assemble the viral genome. The purpose of this study was to develop a workflow to enrich the ARV genomic content in a sample before subjecting it to next-generation sequencing (NGS). Herein, we compare four different ARV purification and enrichment approaches at the virion, RNA and cDNA levels to determine which treatment or treatment combination would provide a higher proportion of ARV-specific reads after WGS. Seven ARV isolates were subjected to different combinations of virion purification via ultracentrifugation in sucrose density gradient or Capto Core 700 resin with or without a subsequent Benzonase treatment, followed by a chicken rRNA depletion step after RNA extraction and a final ARV cDNA amplification step using a single-primer amplification assay. Our results show that the combination of Capto Core 700 resin, Chicken rRNA depletion and cDNA amplification is the most cost-effective strategy to obtain ARV whole genomes after short-read sequencing.

Evaluation of restricted access media for the purification of cell culture-derived Orf viruses

Recently, multimodal chromatography using restricted access media (RAM) for the purification of nanoparticles, such as viruses has regained increasing attention. These chromatography resins combine size exclusion on the particle shell and adsorptive interaction within the core. Accordingly, smaller process-related impurities, for example, DNA and proteins, can be retained, while larger product viruses can pass unhindered. We evaluated a range of currently available RAM, differing in the shells' pore cut-off and the core chemistry, for the purification of a cell culture-derived clarified model virus, namely the Orf virus (ORFV). We examined impurity depletion and product recovery as relevant criteria for the evaluation of column performance, as well as scale-up robustness and regeneration potential for evaluating a multiple use application. The results indicate that some columns, for example, the Capto Core, enable both a high DNA and protein removal, while others, for example, the Monomix Core 60 (MC60), are more suitable for DNA depletion. Furthermore, column regeneration is facilitated by using columns with larger shell pores (5000 vs. 700 kDa) and weaker binding interactions (anion exchange vs. multimodal). According to these findings, the choice of RAM resins should be selected according to the respective feed sample composition and the planned number of application cycles.

Affinity and Pseudo-Affinity Membrane Chromatography for Viral Vector and Vaccine Purifications: A Review

Several chromatographic approaches have been established over the last decades for the production of pharmaceutically relevant viruses. Due to the large size of these products compared to other biopharmaceuticals, e.g., proteins, convective flow media have proven to be superior to bead-based resins in terms of process productivity and column capacity. One representative of such convective flow materials is membranes, which can be modified to suit the particular operating principle and are also suitable for economical single-use applications. Among the different membrane variants, affinity surfaces allow for the most selective separation of the target molecule from other components in the feed solution, especially from host cell-derived DNA and proteins. A successful membrane affinity chromatography, however, requires the identification and implementation of ligands, which can be applied economically while at the same time being stable during the process and non-toxic in the case of any leaching. This review summarizes the current evaluation of membrane-based affinity purifications for viruses and virus-like particles, including traditional resin and monolith approaches and the advantages of membrane applications. An overview of potential affinity ligands is given, as well as considerations of suitable affinity platform technologies, e.g., for different virus serotypes, including a description of processes using pseudo-affinity matrices, such as sulfated cellulose membrane adsorbers.

Removal of chromatin by salt-tolerant endonucleases for production of recombinant measles virus

Host cell DNA is a critical impurity in downstream processing of enveloped viruses. Especially, DNA in the form of chromatin is often neglected. Endonuclease treatment is an almost mandatory step in manufacturing of viral vaccines. In order to find the optimal performer, four different endonucleases, two of them salt tolerant, were evaluated in downstream processing of recombinant measles virus. Endonuclease treatment was performed under optimal temperature conditions after clarification and before the purification by flow-through chromatography with a core shell chromatography medium: Capto™ Core 700. Virus infectivity was measured by TCID50. DNA and histone presence in process and purified samples was determined using PicoGreen™ assay and Western blot analysis using an anti-histone antibody, respectively. All tested endonucleases allowed the reduction of DNA content improving product purity. The salt-tolerant endonucleases SAN and M-SAN were more efficient in the removal of chromatin compared with the non-salt-tolerant endonucleases Benzonase® and DENARASE®. Removal of chromatin using M-SAN was also possible without the addition of extra salt to the cell culture supernatant. The combination of the endonuclease treatment, using salt-tolerant endonucleases with flow-through chromatography, using core-shell particles, resulted in high purity and purification efficiency. This strategy has all features for a platform downstream process of recombinant measles virus and beyond.

Wavelength dependence of ultraviolet light inactivation for SARS-CoV-2 omicron variants

Ultraviolet (UV) irradiation offers an effective and convenient method for the disinfection of pathogenic microorganisms. However, UV irradiation causes protein and/or DNA damage; therefore, further insight into the performance of different UV wavelengths and their applications is needed to reduce risks to the human body. In this paper, we determined the efficacy of UV inactivation of the SARS-CoV-2 omicron BA.2 and BA.5 variants in a liquid suspension at various UV wavelengths by the 50% tissue culture infection dose (TCID50) method and quantitative polymerase chain reaction (qPCR) assay. The inactivation efficacy of 220 nm light, which is considered safe for the human body, was approximately the same as that of health hazardous 260 nm light for both BA.2 and BA.5. Based on the inactivation rate constants determined by the TCID50 and qPCR methods versus the UV wavelength, the action spectra were determined, and BA.2 and BA.5 showed almost the same spectra. This result suggests that both variants have the same UV inactivation characteristics.

A Facile Method to Coat Nanoparticles with Lipid Bilayer Membrane: Hybrid Silica Nanoparticles Disguised as Biomembrane Vesicles by Particle Penetration of Concentrated Lipid Layers

Natural membrane vesicles, including extracellular vesicles and enveloped viruses, participate in various events in vivo. To study and manipulate these events, biomembrane-coated nanoparticles inspired by natural membrane vesicles are developed. Herein, an efficient method is presented to prepare organic-inorganic hybrid materials in high yields that can accommodate various lipid compositions and particle sizes. To demonstrate this method, silica nanoparticles are passed through concentrated lipid layers prepared using density gradient centrifugation, followed by purification, to obtain lipid membrane-coated nanoparticles. Various lipids, including neutral, anionic, and cationic lipids, are used to prepare concentrated lipid layers. Single-particle analysis by imaging flow cytometry determines that silica nanoparticles are uniformly coated with a single lipid bilayer. Moreover, cellular uptake of silica nanoparticles is enhanced when covered with a lipid membrane containing cationic lipids. Finally, cell-free protein expression is applied to embed a membrane protein, namely the Spike protein of severe acute respiratory syndrome coronavirus 2, into the coating of the nanoparticles, with the correct orientation. Therefore, this method can be used to develop organic-inorganic hybrid nanomaterials with an inorganic core and a virus-like coating, serving as carriers for targeted delivery of cargos such as proteins, DNA, and drugs.

