Development of a downstream process for the production of an inactivated whole hepatitis C virus vaccine

Impact of the Membrane Structure of the Stationary Phase on Steric Exclusion Chromatography (SXC) of Lentiviral Vectors

For steric exclusion chromatography (SXC), hydrophilic stationary phases are used to capture the target molecule in the presence of polyethylene glycol. The influence of the structure and pore size of the stationary phase on the process requirements are not yet well understood. To better understand the SXC process, membranes with different pore sizes that served as a stationary phase were compared for the purification of lentiviral vectors (LVs). A design of experiments (DoE) was performed to assess the combined impact of PEG concentration and membrane pore size on the purification performance. A visualization experiment showed that the LVs were captured on the first membrane layer for a pore size up to 2.2 µm, and for a pore size larger than 2.2 µm, LVs were also partly found on the second and third membrane layers. Moreover, we could observe that increasing membrane pore size requires a higher PEG concentration to achieve comparable LV recoveries. Using five membrane layers as a stationary phase was sufficient to achieve good performance, supporting the visualized capture results. In conclusion, we could show that each stationary phase has its optimal PEG buffer compositions for SXC, depending on the membrane structure and pore size.

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.

Hepatitis C virus RNA is 5'-capped with flavin adenine dinucleotide

RNA viruses have evolved elaborate strategies to protect their genomes, including 5' capping. However, until now no RNA 5' cap has been identified for hepatitis C virus^1,2 (HCV), which causes chronic infection, liver cirrhosis and cancer³. Here we demonstrate that the cellular metabolite flavin adenine dinucleotide (FAD) is used as a non-canonical initiating nucleotide by the viral RNA-dependent RNA polymerase, resulting in a 5'-FAD cap on the HCV RNA. The HCV FAD-capping frequency is around 75%, which is the highest observed for any RNA metabolite cap across all kingdoms of life^4-8. FAD capping is conserved among HCV isolates for the replication-intermediate negative strand and partially for the positive strand. It is also observed in vivo on HCV RNA isolated from patient samples and from the liver and serum of a human liver chimeric mouse model. Furthermore, we show that 5'-FAD capping protects RNA from RIG-I mediated innate immune recognition but does not stabilize the HCV RNA. These results establish capping with cellular metabolites as a novel viral RNA-capping strategy, which could be used by other viruses and affect anti-viral treatment outcomes and persistence of infection.

Size-selective downstream processing of virus particles and non-enveloped virus-like particles

Non-enveloped virus-like particles (VLPs) are versatile protein nanoparticles with great potential for biopharmaceutical applications. However, conventional protein downstream processing (DSP) and platform processes are often not easily applicable due to the large size of VLPs and virus particles (VPs) in general. The application of size-selective separation techniques offers to exploit the size difference between VPs and common host-cell impurities. Moreover, size-selective separation techniques offer the potential for wide applicability across different VPs. In this work, basic principles and applications of size-selective separation techniques are reviewed to highlight their potential in DSP of VPs. Finally, specific DSP steps for non-enveloped VLPs and their subunits are reviewed as well as the potential applications and benefits of size-selective separation techniques are shown.

An inactivated SARS-CoV-2 vaccine induced cross-neutralizing persisting antibodies and protected against challenge in small animals

Vaccines have relieved the public health burden of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and globally inactivated vaccines are most widely used. However, poor vaccination accessibility and waning immunity maintain the pandemic, driving emergence of variants. We developed an inactivated SARS-CoV-2 (I-SARS-CoV-2) vaccine based on a viral isolate with the Spike mutation D614G, produced in Vero cells in a scalable bioreactor, inactivated with β-propiolactone, purified by membrane-based steric exclusion chromatography, and adjuvanted with MF59-like adjuvant AddaVax. I-SARS-CoV-2 and a derived split vaccine induced persisting neutralizing antibodies in mice; moreover, lyophilized antigen was immunogenic. Following homologous challenge, I-SARS-CoV-2 immunized hamsters were protected against disease and lung pathology. In contrast with reports for widely used vaccines, hamster plasma similarly neutralized the homologous and the Delta (B.1.617.2) variant viruses, whereas the Omicron (B.1.1.529) variant was neutralized less efficiently. Applied bioprocessing approaches offer advantages regarding scalability and production, potentially benefitting worldwide vaccine coverage.

