Recovery of infective virus particles in ion-exchange and hydrophobic interaction monolith chromatography is influenced by particle charge and total-to-infective particle ratio

Vaccine process technology-A decade of progress

In the past decade, new approaches to the discovery and development of vaccines have transformed the field. Advances during the COVID-19 pandemic allowed the production of billions of vaccine doses per year using novel platforms such as messenger RNA and viral vectors. Improvements in the analytical toolbox, equipment, and bioprocess technology have made it possible to achieve both unprecedented speed in vaccine development and scale of vaccine manufacturing. Macromolecular structure-function characterization technologies, combined with improved modeling and data analysis, enable quantitative evaluation of vaccine formulations at single-particle resolution and guided design of vaccine drug substances and drug products. These advances play a major role in precise assessment of critical quality attributes of vaccines delivered by newer platforms. Innovations in label-free and immunoassay technologies aid in the characterization of antigenic sites and the development of robust in vitro potency assays. These methods, along with molecular techniques such as next-generation sequencing, will accelerate characterization and release of vaccines delivered by all platforms. Process analytical technologies for real-time monitoring and optimization of process steps enable the implementation of quality-by-design principles and faster release of vaccine products. In the next decade, the field of vaccine discovery and development will continue to advance, bringing together new technologies, methods, and platforms to improve human health.

Enhanced Downstream Processing for a Cell-Based Avian Influenza (H5N1) Vaccine

H5N1 highly pathogenic avian influenza virus (HPAIV) infections pose a significant threat to human health, with a mortality rate of around 50%. Limited global approval of H5N1 HPAIV vaccines, excluding China, prompted the need to address safety concerns related to MDCK cell tumorigenicity. Our objective was to improve vaccine safety by minimizing residual DNA and host cell protein (HCP). We developed a downstream processing method for the cell-based H5N1 HPAIV vaccine, employing CaptoTM Core 700, a multimodal resin, for polishing. Hydrophobic-interaction chromatography (HIC) with polypropylene glycol as a functional group facilitated the reversible binding of virus particles for capture. Following the two-step chromatographic process, virus recovery reached 68.16%. Additionally, HCP and DNA levels were reduced to 2112.60 ng/mL and 6.4 ng/mL, respectively. Western blot, high-performance liquid chromatography (HPLC), and transmission electron microscopy (TEM) confirmed the presence of the required antigen with a spherical shape and appropriate particle size. Overall, our presented two-step downstream process demonstrates potential as an efficient and cost-effective platform technology for cell-based influenza (H5N1 HPAIV) vaccines.

Preferential exclusion chromatography as a capture step for extracellular AAV harvest from adherent and suspension productions

Preferential exclusion chromatography (PXC) sometimes described as hydrophobic interaction chromatography is a well-known, but not widely used technique for purification of Adeno-associated viruses. It employs high molarity of preferentially excluded cosolvent (salt in our case). The downside of this method is that high molarity of salt can lead to aggregation and precipitation of different compounds from the sample. In the case of viruses that are excreted to medium, the concentration of impurities is much lower compared to cell lysates, and PXC can be used as a first chromatographic, serotype independent step to concentrate and purify adeno-associated virus (AAV). Here, we explored PXC for adherent and suspension harvests using monolithic chromatographic columns (CIMmultus). Suspension extracellular adeno-associated virus, serotype 9 (AAV9) harvest had more impurities compared to adherent harvest, therefore it required higher input regarding method development. Final conditions for suspension harvest included higher molarity of binding salt and using more open channel format of chromatographic column (6 µm channel size). Vector genome analysis with droplet digital polymerase chain reaction (ddPCR) revealed 84% and 97% recovery for suspension and adherent AAV9 harvest, respectively. After PXC capture step, adherent AAV9 was purified by already described ion exchange techniques. Overall process vector genome recovery, from clarified harvest to anion exchange elution fraction, was 54% measured by ddPCR. Residual host cell DNA was measured at 40 ng per 1E13 vector genome, and empty AAV was below 5% in final anion exchange chromatography fraction.