A versatile multimodal chromatography strategy to rapidly purify protein nanostructures assembled in cell lysates

BACKGROUND

Protein nanostructures produced through the self-assembly of individual subunits are attractive scaffolds to attach and position functional molecules for applications in biomaterials, metabolic engineering, tissue engineering, and a plethora of nanomaterials. However, the assembly of multicomponent protein nanomaterials is generally a laborious process that requires each protein component to be separately expressed and purified prior to assembly. Moreover, excess components not incorporated into the final assembly must be removed from the solution and thereby necessitate additional processing steps.

RESULTS

We developed an efficient approach to purify functionalized protein nanostructures directly from bacterial lysates through a type of multimodal chromatography (MMC) that combines size-exclusion, hydrophilic interaction, and ion exchange to separate recombinant protein assemblies from excess free subunits and bacterial proteins. We employed the ultrastable filamentous protein gamma-prefoldin as a material scaffold that can be functionalized with a variety of protein domains through SpyTag/SpyCatcher conjugation chemistry. The purification of recombinant gamma-prefoldin filaments from bacterial lysates using MMC was tested across a wide range of salt concentrations and pH, demonstrating that the MMC resin is robust, however the optimal choice of salt species, salt concentration, and pH is likely dependent on the protein nanostructure to be purified. In addition, we show that pre-processing of the samples with tangential flow filtration to remove nucleotides and metabolites improves resin capacity, and that post-processing with Triton X-114 phase partitioning is useful to remove lipids and any remaining lipid-associated protein. Subsequently, functionalized protein filaments were purified from bacterial lysates using MMC and shown to be free of unincorporated subunits. The assembly and purification of protein filaments with varying amounts of functionalization was confirmed using polyacrylamide gel electrophoresis, Förster resonance energy transfer, and transmission electron microscopy. Finally, we compared our MMC workflow to anion exchange chromatography with the purification of encapsulin nanocompartments containing a fluorescent protein as a cargo, demonstrating the versatility of the protocol and that the purity of the assembly is comparable to more traditional procedures.

CONCLUSIONS

We envision that the use of MMC will increase the throughput of protein nanostructure prototyping as well as enable the upscaling of the bioproduction of protein nanodevices.

Protein adsorption on core-shell resins for flow-through purifications: Effect of protein molecular size, shape, and salt concentration

This work addresses the functional properties of the core-shell resins Capto Core 400 and 700 for a broad range of proteins spanning 66.5 to 660 kDa in molecular mass, including bovine serum albumin (BSA) in monomer and dimer form, fibronectin, thyroglobulin, and BSA conjugates with 10 and 30 kDa poly(ethylene glycol) chains. Negatively charged latex nanoparticles (NPs) with nominal diameters of 20, 40, and 100 nm are also studied as surrogates for bioparticles. Protein binding and its trends with respect to salt concentration depend on the protein size and are different for the two agarose-based multimodal resins. For the smaller proteins, the amount of protein bound over practical time scales is limited by the resin surface area and is larger for Capto Core 400 compared with Capto Core 700. For the larger proteins, diffusion is severely restricted in Capto Core 400, resulting in lower binding capacities than those observed for Capto Core 700 despite the larger surface area. Adding 500 mM NaCl reduces the local bound protein concentration and diffusional hindrance resulting in higher binding capacities for the large proteins in Capto Core 400 compared with low ionic strength conditions. The NPs are essentially completely excluded from the Capto Core 400 pores. However, 20 and 40 nm NPs bind significantly to Capto Core 700, further hindering protein diffusion. A model is provided to predict the dynamic binding capacities as a function of residence time.

Isolation and characterization of Newcastle disease virus from biological fluids using column chromatography

Newcastle disease virus (NDV), belonging to the species avian orthoavulavirus 1, genus Orthoavulavirus, and family Paramyxoviridae, is responsible for Newcastle disease in poultry and other avian species. It has shown significant potential as an oncolytic virus and as a vector for vaccine delivery. NDV from infected biological serum is usually isolated or purified using density gradient ultracentrifugation. However, it has many disadvantages, including the fact that it is time consuming and can process only a limited quantity of sample at one time. In our study, native agarose gel electrophoresis and dynamic light scattering (DLS) analysis showed that NDV carried a net negative surface charge. Thus, we purified the virus using a HiTrap Q Sepharose Fast Flow anion exchange column with salt elution. Hemagglutination assay and plaque assay showed that the procedure yielded high-purity NDV particles with a recovery of more than 80%, and the process was fast and simple. The purity of the virus was confirmed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blot analysis. The hydrodynamic volume and 'dry state' diameter of the purified NDV were analyzed using dynamic light scattering and transmission electron microscopy and were to be in the range of 200-300 nm. The viruses did not exhibit any deviation from their known physical properties. The genome of the virus was also detected by amplifying a 423-bp region using reverse transcription-polymerase chain reaction. Our study confirmed that NDV could be effectively purified using an anion exchange column. In addition, the procedure could be easily upscaled or downscaled based on the experimental requirements.

Seroprevalence of Binding and Neutralizing Antibodies against 39 Human Adenovirus Types in Patients with Neuromuscular Disorders

High pre-existing antibodies against viral vectors reduce their functionality and may lead to adverse complications. To circumvent this problem in future gene therapy approaches, we tested the seroprevalence of a large range of human adenovirus types in patients with neuromuscular disorders (NMDs) to find appropriate viral vector candidates for gene replacement therapy for NMDs. Binding and neutralizing antibodies against 39 human adenovirus types were tested in the sera of 133 patients with NMDs and 76 healthy controls aged 17-92 years. The influence of age, sex, and NMDs on antibody levels was analyzed. The seroprevalence of different adenoviruses in the cohort varied widely. The highest levels of binding antibodies were detected against HAdV-D27, -C1, -D24, -D70, -B14, -C6, -D13, -B34, and -E4, whereas the lowest reactivity was detected against HAdV-F41, -A31, -B11, -D75, -D8, -D65, -D26, -D80, and -D17. The highest neutralizing reactivity was observed against HAdV-B3, -C2, -E4, -C1, -G52, -C5, and -F41, whereas the lowest neutralizing reactivity was observed against HAdV-D74, -B34, -D73, -B37, -D48, -D13, -D75, -D8, -B35, and -B16. We detected no influence of sex and only minor differences between different age groups. Importantly, there were no significant differences between healthy controls and patients with NMDs. Our data show that patients with NMDs have very similar levels of binding and neutralizing antibodies against HAdV compared to healthy individuals, and we identified HAdV-A31, -B16, -B34, -B35, -D8, -D37, -D48, -D73, -D74, -D75, and -D80 as promising candidates for future vector development due to their low binding and neutralizing antibody prevalence.

Comparison of sample preparation techniques for the physicochemical characterization of Orf virus particles

The determination of the electrostatic charge of biological nanoparticles requires a purified, mono-disperse, and concentrated sample. Previous studies proofed an impact of the preparation protocol on the stability and electro-hydrodynamics of viruses, whereas commonly used methods are often complex and do not allow the required sample throughput. In the present study, the application of the (I) steric exclusion chromatography (SXC) for the Orf virus (ORFV) purification and subsequent physicochemical characterization was evaluated and compared to (II) SXC followed by centrifugal diafiltration and (III) sucrose cushion ultracentrifugation. The three methods were characterized in terms of protein removal, size distribution, infectious virus recovery, visual appearance, and electrophoretic mobility as a function of pH. All preparation techniques achieved a protein removal of more than 99 %, and (I) an infectious ORFV recovery of more than 85 %. Monodisperse samples were realized by (I) and (III). In summary, ORFV samples prepared by (I) and (III) displayed comparable quality. Additionally, (I) offered the shortest operation time and easy application. Based on the obtained data, the three procedures were ranked according to eight criteria of possible practical relevance, which delineate the potential of SXC as virus preparation method for physicochemical analysis.