Scaling Up of Steric Exclusion Membrane Chromatography for Lentiviral Vector Purification

Lentiviral vectors (LVs) are widely used in clinical trials of gene and cell therapy. Low LV stability incentivizes constant development and the improvement of gentle process steps. Steric exclusion chromatography (SXC) has gained interest in the field of virus purification but scaling up has not yet been addressed. In this study, the scaling up of lentiviral vector purification by SXC with membrane modules was approached. Visualization of the LVs captured on the membrane during SXC showed predominant usage of the upper membrane layer. Furthermore, testing of different housing geometries showed a strong influence on the uniform usage of the membrane. The main use of the first membrane layer places a completely new requirement on the scaling of the process and the membrane modules. When transferring the SXC process to smaller or larger membrane modules, it became apparent that scaling of the flow rate is a critical factor that must be related to the membrane area of the first layer. Performing SXC at different scales demonstrated that a certain critical minimum surface area-dependent flow rate is necessary to achieve reproducible LV recoveries. With the presented scaling approach, we were able to purify 980 mL LVs with a recovery of 68%.

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.

A Summary of Practical Considerations for the Application of the Steric Exclusion Chromatography for the Purification of the Orf Viral Vector

Steric exclusion chromatography (SXC) is a promising purification method for biological macromolecules such as the Orf virus (ORFV) vector. The method's principle is closely related to conventional polyethylene glycol (PEG) precipitation, repeatedly implementing membranes as porous chromatographic media. In the past decade, several purification tasks with SXC showed exceptionally high yields and a high impurity removal. However, the effect of varying process parameters, on the precipitation success and its limitations to SXC, is not yet well understood. For this reason, the precipitation behavior and SXC adaptation for ORFV were investigated for the PEG/ORFV contact time, the membranes pore size, and the type and concentration of ions. All three parameters influenced the ORFV recoveries significantly. A small pore size and a long contact time induced filtration effects and inhibited a full virus recovery. The application of salts had complex concentration-dependent effects on precipitation and SXC yields, and ranged from a complete prevention of precipitation in the presence of kosmotropic substances to increased efficiencies with Mg²⁺ ions. The latter finding might be useful to reduce PEG concentrations while maintaining high yields. With this knowledge, we hope to clarify several limitations of SXC operations and improve the tool-set for a successful process adaptation.

Inactivated whole hepatitis C virus vaccine employing a licensed adjuvant elicits cross-genotype neutralizing antibodies in mice

BACKGROUND & AIMS

A prophylactic vaccine is required to eliminate HCV as a global public health threat. We developed whole virus inactivated HCV vaccine candidates employing a licensed adjuvant. Further, we investigated the effects of HCV envelope protein modifications (to increase neutralization epitope exposure) on immunogenicity.

METHODS

Whole virus vaccine antigen was produced in Huh7.5 hepatoma cells, processed using a multistep protocol and formulated with adjuvant (MF-59 analogue AddaVax or aluminium hydroxide). We investigated the capacity of IgG purified from the serum of immunized BALB/c mice to neutralize genotype 1-6 HCV (by virus neutralization assays) and to bind homologous envelope proteins (by ELISA). Viruses used for immunizations were (i) HCV5aHi with strain SA13 envelope proteins and modification of an O-linked glycosylation site in E2 (T385P), (ii) HCV5aHi(T385) with reversion of T385P to T385, featuring the original E2 sequence determined in vivo and (iii) HCV5aHi(ΔHVR1) with deletion of HVR1. For these viruses, epitope exposure was investigated using human monoclonal (AR3A and AR4A) and polyclonal (C211 and H06) antibodies in neutralization assays.

RESULTS

Processed HCV5aHi formulated with AddaVax induced antibodies that efficiently bound homologous envelope proteins and broadly neutralized cultured genotype 1-6 HCV, with half maximal inhibitory concentrations of between 14 and 192 μg/ml (mean of 36 μg/ml against the homologous virus). Vaccination with aluminium hydroxide was less immunogenic. Compared to HCV5aHi(T385) with the original E2 sequence, HCV5aHi with a modified glycosylation site and HCV5aHi(ΔHVR1) without HVR1 showed increased neutralization epitope exposure but similar immunogenicity.

CONCLUSION

Using an adjuvant suitable for human use, we developed inactivated whole HCV vaccine candidates that induced broadly neutralizing antibodies, which warrant investigation in further pre-clinical studies.

LAY SUMMARY

A vaccine against hepatitis C virus (HCV) is needed to prevent the estimated 2 million new infections and 400,000 deaths caused by this virus each year. We developed inactivated whole HCV vaccine candidates using adjuvants licensed for human use, which, following immunization of mice, induced antibodies that efficiently neutralized all HCV genotypes with recognized epidemiological importance. HCV variants with modified envelope proteins exhibited similar immunogenicity as the virus with the original envelope proteins.