Purification of a recombinant oncolytic virus from clarified cell culture media by anion exchange monolith chromatography

The use of viral vectors for vaccine, gene therapy, and oncolytic virotherapy applications has received increased attention in recent years. Large-scale purification of viral vector-based biotherapeutics still presents a significant technical challenge. Chromatography is the primary tool for the purification of biomolecules in the biotechnology industry; however, the majority of chromatography resins currently available have been designed for the purification of proteins. In contrast, convective interaction media monoliths are chromatographic supports that have been designed and successfully utilized for the purification of large biomolecules, including viruses, viruslike particles, and plasmids. We present a case study on the development of a purification method for recombinant Newcastle disease virus directly from clarified cell culture media using strong anion exchange monolith technology (CIMmultus QA, BIA Separations). Resin screening studies showed at least 10 times higher dynamic binding capacity of CIMmultus QA compared to traditional anion exchange chromatography resins. Design of experiments was used to demonstrate a robust operating window for the purification of recombinant virus directly from clarified cell culture without any further pH or conductivity adjustment of the load material. The capture step was successfully scaled up from 1 mL CIMmultus QA columns to the 8 L column scale and achieved a greater than 30-fold reduction in process volume. Compared to the load material, total host cell proteins were reduced by more than 76%, and residual host cell DNA by more than 57% in the elution pool, respectively. Direct loading of clarified cell culture onto a high-capacity monolith stationary phase makes convective flow chromatography an attractive alternative to centrifugation or TFF-based virus purification procedures.

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.

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.

A scalable, integrated downstream process for production of a recombinant measles virus-vectored vaccine

Purification of very large and complex, enveloped viruses, such as measles virus is very challenging, it must be performed in a closed system because the final product cannot be sterile filtered and often loss of virus titer and poor product purity has been observed. We developed a purification process where the clarified and endonuclease treated culture supernatant is loaded on a restricted access chromatography medium where small impurities are bound and the virus is collected in the flow-through, which is then concentrated, and buffer exchanged by ultra/diafiltration. Up to 98.5% of host cell proteins could be captured by direct loading of clarified and endonuclease treated cell culture supernatant. Reproducible process performance and scalability of the chromatography step were demonstrated from small to pilot scale, including loading volumes from 50 mL up to 9 L. A 10-fold virus concentration was achieved by the ultrafiltration using a 100 kDa flat-sheet membrane. The order of individual process steps had a large impact on the virus infectivity and total process yields. The developed process maintained virus infectivity and is twice as fast as the traditional process train, where concentration is performed before loading on the chromatography column. Capturing impurities by the restricted access medium makes it a platform purification process with a high flexibility, which can be easily and quickly adapted to other vectors based on the measles virus vector platform.

A Combined Ultrafiltration/Diafiltration Process for the Purification of Oncolytic Measles Virus

Measles virus (MV) is an important representative of a new class of cancer therapeutics known as oncolytic viruses. However, process intensification for the downstream purification of this fragile product is challenging. We previously found that a mid-range molecular weight cut-off (300 kDa) is optimal for the concentration of MV. Here, we tested continuous and discontinuous diafiltration for the purification of MV prepared in two different media to determine the influence of high and low protein loads. We found that a concentration step before diafiltration improved process economy and MV yield when using either serum-containing or serum-free medium. We also found that discontinuous diafiltration conferred a slight benefit in terms of the permeate flow, reflecting the repetitive dilution steps and the ability to break down parts of the fouling layer on the membrane. In summary, the combined ultrafiltration/diafiltration process is suitable for the purification of MV, resulting in the recovery of ~50% infectious virus particles with a total concentration factor of 8 when using 5 diavolumes of buffer.

Production- and Purification-Relevant Properties of Human and Murine Cytomegalovirus

There is a large unmet need for a prophylactic vaccine against human cytomegalovirus (HCMV) to combat the ubiquitous infection that is ongoing with this pathogen. A vaccination against HCMV could protect immunocompromised patients and prevent birth defects caused by congenital HCMV infections. Moreover, cytomegalovirus (CMV) has a number of features that make it a very interesting vector platform for gene therapy. In both cases, preparation of a highly purified virus is a prerequisite for safe and effective application. Murine CMV (MCMV) is by far the most studied model for HCMV infections with regard to the principles that govern the immune surveillance of CMVs. Knowledge transfer from MCMV and mice to HCMV and humans could be facilitated by better understanding and characterization of the biological and biophysical properties of both viruses. We carried out a detailed investigation of HCMV and MCMV growth kinetics as well as stability under the influence of clarification and different storage conditions. Further, we investigated the possibilities to concentrate and purify both viruses by ultracentrifugation and ion-exchange chromatography. Defective enveloped particles were not separately analyzed; however, the behavior of exosomes was examined during all experiments. The effectiveness of procedures was monitored using CCID₅₀ assay, Nanoparticle tracking analysis, ELISA for host cell proteins, and quantitative PCR for host cell DNA. MCMV generally proved to be more robust in handling. Despite its greater sensitivity, HCMV was efficiently (100% recovery) purified and concentrated by anion-exchange chromatography using QA monolithic support. The majority of the host genomic DNA as well as most of the host cell proteins were removed by this procedure.