Analysis of the Prevalence of Binding and Neutralizing Antibodies against 39 Human Adenovirus Types in Student Cohorts Reveals Low-Prevalence Types and a Decline in Binding Antibody Levels during the SARS-CoV-2 Pandemic

Vectors based on human adenoviruses (HAdVs) are important for the development of novel immunizations, oncolytic therapies, and gene therapies. The use of HAdV-based vaccines against Ebola virus, the rapid adaptation of the vector technology for vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and their very good efficacy have shown the great potential of HAdV-based vaccines.

The Efficacy of Commercial Surface Sanitizers against Norovirus on Formica Surfaces with and without Inclusion of a Wiping Step

Commonly used surface sanitizers often lack activity against human noroviruses (hNoVs). The impact of inactivation versus removal when these products are applied via wiping is poorly characterized. The purpose of this work was to assess the anti-hNoV efficacy of various surface sanitizer chemistries, as applied to a laminate material commonly used for restaurant tabletops, using standard surface assays (ASTM E1053-11) and a newly developed wiping protocol. Four commercially available products with different active ingredient(s) (i.e., ethanol [EtOH], acid + anionic surfactant [AAS], quaternary ammonium compound [QAC], and sodium hypochlorite [NaOCl]) and a water control were evaluated against hNoV GII.4 Sydney, hNoV GI.6, and the cultivable surrogate Tulane virus (TuV). Virus concentration was evaluated using RNase-reverse transcriptase (RT)-quantitative PCR (qPCR) (hNoV) and infectivity assay (TuV). Only the EtOH-based product significantly reduced virus concentration (>3.5 log10 reduction [LR]) by surface assay, with all other products producing ≤0.5 LR. The inclusion of a wiping step enhanced the efficacy of all products, producing complete virus elimination for the EtOH-based product and 1.6 to 3.8 LR for the other chemistries. For hNoVs, no detectable residual virus could be recovered from paper towels used to wipe the EtOH-based product, while high concentrations of virus could be recovered from the used paper towel and the wiped coupon (1.5 to 2.5 log10 lower genome equivalent copies [GEC] compared to control) for the QAC- and AAS-based products and for water. These results illustrate the variability in anti-hNoV activity of representative surface sanitizers and highlights the value of wiping, the efficacy of which appears to be driven by a combination of virus inactivation and removal. IMPORTANCE Human noroviruses (hNoVs) are the leading cause of acute gastroenteritis and food-borne disease worldwide. Noroviruses are difficult to inactivate, being recalcitrant to sanitizers and disinfectants commonly used by the retail food sector. This comparative study demonstrates the variability in anti-hNoV activity of representative surface sanitizers, even those allowed to make label claims based on the cultivable surrogate, feline calicivirus (FCV). It also highlights the importance of wiping in the process of sanitization, which significantly improves product efficacy through the action of physical removal of surface microbes. There is a need for more and better product formulations with demonstrated efficacy against hNoVs, which will likely necessitate the use of alternative cultivable surrogates, such as Tulane virus (TuV). These findings help food safety professionals make informed decisions on sanitizing product selection and application methods in order to reduce the risk of hNoV contamination and transmission in their facilities.

SARS-CoV-2 Production, Purification Methods and UV Inactivation for Proteomics and Structural Studies

Severe acute respiratory syndrome coronavirus-2 is the causative agent of COVID-19. During the pandemic of 2019–2022, at least 500 million have been infected and over 6.3 million people have died from COVID-19. The virus is pleomorphic, and due to its pathogenicity is often handled in very restrictive biosafety containments laboratories. We developed two effective and rapid purification methods followed by UV inactivation that allow easy downstream handling of the virus. We monitored the purification through titering, sequencing, mass spectrometry and electron cryogenic microscopy. Although pelleting through a sucrose cushion, followed by gentle resuspension overnight gave the best particle recovery, infectivity decreased, and the purity was significantly worse than if using the size exclusion resin Capto Core. Capto Core can be used in batch mode, and was seven times faster than the pelleting method, obviating the need for ultracentrifugation in the containment laboratory, but resulting in a dilute virus. UV inactivation was readily optimized to allow handling of the inactivated samples under standard operating conditions. When containment laboratory space is limited, we recommend the use of Capto Core for purification and UV for inactivation as a simple, rapid workflow prior, for instance, to electron cryogenic microscopy or cell activation experiments.

Leveraging high-throughput purification to accelerate viral vector process development

Recombinant adeno-associated virus (AAV) has been broadly used as a delivery tool for gene therapy applications. The development of a robust purification process is essential for delivering high purity and quality AAV products to clinic. The short clinical timelines and material limitations of early-stage development pose unique challenges to developing robust and scalable downstream purification processes. One approach to overcome these limitations is to leverage high throughput (HTP) strategies and automation technologies for purification process development, an approach that is well established in protein biologics and other areas. However, due to the unique challenges related to viral vector purification, implementing HTP approaches for gene therapy process development has not been explored extensively. In this paper, we established a HTP chromatography platform and demonstrated its capability to facilitate gene therapy purification process development using both mini-columns and self-packed resin plates. The end-to-end development workflow for AAV HTP purification is detailed in this work with the expectation of serving as an introductory for the AAV purification development field. Comparable process performance was confirmed between a bench-scale chromatography process and an HTP chromatography format. Slightly lower recovery was observed using the HTP format (62% vs 75%), as well as %full capsid enrichment (71% vs. 82%). Comparable impurity clearance capability was demonstrated between the two different systems as well. It was concluded that the established HTP chromatography formats can serve as a surrogate to bench-scale chromatography development to reduce material needs and development timelines for AAV purification development.

Highly Efficient Purification of Recombinant VSV-∆G-Spike Vaccine against SARS-CoV-2 by Flow-Through Chromatography

This study reports a highly efficient, rapid one-step purification process for the production of the recombinant vesicular stomatitis virus-based vaccine, rVSV-∆G-spike (rVSV-S), recently developed by the Israel Institute for Biological Research (IIBR) for the prevention of COVID-19. Several purification strategies are evaluated using a variety of chromatography methods, including membrane adsorbers and packed-bed ion-exchange chromatography. Cell harvest is initially treated with endonuclease, clarified, and further concentrated by ultrafiltration before chromatography purification. The use of anion-exchange chromatography in all forms results in strong binding of the virus to the media, necessitating a high salt concentration for elution. The large virus and spike protein binds very strongly to the high surface area of the membrane adsorbents, resulting in poor virus recovery (<15%), while the use of packed-bed chromatography, where the surface area is smaller, achieves better recovery (up to 33%). Finally, a highly efficient chromatography purification process with Capto^TM Core 700 resin, which does not require binding and the elution of the virus, is described. rVSV-S cannot enter the inner pores of the resin and is collected in the flow-through eluent. Purification of the rVSV-S virus with Capto^TM Core 700 resulted in viral infectivity above 85% for this step, with the efficient removal of host cell proteins, consistent with regulatory requirements. Similar results were obtained without an initial ultrafiltration step.