The Suitability of Latex Particles to Evaluate Critical Process Parameters in Steric Exclusion Chromatography

The steric exclusion chromatography (SXC) is a rather new method for the purification of large biomolecules and biological nanoparticles based on the principles of precipitation. The mutual steric exclusion of a nonionic organic polymer, i.e., polyethylene glycol (PEG), induces target precipitation and leads to their retention on the chromatographic stationary phase. In this work, we investigated the application of latex particles in the SXC by altering the particle’s surface charge as well as the PEG concentration and correlated both with their aggregation behavior. The parameters of interest were offline precipitation kinetics, the product recovery and yield, and the chromatographic column blockage. Sulfated and hydroxylated polystyrene particles were first characterized concerning their aggregation behavior and charge in the presence of PEG and different pH conditions. Subsequently, the SXC performance was evaluated based on the preliminary tests. The studies showed (1) that the SXC process with latex particles was limited by aggregation and pore blockage, while (2) not the aggregate size itself, but rather the aggregation kinetics dominated the recoveries, and (3) functionalized polystyrene particles were only suitable to a limited extent to represent biological nanoparticles of comparable size and charge.

Cancer vaccines as promising immuno-therapeutics: platforms and current progress

Research on tumor immunotherapy has made tremendous progress in the past decades, with numerous studies entering the clinical evaluation. The cancer vaccine is considered a promising therapeutic strategy in the immunotherapy of solid tumors. Cancer vaccine stimulates anti-tumor immunity with tumor antigens, which could be delivered in the form of whole cells, peptides, nucleic acids, etc. Ideal cancer vaccines could overcome the immune suppression in tumors and induce both humoral immunity and cellular immunity. In this review, we introduced the working mechanism of cancer vaccines and summarized four platforms for cancer vaccine development. We also highlighted the clinical research progress of the cancer vaccines, especially focusing on their clinical application and therapeutic efficacy, which might hopefully facilitate the future design of the cancer vaccine.

High-Titer Hepatitis C Virus Production in a Scalable Single-Use High Cell Density Bioreactor

Hepatitis C virus (HCV) infections pose a major public health burden due to high chronicity rates and associated morbidity and mortality. A vaccine protecting against chronic infection is not available but would be important for global control of HCV infections. In this study, cell culture-based HCV production was established in a packed-bed bioreactor (CelCradle™) aiming to further the development of an inactivated whole virus vaccine and to facilitate virological and immunological studies requiring large quantities of virus particles. HCV was produced in human hepatoma-derived Huh7.5 cells maintained in serum-free medium on days of virus harvesting. Highest virus yields were obtained when the culture was maintained with two medium exchanges per day. However, increasing the total number of cells in the culture vessel negatively impacted infectivity titers. Peak infectivity titers of up to 7.2 log10 focus forming units (FFU)/mL, accumulated virus yields of up to 5.9 × 1010 FFU, and a cell specific virus yield of up to 41 FFU/cell were obtained from one CelCradle™. CelCradle™-derived and T flask-derived virus had similar characteristics regarding neutralization sensitivity and buoyant density. This packed-bed tide-motion system is available with larger vessels and may thus be a promising platform for large-scale HCV production.

Continuous purification of influenza A virus particles using pseudo-affinity membrane chromatography

Robust and flexible continuous unit operations that enable the establishment of intensified bioprocesses is one of the most relevant trends in manufacturing of biopharmaceuticals, including virus-based products. Sulfated cellulose membrane adsorbers (SCMA) are one of the most promising matrices for chromatographic purification of virus particles, like influenza viruses. Here, a three 'column' periodical counter current set-up was used to continuously purify influenza A/PR/8/34 virus particles using SCMA in bind-elute mode. It was possible to recover 67.4% of the HA-activity and to remove 67.4% and 99.8% of the total protein and DNA, respectively. The performance of the continuous process operated over a total of 10 loops, was slightly inferior to was obtained in a comparable batch process. Nevertheless, it was possible to increase the effective usage of binding capacity to 80%, resulting on a productivity of 22.8 kHAU ml_memb^-1 min^-1. As a proof-of-principle, SCMA were successfully used as matrix for purification of cell-derived influenza virus particles, in continuous mode.

In the era of rapid mRNA-based vaccines: Why is there no effective hepatitis C virus vaccine yet?

Hepatitis C virus (HCV) is responsible for no less than 71 million people chronically infected and is one of the most frequent indications for liver transplantation worldwide. Despite direct-acting antiviral therapies fuel optimism in controlling HCV infections, there are several obstacles regarding treatment accessibility and reinfection continues to remain a possibility. Indeed, the majority of new HCV infections in developed countries occur in people who inject drugs and are more plausible to get reinfected. To achieve global epidemic control of this virus the development of an effective prophylactic or therapeutic vaccine becomes a must. The coronavirus disease 19 (COVID-19) pandemic led to auspicious vaccine development against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) virus, which has renewed interest on fighting HCV epidemic with vaccination. The aim of this review is to highlight the current situation of HCV vaccine candidates designed to prevent and/or to reduce HCV infectious cases and their complications. We will emphasize on some of the crossroads encountered during vaccine development against this insidious virus, together with some key aspects of HCV immunology which have, so far, hampered the progress in this area. The main focus will be on nucleic acid-based as well as recombinant viral vector-based vaccine candidates as the most novel vaccine approaches, some of which have been recently and successfully employed for SARS-CoV-2 vaccines. Finally, some ideas will be presented on which methods to explore for the design of live-attenuated vaccines against HCV.