Biological nanoparticles: Relevance as novel target drug delivery systems and leading chromatographic isolation approaches

Nanotechnology is one of the most promising technologies of the 21st century, and it is now presenting an enormous impact on target drug delivery. In this context, the recent use of natural vesicle-like nanoparticles such as extracellular vesicles (i.e., exosomes, microvesicles, and apoptotic bodies) and virus-like particles is rendering encouraging results mostly because these delivery systems present cargo versatility, favorable body circulating advantages, biocompatibility, immunogenicity, and the capacity to be modified superficially to increase their affinity to a certain target or to control their entrance to the cell. However, some of the biggest challenges toward their clinical implementation are poorly standardized processing operations due to their inherent heterogeneity and expensive, long-lasting, and difficult to scale isolation procedures that can also affect the stability of the particles. Under these circumstances, chromatographic procedures represent an attractive and favorable alternative to overcome their downstream processing. Moreover, even when standardized chromatographic purification protocols are still in development, great achievements have been made using size exclusion, ionic exchange, hydrophobic interaction, and affinity protocols, mostly because of the correct harnessing of the nanovesicle membrane properties. In this sense, this review focuses on presenting the current understanding on the most promising therapeutic biological nanoparticles and the chromatographic isolation approaches employed in their recovery, providing at the same time recent findings and a general overview of the aspects that might impact the outcome of chromatographic techniques for this application.

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.

Amino acid-based hydrophobic affinity cryogel for protein purification from ora-pro-nobis (Pereskia aculeata Miller) leaves

The surfaces of the polyacrylamide cryogels were coated with L-tryptophan (cryogel-Trp) or L-phenylalanine (cryogel-Phe) to enhance crude leaf extract-derived ora-pro-nobis (OPN) protein binding via pseudo-specific hydrophobic interactions. Cryogels functionalized with amino acids were prepared and characterized through morphological, hydrodynamic, and thermal analyses. The adsorption capacities of cryogel-Phe and cryogel-Trp were evaluated in terms of type (sodium sulfate or sodium phosphate) and concentration (0.02 or 0.10 mol∙L^-1) of saline solution, pH (4.0, 5.5, or 7.0), and NaCl concentration (0.0 or 0.5 mol∙L^-1). The cryogel-Phe presented a higher adsorptive capacity, achieving its maximum value (q = 92.53 mg∙g^-1) when the crude OPN crude leaf extract was diluted in sodium sulfate 0.02 mol∙L^-1 + NaCl 0.50 mol∙L^-1, at pH = 7.0. The dilution rate significantly (p < 0.05) affected the recovered protein amount after the adsorption and elution processes, reaching 94.45% when the feedstock solution was prepared with a crude extract 5 times. The zeta potential for the eluted OPN proteins was 5.76 mV (pH = 3.23) for both dilution rates. The secondary structure composition mainly included β-sheets (46.50%) and α-helices (13.93%). The cryogel-Phe exhibited interconnected pores ranging 20-300 μm in size, with a Young modulus of 1.51 MPa, and thermal degradation started at 230 °C. These results indicate that the cryogel-Phe exhibited satisfactory properties as promising chromatography support for use in high-throughput purification of crude leaf extract-derived OPN proteins.

Ni-modified magnetic nanoparticles for affinity purification of His-tagged proteins from the complex matrix of the silkworm fat body

Purification of recombinant proteins is often a challenging matter because high purity and high recovery are desired. If the expressed recombinant protein is also in a complex matrix, such as from the silkworm expression system, purification becomes more challenging. Even if purification from the silkworm expression system is troublesome, it benefits from a high capacity for the production of recombinant proteins. In this study, magnetic nanoparticles (MNPs) were investigated as a suitable tool for the purification of proteins from the complex matrix of the silkworm fat body. The MNPs were modified with nickel so that they have an affinity for His-tagged proteins, as the MNP purification protocol itself does not need special equipment except for a magnet. Among the three different kinds of investigated MNPs, MNPs with sizes of 100 nm to 200 nm and approximately 20 nm-thick nickel shells were the most suitable for our purpose. With them, the total protein amount was reduced by up to at least approximately 77.7%, with a protein recovery of around 50.8% from the silkworm fat body. The minimum binding capacity was estimated to be 83.3 µg protein/mg MNP. Therefore, these MNPs are a promising tool as a purification pretreatment of complex sample matrices.