Scaled preparation of extracellular vesicles from conditioned media

Extracellular vesicles (EVs) especially of mesenchymal stem/stomal cells (MSCs) are increasingly considered as biotherapeutic agents for a variety of different diseases. For translating them effectively into the clinics, scalable production processes fulfilling good manufacturing practice (GMP) are needed. Like for other biotherapeutic agents, the manufacturing of EV products can be subdivided in the upstream and downstream processing and the subsequent quality control, each of them containing several unit operations. During upstream processing (USP), cells are isolated, stored (cell banking) and expanded; furthermore, EV-containing conditioned media are produced. During downstream processing (DSP), conditioned media (CM) are processed to obtain concentrated and purified EV products. CM are either stored until DSP or are directly processed. As first unit operation in DSP, clarification removes remaining cells, debris and other larger impurities. The key operations of each EV DSP is volume-reduction combined with purification of the concentrated EVs. Most of the EV preparation methods used in conventional research labs including differential centrifugation procedures are limited in their scalability. Consequently, it is a major challenge in the therapeutic EV field to identify appropriate EV concentration and purification methods allowing scale up. As EVs share several features with enveloped viruses, that are used for more than two decades in the clinics now, several principles can be adopted to EV manufacturing. Here, we introduce and discuss volume reducing and purification methods frequently used for viruses and analyze their value for the manufacturing of EV-based therapeutics.

Isocratic reporter-exclusion immunoassay using restricted-access adsorbents

We introduce analyte-dependent exclusion of reporter reagents from restricted-access adsorbents as the basis of an isocratic reporter-exclusion immunoassay for viruses, proteins, and other analytes. Capto™ Core 700 and related resins possess a noninteracting size-selective outer layer surrounding a high-capacity nonspecific mixed-mode capture adsorbent core. In the absence of analyte, antibody-enzyme reporter conjugates can enter the adsorbent and be captured, and their signal is lost. In the presence of large or artificially-expanded analytes, reporter reagents bind to analyte species to form complexes large enough to be excluded from the adsorbent core, allowing their signal to be observed. This assay principle is demonstrated using M13 bacteriophage virus and human chorionic gonadotropin as model analytes. The simple isocratic detection approach described here allows a rapid implementation of immunoassay for detection of a wide range of analytes and uses inexpensive, generally-applicable, and stable column materials instead of costly analyte-specific immunoaffinity adsorbents.

Separation, characterization, and standardization of extracellular vesicles for drug delivery applications

Extracellular vesicles (EVs) are membranous nanovesicles secreted from living cells, shuttling macromolecules in intercellular communication and potentially possessing intrinsic therapeutic activity. Due to their stability, low immunogenicity, and inherent interaction with recipient cells, EVs also hold great promise as drug delivery vehicles. Indeed, they have been used to deliver nucleic acids, proteins, and small molecules in preclinical investigations. Furthermore, EV-based drugs have entered early clinical trials for cancer or neurodegenerative diseases. Despite their appeal as delivery vectors, however, EV-based drug delivery progress has been hampered by heterogeneity of sample types and methods as well as a persistent lack of standardization, validation, and comprehensive reporting. This review highlights specific requirements for EVs in drug delivery and describes the most pertinent approaches for separation and characterization. Despite residual uncertainties related to pharmacodynamics, pharmacokinetics, and potential off-target effects, clinical-grade, high-potency EV drugs might be achievable through GMP-compliant workflows in a highly standardized environment.

Genome Evolution of Two Genetically Homogeneous Infectious Bursal Disease Virus Strains During Passages in vitro and ex vivo in the Presence of a Mutagenic Nucleoside Analog

The avibirnavirus infectious bursal disease virus (IBDV) is responsible for a highly contagious and sometimes lethal disease of chickens (Gallus gallus). IBDV genetic variation is well-described for both field and live-attenuated vaccine strains, however, the dynamics and selection pressures behind this genetic evolution remain poorly documented. Here, genetically homogeneous virus stocks were generated using reverse genetics for a very virulent strain, rvv, and a vaccine-related strain, rCu-1. These viruses were serially passaged at controlled multiplicities of infection in several biological systems, including primary chickens B cells, the main cell type targeted by IBDV in vivo. Passages were also performed in the absence or presence of a strong selective pressure using the antiviral nucleoside analog 7-deaza-2'-C-methyladenosine (7DMA). Next Generation Sequencing (NGS) of viral genomes after the last passage in each biological system revealed that (i) a higher viral diversity was generated in segment A than in segment B, regardless 7DMA treatment and viral strain, (ii) diversity in segment B was increased by 7DMA treatment in both viruses, (iii) passaging of IBDV in primary chicken B cells, regardless of 7DMA treatment, did not select cell-culture adapted variants of rvv, preserving its capsid protein (VP2) properties, (iv) mutations in coding and non-coding regions of rCu-1 segment A could potentially associate to higher viral fitness, and (v) a specific selection, upon 7DMA addition, of a Thr329Ala substitution occurred in the viral polymerase VP1. The latter change, together with Ala270Thr change in VP2, proved to be associated with viral attenuation in vivo. These results identify genome sequences that are important for IBDV evolution in response to selection pressures. Such information will help tailor better strategies for controlling IBDV infection in chickens.

Protein Adsorption on Core-shell Particles: Comparison of Capto™ Core 400 and 700 Resins

Structural and functional characteristics of the two core-shell resins Capto™ Core 400 and 700, which are useful for the flow-through purification of bioparticles such as viruses, viral vectors, and vaccines, are compared using bovine serum albumin (BSA) and thyroglobulin (Tg) as models for small and large protein contaminants. Both resins are agarose-based and contain an adsorbing core surrounded by an inert shell. Although shell thicknesses are comparable (3.6 and 4.2 µm for Capto Core 400 and 700, respectively), the two resins differ substantially in pore size (pore radii of 19 and 50 nm, respectively). Because of the smaller pores and higher surface area, the BSA binding capacity of Capto Core 400 is approximately double that of Capto Core 700. However, for the much larger Tg, the attainable capacity is substantially larger for Capto Core 700. Mass transfer in both resins is affected by diffusional resistances through the shell and within the adsorbing core. For BSA, core and shell effective pore diffusivities are about 0.25 × 10^-7 and 0.6 × 10^-7 cm²/s, respectively, for Capto Core 400, and about 1.6 × 10^-7 and 2.6 × 10^-7 cm²/s, respectively, for Capto Core 700. These values decrease dramatically for Tg to 0.022 × 10^-7 and 0.088 × 10^-7 cm²/s and to 0.13 × 10^-7 and 0.59 × 10^-7 cm²/s for Capto Core 400 and 700, respectively. Adsorbed Tg further hinders diffusion of BSA in both resins. Column measurements show that, despite the higher static capacity of Capto Core 400 for BSA, the dynamic binding capacity is greater for Capto Core 700 as a result of its faster kinetics. However, some of this advantage is lost if the feed is a mixture of BSA and Tg since, in this case, Tg binding leads to greater diffusional hindrance for BSA.