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.

A high cell density perfusion process for Modified Vaccinia virus Ankara production: Process integration with inline DNA digestion and cost analysis

By integrating continuous cell cultures with continuous purification methods, process yields and product quality attributes have been improved over the last 10 years for recombinant protein production. However, for the production of viral vectors such as Modified Vaccinia virus Ankara (MVA), no such studies have been reported although there is an increasing need to meet the requirements for a rising number of clinical trials against infectious or neoplastic diseases. Here, we present for the first time a scalable suspension cell (AGE1.CR.pIX cells) culture-based perfusion process in bioreactors integrating continuous virus harvesting through an acoustic settler with semi-continuous chromatographic purification. This allowed obtaining purified MVA particles with a space-time yield more than 600% higher for the integrated perfusion process (1.05 × 10¹¹ TCID₅₀ /L_bioreactor /day) compared to the integrated batch process. Without further optimization, purification by membrane-based steric exclusion chromatography resulted in an overall product recovery of 50.5%. To decrease the level of host cell DNA before chromatography, a novel inline continuous DNA digestion step was integrated into the process train. A detailed cost analysis comparing integrated production in batch versus production in perfusion mode showed that the cost per dose for MVA was reduced by nearly one-third using this intensified small-scale process.

Antigenic and immunogenic evaluation of permutations of soluble hepatitis C virus envelope protein E2 and E1 antigens

Yearly, about 1.5 million people become chronically infected with hepatitis C virus (HCV) and for the 71 million with chronic HCV infection about 400,000 die from related morbidities, including liver cirrhosis and cancer. Effective treatments exist, but challenges including cost-of-treatment and wide-spread undiagnosed infection, necessitates the development of vaccines. Vaccines should induce neutralizing antibodies (NAbs) against the HCV envelope (E) transmembrane glycoprotein 2, E2, which partly depends on its interaction partner, E1, for folding. Here, we generated three soluble HCV envelope protein antigens with the transmembrane regions deleted (i.e., fused peptide backbones), termed sE1E2 (E1 followed by E2), sE2E1 (E2 followed by E1), and sE21E (E2 followed by inverted E1). The E1 inversion for sE21E positions C-terminal residues of E1 near C-terminal residues of E2, which is in analogy to how they likely interact in native E1/E2 complexes. Probing conformational E2 epitope binding using HCV patient-derived human monoclonal antibodies, we show that sE21E was superior to sE2E1, which was consistently superior to sE1E2. This correlated with improved induction of NAbs by sE21E compared with sE2E1 and especially compared with sE1E2 in female BALB/c mouse immunizations. The deletion of the 27 N-terminal amino acids of E2, termed hypervariable region 1 (HVR1), conferred slight increases in antigenicity for sE2E1 and sE21E, but severely impaired induction of antibodies able to neutralize in vitro viruses retaining HVR1. Finally, comparing sE21E with sE2 in mouse immunizations, we show similar induction of heterologous NAbs. In summary, we find that C-terminal E2 fusion of E1 or 1E is superior to N-terminal fusion, both in terms of antigenicity and the induction of heterologous NAbs. This has relevance when designing HCV E1E2 vaccine antigens.

Viral hepatitis update: Progress and perspectives

Viral hepatitis, secondary to infection with hepatitis A, B, C, D, and E viruses, are a major public health problem and an important cause of morbidity and mortality. Despite the huge medical advances achieved in recent years, there are still points of conflict concerning the pathogenesis, immune response, development of new and more effective vaccines, therapies, and treatment. This review focuses on the most important research topics that deal with issues that are currently being solved, those that remain to be solved, and future research directions. For hepatitis A virus we will address epidemiology, molecular surveillance, new susceptible populations as well as environmental and food detections. In the case of hepatitis B virus, we will discuss host factors related to disease, diagnosis, therapy, and vaccine improvement. On hepatitis C virus, we will focus on pathogenesis, immune response, direct action antivirals treatment in the context of solid organ transplantation, issues related to hepatocellular carcinoma development, direct action antivirals resistance due to selection of resistance-associated variants, and vaccination. Regarding hepatitis D virus, we describe diagnostic methodology, pathogenesis, and therapy. Finally, for hepatitis E virus, we will address epidemiology (including new emerging species), diagnosis, clinical aspects, treatment, the development of a vaccine, and environmental surveillance.