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.

Quantification of the HIV-1 virus-like particle production process by super-resolution imaging: From VLP budding to nanoparticle analysis

Virus-like particles (VLPs) offer great promise in the field of nanomedicine. Enveloped VLPs are a class of these nanoparticles and their production process occurs by a budding process, which is known to be the most critical step at intracellular level. In this study, we developed a novel imaging method based on super-resolution fluorescence microscopy (SRFM) to assess the generation of VLPs in living cells. This methodology was applied to study the production of Gag VLPs in three animal cell platforms of reference: HEK 293-transient gene expression (TGE), High Five-baculovirus expression vector system (BEVS) and Sf9-BEVS. Quantification of the number of VLP assembly sites per cell ranged from 500 to 3,000 in the different systems evaluated. Although the BEVS was superior in terms of Gag polyprotein expression, the HEK 293-TGE platform was more efficient regarding the assembly of Gag as VLPs. This was translated into higher levels of non-assembled Gag monomer in BEVS harvested supernatants. Furthermore, the presence of contaminating nanoparticles was evidenced in all three systems, specifically in High Five cells. The SRFM-based method here developed was also successfully applied to measure the concentration of VLPs in crude supernatants. The lipid membrane of VLPs and the presence of nucleic acids alongside these nanoparticles could also be detected using common staining procedures. Overall, a complete picture of the VLP production process was achieved in these three production platforms. The robustness and sensitivity of this new approach broaden the applicability of SRFM toward the development of new detection, diagnosis and quantification methods based on confocal microscopy in living systems.

Opportunities to debottleneck the downstream processing of the oncolytic measles virus

Oncolytic viruses (including measles virus) offer an alternative approach to reduce the high mortality rate of late-stage cancer. Several measles virus strains infect and lyse cancer cells efficiently, but the broad application of this therapeutic concept is hindered by the large number of infectious particles required (10⁸-10¹² TCID₅₀ per dose). The manufacturing process must, therefore, achieve high titers of oncolytic measles virus (OMV) during upstream production and ensure that the virus product is not damaged during purification by applying appropriate downstream processing (DSP) unit operations. DSP is currently a production bottleneck because there are no specific platforms for OMV. Infectious OMV must be recovered as intact, enveloped particles, and host cell proteins and DNA must be reduced to acceptable levels to meet regulatory guidelines that were developed for virus-based vaccines and gene therapy vectors. Handling such high viral titers and process volumes is technologically challenging and expensive. This review considers the state of the art in OMV purification and looks at promising DSP technologies. We discuss here the purification of other enveloped viruses where such technologies could also be applied to OMV. The development of DSP technologies tailored for enveloped viruses is necessary to produce sufficient titers for virotherapy, which could offer hope to millions of patients suffering from incurable cancer.

Tangential Flow Filtration for the Concentration of Oncolytic Measles Virus: The Influence of Filter Properties and the Cell Culture Medium

The therapeutic use of oncolytic measles virus (MV) for cancer treatment requires >10⁸ infectious MV particles per dose in a highly pure form. The concentration/purification of viruses is typically achieved by tangential flow filtration (TFF) but the efficiency of this process for the preparation of MV has not been tested in detail. We therefore investigated the influence of membrane material, feed composition, and pore size or molecular weight cut-off (MWCO) on the recovery of MV by TFF in concentration mode. We achieved the recovery of infectious MV particles using membranes with a MWCO ≤ 300 kDa regardless of the membrane material and whether or not serum was present in the feed. However, serum proteins in the medium affected membrane flux and promoted fouling. The severity of fouling was dependent on the membrane material, with the cellulose-based membrane showing the lowest susceptibility. We found that impurities such as proteins and host cell DNA were best depleted using membranes with a MWCO ≥ 300 kDa. We conclude that TFF in concentration mode is a robust unit operation to concentrate infectious MV particles while depleting impurities such as non-infectious MV particles, proteins, and host cell DNA.