Analysis of the Evolution of Pandemic Influenza A(H1N1) Virus Neuraminidase Reveals Entanglement of Different Phenotypic Characteristics

The influenza A virus (IAV) neuraminidase (NA) is essential for virion release from cells and decoy receptors and an important target of antiviral drugs and antibodies. Adaptation to a new host sialome and escape from the host immune system are forces driving the selection of mutations in the NA gene. Phylogenetic analysis shows that until 2015, 16 amino acid substitutions in NA became fixed in the virus population after introduction in the human population of the pandemic IAV H1N1 (H1N1pdm09) in 2009. The accumulative effect of these substitutions, in the order in which they appeared, was analyzed using recombinant proteins and viruses in combination with different functional assays. The results indicate that NA activity did not evolve to a single optimum but rather fluctuated within a certain bandwidth. Furthermore, antigenic and enzymatic properties of NA were intertwined, with several residues affecting multiple properties. For example, the substitution K432E in the second sialic acid binding site, next to the catalytic site, was shown to affect catalytic activity, substrate specificity, and the pH optimum for maximum activity. This substitution also altered antigenicity of NA, which may explain its selection. We propose that the entanglement of NA phenotypes may be an important determining factor in the evolution of NA.IMPORTANCE Since its emergence in 2009, the pandemic H1N1 influenza A virus (IAV) has caused significant disease and mortality in humans. IAVs contain two envelope glycoproteins, the receptor-binding hemagglutinin (HA) and the receptor-destroying neuraminidase (NA). NA is essential for virion release from cells and decoy receptors, is an important target of antiviral drugs, and is increasingly being recognized as an important vaccine antigen. Not much is known, however, about the evolution of this protein upon the emergence of the novel pandemic H1N1 virus, with respect to its enzymatic activity and antigenicity. By reconstructing the evolutionary path of NA, we show that antigenic and enzymatic properties of NA are intertwined, with several residues affecting multiple properties. Understanding the entanglement of NA phenotypes will lead to better comprehension of IAV evolution and may help the development of NA-based vaccines.

A Versatile Processing Workflow to Enable Pathogen Detection in Clinical Samples from Organs Using VIDISCA

In recent years, refined molecular methods coupled with powerful high throughput sequencing technologies have increased the potential of virus discovery in clinical samples. However, host genetic material remains a complicating factor that interferes with discovery of novel viruses in solid tissue samples as the relative abundance of the virus material is low. Physical enrichment processing methods, although usually complicated, labor-intensive, and costly, have proven to be successful for improving sensitivity of virus detection in complex samples. In order to further increase detectability, we studied the application of fast and simple high-throughput virus enrichment methods on tissue homogenates. Probe sonication in high EDTA concentrations, organic extraction with Vertrel™ XF, or a combination of both, were applied prior to chromatography-like enrichment using Capto™ Core 700 resin, after which effects on virus detection sensitivity by the VIDISCA method were determined. Sonication in the presence of high concentrations of EDTA showed the best performance with an increased proportion of viral reads, up to 9.4 times, yet minimal effect on the host background signal. When this sonication procedure in high EDTA concentrations was followed by organic extraction with Vertrel™ XF and two rounds of core bead chromatography enrichment, an increase up to 10.5 times in the proportion of viral reads in the processed samples was achieved, with reduction of host background sequencing. We present a simple and semi-high-throughput method that can be used to enrich homogenized tissue samples for viral reads.

Bacteriophages: from isolation to application

Bacteriophages are considered as a potential alternative to fight pathogenic bacteria during the antibiotic resistance era. With their high specificity, they are being widely used in various applications: medicine, food industry, agriculture, animal farms, biotechnology, diagnosis, etc. Many techniques have been designed by different researchers for phage isolation, purification, and amplification, each of which has strengths and weaknesses. However, all aim at having a reasonably pure phage sample that can be further characterized. Phages can be characterized based on their physiological, morphological or inactivation tests. Microscopy, in particular, has opened a wide gate not only for visualizing phage morphological structure, but also for monitoring biochemistry and behavior. Meanwhile, computational analysis of phage genomes provides more details about phage history, lifestyle, and potential for toxigenic or lysogenic conversion, which translate to safety in biocontrol and phage therapy applications. This review summarizes phage application pipelines at different levels and addresses specific restrictions and knowledge gaps in the field. Recently developed computational approaches, which are used in phage genome analysis, are critically assessed. We hope that this assessment provides researchers with useful insights for selection of suitable approaches for Phage-related research aims and applications.

Manufacturing of bacteriophages for therapeutic applications

Bacteriophages, or simply phages, are the most abundant biological entities on Earth. One of the most interesting characteristics of these viruses, which infect and use bacteria as their host organisms, is their high level of specificity. Since their discovery, phages became a tool for the comprehension of basic molecular biology and originated applications in a variety of areas such as agriculture, biotechnology, food safety, veterinary, pollution remediation and wastewater treatment. In particular, phages offer a solution to one of the major problems in public health nowadays, i.e. the emergence of multidrug-resistant bacteria. In these situations, the use of virulent phages as therapeutic agents offers an alternative to the classic, antibiotic-based strategies. The development of phage therapies should be accompanied by the improvement of phage biomanufacturing processes, both at laboratory and industrial scales. In this review, we first present some historical and general aspects related with the discovery, usage and biology of phages and provide a brief overview of the most relevant phage therapy applications. Then, we showcase current processes used for the production and purification of phages and future alternatives in development. On the production side, key factors such as the bacterial physiological state, the conditions of phage infection and the operation parameters are described alongside with the different operation modes, from batch to semi-continuous and continuous. Traditional purification methods used in the initial phage isolation steps are then described followed by the presentation of current state-of-the-art purification approaches. Continuous purification of phages is finally presented as a future biomanufacturing trend.

Comparison of methods for separating fluorescently labelled placental extracellular vesicles from free stain

The field of extracellular vesicles (EVs) is relatively new and the methods for EV isolation and quantification are still maturing. For example, there is no consensus on how to separate free stain from labelled EVs. Here we report a comparison of the recovery of labelled EVs following separation from free stain using ultracentrifugation, diafiltration with different devices and a charged size exclusion chromatography column. Of the methods we tested, the charged size exclusion column provided the greatest recovery of labelled EVs.