Forced Degradation Studies to Identify Critical Process Parameters for the Purification of Infectious Measles Virus

Oncolytic measles virus (MV) is a promising treatment for cancer but titers of up to 10¹¹ infectious particles per dose are needed for therapeutic efficacy, which requires an efficient, robust, and scalable production process. MV is highly sensitive to process conditions, and a substantial fraction of the virus is lost during current purification processes. We therefore conducted forced degradation studies under thermal, pH, chemical, and mechanical stress to determine critical process parameters. We found that MV remained stable following up to five freeze–thaw cycles, but was inactivated during short-term incubation (< 2 h) at temperatures exceeding 35 °C. The infectivity of MV declined at pH < 7, but was not influenced by different buffer systems or the ionic strength/osmolality, except high concentrations of CaCl₂ and MgSO₄. We observed low shear sensitivity (dependent on the flow rate) caused by the use of a peristaltic pump. For tangential flow filtration, the highest recovery of MV was at a shear rate of ~5700 s⁻¹. Our results confirm that the application of forced degradation studies is important to identify critical process parameters for MV purification. This will be helpful during the early stages of process development, ensuring the recovery of high titers of active MV particles after purification.

Mass spectrometry-based investigation of measles and mumps virus proteome

Background

Measles (MEV) and mumps virus (MUV) are enveloped, non-segmented, negative single stranded RNA viruses of the family Paramyxoviridae, and are the cause of measles and mumps, respectively, both preventable by vaccination. Aside from proteins coded by the viral genome, viruses are considered to contain host cell proteins (HCPs). The presence of extracellular vesicles (ECVs), which are often co-purified with viruses due to their similarity in size, density and composition, also contributes to HCPs detected in virus preparations, and this has often been neglected. The aim was to identify which virus-coded proteins are present in MEV and MUV virions, and to try to detect which HCPs, if any, are incorporated inside the virions or adsorbed on their outer surface, and which are more likely to be a contamination from co-purified ECVs.

Methods

MUV, MEV and ECVs were purified by ultracentrifugation, hydrophobic interaction chromatography and immunoaffinity chromatography, proteins in the samples were resolved by SDS-PAGE and subjected to identification by MALDI-TOF/TOF-MS. A comparative analysis of HCPs present in all samples was carried out.

Results

By proteomics approach, it was verified that almost all virus-coded proteins are present in MEV and MUV particles. Protein C in MEV which was until now considered to be non-structural viral protein, was found to be present inside the MeV virions. Results on the presence of HCPs in differently purified virus preparations imply that actin, annexins, cyclophilin A, moesin and integrin β1 are part of the virions.

Conclusions

All HCPs detected in the viruses are present in ECVs as well, indicating their possible function in vesicle formation, or that most of them are only present in ECVs. Only five HCPs were constantly present in purified virus preparations, regardless of the purification method used, implying they are likely the integral part of the virions. The approach described here is helpful for further investigation of HCPs in other virus preparations.

Electronic supplementary material

The online version of this article (10.1186/s12985-018-1073-9) contains supplementary material, which is available to authorized users.

Purification of virus-like particles (VLPs) expressed in the silkworm Bombyx mori

Virus-like particles (VLPs) are a promising and developing option for vaccination and gene therapy. They are also interesting as shuttles for drug targeting. Currently, several different gene expression systems are available, among which the silkworm expression system is known for its mass production capacity. However, cost-effective purification with high purity of the target protein is a particular bottleneck for this system. The present review evaluates the advances in the purification of VLPs, especially from silkworm larval hemolymph. Beginning with applicable pre-treatments for VLPs over to chromatography methods and quality control of the purified VLPs. Whereupon the main focus is on the different chromatography approaches for the purification, but the structure of the VLPs and their intended use for humans make also the quality control important. Within this, the stability of the VLPs which has to be considered for the purification is as well discussed.

Monolithic anion-exchange chromatography yields rhinovirus of high purity

For vaccine development, 3D-structure determination, direct fluorescent labelling, and numerous other studies, homogeneous virus preparations of high purity are essential. Working with human rhinoviruses (RVs), members of the picornavirus family and the main cause of generally mild respiratory infections, we noticed that our routine preparations appeared highly pure on analysis by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), exclusively showing the four viral capsid proteins (VPs). However, the preparations turned out to contain substantial amounts of contaminating material when analyzed by orthogonal analytical methods including capillary zone electrophoresis, nano electrospray gas-phase electrophoretic mobility molecular analysis (nES GEMMA), and negative stain transmission electron microscopy (TEM). Because these latter analyses are not routine to many laboratories, the above contaminations might remain unnoticed and skew experimental results. By using human rhinovirus serotype A2 (RV-A2) as example we report monolithic anion-exchange chromatography (AEX) as a last polishing step in the purification and demonstrate that it yields infective, highly pure, virus (RV-A2 in the respective fractions was confirmed by peptide mass fingerprinting) devoid of foreign material as judged by the above criteria.