Lentiviral Vector Bioprocessing

Lentiviral vectors (LVs) are potent tools for the delivery of genes of interest into mammalian cells and are now commonly utilised within the growing field of cell and gene therapy for the treatment of monogenic diseases and adoptive therapies such as chimeric antigen T-cell (CAR-T) therapy. This is a comprehensive review of the individual bioprocess operations employed in LV production. We highlight the role of envelope proteins in vector design as well as their impact on the bioprocessing of lentiviral vectors. An overview of the current state of these operations provides opportunities for bioprocess discovery and improvement with emphasis on the considerations for optimal and scalable processing of LV during development and clinical production. Upstream culture for LV generation is described with comparisons on the different transfection methods and various bioreactors for suspension and adherent producer cell cultivation. The purification of LV is examined, evaluating different sequences of downstream process operations for both small- and large-scale production requirements. For scalable operations, a key focus is the development in chromatographic purification in addition to an in-depth examination of the application of tangential flow filtration. A summary of vector quantification and characterisation assays is also presented. Finally, the assessment of the whole bioprocess for LV production is discussed to benefit from the broader understanding of potential interactions of the different process options. This review is aimed to assist in the achievement of high quality, high concentration lentiviral vectors from robust and scalable processes.

Modern Techniques for the Isolation of Extracellular Vesicles and Viruses

Extracellular signaling is pivotal to maintain organismal homeostasis. A quickly emerging field of interest within extracellular signaling is the study of extracellular vesicles (EV), which act as messaging vehicles for nucleic acids, proteins, metabolites, lipids, etc. from donor cells to recipient cells. This transfer of biologically active material within a vesicular body is similar to the infection of a cell through a virus particle, which transfers genetic material from one cell to another to preserve an infection state, and viruses are known to modulate EV. Although considerable heterogeneity exists within EV and viruses, this review focuses on those that are small (< 200 nm in diameter) and of relatively low density (< 1.3 g/mL). A multitude of isolation methods for EV and virus particles exist. In this review, we present an update on methods for their isolation, purification, and phenotypic characterization. We hope that the information we provide will be of use to basic science and clinical investigators, as well as biotechnologists in this emerging field. Graphical Abstract.

A scalable downstream process for the purification of the cell culture-derived Orf virus for human or veterinary applications

The large demand for safe and efficient viral vector-based vaccines and gene therapies against both inherited and acquired diseases accelerates the development of viral vectors. One outstanding example, the Orf virus, has a wide range of applications, a superior efficacy and an excellent safety profile combined with a reduced pathogenicity compared to other viral vectors. However, besides these favorable attributes, an efficient and scalable downstream process still needs to be developed. Recently, we screened potential chromatographic stationary phases for Orf virus purification. Based on these previous accomplishments, we developed a complete downstream process for the cell culture-derived Orf virus. The described process comprises a membrane-based clarification step, a nuclease treatment, steric exclusion chromatography, and a secondary chromatographic purification step using Capto® Core 700 resin. The applicability of this process to a variety of diverse Orf virus vectors was shown, testing two different genotypes. These studies render the possibility to apply the developed downstream scheme for both genotypes, and lead to overall virus yields of about 64 %, with step recoveries of >70 % for the clarification, and >90 % for the chromatography train. Protein concentrations of the final product are below the detection limits, and the final DNA concentration of about 1 ng per 1E + 06 infective virus units resembles a total DNA depletion of 96-98 %.

Selection of chromatographic methods for the purification of cell culture-derived Orf virus for its application as a vaccine or viral vector

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Estimation of the isoelectric point and size of Vero cell-derived Orf virus.

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Limited dynamic binding capacity of tested Orf virus to sulfated cellulose.

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Purification of Orf virus by steric exclusion chromatography lead to 84 % recovery.

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Hydrophobic interaction chromatography suitable for Orf virus purification.

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Promising unit operations for a scalable DSP to produce Orf virus viral vectors.

In recent years, the Orf virus has become a promising tool for protective recombinant vaccines and oncolytic therapy. However, suitable methods for an Orf virus production, including up- and downstream, are very limited. The presented study focuses on downstream processing, describing the evaluation of different chromatographic unit operations. In this context, ion exchange-, pseudo-affinity- and steric exclusion chromatography were employed for the purification of the cell culture-derived Orf virus, aiming at a maximum in virus recovery and contaminant depletion. The most promising chromatographic methods for capturing the virus particles were the steric exclusion- or salt-tolerant anion exchange membrane chromatography, recovering 84 % and 86 % of the infectious virus. Combining the steric exclusion chromatography with a subsequent Capto™ Core 700 resin or hydrophobic interaction membrane chromatography as a secondary chromatographic step, overall virus recoveries of up to 76 % were achieved. Furthermore, a complete cellular protein removal and a host cell DNA depletion of up to 82 % was possible for the steric exclusion membranes and the Capto™ Core 700 combination.

The study reveals a range of possible unit operations suited for the chromatographic purification of the cell culture-derived Orf virus, depending on the intended application, i.e. a human or veterinary use, and the required purity.

Polysaccharide-based chromatographic adsorbents for virus purification and viral clearance

Viruses still pose a significant threat to human and animal health worldwide. In the fight against viral infections, high-purity viral stocks are needed for manufacture of safer vaccines. It is also a priority to ensure the viral safety of biopharmaceuticals such as blood products. Chromatography techniques are widely implemented at both academic and industrial levels in the purification of viral particles, whole viruses and virus-like particles to remove viral contaminants from biopharmaceutical products. This paper focuses on polysaccharide adsorbents, particulate resins and membrane adsorbers, used in virus purification/removal chromatography processes. Different chromatographic modes are surveyed, with particular attention to ion exchange and affinity/pseudo-affinity adsorbents among which commercially available agarose-based resins (Sepharose®) and cellulose-based membrane adsorbers (Sartobind®) occupy a dominant position. Mainly built on the development of new ligands coupled to conventional agarose/cellulose matrices, the development perspectives of polysaccharide-based chromatography media in this antiviral area are stressed in the conclusive part.

Capture and purification of Human Immunodeficiency Virus-1 virus-like particles: Convective media vs porous beads

Downstream processing (DSP) of large bionanoparticles is still a challenge. The present study aims to systematically compare some of the most commonly used DSP strategies for capture and purification of enveloped viruses and virus-like particles (eVLPs) by using the same staring material and analytical tools. As a model, Human Immunodeficiency Virus-1 (HIV-1) gag VLPs produced in CHO cells were used. Four different DSP strategies were tested. An anion-exchange monolith and a membrane adsorber, for direct capture and purification of eVLPs, and a polymer-grafted anion-exchange resin and a heparin-affinity resin for eVLP purification after a first flow-through step to remove small impurities. All tested strategies were suitable for capture and purification of eVLPs. The performance of the different strategies was evaluated regarding its binding capacity, ability to separate different particle populations and product purity. The highest binding capacity regarding total particles was obtained using the anion exchange membrane adsorber (5.3 × 10¹² part/mL membrane), however this method did not allow the separation of different particle populations. Despite having a lower binding capacity (1.5 × 10¹¹ part/mL column) and requiring a pre-processing step with flow-through chromatography, Heparin-affinity chromatography showed the best performance regarding separation of different particle populations, allowing not only the separation of HIV-1 gag VLPs from host cell derived bionanoparticles but also from chromatin. This work additionally shows the importance of thorough sample characterization combining several biochemical and biophysical methods in eVLP DSP.

Interference chromatography: a novel approach to optimizing chromatographic selectivity and separation performance for virus purification

Background

Oncolytic viruses are playing an increasingly important role in cancer immunotherapy applications. Given the preclinical and clinical efficacy of these virus-based therapeutics, there is a need for fast, simple, and inexpensive downstream processing methodologies to purify biologically active viral agents that meet the increasingly higher safety standards stipulated by regulatory authorities like the Food and Drug Administration and the European Agency for the Evaluation of Medicinal Products. However, the production of virus materials for clinical dosing of oncolytic virotherapies is currently limited—in quantity, quality, and timeliness—by current purification technologies. Adsorption of virus particles to solid phases provides a convenient and practical choice for large-scale fractionation and recovery of viruses from cell and media contaminants. Indeed, chromatography has been deemed the most promising technology for large-scale purification of viruses for biomedical applications. The implementation of new chromatography media has improved process performance, but low yields and long processing times required to reach the desired purity are still limiting.

Results

Here we report the development of an interference chromatography-based process for purifying high titer, clinical grade oncolytic Newcastle disease virus using NatriFlo® HD-Q membrane technology. This novel approach to optimizing chromatographic performance utilizes differences in molecular bonding interactions to achieve high purity in a single ion exchange step.

Conclusions

When used in conjunction with membrane chromatography, this high yield method based on interference chromatography has the potential to deliver efficient, scalable processes to enable viable production of oncolytic virotherapies.

Purification of cell-derived Japanese encephalitis virus by dual-mode chromatography

Purification of the enveloped virus poses a challenge as one must retain viral infectivity to preserve immunogenicity. The traditional process of virus purification is time-consuming, laborious and hard to scale up. Here, a rapid, simple and extensible laboratory program for the purification of Japanese encephalitis virus (JEV) was developed by using differential centrifugation, ultrafiltration, Sepharose 4 fast flow gel chromatography, and Capto^TM Core 700 chromatography. The entire process recovered 61.64% of the original virus, and the purified virus particles maintained good activity and immunogenicity. The purification process described has potential application in large-scale production of high-purity JEV.

Proteomics as a tool for live attenuated influenza vaccine characterisation

Many viral vaccines, including the majority of influenza vaccines, are grown in embryonated chicken eggs and purified by sucrose gradient ultracentrifugation. For influenza vaccines this process is well established, but the viral strains recommended for use in vaccines are updated frequently. As viral strains can have different growth properties and responses to purification, these updates risk changes in the composition of the vaccine product. Changes of this sort are hard to assess, as influenza virions are complex structures containing variable ratios of both viral and host proteins. To address this, we used liquid chromatography and tandem mass spectrometry (LC-MS/MS), a flexible and sensitive method ideally suited to identifying and quantifying the proteins present in complex mixtures. By applying LC-MS/MS to the pilot scale manufacturing process of the live attenuated influenza vaccine (LAIV) FluMist® Quadrivalent vaccine (AstraZeneca), we were able to obtain a detailed description of how viral and host proteins are removed or retained at each stage of LAIV purification. LC-MS/MS allowed us to quantify the removal of individual host proteins at each stage of the purification process, confirming that LAIV purification efficiently depletes the majority of host proteins and identifying the small subset of host proteins which are associated with intact virions. LC-MS/MS also identified substantial differences in the retention of the immunosuppressive viral protein NS1 in purified virions. Finally, LC-MS/MS allowed us to detect subtle variations in the LAIV production process, both upstream of purification and during downstream purification stages. This demonstrates the potential utility of LC-MS/MS for optimising the purification of complex biological mixtures and shows that it is a promising approach for process optimisation in a wide variety of vaccine manufacturing platforms.

Breast Tumor-Associated Metalloproteases Restrict Reovirus Oncolysis by Cleaving the σ1 Cell Attachment Protein and Can Be Overcome by Mutation of σ1

Reovirus is undergoing clinical testing as an oncolytic therapy for breast cancer. Given that reovirus naturally evolved to thrive in enteric environments, we sought to better understand how breast tumor microenvironments impinge on reovirus infection. Reovirus was treated with extracellular extracts generated from polyomavirus middle T-antigen-derived mouse breast tumors. Unexpectedly, these breast tumor extracellular extracts inactivated reovirus, reducing infectivity of reovirus particles by 100-fold. Mechanistically, inactivation was attributed to proteolytic cleavage of the viral cell attachment protein σ1, which diminished virus binding to sialic acid (SA)-low tumor cells. Among various specific protease class inhibitors and metal ions, EDTA and ZnCl₂ effectively modulated σ1 cleavage, indicating that breast tumor-associated zinc-dependent metalloproteases are responsible for reovirus inactivation. Moreover, media from MCF7, MB468, MD-MB-231, and HS578T breast cancer cell lines recapitulated σ1 cleavage and reovirus inactivation, suggesting that inactivation of reovirus is shared among mouse and human breast cancers and that breast cancer cells by themselves can be a source of reovirus-inactivating proteases. Binding assays and quantification of SA levels on a panel of cancer cells showed that truncated σ1 reduced virus binding to cells with low surface SA. To overcome this restriction, we generated a reovirus mutant with a mutation (T249I) in σ1 that prevents σ1 cleavage and inactivation by breast tumor-associated proteases. The mutant reovirus showed similar replication kinetics in tumorigenic cells, toxicity equivalent to that of wild-type reovirus in a severely compromised mouse model, and increased tumor titers. Overall, the data show that tumor microenvironments have the potential to reduce infectivity of reovirus.IMPORTANCE We demonstrate that metalloproteases in breast tumor microenvironments can inactivate reovirus. Our findings expose that tumor microenvironment proteases could have a negative impact on proteinaceous cancer therapies, such as reovirus, and that modification of such therapies to circumvent inactivation by tumor metalloproteases merits consideration.

Modern Techniques for the Isolation of Extracellular Vesicles and Viruses

Extracellular signaling is pivotal to maintain organismal homeostasis. A quickly emerging field of interest within extracellular signaling is the study of extracellular vesicles (EV), which act as messaging vehicles for nucleic acids, proteins, metabolites, lipids, etc. from donor cells to recipient cells. This transfer of biologically active material within a vesicular body is similar to the infection of a cell through a virus particle, which transfers genetic material from one cell to another to preserve an infection state, and viruses are known to modulate EV. Although considerable heterogeneity exists within EV and viruses, this review focuses on those that are small (< 200 nm in diameter) and of relatively low density (< 1.3 g/mL). A multitude of isolation methods for EV and virus particles exist. In this review, we present an update on methods for their isolation, purification, and phenotypic characterization. We hope that the information we provide will be of use to basic science and clinical investigators, as well as biotechnologists in this emerging field. Graphical Abstract.

The 2nd sialic acid-binding site of influenza A virus neuraminidase is an important determinant of the hemagglutinin-neuraminidase-receptor balance

Influenza A virus (IAV) neuraminidase (NA) receptor-destroying activity and hemagglutinin (HA) receptor-binding affinity need to be balanced with the host receptor repertoire for optimal viral fitness. NAs of avian, but not human viruses, contain a functional 2nd sialic acid (SIA)-binding site (2SBS) adjacent to the catalytic site, which contributes to sialidase activity against multivalent substrates. The receptor-binding specificity and potentially crucial contribution of the 2SBS to the HA-NA balance of virus particles is, however, poorly characterized. Here, we elucidated the receptor-binding specificity of the 2SBS of N2 NA and established an important role for this site in the virion HA-NA-receptor balance. NAs of H2N2/1957 pandemic virus with or without a functional 2SBS and viruses containing this NA were analysed. Avian-like N2, with a restored 2SBS due to an amino acid substitution at position 367, was more active than human N2 on multivalent substrates containing α2,3-linked SIAs, corresponding with the pronounced binding-specificity of avian-like N2 for these receptors. When introduced into human viruses, avian-like N2 gave rise to altered plaque morphology and decreased replication compared to human N2. An opposite replication phenotype was observed when N2 was combined with avian-like HA. Specific bio-layer interferometry assays revealed a clear effect of the 2SBS on the dynamic interaction of virus particles with receptors. The absence or presence of a functional 2SBS affected virion-receptor binding and receptor cleavage required for particle movement on a receptor-coated surface and subsequent NA-dependent self-elution. The contribution of the 2SBS to virus-receptor interactions depended on the receptor-binding properties of HA and the identity of the receptors used. We conclude that the 2SBS is an important and underappreciated determinant of the HA-NA-receptor balance. The rapid loss of a functional 2SBS in pandemic viruses may have served to balance the novel host receptor-repertoire and altered receptor-binding properties of the corresponding HA protein.

The CARD9-Associated C-Type Lectin, Mincle, Recognizes La Crosse Virus (LACV) but Plays a Limited Role in Early Antiviral Responses against LACV

La Crosse virus (LACV) is a mosquito-transmitted arbovirus and the main cause of virus-mediated neurological diseases in children. To date, little is known about the role of C-type lectin receptors (CLRs)—an important class of pattern recognition receptors—in LACV recognition. DC-SIGN remains the only well-described CLR that recognizes LACV. In this study, we investigated the role of additional CLR/LACV interactions. To this end, we applied a flow-through chromatography method for the purification of LACV to perform an unbiased high-throughput screening of LACV with a CLR-hFc fusion protein library. Interestingly, the CARD9-associated CLRs Mincle, Dectin-1, and Dectin-2 were identified to strongly interact with LACV. Since CARD9 is a common adaptor protein for signaling via Mincle, Dectin-1, and Dectin-2, we performed LACV infection of Mincle^−/− and CARD9^−/− DCs. Mincle^−/− and CARD9^−/− DCs produced less amounts of proinflammatory cytokines, namely IL-6 and TNF-α, albeit no reduction of the LACV titer was observed. Together, novel CLR/LACV interactions were identified; however, the Mincle/CARD9 axis plays a limited role in early antiviral responses against LACV.

A Measles Virus-Based Vaccine Candidate Mediates Protection against Zika Virus in an Allogeneic Mouse Pregnancy Model

The impact of the Zika virus (ZIKV) epidemic highlights the need for vaccines that reduce or prevent infection and reliably prevent teratogenic complications. The live-attenuated measles virus (MV) vaccine strains are a promising vaccine platform, since they induce robust humoral and cellular immune responses against additional antigens and have an excellent safety record. To explore its potential to protect against ZIKV, we compared a recombinant Schwarz strain MV that encodes ZIKV prM and soluble E proteins (MV-Zika-sE) with a prototypic alum-adjuvanted whole inactivated ZIKV particle vaccine. Analysis of MV-Zika-sE-infected cells confirmed antigen expression, and the virus replicated with vaccine strain characteristics. Immunized IFNAR-/--CD46Ge mice developed E protein-specific and neutralizing antibodies, and ZIKV E-specific cellular immune responses were observed by gamma interferon (IFN-γ) enzyme-linked immunospot (ELISpot) and in vitro T cell proliferation assays. To analyze protective efficacy, vaccinated female mice were challenged with ZIKV after allogeneic mating. In MV-Zika-sE-vaccinated mice, weight gain was similar to that in uninfected mice, while no plasma viremia was detectable in the majority of the animals. In contrast, infected control animals gained less weight and experienced about 100-fold higher viremia over at least 3 days. Moreover, vaccination with MV-Zika-sE reduced the ZIKV load in different organs and the placentas and prevented infection of the fetus. Consequently, no fetal growth retardation, anemia, or death due to ZIKV infection was seen in MV-Zika-sE-vaccinated dams. In contrast, the inactivated ZIKV vaccine had little to no effect in our studies. Therefore, the MV-derived ZIKV vaccine is a promising candidate for further preclinical and clinical development.IMPORTANCE Zika virus (ZIKV) is a mosquito-borne flavivirus that causes a variety of neurological complications, including congenital birth defects. Despite the urgent need, no ZIKV vaccine has yet been licensed. Recombinant vaccine strain-derived measles viruses (MV) constitute a promising vector platform to induce immunity against foreign pathogens by expressing antigens from additional transcription units while at the same time possessing a remarkable safety profile. This concept has already been validated against different pathogens, including at least 3 other flaviviruses, and our data show that vaccination with MV expressing soluble ZIKV E protein significantly diminishes infection and prevents fetal loss or damage in an allogeneic mouse pregnancy model. It can thus be regarded as a promising emergency vaccine candidate with the potential for inclusion in routine vaccination settings in areas of endemicity to prevent teratogenic effects of circulating ZIKV during pregnancy, comparable to standard rubella virus vaccination.

Development of a Whole-Virus ELISA for Serological Evaluation of Domestic Livestock as Possible Hosts of Human Coronavirus NL63

Known human coronaviruses are believed to have originated in animals and made use of intermediate hosts for transmission to humans. The intermediate hosts of most of the human coronaviruses are known, but not for HCoV-NL63. This study aims to assess the possible role of some major domestic livestock species as intermediate hosts of HCoV-NL63. We developed a testing algorithm for high throughput screening of livestock sera with ELISA and confirmation with recombinant immunofluorescence assay testing for antibodies against HCoV-NL63 in livestock. Optimization of the ELISA showed a capability of the assay to significantly distinguish HCoV-NL63 from HCoV-229E (U = 27.50, p < 0.001) and HCoV-OC43 (U = 55.50, p < 0.001) in coronavirus-characterized sera. Evaluation of the assay with collected human samples showed no significant difference in mean optical density values of immunofluorescence-classified HCoV-NL63-positive and HCoV-NL63-negative samples (F (1, 215) = 0.437, p = 0.509). All the top 5% (n = 8) most reactive human samples tested by ELISA were HCoV-NL63 positive by immunofluorescence testing. In comparison, only a proportion (84%, n = 42) of the top 25% were positive by immunofluorescence testing, indicating an increased probability of the highly ELISA reactive samples testing positive by the immunofluorescence assay. None of the top 5% most ELISA reactive livestock samples were positive for HCoV-NL63-related viruses by immunofluorescence confirmation. Ghanaian domestic livestock are not likely intermediate hosts of HCoV-NL63-related coronaviruses.